Chiral colloids: homogeneous suspension of individualized SiO2 helical and twisted nanoribbons

Porphyrin-Based Hybrid Nanohelices: Cooperative Effect between Molecular and Supramolecular Chirality on Amplified Optical Activity

The development of chiral receptors for discriminating the configuration of the analyte of interest is increasingly urgent in view of monitoring pollution in water and waste liquids. Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and makes the dye@nanohelix system disperse in a suspension of water without aggregation. We noted strong induction and amplification of chiroptical activity in both achiral and chiral (proline-based or hemicucurbituril-based) porphyrin derivatives with and without zinc ions once confined and organized in nanometer silica helices. The results clearly demonstrated that the organization-induced chirality amplification of porphyrins dominates the molecular chirality, and the amplification is more efficient for more flexible porphyrins (especially free-base and achiral).

Highly Stable Low-Strain Flexible Sensors Based on Gold Nanoparticles/Silica Nanohelices

Flexible strain sensors based on nanoparticle (NP) arrays show great potential for future applications such as electronic skin, flexible touchscreens, healthcare sensors, and robotics. However, even though these sensors can exhibit high sensitivity, they are usually not very stable under mechanical cycling and often exhibit large hysteresis, making them unsuitable for practical applications. In this work, strain sensors based on silica nanohelix (NH) arrays grafted with gold nanoparticles (AuNPs) can overcome these critical aspects. These 10 nm AuNPs are functionalized with mercaptopropionic acid (MPA) and different ratios of thiol-polyethylene glycol-carboxylic acid (HS-PEG7-COOH) to optimize the colloidal stability of the resulting NH@AuNPs nanocomposite suspensions, control their aggregation state, and tune the thickness of the insulating layer. They are then grafted covalently onto the surface of the NHs by chemical coupling. These nanomaterials exhibit a well-defined arrangement of AuNPs, which follows the helicity of the silica template. The modified NHs are then aligned by dielectrophoresis (DEP) between interdigitated electrodes on a flexible substrate. The flexibility, stability, and especially sensitivity of these sensors are then characterized by electromechanical measurements and scanning electron microscopy observations. These strain sensors based on NH@AuNPs nanocomposites are much more stable than those containing only nanoparticles and exhibit significantly reduced hysteresis and high sensitivity at very slight strains. They can retain their sensitivity even after 2 million consecutive cycles with virtually unchanged responsiveness. These improved performances come from their mechanical stability and the use of nanohelices as stable mechanical templates.

Effect of Solvent on Convectively Driven Silica Particle Assembly: Decoupling Surface Tension, Viscosity, and Evaporation Rate

The process of convectively self-assembling particles in films suffers from low reproducibility due to its high dependency on particle concentration, as well as a variety of interactions and physical parameters. Inhomogeneities in flow rates and instabilities at the air-liquid interface are mostly responsible for reproducibility issues. These problems are aggravated by adding multiple components to the dispersion, such as binary solvent mixtures or surfactant/polymer additives, both common approaches to control stick-slip behavior. When an additive is used, not only does it change the surface tension, but also the viscosity and the evaporation rate. Worse yet, gradients in these three properties can form, which then lead to Marangoni currents. Here, we use a series of alcohols to study the role of viscosity independently of other solvent properties, to show its impact on stick-slip behavior and interband distances. We show that mixtures of glycerol and alcohol or poly(acrylic acid) and alcohol lead to more complex patterning. Marangoni currents are not always observed in co-solvent systems, being dependent on the rate of solvent evaporation. To produce homogeneous particle assemblies and control stick-slip behavior, gradients must be avoided, and the surface tension and viscosity need both be carefully controlled.

