Preparation of anthryl group-tagged helical poly(γ-benzyl L-glutamate) self-assembled film on gold surface and its interaction with DNA

A novel poly(γ-benzyl-L-glutamate) (PBLG, 1), which has an anthryl group at the C-terminus of PBLG segment, has been synthesized, and its immobilization onto gold surface based on a specific interhelix interaction and DNA binding property at a self-assembled monolayer surface have been studied. A PBLG carrying a S-S bond at the C-terminus, 3, formed self-assembled monolayers on a gold surface. Within a resulting monolayer of 3, helical rods of the PBLG segment were oriented in the antiparallel manner, allowing an attractive interaction between helix macrodipoles. When a helix-breaking solvent such as DMSO was added to the solution, about a half amount of the adsorbate was released from the monolayer, followed by weakening the interhelix interaction, and a porous monolayer including molecular cavities was formed. Such a cavity size should fit the occupied volume of the helices present in the original assembly. Guest helices of 1 and 2, which has a similar molecular structure to that of I except for the lack of the anthryl moiety, could interact with the host porous monolayer of 1 on gold substrates. The binding properties of DNA onto 1, 2, and 3 mixed monolayers, in which anthryl groups must be located at the monolayer surface, were examined by means of quartz crystal microbalance and X-ray photoelectron spectroscopy. The results indicated that DNA bound to the PBLG mixed monolayers when the anthryl groups at the monolayer surface were in an optimized distribution.