Chiral Solids Research Articles

Charge transport in chiral solids as a possible tool in search of dark matter signals

Charge transport in chiral solids as a possible tool in search of dark matter signals

Chiral Perovskite Nanocrystals for Asymmetric Reactions: A Highly Enantioselective Strategy for Photocatalytic Synthesis of N-C Axially Chiral Heterocycles.

Catalytic approaches to generate enantiospecific chiral centers are the major premise of modern organic chemistry. Heterogeneous catalysis is responsible for the vast majority of chemical transformations, yet the direct employment of chiral solid catalysts for asymmetric synthesis is mostly overlooked. Here, we demonstrated that a heterogeneous metal-halide perovskite nanocrystal (NC) catalyst is active for asymmetric organic synthesis under visible-light activation. Chiral 1-phenylethylamine (PEA)-hybridized perovskite PEA/CsPbBr3 NC photocatalysts exhibit an enantioselective (up to 99% enantiomer excess, ee) avenue to produce N-C axially chiral N-heterocycles, i.e., N-arylindoles from N-arylamine photo-oxidation. Mechanistic investigation indicated a discriminated prochiral binding of the N-arylamine substrates onto the chiral-NC surface with ca. -2.4 kcal/mol enantiodifferentiation. Our perovskite NC heterogeneous catalytic system not only demonstrates a promising strategy to address the long-term challenges in atroposelective pharmaceutical scaffold synthesis but also paves the road to directly employ chiral solids for asymmetric synthesis.

Chirality in the Solid State: Chiral Crystal Structures in Chiral and Achiral Space Groups.

Chirality depends on particular symmetries. For crystal structures it describes the absence of mirror planes and inversion centers, and in addition to translations, only rotations are allowed as symmetry elements. However, chiral space groups have additional restrictions on the allowed screw rotations as a symmetry element, because they always appear in enantiomorphous pairs. This study classifies and distinguishes the chiral structures and space groups. Chirality is quantified using Hausdorff distances and continuous chirality measures and selected crystal structures are reported. Chirality is discussed for bulk solids and their surfaces. Moreover, the band structure, and thus, the density of states, is found to be affected by the same crystal parameters as chirality. However, it is independent of handedness. The Berry curvature, as a topological measure of the electronic structure, depends on the handedness but is not proof of chirality because it responds to the inversion of a structure. For molecules, optical circular dichroism is one of the most important measures for chirality. Thus, it is proposed in this study that the circular dichroism in the angular distribution of photoelectrons in high symmetry configurations can be used to distinguish the handedness of chiral solids and their surfaces.

Passive odd viscoelasticity.

Active chiral viscoelastic materials exhibit elastic responses perpendicular to the applied stresses, referred to as odd elasticity. We use a covariant formulation of viscoelasticity combined with an entropy production analysis to show that odd elasticity is not only present in active systems but also in broad classes of passive chiral viscoelastic fluids. In addition, we demonstrate that linear viscoelastic chiral solids require activity in order to manifest odd elastic responses. To model the phenomenon of passive odd viscoelasticity we propose a chiral extension of Jeffreys model. We apply our covariant formalism in order to derive the dispersion relations of hydrodynamic modes and obtain clear imprints of odd viscoelastic behavior.

Torsion of Chiral Porous Elastic Beams

This paper is concerned with the equilibrium theory of chiral porous elastic solids. We study the problem of torsion, bending and extension of chiral cylinders. First, it is shown that the solution can be found as a vector field which has the property that its partial derivative with respect to axial coordinate corresponds to a rigid deformation. Then, we reduce the problem to the study of some two-dimensional problems. With the help of these results we can investigate the bending by terminal couples and the problems of extension and torsion. The solution is used to study the torsion of a chiral circular cylinder.

