Double-brush Langmuir-Blodgett monolayers of alpha-helical diblock copolypeptides

The synthesis of amphiphilic diblock copolypeptides consisting of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) and their monolayer behavior at the air-water interface have been studied. PLGA-b-PMLGSLG was synthesized via a diblock copolymer precursor consisting of poly(gamma-tert-butyl-L-glutamate) (PtBuLG) and PMLGSLG blocks, with the tert-butyl group as a mild acid-labile protecting group for the carboxylic acid. The polymerization conditions were found to influence the alpha-helix to beta-sheet content ratio and can be tuned to significantly enhance the cliblock copolypeptide helicity. Purely alpha-helical PtBuLG-b-PMLGSLG diblock copolymers were successfully prepared. After removal of the tert-butyl group, the study of the PLGA-b-PMLGSLG amphiphilic cliblock copolymers in Langmuir monolayers; and Langmuir-Blodgett films demonstrated the formation of a stable alpha-helical double-brush structure, with the helices tilted away from the substrate surface. These double-brush monolayers combine the unique properties arising from the unidirectionally aligned helix macrodipole and the liquid-like features of the side chain mantle of the PMLGSLG block. Such systems are promising for thin film applications requiring incorporation and orientation of bio- and optical molecules. (C) 2010 Elsevier Ltd. All rights reserved.