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Photoprocesses of Copper Complexes That Bind to DNA
... [56] In addition, phen-copper complexes induced DNA cleavage. [57,58] The effect of the N-heterocyclic and the type of organotin fragment on the topology and properties of the SCPs including the CuCN/base adducts were investigated in the present study. Fluorescent phen ligand was choosing as a planar fused phenyl rings system, which behaves as a rigid bi-connecting moiety. ...
... The mean IC50 is the concentration of drug that caused a 50% reduction in cell proliferation and is the average with ± Standard Definition (SD) from at least three independent determinations, Table S10 and Figure 7. Thus, SCP1 and SCP2 at IC50 concentration inhibit significant cell viability of the tested cancer cells relative to the control group but they need more experimentation in vitro and in vivo. The activity of organotin complexes may be related to the average Sn-N bond lengths, [57] implying that the mode of action of the drugs acquires pre-dissociation of the ligand by hydrolysis, which may favor transport of the active species to the site of action in the cells. The high cytotoxicity of SCP2 rather than SCP1 may be due to the phenyl ligands and the Sn-N bond lengths of SCP2 (2.040-2.057 ...
The nanosized supramolecular coordination polymers (SCPs) 3∞[Cu(μ2CN)2]2.(Me3Sn)2.(phen)2], SCP1, and [Cu2(CN)4(Ph3Sn)2(phen)], SCP2, were prepared utilizing self‐assembly method under ultrasonic irradiation. Single crystal X‐ray diffraction (XRD) of SCP1 supports the presence of two anionic [Cu(μ2CN)2]− fragments connected by two (Me3Sn)+ cations, while the two phenanthroline (phen) molecules coordinate to the Cu atoms. The two Cu atoms are crystallographically different, while they are chemically identical forming tetrahedral geometry. The structure of SCP2 was achieved by calculations using DFT (the density functional theory) and spectroscopic studies. The geometries around the Cu atoms adopt triagonal plane and tetrahedral structure. Spectroscopic data, energy‐dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), and analytical analysis confirm the chemical formula of SCP2. The nanosized tested compounds 1 and 2 are designed to investigate their action on viability and proliferation of five human cancer cell lines. In addition, 2, 2'‐azino‐bis (3‐ethyl benzthiazoline‐6‐sulfonic acid) (ABTS) assay and rate erythrocyte hemolysis were used to test the antioxidant activity of the nanosized SCP1 and SCP2. Also, the SCP1 and 2 exhibit good antimicrobial activity keeping them as promising drug candidates for the treatment of bacterial and fungal infections. New nanosized 3∞[Cu(μ2CN)2]2.(Me3Sn)2.(phen)2], SCP1, and [Cu2(CN)4(Ph3Sn)2(phen)], SCP2 were prepared by self‐assembly method under ultrasonic radiation. 1 and 2 are designed to investigate their action on viability and proliferation of five human cancer cell lines. 2, 2'‐azino‐bis (3‐ethyl benzthiazoline‐6‐sulfonic acid) (ABTS) assay and rate erythrocyte hemolysis were used to test the antioxidant activity of the nanosized SCP1 and SCP2. SCP1 and SCP2 exhibit good antimicrobial activity keeping them as promising drug candidates for the treatment of bacterial and fungal infections.
... [87][88][89] Pioneering studies from McMillin's group in 1980s and 1990s showed that introducing bulky substituents onto the 2-and 9positions of the phenanthroline ligand can effectively restrict this structural distortion in the excited state and lead to longer excited-state lifetime. [90][91][92][93][94][95] They also showed cooperative effects of additional methyl groups in 3-and 8-positions which boost the inuence of the substituents in the 2-and 9-positions in the subsequent work. 96 This increase in lifetime occurs because the alkyl substituents physically block the attening Jahn-Teller distortion that occurs in the MLCT excited state, which is the origin of the short lifetimes in unsubstituted analogues. ...
To function effectively in a photocatalytic application, a photosensitizer's light absorption, excited-state lifetime, and redox potentials, both in the ground state and excited state, are critically important. The absorption profile is particularly relevant to applications involving solar harvesting, whereas the redox potentials and excited-state lifetimes determine the thermodynamics, kinetics, and quantum yields of photoinduced redox processes. This perspective article focuses on synthetic inorganic and organometallic approaches to optimize these three characteristics of transition-metal based photosensitizers. We include our own work in these areas, which has focused extensively on exceptionally strong cyclometalated iridium photoreductants that enable challenging reductive photoredox transformations on organic substrates, and more recent work which has led to improved solar harvesting in charge-transfer copper(i) chromophores, an emerging class of earth-abundant compounds particularly relevant to solar-energy applications. We also extensively highlight many other complementary strategies for optimizing these parameters and highlight representative examples from the recent literature. It remains a significant challenge to simultaneously optimize all three of these parameters at once, since improvements in one often come at the detriment of the others. These inherent trade-offs and approaches to obviate or circumvent them are discussed throughout.
... [33][34][35] The d 10 Cu(I) center allows the Cu(I)diimine complexes to access the metal-to-ligand charge transfer (MLCT) state by absorbing visible light ranging from 400 to 550 nm. 35 The excited state lifetimes of Cu(I)diimine complexes were historically shorter than Ru(II)poly(pyridyl) complexes, 33,36 but a large and growing literature has explored ligand designs that can extend their excited state lifetimes well into the microsecond regime. [37][38][39][40][41] Furthermore, the ease of oxidation of the Cu(I) center results in these complexes acting as strong electron donors during photochemical processes. ...
Developing efficient photocatalysts that perform multi electron redox reactions is critical to achieving solar energy conversion. One can reach this goal by developing systems which mimic natural photosynthesis and exploit strategies such as proton-coupled electron transfer (PCET) to achieve photochemical charge accumulation. We report herein a heteroleptic Cu(i)bis(phenanthroline) complex, Cu-AnQ, featuring a fused phenazine-anthraquinone moiety that photochemically accumulates two electrons in the anthraquinone unit via PCET. Full spectroscopic and electrochemical analyses allowed us to identify the reduced species and revealed that up to three electrons can be accumulated in the phenazine-anthraquinone ring system under electrochemical conditions. Continuous photolysis of Cu-AnQ in the presence of sacrificial electron donor produced doubly reduced monoprotonated photoproduct confirmed unambiguously by X-ray crystallography. Formation of this photoproduct indicates that a PCET process occurred during illumination and two electrons were accumulated in the system. The role of the heteroleptic Cu(i)bis(phenanthroline) moiety participating in the photochemical charge accumulation as a light absorber was evidenced by comparing the photolysis of Cu-AnQ and the free AnQ ligand with less reductive triethylamine as a sacrificial electron donor, in which photogenerated doubly reduced species was observed with Cu-AnQ, but not with the free ligand. The thermodynamic properties of Cu-AnQ were examined by DFT which mapped the probable reaction pathway for photochemical charge accumulation and the capacity for solar energy stored in the process. This study presents a unique system built on earth-abundant transition metal complex to store electrons, and tune the storage of solar energy by the degree of protonation of the electron acceptor.
... 45,46 Even in solution, the environment can play a role on the luminescence quenching. 47,48 For instance, solvent molecules participate in emission quenching, even in the solid state. Through hydrogen bonds between carboxylate and carboxyl groups, both in solution and the solid state, self-assembled species such as supramolecular dimers could be formed. ...
The ability of mononuclear first-row transition metal complexes as dynamic molecular systems to perform selective functions under the control of an external stimulus that appropriately tunes their properties may greatly impact several domains of molecular nanoscience and nanotechnology. This study focuses on two mononuclear octahedral cobalt(ii) complexes of formula {[CoII(HL)2][CoII(HL)L]}(ClO4)3·9H2O (1) and [CoIIL2]·5H2O (2) [HL = 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine], isolated as a mixed protonated/hemiprotonated cationic salt or a deprotonated neutral species. This pair of pH isomers constitutes a remarkable example of a dynamic molecular system exhibiting reversible changes in luminescence, redox, and magnetic (spin crossover and spin dynamics) properties as a result of ligand deprotonation, either in solution or solid state. In this last case, the thermal-assisted spin transition coexists with the field-induced magnetisation blockage of “faster” or “slower” relaxing low-spin CoII ions in 1 or 2, respectively. In addition, pH-reversible control of the acid-base equilibrium among dicationic protonated, cationic hemiprotonated, and neutral deprotonated forms in solution enhances luminescence in the UV region. Besides, the reversibility of the one-electron oxidation of the paramagnetic low-spin CoII into the diamagnetic low-spin CoIII ion is partially lost and completely restored by pH decreasing and increasing. The fine-tuning of the optical, redox, and magnetic properties in this novel class of pH-responsive, spin crossover molecular nanomagnets offers fascinating possibilities for advanced multifunctional and multiresponsive magnetic devices for molecular spintronics and quantum computing such as pH-effect spin quantum transformers.
... Cuprous complexes have received continuous attention for their potential applications in organic electroluminescence (OEL) (Costa et al., 2012), photochemical catalysis (Kuramochi et al., 2014), solar energy conversion (Robertson, 2008), probes of biological systems (McMillin & McNett, 1998), luminescence-based sensors (Zhao et al., 2010) and lightdriven fuel production (Stoll et al., 2014;Luo et al., 2013). Although precious metal complexes, such as Re I , Ru II , Ir III and Pt II , were developed and utilized earlier, their expense and the scarcity of resources greatly limited their application (Zhao et al., 2010;Volz et al., 2015;Chai et al., 2015a;Wang et al., 2020a). ...
Luminescent cuprous complexes are an important class of coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title heteroleptic cuprous complex, [2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl-κ²P,P′](2-phenylpyridine-κN)copper(I) hexafluoridophosphate, rac-[Cu(C44H32P2)(C11H9N)]PF6, conventionally abbreviated rac-[Cu(BINAP)(2-PhPy)]PF6 (I), where BINAP and 2-PhPy represent 2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl and 2-phenylpyridine, respectively, is described. In this complex, the asymmetric unit consists of a hexafluoridophosphate anion and a heteroleptic cuprous complex cation, in which the cuprous centre in a CuP2N coordination triangle is coordinated by two P atoms from the BINAP ligand and by one N atom from the 2-PhPy ligand. Time-dependent density functional theory (TD–DFT) calculations show that the UV–Vis absorption of I should be attributed to ligand-to-ligand charge transfer (LLCT) characteristic excited states. It was also found that the paper-based film of this complex exhibited obvious luminescence light-up sensing for pyridine.
... The restriction of the structural distortion from the tetrahedral to the flattened structure in the excited state will improve the quantum yield. 20,32,33 In 2b and 3b, the copper ions are fourcoordinated and pulled by two halogens, which make them less easy to distort and deform. Consequently, 2b and 3b show higher quantum yields than 1a and 2a. ...
Reaction of [Cu(CH3CN)4]ClO4 and 2-(diphenylphosphino) pyridine (dppy) along with different halogen reagents NH4X (X = Cl-, Br- and I-), four luminescent di-copper(I) coordination compounds, namely [Cu2(μ-dppy)3Cl]ClO4·H2O (1a), [Cu2(μ-dppy)3Br]ClO4 (2a), Cu2(μ-Br)2(μ-dppy)(η-dppy)2 (2b) and [Cu2(μ-I)2(μ2-dppy)(η-dppy)2] (3b) were isolated, respectively. Intriguingly, the X-ray crystallographic studies revealed that there were two kinds of Cu2-core structural evaluation induced by variable halogen anions. With Cl- acting as co-ligand, 1a featured the trefoil-like Cu2-core with three μ2-dppy in a head-to-head orientation bridging two Cu(I) and one terminal Cl- occupying one axial position. To replace of Cl- by I-, 3b was comprised of the butterfly-like Cu2-core, being bridged by two I- anions and one μ2-dppy, along with two terminal dppy. While Br- was employed, two above proto-type Cu2-core based 2a and 2b were obtained, respectively. All these four di-copper(I) compounds exhibit intense green photoluminescence with microsecond lifetimes.
