Control over selective recognition of biomolecules on inorganic nanoparticles is a major challenge for the synthesis of new catalysts, functional carriers for therapeutics, and assembly of renewable biobased materials. We found low sequence similarity among sequences of peptides strongly attracted to amorphous silica nanoparticles of various size (15-450 nm) using combinatorial phage display methods. Characterization of the surface by acid base titrations and zeta potential measurements revealed that the acidity of the silica particles increased with larger particle size, corresponding to between 5% and 20% ionization of silanol groups at pH 7. The wide range of surface ionization results in the attraction of increasingly basic peptides to increasingly acidic nanoparticles, along with major changes in the aqueous interfacial layer as seen in molecular dynamics simulation. We identified the mechanism of peptide adsorption using binding assays, zeta potential measurements, IR spectra, and molecular simulations of the purified peptides (without phage) in contact with uniformly sized silica particles. Positively charged peptides are strongly attracted to anionic silica surfaces by ion pairing of protonated N-termini, Lys side chains, and Arg side chains with negatively charged siloxide groups. Further, attraction of the peptides to the surface involves hydrogen bonds between polar groups in the peptide with silanol and siloxide groups on the silica surface, as well as ion-dipole, dipole-dipole, and van-der-Waals interactions. Electrostatic attraction between peptides and particle surfaces is supported by neutralization of zeta potentials, an inverse correlation between the required peptide concentration for measurable adsorption and the peptide pI, and proximity of cationic groups to the surface in the computation. The importance of hydrogen bonds and polar interactions is supported by adsorption of noncationic peptides containing Ser, His, and Asp residues, including the formation of multilayers. We also demonstrate tuning of interfacial interactions using mutant peptides with an excellent correlation between adsorption measurements, zeta potentials, computed adsorption energies, and the proposed binding mechanism. Follow-on questions about the relation between peptide adsorption on silica nanoparticles and mineralization of silica from peptide-stabilized precursors are raised.

Biomineral formation is widespread in Nature and occurs in bacteria, single-celled protists, plants, invertebrates and vertebrates. Minerals formed in the biological environment often show unusual physical properties (e.g., strength, degree of hydration) and often have structures that exhibit order on many length scales. Biosilica, found in single cell organisms through to higher plants and primitive animals (sponges) is formed from an environment that is undersaturated with respect to silicon and under conditions of around neutral pH and low temperature ca. 4–40 °C. Formation of the mineral may occur intra- or extra-cellularly and specific biochemical locations for mineral deposition that include lipids, proteins and carbohydrates are known. In most cases the formation of the mineral phase is linked to cellular processes, understanding of which could lead to the design of new materials for biomedical, optical and other applications. In this contribution we describe the aqueous chemistry of silica, from uncondensed monomer through to colloidal particles and three dimensional structures, relevant to the environment from which the biomineral forms. We then describe the chemistry of silica formation from alkoxides such as tetraethoxysilane as this and other silanes have been used to study the chemistry of silica formation using silicatein and such precursors are often used in the preparation of silicas for technological applications. The focus of this article is on the methods, experimental and computational by which the process of silica formation can be studied with emphasis on speciation.

Biomolecule-mediated ZnO synthesis has great potential for the tailoring of ZnO morphology for specific application in biosensors, window materials for display and solar cells, dye-sensitized solar cells (DSSCs), biomedical materials, and photocatalysts due to its specificity and multi-functionality. In this contribution, the effect of a ZnO-binding peptide (ZnO-BP, G-12: GLHVMHKVAPPR) and its GGGC-tagged derivative (GT-16: GLHVMHKVAPPRGGGC) on the growth of ZnO crystals expressing morphologies dependent on the relative growth rates of (0001) and (10 10) planes of ZnO have been studied. The amount of peptide adsorbed was determined by a depletion method using oriented ZnO films grown by Atomic Layer Deposition (ALD), while the adsorption behavior of G-12 and GT-16 was investigated using XPS and a computational approach. Direct evidence was obtained to show that (i) both the ZnO-BP identified by phage display and its GGGC derivative (GT-16) are able to bind to ZnO and modify crystal growth in a molecule and concentration dependent fashion, (ii) plane selectivity for interaction with the (0001) versus the (10 10) crystal planes is greater for GT-16 than G-12; and (iii) specific peptide residues interact with the crystal surface albeit in the presence of charge compensating anions. To our knowledge, this is the first study to provide unambiguous and direct quantitative experimental evidence of the modification of ZnO morphology via (selective and nonselective) adsorption-growth inhibition mechanisms mediated by a ZnO-BP identified from phage display libraries.

