Stephansen, Anne Boutrup3; Larsen, Martin Alex Bjørn3; Klein, Liv Bærenholdt4; Sølling, Theis Ivan3
1 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet2 Department of Chemistry, Faculty of Science, Københavns Universitet3 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet4 Department of Chemistry, Faculty of Science, Københavns Universitet
an electronic or a structural property?
Photostability is an essential property of molecular building blocks of nature. Disulfides are central in the structure determination of proteins, which is in striking contradiction to the result that the S-S bond is a photochemically labile structural entity that cleaves to form free radicals upon light exposure. In an earlier contribution we hypothesized that the key to the photostability of some disulfides may be found in a cyclic structural arrangement. Here we provide further evidence to support this hypothesis by showing that straight chain disulfides undergo ultrafast S-S dissociation on a sub 50 fs timescale without further ado. In a cyclic motif resembling the cysteine-disulfide bond in proteins, light can perturb the S-S bond to generate short-lived diradicaloid species, but the sulfur atoms are conformationally restricted by the ring that prevents the sulfur atoms from flying apart. Conversely, in a straight chain conformation, light perturbation results in two separated R S · radicals because there is no restoring force to counteract the repulsive motion of the sulfur atoms. For the cyclic conformation this restoring force is provided by the cyclic framework, and thus the photostability of disulfide-bonds must be ascribed a cyclic structural arrangement.
Chemical Physics, 2014, Vol 442, p. 77-80
CASSCF; Disulfide; Photodissociation; Photostability; Time-resolved mass spectrometry