... In particular, structural or conformational rigidity is very important, as changes in excited-state structures can give rise to un-productive relaxation pathways that compromise radiative decay. For example, rigid and bulky ligands based on phenanthrolines, 11 phosphines, 10 and carbenes 7,12 have been employed to reduce nonradiative decay rates, thereby achieving Φ PL close to unity. ...
We describe a novel manifestation of rigidochromic behavior in a series of tetranuclear Cu(I)-pyrazolate (Cu4pz4) macrocycles, with implications for solid-state luminescence at deep-blue wavelengths (<460 nm). The Cu4pz4 emissions are remarkably sensitive to structural effects far from the luminescent core: when 3,5-di-tert-butylpyrazoles are used as bridging ligands, adding a C4 substituent can induce a blue shift of more than 100 nm. X-ray crystal and computational analyses reveal that C4 units influence the conformational behavior of adjacent tert-butyl groups, with a subsequent impact on the global conformation of the Cu4pz4 complex. Emissions are mediated primarily through a cluster-centered triplet (3CC) state; compression of the Cu4 cluster into a nearly close-packed geometry prevents the reorganization of its excited-state structure and preserves the 3CC energy at a high level. The remote steric effect may thus offer alternative strategies toward the design of phosphors with rigid excited-state geometries.
... Cu(I)-based emitters are considered as an attractive alternative to those containing platinum group metals for the development of luminescent materials because copper is abundant and inexpensive compared to other noble metals [1][2][3][4][5][6][7][8][9][10][11]. Due to their flexible coordination properties, Cu(I) halides-aggregates have been incorporated in coordination oligomers or polymers, which exhibit a range of photophysical properties [12][13][14][15]. ...
The synthesis, structural, and photophysical investigations of CuI complexes with a disilanylene-bridged bispyridine ligand 1 are herein presented. Dinuclear (2) and ladder-like (3) octanuclear copper(I) complexes were straightforwardly prepared by exactly controlling the ratio of CuI/ligand 1. Single-crystal X-ray analysis confirmed that dinuclear complex 2 had no apparent π…π stacking whereas octanuclear complex 3 had π…π stacking in the crystal packing. In the solid state, the complexes display yellow-green (λem = 519 nm, Φ = 0.60, τ = 11 µs, 2) and blue (λem = 478 nm, Φ = 0.04, τ = 2.6 µs, 3) phosphorescence, respectively. The density functional theory calculations validate the differences in their optical properties. The difference in the luminescence efficiency between 2 and 3 is attributed to the presence of π…π stacking and the different luminescence processes.
... Tetrakis and tris complexes with d 10 configurations tend to cause flattening and T-shaped distortion in the excited states, respectively. 51,52 Our calculation also shows that the triplet-optimized structures of complexes 1 4 and 1 3 are distorted toward square-planar and T-shaped triangular geometries, respectively (Figure 7). The former distortion, flattening, was frequently found for copper(I) complexes. ...
... 12 In the lack of such a property, this complex was evaluated by McMillin and others as a DNA binding agent, aiming to gain insight into the DNA binding phenomena and taking advantage of the photophysical properties of the complex. 13,14,15,16 Later, Kellett et al. evaluated the nuclease activity of [Cu(phen)2(phthalate)] and [Cu2(phen)4(-terephthalate)] 2+ Cu II complexes 17 which, along with others of similar structures, 18,19,20 were able to cleave DNA by an oxidative mechanism in the absence of exogenous reductants. Therefore, these compounds were the first "self-activating" chemical nucleases reported, according to the denomination given by the authors. ...
The interplay between coordination geometry and reactivity in copper complexes has been widely studied for years. For
CuII, it is known that the reduction is favored when the geometry is closer to that of the CuI
state, which is mainly tetrahedral.
Conversely, the reduction of CuII complexes in the absence of exogenous reducers has been barely addressed. Herein, we
report on the ability of a classic CuII complex to be partially reduced in acetonitrile solutions containing water, in the absence
of external reducers. The role of the structure on the spontaneous reduction is presented by contrasting the geometric
features with a related complex, [Cu(phen)2(CH3CN)]2+, which is inert towards the redox process mediated by water. The
participation of water in the reduction of [Cu(dmp)2(CH3CN)]2+ is associated with the production of hydroxyl radical. This,
prompted us to evaluate the use of [Cu(dmp)2(CH3CN)]2+ as an anticancer metallodrug, showing an activity stronger than
[Cu(phen)2(CH3CN)]2+ on 2D and 3D models of bone, lung, and breast cancer cell lines. Furthermore, both complexes are
more active than cisplatin. The main mechanism of action is the intracellular ROS generation, with a higher production of
cytotoxic species by [Cu(dmp)2(CH3CN)]2+. Certainly, the performance of [Cu(dmp)2(CH3CN)]2+ as an anticancer agent and its
reactivity in solution phase are connected through the geometrical constraints imparted by the dmp ligands.
... The distinct absorption and emission spectra of CuPP ( Supplementary Fig. 12b) indicate a significant structural change in its excited state. Since Cu(I) complexes tend to adopt distorted geometries compared to their Cu(II) analogs 40,[57][58][59][60] , the nature of the emission of CuPP is likely from a Cu(I) excited state generated from a LMCT process. Excitation-emission spectra (Fig. 3b, c) show that the emission of CuPP is most intense when excited at 375 nm. ...
CO 2 reduction through artificial photosynthesis represents a prominent strategy toward the conversion of solar energy into fuels or useful chemical feedstocks. In such configuration, designing highly efficient chromophores comprising earth-abundant elements is essential for both light harvesting and electron transfer. Herein, we report that a copper purpurin complex bearing an additional redox-active center in natural organic chromophores is capable to shift the reduction potential 540 mV more negative than its organic dye component. When this copper photosensitizer is employed with an iron porphyrin as the catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1 H -benzo[ d ]imidazole as the sacrificial reductant, the system achieves over 16100 turnover number of CO from CO 2 with a 95% selectivity (CO vs H 2 ) under visible-light irradiation, which is among the highest reported for a homogeneous noble metal-free system. This work may open up an effective approach for the rational design of highly efficient chromophores in artificial photosynthesis.
... Metallo-intercalators act as a pivotal role in developing the chemistry of nucleic acids, especially for their importance in versatile applications like footprinting of DNA, design of structural probes, the development of therapeutic agents, etc [1][2][3][4][5][6][7]. Thus, enormous numbers of metallo-intercalators consisting of planar N-donor heterocyclics are widely utilized as vital chemical or photochemical reagents in the progress of nucleic acids chemistry. ...
In this work, an effort has been made to examine the counteranionic behavior of thiocyanide ion towards the stabilization of a dicationic tris(2,2'-bipyridine)nickel(II) complex in crystalline phase. The complex, [Ni(bipy)3].2NCS (1) [bipy = 2,2'-bipyridine] was designed, synthesized and structurally characterized. The crystal structure analysis reveals that 1 crystallises in a hexagonal system with P6/mcc space group and adopts an octahedral geometry. The nickel(II) complex exhibits important cytotoxic behaviour towards lung cancer cell (A549). IC50 value is calculated through MTT assay and determined as 131 µG/mol. Relative percentage of morphological changes is further determined and ~63% of the cells are destroyed through apoptosis mode with in 24 h incubation.
... Those mixed-ligand complexes containing nitrogen donor ligands have also great potential in antimicrobial [1][2][3][4], antioxidant [5], anticancer, and catalytic activities [6][7][8][9]. The photo-physical properties of Cu(II) complexes including polypyridine ligands resulted in effective DNA binder complexes [10][11][12][13][14][15]. The anticancer effectiveness Cu(II) complexes are categorized according to their ability to inhibit DNA binding [16]. ...
Two dicationic Cu(II) complexes of [Cu(phen)(NNN)]Br2 (1-2) general formula [phen = 1,10-phenanthroline, NNN = diethelenetriamine (dien) (1) and dipropylenetriamine (dipn)(2)], have been synthesized in very good yields. The two complexes were characterized via UV-vis., CHN-EA, MS, FT-IR, thermal, and X-ray crystallographic techniques. XRD data for 1 showed a distorted square pyramidal Cu(II) ions geometry center with three uncoordinated water molecules. TGA were performed to evaluate the interactions strength and found to support the XRD molecular interactions results. The time-dependent density functional theory (TD-DFT) and electron transfer processes were modeled, and consequently the absorption maxima around 610 and 280 nm were attributed to d–d and Phen(π)→Phen(π٭) transitions. Positive Gutmann's solvatochromism behavior of both complexes have been recorded. Furthermore, the ability of the two complexes for DNA binding was evaluated via absorption studies in the visible region showing high Kb constant values.
... Luminescent transition metal complexes have gained much attention due to their potential applications in organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) [1][2][3][4][5][6][7]. Copper(I) complexes have been extensively studied because of their relative abundance and low cost, and they have demonstrated a wave variety of applications in solar energy conversion, luminescence-based sensors, catalysis, and probes of biological systems [4,[8][9][10][11][12][13][14][15][16]. Use of bulky and rigid ligands regulates the structure and configuration of copper(I) complexes, leading to effective suppression of nonradiative processes, which is the key to synthesize highly efficient Cu(I)-complexes [17][18][19][20]. ...
A new phosphole derivative, 2,5-di(2-quinolyl)-1-phenylphosphole (1), was synthesized by using the Fagan–Nugent method. Phosphole 1 was obtained as an air-stable solid in high yield (73%). Additionally, two new copper–phosphole complexes, [CuX(Phosphole)2] (X = Cl (2a), I (2b), Phosphole=1), have been synthesized by reaction of CuX (X = Cl, I) and 1. All compounds were characterized by NMR, ESI-MS, UV–Vis, and fluorescence spectroscopy. The photophysical properties of all compounds were analyzed. UV–Vis spectra of 2a-b show π–π* transitions with shifts very similar to the free phosphole due to that their symmetrical structures inhibiting an efficient intraligand charge transfer, ILCT. Compounds 1, 2a-b exhibit fluorescence between 460 and 583 nm with quantum yields of Φf =0.04 − 0.11. The emission energy of 2b is higher than 2a, suggesting that λ max is affected by the ligand-field strength of the halide in the complexes (I¯ < Cl¯). The suggested structures of 2a-b were analyzed computationally at the PBEPBE/def2svp level of theory. The rotation barrier of the quinolyl group was analyzed by a scan analysis. Then, the 3 D structures of 2a-b were obtained in good agreement with the experimental results.
... The decreased intensity for both positive and negative bands is a typical feature of intercalative interaction. MBQ colloid was likely to intercalate into the DNA helix structure among different base pairs, thereby inducing the structure alternation (McMillin and McNett, 1998). Changes of CD bands are also associated with the alteration of hydration of the helix around the phosphate backbone (Wang et al., 2000). ...
The proliferation and spread of antibiotic resistance genes (ARGs) is becoming a worldwide crisis. Extracellular DNA encoding ARGs (eARGs) in aquatic environment plays a critical role in the dispersion of antimicrobial resistance genes. Strategies to control the dissemination of eARGs are urgently required for ecological safety and human health. Towards this goal, magnetic biochar/quaternary phosphonium salt (MBQ), was used to investigate the efficiency and removal mechanism for eARGs. Magnetic biochar modified by quaternary phosphonium salt enhanced the adsorption capacity of extracellular DNA to approximately 9 folds, compared to that of the unmodified. DNA adsorption by MBQ was mainly dominated by chemisorption in heterogeneous systems and was promoted in acidic and low-salt environment. The generation of •OH and MBQ colloid jointly cleaved DNA into fragments, facilitating the adsorption of the phosphate backbone of DNA onto MBQ through electrostatic force as well as the conformational transition of DNA. Furthermore, quantification of extracellular DNA after MBQ was applied in water demonstrated that over 92.7% of resistance genes were removed, indicating a significantly reduced risk of propagation of antimicrobial resistance in aquatic environments. These findings have a practical significance in the application of MBQ in mitigating the spread of ARGs in aquatic environment.
