Chiral Chain Research Articles

Single-Molecule Unidirectional Processive Movement along a Helical Polymer Chain in Non-aqueous Medium.

In this work, a molecule “walking” along a single chain of a synthetic helical polymer, which is used as a rail on a substrate in an organic solvent at room temperature, is observed. The walking comprises the unidirectional processive movement of a short-chain molecule along a chiral helical chain in 3 nm steps, driven by Brownian motion and a tapping effect of the atomic force microscopy tip based on a flash ratchet mechanism. Furthermore, the rail consists of a long-chain substituted phenylacetylene polymer with pendant cholesteryl groups, along which the short-chain molecule can walk as a result of van der Waals interactions. The macromolecular motion is videoed using a fast-scanning atomic force microscope, and additionally, this phenomenon is also simulated by all-atom molecular dynamics calculations. On the basis of these results, we propose the principle of a polymer molecular motor. This is the first report of a synthetic walking machine of a chiral helical polymer driven by thermal fluctuation as an artificial life function.

Probing of the topological phase transition in a disordered 1D acoustic system

The methods to determine the Zak phase introduced by previous studies are usually limited to the periodic systems protected by the inversion symmetry. In this work, we build a one-dimensional chiral symmetric acoustic chain with controllable disorder to break its inversion symmetry. By the mean chiral displacement method, we detect the Zak phase in order to observe the topological phase transition induced purely by disorder. The finding exhibits the topological Anderson insulator phase, in which an otherwise trivial acoustic Su–Schrieffer–Heeger model is driven non-trivial by disorder accompanied by the change of the topological sign. This method could also be utilized in chiral symmetry broken and non-Hermitian systems. The result reveals that disorder introduced in the acoustic devices may induce the change of the topological phase, which is promising for the design of new acoustic devices.

Topological states in chiral electronic chains

We consider the influence of topological phases, or their vicinity, on the spin density and spin polarization through a chiral chain. We show the quantization of the Berry phase in a one-dimensional polarization helix structure, under the presence of an external magnetic field, and show its influence on the spin density. The polar angle of the momentum space spin density becomes quantized in the regime that the Berry phase is quantized, as a result of the combined effect of the induced spin-orbit coupling and the external transverse magnetic field, while the edge states do not show the polar angle quantization, in contrast with the bulk states. Under appropriate conditions, the model can be generalized to have similarities with a chain with nonhomogeneous Rashba spin-orbit couplings, with zero- or low-energy edge states. Due to the breaking of time-reversal symmetry, we recover the effect of chiral-induced spin polarization and spin transport across the chiral chain, when coupling to external leads. Some consequences of the quantized spin polarization and low-energy states on the spin transport are discussed.

Light Interaction with Cluster Chiral Nanostructures by High-Order Bessel Beam

Interactions between cluster chiral nanoparticles and a high-order Bessel beam (HOBB) with arbitrary illuminations are investigated. The generalized Lorenz–Mie theory (GLMT) is applied to derive the expansions of HOBB. Based on the additional theorem, multiple scattering results of cluster chiral nanoparticles are obtained by taking into account the tangential continuous boundary conditions. The present theory and codes proved to be effective when confronted with the simulations obtained from the Computer Simulation Technology (CST) software. Numerical results concerning the effects of beam order, beam conical angle, incident angles, beam polarization state, the chirality, and the material loss on the scattering of various types of aggregated chiral particles are displayed in detail, including the linearly chiral sphere chain, the chiral cube array, and the complex models composed of aggregated chiral spheres. This study may provide critical support to analytically understand the optical scattering characteristics with aggregated chiral particles of complex shapes, and may find important applications in manipulating collective chiral particles.

Quantization of topological indices in critical chains at low temperatures

Various types of topological phenomena at criticality are currently under active research. In this paper we suggest to generalize the known topological quantities to finite temperatures, allowing us to consider gapped and critical (gapless) systems on the same footing. It is then discussed that the quantization of the topological indices, also at critically, is retrieved by taking the low-temperature limit. This idea is explicitly illustrated on a simple case study of chiral critical chains where the quantization is shown analytically and verified numerically. The formalism is also applied for studying robustness of the topological indices to various types of disordering perturbations.