Chiral Isocamphoric Acid: Founding a Large Family of Homochiral Porous Materials

AbstractHomochiral metal–organic frameworks (MOFs) are an important class of chiral solids with potential applications in chiral recognition; however, relatively few are available. Of great importance is the availability of low‐cost, racemization‐resistant, and versatile enantiopure building blocks. Among chiral building blocks, d‐camphoric acid is highly prolific, yet, its trans‐isomer, l‐isocamphoric acid, has remained unknown in the entire field of solid‐state materials. Its rich yet totally untapped synthetic and structural chemistry has now been investigated through the synthesis of a large family of homochiral metal isocamphorates. The first observation of diastereoisomerism in isostructural MOFs is presented. Isocamphorate has a powerful ability to create framework topologies unexpected from common inorganic building blocks, and isocamphoric acid should allow access to hundreds of new homochiral materials.

Chiral Isocamphoric Acid: Founding a Large Family of Homochiral Porous Materials.

Homochiral metal-organic frameworks (MOFs) are an important class of chiral solids with potential applications in chiral recognition; however, relatively few are available. Of great importance is the availability of low-cost, racemization-resistant, and versatile enantiopure building blocks. Among chiral building blocks, d-camphoric acid is highly prolific, yet, its trans-isomer, l-isocamphoric acid, has remained unknown in the entire field of solid-state materials. Its rich yet totally untapped synthetic and structural chemistry has now been investigated through the synthesis of a large family of homochiral metal isocamphorates. The first observation of diastereoisomerism in isostructural MOFs is presented. Isocamphorate has a powerful ability to create framework topologies unexpected from common inorganic building blocks, and isocamphoric acid should allow access to hundreds of new homochiral materials.

Elastic Metamaterials Making Use of Chirality: A Review

Metamaterials are artificially designed composite materials exhibiting unusual physical properties not easily found in nature. In most cases, these properties appear in a wave environment where local resonance comes into play. Therefore the design principle of these metamaterials relies intimately on creation of appropriate local resonances and their interplay with background waves. In this review, we show that the coupling between rotation and bulk deformations of two-dimensional chiral solids is able to provide a unique resonant mechanism in designing elastic metamaterials, and the recent advances in this area will be reviewed. We begin with a metamaterial with a single-negative parameter by integrating a chiral lattice with resonating inclusions, and demonstrate that this metamaterial not only is suitable for broadband vibration isolation but also provides a mixed-type resonance due to microstructure chirality. This mixed-type resonance is further explored to realize elastic metamaterial with double-negative parameters, which can refract elastic wave with a negative refraction angle. Finally, we present also recent development on micropolar constitutive models, which are potentially suitable for modeling chiral elastic metamaterials.

Supramolecular Chemistry Controlled by Conformational Space during Structure Direction of Nanoporous Materials: Self-Assembly of Ephedrine and Pseudoephedrine

In an attempt to produce chiral solids, where chirality arises from an asymmetric ordering of the spatial distribution of dopants, we have studied the supramolecular aggregation of π–π-type interactions between aromatic rings of two closely related diastereoisomers, (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine, during structure direction of the microporous AFI large-pore aluminophosphate framework. Despite their very similar molecular structures, differing only in the stereochemistry of the hydroxyl substituent, fluorescence spectroscopy clearly shows completely different aggregation behaviors of the two isomers, with ephedrine displaying a much stronger aggregation trend than pseudoephedrine in aqueous solution; interestingly, this supramolecular behavior is reproduced when the molecules are occluded within the AFI framework during crystallization. A molecular mechanics study of the conformational behavior of the two chiral flexible molecules, both in a vacuum and in aqueous solution, revealed that the lower trend of pseudoephedrine to form supramolecular aggregates is caused by the occurrence of a particular conformation with a folded molecular structure. This conformation, which is stable for pseudoephedrine but not for ephedrine, provokes steric hindrance that prevents the approaching of a neighboring molecule to form an aggregate, hence providing an explanation for the experimental observations. Our work represents the first example in which the conformational space of a molecule determines its supramolecular aggregation behavior during structure direction and could play a role in molecular-recognition phenomena in host–guest systems.

