Chirality Inversion Research Articles

Hydrogen bond, protonation, and coordination-induced supramolecular chirality inversion in glutamide-based amphiphilic self-assembly

In this study, we have synthesized two types of Y-shaped chiral amphiphiles, namely L-BG and L-PG, with a benzene or pyridine ring at the terminal position, respectively. The optimized conformations of both amphiphiles indicate the presence of intramolecular interactions. In dimethylformamide (DMF) solution at the monomeric state, both amphiphiles exhibit positive cotton effects; however, in DMF/H2O mixed solution, the cotton effects are inverted. Molecular dynamics simulations reveal that both intermolecular and intramolecular hydrogen bonds facilitate the inversion of supramolecular chirality. Additionally, protonation and coordination of L-PG assembly results in chirality inversion and transformation of emission. This study emphasizes the significance of both inter- and intramolecular hydrogen bonds in the assembly process, providing insights into stimuli-responsive chiral supramolecular materials.

Pathway-directed recyclable chirality inversion of coordinated supramolecular polymers

It remains challenging to elucidate the fundamental mechanisms behind the dynamic chirality inversion of supramolecular assemblies with pathway complexity. Herein, metal coordination driven assembly systems based on pyridyl-conjugated cholesterol (PVPCC) and metal ions (Ag+ or Al3+) are established to demonstrate pathway-directed, recyclable chirality inversion and assembly polymorphism. In the Ag(I)/PVPCC system, a competitive pathway leads Ag-Complex to form either kinetically controlled supramolecular polymer (Ag-SP I) or thermodynamically favored Ag-SP II, accompanied by reversible chiroptical inversion. Conversely, the Al(III)/PVPCC system displays a solvent-assisted consecutive pathway: the Al-Complex initially forms ethanol-containing Al-SP II, and subsequently converts into ethanol-free Al-SP I with opposite chiroptical performance upon thermal treatment. Moreover, stable chirality inversion in the solid state enables potential dynamic circularly polarized luminescence encryption when Ag(I)/PVPCC is co-assembled with thioflavin T. These findings provide the guidance for the dynamic modulation of chirality functionality in supramolecular materials for applications in information processing, data encryption, and chiral spintronics.

Regulating Catalytic Oxidation Enantiomers Behavior by Imparting Chiral Microenvironment in Zr-Based Metal-Organic Frameworks.

Chiral inversions of enantiomers have significantly different biological activities, so it is important to develop simple and effective methods to efficiently identify optically pure compounds. Inspired by enzyme catalysis, the construction of chiral microenvironments resembling enzyme pockets in the pore space structure of metal-organic frameworks (MOFs) to achieve asymmetric enantioselective recognition and catalysis has become a new research hotspot. Here, a super-stable porphyrin-containing material PCN-224 is constructed by solvothermal method and a chiral microenvironment around the existing catalytic site of the material is created by post-synthesis modifications of the histidine (His) enantiomers. Experimental and theoretical calculations results show that the modulation of chiral ligands around Zr oxide clusters produces different spatial site resistances, which can greatly affect the adsorption and catalytic level of the enantiomeric molecules of tryptophan guests, resulting in a good enantioselective property of the material. It provides new ideas and possibilities for future chiral recognition and asymmetric catalysis.

Multiple Chirality Switching of a Dye‐Grafted Helical Polymer Film Driven by Acid & Base

AbstractA stimuli‐responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly‐designed acid & base‐sensitive dye‐grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base‐driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three‐state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Multiple Chirality Switching of a Dye-Grafted Helical Polymer Film Driven by Acid & Base.

A stimuli-responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly-designed acid & base-sensitive dye-grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base-driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three-state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Chirality Sensing of Amino Acid Esters by S-2-Methylbutanamido-Substituted m-Phthalic Diamide-Linked Zinc Bisporphyrinate.

To understand the role of an additional coordination site in the linker in chirality sensing, we designed and synthesized an S-2-methylbutanamido-substituted m-phthalic diamide-linked zinc bisporphyrinate, [Zn2(S-MAABis)] and investigated its ability to sense the chirality of amino acid esters. The 1H NMR spectra and the crystal structure showed that the amido oxygen adjacent to the chiral carbon was coordinated with zinc. NMR and UV-vis titration showed that the binding of [Zn2(S-MAABis)] to amino acid esters occurred via two equilibria, forming 1:1 and 1:2 host-guest complexes. The CD spectra suggested that [Zn2(S-MAABis)] can effectively recognize the absolute configuration of amino acid esters. The sign of the CD spectra remained unchanged during the titration, indicating that the corresponding 1:1 and 1:2 host-guest complexes had the same chirality. This is different from previously studied amino-substituted m-phthalic diamide-linked zinc bisporphyrinate [Zn2(AmBis)], which showed chirality inversion during titration. Theoretical calculations indicated that the additional coordination sites (amido or amino) in the 1:1 host-guest complexes played different roles, leading to differences in chirality. Our studies suggest that the introduction of a coordination site can influence the chirality transfer process, but the results of chirality transfers are dependent on the specific binding modes.