Six platinum complexes bearing monodentate phosphine ligands were prepared and their structures and photophysical properties examined. The complexes were photoluminescent in the solid state, with a maximum quantum yield of 72%. The tris(phosphine) platinum complexes displayed more red-shifted emissions than the tetrakis complexes. The nature of the emissive excited states is discussed based on the results of density functional theory and time-dependent density-functional theory calculations.
We report the synthesis and luminescent properties of a rare copper(I) alkynyl complex assembled from the diphosphane bis-diphenyphosphinobenzene (dppb) and phenylacetylide ligands with an extremely short Cu(I)···Cu(I) separation. The complex...
The luminescence properties of a synthesized series of Cu 4 I 4 clusters with a stair-step, cubane, and octahedral geometries supported by novel As,N-ligands, were reported and rationalized.
Carbazole is a heterocyclic motif that can be found in a diverse array of natural and unnatural products displaying a wide range of biological and physiological properties. Furthermore, this heterocycle is part of electronic materials like photoconducting polymers and organic optoelectronic materials owing to its excellent photophysical characteristics. Consequently, the development of synthetic strategies for carbazole scaffolds holds potential significance in biological and material fields. In this regard, a variety of preparation methods has been developed to exploit their efficient and distinct formation of new C−C and C‐heteroatom bonds under mild conditions and enabling broad substrate diversity and functional group tolerance. Therefore, this review focuses on the synthesis of a set of carbazole derivatives describing a variety of methodologies that involve direct irradiation, photosensitization, photoredox, electrochemical and thermal cyclization reactions.
Two novel Cu(I) tetradentate heteroleptic complexes, including nitrile-substituted bipyridines that can be anchored to semiconductor surfaces to be assembled in DSSCs, were synthesized and characterized by spectroscopic and electrochemical techniques. The crystal structures of both species were determined by X-ray diffraction. Results from DFT and TD-DFT calculations were found to be consistent with the experimental data. Emission at room temperature was observed for both complexes in the solid state, making them promising alternatives for the development of light-emitting diodes. We report for the first time the experimental evidence of photovoltaic conversion devices formed by Cu(I) complexes anchored to a TiO2 surface by means of nitrile groups present in substituted bipyridines, and subsequently tested as sensitizers for DSSCs, obtaining efficiency values for light to electrical energy conversion similar to those previously reported for analogous complexes with anchoring carboxylic groups.
In this report, two new heteroleptic complexes with compositions [Ni(mtsq)1.85Cl0.15(dppe)](CH2Cl2)0.06(CH3OH)0.09 (Ni-mtsq) and [Cu(mtsq)(PPh3)2] (Cu-mtsq) (dppe = 1,2-bis-(diphenylphosphino)ethane; PPh3 = triphenylphosphane and mtsq = 3-ethoxycyclobutenedione-4-thiolate) have been synthesized and characterized spectroscopically...
New phosphorescent “carbene-metal-carboranyl” (CMC) Cu(I) and Au(I) complexes based on the diamidocarbene (DAC) ligand show up to 68% photoluminescence quantum yield and microsecond range lifetimes. CMC organic light emitting diodes...
A novel tetranuclear Cu(ii) complex (TNC) was successfully synthesized and characterized by X-ray single crystal diffraction. The interaction of the complex with calf thymus DNA (CT-DNA) has been studied by UV-vis absorption titration, fluorescence technology and molecular docking. The results indicated that TNC could bind to the DNA through an intercalative mode. The agarose gel electrophoresis experiment showed that TNC could cleave supercoiled plasmid DNA into linear DNA. The anticancer activity of TNC was tested on four cancer cell lines: MCF7, A549, 4T1 and HepG2. The results indicated that TNC shown significant activity against all of above cell lines.
Methods of DNA cleavage have broad bioapplications in gene editing, disease treatment, and biosensor design. The traditional method for DNA cleavage is mainly through oxidation or hydrolysis mediated by small molecules or transition metal complexes. However, DNA cleavage by artificial nucleases using organic polymers has been rarely reported. Methylene blue has been extensively studied in the fields of biomedicine and biosensing due to its excellent singlet oxygen yield, redox properties, and good DNA affinity. Methylene blue mainly relies on light and oxygen for DNA cleavage, and the cutting rate is slow. Here, we synthesize cationic methylene-blue-backboned polymers (MBPs) that can bind DNA efficiently and induce DNA cleavage through free radical mechanisms in the absence of light and exogenous reagents, showing high-efficiency nuclease activity. In addition, MBPs with different structures showed selectivity for DNA cleavage, and the cleavage efficiency of the flexible structure was significantly higher than that of the rigid structure. Studies on the DNA cleavage mechanism have shown that the cleavage mechanism of MBPs is not through the common ROS-mediated oxidative cleavage pathway, but through the radical of MBP• inducing DNA cleavage. Meanwhile, MBPs can simulate topoisomerase I (Topo I)-mediated topological rearrangement of superhelical DNA. This work paved a way for the application of MBPs in the field of artificial nucleases.
Earth-abundant copper(I) coordination complexes of an imine-phosphine and a diimine have been developed as visible-light photocatalysts. Reaction of [Cu(MeCN)4]BF4 with hetero-bidentate phosphinopyrazole (phpz) ligand R1R2C3HN2PPh3 (R1 = R2 = H (1a); R1 = H, R2 = Me (1b); R1 = H, R2 = Ph (1c); R1 = R2 = Me (1d)) and 2,9-dimethyl-1,10-phenanthroline (dmp) gave four heteroleptic bis-chelate Cu(I) complexes [Cu(dmp)(R1R2C3HN2PPh3)]BF4 (R1 = R2 = H (2a); R1 = H, R2 = Me (2b); R1 = H, R2 = Ph (2c); R1 = R2 = Me (2d)) with distorted tetrahedral geometries. Complexes 2a-2d exhibited broad absorption in the visible spectrum and could facilitate photochemical intermolecular atom-transfer radical addition reactions of CBr4, or CCl3Br, CHI3 to styrenes in yields up to 91% and with a broad substrate scope. The absorption, emission, redox potential and photocatalytic activity were dependent on the substituents on the phpz ligand. Mechanistic studies supported an atom-transfer radical addition (ATRA) mechanism.
This manuscript describes the synthesis and coinage metal complexes of pyridine appended 1,2,3-triazolyl-phosphine [2-{(C6H4N)(C2(PPh2)N3C6H5)}] (1), photophysical studies and their catalytic application. The reactions of 1 with copper salts afforded dimeric complexes [{Cu(μ2-X)}2{2-(C6H4N)(C2(PPh2)N3C6H5)}2] (2, X = Cl; 3, X = Br; and 4, X = I). The crystal structure indicates that the Cu⋯Cu distance in 4 (2.694 Å) is significantly shorter than that in complexes 3 (3.0387 Å) and 2 (3.104 Å), indicating strong cuprophilic interactions which is also supported by NBO calculations, signifying the involvement of 3dz2 orbitals from each Cu atom contributing to the bonding interaction. The fluorescence studies on complexes 2-4 carried out in the solid state showed broad emission bands around 560 nm on excitation at λex = 420 nm. Complex 4 on treatment with two equivalents of 1,10-phenanthroline yielded a mononuclear complex 5 which showed almost complete quenching of fluorescence in the solid state, clearly indicating that the emissive properties of 4 are mainly due to the Cu⋯Cu interaction, along with (M + X)LCT. The reactions of 1 with silver salts led to the isolation of dimeric complexes [{Ag(μ2-X)}2{2-(C6H4N)(C2(PPh2)N3C6H5)}2] (6, X = Cl; 7, X = Br; and 8, X = I) in good yield. The reaction between 1 and [AuCl(SMe2)] yielded [{AuCl}{2-(C6H4N)(C2(PPh2)N3C6H5)}] (9). The molecular structures of 2-5 and 7-9 were confirmed by single crystal X-ray analysis. The complex 4 is found to be an excellent catalyst for C-O coupling under mild conditions.
Two new complexes, [Cu(dmp)(2-bdppmapy)](CF3SO3)·CH2Cl2 (1) and [Cu(imidazo[4,5-f])(2-bdppmapy)](SCN) (2) (2-bdppmapy = N,N-bis[(diphenylphosphino)methyl]-2-pyridinamine, dmp = 2,9-dimethyl-(1,10)phenanthroline and imidazo[4,5-f] = 1H-imidazo[4,5f][1,10]phenanthroline), have been synthesized in mixed solvents of CH3OH and CH2Cl2 (1:1, V/V). On the basis of studying the structure and photophysical properties of the Cu(I) complexes, the effects of different N ligands and counter anions on the luminescence properties of the Cu(I) complexes were characterized by single-crystal X-ray diffraction, fluorescence spectra and terahertz time-domain spectroscopy (THz-TDS). The research shows that 1 exhibits excellent photoluminescence quantum yields. It is ascribed to the unique stacked structure. In addition, the relationship between the multiple weak forces, structure, and photophysical properties of the complexes was investigated.
Herein, a series of ionic mononuclear Cu(I) complexes, [Cu(phen)(bdppmapy)]Cl (1a), [Cu(phen)(bdppmapy)]Br (2a), [Cu(phen)(bdppmapy)]I (3a), [Cu(phen)(bdppmapy)]SCN (4a), [Cu(Dpq)(bdppmapy)]Cl (1b), [Cu(Dpq)(bdppmapy)]Br (2b), [Cu(Dpq)(bdppmapy)]I (3b) and [Cu(Dpq)(bdppmapy)]SCN (4b) {phen = [1,10]phenanthroline; Dpq =...
Enantiopure copper(I) chloride complexes bearing a monodentate N-(carbo[6]helicenyl)-NHC ligand have been prepared and characterized experimentally and computationally. Their high stability enables the stereochemistry to be probed by X-ray crystallography and NMR spectroscopy. The resolved enantiomeric complexes emit circularly polarized blue fluorescence with glum ∼1.3 × 10-3 in solution. The photophysical and chiroptical properties of these systems, with their helicene-centred origin, are similar to those of the organic helicene-benzimidazole precursor proligand, although the reverse axial chirality configuration is preferentially observed for the complex compared to the ligand.
Oxygen sensing comprises an emerging technique that is being used in a variety of scientific and technological fields, ranging from medicine to life science. How to detect and identify oxygen quickly and accurately has become an important topic. The optical oxygen sensing technique using luminescent probes has a variety of features that make it capable of detecting molecular oxygen content (e.g. high selectivity, high sensitivity, excellent reversibility, immediate and non-invasive detection). As a suitable non-precious metal oxygen-sensitive probe, the Cu(I) complex is considered to be a promising substitute for traditional precious metal complexes. This review summarizes the results of the studies that have been conducted in the development and design of luminescent Cu(I) complexes, along with their photophysical characteristics related to oxygen sensing. Representative examples are chosen for discussion. In addition, the challenges and future directions for Cu(I) complexes as sensing materials are also presented.
