Fast Structural Transformations of Organic Molecules

Peptide Conformational Dynamics and Vibrational Stark Effects Following Photoinitiated Disulfide Cleavage

“…100 fs time resolution of the instrument. The transients compare well with typical absorbance spectra of p -aminophenylthiyl radicals and p -tolylthiyl radicals, ,, showing that fast photocleavage of the disulfide bond has taken place. From the observed transient absorbance we estimated a disulfide bond dissociation quantum yield of 0.10 ± 0.04 at a delay time of 0.5 ps for peptide 2 .…”

“…This behavior is similar to that observed for p -aminophenylthiyl radicals after photolysis of bis( p -aminophenyl) disulfide in acetonitrile, which was attributed to dielectric and vibrational relaxation. Part of the shift is believed to arise from an internal charge separation between the amino group and the sulfur atom, as is discussed further below. On a longer time scale, the width of the absorbance band (fwhm) increases from 115 nm at 50 ps to 130 nm at 3.5 ns without any significant shift of the position of the maximum (Figure B).…”

“…This interpretation is consistent with studies of model compounds. Significant geminate (cage) recombination of phenylthiyl radical pairs was seen after photolysis of diphenyl disulfide. , On the other hand, no geminate recombination of aminophenylthiyl radical pairs was detected after photolysis of bis( p -aminophenyl) disulfide in polar solvents . We designed peptide 2 based on this reported lack of geminate recombination of p -aminothiyl radicals.…”

“…A number of processes can be expected to occur after the light is absorbed. The bond-breaking step is known to occur on the femtosecond time scale from studies with model compounds. − After dissociation the radicals may undergo recombination to form the original disulfide. For model disulfides that are not constrained by the peptide the recombination has a geminate phase that is kinetically distinct from the diffusion-controlled bimolecular recombination.…”

Chemical reaction dynamics of some simple molecules in solution

“…The photodissociation of many aromatic disulphides into arylthiyl radicals has been studied by using ultrafast spectroscopic methods and geminate recombination was reported in some cases (Autrey et al 1995;Borisevich et al 1990Borisevich et al , 1992Bultmann & Ernsting 1996;Ernsting 1993;Hirata et al 1997;Nakamura et al 1980;Scott & Liu 1989). As a preliminary to our recent studies of disulphide bond cleavage in model peptides (Lu et al 1997;Volk et al 1997b) we carried out femtosecond measurements on a number of aromatic disulphides.…”