Role of chiral configuration in the photoinduced interaction of d-and l-tryptophan with optical isomers of ketoprofen in linked systems

The study of the L-and D-amino acid properties in proteins and peptides has attracted considerable attention in recent years, as the replacement of even one L-amino acid by its D-analogue due to aging of the body is resulted in a number of pathological conditions, including Alzheimer’s and Parkinson’s diseases. A recent trend is using short model systems to study the peculiarities of proteins with D-amino acids. In this report, the comparison of the excited states quenching of Land D-tryptophan (Trp) in a model donor–acceptor dyad with (R)-and (S)-ketoprofen (KP-Trp) was carried out by photochemically induced dynamic nuclear polarization (CIDNP) and fluorescence spectroscopy. Quenching of the Trp excited states, which occurs via two mechanisms: prevailing resonance energy transfer (RET) and electron transfer (ET), indeed demonstrates some peculiarities for all three studied configurations of the dyad: (R,S)-, (S,R)-, and (S,S)-. Thus, the ET efficiency is identical for (S,R)-and (R,S)-enantiomers, while RET differs by 1.6 times. For (S,S)-, the CIDNP coefficient is almost an order of magnitude greater than for (R,S)-and (S,R)-. To understand the source of this difference, hyperpolarization of (S,S)-and (R,S)-has been calculated using theory involving the electron dipole–dipole interaction in the secular equation.