FORMATION OF ORIENTED HELICAL PEPTIDE LAYERS ON A GOLD SURFACE DUE TOTHE SELF-ASSEMBLING PROPERTIES OF PEPTIDES

Several hydrophobic alpha-helical peptides containing a disulfide grou p were synthesized, and the formation of oriented self-assembled monol ayers (SAMs) on gold surface was investigated. The orientation of heli ces in the SAMs was determined by Fourier transform infrared reflectio n-absorption spectroscopy measurements. The tilt angle of the helix ax is from the surface normal was sensitively affected by the choice of s olvent used in the preparation of SAMs, the nature of component amino acids, the molecular structure (either one-helix or two-helix peptide) , and the length of peptide chain. The tilt angle was smaller when eth anol was used in the preparation of SAMs rather than N,N-dimethylforma mide. Lipo-(Ala-Aib)(8)-OBzl (Lipo and OBzl represent a lipoic acid gr oup and a benzyl ester group, respectively) showed a smaller tilt angl e than Lipo-(Lys(Z)-Aib)(8)-OCH3. A one-helix peptide with a Lipoic ac id group at the N-terminal showed a smaller tilt angle than a two-heli x peptide, in which the two helix peptides were connected by a disulfi de linkage. The longest peptide, Lipo-(Ala-Aib)(12)-OBzl, showed the s mallest tilt angle of 30 degrees when the SAM was prepared in an ethan ol solution. Taken together, helix-helix interaction should play a mor e important role in regulating the orientation of helical peptides in the SAM than the Au-disulfide interaction. Lipo(Ala-Aib)(12)-OBzl form ed a nearly vertically oriented SAM with a parallel orientation of hel ices due td the highly self-assembling properties of the peptide.