Molecular Dissymmetry Research Articles

Molecular ordering-enhanced circularly polarized luminescence of chiral 1,10-phenanthroline derivatives.

2,9-Bis((1R,2S,5R)-2-isopropyl-5-methylcyclohexanoxy)-1,10-phenanthroline [2,9-di-L-menthoxy-1,10-phenanthroline] (Men2Phen) and 2,9-bis(2-(S)-methylbutoxy)-1,10-phenanthroline (MB2Phen) were synthesized as chiral derivatives of 1,10-phenanthroline (Phen). Differences in rigidity and bulkiness of the chiral substituents at the 2- and 9-positions of the Phen backbone led to distinctive molecular dissymmetry in the ground state resulting in remarkable differences in circular dichroism. Men2Phen exhibited efficient circularly polarized luminescence (CPLm) at an anisotropy factor of 10-2 in the solid state based on molecular ordering disclosed by X-ray crystal analysis, while it showed much lower anisotropy factor in solution. MB2Phen, which was rather amorphous and did not afford good crystals, showed only negligible CPLm both in the solid state and in solution.

Acoustic properties of piezoelectric cubic crystals

AbstractThis paper is offered as a complementary adjunct to the many treatments of the electronic and photonic properties of cubic III–V and II–VI compounds appearing in the literature. These crystals typically exhibit piezoelectricity, due to the molecular dissymmetry, thereby allowing the inclusion of classical mechanical/acoustic features along with the quantum. We discuss the history of this modality and then illustrate its use by applying it to an electro‐elastic problem that has the estimable virtues of having an exact solution, along with wide practical applicability: determination of the piezocoupling values governing the excitation of thickness vibrations in thin cubic films or plates of arbitrary crystallographic orientation by electric fields directed either along, or lateral to, the thickness. Explicit results are given for orientations along the great‐circle paths connecting the principal directions [100], [110], and [111]. The formalism is then applied to GaAs as an example; it is further demonstrated that various results, such as the orientational variations of piezocoupling factors, are generally applicable to other members of the III–V and II–VI families by scaling. Ancillary aspects, such as errors due to misorientations, nonlinearities, and equivalent circuit representations, are described and discussed. This work is dedicated to Gerald W. Farnell (1925–2015), Prof. Emeritus, McGill University, Montréal, Canada.

Louis Pasteur, molecular dissymmetry, therapeutic chemistry and neuropharmacology.

Louis Pasteur is celebrated as the founding father of microbiology. But he was a chemist by training and discovered molecular dissymmetry experimentally. All his life, his constant preoccupation will be to apply the method and strategies of the fundamental sciences to living processes, "from the molecule to the brain". His fundamental aim will be, beyond the biology of microbes, the chemistry of life, a disposition which signs the originality of his work. More unexpectedly, Pasteur was at the origin of therapeutic chemistry-which his successors, and especially Daniel Bovet, brilliantly illustrated at the Pasteur Institute and which they would pursue with the pharmacology of the nervous system or "neuropharmacology".

Pasteur and chirality: A story of how serendipity favors the prepared minds.

During the XIXth century, France has been the theater of many discoveries in stereochemistry thanks to prestigious physicists, chemists, and crystallographers. Among them, Louis Pasteur is certainly the father of molecular chirality (the so‐called molecular dissymmetry), and because of the exceptionally favored conditions of his famous discovery on the resolution of tartrates, his findings have often been attributed to serendipity. But let us not forget that “in the fields of observation, chance only favors the prepared minds.”

Preparative enantioseparation of (RS)-baclofen: determination of molecular dissymmetry.