A series of mononuclear heteroleptic copper(II) complexes with diethylenetriamine (DETA) and bidentate N-donor ligands, [Cu(DETA)(5,6-DMPhen)](ClO4)2 1, [Cu(DETA)(4,7-DMPhen)](ClO4)2, 2, [Cu(DETA)(3,4,7,8-TMPhen)](BPh4)2, 3, [Cu(DETA)(8-AQ)](ClO4)2, 4, [Cu(DETA)(2-AEP)](ClO4)2, 5, [Cu(DETA)(2-AMP)](ClO4)2, 6, [Cu(DETA)(1,2-DACH)](ClO4)2, 7 and [Cu(DETA)(1,3-DAP)](ClO4)2, 8, with biologically relevant N-donor ligands 5,6-dimethyl-1,10-phenanthroline (5,6-DMPhen), 4,7-dimethyl-1,10-phenanthroline (4,7-DMPhen), 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-TMPhen), 8-aminoquinoline (8-AQ), 2-aminomethylpyridine (2-AMP), 2-aminoethylpyridine (2-AEP), 1,2-diaminocyclohexane (1,2-DACH) and 1,3-diaminopropane (DAP) respectively. All the complexes (1-8) were structurally determined by a single-crystal X-ray diffraction technique and characterized by CHN, UV-Vis, FT-IR, and ESI-MS. X-ray analysis revealed that the geometry around the copper center in all complexes (1-8) is distorted trigonal bipyramidal. All complexes strongly bind with ct-DNA via groove/electrostatic interactions. Their binding with DNA was supported by UV-Vis and CD spectral studies. Docking studies revealed that copper(II) complexes containing aromatic N-donor ligands (5,6-DMPhen, 4,7-DMPhen, 3,4,7,8-TMPhen & 8-AQ) have a stronger binding affinity than complexes with aliphatic N-donor ligands (2-AMP, 2-AEP, 1,2-DACH & DAP) towards DNA. All complexes exhibited good antibacterial activity against American standard ATCC Escherichia coli (ATCC 25922) and clinically isolated Escherichia coli (E1) bacterial strains.
Cu(I) 4H-imidazolato complexes are excellent photosensitizers with broad and intense light absorption properties, based on an earth-abundant metal, and hold great promise as photosensitizers in artificial photosynthesis and for accumulation of redox equivalents. In this study, the excited-state relaxation dynamics of three novel heteroleptic Cu(I) 4H-imidazolato complexes with phenyl, tolyl, and mesityl side groups are systematically investigated by femtosecond and nanosecond time-resolved transient absorption spectroscopy and theoretical methods, complemented by steady-state absorption spectroscopy and (spectro)electrochemistry. After photoexcitation into the metal-to-ligand charge transfer (MLCT) and intraligand charge transfer absorption band, fast (0.6-1 ps) intersystem crossing occurs into the triplet MLCT manifold. The triplet-state population relaxes via the geometrical planarization of the N-aryl rings on the Cu(I) 4H-imidazolato complexes. Depending on the initial Franck-Condon state, the remaining small singlet state population relaxes into two geometrically distinct minima geometries with similar energy, S1/2,relax and S3/4,relax. Subsequent ground-state recovery from S1/2,relax and internal conversion from S3/4,relax to S1/2,relax take place on a 100 ps time scale. The internal conversion can be understood as hole transfer from a dyz-orbital to a dxz-orbital, which is accompanied with the structural reorganization of the coordination environment. Generally, the photophysical processes are determined by the steric hindrance of the side groups on the ligands. And the excited singlet-state pathways are dependent on the excitation wavelength.
The three Cu(I) complexes [Cu(POP)(N^N)]PF6, N^N = 2-(1H-imidazol-2-yl)-5-(naphthalen-2-ylethynyl)pyridine (P1), 2-(1H-imidazol-2-yl)-5-(phenanthren-9-ylethynyl)pyridine (P2), 2-(5-(naphthalen-2-ylethynyl)pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (P3), were prepared and characterized. The photophysical properties of these Cu(I) complexes is tuned by extending π- system of the N^N ligand through the addition of polyaromatic groups such as naphthalene and phenanthrene into the pyridine ring part of the diimine ligands via an acetylide linker or phenanthrene-fused imidazole ring. The resulting complexes exhibit higher absorption ability in the visible region. The emissions are in the range of 582-601 nm with quantum yields of 2.30-7.70% and the excited lifetimes of 77.4-115.8 μs for all complexes at room temperature. The photophysical properties were further explained by DFT and TDDFT methods.
A new ligand (L), 2-(2,3,6,7-tetramethoxy-9-(pyridin-2-yl)-9,10-dihydroanthracen-10-yl) pyridine, has been designed and synthesized. The anthracene ring in the ligand is curved and cannot form a large π bond conjugated system. Ligands have no fluorescence or other optical properties. When the ligand reacts with cuprous nitrate (CuNO3) to form complex (1), [LCuNO3], the anthracene ring magically straightens, and the maximum deviation of all the atoms on the anthracene ring from the anthracene ring plane is only 0.05873 Å. Complex (1) has a large two-photon absorption cross-sectional area and strong fluorescence properties. The nonlinear absorption of complex (1) (in DMF) was measured by the open-aperture Z-scan technique at a 532 nm wavelength. The results of Z-scan experiments show that complex (1) has remarkable nonlinear optical absorption effects with the two-photon absorption cross-section σ = 5969.78 GM. The ligand (L) and complex (1) all have certain thermal stability and their melting points are 169 °C for (L), and 297 °C for (1), respectively. Their properties indicate that they have potential applications.
The controlling self-assembly of cuprous iodide cluster-based supramolecular architectures with tunable structure is still a big challenge up to date. We adopt conformation-adaptive self-assembly strategy to precisely construct two [CumIn]...
Two new monometallic copper(I) complexes bearing 1,3-bis(diphenylphosphino)propane (dppp) and functional 6-cyano-2,2′-bipyridine ligands, [Cu(dppp)(cbpy)](ClO4) (1) and [Cu(dppp)(mcbpy)](ClO4) (2) (cbpy = 6-cyano-2,2′-bipyridine; mcbpy = 4,4′-dimethyl-6-cyano-2,2′-bipyridine), have been synthesized and characterized. It is revealed that complexes 1 and 2 display a distorted N2P2 tetrahedral configuration formed by two N donors of the 2,2ʹ-bipyridyl ring and two P atoms of dppp. It is shown that the introduction of two electron-donating methyl groups at the 4- and 4′-positions of 6-cyano-2,2′-bipyridine is favorable for improving luminescence properties of Cu(I) complexes.
Three new heteroleptic [Cu(NN)P2]⁺ type cuprous complexes 1–3 were designed and synthesized by utilizing a diimine ligand 5-methyl-2-(2′-pyridyl)-benzoxazole (MePBO) and different phosphine ligands PPh3 (1), m-Tol3P (2) and POP (3), (PPh3=triphenylphosphine, m-Tol3P=tris(3-methylphenyl)phosphine, POP=bis[2-(diphenylphosphino)phenyl]ether), respectively. All complexes were characterized by single-crystal X-ray diffraction, spectroscopic analysis (IR, UV-Vis), elemental analysis, and photoluminescence study. Single-crystal X-ray diffraction revealed that complexes 1–3 all adopt discrete cation complex structure with a tetrahedral CuN2P2 coordination geometry with diverse P−Cu−P angles. Their UV-Vis absorption spectra exhibit a blue-shift sequence under the enlarging of P−Cu−P angle from 3 to 2 then to 1. The PL emission peak wavelengths of 1–3 also present similar blue-shift sequence (3→1/2). Their microsecond PL lifetime indicates that their PL behavior belongs to phosphorescence. TD-DFT calculation and wavefunction analysis illuminate that the S1 and T1 states of 1–3 should all be assigned as (ML+L′L)CT states. Their UV-Vis absorption and phosphorescence should be attributed to the charge transfer from the P−Cu−P segment to the MePBO ligand. Therefore, as P−Cu−P angle increases (lower HOMO), the energy of S1 and T1 states also increase, following the change of PL color. Additionally, the steric hindrance from substituents of phosphine ligand, as well as extra strong intra-molecular π−π stacking interactions should effectively inhibit nonradiative decay so that an abnormal PL emission blue-shift is observed from 1 to 2.
The binding peculiarities of the water-soluble meso-tetra-(4N-hydroxyethylpyridyl) porphyrin (H2TOEtPyP4) and its Cu- and Co-derivatives (CuTOEtPyP4 and CoTOEtPyP4) with synthetic double-stranded alternating polynucleotide poly(dG-dC).poly(dG-dC) were investigated by UV/Vis absorption and circular dichroism (CD) methods. It was shown that the porphyrins with planar structure such as H2TOEtPyP4 and CuTOEtPyP4 interact with poly(dG-dC).poly(dG-dC) via intercalation at low relative concentrations (r = [porphyrin]/[polynucleotide]), while at high r - via intercalation and external binding modes. In the case of no planar porphyrin CoTOEtPyP4 complexation occurs only by external binding mode. The binding constant Kb and the exclusion parameter n calculated for H2TOEtPyP4, CuTOEtPyP4 and CoTOEtPyP4 porphyrins with poly(dG-dC).poly(dG-dC) complexes was 1.50 x10⁷, M⁻¹ (n = 1.76); 9.29 x10⁷, M⁻¹ (n = 1.18); and 0.28 x10⁷, M⁻¹ (n = 2.65) correspondingly. The values of binding parameters for each porphyrin–poly(dG-dC).poly(dG-dC) complexes demonstrated good agreement with the proposed binding models.
Communicated by Ramaswamy H. Sarma
Heteroleptic copper(i)-phosphine complexes have attracted considerable attention because of their diverse structures, and photophysical and catalytic properties. In this work, a series of heteroleptic diimine-diphosphine Cu(i) complexes (C1-C10) were synthesized quantitively using the designed bipyridine (L1-L4) and bidentate polyphosphine (L5-L8) as functional ligands. These mixed ligand-copper(i) complexes were fully characterized by 1H and 13C NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and elemental analysis. The detailed structures of complexes C1, C2, C5, C6, C9 and C10 were confirmed by single-crystal X-ray diffraction analysis. Moreover, these phosphine-Cu(i) complexes exhibited intense emissions either in the solid state or in solution under UV light excitation. The emissive complexes C1-C4 displayed highly sensitive luminescence sensing towards silver ions in a quenching fashion (turn-off). Furthermore, all the phosphine-protected copper(i) complexes exhibited high catalytic activity towards azide-alkyne cycloaddition (CuAAC) in water. © 2021 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Catalytic activity of copper(I) complexes supported by phenanthroline-containing catenane ligands towards a new C(sp³)–O dehydrogenative cross-coupling of phenols and bromodicarbonyls is reported. As the phenanthrolines are interlocked by the strong and flexible mechanical bond in the catenane, the active catalyst with an open copper coordination site can be revealed only transiently and the stable, coordinatively saturated Cu(I) pre-catalyst is quickly regenerated after substrate transformation. Compared with a control Cu(I) complex supported by non-interlocked phenanthrolines, the catenane-supported Cu(I) is highly efficient with a broad substrate scope, and can be applied in gram-scale transformations without a significant loss of the catalytic activity. This work demonstrates the advantages of the catenane ligands that provide a dynamic and responsive copper coordination sphere, highlighting the potential of the mechanical bond as a design element in transition metal catalyst development.
A series of dithienylethene-containing copper(I) diimine complexes have been synthesized and structurally characterized. Systematic studies on their photophysics, electrochemistry, and photochromism have been carried out. The photoinduced color changes of the copper(I) complexes have been achieved by photoexcitation into the metal-to-ligand charge-transfer (MLCT) absorption bands, indicating the photosensitization of light-induced cyclization by the 3MLCT excited state. In addition, by an increase in either the steric bulkiness around the copper(I) center or the structural rigidity of the complexes, the quantum efficiencies of photoluminescence and photocyclization can be effectively enhanced because of suppression of the flattening distortion of the complexes at the MLCT excited state. Furthermore, one of the complexes has been employed as an active component in the fabrication of solution-processed resistive memory devices. Notable lowering of the switching threshold voltage of the binary memory devices has been realized through photocyclization of the dithienylethene-containing copper(I) system.
