| Abstract
| - A series of thioxo compounds, thioacetamide, N-methylthioacetamide, a cyclic thioxoamide [(S)-5-thioxopyrrolidine-2-carboxylic acid ethyl ester], two thioxylated dipeptides (Ala-Ψ[CS-NH]-Ala and Phe-Ψ[CS-NH]-Ala) and a thioxylated dodecapeptide (Lys-Glu-Thr-Ala-Ala-Ala-Lys-Phe-Glu-Arg-Gln-His-Ψ[CS-NH]-Nle-Asp-Ser-Ser-Thr-Ser-Ala-Ala, or [thioxo-His12]-S-peptide; Nle = norleucine) are investigated byultrafast spectroscopy in the visible and near UV. The different molecules show very similar absorptiondynamics featuring a rise of a strong visible absorption band on the subpicosecond and picosecond timescale. The decay of the visible absorption occurs within 150−600 ps. The observations are interpreted by theultrafast formation of triplet states and their decay on the subnanosecond time scale. Comparison with publishedIR experiments on N-methylthioacetamide indicates that the cis−trans isomerization around the thioxopeptidebond is terminated within less than 1 ns.
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