Chiroptical Activity in All-Inorganic Intrinsically Chiral Perovskite-like Nanocrystals Synthesized via Enantioselective Strategy

Enantiomeric control of intrinsically chiral inorganic nanocrystals (NCs), despite being reported in few systems over the past years, still remains a challenging task. Here, we succeeded in the enantioselective synthesis of intrinsically chiral perovskite-like CsCuCl₃ NCs in the presence of chiral amino acids using an antisolvent crystallization method at room temperature. The d-/l-ligand-induced enantiomeric NCs showed the relevant characteristic chiroptical responses. Interestingly, under the addition of each d- or l-form of the ligand, the chiroptical activity of the NCs could be tailored through facilely tuning the Cs/Cu feed ratios and amino acid types. The polarity of such amino acids and their coordination configurations with the NC structures contributed to the distinct behaviors. The ability to manipulate the ligand-induced enantioselective strategy would open pathways for the controllable synthesis of intrinsically chiral inorganics and enable a better understanding of the origins of precursor-ligand-associated chiral discrimination and crystallization phenomena.

Disentangling Excimer Emission from Chiral Induction in Nanoscale Helical Silica Scaffolds Bearing Achiral Chromophores

The synthesis and characterization of diketopyrrolopyrroles and perylenemonoimidodiesters linked to a substituted benzoic acid in the ortho, meta, and para positions, are reported. Grafting of these dyes on the surface of chiral silica nanohelices is used to probe how the morphology of the platform at the mesoscopic level affects the induction of chiroptical properties onto achiral molecular chromophores. The grafted structures are weakly (diketopyrrolopyrroles) or strongly (perylenemonoimidodiesters) emissive, exhibiting both locally-excited state emission and a broad, structureless emission assigned to excimers. The dissymmetry factors obtained using circular dichroism highlight optimized supramolecular organization between the chromophores for enhancing the chiroptical properties of the system. In the ortho- derivatives, poor organization due to steric hindrance is reflected in a low density of chromophores on walls of the silica-nanostructures (<0.1 vs. >0.3 and up to 0.6 molecules/nm² for the ortho and meta or para derivatives, respectively) and lower g_abs values than in the other derivatives (g_abs <2×10^-5 vs 6×10^-5 for the ortho and para derivatives, respectively). The para derivatives presented a better organization and increased values of g_abs . All grafted chromophores evidence varying degrees of excimer emission which was not found to directly correlate to their grafting density.

Cooperative interaction between organic and inorganic moieties in hybrid silica nanohelices for enantioselective interaction

Hybrid nanometric helical structures formed by the molecular assemblies of dicationic gemini surfactants with tartrate counterions covered with helical silica walls interact differently with matching or mismatching enantiomers of the tartrate. The difference of the interaction is based on the cooperativity between the chiral crystalline gemini surfactant molecular organization/conformation and the rigid chiral nanospace formed by the helical silica wall.

Self-assembled inorganic chiral superstructures

Controlled assembly of inorganic nanoparticles with different compositions, sizes and shapes into higher-order structures of collective functionalities is a central pursued objective in chemistry, physics, materials science and nanotechnology. The emerging chiral superstructures, which break spatial symmetries at the nanoscale, have attracted particular attention, owing to their unique chiroptical properties and potential applications in optics, catalysis, biology and so on. Various bottom-up strategies have been developed to build inorganic chiral superstructures based on the intrinsic configurational preference of the building blocks, external fields or chiral templates. Self-assembled inorganic chiral superstructures have demonstrated significant superior optical activity from the strong electric/magnetic coupling between the building blocks, as compared with the organic counterparts. In this Review, we discuss recent progress in preparing self-assembled inorganic chiral superstructures, with an emphasis on the driving forces that enable symmetry breaking during the assembly process. The chiroptical properties and applications are highlighted and a forward-looking trajectory of where research efforts should be focused is discussed.

Chiral optical scattering from helical and twisted silica nanoribbons

Helical and twisted silica nanoribbons, deposited in an in-plane direction and with a random orientation, on a quartz substrate showed chiral optical scattering, and the helical nanoribbons had a g-factor of the order of 10^-2 below 250 nm. Their signs depend on the handedness of the nanohelices. The effect of the morphology and the orientation of the helices on the chiral optical scattering were investigated with simulations via the boundary element method.