Deformation of chiral elastic cylinders composed of two materials

The behavior of chiral elastic materials is of interest to the fields of auxetic materials, carbon nanotubes, honeycomb structures and mechanics of bone. The chiral effects cannot be described within classical elasticity. In this paper we study the deformation of isotropic chiral solids by using the theory of Cosserat elasticity. We investigate the behavior of a bar composed by two different materials. The intended applications of the solution are to bone implants and various compound cylinders. The bar is reinforced by a longitudinal rod and is subjected to extension, bending and torsion. It is shown that the compression of the composed cylinder, in contrast with the result predicted by the theory of achiral materials, is accompanied by torsion and bending. The method is used to investigate the case of a circular cylinder reinforced by a circular rod. In this case the compression of the bar produces only a twist around its axis.

Third-rank piezoelectricity in isotropic chiral solids

The highest symmetry in which piezoelectricity was thought to occur is cubic. Here, it is shown that third rank piezoelectricity can occur in isotropic chiral solids. Polarization is coupled via an isotropic third rank tensor to the antisymmetric part of the stress. Asymmetric stress can occur if balanced by moments distributed over area or volume. Such moments occur in heterogeneous solids, in which there exists a characteristic length associated with the microstructure: the Cosserat or micropolar solids. Effects associated with nonzero structure size are predicted, including radial polarization in response to torsion. These effects do not occur in gradient type flexoelectric materials; they are governed by a different tensorial rank and symmetry.

Multi odd–even effects on cell parameters, melting points, and optical properties of chiral crystal solids based on S-naproxen

Chiral solids based onS-naproxen alternatively crystallize inP21andP212121, respectively, which show the odd–even effects on cell parameters, melting points, and luminescence.

Syntheses of Zn or Cd complexes from dicarboxylate ligand exhibiting an axial chirality and auxiliary ligand

Coordination complexes [Cd(bpy-3,3′-dc)(bibp)(H2O)3]n (1), [Zn(bpy-3,3′-dc)(bibp)(H2O)2.5]n (2), [Cd2(bpy-3,3′-dc)(ptd)2(H2O)6](ClO4)2(H2O)5 (3) and [Zn2(bpy-3,3′-dc)(ptd)2(H2O)6](ClO4)2(H2O)6(CH3CN) (4) have been synthesized by the reaction of 2,2′-bipyridine-3,3′-dicarboxylic acid (H2bpy-3,3′-dc) and bipb or ptd with the Zn(II) or Cd(II) salts using different methods, where the bipb and ptd are 2,2′-bis(imidazol-1-ylmethyl)-biphenyl and 1,10-Phenanthroline-5,6-dione, respectively. Compound 1 featured a 1D chain, in which the metal centers bridged by bpy-3,3′-dc was chiral. Two chiral chains linked by bibp ligands were formed in a centro-symmetric fashion. Complex 2 was a two-dimensional network arising from two kinds of 21 helical chains. Being linked by a bpy-3,3′-dc ligand, the two metal centers in 3 and 4 exhibited the same absolute configuration. These binuclear units acted as chiral origins and were interconnected by directional hydrogen-bond interactions to form a 3D homochiral network. Significant CD signals exhibited that chiral solids were crystallized through the spontaneous resolution.

Nonlinear spin excitations in chiral magnetic solids

Comparative analysis of nonlinear spin excitations in inorganic and metal-organic magnets was performed. The properties of nonlinear magnetic excitations in molecular magnets were established: differences in the remagnetization modes of chiral and racemic crystals, effect of chirality of crystals on the soliton spin excitations, decrease in the threshold microwave power at transition to the nonlinear ferromagnetic resonance mode. It is shown that the domain wall dynamics and development of Suhl’s instability provide additional information on the microscopic mechanisms of magnetization of molecular metal-organic magnets in comparison with inorganic magnets.