The present work reports preparative enantioseparation of (RS)-baclofen using thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Diastereomers were synthesized using a new monochloro-s-triazine-based chiral derivatizing reagent (CDR), namely, N-(4-chloro-6-piperidinyl-[1,3,5]-triazine-2-yl)-L-phenylalanine, under microwave irradiation. Acetonitrile-0.1% aq. triflouroacetic acid in gradient elution mode and CH3 OH-CH2 Cl2 (4:5; v/v) were successful as mobile phase in HPLC and TLC, respectively. The two diastereomers were isolated by preparative TLC. Molecular dissymmetry was established by developing the lowest energy optimized structures of the diastereomers based on Density Functional Theory and with the help of (1) H NMR showing anisotropic effect associated with aromatic ring of s-triazine (in the CDR). The configuration of diastereomers was established as [L-Phe-(R)-Bac] and [L-Phe-(S)-Bac], where the first notation refers to the configuration of chiral auxiliary (of the CDR) and the second to that of the analyte Bac. Limits of detection were found to be 0.056 and 0.061 ng mL(-1), respectively, for the two diastereomers. Determination of absolute configuration of the two diastereomers lent support to the elution order and separation mechanism.

Stimuli-responsive, thixotropic bicomponent hydrogel of melamine–Zn(II)-orotate complex

Zinc(II)-orotate complex (ZnOA) has been synthesised, and it is used to produce supramolecular complex with melamine (M) at 1:1 molar ratio. During sonication for 5–6 min, the supramolecular complex is transformed into a bi-component hydrogel (S-gel). The spectroscopic tools such as FTIR and UV–vis spectra suggest that the H-bonding interaction between M and ZnOA produces a supramolecular complex which further forms J-aggregates during gelation. The circular dichroism spectra indicate the change in ellipticity with temperature that arises from the molecular dissymmetry during stacking of the ZnOAM complexes. The microscopic images indicate that the hydrogel network is formed with short helical nano-fibres. The energy-minimised structure of ZnOAM complex exhibits a well-defined d value of 11.3 Å obtained from X-ray scattering of the xerogel. The frequency-dependent rheological experiment (storage modulus (G′) is greater than loss modulus (G″)) characterises it as a gel. The gel shows thixotropic and stimuli-responsive behaviour.

Topological Model for Dipole–Quadrupole Polarizability and Its Application to Analysis of Discriminating Intermolecular Interactions

A simplified model for calculating the dipole and dipole–quadrupole polarizabilities Ai,jk is suggested. The model is based on the mean energy method and on the topological approximation to the bond order matrix. Pseudoinvariants of the Ai,jk tensor are calculated to evaluate the degree of molecular dissymmetry, which is responsible for the discriminating intermolecular forces. The method is illustrated by calculations for a number of chiral molecules and comparison of the calculated indices with the experimentally evaluated twisting ability of molecules during the nematic–cholesteric phase transition.

Algorithm for estimating molecular dissymmetry

A simple criterion for estimating molecular dissymmetry and an algorithm of its calculation are suggested. Calculations are performed for compounds belonging to different point groups. The new molecular characteristic may be used to predict the magnitude and sign of optical rotation.

Quantum-chemical quantification of molecular complexity and chirality

We introduce a number of molecular complexity indexes on the grounds of quantization of notions known in the differential geometry of curves (specifically, electron trajectories). Mean lengths, L( Ψ) and L, reflect the general spatial extent of a many-electron system in a given state Ψ and, correspondingly, of the molecular structure as a whole. Analogously, mean curvatures, K( Ψ) and K, give a measure of the non-linearity of electron distribution. A mean torsion, τ( ψ), along with related indexes κ and κ f , presents a degree of molecular dissymmetry, i.e. a measure of chirality. In fact, all these indexes possess additivity properties and correct asymptotics under decomposition into separate parts or individual atoms. A topological approach to a one-electron hamiltonian through an adjacency matrix of the corresponding molecular graph is examined when calculating the above indexes. Some typical planar and nonplanar structures (Hückel-like systems, simple models of chiral allenes and chiral octahedral complexes with bidentate ligands) are studied.