Chirality inversion of circularly polarized luminescence materials

Chirality inversion of circularly polarized luminescence materials

Photoisomerization-modulated supramolecular chirality inversion and energy-transfer efficiency in a cyanostilbene-glutamide-based self-assembly system

Manipulating chirality and energy transfer simultaneously in a single self-assembly system is important but remains challenging. In this study, we design a cyanostilbene-glutamide-based amphiphile L-GC bearing a long alkyl chain. It can form gels in methanol and exhibit circular dichroism (CD) signals. Upon ultraviolet-light irradiation, the CD signals are inverted and the morphology transforms from fibers to spheres. Chirality and energy transfer can be achieved when L-GC co-assembles with the energy acceptor DBTOC18, which is conjugated to a long alkyl chain. Moreover, the energy-transfer efficiency of the co-assembly can be modulated via photoirradiation-induced isomerization. Molecular dynamics simulation was conducted to elucidate the photomodulated assembly behavior. This study realizes the dual modulation of chirality and energy and presents some perspectives for information exchange in chiroptical materials.

Large-area preparation of rainbow cholesteric liquid crystal polymer network films using a photoisomerizable chiral dopant

ABSTRACT Since the cholesteric liquid crystal polymer network (CLCN) films with a structural colour have been applied for decoration, those with colourful patterns become more attractive. They have been successfully prepared using photochromic cholesteric liquid crystals with the addition of photoisomerizable chiral dopants. Herein, two isosorbide derivatives with benzoate and cinnamate groups were synthesised using isomannide through chirality inversion and without using protecting groups. CLCN films were prepared using these two isomers as the chiral dopants. The structural colour of the films can be tuned by the photoisomerisation of the chiral dopants. Colourful patterns were also prepared using photomasks, which were suitably applied for decoration and anti-counterfeiting. Although the isomer with a higher melting point tended to induce the crystallisation of the CLC mixtures, the CLC mixtures prepared using the isomer with a lower melting point were stable at room temperature. Rainbow CLCN films were prepared using photomasks on a coating line.

Host–guest complexation‐induced chirality switching of pillararenes by perylene diimide‐based hexagonal metallacages

AbstractChirality in confined nanospaces has brought some new insights into chirality transfer, amplification, and chiroptical properties. However, chirality switching, which is a common phenomenon in biological systems, has never been realized in confined environments. Herein, we report a type of hexagonal metallacages that shows good host–guest interactions with ethoxy pillar[5]arene and pillar[6]arene, as confirmed by single‐crystal X‐ray analysis. Importantly, when a chiral pillar[5]arene‐based molecular universal joint (MUJ) is used as the guest, the host–guest complexation would drive the alkyl ring of the MUJ flip from outside to inside the cavity of its pillar[5]arene unit, which enables the configuration change along with the chirality inversion of the MUJ. Moreover, the host–guest complexation facilitates the chirality transfer from guests to hosts, giving circularly polarized luminescence to the system. This study provides a unique metallacage‐pillararene recognition motif for the chirality switching of planar chiral pillararenes, which will promote the construction of host–guest systems with tunable chirality for advanced applications.

Multiple‐State Control over Supramolecular Chirality through Dynamic Chemistry Mediated Molecular Engineering

AbstractDynamic chemistry utilizing both covalent and noncovalent bonds provides valid protocols in manipulating properties of self‐assemblies and functions. Here we employ dynamic chemistry to realize multiple‐route control over supramolecular chirality up to five states. N‐protected fluorinated phenylalanine in the carboxylate state self‐assembled into achiral nanoparticles ascribed to the amphiphilicity. Protonation promoted one‐dimensional growth into helices with shrunk hydrophilicity, which in the presence of disulfide pyridine undergo chirality inversion promoted by the hydrogen bonding‐directed coassembly. Further interacting with the water‐soluble reductant cleavages the disulfide bond to initiate the rearrangement of coassemblies with a chirality inversion as well. Finally, by tuning the pH environments, aromatic nucleophilic substitution reaction between reduced products and perfluorinated phenylalanine occurs, giving distinct chiral nanoarchitectures with emerged luminescence and circularly polarized luminescence. We thus realized a particular five‐state control by combining dynamic chemistry at one chiral compound, which greatly enriches the toolbox in fabricating responsive chiroptical materials.

