PEPTIDE CONFORMATIONAL DYNAMICS AND VIBRATIONAL STARK EFFECTS FOLLOWING PHOTOINITIATED DISULFIDE CLEAVAGE

Photoinitiation of relaxation of two peptides (labeled 1 and 2) and spectroscopic studies of the ensuing dynamics have led to new information about peptide conformational dynamics. Following photolysis of the aryl disulfide chromophore that constrains a peptide to be distorted from its equilibrium form, the S−S bond is broken in <200 fs, and the liberated thiyl radicals either undergo geminate recombination or diffuse apart to allow the peptides to change conformation. From anisotropy measurements, overall peptide rotation is on the time scale of 600 ps. At an even earlier time (ca. 100 ps), transient IR measurements show a bleaching of the amide I‘ region, arising from a vibrational Stark effect produced upon ring opening of peptide 2. We did not detect any significant shift in the amide I‘ region up to 2 ns, suggesting no significant helix formation in this time domain. Thiyl radicals arising from peptide 2 recombine with a power law rate over the time range from picoseconds to microseconds signaling an...