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

Chiral Skeletons of Mesoporous Silica Nanospheres to Mitigate Alzheimer’s β-Amyloid Aggregation

Chiral mesoporous silica (mSiO₂) nanomaterials have gained significant attention during the past two decades. Most of them show a topologically characteristic helix; however, little attention has been paid to the molecular-scale chirality of mSiO₂ frameworks. Herein, we report a chiral amide-gel-directed synthesis strategy for the fabrication of chiral mSiO₂ nanospheres with molecular-scale-like chirality in the silicate skeletons. The functionalization of micelles with the chiral amide gels via electrostatic interactions realizes the growth of molecular configuration chiral silica sols. Subsequent modular self-assembly results in the formation of dendritic large mesoporous silica nanospheres with molecular chirality of the silica frameworks. As a result, the resultant chiral mSiO₂ nanospheres show abundant large mesopores (∼10.1 nm), high pore volumes (∼1.8 cm³·g^-1), high surface areas (∼525 m²·g^-1), and evident CD activity. The successful transfer of the chirality from the chiral amide gels to composited micelles and further to asymmetric silica polymeric frameworks based on modular self-assembly leads to the presence of molecular chirality in the final products. The chiral mSiO₂ frameworks display a good chiral stability after a high-temperature calcination (even up to 1000 °C). The chiral mSiO₂ can impart a notable decline in β-amyloid protein (Aβ42) aggregation formation up to 79%, leading to significant mitigation of Aβ42-induced cytotoxicity on the human neuroblastoma line SH-ST5Y cells in vitro. This finding opens a new avenue to construct the molecular chirality configuration in nanomaterials for optical and biomedical applications.

Chirality Detection by Raman Spectroscopy: The Case of Enantioselective Interactions between Amino Acids and Polymer-Modified Chiral Silica

In chirality research area, it is of interest to reveal the chiral feature of inorganic nanomaterials and their enantioselective interactions with biomolecules. Although common Raman spectroscopy is not regarded as a direct chirality analysis tool, it is in fact effective and sensitive to study the enantioselectivity phenomena, which is demonstrated by the enantio-discrimination of amino acid enantiomers using the polydopamine-modified intrinsically chiral SiO₂ nanofibers in this work. The Raman scattering intensities of an enantiomer of cysteine are more than twice as high as those of the other enantiomer with opposite handedness. Similar results were also found in the cases of cystine, phenylalanine, and tryptophan enantiomers. In turn, these organic molecules could be used as chirality indicators for SiO₂, which was clarified by the unique Raman spectra-derived mirror-image relationships. Thus, an indirect chirality detection method for inorganic nanomaterials was developed.

Chiral Nucleating Agents Affecting the Handedness of Lamellar Twist in the Banded Spherulites in Poly(ε-Caprolactone)/Poly(Vinyl Butyral) Blends

Chiral silica, which acts as a nucleating agent of poly(ε-caprolactone) (PCL), was demonstrated to induce excess handedness of lamellar twist in the banded spherulites of PCL blended with poly(vinyl butyral). The d- and l-forms of silica enhanced the right- and left-handed twists, respectively. The influences of chiral silica on the twist handedness were statistically significant. These results indicate that the handedness of twisting can be controlled upon primary nucleation. The organic substances used as chiral templates of silica had no effect on the handedness; silica was shown to govern the handedness. The possible mechanisms of the chirality transfer are discussed.

Unusual chirality transfer from silica to metallic nanoparticles with formation of distorted atomic array in crystal lattice structure

Transfer of chirality from chiral organic molecules to metallic nanoparticles (NPs) is a very attractive field of research and some unique approaches to obtaining chiral metallic NPs have been developed. However, to date, there has been no report in the literature that the chiral information of silica can be transferred into metallic NPs. In this work, a new chirality transfer system to metallic NPs from chiral silica has been achieved. The chiral transfer was performed by simple two steps: (1) trapping metal cations of silver (Ag) and gold (Au) in chiral silica of nano fibrous bundles embedding poly(ethyleneimine) inside and (2) thermoreducing the metal ions into metallic NPs. The metallic NPs of Au and Ag grown around a silica frame, using a thermo-reduction (calcination) process, showed a spherical shape with a size of about 30 nm. Interestingly, the metallic NPs detached or isolated from the silica via crushing and/or hydrolysis of the silica showed remarkable circular dichroism activity in their plasmon absorption band with an exciton coupling feature. Using an atomic resolution scanning transmission protocol, it was found that the chiral metallic NPs have a definite distortion in the atomic array in their crystal lattice structures. In comparison, achiral metallic NPs, which were prepared using a similar method around achiral silica bundles, showed a precisely ordered atomic line without distortion.

