Chiral Structure Research Articles

Giant circular dichroism in all-dielectric planar chiral Meta-GMR

In this paper, we introduce a simplified approach involving a single-layer dielectric meta-surface on top of planar waveguide that can achieve a high circular dichroism (CD) value of 0.95 under normal incidence. Within this intrinsic chiral structure, we harness the distinctive characteristics of guided mode resonance (GMR) [1] to induce out-of-plane electric/magnetic field vectors during lateral light propagation, thereby enhancing its optical chirality. Notably, the enhanced CD value becomes prominent at a half-wave plate thickness. This meta-GMR design enables giant CD in both of reflection and transmission, offering promising applications in biosensing, especially for chiral molecules.

Structural, Optical, and Mechanical Insights into Cellulose Nanocrystal Chiral Nematic Film Engineering by Two Assembly Techniques.

Iridescent cellulose nanocrystal (CNC) films with chiral nematic nanostructures exhibit great potential in optical devices, sensors, painting, and anticounterfeiting applications. CNCs can assemble into a chiral nematic liquid crystal structure by evaporation-assisted self-assembly (EISA) and vacuum-assisted self-assembly (VASA) techniques. However, there is a lack of comprehensive examinations of their structure-property correlations, which are essential for fabricating materials with unique properties. In this work, we gained insights into the optical, mechanical, and structural differences of CNC films engineered using the two techniques. In contrast to the random self-assembly at the liquid-air interface in EISA, the continuous external pressure in the VASA process forces CNCs to assemble at the filter-liquid interface. This results in fewer defects in the interfaces between tactoids and highly ordered cholesteric phases. Owing to the distinct CNC assembly behaviors, the films prepared by these two methods show great differences in the nanostructure, microstructure, and macroscopic morphology. Consequently, the highly ordered cholesteric structure gives VASA-CNC films a more uniform structural color and enhanced mechanical performance. These fundamental understandings of the relationship of structure-property nanoengineering through various assembly techniques are essential for designing and constructing high-performance chiral iridescent CNC materials.

Hyperspectral Detection of the Fluorescence Shift between Chirality-Sorted Empty and Water-Filled Single-Wall Carbon Nanotube Enantiomers.

Single-wall carbon nanotubes (SWCNTs) have extraordinary electronic and optical properties that depend strongly on their exact chiral structure and their interaction with their inner and outer environment. The fluorescence (PL) of semiconducting SWCNTs, for instance, will shift depending on the molecules with which the SWCNT's hollow core is filled. These interaction-induced shifts are challenging to resolve on the ensemble level in samples containing a mixture of different filling contents due to the relatively large inhomogeneous line width of the ensemble SWCNT PL compared to the size of these shifts. To circumvent this inhomogeneous broadening, single-tube spectroscopy and hyperspectral imaging are often applied, which until now required time-consuming statistical studies. Here, we present hyperspectral PL microscopy combined with automated SWCNT segmenting based on either principal component analysis or a convolutional neural network, capable of both spatially and spectrally resolving the PL along the length of many individual SWCNTs at the same time and automatically fitting peak positions and line widths of individual SWCNTs. The methodology is demonstrated by accurately determining the emission shifts and line widths of thousands of left- and right-handed empty and water-filled SWCNTs coated with a chiral surfactant, resulting in four statistical distributions which cannot be resolved in ensemble spectroscopy of unsorted samples. The results demonstrate a robust method to quickly probe ensemble properties with single-enantiomer spectral resolution. Moreover, it promises to be an absolute quantitative method to characterize the relative abundances of SWCNTs with different handedness or filling content in macroscopic samples, simply by counting individual species.

Slow Photonic Effect Inducing Improved H2 Generation in Photonic Films with Chiral Nematic Structure

AbstractIntegrating photonic crystals (PCs) into the design of a photocatalyst can significantly enhance its light‐harvesting capability. PCs can manipulate the propagation of light uniquely within a material and reduce its group velocity, thereby enhancing the absorption factor for photocatalysts. However, the slow photon effect in photoactive films with chiral nematic structures has not been reported yet, especially at the blue edge of the photonic bandgap. This work proposes a straightforward one‐pot method to fabricate various photonic films with chiral nematic, namely g‐C3N4/SiO2, TiO2/SiO2, and g‐C3N4/TiO2/SiO2. The sol‐gel biotemplating formulation using cellulose nanocrystals successfully leads to the elaboration of films exhibiting variable iridescent colors with photonic bandgap from UV to visible range. The tunable wavelength of the Bragg peak reflection offers the opportunity to access a region with a slow photonic effect, which directly impacts the light‐harvesting properties of the photoactive material. It is demonstrated that the H2 generation is significantly enhanced when the blue edge of the photonic bandgap position overlapped with the absorbance band of the photocatalyst. These results offer the opportunity to design photonic materials with chiral nematic structure and optimize the photocatalytic performance for energy application.

