Chiral discrimination in the hydrogen-atom transfer between tyrosine and benzophenone in rigid peptides

The present study was undertaken in order to address possible chiral discrimination in the intramolecular abstraction of phenolic hydrogens by benzophenone triplets in suitably constructed molecular dyads. Nanosecond time-resolved laser flash photolysis experiments have been performed to probe the stereoselectivity of the triplet quenching in cyclic dipeptides containing two chromophores: benzophenone and phenol. These experiments revealed marked stereoselectivity of the hydrogen-atom transfer due to the structural constraints of the peptide matrix. Extensive density functional theory (DFT) calculations have been performed to gain an understanding of the geometrical requirements underpinning these observed differences.