Biomimetic Synthesis of Shaped and Chiral Silica Entities Templated by Organic Objective Materials

Siliplant1 B-domain precipitates silica spheres, aggregates, or gel, depending on Si-precursor to peptide ratios

Silica is extensively deposited by plants, however, only little is known about the molecular control over this process. Siliplant1 is the only known plant protein to precipitate biosilica. The protein contains seven repeats made of three domains. One of the domains exhibits a conserved sequence, which catalyzes silica precipitation in vitro. Here, silica was synthesized by the activity of a peptide carrying this conserved sequence. Infrared spectroscopy and thermal gravimetric analyses showed that the peptide was bound to the mineral. Scanning electron microscopy showed that silica-peptide particles of 22 ± 4 nm aggregated to spherical structures of 200-300 nm when the ratio of silicic acid to the peptide was below 183:1 molecules. When the ratio was about 183:1, similar particles aggregated into irregular structures, and silica gel formed at higher ratios. Solid-state NMR spectra indicated that the irregular aggregates were richer in Si-O-Si bonds as well as disordered peptide. Our results suggest that the peptide catalyzed the condensation of silicic acid and the formation of ∼20 nm particles, which aggregated into spheres. Excess of the peptide stabilized surface Si-OH groups that prevented spontaneous Si-O-Si bonding between aggregates. Under Si concentrations relevant to plant sap, the peptide and possibly Siliplant1, could catalyze nucleation of silica particles that aggregate into spherical aggregates.

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.

Designing sequence-defined peptoids for fibrillar self-assembly and silicification

In the biological environment, mineral crystals exquisitely controlled by biomacromolecules often show intricate hierarchical structures and superior mechanical properties. Among these biominerals, spicules, hybrid silica/protein superstructures serving as skeletal elements in demosponges, represent an excellent example for motivating the synthesis of silica materials. Herein, by designing sequence-defined peptoids containing side chains with a strong binding to silica, we demonstrated that self-assembly of these peptoids into fiber structures enables the mimicking of both biocatalytic and templating functions of silicatein filaments for the formation of silica fibers at near-neutral pH and ambient temperature. We further showed that the presence of amino groups is significant for the nucleation of silica on self-assembled peptoid nanofibers. Molecular dynamics simulation further confirmed that having silica-binding of amino side chains is critical for self-assembled peptoid fibers in triggering silica formation. We demonstrated that tuning inter-peptoid interactions by varying carboxyl and amino side chains significantly influences the assembly kinetics and final morphologies of peptoid assemblies as scaffolds for directing silica mineralization to form silica spheres, fibers, and sheets. The formation of silica shell on peptoid fibers increased the mechanical property of peptoid hydrogel materials by nearly 1000-fold, highlighting the great potential of using silicification to enhance the mechanical property of hydrogel materials for applications including tissue engineering. Since peptoids are highly robust and programmable, we expect that self-assembly of peptoids containing solid-binding side chains into hierarchical materials opens new opportunities in the design and synthesis of highly tunable scaffolds that direct the formation of composite nanomaterials.

Diatom-inspired multiscale mineralization of patterned protein-polysaccharide complex structures

Marine diatoms construct their hierarchically ordered, three-dimensional (3D) external structures called frustules through precise biomineralization processes. Recapitulating the remarkable architectures and functions of diatom frustules in artificial materials is a major challenge that has important technological implications for hierarchically ordered composites. Here, we report the construction of highly ordered, mineralized composites based on fabrication of complex self-supporting porous structures-made of genetically engineered amyloid fusion proteins and the natural polysaccharide chitin-and performing in situ multiscale protein-mediated mineralization with diverse inorganic materials, including SiO2, TiO2 and Ga2O3. Subsequently, using sugar cubes as templates, we demonstrate that 3D fabricated porous structures can become colonized by engineered bacteria and can be functionalized with highly photoreactive minerals, thereby enabling co-localization of the photocatalytic units with a bacteria-based hydrogenase reaction for a successful semi-solid artificial photosynthesis system for hydrogen evolution. Our study thus highlights the power of coupling genetically engineered proteins and polysaccharides with biofabrication techniques to generate hierarchically organized mineralized porous structures inspired by nature.

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.

