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Basic Terminology of Stereochemistry (IUPAC Recommendations 1996)
Pure and Applied Chemistry
... The phenomenon of homeomorphic conversions in fused bicycloalkanes was first documented in the literature by [7] and 1972. [10] This is one of the in/out-isomerism [5,11] in fused bicycloalkanes. ...
... In the case of bicyclo[k.l.0]alkanes (k � l > 0), which lack an atom inside the fused bridge, they have cis-and trans-isomers. [11] However, this notation is not applicable to the usual bicyclo[k.l.m]alkane (k � l � m > 0). Moreover, the previously mentioned out/in-notation does not clearly differentiate the two topologies in a fused bicycloalkane. ...
... In 1990, Saunders and Krause reported the synthesis of bicyclo[6.5.1]tetradecane (11). [25] This bicycloalkane was designed to have nearly identical MM2 strain energy for the out,out-, in,in-, and in,out-structures (Scheme 4). ...
Fused bicycloalkanes have several structures with different orientations of the substituents, such as out,out‐, in,in, and in,out‐structures. Some bicycloalkanes can undergo homeomorphic conversions between certain structures, for instance an out,out‐structure can convert to an in,in‐structure. This homeomorphism can be achieved by one chain passing through the macroring. In this report, topological structural chemistry of fused bicycloalkanes and their analogues allowing homeomorphic conversions were reviewed. Although the concept of homeomorphism in fused bicycloalkanes was proposed 50 years ago, comprehensive research on their structural chemistry is still ongoing. These understandings are highly relevant to the fundamentals of many fields of chemistry, including structural chemistry, theoretical chemistry, natural products chemistry, and materials science.
... The torsion angle defined by the dihedral angle formed by a H-C-C-H chain is an important parameter to specify the conformation: the torsion angle is 60°for the staggered ethane. 4) The conformation in which two H atoms on adjacent C atoms are in closest proximity is called eclipsed conformation, where the torsion angle is 0°. This conformation is usually unstable and located at an energy maximum. ...
... These three forms are conformational isomers (conformers), which are stereoisomers that differ in conformations located at the energy minima. 4) Conformers B are C are chiral and mirror images of each other, namely, they are enantiomers. If necessary, B and C are distinguished into Dsc and !sc forms, respectively, to specify the direction of the two substituents. ...
... 53) The gauche effect is defined by the IUPAC Recommendations as follows: the stabilization (or destabilization) of the gauche conformation in a two-carbon unit bonded vicinally to various atoms or atomic groups (substituents). 4) This effect, which originated from the discovery of the conformers of 1,2-disubstituted ethanes, has been a key topic in organic chemistry for a long time. Many researchers have tackled this problem mainly by theoretical calculations such as MO analysis. ...
In 1932, Mizushima and Higasi reported the dependence of the dipole moments of 1,2-dichloroethane on both temperature and solvent in the Proceedings of the Imperial Academy, Japan. This report was followed by their first proposal of the existence of conformers that exchanged by internal rotation about a C–C single bond based on experimental data. Their monumental work marked the beginning of the essential concept of conformation in modern stereochemistry. Their proposal was later confirmed by the direct observation of the anti and gauche conformers of 1,2-dichloroethane by Raman spectroscopy, and further supported by other experimental and theoretical methods. The relative stabilities of the anti and gauche conformers of 1,2-dichloroethane and other 1,2-disubstituted ethanes were discussed in terms of steric, electrostatic, and stereoelectronic effects based on analysis of calculated data. Those studies influenced the development of subsequent research in organic chemistry, such as the conformational analysis of cyclohexane derivatives and the isolation of chiral gauche conformers.
... There also is a source of heterogeneity called handedness, which corresponds to the enantiomers of chiral SWNTs ( Figure 3C), which are nonsuperimposable mirror image forms that have opposite C h and oppositely directed acetylenic lines (red in Figure 3C). [50,51] Unlike R-and S-nomenclature used to classify enantiomers of chemical substances, supramolecule nomenclature is used to designate optical isomers of SWNTs [52,53] as being right-handed or P (or þ) and left-handed M (or À) supramolecules. [52] Without using supramolecular nomenclature, the handedness can be expressed as (m, n) for P-and (n, m) for M-(n, m). ...
... [50,51] Unlike R-and S-nomenclature used to classify enantiomers of chemical substances, supramolecule nomenclature is used to designate optical isomers of SWNTs [52,53] as being right-handed or P (or þ) and left-handed M (or À) supramolecules. [52] Without using supramolecular nomenclature, the handedness can be expressed as (m, n) for P-and (n, m) for M-(n, m). The optical and electrical properties of SWNT enantiomers are equivalent except in their response to circularly polarized light, like in circular dichroism (CD) spectroscopy where the relative abundances of the enantiomers, referred to as enantiomeric excess (ee), determine the magnitude of the CD signal. ...
Sorting single‐walled carbon nanotubes (SWNTs) that are heterogeneous into homogeneous groups based on their electronic type, chirality, and handedness is crucial for optoelectronic and biological applications. To achieve this, researchers have utilized dispersants with different binding affinities to sort SWNTs according to their chiralities. This review article provides an overview of the methods developed for sorting SWNTs using dispersants, with a particular focus on the role played by dispersant binding affinities. The article is organized into six sections, including an introduction, a background on SWNTs and dispersant‐based individualization of SWNTs, information on dispersants and their binding affinities, separation methods for SWNTs based on controlling the dispersant binding affinity, parameters used to control dispersant binding affinity, and a conclusion. It is hoped that this review will enhance understanding of the intricate interactions between dispersants and SWNTs, leading to the development of new SWNT sorting methods for future applications.
