Organized polyelectrolyte monolayers as a structural model of biopolymer

Abstract

Peculiar surface properties of polyelectrolyte assemblies on water or gold substrates were demonstrated, in particular, in terms of interactions with guest molecules including macromolecules. Polyacids such as poly(methacrylic acid) (PMAA) and poly( l-glutamic acid) (PLGA) were employed as polyelectrolytes. One terminus of these polymer segments was modified with two long alkyl chains. To assemble on gold surfaces, disulfides were additionally incorporated into the chain ends of alkyl groups. PMAA-functionalized monolayers on water were found to read out the chain length of poly(ethylene glycol)s in the subphase. Other host-guest combinations were also found out to have a similar ability for chain length recognition. Self-assembled, PMAA-functionalized monolayers on gold were studied in terms of two-dimensional control of molecular mapping at gold surfaces and host-guest interactions. PLGA-functionalized monolayers showed unique conformational changes at an air-water interface: a stable β-sheet structure could be produced by assembling the PLGA segment. The secondary structural variation of the PLGA segment (α-helix, β-sheet and random coil) was readily controlled by changing the monolayer phase. The assembled structure of the helical PLGA segments showed an ability to capture α-amino acid enantioselectively.