Frederick D Lewis

Northwestern University | NU · Department of Chemistry

The initial studies of the dynamics of photoinduced charge separation conducted in our laboratories 20 years ago found strongly distance-dependent rate constants over short distances but failed to detect intermediates in the transport of positive charge (holes). These observations were consistent with the single-step superexchange or tunneling mech...

The ground- and excited-state electronic interactions between the nucleobase analog 8 (4' phenylethynyl)deoxyguanine, EG, with the natural nucleobases and 7-deazaguanine as well as between adjacent EG base analogs have been characterized using a combination of steady-state spectroscopy and time-resolved fluorescence, absorption, and stimulated Rama...

The dynamics of electron injection have been investigated in intramolecular i-motif conjugates possessing stilbenediether (Sd) and perylenediimide (PDI) chromophores separated by either four or six hemi-protonated cytosine C-C base pairs assembled with synthetic loops. Circular dichroism spectra are consistent with the formation of i-motif structur...

Steady state spectroscopy, femtosecond transient absorption spectroscopy (fsTA), and femtosecond stimulated Raman spectroscopy (FSRS) of DNA mini-hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker and 1-3 adenine-thymine (A-T) or guanine-cytosine (G-C) base pairs have been investigated. Ultraviolet and circular dichroism (UV and CD)...

The dynamics and efficiency of photoinduced charge transport has been investigated in DNA capped hairpins possessing a stilbenedicarboxamide (Sa) hole donor and stilbenediether (Sd) hole acceptor separated by DNA G-quadruplex structures possessing 2-to-4 tetrads by means of femtosecond and nanosecond transient absorption spectroscopy with global an...

Charge transport through the DNA double helix is of fundamental interest in chemistry and biochemistry, but also has potential technological applications such as for DNA-based nanoelectronics. For the latter, it is of considerable interest to explore ways to influence or enhance charge transfer. In this Article we demonstrate a new mechanism for DN...

The excited state behavior of DNA hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker separated from a single guanine‒cytosine (G‒C) base pair by zero-to-six adenine‒thymine (A‒T) base pairs has been investigated by a combination of femtosecond and nanosecond transient absorption spectroscopy and femtosecond stimulated Raman spectrosc...

The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV-induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine-thymine double-stranded structures (AT)n . Fluorescence measurements on (AT)n hairpins (six and ten base pairs) and duplexes (20...

Molecular structures that direct charge transport in two or three dimensions could help to enable the development of molecule-based electrical switches and gates. As a step toward this goal, we use theory, modeling and simulation to explore DNA three-way junctions (TWJs). Molecular dynamics simulations and quantum calculations, indicate that DNA TW...

The effects of an artificial cyclohexyl base pair on the quantum yields of fluorescence and dynamics of charge separation and charge recombination have been investigated for several synthetic DNA hairpins. The hairpins possess stilbenedicarboxamide, perylenediimide, or naphthalenediimide linkers and base-paired stems. In the absence of the artifici...

DNA-based molecular electronics will require charges to be transported from one site within a 2D or 3D architecture to another. While this has been shown previously in linear, π-stacked DNA sequences, the dynamics and efficiency of charge transport across a DNA three-way junction (3WJ) have yet to be determined. Here, we present an investigation of...

The mechanism and dynamics of photoinduced electron injection and charge recombination have been investigated for several series of DNA hairpins. The hairpins possess a stilbenediether linker which serves as an electron donor and base pair stems which possess different pyrimidine bases adjacent to the linker. Hairpins with adjacent thymine-adenine...

The dynamics of charge separation and charge recombination have been determined for lipid complexes of DNA capped hairpins possessing stilbene electron acceptor and donor chromophores separated by base pair domains which vary in length and base sequence in chloroform solution by means of femtosecond time-resolved transient absorption spectroscopy....

The mechanism and dynamics of photoinduced electron transfer in two families of DNA hairpins possessing Michler's Ketone linkers have been investigated by means of steady state and time-resolved transient absorption and emission spectroscopies. The excited state behavior of the diol linker employed in hairpin synthesis is similar to that of Michler...

The effect of Mg2+ cations on the electronic spectra and dynamics and efficiency of hole transport has been determined by means of femtosecond time-resolved transient absorption spectroscopy for DNA hairpins possessing stilbene electron acceptor and donor chromophores. The results are compared with those obtained previously for the same hairpins in...