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Preparation of industrially important aluminium oxide, aluminium hydroxide and aluminium salt materials is often based on the hydrolysis of aluminium-ion solutions. [1] One of the frequently employed processes is neutralisation of Al-ion solutions with alkali or acid. [2] A number of reaction conditions affect the structure and properties of the resulting Alcontaining materials, such as pH, temperature, ionic strength, type of anion, etc. [1,2] Better control of materials synthesis through aqueous routes can be obtained by known speciation of Al-ions. The key problem of Al aqueous speciation in solutions with noncomplexing anions (chloride, nitrate, etc.) is the presence of large Al polycations of the Keggin type ± Al 13 -mer (I) and Al 30 -mer (II). [3,4] These polycations are used in a number of material science applications including clay pillaring, [5] preparation of Al 2 O 3 nanoparticles, [6] antiperspirant actives, [7] catalysts, [8] composite materials, [9] etc. The Al 13 -mer has been studied for decades, [10] whereas the structure of the Al 30 -mer has been identified recently. [3,4] Thermodynamic and kinetic data on the Al 30 -mer are not available in the literature.Aim: Preliminary results of a multi-technique study for Al-speciation are presented for model aqueous systems at high temperature and medium Al concentrations for the formation of large aluminium polycations. Information on the reaction pathway may aid in the development of routes to solutions containing single species that can be used in model studies to investigate the effects of aluminium in the environment as well as in the generation of materials from molecular scale precursors.Results and Discussion: The pH-metric titration curves reconstructed from multi-batch measurements (Fig. 2) show all major inflexions characteristic of the analogous systems at room temperature: [11] (1) h < 0.2 ± hydrolysis of Al monomers; (2) 0.2 < h < 2.6 ± formation of Al polycations including Al dimers/trimers, Al 13 -mers and Al 30 -mers; (3) 2.6 < h < 3.0 ± collapse of Al polycations and formation of the metastable colloidal phase of Al hydroxide; (4) h~3.0 ± bulk precipitation of Al hydroxide; (5) h > 3.0 ± gradual dissolution of Al hydroxide with the formation of Al(OH) 4 ± . At prolonged hydrolysis times the early hydrolysis stages (inflexion 1) did not change profoundly. The greatest time-dependent change was observed at stages (3), (4) and (5) in Figure 2. The major inflexion (4) moves to slightly higher hydrolysis ratios (from h~2.8 at 0 h to h~3.0 at 48 h). Other inflexions retained their position during 48 h of experiment. 27 Al solution NMR spectroscopy revealed a number of Al species present in the sample batches. Assignment of the NMR signals and corresponding Al species is given in Table 1. 27 Al solution NMR spectra of the sample solutions of hydrolysed Al-ions (Fig. 3) indicate all species listed in COMMUNICATIONS 836

With both mild synthesis conditions, a high level of organisation and functionality, biosilicas constitute a source of wonder and inspiration for both materials scientists and biologists. In order to understand how such biomaterials are formed and to apply this knowledge to the generation of novel bioinspired materials, a detailed study of the materials, as formed under biologically relevant conditions, is required. In this contribution, data from a detailed study of silica speciation and condensation using a model bio-inspired silica precursor (silicon catechol complex, SCC) is presented. The silicon complex quickly and controllably dissociates under neutral pH conditions to well-defined, metastable solutions of orthosilicic acid. The formation of silicomolybdous (blue) complexes was used to monitor and study different stages of silicic acid condensation. In parallel, the rates of silicomolybdic (yellow) complex formation, with mathematical modelling of the species present was used to follow the solution speciation of polysilicic acids. The results obtained from the two assays correlate well and monomeric silicic acid, trimeric silicic acids and different classes of oligomeric polysilicic acids and silica nuclei can be identified and their periods of stability during the early stages of silica condensation measured. For experiments performed at a range of temperatures (273–323K) an activation energy of 77kJ·mol−1 was obtained for the formation of trimers. The activation energies for the forward and reverse condensation reactions for addition of monomers to polysilicic acids (273–293 ± 1K) were 55.0 and 58.6kJ·mol−1 respectively. For temperatures above 293K, these energies were reduced to 6.1 and 7.3 kJ·mol−1 indicating a probable change in the prevailing condensation mechanism. The impact of pH on the rates of condensation were measured. There was a direct correlation between the apparent third order rate constant for trimer formation and pH (4.7–6.9 ± 0.1) while values for the reversible first order rates reached a plateau at circumneutral pH. These different behaviours are discussed with reference to the generally accepted mechanism for silica condensation in which anionic silicate solution species are central to the condensation process. The results presented in this paper support the use of precursors such as silicon catecholate complexes in the study of biosilicification in vitro. Further detailed experimentation is needed to increase our understanding of specific biomolecule silica interactions that ultimately generate the complex, finely detailed siliceous structures we observe in the world around us.

Composite or hybrid materials are commonly found in Nature, formed through the concentration and subsequent nucleation of ions upon organic templates that are most often protein based. Examples include the deposition of calcium containing salts in bone, teeth and the inner ear and iron oxide structures in magnetotactic bacteria. Biological organisms use a limited number of metal ions, the principal ones being calcium and iron, with lesser amounts of strontium, and barium. The ability to utilize other ions to generate composites offers the possibility of new material properties. New materials incorporating silver would be useful in the context of antimicrobial functions. Therefore, in the present study, a new route to such functionalized biomaterials is reported. Genetically engineered fusion proteins are created by the incorporation of nucleotides corresponding to short silver binding peptides identified by a combinatorial biopanning process into the consensus sequence of silk from the spider, Nephila clavipes. The resulting chimeric silk–silver binding proteins nucleated Ag ions from a solution of silver nitrate while the silk protein provided a stable template material which could be processed into films, fibers, and three‐dimensional scaffolds. The silk films inhibited microbial growth of both Gram‐positive and Gram‐negative microrganisms on agar plates and in liquid culture, thus highlighting the potential of these chimeric material systems as antimicrobial biomedical coatings.

Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular aggregates upon lowering the solvent quality. This supramolecular organization largely determines the optical and electronic properties of these polymers. However, despite numerous studies the exact mechanism and kinetics of the aggregation process and the role of external stimuli are still poorly understood. Classical characterization techniques such as electronic spectroscopy, dynamic light scattering, and diffraction-based techniques have not been able to provide a full understanding. Here we use second-harmonic scattering (SHS) and third-harmonic scattering (THS) techniques to investigate this supramolecular aggregation mechanism. Our results indicate that the actual supramolecular aggregation is preceded by the formation of structured polymer-solvent clusters consistent with a nonclassical crystallization pathway.