Mixed-ligand Cu(I) complexes have attracted attention as alternatives to the noble- and/or rare-metal complexes, because of their remarkable photofunctions. To develop mixed-ligand Cu(I) complexes with rich photofunctions, an investigation of a suitable combination of ligands has captured more and more research interests. Herein, we report the first examples of emissive heteroleptic diphosphine-disulfide Cu(I) complexes combined with diphosphine ligands. The systematic study using a series of diphosphine ligands revealed that large π-conjugated bridging moieties between the two P atoms in the diphosphine ligands result in higher light-emission performance. When the diphosphine ligand was (R)-BINAP ((R)-BINAP = (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), the Cu(I) complex had an emission quantum yield (Φem) of 0.13 and a long emission lifetime (τem = 118 μs).
Three novel water-soluble Cu (II) complexes featuring miscellaneous acylhydrazone tricationic porphyrin ligands (named as Cu-Por1, Cu-Por2 and Cu-Por3) were successfully prepared and isolated. Numerous physicochemical techniques demonstrated that all the complexes exhibited favourable binding properties with calf thymus DNA (ct-DNA), especially Cu-Por3 had stronger binding affinity compared with other analogues. In addition, the antiproliferative activity of the three complexes has been evaluated by MTT assay, suggesting excellent cytotoxicity to A549, H-1975, HepG2, and T47D tumor cell lines, and little toxicity to Hs 578Bst normal breast cancer cells due to the specific targeting of porphyrins. The extraction method was also carried out to determine the cell uptake capacity of the three complexes on the tested cancer cell lines. At the same time, fluorescence microscopy analysis demonstrated that Cu-Por1 and Cu-Por3 could promote the apoptosis of H-1975 or HepG2 cells with shrunken or fragmented nuclei cells. Moreover, flow cytometry experiments further confirmed the excellent anti-tumor activity of these types of porphyrin derivatives. Our findings disclosed that this type of porphyrin complexes would represent a powerful platform for the development of novel and useful metal anticancer drugs.
This volume has evolved from a laboratory methods book that one of us first compiled nearly fifteen years ago. Since that time the book has undergone many minor revisions in order to include new methods and updated versions of older methods. The result has been an increasingly useful and more widely circulated book. However, the recent series of technological explosions generally lumped together under the name of "recombinant DNA technology" has been a turning point in the evolution of this previously underground publication. Minor revisions will no longer do. To keep the book useful we have had to make major revi sions and additions. The result is a dramatically expanded book that should be more useful to more people. The larger size and wider usefulness of the book have made this more formal publication seem a reasonable step to take. One of the reasons that this volume should be useful to many people is that it includes only procedures that have been used repeatedly by us and that have proven highly reliable both to ourselves and to others in our laboratories.
The π and σ lone pair electron system of the phthalocyanine molecule has been studied by a semiempirical SCF-MO method. Electronic transitions of both π-π* and n-π* types have been considered. The excited states have been calculated by means of the method of superposition of configurations where all singly excited states are included. Assignments for the electronic spectrum of phthalocyanine could be made in good agreement with experiment. The position of the lowest electronically allowed n-π* transition is predicted to be found in the region of the strong Soret band.
Coupling of an unpaired d electron to the porphyrin phosphorescent triplet gives rise to a “tripdoublet” and a quartet state. Luminescence from Cu porphin and Cu octalkylporphin is largely tripdoublet at liquid nitrogen temperature and quartet at liquid hydrogen temperature, while Cu tetraphenylporphin is quartet at both temperatures.
Exciting the metal-to-ligand charge transfer excited states of several CuI complexes gives rise to photoluminescence which appears to originate from the charge transfer excited states.
Structure parameters around the CuII ion in a reaction intermediate formed in the course of CuII ion incorporation into an HgII porphyrin were directly determined using a new stopped-flow EXAFS apparatus, and elongation of the Cu–N bond in the unstable heterodinuclear porphyrin intermediate was observed
The binding of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin [TMpyP(4)] to poly[d(G-C)2] and to five synthetic self-complementary oligodeoxyribonucleotides [5′→3′; d(TATATGCGCATATA)2 (I), d(ATATACGCGTATAT)2 (II), d(TATATCGCGATATA)2 (III), d(TATGGGTACCCATA)2 (IV), d(TATATGCATATA)2 (V)] was studied. For poly-[d(G-C)2], I, II, and III, TMpyP(4) binding was accompanied by a characteristic 31P NMR signal at ∼-0.9 ppm relative to trimethyl phosphate. Pronounced upfield shifts of some of the imino 1H signals were also observed. In contrast, IV and V did not exhibit these characteristics on TMpyP(4) addition. A related porphyrin species, meso-tetrakis(N,N,N-trimethylanilinium-4-yl)porphyrin (TMAP), is an outside binder and does not induce these pronounced changes in the spectra of I. Detailed analysis of the imino 1H signals in I-TMpyP(4) and assignment by 17O labeling of the downfield 31P signal to 5′CpG3′ in I-TMpyP(4) support selective symmetric binding at the 5′CpG3′ sequence in I. Less detailed study of II-TMpyP(4) and III-TMpyP(4) and the absence of the effects with IV and V support 5′CpG3′ binding to II, III, and poly[d(G-C)2]. An analogue of I with the C in the 5′CpG3′ binding site replaced by a T, namely d(TATATGTGCATATA)2 (VI), forms a duplex with adjacent GT mismatches. TMpyP(4) does not induce pronounced spectral changes for VI. An unusual feature of the 5′CG3′ TMpyP(4) binding for I, II, and III is that imino 1H signals for two base pairs on either side of the binding site are also shifted upfield. These upfield shifts and the downfield 31P shift are consistent with selective intercalation at the 5′CG3′ sequence by the highly anisotropic porphyrin ring. However, other outside binding sites compete with this most favored binding. Nevertheless, TMpyP(4) binding is unusually selective compared to that of other synthetic molecules that form noncovalent DNA adducts.
H NMR spectroscopy was used to study the binding of Δ-Co(en)3³⁺ to the dodecanucleotide d(TCGGGATCCCGA)2. Intermolecular NOE cross peaks between the metal complex methylene protons and the dodecanucleotide unambiguously establish that Δ-Co(en)3³⁺ selectively binds at GG sequences in the major groove. The NMR experiments indicated that the dodecanucleotide maintains a B-type DNA conformation upon metal complex binding.
The X-ray structure of [Cu(dnpp)2]PF6, where dnpp denotes 2,9-dineopentyl-1,10-phenanthroline, reveals a flattened tetrahedral copper complex with a dihedral angle between the least-squares planes of the ligands of only 63.4(1)°. Steric interactions involving γ methyl groups of the substituents have an important role in shaping the complex, but lattice forces are ultimately responsible for the flattened geometry. Crystal data: [Cu(C22H28N2)2]PF6, triclinic, P1̄, a = 10.2755(10) Å, b = 13.9750(12) Å, c = 16.4354(12) Å, α = 79.376(7)°, β = 86.989(7)°, γ = 69.981(7)°, Z = 2. Spectral measurements involving four other Cu(NN)2+ systems, where NN denotes a 2,9-dialkyl-1,10-phenanthroline ligand, reveal that the room-temperature emission maxima fall at shorter wavelengths (20−50 nm) in the solid state as compared with fluid solution. The emission from Cu(dnpp)2+ is unique in that it maximizes at a slightly longer wavelength in the rigid solid (670 nm vs 665 nm in CH2Cl2). The spectral data support the following conclusions regarding structures in fluid solution: (1) The vibrationally relaxed excited state of Cu(dnpp)2+ adopts a structure similar to that observed in the solid. (2) However, the ground state assumes a less flattened, more tetrahedral geometry.
The crystal structures of the title compounds have been determined from diffractometer data and refined with use of the least-squares method. Crystal data for CuC28H32N4O4Cl are space group Pbcn, Z = 4, a = 16.507 (3) Å, b = 13.628 (2) Å, c = 12.284 (2) Å, V= 2763.4 Å3, and R = 0.093 for 1593 reflections. The perchlorate anions are uncoordinated, and the copper(I) environment (CuN4) is pseudotetrahedral with a dihedral angle of 68° between the symmetry-related halves of the molecule. Crystal data for CuC28H32N4O8Cl2, are space group P21/c, Z = 4, a = 17.775 (2) Å, b = 12.785 (3) Å, c = 14.514 (2) Å, β= 110.51 (3)°, V = 3089.2 Å3, and R = 0.048 for 2084 reflections. The copper atom is five-coordinate, and the stereochemistry of the complex is distorted trigonal bipyramidal with a perchlorate anion bound at an equatorial position. Crystal data for CuC28H36N4O8Cl2 are space group P21/c, Z = 8, a = 14.594 (2) Å, b = 16.192 (3) Å, c = 28.934 (2) Å, β= 103.50 (4)°, V= 6648.4 Å3, and R = 0.113 for 3921 reflections. In this structure the perchlorate anions are uncoordinated and a water molecule is bound at one of the equatorial positions of a distorted trigonal bipyramid about copper. Previous studies of bis(4,4′,6,6′-tetramethyl-2,2′-bipyridyl)copper(II) diperchlorate have been interpreted in terms of a distorted-tetrahedral geometry about copper. An analogous species has been suggested to be the reactive form in an electron-transfer reaction involving ferrocyanide and a corresponding phenanthroline complex of copper(II). The present work suggests that a five-coordinate form is likely to be the dominant species in solution for complexes with these types of ligands.
Rates of phenyl ring rotation in gallium chloro complexes of para-substituted tetraphenylporphyrins were studied by variable-temperature 1H NMR of the phenyl resonances. Para substituents examined were trifluoromethyl, chloro, methyl, isopropyl, methoxy, and diethylamino. Activation parameters obtained by total line shape analysis are in the ranges ΔG‡298 = 12.8-15.0 kcal/mol, ΔH‡ = 9.2-12.5 kcal/mol, and ΔS‡ = -12.4 to -8.1 eu. Rates of ring rotation for the gallium complexes are the fastest observed to date for metallotetraphenylporphyrin complexes. Rates are faster for electron-donating substituents than for electron-withdrawing substituents but do not give a linear correlation with Hammett σp values.
The complex Pt(II)(hematoporphyrinH2)Cl2 which contains free base porphyrin as a bidentate ligand is light sensitive. In DMF a photosubstitution takes place. The porphyrin is released with φ∼ 2×10−3 at λin = 405 nm. It is assumed that the photolysis originates from a ligand field state which is populated from ππ∗ intraligand states. In a secondary photolysis the porphyrin undergoes a decomposition in agreement with previous results.
Exciplexes are less common in transition metal photochemistry than in organic photochemistry. However, Lewis bases and coordinating anions quench metal-to-ligand charge-transfer excited states of Cu(I) systems, and the quenching is ascribed to exciplex formation. A variety of structural arguments and steric effects lend strong support to the model. These results are related to the broader context of transition metal systems, and future areas of potential interest are briefly discussed.
Medium dependence of the emission spectra of several meso-substituted copper porphyrins was studied at 300-77 K. Copper porphyrins emit from the lowest excited (porphyrin triplet) states in fluid solution as well as in rigid media. Emission spectra of several copper porphyrins in toluene liquid solution were red-shifted from those in rigid media such as PMMA (poly(methylmethacrylate)) film. The copper porphyrins, which give red-shifted emission in toluene solution, have 2,4b13(a2ueg)] configuration in the lowest excited states and the amount of the shift depends on meso-substituents ranging up to 1300 cm−1. As the emission spectra in toluene rigid glass at 77 K coincide with those in PMMA film, the observed shift in 2,4[b13(a2ueg)]-type porphyrins is attributable to distortion of the excited molecules in fluid solution. T(2,4,6-(MeO)3)PPCu, in which bulky meso-substituents are likely to suppress torsion of the phenyl rings and distortion of the porphyrin plane, was found to show no shift of emission spectra, in spite of the 2,4[b13(a2ueg)] configuration. In the case of TPrPCu, which has no phenyl group, red shift occurs as a result of the medium being changed to become non-rigid. An out-of-plane distorted structure is proposed. Lifetimes of the emission in toluene solution are remarkably shorter in the copper porphyrins that show a larger emission red-shift from the emission in PMMA film. This relation suggests that the distortion modes are connected with enhancement of the radiationless decay.