Solvent Effects on the Structural and Magnetic Properties of FeIII Spin-Crossover Complexes

Molecular devices based on spin-crossover (SCO) compounds are important targets for molecular electronics. In this study, six air-stable FeIII complexes have been prepared: [Fe(naphBzen)2]Cl (1), [Fe(naphBzen)2]Cl·0.5hexane (1·0.5hexane); [Fe(naphBzen)2]Cl·2CHCl3·1.15hexane (1·2CHCl3·1.15hexane), [Fe(naphBzen)2]Br (2), [Fe(naphBzen)2]Br·0.5hexane (2·0.5hexane), and [Fe(naphBzen)2]Br·2CHCl3 (2·2CHCl3). The hexane solvates are isostructural, crystallizing in the tetragonal space group I41/a. Weak van der Waals interactions between the cations result in the Fe1 and Fe2 centers packing into chiral chains and exhibiting two-step SCO. In contrast, the nonisostructural CHCl3 solvates have a single Fe center and crystallize in the triclinic space group P1̅ and are LS up to 350 K. The solvent-free systems are also not isostructural with [Fe(naphBzen)2]Cl, crystallizing in the triclinic space group P1̅, while [Fe(naphBzen)2]Br undergoes a phase transition from tetragonal P43 to P43212 upon heating from 150 to 280 K. In both cases the compounds are trapped in the LS state. Magnetic data reveals that SCO occurs only in the hexane solvates, indicating that even very weak interactions can be critical in observing spin-crossover behavior.

Amplification of circularly polarized luminescence from chiral cyclometalated platinum(II) complexes by the formation of excimer

Circularly polarized organic light-emitting diodes (CP-OLEDs) have raised increasing interests owing to their potential application in next-generation displays. In this work, by introducing chiral alkyl chain into tridentate chelating ligand 2,6-bis(N-alkylbenzimidazol-2’-yl)benzene, three chiral Pt(II) complexes are successfully designed and synthesized. All the complexes exhibited bright green emission in dilute acetonitrile solution, while strong yellow-orange emission in highly concentrated solution. However, when these complexes are doped into polymer polymethyl methacrylate, the green emission stemmed from the intrinsic single molecule would be changed into red emission from excimer through adjusting the doping levels. More importantly, the CPL signals could be amplified by an order of magnitude in comparison with solution state. Furthermore, the monochrome devices based on these complexes were successfully fabricated, and achieved good device performances with the maximum luminance of up to 1720 cd m−2 and electroluminescence dissymmetry values of around 2.6 × 10−3. These results indicate that such design strategy for Pt(II) complexes with tridentate cyclometalled ligands would be important for the development of high-performance CP-OLEDs.

Induction of Chirality in Boron Imidazolate Frameworks: The Structure-Directing Effects of Substituents.

By enhancing steric hindrance of substituents on the imidazole ring, the fan-shaped molecule of a tridentate boron imidazolate ligand (KBH(2-ipim)3, 2-ipim = 2-isopropylimidazolate) with racemic chirality was obtained. Then, seven novel boron imidazolate frameworks (BIFs) were prepared by mixing KBH(2-ipim)3 ligands with various derivatives of benzene carboxylic acid under solvothermal conditions. All of these seven materials contain a ladder-like zinc-boron-imidazolate chain as a basic building block, and the ligand BH(2-ipim)3- exists in the same handedness in one chain. The structural variations are associated with the position of substituents of the auxiliary ligand. Of particular interest is the spontaneous resolution of BH(2-ipim)3- ligands into two independent enantiomorphous homochiral structures, BIF-131-S and BIF-131-R, which contain both a chiral chain and an absolute helix embedded in the nets.

