Peculiarities of Electron Transfer in Chiral Linked Systems

Abstract

Electron transfer (ET) is one of the most universal reactions in chemistry and biology. Recent studies conducted on the examples of photoinduced ET (PET) in chiral linked systems (dyads) have shown several important features indicative for ET in chiral systems. The peculiarity of processes with PET in such systems is primarily the stereoselectivity; there is difference in ET rates and fluorescence quantum yields in dyad diastereomers. The next feature is the spin selectivity of back ET in the biradical-zwitterions (BZs) that are formed under the dyad diastereomer UV irradiation. This is the difference in the enhancement coefficients of chemically induced dynamic nuclear polarization (CIDNP) originated in BZs. The probable cause of this effect is the variation in the spin density values, resulting from difference in the spatial structure of BZ in (R,S)-and (S,S)-configurations. The latter, in turn, is due to the fact that these dyads react in the form of associates-dimers. The impact of dimerization on the effectiveness of ET in chiral systems is an example of the chiral catalysis. The study of ET in chiral linked systems reveals reasons for the various reactivities of chiral molecules, including the difference in therapeutic activity of drug enantiomers.

Stereoselectivity of Electron and Energy Transfer in the Quenching of (S/R)-Ketoprofen-(S)-Tryptophan Dyad Excited State

“…It is also worth noting that in all previously studied chiral dyads, the fluorescence of ( R,S )-diastereomers was quenched more efficiently than for ( S,S ) analogues [ 5 , 6 , 7 ]. This also occurs in single-chromophore systems, where fluorescence quenching is exclusively the result of ET [ 4 , 5 , 6 , 7 , 12 ]. Additionally, the results of this study show that one of the most defining properties of chiral systems is the stereospecificity of their activity.…”

“…It is also worth noting that in all previously studied chiral dyads, the fluorescence of (R,S)-diastereomers was quenched more efficiently than for (S,S) analogues [5][6][7]. This also occurs in single-chromophore systems, where fluorescence quenching is exclusively the result of ET [4][5][6][7]12].…”

“…In recent decades, studies of photoinduced ET in linked systems-dyads with two chiral biologically active partners (drugs, amino acids)-have attracted considerable attention [3][4][5][6][7]. This interest is due to the fact that such dyads are considered as a model to study the mechanisms of drugs binding with enzymes and receptors.…”

“…Although all active sites include chiral amino acid residues, the model is relevant when the interaction between drugs and protein involves stages with charge transfer [7]. Therefore, there is a point of view that upon the binding of chiral drug with the amino acids located in the active site of the enzymes or receptors, an analogue of diastereomer is formed [4][5][6][7].…”

Optical Configuration Effect on the Structure and Reactivity of Diastereomers Revealed by Spin Effects and Molecular Dynamics Calculations

“…Calculations have shown that the spin selectivity can be explained by the difference in the HFI Scheme 1. The path of the CIDNP formation under the UV irradiation of dyads I-II, where naproxen (NPX) linked with N-methylpyrrolidine (Pyr) [5]. The quantitative aspects of photoexcitation degradation are described in detail in Supplementary Materials (Scheme S1).…”