... According to the IUPAC definition helicenes [1] are "ortho-fused polycyclic aromatic or heteroaromatic compounds in which all rings (minimum five) are angularly arranged so as to give helically shaped molecules, which are thus chiral". [2] This not only allows for the condensation of benzene rings (Figure 1, top) or their hetero analogues, [3] but similarly of, e. g., five- [4] or seven-membered rings. [5] Actually, we consider the IUPAC definition to be not fully suitable for the description of this class of compounds, since the term 'aromatic' is not well-defined and occasionally even antiaromatic rings can be present in helicenes. ...
... The NMR data are in full agreement with published data. [37] N- [2][3][4]4,5, ...
6,10‐Dipropyl‐5,9‐diaza[5]‐ and ‐[6]helicene were synthesized by ortho,ortho’ fusion of ortho‐teraryldicarboxamides. Key steps in the synthesis of the teraryls are azide formation with subsequent reduction and amidation followed by Suzuki cross couplings. The ortho fusions were achieved with phosphorus pentoxide and phosphoryl oxide. The total syntheses could be accomplished with 10 % and 3 %, respectively, in seven consecutive steps starting with meta‐dibromobenzene. The helicenes were investigated by UV/Vis and fluorescence spectroscopy and by quantum chemical calculation of, inter alia, the HOMO‐LUMO gaps. Racemization barriers of the helicenes were calculated, whereupon the optical resolution of 5,9‐diaza[6]helicene was attempted and carried out successfully; ECD spectra were measured of its enantiomers.
... Se dice que estos objetos no poseen elementos de simetría, como un plano en el espejo, un centro de inversión o un eje de rotación-reflexión. Estos objetos que no presentan ningún elemento de simetría se conocen como objetos asimétricos (Moss, 1996). Para poder entender mejor lo que es la quiralidad se puede empezar con el ejemplo de nuestras manos. ...
... Asimismo, los compuestos meso se definen como compuestos que poseen centros asimétricos, pero son aquirales debido a la presencia de un plano de simetría. Las estructuras del ácido tartárico en la Fig. 5 ejemplifican estos conceptos (Moss, 1996;Wade, 2017). TECNOCIENCIA CHIHUAHUA, Vol. ...
En este artículo, se discuten algunos conceptos sobre la quiralidad, tanto en compuestos orgánicos como en complejos de los metales de transición, haciendo énfasis en esta última clase de derivados. Dado que los centros metálicos pueden adoptar diferentes geometrías, la forma en la que se arreglan en el espacio y generan quiralidad es diferente del clásico ejemplo del carbono en la química orgánica. La quiralidad en los compuestos de coordinación se debe a los ligantes, ya sea por la presencia de un átomo quiral en su estructura, o bien, por su conformación espacial, generando en estos casos una quiralidad asociada al metal, la cual será el principal enfoque de este texto. Por otra parte, las aplicaciones principales de los complejos con quiralidad centrada en el metal están asociadas a la catálisis asimétrica, por lo que se describen algunos ejemplos relevantes. DOI: https://doi.org/10.54167/tch.v17i4.1345
... KR represents one of the most classic strategies for quick access to optically pure compounds in both bench experimental research and industrial manufacturing. The IUPAC in 1996 defined a KR process as "the achievement of partial or complete resolution by virtue of unequal rates of reaction of the enantiomers in a racemate with a chiral agent (reagent, catalyst, solvent, etc.)." [10]. NHC-catalyzed KR reactions were first reported by Suzuki and co-workers [11] in 2004 when they used a chiral imidazolium-derived NHC catalyst for the asymmetric acylation of secondary alcohols. ...
... As defined by the IUPAC in 1996, desymmetrization is "the modification of an object which results in the loss of one or more symmetry elements, such as those which preclude chirality (mirror plane, center of inversion, rotation-reflection axis), as in the conversion of a prochiral molecular entity into a chiral one [10]." A seminal report on the desymmetrization of achiral functional molecules appeared in the 1940s, when Ogston [95] showed the possible desymmetrization decarboxylation of L-serine under the promotion of chiral enzymes. ...
N-heterocyclic carbene-catalyzed enantioselective kinetic resolutions, dynamic kinetic resolutions, and desymmetrization reactions are systematically reviewed. The content is organized according to the activation modes involved in these transformations. Future advances within this highly active research field are discussed from our perspectives on the topic.
... Handedness is intrinsically linked to rotational direction in physics. For instance, in chemistry, helicity refers to the sense of rotation of helical structures, with righthanded helices assigned a positive helicity value and lefthanded helices assigned a negative helicity value [24]. Similarly, in hydrodynamics, the handedness of a flow is determined by the sign of its helicity, which measures the degree of linkage of the streamlines [13]. ...