Multiple-State Control over Supramolecular Chirality through Dynamic Chemistry Mediated Molecular Engineering.

Dynamic chemistry utilizing both covalent and noncovalent bonds provides valid protocols in manipulating properties of self-assemblies and functions. Here we employ dynamic chemistry to realize multiple-route control over supramolecular chirality up to five states. N-protected fluorinated phenylalanine in the carboxylate state self-assembled into achiral nanoparticles ascribed to the amphiphilicity. Protonation promoted one-dimensional growth into helices with shrunk hydrophilicity, which in the presence of disulfide pyridine undergo chirality inversion promoted by the hydrogen bonding-directed coassembly. Further interacting with the water-soluble reductant cleavages the disulfide bond to initiate the rearrangement of coassemblies with a chirality inversion as well. Finally, by tuning the pH environments, aromatic nucleophilic substitution reaction between reduced products and perfluorinated phenylalanine occurs, giving distinct chiral nanoarchitectures with emerged luminescence and circularly polarized luminescence. We thus realized a particular five-state control by combining dynamic chemistry at one chiral compound, which greatly enriches the toolbox in fabricating responsive chiroptical materials.

Circularly Polarized Luminescence of Tetradentate-Ligand-Based Chiral MOFs: Structural Evidence of Chirality Inversion

Circularly Polarized Luminescence of Tetradentate-Ligand-Based Chiral MOFs: Structural Evidence of Chirality Inversion

Temperature-Induced Sign Inversion of Circularly Polarized Luminescence of Binaphthyl-Bridged Tetrathiapyrenophanes.

D2-symmetric (R)-binaphthyl-bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature-induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left-handed twist excimer at low temperatures, while they form a thermodynamically favored right-handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers.

Engineering tertiary chirality in helical biopolymers

Tertiary chirality describes the handedness of supramolecular assemblies and relies not only on the primary and secondary structures of the building blocks but also on topological driving forces that have been sparsely characterized. Helical biopolymers, especially DNA, have been extensively investigated as they possess intrinsic chirality that determines the optical, mechanical, and physical properties of the ensuing material. Here, we employ the DNA tensegrity triangle as a model system to locate the tipping points in chirality inversion at the tertiary level by X-ray diffraction. We engineer tensegrity triangle crystals with incremental rotational steps between immobile junctions from 3 to 28 base pairs (bp). We construct a mathematical model that accurately predicts and explains the molecular configurations in both this work and previous studies. Our design framework is extendable to other supramolecular assemblies of helical biopolymers and can be used in the design of chiral nanomaterials, optically active molecules, and mesoporous frameworks, all of which are of interest to physical, biological, and chemical nanoscience.

Photoisomerization and thermal reconstruction induced supramolecular chirality inversion in nanofiber determined by minority isomer

Here, amphiphile GCH based on glutamide-cyanostilbene is designed and synthesized, it is found that it can assembly in acetonitrile, and shows circular dichroism signals. After Z-E isomerizaition by UV irradiation, the CD signal of the assembly can be inverted. Unexpectedly, after another heating and cooling process, the circular dichroism signals can be totally inverted even though the E-isomers are in minority. Finally, the molecular dynamics (MD) simulations deeply elucidate the supramolecuar chirality inversion mechanism. This work brings some new insights into the control of chirality inversion, which may provide a perspective for the smart chiroptical materials construction.

Reversible chirality inversion of an AuAgx-cysteine coordination polymer by pH change

Responsive chiral systems have attracted considerable attention, given their potential for diverse applications in biology, optoelectronics, photonics, and related fields. Here we show the reversible chirality inversion of an AuAgx-cysteine (AuAgx-cys) coordination polymer (CP) by pH changes. The polymer can be obtained by mixing HAuCl4 and AgNO3 with L-cysteine (or D-cysteine) in appropriate proportions in H2O (or other surfactant solutions). Circular dichroism (CD) spectrum is used to record the strong optical activity of the AuAg0.06-L-cys enantiomer (denoted as L0.06), which can be switched to that of the corresponding D0.06 enantiomer by alkalization (final dispersion pH > 13) and can be switched back after neutralization (final dispersion pH <8). Multiple structural changes at different pH values (≈9.6, ≈13) are observed through UV-Vis and CD spectral measurements, as well as other controlled experiments. Exploration of the CP synthesis kinetics suggests that the covalent bond formation is rapid and then the conformation of the CP materials would continuously evolve. The reaction stoichiometry investigation shows that the formation of CP materials with chirality inversion behavior requires the balancing between different coordination and polymerization processes. This study provides insights into the potential of inorganic stereochemistry in developing promising functional materials.

