Spin Selectivity in Chiral Linked Systems

Abstract

This work has shown spin selectivity in electron transfer (ET) of diastereomers of (R,S)-naproxen-(S)-N-methylpyrrolidine and (R,S)-naproxen-(S)-tryptophan dyads. Photoinduced ET in these dyads is interesting because of the still unexplained phenomenon of stereoselectivity in the drug activity of enantiomers. The chemically induced dynamic nuclear polarization (CIDNP) enhancement coefficients of (R,S)-diastereomers are double those of the (S,S)-analogue. These facts are also interesting because spin effects are among the most sensitive, even to small changes in spin and molecular dynamics of paramagnetic particles. Therefore, CIDNP reflects the difference in magnetoresonance parameters (hyperfine interaction constants (HFIs), g-factor difference) and lifetimes of the paramagnetic forms of (R,S)- and (S,S)-diastereomers. The difference in HFI values for diastereomers has been confirmed by a comparison of CIDNP experimental enhancement coefficients with those calculated. Additionally, the dependence of the CIDNP enhancement coefficients on diastereomer concentration has been observed for the naproxen-N-methylpyrrolidine dyad. This has been explained by the participation of ET in homo-(R,S-R,S or S,S-S,S) and hetero-(R,S-S,S) dimers of dyads. In this case, the effectivity of ET, and consequently, CIDNP, is supposed to be different for (R,S)- and (S,S)-homodimers, heterodimers, and monomers. The possibility of dyad dimer formation has been demonstrated by using high-resolution X-ray and NMR spectroscopy techniques.

Role of Association in Chiral Catalysis: From Asymmetric Synthesis to Spin Selectivity

“…Two dyads have demonstrated a new peculiarity of chiral systems: spin selectivity of ET. Spin selectivity manifests itself as a difference in the CIDNP enhancement coefficients of the ( R , S ) and ( S , S ) dyad diastereomers . Because the effects of CIDNP, formed under UV irradiation of diastereomer mixtures, correlate with dimer concentrations (( R , S )‐( R , S ), ( S , S )‐( S , S ) and ( R , S )‐( S , S )), ET might be considered another example of chiral catalysis.…”

“…As a matter of fact, chiral catalysis has recently been experimentally detected in the elementary process of ET occurring in donor–acceptor chiral dyads . Two dyads have demonstrated a new peculiarity of chiral systems: spin selectivity of ET.…”

“…The source of spin selectivity has been shown to be the difference in magnetic resonance parameters, namely, the hyperfine interaction (HFI) constants in the paramagnetic forms of the ( R , S ) and ( S , S ) diastereomers. These paramagnetic particles are formed through intramolecular photoinduced ET in dimers of dyads …”

“…The donor–acceptor interaction in these dyads can be considered as a model of drug–enzyme binding . In turn, the spin selectivity of ET in diastereomers with ( S )‐ and ( R )‐NPX suggests some difference in the oxidation–reduction properties of enantiomers as a part of diastereomers.…”

Kinetics of Reversible Protonation of Transient Neutral Guanine Radical in Neutral Aqueous Solution

“…[18][19] This is a nuclear magnetic resonance (NMR) phenomenon, which arises in spinselective recombination of radicals and is observed as anomalously enhanced intensity of absorptive or even emissive phase of the NMR spectral lines of diamagnetic products of radical reactions. [23] Important practical aspects of the CIDNP application in organic and physical chemistry are detailed in several recent reviews. The hyperpolarization formed is sensitive to the magnetic resonance parameters of the radicals and therefore allows for determination of structure of shortlived radicals.…”