We compare the various chirality measures most widely used in the literature to quantify chiral symmetry in extended solids, i.e., the continuous chirality measure, the Hausdorff distance, and the angular momentum. By studying these functions in an algebraically tractable case, we can evaluate their strengths and weaknesses when applied to more complex crystals. Going beyond those classical calculations, we propose a new method to quantify the handedness of a crystal based on a pseudoscalar function, i.e., the helicity. This quantity, borrowed from hydrodynamics, can be computed from the eigenvector carrying the system from the high-symmetry non-chiral phase to the low-symmetry chiral phase. Different model systems like K$_3$NiO$_2$, CsCuCl$_3$ and MgTi$_2$O$_4$ are used as test cases where we show the superior interest of using helicity to quantify chirality together with the handedness distinction.
... The allyl ligand binds to palladium in an η 3 -fashion with its two terminal atoms occupying cis-positions and the coordination sphere is completed by a chloride (Figure 5a), also shown in Scheme 5. A square-planar complex may be chiral under certain conditions even if it does not consist of chiral ligand(s). 39 The chirality in a generic d 8 cis-M( Me py)AB2 platform, shown in Figure 5b with 2-methylpyridine (a monodentate planar ring with only Cs local symmetry) asone of the ligands, originates from the rotation around the M-N bond that generates the opposite enantiomer; this pair of enantiomers can be described in terms of axial chirality.40,41 In addition to pyridine and some other heterocyclic ligands, square-planar metal complexes incorporating carbene ligands with the heterocyclic ring perpendicular to the coordination plane showing axial chirality are well documented. ...
We have developed an efficient and versatile approach to the synthesis of a family of 1,2,3-triazole-based mesoionic N-heterocyclic olefin (mNHO) ligands and investigated their coordination to palladium, gold, and boron...
... To exemplify the concept of a chiral metal, we can make an analogy with chiral crystals and their symmetry properties. We can then generally identify a chiral metal with an electronic state that has a well defined handedness, owing to the lack of inversion, mirror or other roto-inversion symmetries 36,37 . In this study, we start from this description to introduce the concept of a surface spin-orbital chiral metal to indicate a conducting electronic state of matter that has a well defined handedness, owing to an interaction driven by a magnetochiral order that lacks mirror symmetries, resulting from the internal spin-orbital structure, but has the same translational symmetry as the hosting crystal. ...
The relation between crystal symmetries, electron correlations and electronic structure steers the formation of a large array of unconventional phases of matter, including magneto-electric loop currents and chiral magnetism1–6. The detection of such hidden orders is an important goal in condensed-matter physics. However, until now, non-standard forms of magnetism with chiral electronic ordering have been difficult to detect experimentally⁷. Here we develop a theory for symmetry-broken chiral ground states and propose a methodology based on circularly polarized, spin-selective, angular-resolved photoelectron spectroscopy to study them. We use the archetypal quantum material Sr2RuO4 and reveal spectroscopic signatures that, despite being subtle, can be reconciled with the formation of spin–orbital chiral currents at the surface of the material8–10. As we shed light on these chiral regimes, our findings pave the way for a deeper understanding of ordering phenomena and unconventional magnetism.
... This concept is illustrated in Figure 7, where the DPP-C12 molecules on either side of the red dashed line show the same stacking structure, but their chirality is different. The SAMNs formed by these stacks do not obey the definition of racemic compounds [17] due to their aperiodic nature. In addition, they also do not belong to the solid solution [18] as they are periodic in one direction. ...
In recent years, there has been significant focus on investigating and controlling chiral self‐assembly, specifically in the context of enantiomeric separation. This study explores the self‐assembly behavior of 4‐dodecyl‐3,6‐di(2‐pyridyl)pyridazine (DPP−C12) at the interface between heptanoic acid (HA) and highly oriented pyrolytic graphite (HOPG) using a combination of scanning tunneling microscopy (STM) and multiscale molecular modeling. The self‐assembled monolayer structure formed by DPP−C12 is periodic in one direction, but aperiodic in the direction orthogonal to it. These structures resemble 1D disordered racemic compounds. Upon introducing palladium [Pd(II)] ions, complexing with DPP−C12, these 1D disordered racemic compounds spontaneously transform into 2D racemic conglomerates, which is rationalized with the assistance of force‐field simulations. Our findings provide insights into the regulation of two‐dimensional chirality.
... In principle, the efficiency of a non-stereoselective reaction should not be affected by the configuration of the substrates. [7] Therefore, we decided to perform detailed investigations to elucidate this phenomenon. ...
Recently, we have investigated the amino acid L‐lysine promoted CO2 capture and in‐situ hydrogenation to produce formate applying ruthenium‐ and manganese‐based catalysts (Chem. Sci. 2021, 12, 6020, Nature Energy 2022, 7, 438). Noteworthy, following this process CO2 can be captured from ambient air and directly converted to formate (TON>50,000). In this Comment, we report how hydrochloride impurities in the amino acid affect the CO2 capture efficiency and therewith lead to an ostensibly different behaviour of D‐ and L‐lysine in the CO2 capture. The results demonstrate the importance of careful analysis of all educts.
... Enantiomers, two stereoisomers in a mirror-image relationship, are one of the most difficult combinations to distinguish in molecular science. The purity of an enantiomer is described by the enantiomeric excess 19 or enantiomeric ratio (er), 20 an important index that is frequently used to evaluate the outputs in asymmetric synthesis. To analyze the er of a mixture of enantiomer crystals by image-based ML, we prepared 300 different mixtures of an enantiomer pair: L-and D-tartaric acids. ...