Lanthanide ion-doped silica nanohelix: a helical inorganic network acts as a chiral source for metal ions

We demonstrate that lanthanide ions doped in nanometrical silica helices with a chirally arranged siloxane network without any organic mediates show induced chiroptical properties such as circular dichroism and circularly polarized luminescence.

Tuning the Chiroptical Properties of Elongated Nano-objects via Hierarchical Organization

Chiral materials appear as excellent candidates to control and manipulate the polarization of light in optical devices. In nanophotonics, the self-assembly of colloidal plasmonic nanoparticles gives rise to strong resonances in the visible range, and when such organizations are chiral, a strong chiroplasmonic effect can be observed. In the present work, we describe the optical properties of chiral artificial nanophotonic materials, Goldhelices, which are hierarchically organized by grazing incidence spraying. These Goldhelices are made by plasmonic nanoparticles (gold) grafted onto helical templates made from silica nanohelices. A comparison of oriented versus non-oriented surfaces has been performed by Mueller matrix polarimetry, showing the importance of the organization of the Goldhelices regarding their interaction with light. Moreover, mono- versus multilayer photonic films are created, and the measured optical properties are discussed and compared to simulations.

Near perfect head-to-head selectivity on the supramolecular photocyclodimerisation of 2-anthracenecarboxylate with self-organised gemini surfactant bilayers

Near perfect head-to-head selectivity upon supramolecular [4+4] photocyclodimerisation of 2-anthracenecarboxylate were achieved through silicificated self-organised gemini surfactant bilayers in water at room temperature.

Chirality induction on non-chiral dye-linked polysilsesquioxane in nanohelical structures

Chirally arranged organic dye-linked polysilsesquioxane was prepared, through a sol–gel transcription using its non-chiral precursor with a chiral supramolecular template, and its chiroptical properties were investigated.

Chiroptical phenolic resins grown on chiral silica-bonded amine residues

Chiral silica bonded covalently with amine residues as an asymmetric medium to asymmetrically mediate the polymerization of resorcinol and formaldehyde to give chiroptical phenolic resins.

Mitigating Human IAPP Amyloidogenesis In Vivo with Chiral Silica Nanoribbons

Amyloid fibrils generally display chirality, a feature which has rarely been exploited in the development of therapeutics against amyloid diseases. This study reports, for the first time, the use of mesoscopic chiral silica nanoribbons against the in vivo amyloidogenesis of human islet amyloid polypeptide (IAPP), the peptide whose aggregation is implicated in type 2 diabetes. The thioflavin T assay and transmission electron microscopy show accelerated IAPP fibrillization through elimination of the nucleation phase and shortening of the elongation phase by the nanostructures. Coarse-grained simulations offer complementary molecular insights into the acceleration of amyloid aggregation through their nonspecific binding and directional seeding with the nanostructures. This accelerated IAPP fibrillization translates to reduced toxicity, especially for the right-handed silica nanoribbons, as revealed by cell viability, helium ion microscopy, as well as zebrafish embryo survival, developmental, and behavioral assays. This study has implicated the potential of employing chiral nanotechnologies against the mesoscopic enantioselectivity of amyloid proteins and their associated diseases.