The structure and electronic spectra of six DNA conjugates possessing two face-to-face perylenediimide (PDI) chromophores have been investigated. Structures of hairpins possessing two adjacent PDI base analogues opposite a tetrahydrofuran abasic site on the same or opposite strands were simulated using molecular dynamics. These structures are compa...

The structure and properties of the electron donor-acceptor complexes formed between methyl viologen (MV) and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and 1H NMR spectroscopy. Theoretical calculatio...

The photochemical reactions of eleven synthetic DNA hairpins possessing a single TT step either in a base-paired stem or in a hexanucleotide linker have been investigated. The major reaction products have been identified as the cis-syn (2 + 2) adduct and the (6 - 4) adduct on the basis of their spectroscopic properties including 1D and 2D NMR spect...

We report the self-assembly and thermal dissociation of DNA dumbbell conjugates having a perylenediimide (PDI) linker on each end separated by 6-16 A-T base pairs. In the presence of NaCl these dumbbells form one-dimensional supramolecular assemblies as a consequence of hydrophobic association of their PDI sticky ends. The dependence of assembly fo...

DNA hairpins having both a tethered anthraquinone (Aq) end-capping group and a perylenediimide (PDI) base surrogate were synthesized, wherein Aq and PDI are each separated from a G-C base pair hole trap by A-T and I-C base pairs (G = guanine, A = adenine, T= thymine, C = cytosine, I = inosine). Selective photoexcitation of PDI at 532 nm generates a...

Double-stranded DNA conjugates with the sequence (dA)10·(dT)10 and hexaethylene glycol linkers at one end (hairpin) or both ends (dumbbell) were studied in buffer solution by deep UV femtosecond transient absorption spectroscopy. These covalently constrained duplexes have greatly enhanced thermal stability compared to A·T duplex oligonucleotides th...

Guanine-cytosine hairpins, containing a hexaethylene glycol bridge, are studied by steady-state fluorescence spectroscopy and time-correlated single photon counting; their properties are compared to those of duplexes with the same sequence. It is shown that, both in hairpins and in duplexes, base pairing induces quenching of the ππ* fluorescence, t...

The π-stacked bases of B-DNA constitute a helical ruler present nowhere else in nature. When two chromophores are placed at the ends of a base-pair domain with fixed orientations of their transition dipole moments, insertion of an additional base pair between the chromophores increases the distance between the chromophores by ca. 3.4 Å and the angl...

We developed a model for hole migration along relatively short DNA hairpins with fewer that seven adenine (A):thymine (T) base pairs. The model was used to simulate hole migration along poly(A)-poly(T) sequences with a particular emphasis on the impact of partial hole localization on the different rate processes. The simulations, performed within t...

We developed a model for hole migration along relatively short DNA hairpins with fewer that seven adenine (A):thymine (T) base pairs. The model was used to simulate hole migration along poly(A)-poly(T) sequences with a particular emphasis on the impact of partial hole localization on the different rate processes. The simulations, performed within t...

Experimental investigations of photoinduced charge transport in synthetic DNA capped hairpins possessing electron acceptor and donor stilbene chromophores at either end have established the mechanism, dynamics, and efficiency of charge transport in DNA. The mechanism for charge transport in repeating A-T base pairs (A-tracts) was found to change fr...

We report here the effect of replacing one or both of the purine or pyrimidine blocks of a diblock stilbene donor-acceptor capped hairpin with locked nucleic acid (LNA) bases on the dynamics and efficiency of hole transport. The structures of the DNA and LNA:DNA hybrids are tentatively assigned to B- or A-type structures on the basis of their circu...

In this article, a theoretical study of the electronic and spectroscopic properties of well-defined DNA hairpins is presented. The excited states in the hairpins are described in terms of an exciton Hamiltonan model, and the structural dynamics of the DNA model systems is explicitly taken into account by molecular dynamics simulations. The results...

A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were...

Irradiation of alkane-linked DNA hairpins possessing TTT steps with flanking purine bases yields products identified as the cis-syn (2 + 2) dimers formed between the central thymine and its 3'- and 5'-neighbors. Selective formation of the 3'-dimer is attributed to ground state conformational effects and electron transfer quenching by purine bases.

The thermal stability and ultraviolet and circular dichroism spectra of nine synthetic DNA hairpins possessing one or more (P)C-G base pairs ((P)C = pyrrolocytosine) have been investigated. One group of hairpins possess 1-5 sequential (P)C-G base pairs while another group possess two (P)C-G base pairs separated by 1-3 A-T base pairs. The first grou...