Visual observations are frequently used for the preliminary evaluation of the chemical contents of mixtures, but their accuracy largely depends on the observer's experience and intuition, which are difficult to share. Here, we report component ratio prediction using image-based machine learning (ML), which is applicable to the analysis of various solid mixtures, such as mixtures of organics and inorganics, polymorphous crystals, and enantiomers. The trained model with 300 images could predict the sugar/dietary salt weight ratio from an image with 4% error. The ML prediction pipeline was shown to be broadly applicable to polymorphic glycine, D/L-tartaric acid, and four-component systems. As an application demonstration, we also used our ML system to analyze the yield of a solid-state decarboxylation reaction. These results demonstrated that accumulation of researchers' experience derived from visual information can be shared as trained ML models and used as a quantitative analysis method.
... Form I contains two enantiomers I-A and I-B in equal numbers, that is, the crystal is a true racemate. 43 The azine is characterized by the torsion angle τ = ∠(CN-NC) and the phenyl twists ϕ i , that is, the dihedral angles ϕ 1 = ∠(C7-C2-C1N1) and ϕ 2 = ∠(C15-C10-C9N2). In form I, the phenyl twists are conrotatory because the dihedral angles ϕ 1 = 29.32°and ...
The central question of the paper concerns the CEISR effect in the case of symmetrical p -disubstituted acetophenone azines. We use intermolecular interaction inventory analyses to firmly establish the inequivalence or equivalence of the two arenes.
... Its adsorption on a surface results in two opposite enantiomerically oriented motifs indicating that the molecule is prochiral [15] and that the surface plane serves as a 2D mirror (orange dashed line in Figure 1b). The two enantiomeric motifs are defined by treating the surface as a substituent to a tetrahedral center and then applying the Cahn-Ingold-Prelog priority rules [44]. The surface is considered to have the highest priority (3), and the hydrogen (of the CH bridging the two rings) is considered to have the lowest (0). ...
Barbituric acid derivative (TDPT) is an achiral molecule, and its adsorption on a surface results in two opposite enantiomerically oriented motifs, namely TDPT-Sp and Rp. Two types of building blocks can be formed; block I is enantiomer-pure and is built up of the same motifs (format SpSp or RpRp) whereas block II is enantiomer-mixed and composes both motifs (format SpRp), respectively. The organization of the building blocks determines the formation of different nanoarchitectures which are investigated using scanning tunneling microscopy at a liquid/HOPG interface. Sophisticated, highly symmetric “nanowaves” are first formed from both building blocks I and II and are heterochiral. The “nanowaves” are metastable and evolve stepwisely into more close-packed “nanowires” which are formed from enantiomer-pure building block I and are homochiral. A dynamic hetero- to homochiral transformation and simultaneous multi-scale phase transitions are demonstrated at the single-molecule level. Our work provides novel insights into the control and the origin of chiral assemblies and chiral transitions, revealing the various roles of enantiomeric selection and chiral competition, driving forces, stability and molecular coverage.
... The hydrogen atom of the X-H group can be in syn or anti forms with respect to the imine group. 94 The hydrogen atom of the imine group may be in cis or trans configurations with respect to the X-H group. Thus, there are four combinations, that is, syn-cis, syn-trans, anti-cis, and anti-trans, which hereafter will be called as in Fig. 2, sc, st, ac and at, respectively. ...
The equilibrium structure of selenophenol has been investigated using rotational spectroscopy and high-level quantum mechanical calculations, offering electronic and structural insight into the scarcely studied selenium compounds. The jet-cooled broadband microwave spectrum was measured in the 2–8 GHz cm-wave region using broadband (chirped-pulse) fast-passage techniques. Additional measurements up to 18 GHz used narrow-band impulse excitation. Spectral signatures were obtained for six isotopic species of selenium (80Se, 78Se, 76Se, 82Se, 77Se, and 74Se), together with different monosubstituted 13C species. The (unsplit) rotational transitions associated with the non-inverting μa-dipole selection rules could be partially reproduced with a semirigid rotor model. However, the internal rotation barrier of the selenol group splits the vibrational ground state into two subtorsional levels, doubling the dipole-inverting μb transitions. The simulation of the double-minimum internal rotation gives a very low barrier height (B3PW91: 42 cm−1), much smaller than for thiophenol (277 cm−1). A monodimensional Hamiltonian then predicts a huge vibrational separation of 72.2 GHz, justifying the non-observation of μb transitions in our frequency range. The experimental rotational parameters were compared with different MP2 and density functional theory calculations. The equilibrium structure was determined using several high-level ab initio calculations. A final Born–Oppenheimer (reBO) structure was obtained at the coupled-cluster CCSD(T)_ae/cc-wCVTZ level of theory, including small corrections for the wCVTZ → wCVQZ basis set enlargement calculated at the MP2 level. The mass-dependent method with predicates was used to produce an alternative rm(2) structure. The comparison between the two methods confirms the high accuracy of the reBO structure and offers information on other chalcogen-containing molecules.
... The IUPAC defines helicenes [1] as "ortho-fused polycyclic aromatic or heteroaromatic compounds in which all rings (minimum five) are angularly arranged so as to give helically shaped molecules, which are thus chiral". [2] Following a more recent definition, at least six fused rings are required in a helicene, [3] although smaller arrangements are repeatedly named accordingly. [1b,4] This definition not only allows for the presence of benzene rings (A, B; Figure 1), but also of cyclopentadiene (C) [5] or heteroaromatic rings. ...