Fundamental solutions for chiral solids in gradient elasticity

This paper is concerned with the linear theory of gradient elasticity. The deformation of homogeneous and isotropic chiral materials subjected to concentrated body forces is investigated. First, a counterpart of the Cauchy–Kowalewski–Somigliana solution in the dynamic theory of classical elasticity is established. Then, a general solution of the field equations that is analogous to the Boussinesq–Somigliana–Galerkin solution in the classical elastostatics is presented. The results are used to derive the fundamental solutions of the displacement equations in the equilibrium theory and in the case of steady vibrations.

Elemental tellurium as a chiralp-type thermoelectric material

The thermoelectric transport properties of elemental tellurium are investigated by density functional theory combined with the Boltzmann transport equation in the rigid band approximation. We find that the thermoelectric transport properties parallel and perpendicular to the helical chains are highly asymmetric (almost symmetric) for p- (n-) type doped tellurium due to the anisotropic (isotropic) hole (electron) pockets of the Fermi surface. The electronic band structure shows that the lone-pair derived uppermost heavy-hole and extremely light-hole lower valence bands offer the opportunity to obtain both a high Seebeck coefficient and electrical conductivity along the chains through Sb or Bi doping. Furthermore, the stairlike density of states yields a large asymmetry for the transport distribution function relative to the Fermi energy which leads to large thermopower. The calculations reveal that tellurium has the potential to be a good p-type thermoelectric material with an optimum figure of merit zT of 0.31 (0.56) at room temperature (500 K) at a hole concentration around 1×10^19 cm^−3. Exploiting the rich chemistry of lone pairs in chiral solids may have important implications for the discovery of high-zT polychalcogenide-based thermoelectric materials.

Chiral effect in plane isotropic micropolar elasticity and its application to chiral lattices

In continuum mechanics, the non-centrosymmetric micropolar theory is usually used to capture the chirality inherent in materials. However, when reduced to a two dimensional (2D) isotropic problem, the resulting model becomes non-chiral. Therefore, influence of the chiral effect cannot be properly characterized by existing theories for 2D chiral solids. To circumvent this difficulty, based on reinterpretation of isotropic tensors in the 2D case, we propose a continuum theory to model the chiral effect for 2D isotropic chiral solids. A single material parameter related to chirality is introduced to characterize the coupling between the bulk deformation and the internal rotation, which is a fundamental feature of 2D chiral solids. Coherently, the proposed continuum theory is applied for the homogenization of a triangular chiral lattice, from which the effective material constants of the lattice are analytically determined. The unique behavior in the chiral lattice is demonstrated through the analyses of a static tension problem and a plane wave propagation problem. The results, which cannot be predicted by the non-chiral model, are verified by the exact solution of the discrete model.

Influencing the Symmetry of High‐Nuclearity and High‐Spin Manganese Oxo Clusters: Supramolecular Approaches to Manganese‐Based Keplerates and Chiral Solids

Influencing the Symmetry of High‐Nuclearity and High‐Spin Manganese Oxo Clusters: Supramolecular Approaches to Manganese‐Based Keplerates and Chiral Solids

ChemInform Abstract: Enantioselective Catalysis by Chiral Solids: Approaches and Results

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.

Induction of chiral porous solids containing only achiral building blocks

In many areas of chemistry the synthesis of chiral compounds is a target of increasing importance. They play a vital role in biological function and in many areas of society and science, including biology, medicine, biotechnology, chemistry and agriculture. Many pharmaceutical molecules, like their biological targets, are chiral and it is therefore easy to understand the growing demand for efficient methods of producing enantiomerically pure compounds. This is equally true for the preparation of chiral solids, which have potential applications in asymmetric catalysis, chiral separations and the like. In this Review we will consider recent progress and future potential in the development of methods for the preparation of chirally pure solids, in particular where the building blocks of the structure are achiral themselves. We will discuss strategies for the synthesis of both inorganic (for example, zeolites) and inorganic-organic hybrid (for example, metal organic framework) chiral porous solids.