Role of Chiral Configuration in the Photoinduced Interaction of D- and L-Tryptophan with Optical Isomers of Ketoprofen in Linked Systems

• Main Authors: Aleksandra A. Ageeva, Ilya M. Magin, Alexander B. Doktorov, Victor F. Plyusnin, Polina S. Kuznetsova, Alexander A. Stepanov, Alexander A. Alekseev, Nikolay E. Polyakov, Tatyana V. Leshina
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: International Journal of Molecular Sciences
• Subjects: chiral linked systems; diastereomers; enantiomers; electron transfer; resonance energy transfer; magnetic dipole–dipole interaction of electrons
• Online Access: https://www.mdpi.com/1422-0067/22/12/6198

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 L- and D-tryptophan (Trp) in a model donor–acceptor dyad with (<i>R</i>)- and (<i>S</i>)-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: (<i>R,S</i>)-, (<i>S,R</i>)-, and (<i>S,S</i>)-. Thus, the ET efficiency is identical for (<i>S,R</i>)- and (<i>R,S</i>)-enantiomers, while RET differs by 1.6 times. For (<i>S,S</i>)-, the CIDNP coefficient is almost an order of magnitude greater than for (<i>R,S</i>)- and (<i>S,R</i>)-. To understand the source of this difference, hyperpolarization of (<i>S,S</i>)-and (<i>R,S</i>)- has been calculated using theory involving the electron dipole–dipole interaction in the secular equation.