The synthesis of three penta‐ and three hexahelicenes containing two terminal thiophene units is described. The syntheses of pentahelicenes consist of 1,4‐bisalkynylation of a benzene precursor and double Suzuki coupling in 2,3‐position to introduce thiophene units. The ortho,ortho’ fusion yielding the final products was achieved with Fürstner's protocol using platinum(II) chloride or JohnPhos‐complexed gold(I) as catalysts. A similar approach to hexahelicenes started with a naphthalene derivative, where 2,7‐bisalkynylation and subsequent double Suzuki coupling with thiophene‐2‐boronic acid at 1,8‐position furnished precursors, in which ortho,ortho’ fusion to the respective hexahelicenes was achieved with platinum(II) chloride or, favourably, with indium(III) chloride. UV/Vis spectra and cyclic voltammograms were recorded for all helicenes and HOMO/LUMO gaps were calculated with DFT methods.
... According to the current definitions of isomerization and stereochemical non-rigidity by IUPAC, 9 a barrier height of 20 kcal mol −1 , equivalent to a temperature-dependent first-order half-life time (t 1/2 ) of approximately 1000 s at 298 K, is required for experimental isolation of individual isomers. 10 Literature lacks a consensus regarding the origin of the isomerization and the NMR signal duplication and the topic remain overlooked. For 6,8-di-C-glycosyl flavonoids (Fig. 1), the steric hindrance with C 7 substituents, such as -OCH 3 , is considered as the main cause of restricted rotation, while flavonoids with C 7 = OH do not exhibit signal duplication. ...
C-glycosyl-flavonoids are phytochemical natural products that possess different biological applications. Several compounds from this class exhibit rotational isomerism, evidenced by NMR signal duplication. This phenomenon is usually associated with the...
... However, at interfaces other factors are in play due to restrictions in space at the interface and less favorable conformers, such as the gauche (the second least stable form), might be favored. 41 The detection of an active methylene group in gauche form for organic moieties at interfaces by VSFG is very common as shown later on, which can be utilized as an indicator of surface order and the constrains present. ...
Interfacial interactions between water and oil phases are present in various fields, in which other additives, such as surfactants, are utilized to minimize the surface stress between these phases to form an emulsion. However, the consequence of adding additives is not always easy to understand or to control, due to the plethora of parameters that control the production of an emulsion phase. There are several macroscopic techniques to study the properties of emulsions. Nevertheless, these techniques cannot describe the mechanistic steps at molecular level for interfaces with nanometer thicknesses. Among surface sensitive techniques, VSFG (vibrational sum frequency generation) has been utilized to study various parameters that control the formation of surfactant monolayers at water-oil interfaces. In this brief-review, basics about utilization of VSFG along with recent advances for studying the water-oil interfaces will be presented, aiming at familiarizing other scientists with the current understanding of the water-oil interfaces as studied by VSFG
We have synthesized δ-Co2.5Zn17.5–xMnx (x = 0.4–3.5) pseudo-binary alloys of 10 different compositions by a high-temperature solid-state synthetic route, determined their crystal structures and the Mn substitution pattern, and estimated the existence range of the δ-phase. The alloys crystallize in two chiral enantiomorphic space groups P62 and P64, where the basic atomic polyhedron of the chiral structure is an icosahedron and the neighboring icosahedra share vertices to form an infinitely long double helix along the hexagonal axis (like in the δ-Co2.5Zn17.5 parent binary phase). The alloys are pure δ-phase up to the Mn content x ≈ 3.5. The Mn atoms partially substitute Zn atoms at particular crystallographic sites located on the icosahedra. The study of magnetism was performed on the Co2.5Zn17.1Mn0.4 alloy with the lowest Mn content. Contrary to the expectation that structural chirality may induce the formation of a nontrivial magnetic state, a spin glass state with no relation to the structural chirality was found. The magnetic sublattice contains all of the necessary ingredients (randomness and frustration) for the formation of a spin glass state. Typical out-of-equilibrium dynamic phenomena of a spin system with broken ergodicity were detected below the spin freezing temperature Tf ≈ 8 K.
A novel analytical method was developed for the simultaneous quantification of the R/S-enantiomers of amphetamine, methamphetamine, MDA and MDMA in hair samples using liquid chromatography-tandem mass spectrometry (LC–MS-MS). This method involved a straightforward derivatization step with dansyl chloride and the use of a chiral column, enabling the separation and quantification of all eight enantiomers in a single analysis. The method exhibited excellent linearity across a concentration range of 0.03–3.00 ng/mg for each enantiomer. Precision and accuracy were within acceptable limits, with bias and relative standard deviation (RSD) values consistently below 6% and 9%, respectively. Selectivity and specificity assessments confirmed the absence of any interference from contaminants or co-extracted drugs. The method demonstrated high sensitivity, with limits of detection (LOD) below 8 pg/mg and limits of quantification (LOQ) below 19 pg/mg for all analytes. Extraction recovery exceeded 79%, and matrix effects were minimal for all analytes. Processed sample stability evaluations revealed consistent results with deviations below 11% for all analytes. Application of the method to 32 authentic human hair samples provided valuable insights into amphetamine use patterns, allowing differentiation between medical amphetamine consumption and illicit use based on enantiomeric composition. Additionally, the method detected co-use of methamphetamine, MDA or MDMA in some samples, highlighting its applicability in drug monitoring and real-life case scenarios within a forensic institute. This innovative analytical approach offers a sensitive and selective method for enantiomeric differentiation of amphetamine, methamphetamine, MDA and MDMA in human hair samples, providing a valuable tool for forensic and clinical investigations.