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.

Novel properties and applications of carbon nanodots

In the most recent decade, carbon dots have drawn intensive attention and triggered substantial investigation. Carbon dots manifest superior merits, including excellent biocompatibility both in vitro and in vivo, resistance to photobleaching, easy surface functionalization and bio-conjugation, outstanding colloidal stability, eco-friendly synthesis, and low cost. All of these endow them with the great potential to replace conventional unsatisfactory fluorescent heavy metal-containing semiconductor quantum dots or organic dyes. Even though the understanding of their photoluminescence mechanism is still controversial, carbon dots have already exhibited many versatile applications. In this article, we summarize and review the recent progress achieved in the field of carbon dots, and provide a comprehensive summary and discussion on their synthesis methods and emission mechanisms. We also present the applications of carbon dots in bioimaging, drug delivery, microfluidics, light emitting diode (LED), sensing, logic gates, and chiral photonics, etc. Some unaddressed issues, challenges, and future prospects of carbon dots are also discussed. We envision that carbon dots will eventually have great commercial utilization and will become a strong competitor to some currently used fluorescent materials. It is our hope that this review will provide insights into both the fundamental research and practical applications of carbon dots.

Convenient chirality transfer from organics to titania: construction and optical properties

Polyethyleneimine (PEI) complexed with chiral d- (or l-) tartaric acid (tart) in water can self-organize into chiral and crystalline PEI/tart assemblies. It has been previously confirmed that the complexes of PEI/tart could work as catalytic/chiral templates to induce the deposition of SiO₂ nanofibres with optical activity but without outwards shape chirality such as helices. In this work, we found that the templating functions of PEI/tart were still effective to prompt the deposition of TiO₂ to form chiral PEI/tart@TiO₂ hybrid nanofibres under aqueous and room temperature conditions within two hours. Furthermore, the co-deposition of TiO₂ and SiO₂ was also fulfilled to yield chiral PEI/tart@TiO₂/SiO₂ nanofibres. These TiO₂-containing hybrid nanofibres showed non-helical shapes on the length scale; however, chiroptical signals with mirror relation around the UV-Vis absorption band of TiO₂ remarkably appeared on their circular dichroism (CD) spectra. By means of the protocols of XRD, TEM, SEM, UV-Vis, CD and XPS, structural features and thermoproperties of the chiral TiO₂ and SiO₂/TiO₂ were investigated.

Polyethyleneimine (PEI) complexed with chiral d- (or l-) tartaric acid (tart) in water can self-organize into chiral and crystalline PEI/tart assemblies which can prompt titania deposition and impart their chirality to the resulting titania.

Unexpected "Hammerlike Liquid" to Pulverize Silica Powders to Stable Sols and Its Application in the Preparation of Sub-10 nm SiO2 Hybrid Nanoparticles with Chirality

Silane coupling agents are well-known as surface modifiers for various kinds of silica (SiO2). However, in the present research, it has been found that they can also work as "hammerlike liquid" to pulverize different kinds of bulk amorphous SiO2 in aqueous systems. This new function was typically clarified by using 3-aminopropyltrimethoxysilane (APS) and bundles of chiral SiO2 nanofibers (with average diameter of ∼10 nm) as raw materials. By a simple reflux of the mixture of SiO2 nanofibers and excessive APS in pure H2O, the solid-containing mixture turned into a completely clear solution that contained sub-10 nm, amine-modified, and water-soluble hybrid SiO2 sols (HS-sols). Moreover, this solution showed blue luminescence under ultraviolet irradiation. Furthermore, the circular dichroism and vibrational circular dichroism spectra revealed that the HS-sols are optically active even though the pristine chiral SiO2 nanofibers were completely destroyed. It was considered that the chirality of SiO2 nanofibers was due to the asymmetric arrangement of Si and O atoms in chiral domains (<10 nm) on the Si-O-Si network of SiO2, and these domains are still preserved in chiral HS-sols. This green method has high potential for the recycling of rich SiO2 sources to obtain functional SiO2 nanomaterials with applications such as optical display, imaging, and chiral recognition. Also, it offers a tool for the analysis of the structural properties of SiO2 on the molecular scale.