Amino Acid Polymerization on Silica Surfaces

Abstract

The polymerization of unactivated amino acids (AAs) is an important topic because of its applications in various fields including industrial medicinal chemistry, and prebiotic chemistry. Silica as a promoter for this reaction, is interesting owing to its large abundance and low cost. The amide/peptide bond synthesis on silica has been largely demonstrated but suffers from a lack of knowledge regarding its reaction mechanism, the key parameters and surface features that influence adsorption and reactivity, the product selectivity, the role of the water, etc. This review addresses these problems by summarizing experimental and modeling results and attempts to rationalize some apparent divergences in published results. After presenting the main types of silica surface sites and other relevant macroscopic features, we discuss the different deposition procedures of AAs, whose importance is often neglected. We address the possible AA adsorption mechanisms including covalent grafting and H‐bonding and show their dependance on silanol types and density. We then consider how the adsorption mechanisms determine the occurrence and outcome of AA condensation (cyclic dimers or long linear chains), and outline some recent results suggesting significant polymerization selectivity, as well as the formation of specific elements of secondary structure in the growing polypeptide chains.