The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space that allows for photo‐induced molecular motion in the crystalline state. This study describes a photo‐responsive single crystal based on hydrogen‐bonded (H‐bonded) network of dihydrodimethylbenzo[e]pyrene derivative 4BDHP. A crystal composed of H‐bonded undulate layers, 4BDHP‐2, underwent photoisomerization in the crystalline state due to loose stacking of the layers, resulting loss of crystallinity. Enantio‐pure crystal (S,S)‐4BDHP‐2, on the other hand, allowed to reveal the structure of the photoisomerized crystal, in which the closed form (4BDHP) and open form (4CPD) were arranged alternately with keeping crystalline periodicity, although side reactions were also implied. The present proof‐of‐concept system of a photochromic framework that retains crystalline periodicity after photoisomerization may provide new light‐driven porous functional materials.
The molecular conformation, crystalline morphology, and properties of photochromic organic crystals can be controlled through photoirradiation, making them promising candidates for functional organic materials. However, photochromic porous molecular crystals with a networked framework structure are rare due to the difficulty in maintaining space that allows for photo‐induced molecular motion in the crystalline state. This study describes a photo‐responsive single crystal based on hydrogen‐bonded (H‐bonded) network of dihydrodimethylbenzo[e]pyrene derivative 4BDHP. A crystal composed of H‐bonded undulate layers, 4BDHP‐2, underwent photo‐isomerization in the crystalline state due to loose stacking of the layers. Particularly, enantio‐pure crystal (S,S)‐4BDHP‐2 allowed to reveal the structure of the photoisomerized crystal, in which the closed form (4BDHP) and open form (4CPD) were arranged alternately with keeping crystalline periodicity, although side reactions were also implied. The present proof‐of‐concept system of a photochromic framework that retains crystalline periodicity after photo‐isomerization may provide new light‐driven porous functional materials.
The first reliable observation of desolvation- and temperature-induced solid phase racemization of the entire tris-chelates complex is reported. The capability of π…π stacking interactions to prevent such processes was revealed...
Many drugs are chiral with their chirality determining their biological interactions, safety, and efficacy. Since the 1980s, there has been a regulatory preference to bring single enantiomer to market. This perspective discusses trends related to chirality that have developed in the past decade (2013–2022) of new drug approvals. The EMA has not approved a racemate since 2016, while the average for the FDA is one per year from 2013 to 2022. These 10 include drugs which have been previously marketed elsewhere for several decades, analogues of pre-existing drugs, or drugs where the undefined stereocenter does not play a role in therapeutic activity. Two chiral switches were identified which were both combined with drug repurposing. This combination strategy has the potential to produce therapeutically valuable drugs in a faster time frame. Two class III atropisomers displaying axial chirality were approved between 2013 and 2022, one as a racemate and one as a single enantiomer.
Dynamic 3D covalent organic frameworks (COFs) have shown concerted structural transformation and adaptive gas adsorption due to the conformational diversity of organic linkers. However, the isolation and observation of COF rotamers constitute undergoing challenges due to their comparable free energy and subtle rotational energy barrier. Here, we report the atomic-level observation and structural evolution of COF rotamers by cryo-3D electron diffraction and synchrotron powder X-ray diffraction. Specifically, we optimize the crystallinity and morphology of COF-320 to manifest its coherent dynamic responses upon adaptive inclusion of guest molecules. We observe a significant crystal expansion of 29 vol% upon hydration and a giant swelling with volume change up to 78 vol% upon solvation. We record the structural evolution from a non-porous contracted phase to two narrow-pore intermediate phases and the fully opened expanded phase using n -butane as a stabilizing probe at ambient conditions. We uncover the rotational freedom of biphenylene giving rise to significant conformational changes on the diimine motifs from synclinal to syn-periplanar and anticlinal rotamers. We illustrate the 10-fold increment of pore volumes and 100% enhancement of methane uptake capacity of COF-320 at 100 bar and 298 K. The present findings shed light on the design of smarter organic porous materials to maximize host–guest interaction and boost gas uptake capacity through progressive structural transformation.
Diarylethenes are an important class of photoswitches that usually exist in interconvertible parallel (photoinert) and antiparallel (photochromic) conformational states. Recent research afforded sterically congested diarylethenes that exist as stable and separable configurational atropisomers. Rational manipulation of stereochemistry is a robust strategy for regulating diarylethene photochemistry. Here, we present a brief account of the conformer/atropisomer-dependent photochromism of diarylethene photoswitches, and we discuss a recent advance at the interface of diarylethene photochemistry and polymer mechanochemistry: our group recently introduced a mechanical approach for converting a parallel diarylbenzothiadiazole into its antiparallel configurational diastereomers, thereby turning on its photochromic reactivity. After mechanical activation, UV light changes the converted diarylethene molecule into a colored ring-closed form by a 6π-electrocyclization reaction that permits the visualization of the mechanical activation event. Besides the fundamentally new mechanism of converting a molecule into its configurational diastereomers through force–stereochemistry coupling, the conversion of atropisomer stereochemistry is a noncovalent process and features high mechanical reactivity in comparison to conventional mechanophores, which require covalent bond scission. This new type of configurational mechanophore holds promise for various applications, such as high-sensitivity stress sensing, lithography, and information storage.