Linear-Polyethyleneimine-Templated Synthesis of N-Doped Carbon Nanonet Flakes for High-performance Supercapacitor Electrodes

Novel N-doped carbon nanonet flakes (NCNFs), consisting of three-dimensional interconnected carbon nanotube and penetrable mesopore channels were synthesized in the assistance of a hybrid catalytic template of silica-coated-linear polyethyleneimine (PEI). Resorcinol-formaldehyde resin and melamine were used as precursors for carbon and nitrogen, respectively, which were spontaneously formed on the silica-coated-PEI template and then annealed at 700 °C in a N2 atmosphere to be transformed into the hierarchical 3D N-doped carbon nanonetworks. The obtained NCNFs possess high surface area (946 m2 g-1), uniform pore size (2-5 nm), and excellent electron and ion conductivity, which were quite beneficial for electrochemical double-layered supercapacitors (EDLSs). The supercapacitor synthesized from NCNFs electrodes exhibited both extremely high capacitance (up to 613 F g-1 at 1 A g-1) and excellent long-term capacitance retention performance (96% capacitive retention after 20,000 cycles), which established the current processing among the most competitive strategies for the synthesis of high performance supercapacitors.

Bioinspired Approach to Silica Nanoparticle Synthesis Using Amine-Containing Block Copoly(vinyl ethers): Realizing Controlled Anisotropy

Core-shell polymer-silica hybrid nanoparticles smaller than 50 nm in diameter were formed in the presence of micelles of poly(2-aminoethyl vinyl ether-block-isobutyl vinyl ether) (poly(AEVE_m-b-IBVE_n)) through the hydrolysis and polycondensation of alkoxysilane in aqueous solution at a mild pH and temperature. The size of the nanoparticles as well as the number and size of the core parts were effectively controlled by varying the molecular weight of the copolymers. The polymers could be removed by calcination to give hollow silica nanoparticles with Brunauer-Emmett-Teller surface areas of more than 500 m² g^-1. Among these, silica nanoparticles formed with poly(AEVE₁₁₅-b-IBVE₄₀) displayed an anisotropy of single openings in the shell. The use of an alternative copolymer, poly(AEVE-b-2-naphthoxyethyl vinyl ether) (poly(AEVE₁₁₃-b-βNpOVE₄₀)), yielded core-shell nanoparticles with less pronounced anisotropy. These results showed that the degree of anisotropy could be controlled by the rigidity of micelles; the micelle of poly(AEVE₁₁₅-b-IBVE₄₀) was more deformable during silica deposition than that of poly(AEVE₁₁₃-b-βNpOVE₄₀) in which aromatic interactions were possible. This bioinspired, environmentally friendly approach will enable large-scale production of anisotropic silica nanomaterials, opening up applications in the field of nanomedicine, optical materials, and self-assembly.

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.

Multiple Routes to Smart Nanostructured Materials from Diatom Microalgae: A Chemical Perspective

Diatoms are unicellular photosynthetic microalgae, ubiquitously diffused in both marine and freshwater environments, which exist worldwide with more than 100 000 species, each with different morphologies and dimensions, but typically ranging from 10 to 200 µm. A special feature of diatoms is their production of siliceous micro- to nanoporous cell walls, the frustules, whose hierarchical organization of silica layers produces extraordinarily intricate pore patterns. Due to the high surface area, mechanical resistance, unique optical features, and biocompatibility, a number of applications of diatom frustules have been investigated in photonics, sensing, optoelectronics, biomedicine, and energy conversion and storage. Current progress in diatom-based nanotechnology relies primarily on the availability of various strategies to isolate frustules, retaining their morphological features, and modify their chemical composition for applications that are not restricted to those of the bare biosilica produced by diatoms. Chemical or biological methods that decorate, integrate, convert, or mimic diatoms' biosilica shells while preserving their structural features represent powerful tools in developing scalable, low-cost routes to a wide variety of nanostructured smart materials. Here, the different approaches to chemical modification as the basis for the description of applications relating to the different materials thus obtained are presented.

Polymer brush guided templating on well-defined rod-like cellulose nanocrystals

Precisely grafted polymer brushes on cellulose nanocrystals guide the formation of silica and yield uniform CNC-based hybrid nanomaterials which are subsequently used in the fabrication of hollow and highly porous silica nanorods.

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.