Asymmetric transport in long-range interacting chiral spin chains

Harnessing power-law interactions (1/r^\alpha1/rα) in a large variety of physical systems are increasing. We study the dynamics of chiral spin chains as a possible multi-directional quantum channel. This arises from the nonlinear character of the dispersion with complex quantum interference effects. Using complementary numerical and analytical techniques, we propose a model to guide quantum states to a desired direction. We illustrate our approach using the long-range XXZ model modulated by Dzyaloshinskii-Moriya (DM) interaction. By exploring non-equilibrium dynamics after a local quantum quench, we identify the interplay of interaction range \alphaα and Dzyaloshinskii-Moriya coupling giving rise to an appreciable asymmetric spin excitations transport. This could be interesting for quantum information protocols to transfer quantum states, and it may be testable with current trapped-ion experiments. We further explore the growth of block entanglement entropy in these systems, and an order of magnitude reduction is distinguished.

Chiral waves in structured elastic systems: dynamics of a meta-waveguide

Summary The notion of meta-surfaces is well established for waves interacting with arrays of periodic resonators. Here, an infinite elastic rod, attached to a system of gyroscopic spinners, is considered. This forms a waveguide with unusual dispersion properties and will be referred to as a chiral meta-waveguide. A class of transient and time-harmonic formulations describing waves in elastic chiral meta-waveguides is addressed. Consideration of a chiral elastic chain leads to the governing equations of the homogenised continuous system. Both analytical and numerical solutions are presented. Features observed for chiral waveforms show resemblance with formulations of quantum physics rather than linear elasticity. For an elementary example related to an elastic chiral rod, with the absence of pre-tension, it is noted that the longitudinal velocity satisfies the Klein–Gordon equation. For full vector problems, corresponding to an elastic chiral rod with pre-tension, time-harmonic Green’s matrix functions are derived for the case of large values of the gyricity parameter. This case is especially interesting because of the presence of both exponentially localised and oscillatory terms in the representation of Green’s matrix components.

Self-consistent field theory of chiral nematic worm-like chains.

Many macromolecules of biological and technological interest are both chiral and semi-flexible. DNA and collagen are good examples. Such molecules often form chiral nematic (or cholesteric) phases, as is well-documented in collagen and chitin. This work presents a method for studying cholesteric phases in the highly successful self-consistent field theory of worm-like chains, offering a new way of studying many biologically relevant molecules. The method involves an effective Hamiltonian with a chiral term inspired by the Oseen-Frank (OF) model of liquid crystals. This method is then used to examine the formation of cholesteric phases in chiral-nematic worm-like chains as a function of polymer flexibility, as well as the optimal cholesteric pitch and distribution of polymer segment orientations. Our approach not only allows for the determination of the isotropic-cholesteric transition and segment distributions, beyond what the OF model promises, but also explicitly incorporates polymer flexibility into the study of the cholesteric phase, offering a more complete understanding of the behavior of semiflexible chiral-nematic polymers.

Synthesis of chiral boron imidazolate frameworks with second-order nonlinear optics

The synthesis of crystalline homochiral MOF materials is very important for their potential application in enantioselective processes and asymmetric catalysis. In this paper, four novel zinc based chiral boron imidazolate frameworks (BIFs), Zn2[BH(2-eim)3](BA)2(OH) (BIF-132-BA, 2-eim ​= ​2-ethylimidazolate, BA ​= ​benzoate), Zn[HBH(2-ipim)3](OHBA)(Ac) (BIF-133-OHBA, 2-ipim ​= ​2-isopropylimidazolate, OHBA ​= ​o-hydroxybenzoate, Ac ​= ​acetate), Zn[HBH(2-ipim)3](PHBA)(Ac) (BIF-133-PHBA, PHBA ​= ​p-hydroxybenzoate), and Zn[HBH(2-ipim)3](DHBA)(Ac) (BIF-133-DHBA, DHBA ​= ​2,4-dihydroxybenzoate) were prepared via solvothermal synthesis. Single-crystal X-ray diffraction demonstrated that the existence of hydrogen bonds between adjacent chains results in two different structure features of BIF-131: a chiral ladder-like 1D chain (BIF-133-OHBA) and two supramolecular 2D layers (BIF-133-PHBA and BIF-133-DHBA). Then, the optical activities of as-synthesied crystals were preliminarily studied by circular dichroism (CD) spectroscopy. In addition, because they crystallized in noncentrosymmetric space groups, the powder second-harmonic generation (SHG) measurements were carried out and the SHG response of BIF-133-PHBA was almost comparable to potassium dihydrogen phosphate (KDP).

