Biomimetic Silica Formation: Effect of Block Copolypeptide Chemistry and Solution Conditions on Silica Nanostructure

Abstract

Developing new technologies as a consequence of controlling structure, chemistry, and functionality at the nanometer length scale is the ultimate goal of nanotechnology. One route to this goal is to draw lessons from nature, which has developed the ability to fabricate inorganic and inorganic-hybrid materials such as silica diatoms and nacre that have properties that the materials science community can only aspire to achieve. [1][2][3][4][5][6][7] The development of so-called biomimetic or bioinspired synthesis methods to develop hard matter with new or unusual properties has become an area of tremendous growth. One aspect of this problem is the synthesis of silica materials using amines or polyamines under ambient conditions. Numerous works have demonstrated materials with unusual properties, particularly with respect to morphology and microstructure. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Of particular relevance to the current work are the numerous reports of silicas made in the presence of poly-L-lysine. From this body of literature it is clear that one can make silicas with various morphologies through manipulation of pH, salt, flow versus quiescent conditions, etc. Further, recent works from several labs have shown the poly-L-lysine chain conformation can be used to control silica morphology. [25,26] It is this point in particular that is explored in the current investigation. Our lab has made two contributions to this blossoming area. First, we have demonstrated that the conformation of polypeptide chains can be used to manipulate the porosity of the oxide obtained. [27,28] Second, we have shown that individual supramolecular objects (vesicles) formed by block copolypeptides can be used as templates to form nanostructured hard materials. [29] In the latter case the block copolypeptides studied were Lys-b-Phe block copolypeptides that form kinetically trapped structures in solution. Here we report the formation of silicas in the presence of a series of block copolypeptides, but mainly Lys-b-Gly block copolypeptides which appear to form more reversible structures as compared to the materials we reported previously. This manuscript reports on how the polypeptide chemistry and solution conditions influence both the morphology and porosity of the hard material they assemble. This latter point has been sparingly studied, yet for many applications this property will be essential. In all cases the block copolypeptides investigated here form supramolecular structures in solution, typically vesicles. However, the Lys-b-Gly block copolypeptides form structures that appear to be more reversible in nature as compared to the objects formed by the Lys-b-Ala and Lys-b-Phe block copolypeptides that appear to be kinetically trapped structures. The critical aggregation concentrations for the polymers studied below are given in the supporting information and are between 0.8-1.7 lM. The syntheses described below use between 3.0-4.0 lM solutions (Methods II, III) or 9.0-10.0 lM solutions (Method I), a...

Bioassisted synthesis of catalytic gold/silica nanotubes using layer-by-layer assembled polypeptide templates

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