High‐Temperature‐Resistant Chiral Silica Generated on Chiral Crystalline Templates at Neutral pH and Ambient Conditions

Abstract

In memory of Tadatomi NishikuboChirality is one of the fundamental issues in the related fields of biology, medicine, chemistry, and physics, [1] because components of life, medicine, and display devices are composed of chiral molecules, such as DNA, proteins, cellulose, sugar, amino acids, drugs, and liquid crystalline molecules. However, chirality is not restricted to these molecular regimes. Solid minerals and inorganic materials also have chirality, which arises from the geometric properties and the atomic structure of surfaces. [1][2][3] A difference between molecular and mineral chirality would be in its resilience; the former is temporary at the limited environment, while the latter will be semi-permanent even under the harsh conditions. Therefore, artificial chiral minerals would have great potential for memory, preservation, and development of organic chiral systems.Helical mesoporous silica, which was pioneered by Tatsumi et al, [4] is one of current topics in chiral mineral materials. Its chirality is induced by a templated sol-gel reaction where special micelles self-assembled from chiral molecules serve as templates to direct helical morphology, thereby imprinting the chiral topology in silica. [4,5] Although this is a refined process to simultaneously control the morphology and chirality, in conventional chiral mesoporous silica formation, the hydrolytic condensation of alkoxysilane is catalyzed by the added HCl or NaOH solution rather than by micellar template itself. [6][7][8][9] In the design of silica materials, the greatest designer and authority is surely biosilica, such as diatoms and sponges, which have very beautiful, complex, and sophisticated shapes in nano-and microdimensions with silica skeletons. [10][11][12][13] In this sense, diatoms and sponges are eternal texts with a lot of sources of inspiration for the synthesis of silica-based nano/microscale materials, including chiral silica. It is well known that in the biogenic silica formation, organized organic matrices, such as silaffins (polypeptides), silicateins (proteins), and long-chain polyamines play as catalysts (temporal control) and templates (spatial control) in silica deposition under neutral pH and ambient conditions. [14][15][16][17][18][19][20][21][22][23][24] As mimicking those organic matrices, a lot of organic molecules and polymers having amino groups have been used in the biomimetic silica deposition, and major achievements have been accomplished in this field over the past decade. [25][26][27][28][29][30][31][32][33][34][35][36][37] However, no efforts were put on the construction of chiral silica, although many biomimetic silicas were deposited by co-precipitation with chiral polypeptides. [25][26][27][28] Among biomimetic silica formation, the silicateins particularly attracted our interest because they form axial filaments (fibrils) and act as templates to deposit silica around the surface of the fibrils to give fibrous hybrids consisted of axial filaments and silica shell. [20,22,23] Recently, we have established...

Silica–Polypyrrole Hybrids as High‐Performance Metal‐Free Electrocatalysts for the Hydrogen Evolution Reaction in Neutral Media

“…[15] 3) TheS i2pX PS spectrum of the SiO 2 /PPy NTs-CFs (Figure 2c)s hows that the Si 2p 3/2 peak is shifted to al ower binding energy (À0.15 eV) compared with that of the SiO 2 NDs-CFs;i na ddition, aS i III peak appears at 102.6 eV,i ndicating the formation of low-valent Si after hybridization and that Si receives extra electrons from PPy. [16] 4) TheN1s XPS spectrum of the SiO 2 /PPy NTs-CFs (Figure 2d)shows that the À N = , À NH À ,and À N + À characteristic peaks are positively shifted by 0.40, 0.13, and 0.38 eV, respectively,r elative to those of the PPy NTs-CFs, suggesting ad ecrease in electron density around the Natoms. [17] Taken together, these results show that there are strong electronic interactions between SiO 2 and PPy in the SiO 2 / PPy NTs-CFs,a nd that SiO 2 is negatively charged.…”

Understanding Silica from the Viewpoint of Asymmetry

“…As expected, the silica formation proceeded very smoothly around crystalline aggregates of d ‐Tart/PEI, l ‐Tart/PEI, and dl ‐Tart/PEI from an aqueous solution of TMOS at room temperature within a short time. Surprisingly, after sintering them at a high temperature, the silica templated by d ‐Tart/PEI and l ‐Tart/PEI exhibited remarkable CD activity with a mirror relationship at wavelengths below 200 nm, which arose from the absorption of the Si−O bond . In the control, the silica templated by dl ‐Tart/PEI did not show CD activity (Figure ).…”

“…What we are interested in is what will happen when water is replaced by organic acids in regard to the association with PEI. Fortunately, it was determined that many sugar acids, such as tartaric acid (Tart), lactic acid, and glucaric acid, can be complexed with PEI in water and then self‐assembled to crystalline aggregates with nanofibrous structures at a molar ratio of NH/COOH/H 2 O=1:1:1 . In these crystalline aggregates, the amine (‐NH‐) and carbolic acid (O=C−OH) groups should present as a charged pair ‐HNH⋅⋅⋅OC=O.…”

“… Top: Schematic representation of silica deposition. Bottom: Diffuse reflected CD spectra for (a) hybrid state of silica/PEI/Tart and (b) silica prepared by calcination at 600 °C …”

Double Chiral Hybrid Materials: Formation of Chiral Phenolic Resins on Polyamine-associated Chiral Silica

“…16 On the other hand, we also succeeded in the synthesis of chiral silica promoted by crystalline complexes self-assembled from polyethyleneimine (PEI) and enantiomeric tartaric acid (tart). 17 By combining the above two achievements, herein, we attempted the synthesis of chiral phenolic resins (RF) by polymerization of resorcinol (R) and formaldehyde (F), employing the SiO 2 /PEI chiral hybrid, in which silica is the chiral source and PEI is a catalyst. The RF isolated after removing chiral silica via treatment with HF (3% aq) showed remarkable optical activity but without helical outward on the length-scale over tens nm.…”