Nebula-Relay Hypothesis: The Chirality of Biological Molecules in Molecular Clouds

The chiral puzzle of biological molecules is thought to be closely related to the origin of life and is still a mystery so far. Previously, we proposed a new model on the origin of life, Nebula-Relay hypothesis, which assumed that the life on Earth originated at the planetary system of the Sun’s predecessor star and then filled in the pre-solar nebula after its death. As primitive lives existed in the pre-solar nebula for a long time, did the chiral biomolecules form during this period? We explore such a possibility in this work and find that the ultra-low temperature environment of molecular clouds is beneficial to generating the chiral polymer chain of biological molecules.

A Highly Selective and Sensitive Chiral Derivatization Method for High- Performance Liquid Chromatographic Determination of the Stereoisomer Composition of Natural Products With Chiral Branched Alkyl Chains.

In the study of chiral biologically active compounds such as pheromones, the analysis of the stereoisomer composition is essential to gain more insight into their stereochemical diversity, which affects the pheromone communication channels and therefore the diversification of species. This mini-review summarizes the development of fluorescence derivatization reagents for high-performance liquid chromatographic (HPLC) determination of the absolute configuration and stereoisomer composition of natural products with a chiral branched alkyl chain. The diastereomeric separation of anteiso fatty acids bearing a branched methyl group up to the C-26 position was achieved by reversed-phase HPLC under very low column temperature conditions using (1S,2S)-2-(2,3-anthracenedicarboximido)cyclohexanol as a derivatization reagent, enabling fluorescent detection of these compounds at femtomole levels. This method was also applicable to chiral alcohols and amines with chiral branched methyl groups using similar reagents containing a carboxyl group. These reagents were successfully applied to determine the absolute configurations and stereoisomer composition of the chiral alkyl chain of natural compounds including some insect pheromones, miyakosyne A, and plakoside A. The combination of these reagents and two-dimensional HPLC constitutes a very powerful tool for the analysis of the stereoisomers of natural crude samples. Furthermore, the analysis of some natural bioactive substances using this method demonstrated that natural substances are not always optically pure, consisting instead of stereoisomer mixtures exhibiting stronger activity than optically pure enantiomers. These results cast doubts on the concept of biological homochirality and demonstrate that natural pheromones do not always show the highest activity among all stereoisomers.

Induction of chiral polymers from metal-organic framework for stereoselective recognition

So far, the fabrication of chiral metal-organic framework (CMOF) is difficult to predict and the chiral functionality mainly comes from the building blocks that is a part of the frameworks. The induction effect in the chiral nanochannels of the metal-organic framework (MOF) makes achiral polymers have chiral properties, which has not been well explored. Therefore, CMOFs with chiral nanochannels or chiral pores appear to have special functions. Herein, CMOFs (D-his-ZIF-8) with chiral micropores or chiral nanochannels are prepared through a simple 2-methyl imidazolate in-situ substitution by d-histidine. The unmodified polyaniline with chirality (c-PANI) was synthesized in chiral nanochannels and pores of CMOF, which brought about chiral induction from the chiral nanochannels and pores of CMOF to c-PANI chains. The circular dichroism shows that the c-PANI chains released from the chiral nanochannel still maintains the chiral properties even leaves the chiral nanochannel. It can be seen from the electrochemical results that c-PANI has excellent conductivity, and the conductivity of CMOF is very poor. Electrochemical recognition showed that both CMOF and c-PANI have certain chiral recognition effects for L-Trp and D-Trp, from which the optimal recognition effect was obtained from c-PANI chains. This shows that the excellent conductivity of c-PANI not only expands the electrochemical signal, but also the helical structure of the c-PANI chains accelerates the distinction of chiral molecules. This study provides a novel perspective to induce chiral polymer chains with better conductivity in the nanochannels of CMOF.