Extended-Hückel and multiple-scattering Xα molecular orbital calculations are reported for the Cu(ethanediimine)+2 complex. The results obtained are in agreement. From the calculated electronic transition energies, it is inferred that the lowest excited state is a B2 state of metal-to-ligand charge-transfer type, confirming resonance Raman results.
Resonance light scattering (RLS) and circular dichroism (CD) spectroscopies have been used to investigate the interactions of several cationic porphyrins with poly(dA) and poly(rA). Neither tetrakis(N-methylpyridinium-4-yl)porphine nor its zinc(II) derivative (H2T4 and ZnT4) show any tendency to form extended porphyrin assemblies in the presence of poly(dA). However, the poly(dA) complex of CuT4 involves considerable porphyrin self-stacking. In the presence of poly(rA), only ZnT4 of these three porphyrin derivatives, fails to assemble. Differences in the interactions of trans-bis(N-methyl-pyridinium-4-yl)diphenylporphine (t-H2Pagg) with these two single-stranded nucleic acid polymers are described. Whereas the porphyrin is capable of forming extended assemblies with either poly(dA) or poly(rA), increasing the salt concentration in the latter system results in a reversal of the induced circular dichroism spectrum in the Sorel region indicating a conformational change of the porphyrin assembly.
To elucidate the interaction mechanism of water-soluble copper(II) tetrakis(4-N-methylpyridyl)porphyrin (CuII-
(TMpy-P4)) with synthetic polynucleotides such as poly(dA-dT)2 and poly(dG-dC)2, the exciplex formation
dynamics of photoexcited CuII(TMpy-P4) with added polynucleotides have been investigated by using
femtosecond transient absorption as well as transient Raman spectroscopic methods. The nanosecond transient
Raman spectra of CuII(TMpy-P4) mixed with poly(dA-dT)2 clearly demonstrate the exciplex formation between
photoexcited CuII(TMpy-P4) and poly(dA-dT)2. On the other hand, the exciplex formation of photoexcited
CuII(TMpy-P4) with poly(dG-dC)2 is not so manifest as compared with that mixed with poly(dA-dT)2. The
transient absorption of CuII(TMpy-P4) mixed with poly(dG-dC)2 exhibits a rise component of 1.3 ps in addition
to the very slow decay component (ô � 22 ns). This observation is quite different from that of CuII(TMpy-
P4) in aqueous solution or CuII(TMpy-P4) mixed with poly(dA-dT)2, because the exciplex formed in poly-
(dG-dC)2, if any, is so short-lived that it returns quickly back to four-coordinate CuII(TMpy-P4) intercalated
at poly(dG-dC)2, which blocks the axial coordination by water molecules and consequently gives rise to a
long lifetime (ô � 22 ns).
Binding and spectroscopic parameters for a series of mixed-ligand complexes on binding to DNA have been determined. The application of mixed-ligand complexes permits the variation in geometry, size, hydrophobicity, and hydrogen-bonding ability by systematic variation of complex ligands and the determination of how these factors contribute to DNA binding affinity. Ligands employed include 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-diphenylphenanthroline (DIP), 5-nitrophenanthroline (5-NO2-phen), 4,5-diazafluorene-9-one (flone), and 9,10-phenanthrenequinonediimine (phi). Measurements include equilibrium binding isotherms and enantioselectivities associated with binding, the degree of absorption hypochromism and red shift in the ruthenium charge-transfer band, increases in emission intensities and excited-state lifetimes, perturbations in excited-state resonance Raman spectra (which reflect changes in excited-state charge-transfer distributions as a result of binding to DNA), and determinations of helical unwinding. The complexes examined, with the exception of Ru(bpy)32+, all appear to intercalate and surface-bind to DNA, and for those that bind appreciably, enantioselectivity is observed. Based upon the measurements of spectroscopic properties and binding isotherms, the intercalating ability appears to increase over the series bpy ≪ phen ≤ DIP ≪ phi. Correlations between hydrophobicity and DNA binding affinity are observed. The introduction of hydrogen-bonding functionalities provides no net increase in DNA binding affinity. Most critical in determining overall affinity appears to be the shape of the complex and how that shape matches the DNA. The array of well-defined shapes and structures, conveniently prepared and varied for these mixed-ligand complexes, coupled with the spectroscopic handle available by monitoring perturbations in the charge-transfer state of the ruthenium(II) complexes, can be useful in systematic studies of DNA recognition as well as that of other biopolymers.
Relaxation processes of excited copper porphyrins were studied with relevance to the structure of the substates of the lowest excited states. Lifetimes of luminescence at room temperature were determined as 17, 29, 69, and 105 ns for T(EtO)PPCu [T(EtO) PP: 5, 10, 15, 20‐tetra (p‐ethoxyphenyl)porphin], TPPCu(TPP: 5, 10, 15, 20‐tetraphenylporphin), TFPPCu[TFPP: 5, 10, 15, 20‐tetra(pentafluorophenyl)porphin], and OEPCu(OEP: 2, 3, 7, 8, 12, 13, 17, 18‐octaethylporphin) in toluene, respectively. Emission intensities and lifetimes of OEPCu and TFPPCu measured as a function of temperature show a variation ascribed to a Boltzmann distribution between the lowest trip–doublet and –quartet with an energy gap of 300–400 cm−1. The anomalous temperature dependence for TPPCu and T(EtO)PPCu is explained by a larger energy gap and larger vibronic distortions in the excited state. The difference in behavior is attributed to the orbital nature of the triplet: ‖2,4[b31(a1e)]〉 for OEPCu and TFPPCu but ‖2,4[b31(a2e)]〉 for TPPCu and T(EtO)PPCu. The assumption of a low energy charge transfer state is not necessary for our analysis.
Calorimetric studies of the triethylamine-iodine system in n-heptane revealed that the measured heat of reaction of the amine and iodine to form a 1:1 complex was strongly dependent upon the amine concentration. This result is explained in terms of the existence of a second iodine(I) complex, [(Et3N)2I+][I-], which is in equilibrium with the 1:1 complex. The molar heats of reaction that accompany the formation of 1:1 complexes were measured for seven amine-iodine systems in n-heptane by the method of thermometric titration and found to compare favorably with those values obtained by spectroscopic techniques. The sensitivity of iodine(I) compounds to hydrolysis and disproportionation is discussed.
The crystal and molecular structures of copper tetraphenylporphine, palladium tetraphenylporphine, zinc tetraphenylporphine dihydrate, and ferric hydroxide tetraphenylporphine monohydrate were determined from three-dimensional X-ray diffraction data. These structures are all_tetragonal. The space group of both copper tetraphenylporphine and palladium tetraphenylporphine is I42d with four molecules per unit cell. The other two porphyrins have two molecules per unit cell. The space group of the zinc porphyrin is I4/m and the molecular symmetry is 4/m. The iron porphyrin has space group 14 and a molecular symmetry of 4. The molecular configuration changes from a planar to a buckled, nonplanar one depending on the crystal packing and on the substituents attached to the porphine nucleus. Copper and palladium tetraphenylporphine are very nonplanar, while the porphine nucleus of the zinc compound is planar. The iron porphyrin is nearly planar except that the iron atom is 0.2 Å. above the plane of the four nitrogen atoms in the porphyrin ring.
While Cu II porphyrins are known to luminesce, Ag II complexes do not. It is shown here that silver(III) octaethylporphyrin has no emission while gold(III) tetraphenylporphyrin has a moderately intense phosphorescence with a nonexponential decay fit with two decay times of 63 and 184 μs. I n contrast to Cu II and Au III porphyrins, the Ag complexes have a metal redox potential, II ⇄ III, between that of ring oxidation and ring reduction suggesting that luminescence is quenched by low-energy charge transfer transitions Ag II → ring or ring → Ag III. Near-infrared (1100-700 nm) absorption spectra confirm the presence of weak absorption bands in Ag II and Ag III complexes that are not observed in complexes of Cu II and Au III. The near-IR absorption of Cu II(TPP) and the quenching of its unusually broad emission by pyridine suggest that a charge transfer state is close to the emitting level. Iterative extended Hückel calculations explain these facts by the energy of orbital b 1g(d x2-y2), which rises along the series Cu < Ag < Au.
Tris(2,2′-bipyridyl) complexes of divalent iron-group metals are characterized by a number of remarkable, low-lying charge-transfer states. A detailed elaboration of the intensity mechanism, governing these transitions, provides a direct understanding of an otherwise complex excited-state system. The treatment uses a general MO language and is mainly based on symmetry properties. As a result, new assignments are proposed for the visible and near-UV spectra of M(bpy)32+ complexes (M = Fe(II), Ru(II)). Attention is drawn to the apparent spectroscopic relevance of the Orgel criterion for ligand orbital classification.
Excited-state dynamics of copper(II) tetraphenylporphyrin left bracket Cu(TPP) right bracket and copper(II) etioporphyrin left bracket Cu(Etio) right bracket depends dramatically on the coordinating properties of the solvent system. Relaxation of transient absorption and recovery of ground-state bleaching following excitation with 35-ps flashes at 355 nm range from greater than 10 ns in the noncoordinating solvent, toluene, to approx. 100 ps in the coordinating solvent, piperidine. Lifetimes of intermediate duration are observed in toluene/piperidine mixtures; for Cu(TPP) the time constants are 650 ps and 2. 1 ns in 1 and 0. 3 M piperidine, respectively. Analogous results are found for Cu(Etio) and in pyridine. Despite such variation in kinetic behavior, transient difference spectra observed for both Cu porphyrins are essentially independent of solvent.
Rates of hydrolysis of the vinyl ether functional group of prostacyclin and its methyl ester were measured in aqueous solution at 25°C over the acidity range -log [H+] = 1-8. The rate profile for prostacyclin shows a break, from which pKa = 5.03 ± 0.15 may be inferred for the carboxylic acid group of this molecule and a 102-fold greater reactivity may be deduced for the carboxylate over the carboxylic acid form. The hydrogen ion catalytic coefficient for reaction of the carboxylic acid form, kH+ = 439 ± 4 M-1 s-1, is similar to that of prostacyclin methyl ester, kH+ = 418 ± 5 M-1 s-1, and is normal for a vinyl ether of this structure. Kinetic isotope effects and unusually weak catalysis by external general acids suggest that the abnormal reactivity of the carboxylate form is the result of intramolecular general-acid catalysis by the carboxylic acid group; an effective molarity of 0.6 M can be estimated for this process.
The nuclease activity of 1,10-phenanthroline-copper ion (OP-Cu) proceeds by an obligatory, ordered mechanism, whether the reaction is potentiated by thiol or superoxide. Freely diffusing 1,10-phenanthroline-cupric ion is reduced to the cuprous complex (eq 1a), which binds reversibly to the DNA (eq 1b). The noncovalently bound complex is then oxidized by hydrogen peroxide to generate the copper-oxo species directly responsible for strand scission (eq 1c). 1,10-Phenanthroline-cupric (OP) 2Cu 2+ ↔ 1e- (OP) 2Cu + (1a) DNA + (OP) 2Cu + ↔ DNA-(OP) 2Cu + (1b) DNA-(OP) 2Cu + → H2O2 nicked products (1c) ion bound to DNA cannot be on the main reaction pathway because its reduction is not fast enough to be a kinetically competent step in the overall reaction. The tetrahedral cuprous complex is therefore the binding species responsible for the sequence-dependent reactivity of the nuclease. Cleavage patterns produced by the copper complexes of substituted 1,10-phenanthrolines are consistent with the nonintercalative binding of the tetrahedral complex in the minor groove. A model is proposed for this interaction.
