MACRODIPOLE INTERACTION OF HELICAL-PEPTIDES IN A SELF-ASSEMBLED MONOLAYER ON GOLD SUBSTRATE

Monolayers of helical peptides on gold substrates were prepared by a s elf-assembly approach aiming at fabricating a regular structure by the use of the specific interaction between neighboring helices. Two kind s of helical peptides were synthesized. One has a disulfide group at t he N-terminal of the helix part, and the other, at the C-terminal of t he same helix. Self-assembled monolayers (SAMs) were prepared by dippi ng a gold substrate into each peptide solution. The thickness and the molecular orientation of each monocomponent SAM indicated that the hel ical peptides were adsorbed on the surface with a preferred orientatio n parallel to the surface. However, those of an equimolar mixed SAM sh owed that the peptide took an appreciably vertical orientation on the surface. These observations indicated that an antiparallel helix packi ng is significantly more favorable than a parallel one. It is strongly suggested that the SAM structure is regulated by a dipolar interactio n between helical peptides since the geometric fitting among the molec ules in the parallel packing could be hardly different from that in th e antiparallel packing.