Quantum yields for thymine photodimerization (Φ(TT)) have been determined for a series of short DNA single-strand and base-paired hairpin structures possessing a single thymine-thymine step with flanking purines. Values of Φ(TT) are strongly dependent upon the oxidation potential of the flanking purine, decreasing in the order: inosine > adenine >...

Cyclobutane-pyrimidine dimer yields in UV-irradiated DNA are controlled by the equilibrium between forward and reverse photoreactions. Past studies have shown that dimer yields are suppressed at sites adjacent to a purine base, but the underlying causes are unclear. In order to investigate whether this suppression is the result of repair by electro...

Transport of positive charge or holes in DNA occurs via a thermally activated multi-step hopping mechanism. The fastest hopping rates reported to date are those for repeating poly(purine) sequences in which hopping occurs via a random walk mechanism with rate constants of k(hop) = 4.3 × 10(9) s(-1) for poly(dG) and 1.2 × 10(9) s(-1) for poly(dA). W...

The effects of a flanking purine base on the thymine-thymine photodimerization efficiencies and product distributions have been determined for the trinucleotides 5′-ATT, TTA, GTT, and TTG and the results compared to those for the dinucleotide TT. The highest quantum yield and selectivity for formation of the major cis–syn (2 + 2) dimer was observed...

Alkane linkers derived from α,ω-alkane diols have been employed for the preparation of DNA mini-hairpins, which are suitable for studies of the spectroscopy and photochemistry of short base pair domains. The solution structure of a DNA hairpin having a n-dodecane linker and six AT base pairs has been determined using (1)H NMR data with restrained m...

The molecular structure, absorption, and fluorescence spectra of N,N'-dimethyl-N,N'-di-1-pyrenylurea and N,N'-dimethyl-N,N'-di-2-pyrenylurea have been investigated and compared to the properties of N,N,N'-trimethyl-N'-pyrenylurea model compounds. Di-1-pyrenylurea exists as a mixture of folded (E,E) syn- and anti-rotamers that interconvert via flipp...

IntroductionSpectral Signatures of Charge TransferCharge Injection into A-TractsCrossover from Superexchange to Hopping in Sa–An–SdSymmetry Breaking in Sa–An–SaInfluence of a Single G on Charge TransportMolecular Wire Behavior in Sa–A2–3G1–7–SdCharge Transfer through Alternating SequencesTheoretical Descriptions of Charge Transfer through DNAConclu...

The synthesis and properties of synthetic DNA dumbbells having A-tract base pair domains consisting of 6-16 base pairs connected by perylenediimide (PDI) linkers are reported. The dumbbells were prepared in good yield by chemical ligation of nicked-dumbbell precursors having six or more A-T base pairs. The dumbbell structures have been investigated...

Two mechanisms have been reported for the intermolecular photochemical addition reactions of styrenes and stilbenes with amines. Direct irradiation results in electron-transfer quenching of the singlet styrene by the amine, followed by hydrogen transfer and radical pair coupling. Electron-transfer-sensitized irradiation results in the formation of...

The photophysical and photochemical behavior of a series of hairpin-forming DNA conjugates possessing a 5'-tethered pyrenecarboxamide chromophore and one or two bromouracil bases has been investigated. Quenching of the pyrene fluorescence and transient absorption spectra characteristic of the pyrene cation radical are observed only when bromouracil...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

We report the measurement of distance- and temperature-dependent rate constants for charge separation in capped hairpins in which a stilbene hole acceptor and hole donor are separated by A(3)G(n) diblock polypurine sequences consisting of 3 adenines and 1-19 guanines. The longer diblock systems obey the simplest model for an unbiased random walk, p...

The self-assembly of DNA dumbbell conjugates possessing hydrophobic perylenediimide (PDI) linkers separated by an eight-base pair A-tract has been investigated. Cryo-TEM images obtained from dilute solutions of the dumbbell in aqueous buffer containing 100 mM NaCl show the presence of structures corresponding to linear end-to-end assemblies of 10-3...

The results of an integrated experimental and theoretical study of thymine-thymine photodimerization in short single-strand and duplex DNA structures possessing a single locked nucleic acid TT step are reported. Control of ground-state conformation by the locked nucleic acids results in a marked increase in both the quantum yield and the selectivit...