The d sigma* --> p sigma excited state of Pt-2(pop)(4)(4-) (1, pop = P2O5H22-) elicits frank scission of double-stranded DNA as assayed by high-resolution gel electrophoresis. The photoreaction of 1 and a 5'-P-32-labeled 25-mer duplex produces a surprisingly even ladder of phosphate terminated bands with some modified bands that can be assigned as phosphoglycolate termini by comigration with the products of an Fe(EDTA)(2)-/H2O2 reaction. The analogous reaction of the 3'-P-32-labeled duplex also produces phosphate termini and a modified band that can be assigned as a 5'-aldehyde terminus by NaBH4 reduction to the 5'-alcohol and comigration with authentic alcohol termini generated using alkaline phosphatase. These products are consistent with abstraction of the 4' and 5' hydrogens from the deoxyribose function; products indicative of 1' or 3' chemistry were not detected. The reaction is more efficient in the presence of O-2, which appears to trap the radical produced by homolytic C-H activation. The even cleavage ladder argues strongly against a O-1(2) mechanism, and the cleavage is not enhanced in D2O. Further, ethanol does not inhibit the reaction of 1 at concentrations up to 1 M, where the reaction of hydroxyl radical is completely quenched. These experiments point to a mechanism where the tetraanionic complex collides directly with the DNA to effect C-H activation, which is supported by a strong enhancement in cleavage by Mg2+. This unusual reaction has been used to obtain a footprint of lambda repressor bound to the O(R)1 sequence. The resolution of the footprint is similar to that of hydroxyl radical, which permits binding of the repressor to a single side of the DNA helix to be distinguished.
The interaction of a series of isomeric palladium tetrakis(N-methyl-x-pyridinium)porphyrin (x = 2, 3, and 4) with DNA and synthetic polynucleotides has been studied. Both intercalation between base pairs (x = 3 and 4) and electrostatic binding to the external phosphate chain (x = 2) are observed. Once bound to DNA, the excited triplet state of these cationic porphyrins can be quenched by oxygen dissolved in the surrounding aqueous reservoir and by methyl viologen bound to the phosphate chain. Rates' of quenching can be related to the location of the bound porphyrin on the DNA duplex. Singlet and triplet energy transfer is also observed from intercalated acridine orange to a porphyrin (x = 3) that is intercalated into the same helix. The rates of singlet energy transfer are discussed in terms of competing Forster- and Dexter-type mechanisms, and it is concluded that the DNA duplex does not provide a particularly attractive medium for electron exchange.
We have used a variety of physical methods to investigate the ways by which copper phenanthrolines bind to B-form DNA. To vary the composition of the DNA, we have employed poly(dG-dC).poly(dG-dC), M. lysodeikticus DNA, salmon testes DNA, and poly(dA-dT).poly(dA-dT) as hosts. The specific copper complexes we have studied are Cu(dmp)2+ and Cu(bcp)2+ where dmp and bcp denote 2,9-dimethyl-1,10-phenanthroline and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, respectively. The results indicate that the dmp complex binds externally in a solvent-accessible site. However, the solvent cannot access the metal center as readily in the case of the bcp complex because Cu(bcp)2+ is emissive in the presence of DNA. Since the emission retains polarization, the complex does not rotate independently but tumbles with the macromolecule in solution. At low loadings of Cu(bcp)2+ the specific viscosity due to DNA molecules that are rich in adenine-thymine base pairs increases; however, the results are inconsistent with classical intercalative binding. They are more logically interpreted in terms of bridging structures in which one or more bcp complexes link DNA molecules together in solution. High loadings of Cu(bcp)2+ induce further condensation of the DNA and ultimately particulate formation. The techniques we have used in this work include absorption spectroscopy, circular dichroism, emission spectroscopy, emission polarization, and viscometry. The findings are relevant to the chemistry of copper complexes involving unmethylated phenanthrolines, systems widely being used to probe DNA structure.
Different types of DNA have been used to investigate binding interactions of Cu(TMpyP4), where TMpyP4 denotes the deprotonated form of meso-tetrakis(4-(N-methylpyridiniumyl))porphyrin. Physical methods employed include electronic absorption and circular dichroism as well as luminescence spectroscopy. Most of the studies have been carried out at mu = 0.2 M in a pH 7.8 Tris buffer at 25-degrees-C. With DNA samples containing both guanine-cytosine and adenine-thymine base pairs, our results confirm that Cu(TMpyP4) can bind at external sites-most likely within one of the grooves of DNA-or by intercalation (Pasternack, R. F.; Gibbs, E. J.; Villafranca, J. J. Biochemistry 1983, 22, 2406-2414). Moreover, our results show that the distribution between the two types of sites depends on the nucleotide-to-copper ratio and that intercalation is favored at moderate ratios. A guanine-cytosine base pair in combination with any other base pair seems sufficient to define an intercalation site. Novel emission with a lifetime of about 20 ns is observed from the tripdoublet and tripquartet excited states of intercalated Cu(TMpyP4). This emission is normally quenched by a mechanism which involves coordination of the solvent at an axial position of the copper center. Deactivation is proposed to occur via a low-energy d-d state of the five-coordinate complex. Solvent-induced quenching occurs when the complex is externally bound but not when the complex is intercalated because the axial coordination sites are blocked. The results are of interest because porphyrins are important DNA-binding agents and because solvent-induced quenching is becoming recognized as an important type of exciplex phenomenon that can occur in coordinatively unsaturated complexes.
We have investigated the excited-state relaxation dynamics and pathways of copper(II) octaethylporphyrin (CuOEP) and copper(II) tetraphenylporphyrin (CuTPP) in noncoordinating solvents at temperatures between 295 and 77 K. The excited-state deactivation of CuOEP depends markedly on temperature and solvent. For example, the lifetime in methylcyclohexane varies from 270 ns at 295 K to 10 μs at 150 K. The lifetime at 295 K varies from 100 ns to 1 μs with a change in solvent polarity. In contrast, the lifetime of photoexcited CuTPP is 30-40 ns, essentially independent of temperature and solvent. These observations can be explained in terms of a model that includes the participation of a charge-transfer (CT) state, most likely a ring-to-metal (π,d) CT, in the deactivation of the tripdoublet (2T) excited state. Our results suggest that the CT excited state lies 600-800 cm-1 above 2T in CuOEP and between 2T and the quartet (4T) in CuTPP.
Resonance Raman (RR) spectra of a series of water-soluble copper(II) porphyrins mixed with DNA and synthetic oligonucleotides were measured by using CW and pulsed laser excitation. In CW excitation (406.7 and 441.6 nm), all the porphyrins mixed with these nucleic acids exhibit porphyrin core vibrations near 1570 and 1368 cm-1. Upon pulsed laser excitation (416 and 436 nm), some porphyrins mixed with nucleic acids containing ATAT sites exhibit extra bands at 1550 and 1346 cm-1, which originate in the transient exciplex formulated as Cu(porphyrin)*+(AT)-. Under proper experimental conditions, the populations of the ground-state porphyrins and the corresponding exciplexes become nearly equal. In the case of GC/CG intercalating porphyrins, this result suggests that some of these porphyrins are translocated from GC/CG to ATAT sites upon electronic excitation by pulsed laser. Three experiments were carried out, which supported the concept of translocation: (1) A typical GC/CG intercalator, Cu(TMpy-P4), was mixed with a 32-mer containing 26 possible GC/CG intercalation sites and only one ATAT site at the molar ratio of one porphyrin per two duplexes. Under these conditions, most of the porphyrins in their electronic ground states are expected to be intercalated at GC/CG sites. Yet, this solution exhibits a RR spectrum in which the exciplex bands are slightly stronger than the ground-state bands. (2) After Cu(TMpy-P4) was mixed with the 32-mer as in (1), a well-known AT site binder, Co(TMpy-P4), was added to the solution to block any unoccupied ATAT sites. Analysis of the pulsed laser RR spectrum of this solution reveals that at least 32% of the total porphyrin has been translocated from the GC/CG to an ATAT site. (3) The pulsed laser RR spectrum of Cu(TMpy-P4)-DNA at -85-degrees-C indicates that the intensities of the exciplex bands have decreased markedly relative to those at room temperature. This observation suggests that some degree of molecular rearrangement is required to form the exciplex. Finally, the time scale of such translocatioin has been estimated and the biological significance of exciplex formation discussed. Observations have also been made regarding the enhanced photodegradation of DNA caused by this exciplex.
The absorption and emission spectra of a series of [Cu(NN)2]+ systems, where NN denotes a heteroaromatic, chelating ligand derived from 1,10-phenanthroline or 2,2′-bipyridine, have been investigated. Detailed group theoretical assignments of the relevant low-lying charge-transfer states are presented. For the first time, a charge-transfer absorption band has been identified with a polarization perpendicular to the axis joining the metal and the ligand centers (the z axis). One of the most novel properties of the complexes is that they exhibit thermally activated emission. Data presented include absorption and emission polarization measurements from glycerin solutions over the temperature range 90-175 K as well as data from a 4:1 (v/v) ethanol-methanol solution at 90 K. The emisssion can be attributed to two different excited states in thermal communication, and both components of the emission are z polarized. The results are inconsistent with a model that assigns the emissions to spin-orbit components derived from a triplet excited state (Parker, W. L.; Crosby, G. A. J. Phys. Chem. 1989, 93, 5692-5696), but they are in accord with a previous proposal which assigns the thermally activated emission to a singlet state (Kirchhoff, J. R., et al. Inorg. Chem. 1983, 22, 2380-2384).
The resonance Raman spectra of a water-soluble metalloporphyrin Cu(TMpy-P4), complexed with a synthetic nucleic acid, poly(dA-dT), were measured by using excitation wavelengths located within the B (Soret) transition of the porphyrin (417-470 nm), while its excited state was synchronously pumped with 545-nm pulsed excitation corresponding to the Q transition. In the presence of pump pulses, the aqueous solution of the Cu(TMpy-P4)·poly(dA-dT) complex exhibits resonance Raman bands at 1558 and 1353 cm-1 that are not observed in the absence of pump pulses. These new features were previously assigned to electronically excited Cu(TMpy-P4), stabilized by forming an exciplex with the A-T sites of the nucleic acid. Here we present resonance Raman excitation profiles (RREP) of both the excited and ground states of the complex, and we experimentally confirm the very short lifetime of the exciplex. To our knowledge this is the first time that a RREP of a very short lived (ca. 20 ps) intermediate excited state has been obtained with a two-color experiment. We use this to help to characterize the nature of the porphyrin-AT specific complex formed in the porphyrin excited state.
Complexes of a water-soluble metalloporphyrin Cu(TMpy-P4) (CuP) with a variety of synthetic oligonucleotides, single- and double-stranded polynucleotides of different base composition and sequences, have been tested by resonance Raman spectroscopy for the possibility to form an exciplex under high-power pulsed laser excitation at 424 nm, i.e., in the Soret band of the porphyrin. Such a photoinduced exciplex had been previously observed in the CuP interaction with poly(dA-dT), calf thymus DNA, and double-stranded oligomers containing at least four alternating A-T base pairs: it was associated with an A-T-specific stabilization of an electronically excited CuP. The present results show that the presence of A-T sites in the duplexes is not exclusive of other parameters, since the exciplex is also observed in CuP-poly(dT) and CuP-poly(rU) complexes as well. This demonstrates that either thymine or uracil residues are necessary for forming the exciplex. However, the exciplex does not occur in CuP complexes with poly(dA).poly(dT), poly(rA).poly(rU), dTMP, UpU, and d(pT)2: this suggests that the presence of thymine or uracil residues in solution is, in and of itself, not sufficient, but the fixation mode of CuP on polynucleotide and the proper secondary structure of the polymer also play important roles in the process of exciplex formation. An explanation of exciplex building is proposed in terms of a short-lived five-coordinated complex of a (d-d) excited state of CuP with thymine or uracil carbonyl groups as the fifth ligands. The structural properties of thymine- (uracil-) containing polynucleotides required for an effective axial coordination are discussed. A model of porphyrin-DNA interaction is proposed, allowing the lack of exciplex formation in CuP-poly(dA).poly(dT) and CuP-poly(rA).poly(rU) complexes to be explained.