Quantitative aspects of chirality. III. Description of the influence of the structure of chiral compounds on their twisting power in the nematic mesophase by means of the dissymmetry function

AbstractFor a number of chiral α,β‐unsaturated carbonyl compounds, cyclohexanone and cyclohexenone derivatives, existing essentially in the form of single molecular conformation, the correlation dependences were established between the values of the calculated dissymmetry functions (DF) with respect to atomic masses and atom refractions, and the induction effectiveness of helical ordering in the nematic mesophase (twisting power). Such correlative dependencies, as the examples show, allow one to predict safely enough the twisting power of new substances with the ‘fixed’ molecular conformation. Types of dissymmetry functions and kinds of correlative dependences, the most acceptable for these reasons, were revealed. Dissymmetry functions formed on the basis of atom refractions (polarizabilities) describe the influence of the molecular structures of chiral compounds on the twisting power with higher accuracy than those that characterize the dissymmetry of the atomic masses distribution, according to the important role of the dispersion forces in the formation of helical ordering in liquid crystalline systems. The components characterizing the distribution dissymmetry of atomic refractions and masses with respect to the long and two shorter axes as the peculiar characteristics of biaxiality of chiral molecules describe the influence of the molecular structure on the twisting power with the same accuracy as the general DF do. Thus influence of chiral dopant molecules on the interactions between molecules in the uniaxial mesophases is negligible within the limits of the DF method. Based on the calculations for model systems it is established that the presence of the non‐linear cinnamoyl fragment has a decisive influence on the molecular dissymmetry of the chiral α,β‐unsaturated ketones. The alkyl groups influence the molecular dissymmetry only slightly, but it is important that their presence ensures the stabilization of the chiral conformer with the defined helicity of the cinnamoyl fragment.

Electronic and topological chirality indexes for dissymmetric molecular systems

A new quantitative measure of molecular dissymmetry is proposed that is based on quantum-mechanical counterparts of notions extracted from differential geometry. Starting with the so-called torsion of a curve, we arrive at a chirality operator and appropriate average as the chirality index ae. The essential properties of ae are its additivity and also its ability to vanish for the racemic mixture of chiral structures. Some quantum-chemical approaches to calculating ae are presented, e.g., a typical one using only the adjacency matrix and the coordinates of atoms. Quasi-continuous and continuous systems, such as helices and Mobius-like structures, are studied.

Induced optical activity on side‐chain aromatic chromophores in copolymers of (−)‐menthyl acrylate with 1,2‐diphenyl‐1,2‐ethanedione‐2‐O‐acryloyloxime

AbstractIn the present paper the synthesis of optically active copolymers from (−)‐menthyl acrylate (MtA) and 1,2‐diphenyl‐1,2‐ethanedione‐2‐O‐acryloyloxime (BMOA) by radical initiation is described. The copolymers obtained, having different contents of photosensitive O‐acyloxime moieties, were characterized by FT‐IR, 1H NMR and GPC measurements, and their chiroptical properties investigated by circular dichroism. The induced chirality on BMOA co‐units is assigned to isolated rather than to sequential BMOA units. Thus, the induced chirality is due to the molecular dissymmetry of individual O‐acyloxime chromophores flanked by opticaly active MtA units.

Crystallographic consequences of molecular dissymmetry.

The molecular chirality associated with an optically active molecule is manifested in the bulk crystallography of the compound. The historical development of optical activity was greatly aided by systematic studies of the habits of enantiomorphic crystals. The concepts of molecular dissymmetry, crystallography, and chirality are therefore linked. Racemic materials can be characterized by means of their melting-point phase diagrams, and this information used to design rational separations of racemic mixtures into their component enantiomers. Certain compounds are found to resolve spontaneously upon crystallization, and the enantiomers of these conglomerate species may be separated by direct crystallization. Compounds which crystallize as true racemates require resolution through the formation and separation of dissociable diastereomer species. The choice of resolution pathway is therefore determinable through an evaluation of the melting-point phase diagrams. When possible, resolution through direct crystallization represents the simplest, most cost-effective means of enantiomer resolution.

