Intramolecular H-atom transfer reactions in rigid peptides — Correlated solvent and structural effects
A. Lewandowska, G. Hug, G. Hörner
Feb 15, 2011
Citations
4
Citations
Journal
Canadian Journal of Chemistry
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Semantic Scholar
Key Takeaway Key Takeaway: Intramolecular hydrogen-atom transfer reactions in rigid peptides are highly dependent on solvent and relative orientation, with rates ranging from 10 5 s-1 to 2 10 7 s-1, influenced by bulk viscosity and specific solvation effects.
Abstract
The rates and the mechanism of intramolecular hydrogen-atom transfer across the rigid diketopiperazine spacer in two epimeric benzophenone-tyrosine dyads were studied by nanosecond laser flash photolysis in 12 non-protic and protic solvents. Effects of the stereochemistry on the ground-state structures and conformational equilibria and dynamics have been addressed by means of NMR-based population analysis and long-term molecular-dynamics simulations. The ex- cited triplet state of the benzophenone is found to be quenched intramolecularly by the remote phenol moiety with rates that are highly dependent on the solvent and on the relative benzophenone-phenol orientation. In agreement with previous studies, the kinetic diversity, with rates ranging from <10 5 s -1 to 2 � 10 7 s -1 , can be attributed to retarding effects of the bulk viscosity and to effects of specific solvation, which can be both rate retarding and rate accelerating. As an extension of the previous knowledge, however, the phenomenology of the kinetic solvent effects, that is, the nature of the predomi- nating solvent parameter and its absolute impact on the reactivity, is found to be highly correlated with structural effects.