Mimicking Biosilicification: Programmed Coassembly of Peptide–Polymer Nanotapes and Silica (original) (raw)

2007, Angewandte Chemie International Edition

Biological inorganic-bioorganic hybrid materials, from bones [1] to filaments of glass sponges [2, 3] to shells of mollusks, [4] are high-performance composites with properties welladapted to their purpose and frequently superior to synthetic mimics. [5, 6] This is a result of defined hierarchical structures that are formed by self-assembly and templating processes facilitated by proteins, peptides, or polysaccharides. [7] Marine glass sponges, for instance the hexactinellid sponge Euplectella sp., are considered to be one of the most primitive animals in existence. However, they produce integrated composite materials with outstanding mechanical properties. [2, 8] This material exhibits a rather complex design, thus ensuring the control of both mechanical and chemical interfaces between the different components to overcome the brittleness of the main constituent material, glass. [2] Inspired by the formation of bioglass filaments, [9] we report the peptide-directed silicification of self-assembled peptidepolymer nanotapes. The spontaneously formed reinforced silica fibers exhibit a distinct inner structure with six distinguishable levels of hierarchical order. Proteins such as silaffin [10] from diatoms or silicatein [11] from glass sponges catalyze and guide the formation of silica from dilute silicic acid solution at neutral pH in vivo and in vitro. [12] Deming et al. pioneered the mimicking of the functions of such proteins by using poly(cysteine-blocklysine). [13] This approach was further broadened by applying other polypeptides and polypeptide derivatives. [14] In addition, several low-molecular-weight compounds containing aamino acids were used to create chiral, mesoporous silica through sol-gel templating routes. [15] In analogy to the formation of biological glass fibers, we encoded the structural and functional information in a fiberlike nanostructure, which was particularly designed to direct the silicification process (Figure 1). To access these functional nanotapes (Figure 1 a), a peptide-polymer conjugate, which combines polyethylene oxide (PEO) with an oligopeptide segment, was synthesized and assembled as