Chiral structures of 6,12-dibromochrysene on Au(111) and Cu(111) surfaces

Nanoscale low-dimensional chiral architectures are increasingly receiving scientific interest, because of their potential applications in many fields such as chiral recognition, separation and transformation. Using 6,12-dibromochrysene (DBCh), we successfully constructed and characterized the large-area two-dimensional chiral networks on Au(111) and one-dimensional metal-liganded chiral chains on Cu(111) respectively. The reasons and processes of chiral transformation of chiral networks on Au(111) were analyzed. We used scanning tunneling spectroscopy (STS) to analyze the electronic state information of this chiral structure. This work combines scanning tunneling microscopy (STM) with non-contact atomic force microscopy (nc-AFM) techniques to achieve ultra-high-resolution characterization of chiral structures on low-dimensional surfaces, which may be applied to the bond analysis of functional nanofilms. Density functional theory (DFT) was used to simulate the adsorption behavior of the molecular and energy analysis in order to verify the experimental results.

New quaterphenyls laterally substituted by methyl group and their influence on the self-assembling behaviour of ferroelectric bicomponent mixtures

ABSTRACT Design of new functional binary mixtures possessing the self-assembling behaviour remains a highlighted task in order to tune the resulting properties of soft materials according to specific application demands. Three new chiral compounds with a quaterphenyl core substituted by the methyl group in different positions and having different linkage groups between the chiral chain and the rigid core were synthesised and used as smart dopants to the basic compound possessing a highly tilted orthoconic ferroelectric smectic phase. The main aim is to establish the effect of the miscibility on the basic parameters of the resulting binary mixtures, specifically on the mesomorphic behaviour, values of the spontaneous polarisation, tilt angle, helical pitch length and dielectric behaviour. As the quaterphenyl dopants differ between each other in the linkage group placed between the chiral chain and the rigid core, these compounds influence physical parameters of the resultant mixtures in a different way. A small amount of quaterphenyl dopants does not considerably decrease the tilt angle, but in the case of the -O- atom presence, it results in a visible decrease of the spontaneous polarisation and increase of the helical pitch length. However, in the case of the -COO- group presence, it increases spontaneous polarisation and decreases the helical pitch (<200 nm).

A 1D chiral infinite chain organic metal halide hybrid with excellent SHG switching and moderate spontaneous polarization

A 1D chiral lead-free organic metal halide hybrid C8H20Cl5N2O2Sb (1) was successfully synthesized. Compound 1 reveals a phase transition and has a SHG “ON–OFF” switchable property, and also have ferroelectric.

Self-assembled lanthanide-based helixes: synthetic control of the helical handedness by chirality of the ligand.

The control of the self-assembly of lanthanide helical chain and their helical handedness have been investigated for the first time. Δ- and Λ-form lanthanide chain complexes were obtained by introducing thiazolidine ligands that were synthesised from L- and D-cysteine, respectively, and shared the same formula: [Ln2(L)3(H2O)5]∞·3H2O (Ln: Sm and Eu) (L: 2-(2-hydroxy-3,5-dinitrophenyl)thiazolidine-4-carboxylic acid). The crystallographic, circular dichroism, and luminescence properties of these novel lanthanide chain complexes were studied.

Co-assembled twisted superstructures formed by disc-bent core amphiphiles

Herein, two asymmetric chiral disc-bent core amphiphiles containing hexa‑peri-hexabenzocoronene (HBC), R-HBC-BC and S-HBC-BC, were synthesized to study the effects of chiral alkyl chain on the self-assembly of the disc-bent core amphiphiles. Interestingly, instead of forming chiral superstructure, pure R-HBC-BC or S-HBC-BC self-assembled into irregular crystalline texture resulting from the introduction of the chiral alkyl chains. Surprisingly, the formation of helical superstructure can be achieved by co-assembling the chiral disc-bent core amphiphile with achiral HBC-BC, with twisted superstructures having saddle-like curvature observed, which was different from the conventional spiral superstructures. The shape effect on the chirality transfer mechanism from molecule to hierarchical superstructure was thus proposed based on structural analysis of the twisted superstructures. Such interesting morphological transitions among different self-assembled helical morphologies in thin film may provide new insights for the self-assembly of chiral supramolecules.