Time-resolved resonance Raman (TR(3)) spectroscopic investigations were done on copper(II) tetraphenylporphyrin ((CuTPP)-T-II) and copper(II) octaethylporphyrin (Cu(II)OEP) in various solvents to elucidate the electronic nature of the excited states involved in the deactivation processes. In noncoordinating solvents, the frequency shift and enhancement pattern in the Raman spectrum of excited state (CuTPP)-T-II were identified as the simultaneous contribution from the T-2/T-4 (pi,pi*) manifold and the (pi,d) charge transfer state (CT1). These observations were also consistent with the small energy gap between the-T-2/T-4 (pi,pi*) manifold and the (pi,d) charge transfer state of (CuTPP)-T-II, as suggested by the previous picosecond transient absorption results. On the contrary, our TR(3) spectrum of Cu(II)OEP represented the characteristic features mainly induced by the T-2/T-4 (pi,pi*) manifold with no indication of the contribution from the (pi,d) charge transfer state, which was suggested to be located in an energy well above the T-2/T-4 (pi,pi*) manifold. In coordinating solvents, however, the TR(3) spectra of (CuTPP)-T-II and Cu(II)OEP, as indicated by the significant shifts of the v(2) and v(4) bands relative to those in noncoordinating solvents, exhibited the involvement of a new (pi,d) charge transfer state (CT2) associated with the formation of the five-coordinated species with solvent as an axial ligand in the excited state. The identification of the electronic nature and the axial ligand dynamics in the excited states of Cu-II TPP and Cu(II)OEP was demonstrated by examining the relationship between the core size expansion upon axial ligation and the shift and enhancement pattern of characteristic Raman bands.
We report the transient resonance Raman spectra of five-coordinate Cu(II) complexes of meso-tetraphenylporphine (TPP) and meso-tetraphenylchlorin (TPC). With piperidine as a ligand, we observe a Raman spectrum that is consistent with either a (d,d) or a (d,pi*) excited state. With tetrahydrofuran (THF) as a ligand, two distinct excited states are observed. One of them is assigned to either a (d,pi*) or a (d,d) state by analogy with the spectrum in piperidine. The other shows spectral features that are similar to those observed for the cation radical of CuTPP. We assign the second state to a ring-to-metal (pi,d) charge-transfer excited state. The transient Raman spectrum of CuTPC in THF shows features that are consistent with a (pi,d) charge-transfer excited state only. Our results provide the first direct spectroscopic evidence for the existence of charge-transfer and, possibly, (d,d) excited states that Lie close in energy to the tripmultiplet excited states of CuTPP and CuTPC.
This investigation focuses on a series of pseudotetrahedral complexes of the form Cu(NN)2+, where NN denotes a 1,10-phenanthroline ligand with alkyl substituents in the 2 and 9 positions and the counterion is PF6-. In these copper(I) systems, steric effects are of considerable interest because the electronic configuration predisposes the reactive charge-transfer excited state to undergo a flattening distortion or to add a fifth ligand. Both effects lead to emission quenching and a shorter excited-state lifetime. Bulky substituents inhibit these processes, but the spatial distribution of the atoms involved is more important than the total molecular volume in determining the influence of a substituent. According to the results of this study, the effective size decreases in the following order: sec-butyl > neopentyl > n-octyl ≈ n-butyl > methyl. In conjunction with the electrochemical data, the absorption and the emission spectra reveal three kinds of steric effects: (1) Clashes between substituents on opposite phenanthroline ligands hinder D2 flattening distortions in the oxidized form of the complex and in the charge-transfer excited state of the Cu(NN)2+ system itself. (2) Steric interactions connected with a highly branched substituent, like the neopentyl group, destabilize the Cu(NN)2+ ground state. (3) Finally, the presence of bulky groups disfavors expansion of the coordination number. The complex with sec-butyl substituents is noteworthy because it exhibits the longest excited-state lifetime (400 ns in CH2Cl2) ever measured for a Cu(NN)2+ system in fluid solution. In addition, it exhibits a luminescence lifetime of 130 ns in acetonitrile which is ordinarily a potent quencher of photoexcited Cu(NN)2+ systems.
For a series of copper(II) porphyrins, we report EPR data from solid solutions as well as E0 values for the first ring oxidation, emission spectra, and luminescence lifetimes in methylene chloride. Although the EPR parameters are fairly constant, the potentials vary by almost 700 mV, and the room-temperature lifetimes range from 300 ns for Cu(TCl2PP) to 15 ns for Cu(TMeOPP), where TCl2PP denotes 5,10,15,20-tetra(2‘,6‘-dichlorophenyl)porphyrin and TMeOPP denotes 5,10,15,20−tetra(4‘-methoxyphenyl)porphyrin. The data show that the variation in the lifetime of the emitting π−π* state is not due to the thermal population of another excited state of either d−d or charge-transfer parentage. However, the results are consistent with a model originally introduced by Asano et al. who proposed that an important vibronic distortion occurs in the emitting trip-doublet and trip-quartet states when the excitation involves the a2u orbital of the porphyrin (Asano, M.; Kaizu, Y.; Kobayashi, H. J. Chem. Phys. 1988, 89, 6567−6576). In view of the fact that the distortion is unique to the copper systems, we suggest that it involves movement toward a sitting-atop structure, consistent with the role the d10 configuration is likely to have in the excited-state wave function.
1H NMR spectroscopy was used to study the binding of Pt(en)22+ to the dodecanucleotides d(CAATCCGGATTG)2 and d(TCGGGATCCCGA)2. Addition of Pt(en)22+ to d(CAATCCGGATTG)2 induced a significant and selective change in the chemical shift of the A3H2 resonance but only small shifts for the major groove base resonances. Similarly, addition of Pt(en)22+ to d(TCGGGATCCCGA)2 induced a selective change in the chemical shift of the A6H2 resonance. In the NOESY spectrum of d(CAATCCGGATTG)2 with added Pt(en)22+ intermolecular NOE cross-peaks between the methylene protons of the metal complex and the H2 of A3 and A9, as well as the H1‘ of T4, T10, and T11 were observed. Importantly, no NOE cross-peaks from the metal complex to either major groove protons or guanine and cytosine protons were observed. In the NOESY spectrum of d(TCGGGATCCCGA)2 with added Pt(en)22+ intermolecular NOE cross-peaks from the metal complex were only observed to the H2 and H1‘ protons of A6 and the T7H1‘ proton. The results demonstrate that the square planar metal complex Pt(en)22+ selectively binds AT sequences in the DNA minor groove.
Absorption and emission spectra and emission quantum yields are given for free-base (H/sub 2/), Zn, Cu, and Pd derivatives of tetrakis(perfluorophenyl)porphyrin (TFPP). The four-orbital model is used to rationalize differences in the optical properties among the derivatives of TFPP and the same derivatives of porphine (P), octaethylporphyrin (OEP), and tetraphenylporphyrin (TPP). It is concluded from absorption data that the energy difference between the two excited singlets, i.e., /sup 1/E(a/sub 2u/,e/sug g/) - /sup 1/E(a/sub 1u/,e/sub g/), decreases along the series Pd > Cu > Zn > H/sub 2/ and also along the series OEP > P > TFPP > TPP. The theory and date are reviewed, and it is concluded that the energy difference between the two excited triplets, i.e., /sup 3/E(a/sub 2u/,e/sub g/) - /sup 3/E(a/sub 1u/,e/sub g/), also decreases along these series. However the condition of degeneracy, e.g., /sup 1/E(a/sub 2u/,e/sub g/) - /sup 1/E(a/sub 1u/,e/sub g/) = 0, occurs for different molecules in the singlet and triplet cases. Theory also suggests that if /sup 3/E(a/sub 2u/,e/sub g/) > /sup 3/E(a/sub 1u/,e/sub g), the molecule should form a /sup 2/A/sub 1u/ cation radical and if /sup 3/E(a/sub 2u/,e/sub g/) < /sup 3/E(a/sub 1u/,e/sub g/) the molecule should form a /sup 2/A/sub 2u/ radical. 4 figures, 2 tables.
The crystal and molecular structure of the toluene solvate of α,β,γ,δ-tetraphenylporphinatozinc(II) has been determined by x-ray diffraction techniques. The compound crystallizes in the triclinic system, space group P1. The unit cell has a = 11.349 (2) Å, b= 11.404 (2) Å, c= 10.502 (2) Å, α = 110.48 (2)°, β = 103.87 (2)°, γ = 107.65 (2)°, and Z = 1. Measurement of diffracted intensities employed ω scans with graphite-monochromated Mo Kα radiation on a Syntex P1 diffractometer. All independent reflections for (sin θ)/λ ≤ 0.725 Å-1 (5436 unique observed data) were examined. These data were used for the determination of structure and full-matrix least-squares refinement. The final conventional and weighted discrepancy factors were 0.047 and 0.057. The molecule has required Ci-1 symmetry. The average Zn-N bond distance is 2.036 (6) Å with the zinc atom precisely centered in the porphinato plane. The interplanar spacing between the porphyrin mean plane and a toluene plane is 3.34 Å.
Electronic absorption and emission studies have been carried out for Cu(phen)2+, Cu(dmp)2+, and Cu(bcp)2+ interacting with a range of DNA duplexes, where phen denotes 1,10-phenanthroline, dmp denotes 2,9-dimethyl-1,10-phenanthroline, and bcp denotes 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. Hypochromism is observed in the visible absorption bands of all three copper(I) complexes, but the bcp complex is unique in that binding to DNA causes the appearance of a measurable luminescence signal at room temperature. At low DNA-P/Cu ratios Cu(bcp)2+ appears to bind to DNA polymers in an aggregated form, but at high DNA-P/Cu ratios the complex binds as a monomer. The adduct of the bcp complex with DNA must be relatively rigid in the vicinity of the copper center because solvent-induced, exciplex quenching of the excited state is strongly inhibited. This suggests that the complex binds by intercalation, and emission polarization data support this model. The limiting emission intensity varies with the type of DNA used and is greater with poly(dA-dT)-poly(dA-dT) than with poly(dG-dC)-poly(dG-dC), possibly because propeller twisting facilitates intercalation. Interaction probably occurs within the major groove since T4 DNA, which is glycosylated in the major groove, does not induce monomer emission. None of the duplexes studied induced emission from Cu(dmp)2+, presumably because the dmp complex binds by another mechanism. Yeast tRNA was also effective at inducing emission from Cu(bcp)2+; hence the complex is also capable of intercalating into an A-form duplex.
Temperature-dependent quenching studies of CT (charge-transfer) excited states of copper(I) complexes have been carried out in methylene chloride solution by a lifetime method. Activation parameters have been determined for both electron-transfer and energy-transfer quenching of *Cu(dpp)2+ as well as for quenching of *Cu(dmp)2+ by a series of Lewis bases (dpp denotes 2,9-diphenyl-1,10-phenanthroline and dmp denotes 2,9-dimethyl-1,10-phenanthroline). For those reactions involving Lewis bases, the apparent enthalpy of activation ranges from 0 to ca. -15 kJ mol-1 with a bell-shaped dependence on the donor strength. At 25°C the quenching rates vary from 1.4 × 106 M-1 s-1 for the weak donor CH3CN to 5.7 × 108 M-1 s-1 for the relatively strong donor DMF. The results establish that a reversible complex is formed between the excited state and Lewis bases prior to quenching, and the adduct is interpreted to be a five-coordinate exciplex. Finally, reasons that so few examples of exciplexes of transition-metal complexes have been identified are discussed.