1 Diarylethene Conformers and Atropisomers
2 Polymer Mechanochemistry and Configurational Mechanophores
3 Regulating the Stereochemistry and Reactivity of a Diarylethene Atropisomer with Mechanical Force
4 Summary and Future Outlook
Chirality and polarity are the two most important and representative symmetry‐dependent properties. For polar structures, all the twofold axes perpendicular to the principal axis of symmetry should be removed. For chiral structures, all the mirror‐related symmetries and inversion axes should be removed. Especially for duality (polarity and chirality), all of the above symmetries should be broken and that also represents the highest‐level challenge. Herein, a new symmetry‐breaking strategy that employs heteroanionic groups to construct hourglass‐like [Sr3OGeS3]²⁺ and [Sr3SGeS3]²⁺ groups to design and synthesize a new oxychalcogenide Sr18Ge9O5S31 with chiral‐polar duality is proposed. The presence of two enantiomers of Sr18Ge9O5S31 is confirmed by the single‐crystal X‐ray diffraction. Its optical activity and ferroelectricity are also studied by solid‐state circular dichroism spectroscopy and piezoresponse force microscopy, respectively. Further property measurements show that Sr18Ge9O5S31 possesses excellent nonlinear optical properties, including the strong second harmonic generation efficiency (≈2.5 × AGS), large bandgap (3.61 eV), and wide mid‐infrared transparent region (≈15.3 µm). These indicate that the unique microstructure groups of heteroanionic materials are conducive to realizing symmetry‐breaking and are able to provide some inspiration for exploring the chiral‐polar duality materials.
Norcarane is a mechanistic probe of monooxygenase enzymes that is able to detect the presence of cationic or radical intermediates. The addition of substituents around the bicycloheptane ring of the norcarane scaffold can assist in improving enzyme binding affinity and thus improve the regioselectivity of oxidation. Here we prepare in three-step, diastereoselective syntheses, ten norcaranes monosubstituted α to the cyclopropane as advanced probes. Four of these compounds were examined in enzyme binding experiments to evaluate their potential as probe substrates. Additionally, 19 potential products of enzymatic oxidation were generated via two additional synthetic steps for use as product standards in future studies.
Acrylates are used in cosmetics, orthopedics, paints, coatings, adhesives, textiles, and biomedical applications such as contact lenses and bone cements. However, some acrylates are mutagenic and the aim of this article is to explain the mutagenicity in terms of the atomic population redistribution in the molecule using two new descriptors which are based on atomic populations framed in the quantum theory of atoms in molecules. They describe the electron-withdrawing effect of a group of atoms in a molecule. The descriptors consider substituents of prop-2-enoates, the number of the acrolein units and the electrophilicity. The cluster analysis using these descriptors allows to classify acrylates in terms of the number of acrolein backbones and the type of the substituent group. Five main groups can be distinguished: monoacrylates with monomethacrylates, diacrylates with dimethacrylates, triacrylates, trimethacrylate and monoacrylates with electron-rich substituents. The substituents of mutagenic acrylates are electron withdrawing. This makes the acrolein backbone β-carbon more electrophilic and the molecule more reactive.
We present an in‐depth study of the sterically demanding Cp‐synthon (8‐H‐GuaH)Li isolated from natural product guaiazulene (Gua) as a ligand transfer reagent towards late transition metal complex precursors. The synthesis and full characterization of selected, essentially unexplored homo‐ and heteroleptic 8‐H‐guaiazulenide complexes of iron, ruthenium, cobalt, rhodium, platinum, copper and zinc are discussed in detail. In order to demonstrate their potential in catalytic applications, [(GuaH)PtMe3] was selected. The latter proved an even higher catalytic activity in light induced olefin hydrosilylation at catalyst loads as low as 5 ppm than classical [CpPtMe3] in a typical test reaction of silicone elastomer fabrication. Our results demonstrate that traditional petrochemical based Cp metal chemistry and catalysis can be replaced, sometimes even outmatched by superior catalysts based on cheap building blocks from renewable feedstock.
Chiral metasurfaces, with appealing properties for studying light-matter interactions at the nanoscale, have emerged as a promising platform for the realization of chiral optical responses, thereby showing advantages in chirality-related applications. The conventional approaches primarily concentrate on circular dichroism and the high Q factor of the chiral resonances, while little attention has been paid to the aspects of flexibility and controllability in the modulation of optical chirality, further inhibiting the implementation of tunable and multifunctional chiral metadevices. Here, we employ a planar chiral silicon metasurface governed by bound states in the continuum (BICs) to unravel steerable chiral optical responses. In particular, the BIC-based intrinsic and extrinsic planar chiralities can be precisely steered by breaking the in-plane symmetry and the illumination symmetry, respectively. Moreover, a hybrid Si−VO2 metasurface, manifested by the chiral coupled-mode theory, showcases the feasibility of actively tuning the dissipative loss while maintaining chiral quasi-BICs, then yielding desired loss-steered optical chirality. Our results provide alternative insights into tunable optical chirality and pave the way for advancements in chiroptical applications.