The synthesis and properties of three related families of alkane-linked DNA hairpins are reported. The first possesses a dodecane linker (C12) and 2-8 AT base pairs. The second possesses six AT base pairs and straight chain alkane linkers having 8-16 methylenes. The third has three alkane linkers of different length and a constant six base-pair ste...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The synthesis, structure, and electronic spectra of a series of DNA hairpins possessing two perylenediimide (PDI) base pair surrogates are reported. The PDI chromophores are located in opposite strands of the hairpin base pair domain opposite abasic sites and are either adjacent to each other or separated by a variable number of AT or GC base pairs...

The photosensitized electron transfer reactions of several 1- and 9-(aminoalkyl)phenanthrenes with metadicyanobenzene have been investigated. These reactions provide an efficient method of synthesis for the skeletal structures of the aporphine, phenanthropiperidine, and phenanthroazepine alkaloids.

A kinetics model is designed to investigate the charge separation (CT) process in stilbene-capped DNA hairpins composed of AT base pairs. This model combines standard tunneling and hopping electron transport with exciplex formation upon photoexcitation of the acceptor stilbene and its neighboring adenine and is capable of interpreting the CT rate a...

Durchmarsch der Elektronen: Perylendiimid‐Chromophore in DNA‐Haarnadelstrukturen dienen als Basenpaar‐Ersatz und bilden eine reißverschlussartige Einschubstruktur (siehe Bild). Bei der Einelektronenreduktion wurde ein Elektronen‐Hüpfen innerhalb der Chromophorenstapel beobachtet.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The paper presents quantum yield results for the [2+2] and 6-4 photodimerization of TT steps in several DNA structures, including hairpins where the context dependence of the photodimerization yield is determined, and it develops a theoretical model that correctly describes the trends in dimerization yield with DNA structure. The DNA conjugates con...

Synthetic conjugates possessing bis(2-hydroxyethyl)stilbene-4,4'-diether linkers (Sd2) form the most stable DNA hairpins reported to date. Factors that affect stability are length and flexibility of the linkers and Ï-stacking of the stilbene moiety on the adjacent base pair. The crystal structure of the hairpin d(GTâG)-Sd2-d(CAâC) was determined at...

The efficiency of singlet and triplet charge radical ion-pair formation and the dynamics of radical-pair charge recombination in DNA-anthraquinone conjugates have been investigated by means of femtosecond time-resolved transient absorption spectroscopy. Singlet charge separation is more efficient than intersystem crossing, resulting in inefficient...

The dynamics of electron injection and quantum yields for photoinduced dehalogenation have been investigated in a series of DNA hairpins possessing an aminopyrene capping group. Aminopyrene serves as an electron donor and is separated from a bromo- or iodoracil electron trap by 1 to 7 A-T base pairs. Broad band femtosecond transient absorption spec...

The structure, spectroscopy, and photophysical behavior of a series of hairpin-forming conjugates possessing a 5'-tethered N-alkylpyrenecarboxamide chromophore have been investigated. Comparison of the NMR spectra of the conjugates and analogs lacking the tethered pyrene indicates that the pyrene does not behave as an end-capping group but rather i...

The realization of highly efficient photoinduced charge separation across the pi-stacked base pairs in duplex DNA remains elusive. The low efficiencies (<5%) typically observed for charge separation over a dozen or more base pairs are a consequence of slow charge transport and rapid charge recombination. We report here a significant (5-fold or grea...

The charge recombination rate in DNA hairpins is investigated. The distance dependence for the charge recombination rate between stilbene donor (Sd + ) and stilbene acceptor (Sa−) linkers separated by an AT bridge has a double exponential form. We suggest that this dependence is associated with two tunneling channels distinguished by the presence o...

The structure and properties of hairpin-forming bis(oligonucleotide) conjugates possessing perylenediimide (PDI) chromophores as hairpin linkers have been investigated using a combination of spectroscopic and computational methods. These conjugates exist predominantly as monomer hairpins at room temperature in the absence of added salt and as head-...

A series of short DNA hairpins (nG) using perylene-3,4:9,10-bis(dicarboximide) (PDI) as the hairpin linker was synthesized in which the distance between the PDI and a guanine-cytosine (G-C) base pair is systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. Due to the relatively large hydrophobic surf...

Optical spectra of biological polymers contain important information about their structure and function in living organisms. This information can be accessed by extracting an optical interaction of monomers, i.e., their exciton coupling, from experimental data. This coupling is sensitive to molecular structure, geometry, and conformation and can be...