Uncovering supramolecular chirality codes for the design of tunable biomaterials

In neurodegenerative diseases, polymorphism and supramolecular assembly of β-sheet amyloids are implicated in many different etiologies and may adopt either a left- or right-handed supramolecular chirality. Yet, the underlying principles of how sequence regulates supramolecular chirality remains unknown. Here, we characterize the sequence specificity of the central core of amyloid-β 42 and design derivatives which enable chirality inversion at biologically relevant temperatures. We further find that C-terminal modifications can tune the energy barrier of a left-to-right chiral inversion. Leveraging this design principle, we demonstrate how temperature-triggered chiral inversion of peptides hosting therapeutic payloads modulates the dosed release of an anticancer drug. These results suggest a generalizable approach for fine-tuning supramolecular chirality that can be applied in developing treatments to regulate amyloid morphology in neurodegeneration as well as in other disease states.

Helicity Control of Circularly Polarized Luminescence from Aromatic Conjugated Copolymers and Their Mixture Using Reversibly Photoinvertible Chiral Liquid Crystals.

We synthesized cyclic chiral compounds [(R)/(S)-D2s] by linking a photoresponsive bisbenzothienylethene (BTE) moiety with an axially chiral binaphthyl moiety. Chiral nematic liquid crystals (N*-LCs) were prepared by adding chiral compounds as dopants to host N-LCs. These N*-LCs exhibited reversible chirality inversion upon photoisomerization between the open and closed forms of the BTE moiety. Here, the mechanism underlying chirality inversion in photoresponsive N*-LCs was investigated by comparing the helical twisting powers (HTPs) of (R)-D2s with those of analogous compounds. It was found that the helical inversion of N*-LCs containing (R)-D2s is governed by a delicate balance between two types of opposite helicity, i.e., the right-handed helicity of the inherently chiral binaphthyl moiety and the left-handed helicity of the BTE moiety bearing intramolecularly induced chirality. Namely, (R)-D2s induced chirality of the BTE moiety, which is attributed to intramolecular chirality transfer from the axially chiral binaphthyl moiety to the BTE moiety. Thus, (R)-D2s are chiral compounds with double chirality consisting of an intrinsically chiral moiety and an intramolecularly induced chiral moiety. Photocontrol of the helical senses and reversible photoinversion of the N*-LCs are achieved by utilizing UV and visible light irradiation and the steric effects of the substituents at the binaphthyl rings in (R)-D2s. In addition, photocontrol of the induced circularly polarized luminescence (CPL) was achieved using the photoinvertible N*-LC. The achiral aromatic conjugated copolymers that exhibited red, green, and blue fluorescence were dissolved and mixed in the present N*-LC, and they exhibited left- and right-handed white CPL with large dissymmetry factors (|glum|) ranging from 0.2 to 1.0. The CPLs were reversibly photoswitched due to photoisomerization between the open and PSS forms of the chiral compounds through UV and visible light irradiation.

Achiral substituent- and stoichiometry-controlled inversion of supramolecular chirality and circularly polarized luminescence in ternary co-assemblies.

Handedness inversion of supramolecular chirality and circularly polarized luminescence (CPL) in assembled systems containing more than two components with higher complexity is of prominent importance to simulate biological multicomponent species and design advanced chiral materials, but it remains a considerable challenge. Herein, we have successfully developed ternary co-assembly systems based on aromatic amino acids, vinylnaphthalene derivatives and 1,2,4,5-tetracyanobenzene with effective chirality transfer. Notably, the handedness of supramolecular chirality and CPL can be readily inverted by changing the residues of amino acids, the substituents of achiral vinylnaphthalene derivatives, or by adjusting the stoichiometric ratio. The hydrogen bonds, charge transfer interactions, and steric hindrance are proved to be the crucial factors for the chirality inversion. This flexible control over chirality not only offers insights into developing multicomponent chiral materials with desirable handedness from simple molecular building blocks, but also is of practical value for use in chiroptics, chiral sensing, and photoelectric devices.