Cyclohept-1-ene-1-carbaldehyde undergoes photoinduced E → Z isomerization at λ = 350 nm. The ring strain facilitates Diels-Alder cycloaddiions with 1,3-dienes, [3 + 2] cycloadditions with 1,3-dipoles, and ene reactions with olefins. Products are trans-fused at the cycloheptane core and were obtained in yields of up to 82%. Single crystal X-ray analyses corroborated the constitution and relative configuration of key products. With BF3 as a Lewis acid and 2,3-dimethylbuta-1,3-diene, cyclohept-1-ene-1-carbaldehyde reacted in the dark and rearranged stereoselectively to a tricyclic ketone (87%).
Chromophore cis/trans photoisomerization is a fundamental process in chemistry and in the activation of many photosensitive proteins. A major task is understanding the effect of the protein environment on the efficiency and direction of this reaction compared to what is observed in the gas and solution phases. In this study, we set out to visualize the hula twist (HT) mechanism in a fluorescent protein, which is hypothesized to be the preferred mechanism in a spatially constrained binding pocket. We use a chlorine substituent to break the twofold symmetry of the embedded phenolic group of the chromophore and unambiguously identify the HT primary photoproduct. Through serial femtosecond crystallography, we then track the photoreaction from femtoseconds to the microsecond regime. We observe signals for the photoisomerization of the chromophore as early as 300 fs, obtaining the first experimental structural evidence of the HT mechanism in a protein on its femtosecond-to-picosecond timescale. We are then able to follow how chromophore isomerization and twisting lead to secondary structure rearrangements of the protein β-barrel across the time window of our measurements.
This paper describes a mechanical approach to inducing the atropisomerization of a parallel diarylethene into its antiparallel diastereomers exhibiting distinct chemical reactivity. A congested parallel diarylethene mechanophore in the (Ra,Sa)-configuration with mirror symmetry is atropisomerized to its antiparallel diastereomers with C2 symmetry under ultrasound-induced force field. The resulting stereochemistry-converted material gains symmetry-allowed reactivity toward conrotatory photocyclization.
Visual observations are frequently used as a preliminary evaluation of the chemical contents of mixtures, but their accuracy largely depends on the observer’s experience and intuition, which are difficult to share. Here, we report component ratio pre-diction using image-based machine learning (ML), which is applicable to analysis of various solid mixtures, such as mix-tures of organics and inorganics, polymorphous crystals, and enantiomers. The trained model with 300 images could predict the sugar/dietary salt weight ratio from an image within 4% error. The ML prediction pipeline was shown to be broadly ap-plicable to polymorphic glycine, D/L-tartaric acid, and four-component systems. As an application demonstration, we also used our ML system to analyze yield of a solid-state decarboxylation reaction. These results demonstrated that accumulation of researchers’ experience derived from visual information can be shared as trained ML models and used as a quantitative analysis method.
A concise and versatile synthesis of 5-(arylmethylideneamino)-4-(1H-benzo[d]imidazol-1-yl)pyrimidines has been developed, starting from 4-(1H-benzo[d]imidazol-1-yl)pyrimidines, and we report here the synthesis and spectroscopic and structural characterization of three such products, along with those of two intermediates in the reaction pathway. The intermediates 4-[2-(4-chlorophenyl)-1H-benzo[d]imidazol-1-yl]-6-methoxypyrimidine-2,5-diamine, (II), and 4-[2-(4-bromophenyl)-1H-benzo[d]imidazol-1-yl]-6-methoxypyrimidine-2,5-diamine, (III), crystallize as the isostructural monohydrates C18H15ClN5O·H2O and C18H15BrN5O·H2O, respectively, in which the components are linked into complex sheets by O—H⋯N and N—H⋯O hydrogen bonds. In the product (E)-4-methoxy-5-[(4-nitrobenzylidene)amino]-6-[2-(4-nitrophenyl)-1H-benzo[d]imidazol-1-yl]pyrimidin-2-amine, which crystallizes as a 1:1 solvate with dimethyl sulfoxide, C25H18N8O5·C2H6OS, (IV), inversion-related pairs of the pyrimidine component are linked by N—H⋯N hydrogen bonds to form cyclic centrosymmetric R2²(8) dimers to which pairs of solvent molecules are linked by N—H⋯O hydrogen bonds. (E)-4-Methoxy-5-[(4-methylbenzylidene)amino]-6-[2-(4-methylphenyl)-1H-benzo[d]imidazol-1-yl]pyrimidin-2-amine, C27H24N6O, (V), crystallizes with Z′ = 2 and the molecules are linked into a three-dimensional framework structure by a combination of N—H⋯N, C—H⋯N and C—H⋯π(arene) hydrogen bonds. The analogous product (E)-4-methoxy-5-[(4-chlorobenzylidene)amino]-6-[2-(4-methylphenyl)-1H-benzo[d]imidazol-1-yl]pyrimidin-2-amine, C26H21ClN6O, (VI), crystallizes from dimethyl sulfoxide in two forms: one, denoted (VIa), is isostructural with (V), and the other, denoted (VIb), crystallizes with Z′ = 1, but as an unknown solvate in which the pyrimidine molecules are linked by N—H⋯N hydrogen bonds to form a ribbon containing two types of centrosymmetric ring.
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