Chemistry, stereochemistry, and molecular dissymmetry of complexes containing quadridentate ligands with skew six-membered chelate rings

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemistry, stereochemistry, and molecular dissymmetry of complexes containing quadridentate ligands with skew six-membered chelate ringsB. Bosnich and J. MacB. HarrowfieldCite this: Inorg. Chem. 1975, 14, 4, 853–860Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/ic50146a029RIGHTS & PERMISSIONSArticle Views55Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Chemistry, stereochemistry, and molecular dissymmetry of metal complexes containing a quadridentate ligand with chair six-membered chelate rings

Chemistry, stereochemistry, and molecular dissymmetry of metal complexes containing a quadridentate ligand with chair six-membered chelate rings

Absolute configuration of allenes, conversion of molecular dissymmetry into centrodissymmetry by heterogeneous catalytic hydrogenation

Palladium-catalysed hydrogenation of 4-methylhexa-2,3-dienoic acid and its methyl ester has been studied, by product analysis, over the complete range of hydrogen absorption. 4-Methyl[1-14C]hex-cis-2-enoic and 4-methyl[1-14C]hex-3-enoic acid and methyl ester have been employed in co-hydrogenations with the allene, which show that the substantial amount of 4-methylhex-trans-2-enoic acid (or ester) formed in the first stage arises neither directly from the allene, nor by isomerisation of the 3-enoic acid, but by stereomutation of 4-methylhex-cis-2-enoic acid on the catalyst. The conversion of molecular dissymmetry into centrodissymmetry by catalytic hydrogenation can therefore be used to determine the absolute configuration of allenes.(–)-Methyl 4-methylhexa-2,3-dienoate gave (–)-(R)-methyl 4-methylhexanoate on catalytic semi- and full-hydrogenation and, from analysis of steric effects in the transition state for adsorption, the (–)-allene ester has the R-configuration. Semihydrogenation of the (+)-allenic acid, followed by esterification, gave methyl (+)-4-methylhex-2-enoate, oxidised and esterified to (+)-(S)-methyl 2-methylbutyrate: this provides a variant of the method. The assumption of cis-addition of hydrogen from the catalyst surface is formally proved by hydrogenation of (+)-methyl 4-phenyl-penta-2,3-dienoate of established S-configuration.

Transesterification of poly(methyl acrylate) with optically active alcohols

AbstractTransesterifications of atactic and isotactic poly(methyl acrylate) with optically active alcohols such as (S)‐2‐methyl‐butanol, D‐borneol and L‐menthol were carried out in toluene at 100°C using p‐toluenesulfonic acid as catalyst to obtain optically active polymers. In addition a relationship between the conformation and the optical behaviour of the transesterified poly(methyl acrylate) was investigated. The specific rotation of the transesterified atactic poly(methyl acrylate) increased linearly with increasing introduced optically active groups at the lateral chain, in contrast to that of the isotactic poly(methyl acrylate) which increased nonlinearly with increasing introduced asymmetric groups. Since the specific rotations of the transesterified polymers depend on these tacticities the conclusion was drawn that the optical activity is caused not only by the asymmetric group in the lateral chain but also by molecular dissymmetry in the principal chain.

The Chemistry and Stereochemistry of Cercosporin

The structure of cercosporin, a deep red photosensitizing pigment isolated from the cultured mycelia of Cercospora kikuchii (Matsumoto et Tomoyasu) Gardner, has been elucidated as 1,12-bis(2-hydroxypropyl)-2,11-dimethoxy-6,7-methylenedioxy-4,9-dihydroxyperylene-3,10-quinone(Ia). All substituents are symmetrically arranged and the molecule has a two-fold rotation axis. An unusual seven-membered methylenedioxy bridged system endows the molecule with the inherently dissymmetric nature. Isocercosporin(Ib), a stereoisomer of Ia, was separated and the stereochemistry and the molecular dissymmetry of both isomers were also discussed.

The Chemistry and Stereochemistry of Cercosporin

The structure of cercosporin, a deep red photosensitizing pigment isolated from the cultured mycelia of Cercospora kikuchii (Matsumoto et Tomoyasu) Gardner, has been elucidated as 1,12-bis(2-hydroxypropyl)-2,11-dimethoxy-6,7-methylenedioxy-4,9-dihydroxyperylene-3,10-quinone(Ia). All substituents are symmetrically arranged and the molecule has a two-fold rotation axis. An unusual seven-membered methylenedioxy bridged system endows the molecule with the inherently dissymmetric nature. Isocercosporin(Ib), a stereoisomer of Ia, was separated and the stereochemistry and the molecular dissymmetry of both isomers were also discussed.

Optical activity and molecular dissymmetry in coordination chemistry

Abstract