Biomimetic silica deposition promoted by sub-5 μm complexes of dicarboxylic acids/polyethyleneimine microballs: a new approach to tuning silica structures using messenger-like dicarboxylic acids

Acid–base complexes prepared from sub-5 μm polyethyleneimine microballs and dicarboxylic acids promoted silica deposition to give silica microballs with different morphological surface structures which were controlled by the structures of the acids.

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.

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.

Autocatalytic synthesis of multifunctional precursors for fabricating silica microspheres with well-dispersed Ag and Co3O4 nanoparticles

Herein, an autocatalytic route to fabricate dual metal ion-equipped organic/inorganic hybrid silica, an ideal precursor for multifunctional silica-based composites integrated with well-dispersed Ag and Co₃O₄ nanoparticles was demonstrated. Significantly, by rational selection of reactants, such dual metal ion-equipped organic/inorganic hybrid silica can be synthesized through successive spontaneous reactions under near neutral conditions without an additional catalyst. Both the Ag⁺ and Co²⁺ ions are introduced into silica by chemical bonds, which favor the formation of small-sized and well-dispersed Ag and Co₃O₄ nanoparticles without aggregation in the entire silica matrix. After calcination, multifunctional silica composites equipped with well-dispersed Ag and Co₃O₄ nanoparticles were obtained. The as-obtained silica composites, as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), have a spherical morphology and smooth surface. TEM tests also reveal the well dispersed fashion of Ag and Co₃O₄ nanoparticles. In addition, the obtained Ag-Co₃O₄@SiO₂ composites exhibit good catalytic performance in the reduction of methylene blue (MB) with NaBH₄ as a reducing agent, and can be readily recycled by an external magnetic field due to their superparamagnetic properties.

Sub-5 μm balls possessing forest-like poly(methyloxazoline)/polyethyleneimine side chains and templated silica microballs with unusual internal structures

Herein, sub-5 μm microballs, with unusual forest-like structures consisting of a polystyrene network and forest-like poly(2-methyl-2-oxazoline) (PMOZ) and/or linear polyethyleneimine (LPEI) side chains, were synthesized by combining two isolated processes.

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.

Polycondensation and carbonization of phenolic resin on structured nano/chiral silicas: reactions, morphologies and properties

Diversely shaped and chiral nano-carbonaceous materials were obtained using bioinspired polyethyleneimine (PEI)–silica hybrids as catalytic templates and chiral sources.

Protein-templated biomimetic silica nanoparticles

Biomimetic silica particles can be synthesized as a nanosized material within minutes in a process mimicked from living organisms such as diatoms and sponges. In this work, we have studied the effect of bovine serum albumin (BSA) as a template to direct the synthesis of silica nanoparticles (NPs) with the potential to associate proteins on its surface. Our approach enables the formation of spheres with different physicochemical properties. Particles using BSA as a protein template were smaller (∼250-380 nm) and were more monodisperse than those lacking the proteic core (∼700-1000 nm) as seen by dynamic light scattering (DLS), scanning electron microscopy (SEM), and environmental scanning electron microscopy (ESEM) analysis. The absence of BSA during synthesis produced silica nanoparticles without any porosity that was detectable by nitrogen adsorption, whereas particles containing BSA developed porosity in the range of 4 to 5 nm which collapsed on the removal of BSA, thus producing smaller pores. These results were in accordance with the pore size calculated by high-resolution transmission electron microscopy (HTEM). The reproducibility of the BSA-templated nanoparticle properties was determined by analyzing four batches of independent synthesizing experiments that maintained their properties. The high positive superficial charge of the nanoparticles facilitated adsorption under mild conditions of a range of proteins from an E. coli extract and a commercial preparation of laccase from Trametes versicolor. All of the proteins were quantitatively desorbed. Experiments conducted showed the reusability of the particles as supports for the ionic adsorption of the biomolecules. The protein loading capacity of the BSA-based biomimetic particles was determined using laccase as 98.7 ± 6.6 mg·g(-1) of particles.

Synthesis of comb-like poly(ethyleneimine)s and their application in biomimetic silicification

In this paper, we firstly synthesized comb polymers with crystallizable poly(ethyleneimine) (PEI) side chains, and further investigated their self-assembly behavior and catalytic templating role for silicification.