The slow charge recombination in DNA hairpins of various lengths is investigated. The distance dependence for the charge recombination rate between stilbene donor (Sd(+)) and stilbene acceptor (Sa(-)) linkers separated by AT bridges of various lengths has the double exponential form. We suggest that this puzzling dependence is associated with two t...

The synthesis and photophysical properties of the dihydroxypropylamide derivative of pyrene-1,6-dicaboxamide, its aniline dyad, and DNA conjugates are reported. The dicarboxamide serves as a hairpin linker for bis(oligonucleotide) conjugates having short base pair stems. The dihydroxypropyl derivative has a large fluorescence quantum yield and long...

The effect of 280 nm irradiation on a family of synthetic DNA hairpins possessing an alkane linker connecting a six-base pair stem having a single T-T step located at different positions within the hairpin has been investigated. A single adduct assigned to the product of 2+2 dimerization is obtained except in the case of a T-T step located adjacent...

The thermal stability and conformational dynamics of DNA hairpin and dumbbell conjugates having short A-tract base pair domains connected by tri- or hexa(ethylene glycol) linkers is reported. The formation of stable base-paired A-tract hairpins having oligo(ethylene glycol) linkers requires a minimum of four or five A-T base pairs. The formation of...

A perylenediimide chromophore (P) was incorporated into DNA hairpins as a base-pair surrogate to prevent the self-aggregation of P that is typical when it is used as the hairpin linker. The photoinduced charge-transfer and spin dynamics of these hairpins were studied using femtosecond transient absorption spectroscopy and time-resolved EPR spectros...

We report on spectral features for two and three diphenylacetylene chromophores aligned in close proximity in aqueous solution by self assembly of attached oligonucleotide arms. Two duplex systems were examined in detail. One was formed by hybridization (Watson-Crick base pairing) of two oligonucleotide 10-mers, each containing the diphenylacetylen...

The mechanism and dynamics of charge separation and charge recombination in synthetic DNA hairpins possessing a stilbenedicarboxamide linker and a single guanine-cytosine base pair have been reinvestigated. The combination of femtosecond broad-band pump probe spectroscopy, nanosecond transient absorption experiments, and picosecond fluorescence dec...

The excited-state behavior of synthetic DNA dumbbells possessing stilbenedicarboxamide (Sa) linkers separated by short A-tracts or alternating A-T base-pair sequences has been investigated by means of fluorescence and transient absorption spectroscopy. Electronic excitation of the Sa chromophores results in conversion of a locally excited state to...

The dynamics and efficiency of photoinduced charge separation in synthetic DNA hairpins and dumbbells possessing stilbenedicarboxamide (Sa) and stilbene-diether (Sd) linkers separated by short poly(dA)-poly(dT) base pair sequences have been investigated by means of time resolved fluorescence and transient absorption spectroscopy. Charge separation...

Nächster Halt Guanin: Der Wirkungsgrad der photoinduzierten Ladungstrennung zwischen den Donor- und Akzeptorchromophoren einer Polyadeninsequenz, die eine einzelne Guaninbase (G) enthält, hängt empfindlich von der Position von G und von der Gesamtlänge der Polypurinsequenz ab. Quantenausbeuten sprechen für einen stufenweisen Mechanismus mit G als „...

The dynamics and efficiencies of photoinduced charge separation across alternating AT, ATA, ATAT, and ATATA base pair sequences in synthetic DNA hairpins have been determined by means of femtosecond time-resolved transient absorption spectroscopy. When compared to our results for charge transport across poly(A) sequences, both the rate constants an...

The solution structure of a synthetic DNA mini-hairpin possessing a stilbenediether linker and three G:C base pairs has been obtained using (1)H NMR spectral data and constrained torsion angle molecular dynamics. Notable features of this structure include a compact hairpin loop having a short stilbene-guanine plane-to-plane distance and approximate...

The synthesis, structure, and electronic properties of a series of tertiary polyarylureas possessing pyrene and dimethylaniline capping groups separated by zero-to-four phenylenediamine bridging groups are described. These molecules adopt folded pi-stacked structures. The dynamics of photoinduced charge separation and charge recombination are inves...