Responsive cellulose nanocrystal / acrylamide / poly (ethylene glycol) photonic films with chiral nematic structures by co-assembly and photopolymerization

Cellulose nanocrystals (CNCs), acrylamide (AAm) and poly (ethylene glycol) (PEG) can be co-assembled and photopolymerized into responsive, patterned photonic films with chiral nematic (N*) structures. Here, we report stimuli-responsive CNC/AAm/ PEG composite films (CFs) for use in humidity sensing. With the increase of AAm content, the CFs had an increased helical pitch and showed a red shift. With the adding of PEG, the CFs can quickly capture or release water molecules in air, which resulted in the changes of the helical pitch in N* structures and the structural color. After photopolymerization, the elastic modulus, hardness by nanomechanical testing and tensile strength of polymer films (PFs) were improved compared with CFs. The elastic modulus and hardness of PFs increased with the increase of AAm content. PFs and CFs showed different swelling properties in solutions with different EtOH / H2O ratio. Due to the swelling properties difference between CFs and PFs, partial photopolymerized photonic film showed photonic pattern. This research provides a new method to prepare photonic films with sensitive color response to humidity and photonic pattern, which has potential applications in the fields of sensing, anti-counterfeiting, and decoration.

Electronic and magnetic properties of Me-Graphene nanoribbons: A DFT investigation

In the search for semiconducting materials at the nanoscale, theoretical methods have been used to propose a series of nanocarbon sheets featuring a mixture of sp2 and sp3 hybridized carbon atoms, with Me-Graphene as one example. In addition to interesting physical properties shown by these 2D forms, nanoribbon variations of these structures can feature new properties. In this work, we show that the electronic properties of Me-Graphene nanoribbons can be modulated through structural details such as chirality, width, and edge details. Not only the metallic or semiconducting behavior can be switched by choosing selected geometries, but the direct or indirect character of the gap of the semiconducting cases can be triggered by selecting specific chiralities. In particular combinations of chirality and edge structure, we further point out that multiple spin-polarized states emerge, turning these systems into potential materials for spintronics.

The Phononic Properties and Optimization of 2D Multi-Ligament Honeycombs.

Honeycomb structures have attracted much attention for their excellent characteristics of reducing vibration and noise in recent years. In this study, through band analysis of different ligament structures, we aim to optimize the design of a steel structure that can isolate most of the noise in the 1500-5000 Hz range. The present study examines several different chiral structures. We calculate the band gaps of chiral structures under different geometric configurations and identify the variations in band gaps with geometric layouts. It is found that compared to other chiral structures, the triligaments chiral structure exhibits excellent band gap characteristics. The calculation results demonstrate that enhancing axial symmetry while filling central nodes can effectively enhance the structure's band gap properties. Frequency-response functions of different lattice structures are computed, and the results align with the calculations of band structures. This study then analyzes the influence of the number of periods on the magnitude of vibration attenuation, revealing that under the same number of periods, the wider the band gap of the structure, the greater the vibration attenuation. Both the triligaments chiral structure and the vertical triligaments structure possess ideal band gap widths, effectively suppressing wave propagation. Subsequently, harmonic response analyses and transient wave calculations further validate the accuracy of the band structure and frequency-response curve calculations. Our study results provide a new way to design a sound insulation structure that can isolate noise signals within the frequency range from 1500 to 5000 Hz in engineering.

Determination of Limonene Chirality in Oils Obtained from Different Types of Citrus Waste Peels in Türkiye

Limonene constitutes a significant amount in citrus oils. It has a chiral structure and has two different optically active isomers, R-limonene and S-limonene, which are symmetrical to each other. Determining the chiral configurations of limonene plays an important role in determining the beneficial use areas of essential oils. Citrus oils are used in a wide variety of industrial areas, depending on their limonene content. This paper presents the analytical method optimization, validation, and chirality studies of limonene in the citrus oils acquired from different citrus waste peels in Türkiye. An inlet temperature of 250 °C and an injection volume of 2 µL were decided as the optimal conditions for the most accurate measurement of both limonenes in the citrus oil. This method produced results for linearity, sensitivity (LODs and LOQs), repeatability, and reproducibility that were acceptable within the scope of the validation studies. The chirality of limonene was investigated in twenty-six citrus oils (fifteen orange oils, six lemon oils, four mandarin oils, and one grapefruit oil) in Türkiye. While the content of R-limonene in orange oil varied between 56.39% and 72.85%, the content of S-limonene changed from 2.53% to 5.71%. Whereas the constituent of R-limonene in lemon oils ranged from 54.73% to 73.99%, the content of S-limonene varied between 3.78-4.79%. In mandarin oils, the content of R-limonene was determined to be 58.02% and 65.05%, while the content of S-limonene was found as 3.05% and 4.87%. In single grapefruit oil, R-limonene content was 60.69% and S-limonene content was 3.12%.

Dynamics of growing carbon nanotube interfaces probed by machine learning-enabled molecular simulations

Carbon nanotubes (CNTs), hollow cylinders of carbon, hold great promise for advanced technologies, provided their structure remains uniform throughout their length. Their growth takes place at high temperatures across a tube-catalyst interface. Structural defects formed during growth alter CNT properties. These defects are believed to form and heal at the tube-catalyst interface but an understanding of these mechanisms at the atomic-level is lacking. Here we present DeepCNT-22, a machine learning force field (MLFF) to drive molecular dynamics simulations through which we unveil the mechanisms of CNT formation, from nucleation to growth including defect formation and healing. We find the tube-catalyst interface to be highly dynamic, with large fluctuations in the chiral structure of the CNT-edge. This does not support continuous spiral growth as a general mechanism, instead, at these growth conditions, the growing tube edge exhibits significant configurational entropy. We demonstrate that defects form stochastically at the tube-catalyst interface, but under low growth rates and high temperatures, these heal before becoming incorporated in the tube wall, allowing CNTs to grow defect-free to seemingly unlimited lengths. These insights, not readily available through experiments, demonstrate the remarkable power of MLFF-driven simulations and fill long-standing gaps in our understanding of CNT growth mechanisms.

Dispersive surface free energy of adsorbents modified by supramolecular structures of heterocyclic compounds

In the present work, the dispersive surface free energy was calculated by Dorris-Gray method for 30 samples of adsorbents modified with chiral supramolecular structures of uracil, 6-methyluracil, 5-hydroxy-6-methyluracil, 5-fluorouracil, thymine, melamine, cyanuric and barbirutic acids, and perylene-3,4,9,10-tetracarboxylic dianhydride. It was shown that the homologous series of n-alkanes is better suited for measuring dispersive surface free energy than the homologous series of alcohols. It was established that the classical Dorris-Gray method does not allow obtaining well interpretable data for the objects studied. This is due to a noticeable effect that inductive interactions of a polar surface as an inductor with nonpolar alkane molecules have on the calculated values. We suggested to modify the Dorris-Gray method, making it possible to obtain data on the dispersive component of the free energy of adsorption. It was shown that the changes in dispersive surface free energy as a result of the modification correlate well with data on the structure and properties of supramolecular ensembles of the modifiers used. The results obtained can be used to predict the enantioselectivity of chiral adsorbents.

Chiral twisted molecular carbons: Synthesis, properties, and applications

AbstractIn recent years, the precisely controlled synthesis of chiral twisted molecular carbons has emerged as a forefront topic in the research of carbon materials. Molecular carbons refer to carbon nanomaterials synthesized with precision at the atomic level. Through rational design, rigid and stable chiral twisted structures can be synthesized. The exploration in the field of chiral twisted molecular carbons is key to fully understanding the various twisted configurations of carbon materials and delving into the relationship between structure design and functionality. This review explores chiral twisted configurations of carbon nanomaterials such as nanographene, carbon nanobelts, carbon nanosheets, graphdiyne, etc. It emphasizes the role of photocyclization, Scholl reaction, and Diels–Alder reactions in achieving precise chiral control and discusses a range of innovative design strategies. These strategies have led to the development of various twisted structures, such as helical, propeller, and Möbius strip configurations. The introduction of chirality, combined with the inherent exceptional optical properties of nanocarbon materials, has facilitated the creation of materials with superior chiroptical performances. This advancement is driving applications in fields such as optoelectronics and chiral optics.

Chiral Nanoporous Structures Fabricated via Plasmon-Induced Dealloying of Au-Ag Alloy Thin Films

Chiral Nanoporous Structures Fabricated via Plasmon-Induced Dealloying of Au-Ag Alloy Thin Films

Expression of chiral molecular and supramolecular structure on enantioselective catalytic activity

Understanding the structure-function relationships encoded on chiral catalysts is important for investigating the fundamental principles of catalytic enantioselectivity. Herein, the synthesis and self-assembly of naphthalene substituted bis-l/d-histidine amphiphiles (bis-l/d-NapHis) in DMF/water solution mixture is reported. The resulting supramolecular assemblies featuring well-defined P/M nanoribbons (NRs). With combination of the (P/M)-NR and metal ion catalytic centers (Mn+ = Co2+, Cu2+, Fe3+), the (P)-NR-Mn+ as chiral supramolecular catalysts show catalytic preference to 3,4-dihydroxy-S-phenylalanine (S-DOPA) oxidation while the (M)-NR-Mn+ show enantioselective bias to R-DOPA oxidation. In contrast, their monomeric counterparts bis-l/d-NapHis-Mn+ display an inverse and dramatically lower catalytic selectivity in the R/S-DOPA oxidation. Among them, the Co2+-coordinated supramolecular nanostructures show the highest catalytic efficiency and enantioselectivity (select factor up to 2.70), while the Fe3+-coordinated monomeric ones show nearly racemic products. Analysis of the kinetic results suggests that the synergistic effect between metal ions and the chiral supramolecular NRs can significantly regulate the enantioselective catalytic activity, while the metal ion-mediated monomeric bis-l/d-NapHis were less active. The studies on association constants and activation energies reveal the difference in catalytic efficiency and enantioselectivity resulting from the different energy barriers and binding affinities existed between the chiral molecular/supramolecular structures and R/S-DOPA enantiomers. This work clarifies the correlation between chiral molecular/supramolecular structures and enantioselective catalytic activity, shedding new light on the rational design of chiral catalysts with outstanding enantioselectivity.

Regulating the Chiroptical Expression of Aggregated Solvophobic Core by Solvophilic Segments.

The investigation of chiral supramolecular stacking is of essential significance for the understanding of the origin of homochirality in nature. Unlike structurally well-defined amphiphilic liposomes, it remains unclear whether the solvophilic segments of the amphiphilic block copolymer play a decisive role in the construction of asymmetric superstructures. Herein, insights are presented into the stacking patterns and morphological regulation in azobenzene-containing block copolymer assemblies solely by modulating the solvophilic chain length. The solvophilic poly(methacrylic acid) (PMAA) segments of different molecular weights could cause multi-mode chirality inversions involving stacking transitions between intra-chain π-π stacking, inter-chain H- and J-aggregation. Furthermore, the length of the solvophilic PMAA also affects the morphology of the chiral supramolecular assemblies; rice grain-like micelles, worms, nanofibers, floccules, and lamellae can be prepared at different solvophilic-solvophobic balance. The comprehensive mechanism is collectively revealed by utilizing various measurement methods, such as including circular dichroism (CD), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). This study highlights the critical importance of fully dissolved solvophilic segments for the chiroptical regulation of the aggregated core, providing new insights into the arrangement of chiral supramolecular structures in polymer systems.

Nature-Inspired Helicoidal Nanocellulose-Based Multi-Compartment Assemblies with Tunable Chiroptical Properties.

Cellulose-based nanocomposites are highly appealing for the development of next-generation sustainable functional materials. Although many advances have been made in this direction, the true potential of fibrillar nanocomposites has yet to be realized because available fabrication approaches are inadequate for achieving precise structural control at the sub-micrometer scale. Here a spray-assisted alignment methodology of cellulose nanofibrils is combined with the layer-by-layer assembly into an additive manufacturing process in which the alignment direction of each cellulose layer is rationally selected to achieve thin films with a helicoidal arrangement of the nanofibrils. The helicoidal structure of the films is verified by measuring the circular dichroism (CD) of the samples. The sign and position of the structural CD peak show that the handedness and the pitch of the chiral structures can be easily tuned by deliberately selecting simple parameters, such as the number of consecutive cellulose layers sprayed in the same direction, and the angle of rotation between successive stacks of layers. To the authors' knowledge, this approach is unique as it offers the possibility to prepare complex nanocomposite architectures with various nanoscale-controlled sub-structures from different anisometric objects, which is enabling novel designs of composite films with damage-resistant and/or optical filtering functionalities.

Colossal anisotropic absorption of spin currents induced by chirality.

The chiral induced spin selectivity (CISS) effect, in which the structural chirality of a material determines the preference for the transmission of electrons with one spin orientation over that of the other, is emerging as a design principle for creating next-generation spintronic devices. CISS implies that the spin preference of chiral structures persists upon injection of pure spin currents and can act as a spin analyzer without the need for a ferromagnet. Here, we report an anomalous spin current absorption in chiral metal oxides that manifests a colossal anisotropic nonlocal Gilbert damping with a maximum-to-minimum ratio of up to 1000%. A twofold symmetry of the damping is shown to result from differential spin transmission and backscattering that arise from chirality-induced spin splitting along the chiral axis. These studies reveal the rich interplay of chirality and spin dynamics and identify how chiral materials can be implemented to direct the transport of spin current.

Configuration space of helical chiral self-assembly of micro/nano-fibers

As undertaking various key functions, helical chiral structures are widely presented in nature. Herein, we develop a general theoretical framework to guide the formation of helical chiral structures through self-assembly of micro/nano-fibers driven by adhesion. By analyzing the spiral contact geometric characteristics of multiple fibers and extending the JKR theory, an analytical model for adhesive contact between helical interfaces is proposed. Further, the complete configuration space of self-assembled fibers depending on the adhesion work, elastic modulus, aspect ratio, and initial helix angle is theoretically obtained. A diversity of helical configurations that far beyond existing experimental findings are predicted, which stems from the existence of multiple energy minimum points on the configuration-energy map. This work reveals the mechanism of adhesion-driven helical chiral structures, and provides theoretical foundation for guiding high-efficient fabrication of helical chiral structures through self-assembly method, which could promote the wide application of chiral structures in fields such as optics, catalysis and drug screening.

Multifunctional Amino Acid Derivative Coordination Compounds: Novel Contrast Agent and Luminescence Materials.

In this work a family of multidimensional (2-(1H-tetrazol-5-yl)ethyl) amino acid coordination compounds have been synthesized and thoroughly characterized. For this purpose, glycine, valine, phenylalanine and tyrosine have been selected as starting amino acids and Mn2+, Zn2+ and Cd2+ as metallic nodes. From one side, for Mn2+ based dimer magnetic resonance imaging studies have been conducted, prompted by the number and disposition of the coordinated water molecules and taking into consideration the promising future of manganese-based coordination compounds as bio-compatible substitutes to conventional Gd based contrast agents. From another side, d10 block metal-based complexes allowed exploring photoluminescence properties derived by in situ synthesized ligands. Finally, amino acid preserved structural chirality allowed us to examine chiroptical properties, particularly focusing on circularly polarized luminescence.

Self-Assembly for Creating Vertically-Aligned Graphene Micro Helices with Monolayer Graphene as Chiral Metamaterials.

Graphene's emergence enables creating chiral metamaterials in helical shapes for terahertz (THz) applications, overcoming material limitations. However, practical implementation remains theoretical due to fabrication challenges. This paper introduces a dual-component self-assembly technique that enables creating vertically-aligned continuous monolayer graphene helices at microscale with great flexibility and high controllability. This assembly process not only facilitates the creation of 3D microstructures, but also positions the 3D structures from a horizontal to a vertical orientation, achieving an aspect ratio (height/width) of ≈2700. As a result, an array of vertically-aligned graphene helices is formed, reaching up to 4mm in height, which is equivalent to 4 million times the height of monolayer graphene. The benefit of these 3D chiral structures made from graphene is their capability to infinitely extend in height, interacting with light in ways that are not possible with traditional 2D layering methods. Such an impressive height elevates a level of interaction with light that far surpasses what is achievable with traditional 2D layering methods, resulting in a notable enhancement of optical chirality properties. This approach is applicable to various 2D materials, promising advancements in innovative research and diverse applications across fields.

High-Throughput Morphological Chirality Quantification of Twisted and Wrinkled Gold Nanorods.

Chirality in gold nanostructures offers an exciting opportunity to tune their differential optical response to left- and right-handed circularly polarized light, as well as their interactions with biomolecules and living matter. However, tuning and understanding such interactions demands quantification of the structural features that are responsible for the chiral behavior. Electron tomography (ET) enables structural characterization at the single-particle level and has been used to quantify the helicity of complex chiral nanorods. However, the technique is time-consuming and consequently lacks statistical value. To address this issue, we introduce herein a high-throughput methodology that combines images acquired by secondary electron-based electron beam-induced current (SEEBIC) with quantitative image analysis. As a result, the geometric chirality of hundreds of nanoparticles can be quantified in less than 1 h. When combining the drastic gain in data collection efficiency of SEEBIC with a limited number of ET data sets, a better understanding of how the chiral structure of individual chiral nanoparticles translates into the ensemble chiroptical response can be reached.