Protein Amyloid Fibrils as Template for the Synthesis of Silica Nanofibers, and Their Use to Prepare Superhydrophobic, Lotus-Like Surfaces

In this work, amyloid fibrils are used as a template for the preparation of long silica fibers, with a variety of aspect ratios and surface roughness. Starting with β-lactoglobulin fibrils with typical diameters of about 20 nm and a length of several micrometers, two different strategies are followed to grow silica: either in water at acidic pH values, or in ethanol-water mixtures under Stöber conditions and an excellent control of both the thickness and the roughness of the silica layer has been achieved. Silica nanofibers with a thickness ranging from a few nanometers to hundreds of nanometers are prepared. As an application, the rough silica nanotubes are used to create superhydrophobic surfaces by mimicking the structure of the lotus leaf. The papillary structure of the lotus leaf is replicated by depositing 10 μm colloidal particles in either a single colloidal crystal, or in a binary colloidal crystal made with smaller sub-micrometer particles. Then, silica nanofibers are deposited on the binary colloidal crystal surfaces through a layer-by-layer deposition procedure to replicate the nanoscale roughness provided by wax nanotubes. Upon hydrophobization of the silica nanotubes, the final surfaces are highly superhydrophobic, with a water contact angle of 165.5°.

Induced circular dichroism of monoatomic anions: silica-assisted the transfer of chiral environment from molecular assembled nanohelices to halide ions

Induced CD of monoatomic anions was detected using silica-coated molecular assembled nanohelices and multi-step chirality induction was achieved through an in situ chemical reaction via chiralized monoatomic anions.

Silica Mineralization of DNA-Inspired 1D and 2D Supramolecular Polymers

The preparation of hybrid materials from supramolecular polymers through the sol‐gel process is presented. Supramolecular polymers are assembled from phosphodiester‐linked pyrene oligomers and act as water‐soluble one‐ or two‐dimensional templates for silicification. The fibrillary and planar morphologies of the assemblies, as well as the excitonic interactions between the chromophores, remain unaffected by the silicification process.

Self-directing chiral information in solid-solid transformation: unusual chiral-transfer without racemization from amorphous silica to crystalline silicon

Constructing novel chiral inorganic nanomaterials is an emerging branch in chirality research. In this work, by employing a solid magnesiothermic reaction at 500-600 °C, we reduced chiral SiO₂ nanofibers with average diameter ∼10 nm into chiral Si nanoplates with a size of about several hundred nm. The chirality of the as-prepared Si was judged by the pair of signals with a mirror relationship between 400-500 nm that appeared on the solid-state diffuse reflectance circular dichroism (DRCD) spectra for the l- and d-form Si. Furthermore, the chirality was also confirmed by induced vibrational circular dichroism (VCD) signals corresponding to the absorption bands in the infrared range of achiral organics (polyvinylpyrrolidone K90 and trimethoxyphenylsilane) absorbed onto chiral Si. The as-used SiO₂ nanofibers possessed an ultra high-temperature (up to 900 °C) resistant chirality, which would be due to the asymmetric arrangement of Si and O atoms in small chiral domains (<10 nm) on the Si-O-Si network of SiO₂. During the removal of oxygen atoms from Si-O-Si by Mg atoms, the arrangement of newly formed Si-Si bonds as well as the growth of Si crystals were still templated without racemization from the chiral information in SiO₂. Consequently, the subnano/nano-scale (<10 nm) chiral information was in situ transferred via the so-called self-transfer mechanism, even though there was no retention of the outward shapes of the length-scale nanofiber SiO₂ reactants in the Si products. This work offers a feasible chemical method to prepare chiral Si using abundant SiO₂ raw materials.

GoldHelix: Gold Nanoparticles Forming 3D Helical Superstructures with Controlled Morphology and Strong Chiroptical Property

Plasmonic nanoparticles, particularly gold nanoparticles (GNPs) hold a great potential as structural and functional building blocks for three-dimensional (3D) nanoarchitectures with specific optical applications. However, a rational control of their assembly into nanoscale superstructures with defined positioning and overall arrangement still remains challenging. Herein, we propose a solution to this challenge by using as building blocks: (1) nanometric silica helices with tunable handedness and sizes as a matrix and (2) GNPs with diameter varying from 4 to 10 nm to prepare a collection of helical GNPs superstructures (called Goldhelices hereafter). These nanomaterials exhibit well-defined arrangement of GNPs following the helicity of the silica template. Strong chiroptical activity is evidenced by circular dichroism (CD) spectroscopy at the wavelength of the surface plasmon resonance (SPR) of the GNPs with a anisotropy factor (g-factor) of the order of 1 × 10^-4, i.e., 10-fold larger than what is typically reported in the literature. Such CD signals were simulated using a coupled dipole method which fit very well the experimental data. The measured signals are 1-2 orders of magnitude lower than the simulated signals, which is explained by the disordered GNPs grafting, the polydispersity of the GNPs, and the dimension of the nanohelices. These Goldhelices based on inorganic templates are much more robust than previously reported organic-based chiroptical nanostructures, making them good candidates for complex hierarchical organization, providing a promising approach for light management and benefits in applications such as circular polarizers, chiral metamaterials, or chiral sensing in the visible range.

Synthesis of Helical Phenolic Resin Bundles through a Sol-Gel Transcription Method

Chiral and helical polymers possess special helical structures and optical property, and may find applications in chiral catalysis and optical devices. This work presents the preparation and formation process of helical phenolic resins through a sol-gel transcription method. A pair of bola-type chiral low-molecular-weight gelators (LMWGs) derived from valine are used as templates, while 2,4-dihydroxybenzoic acid and formaldehyde are used as precursors. The electron microscopy images show that the phenolic resins are single-handed helical bundles comprised of helical ultrafine nanofibers. The diffused reflection circular dichroism spectra indicate that the helical phenolic resins exhibit optical activity. A possible formation mechanism is proposed, which shows the co-assembly of the LMWGs and the precursors.

Formation of supermolecular chiral gels from l-aspartic acid-based perylenebisimides and benzene dicarboxylic acids

Herein, the gelation mechanism of l-aspartic acid-based perylenebisimides and various isomeric benzene dicarboxylic acids was investigated.

Direct Observation of Siloxane Chirality on Twisted and Helical Nanometric Amorphous Silica

Synthesis of chiral inorganic or hybrid nanomaterials through sol-gel transcription of chiral organic templates has attracted a great deal of interest for more than a decade. However, the chiral nature of these inorganic matrices has never been directly observed. For the first time, we report a direct evaluation of chirality on noncrystalline silica chiral nanoribbons by vibrational circular dichroism (VCD) measurements. Strong Cotton effect around 1150-1000 cm^-1 from Si-O-Si asymmetric stretching vibration was observed. Surprisingly, calcination of these hybrid nanoribbons doubled the intensity of Cotton effects. On the basis of transmission electron microscopy observations, IR, VCD, NMR, and Raman spectroscopies, we demonstrate that the silica chirality originates from twisted siloxane network composed of chiral arrangement of the Si-O-Si bonds. Our findings clearly prove the presence of chiral organization of amorphous silica network, making them very promising chiral platforms for chiral recognition, optical applications, or asymmetric catalysis.

Twisted and tubular silica structures by anionic surfactant fibers encapsulation

Organic molecules imprinting can be used for introducing specific properties and functionalities such as chirality to mesoporous materials. Particularly organic self-assemblies can work as a scaffold for templating inorganic materials such as silica. During recent years chiral imprinting of anionic surfactant for fabrication of twisted rod-like silica structures assisted by co-structuring directing agent were thoroughly investigated. The organic self-assemblies of anionic surfactants can also be used for introducing other shapes in rod-like silica structures. Here we report the formation of amphiphilic N-miristoyl-l-alanine self-assemblies in aqueous solution upon stirring and at presence of l-arginine. These anionic surfactant self-assemblies form fibers that grow by increasing the stirring duration. The fibers were studied using transmission electron microscopy, infra-red spectroscopy and vibrational circular dichroism. Addition of silica precursor 1,2-bis(triethoxysilyl)ethylene and co-structuring directing agent N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride at different stages of fibers' growth leads to formation of different silica structures. By controlling stirring duration, we obtained twisted tubular silica structures as a result of fibers encapsulation. We decorated these structures with gold nanoparticles by different methods and measured their optical activity.

Chiral Nanoarchitectonics: Towards the Design, Self-Assembly, and Function of Nanoscale Chiral Twists and Helices

Helical structures such as double helical DNA and the α-helical proteins found in biological systems are among the most beautiful natural structures. Chiral nanoarchitectonics, which is used here to describe the hierarchical formation and fabrication of chiral nanoarchitectures that can be observed by atomic force microscopy (AFM), scanning tunneling microscopy (STM), scanning electron microscopy (SEM), or transmission electron microscopy (TEM), is one of the most effective ways to mimic those natural chiral nanostructures. This article focuses on the formation, structure, and function of the most common chiral nanoarchitectures: nanoscale chiral twists and helices. The types of molecules that can be designed and how they can form hierarchical chiral nanoarchitectures are explored. In addition, new and unique functions such as amplified chiral sensing, chiral separation, biological effects, and circularly polarized luminescence associated with the chiral nanoarchitectures are discussed.

Memorized chiral arrangement of gemini surfactant assemblies in nanometric hybrid organic–silica helices

The chiral arrangement of non-chiral gemini surfactant molecules induced by enantiomeric tartrate counterions was maintained by hybridization with silica matrices even after the removal of the counterions as chiral sources.

Rational Design of Chiral Nanostructures from Self-Assembly of a Ferrocene-Modified Dipeptide

We report a new paradigm for the rational design of chiral nanostructures that is based on the hierarchical self-assembly of a ferrocene (Fc)-modified dipeptide, ferrocene-L-Phe-L-Phe-OH (Fc-FF). Compared to other chiral self-assembling systems, Fc-FF is unique because of its smaller size, biocompatibility, multiple functions (a redox center), and environmental responsiveness. X-ray and spectroscopic analyses showed that the incorporation of counterions during the hierarchical self-assembly of Fc-FF changed the conformations of the secondary structures from flat β sheets into twisted β sheets. This approach enables chiral self-assembly and the formation of well-defined chiral nanostructures composed of helical twisted β sheets. We identified two elementary forms for the helical twist of the β sheets, which allowed us to create a rich variety of rigid chiral nanostructures over a wide range of scales. Furthermore, through subtle modulations in the counterions, temperature, and solvent, we are able to precisely control the helical pitch, diameter, and handedness of the self-assembled chiral nanostructures. This unprecedented level of control not only offers insights into how rationally designed chiral nanostructures can be formed from simple molecular building blocks but also is of significant practical value for the use in chiroptics, templates, chiral sensing, and separations.

Controlling enantiomeric populations in fluctuating Brownian monolayers of chiral colloids

An ideal parallelogram platelet, although achiral in 3D, has an identifiable chirality when confined in a 2D monolayer. We lithographically fabricate microscale parallelogram platelets, disperse them in an aqueous surfactant solution, and allow them to settle towards a lower glass wall. To reduce the thermal-gravitational height, we add polystyrene nanospheres as a depletion agent to create a depletion attraction between the parallelograms and the wall. Surprisingly, by increasing the volume fraction of the depletion agent, we show that a nearly enantiopure monolayer can be created. We explain this by developing a model of 2D monolayer formation based on anisotropic facial attractions; one face of a platelet is more strongly attracted to the wall than the other as a consequence of an anisotropy introduced by the lithographic process. We study enantiopure Brownian systems of parallelograms as a function of particle area fraction and show that oblique chiral crystals form at high densities. By mixing parallelogram platelets printed in opposite senses, we also dictate the chiral ratio in the monolayer over the entire possible range. This approach is not limited to parallelograms and provides a means for tuning the chiral ratio in fluctuating 2D monolayers composed of a wide variety of chiral shapes.