Upon exposure to UV light, the disubstituted dibenzobarrelene derivative 1a turns green in the solid phase and reverts back to its original pale-yellow color within several hours in the dark. The lifetime of the colored species in degassed benzene at room temperature is 37 +/- 2 s (Ea for decoloration is 14.5 +/- 0.7 kcal mol-1 and log A is 8.92 +/...

The formation and properties of G-quadruplex structures from short single-strand oligonucleotide conjugates possessing two to four guanines and a 5'-terminal pyrenebutanol are reported. The 4-G conjugate forms a stable G-quadruplex under low or high potassium ion concentrations, whereas the 3-G conjugate forms a stable G-quadruplex only in the pres...

The synthesis and properties of a perylenediamide diol linker and several DNA hairpins possessing this linker are described. The diol linker absorbs and fluoresces strongly in the visible. Hairpins having poly(dA)–poly(dT) stems have fluorescence quantum yields and decay times similar to those of the linker, indicating that hole injection does not...

Synthetic DNA conjugates in which one or both ends of a short duplex is capped by a stilbene chromophore have been prepared and characterized crystallographically. Selective excitation of the chromophore can be used to initiate electron transfer processes in which a nucleobase serves as either an electron donor or an electron acceptor. These proces...

The circular dichroism (CD) spectrum of a large biological molecule represented as an array of interacting chromophores is investigated. The configuration-averaged Green function formalism is developed to describe the CD and absorption spectra. The perturbation theory expansion is derived for absorption and CD spectra in the case of strong interact...

The synthesis and properties of nicked dumbbell and dumbbell DNA conjugates having A-tract base pair domains connected by rod-like stilbenedicarboxamide linkers are reported. The nicked dumbbells have one to eight dA-dT base pairs and are missing a sugar-phosphate bond either between the linker and a thymine nucleoside residue or between two thymin...

Introduction Stilbene Energetics and Dynamics Photodimerization Reactions with Electron-Poor Alkenes Reactions with Electron-Rich Alkenes and Dienes Reactions with Amines, Imines, and Protic Solvents Reactions of Singlet Arenes with Stilbenes concluding remarks

Gute Übereinstimmung: Die Kinetik des photoinduzierten Lochtransports über DNA-A-Bereiche mit 1–7 Basenpaaren wurde durch transiente Femtosekundenabsorptionsspektroskopie bestimmt. Die Werte sind bei bis zu vier Basenpaaren stark entfernungsabhängig, bei größeren Abständen dann aber kaum noch. Diese Kinetik-Ergebnisse (□, ▪) stimmen sehr gut mit de...

Short DNA duplexes can be stabilized by the presence of organic chromophores, which serve as hairpin linkers or end-capping groups. Capped hairpins possessing one or more base pairs form stable folded structures in aqueous solution. Increasing the number of base pairs separating the two chromophores increases both the distance between the two chrom...

The synthesis and properties of DNA mini-hairpin conjugates possessing stilbene capping groups have been investigated for two hairpin base sequences with three stilbene capping groups. The two hairpin sequences 5′-TTTCACCGAAA vs. 5′-ATTCACCGAAT differ in the orientation of the terminal base pair, the latter forming the more stable hairpin. Conjugat...

A poly(dT) oligomer can serve as the string on which synthetic hairpins possessing poly(dA) and poly(dT) arms connected by a hydrophobic perylene diimide linker are assembled like beads on a string. The synthetic hairpins form head-to-head dimers and trimers, respectively, in the absence of the poly(dT) string and in the presence of a string with i...

Herein are reported the synthesis, structure, and electronic properties of a series of tertiary di- and polyarylureas possessing pyrene and nitrobenzene end groups separated by a variable number of internal phenylenediamine bridging groups. These molecules adopt folded "protophane" structures in which the adjacent arenes are loosely pi-stacked. The...

The spectroscopic properties and photochemical behavior of molecules having 2-ethynylbiphenyl or 2-phenyldiphenylacetylene structures are reported. These molecules undergo photocyclization reactions to yield phenanthrene and dihydrophenanthrene products via putative isophenanthrene (cyclic allene) intermediates. Phenanthrene formation from the isop...

Solution state x-ray diffraction fingerprinting is demonstrated as a method for experimentally assessing the accuracy of molecular dynamics (MD) simulations. Fourier transforms of coordinate data from MD simulations are used to produce reciprocal space “fingerprints” of atomic pair distance correlations that are characteristic of the ensemble and a...

The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes separated by one to seven A:T base pairs. The application of femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluore...