Chiral Pattern Research Articles

Mapping Structure-Property Relationships of Organic Color Centers

Organic color centers are an emergent class of quantum emitters that hold vast potential for applications in bioimaging, chemical sensing, and quantum information processing. Here, we show that these synthetic color centers follow interesting structure-property relationships through comparative spectral studies of 14 purified single-walled carbon nanotube chiralities and 30 different functional groups that vary in electron-withdrawing capability and bonding configurations. The defect emission is tunable by as much as 400 meV in the near-infrared as a function of host structure and the chemical nature of the color centers. However, the emission energy is nearly free from chiral angle and family patterns of the nanotube host (although this strongly depends on the nanotube diameter), suggesting that a trapped exciton at the organic color centers to some degree electronically decouples from the one-dimensional semiconductor host. Our findings provide important insights for designing and controlling this new family of synthetic color centers.

Nambu–Jona-Lasinio model in a parallel electromagnetic field

We explore the features of the UA(1) and chiral symmetry breaking of the Nambu–Jona-Lasinio model without the Kobayashi–Maskawa–'t Hooft determinant term in the presence of a parallel electromagnetic field. We show that the electromagnetic chiral anomaly can induce both finite neutral pion condensate and isospin-singlet pseudo-scalar η condensate and thus modifies the chiral symmetry breaking pattern. In order to characterize the strength of the UA(1) symmetry breaking, we evaluate the susceptibility associated with the UA(1) charge. The result shows that the susceptibility contributed from the chiral anomaly is consistent with the behavior of the corresponding η condensate. The spectra of the mesonic excitations are also studied.

The two-dimensional elasticity of a chiral hinge lattice metamaterial

We present a lattice structure defined by patterns of slits that follow a rotational symmetry (chiral) configuration. The chiral pattern of the slits creates a series of hinges that produce deformation mechanisms for the lattice due to bending of the ribs, leading to a marginal negative Poisson's ratio. The engineering constants are modeled using theoretical and numerical Finite Element simulations. The results are benchmarked with experimental data obtained from uniaxial and off-axis tensile tests, with an overall excellent agreement. The chiral hinge lattice is almost one order of magnitude more compliant than other configurations with patterned slits and – in contrast to other chiral micropolar media – exhibits an in-plane shear modulus that closely obeys the relation between Young's modulus and Poisson's ratio in homogeneous isotropic linear elastic materials.

Chirality transfer from organic ligands to silver nanostructures via chiral polarisation of the electric field.

Water-soluble ligand protected optically active silver nanostructures were synthesised in a one-step reduction and capping process mediated by thiol-containing biomolecules. The synthesis was performed successfully with d- and l-cysteine and l-glutathione. The chiroptical properties of the obtained nanostructures were investigated by circular dichroism spectroscopy in the ultraviolet and visible wavelength range. They exhibit a g-value of up to 0.7%, which is about one order of magnitude larger compared to particles prepared by citrate reduction followed by a ligand exchange reaction. The structure and composition of the prepared materials were characterised by transmission electron microscopy, energy-dispersive X-ray and X-ray photoelectron spectroscopy. Although these structures do not have a chiral geometry, they show mirror image g-values when capped with d- and l-cysteine. This indicates that the underlying chirality transfer mechanism is based on an electric field polarisation process.

Study of humidity-responsive behavior in chiral nematic cellulose nanocrystal films for colorimetric response

This study focuses on the preparation and characterization of an iridescent chiral nematic cellulose nanocrystal (CNC) film in relation to their use as a humidity-responsive material. A free-standing film with Bragg reflection was successfully prepared. Thermogravimetric analysis demonstrated gradual thermal transitions with two major weight loss regions, while the crystallinity index obtained from X-ray diffraction method was about 78%, implying the presence of disordered regions. A scanning electron microscope confirmed the orientation of CNCs in a chiral nematic pattern with a pitch in the wavelengths of visible light. A dynamic vapor sorption study showed that water vapor can penetrate into the CNC film, leading to an increase of overall mass of up to 20% at 95% RH. The moisture sorption and desorption rates of the CNC film were faster at higher humidity (80% RH). The exposure of CNC film to elevated humidity was simulated to investigate the effect of humidity on their optical semaphore. As the humidity increased, the complementary color was red-shifted upward by about 60–100 nm, which was observable to the naked eye. This is potentially explained by the swelling of the nanocrystals and the expansion of the interspace between the quasi-nematic layers of the CNCs.

Spectroscopic studies of chiral perovskite nanocrystals

As an emerging type of optically active material, semiconductor nanocrystals (NCs) stabilized by chiral molecules have attracted much attention. Owing to the wide range of potential applications of chiral perovskite NCs, the development of these materials is of great importance, but there has been a lack of relevant studies. Here, we describe an investigation of the properties of chiral perovskite NCs obtained using post-synthetic ligand exchange (achiral ligand/chiral ligand). These are found to exhibit mirror-image circular dichroism spectra. It is the chirality of the ligand (enantiomeric 1,2-diaminocyclohexane, DACH) that is most likely responsible for the induction of chiroptical activity in these NCs. Furthermore, their chiroptical properties and the corresponding mechanisms are found to depend strongly on the amount of capping ligand. When excess DACH is used to cap the surface of the NCs, their chiroptical properties are induced mainly by aggregation of DACH on the surface in a chiral pattern. In contrast, when small amounts of DACH are used for the capping, it is mainly surface distortion (or defects) and electronic interaction mechanisms that contribute to the chiroptical behavior of the NCs. In both cases, the anisotropy factors of the NCs are of the order of 10−3, which is comparable to or larger than the values reported for other chiral semiconductor and metal NCs. This work opens the door toward further understanding of chiroptical perovskite NCs and their potential applications.

Structural Biology-Inspired Discovery of Novel KRAS-PDEδ Inhibitors.

Structural biology is a powerful tool for investigating the stereospecific interactions between a protein and its ligand. Herein, an unprecedented chiral binding pattern was observed for inhibitors of KRAS-PDEδ interactions. Virtual screening and X-ray crystallography studies revealed that two enantiomers of a racemic inhibitor could bind at different sites. Fragment-based drug design was used to identify highly potent PDEδ inhibitors that can be used as promising lead compounds for target validation and antitumor drug development.

Chiral Gold Nanoclusters: Atomic Level Origins of Chirality.

Chiral nanomaterials have received wide interest in many areas, but the exact origin of chirality at the atomic level remains elusive in many cases. With recent significant progress in atomically precise gold nanoclusters (e.g., thiolate-protected Aun (SR)m ), several origins of chirality have been unveiled based upon atomic structures determined by using single-crystal X-ray crystallography. The reported chiral Aun (SR)m structures explicitly reveal a predominant origin of chirality that arises from the Au-S chiral patterns at the metal-ligand interface, as opposed to the chiral arrangement of metal atoms in the inner core (i.e. kernel). In addition, chirality can also be introduced by a chiral ligand, manifested in the circular dichroism response from metal-based electronic transitions other than the ligand's own transition(s). Lastly, the chiral arrangement of carbon tails of the ligands has also been discovered in a very recent work on chiral Au133 (SR)52 and Au246 (SR)80 nanoclusters. Overall, the origins of chirality discovered in Aun (SR)m nanoclusters may provide models for the understanding of chirality origins in other types of nanomaterials and also constitute the basis for the development of various applications of chiral nanoparticles.

Chiral Orientation of Skeletal Muscle Cells Requires Rigid Substrate

Reconstitution of tissue morphology with inherent left–right (LR) asymmetry is essential for tissue/organ functions. For skeletal muscle, the largest tissue in mammalian organisms, successful myogenesis requires the regulation of the LR asymmetry to form the appropriate muscle alignment. However, the key factor for reproducing the LR asymmetry of skeletal tissues in a controllable, engineering context remains largely unknown. Recent reports indicate that cell chirality may underlie the LR development in tissue morphogenesis. Here, we report that a rigid substrate is required for the chirality of skeletal muscle cells. By using alternating micropatterned cell-adherent and cell-repellent stripes on a rigid substrate, we found that C2C12 skeletal muscle myoblasts exhibited a unidirectional tilted orientation with respect to the stripe boundary. Importantly, such chiral orientation was reduced when soft substrates were used instead. In addition, we demonstrated the key role of actin stress fibers in the formation of the chiral orientation. This study reveals that a rigid substrate is required for the chiral pattern of myoblasts, paving the way for reconstructing damaged muscle tissue with inherent LR asymmetry in the future.

Chiral Self-Assembly of Nonplanar 10,10'-Dibromo-9,9'-bianthryl Molecules on Ag(111).

We report on the low-temperature scanning tunneling microscopy (STM) measurements of the self-assembly of nonplanar 10,10'-dibromo-9,9'-bianthryl (DBBA) molecules on Ag(111) combined with density functional theory (DFT) calculations. DBBA molecules have two enantiomorphous adsorption configurations, from which more chiral structures can be formed. At a low coverage [0.4 monolayer (ML)], DBBA forms racemic netlike islands consisting of molecular chains along ⟨1 2 3̅⟩Ag. Moreover, the gliding between the molecular chains gives rise to chiral windmill-like patterns in the islands. At 0.8 ML, DBBA forms a racemic row phase and a homochiral hexamer phase. The molecular appearance difference between the two coexisted phases and the DFT calculated molecular adsorption configuration reveal a decrease in the molecular dihedral angle of DBBA, which implies an enhancement in the intermolecular interactions via CH···π and halogen bonds. The transition from a racemic packing mode to a homochiral one suggests that the suitability of steric configurations is dominant in the close-packing mode under enhanced intermolecular interactions.

Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice

The nature of Na ion distribution, diffusion path, and the spin structure of $P2$-type Na$_2$Ni$_2$TeO$_6$ with a Ni honeycomb network has been explored. The nuclear density distribution of Na ions reveals a 2D chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron diffraction technique. The Na diffusion pathway described by the calculated iso-surface of Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni$^{2+}$ spin ordering were examined in detail with the electron density mapping, neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single crystal sample through the $k$-scan in the momentum space corresponding to the AFM peak of ($\frac{1}{2}$, 0, 1).

Spiral Patterning of Au Nanoparticles on Au Nanorod Surface to Form Chiral AuNR@AuNP Helical Superstructures Templated by DNA Origami

Plasmonic motifs with precise surface recognition sites are crucial for assembling defined nanostructures with novel functionalities and properties. In this work, a unique and effective strategy is successfully developed to pattern DNA recognition sites in a helical arrangement around a gold nanorod (AuNR), and a new set of heterogeneous AuNR@AuNP plasmonic helices is fabricated by attaching complementary-DNA-modified gold nanoparticles (AuNPs) to the predesigned sites on the AuNR surface. AuNR is first assembled to one side of a bifacial rectangular DNA origami, where eight groups of capture strands are selectively patterned on the other side. The subsequently added link strands make the rectangular DNA origami roll up around the AuNR into a tubular shape, therefore giving birth to a chiral patterning of DNA recognition sites on the surface of AuNR. Following the hybridization with the AuNPs capped with the complementary strands to the capture strands on the DNA origami, left-handed and right-handed AuNR@AuNP helical superstructures are precisely formed by tuning the pattern of the recognition sites on the AuNR surface. Our strategy of nanoparticle surface patterning innovatively realizes hierarchical self-assembly of plasmonic superstructures with tunable chiroptical responses, and will certainly broaden the horizon of bottom-up construction of other functional nanoarchitectures with growing complexity.

Individual (f,tA)‐ and (f,tC)‐Fullerene‐Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π‐Electron System

AbstractStereoselective electrosynthesis of the first individual (f,tA)‐ and (f,tC)‐1,4‐fullerene derivatives with a non‐inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α‐amino‐acid carbon atom. An application of an auxiliary chiral nickel‐Schiff base moiety as derivatizing agent allowed separation of (f,tA)‐ and (f,tC)‐1,4‐fullerene derivatives using an achiral stationary phase, a separation which has never been done before.

Chiral Vortex Dynamics on Membranes is an Intrinsic Property of FtsZ Driven by GTP Hydrolysis

The primary protein of the bacterial Z ring guiding cell division, FtsZ, has recently been shown to engage in intriguing self-organization together with one of its natural membrane anchors, FtsA. When co-reconstituted on flat supported membranes, these proteins assemble into dynamic chiral vortices whose diameters resemble the cell circumference. These dynamics are due to treadmilling polar FtsZ filaments, supposedly destabilized by the co-polymerizing membrane adaptor FtsA, thus catalysing their turnover. Here we show that FtsA is in fact dispensable and that the phenomenon is an intrinsic property of FtsZ alone when supplemented with a membrane anchor. The emergence of these chiral dynamic patterns occurs at intermediate FtsZ surface densities, in agreement with theoretical predictions, and beyond a threshold GTP concentration. The interplay of membrane tethering, GTP binding, and hydrolysis promotes both, the assembly and the destabilization of FtsZ polymers, leading to the observed treadmilling dynamics. Notably, the vortex chirality is defined by the position of the membrane targeting sequence (mts) and can be inverted when attaching it to the opposite end of FtsZ. This reveals the vectorial character of the filament-supported membrane system consisting of three orthogonal directions, filament polarity, curvature, and membrane attachment.

Individual (f,t A)- and (f,t C)-Fullerene-Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π-Electron System.

Stereoselective electrosynthesis of the first individual (f,t A)- and (f,t C)-1,4-fullerene derivatives with a non-inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α-amino-acid carbon atom. An application of an auxiliary chiral nickel-Schiff base moiety as derivatizing agent allowed separation of (f,t A)- and (f,t C)-1,4-fullerene derivatives using an achiral stationary phase, a separation which has never been done before.

Strongly localized states at the band-inverting interface with periodic lattice dislocations

We have constructed an interface which separates two different phononic crystals (PCs) with respectively effective negative density and negative bulk modulus through band inversion. Besides the eigenstates in weak localization stemming from the sign flipping of imaginary acoustic impedances at the interface, we observed an unusual type of strongly localized states at the band-inverting contact after a periodic lattice dislocation is purposely introduced. From the layered multiple scattering theory, we have uncovered that the underlying physics for these unique interface states in the hetero-structured PC are due to nontrivial constructive interferences of high-ordered Mie-scattered acoustic waves from the mismatched cylinders. The intriguing features include interface resonances of enormous quality factors (∼3×104) and chiral field patterns along the dislocation line. We envision potential applications of the work in slow sound trapping, notch filtering, and nonlinearity strengthening, etc.

Electronic route to stabilize nanoscale spin textures in itinerant frustrated magnets

We unveil novel spin textures in an itinerant fermion model on a frustrated triangular lattice in the limit of low electronic density. Using hybrid Monte Carlo simulations on finite clusters we identify two type of nanoscale spin textures in the background of 120 degree order : (i) a planar ferromagnetic cluster, and (ii) and a non-coplanar cluster with spins oriented perpendicular to the 120 degree plane. Both these textures lead to localization of the electronic wavefunctions and are in-turn stabilized by the concomitant charge modulations. The non-coplanar spin texture is accompanied by an unusual scalar chirality pattern. A well defined electric charge and magnetic moment associated with these textures allow for their easy manipulation by external electric and magnetic fields - a desirable feature for data storage. We identify a localization-delocalization behavior for electronic wavefunctions which is unique to frustrated magnets, and propose a general framework for stabilizing similar spin textures in spin-charge coupled systems.

Instanton-dyon ensemble with two dynamical quarks: The chiral symmetry breaking

This is the second paper of the series aimed at understanding the ensemble of instanton-dyons, now with two flavors of light dynamical quarks. The partition function is appended by the fermionic factor, $(det T)^{N_f}$ and Dirac eigenvalue spectra at small values are derived from the numerical simulation of 64 and 128 dyons. Those spectra show clear chiral symmetry breaking pattern at high dyon density.

Chiral Biomaterials: From Molecular Design to Regenerative Medicine

Chirality is integral to biological complexity. Chiral biomolecules are central to all fundamental recognition, conformational and replication functions in biological systems. Chirality also exists in living cells and higher order biological structures. Less is known about the cellular interactions with chirality, although most living cells are imprinted with chiral‐based signatures. The harnessing of molecular, supramolecular, and structural chirality has been largely overlooked in biomaterials chemistry and the engineering of biological structures for regenerative medicine. Since chirality is a fundamental element of biological architecture its implementation in materials biomimicry is a necessity for mechanical, structural, and biological reasons. Take the latter, new investigations show the direct influence of biomimetic chiral patterning and chiral‐based architecture on stem cell activities and behavior. Biomimetic integration of chirality signatures into medical biomaterials provides a new capability to maximize biological function and compatibility especially for morphogenesis and regeneration.

Chiral selection of single helix formed by diblock copolymers confined in nanopores.

Chiral selection has attracted tremendous attention from the scientific communities, especially from biologists, due to the mysterious origin of homochirality in life. The self-assembly of achiral block copolymers confined in nanopores offers a simple but useful model of forming helical structures, where the helical structures possess random chirality selection, i.e. equal probability of left-handedness and right-handedness. Based on this model, we study the stimulus-response of chiral selection to external conditions by introducing a designed chiral pattern onto the inner surface of a nanopore, aiming to obtain a defect-free helix with controllable homochirality. A cell dynamics simulation based on the time-dependent Ginzburg-Landau theory is carried out to demonstrate the tuning effect of the patterned surface on the chiral selection. Our results illustrate that the chirality of the helix can be successfully controlled to be consistent with that of the tailored surface patterns. This work provides a successful example for the stimulus response of the chiral selection of self-assembled morphologies from achiral macromolecules to external conditions, and hence sheds light on the understanding of the mechanism of the stimulus response.