Chemically Induced Spin Hyperpolarization: Coherence Formation in Reaction Products

Abstract

Chemically induced dynamic nuclear polarization (CIDNP) has emerged as a highly informative method to study spin-dependent radical reactions by analyzing enhanced NMR (nuclear magnetic resonance) signals of their diamagnetic reaction products. In this way, one can probe the structure of elusive radical intermediates and determine their magnetic parameters. A careful examination of experimental CIDNP data at variable magnetic fields shows that formation of hyperpolarized molecules in a coherent state is a ubiquitous though rarely discussed phenomenon. The presence of nuclear spin coherences commonly leads to subsequent polarization transfer among coupled spins in the diamagnetic products of radical recombination reaction that must be taken into account when analyzing the results of CIDNP experiments at low magnetic field. Moreover, such coherent polarization transfer can be efficiently exploited to polarize spins, which do not acquire CIDNP directly. Here we explain under what conditions such coherences can be generated, focusing on the key role of level anti-crossings in coherent polarization transfer, and provide experimental approaches to probing nuclear spin coherences and their time evolution. We illustrate the theoretical consideration of the outlined coherent spin phenomena in CIDNP by examples, obtained for the dipeptide tryptophan–tryptophan.

Impact of Non-Covalent Interactions of Chiral Linked Systems in Solution on Photoinduced Electron Transfer Efficiency

“…An analysis of the time-resolved CIDNP effects in the photoinduced ET in the dyad II, performed in this work, according to existing rules, confirmed the realization of ET through the formation of BZ [15]. In addition, CIDNP effects observed under the UV irradiation of a mixture of diastereomers in solutions have shown a strong dependence of the K values of diastereomers on the ratio of their concentrations for dyads I-III (Figure 3).…”

“…The study of the dyad III by CIDNP and fluorescence quenching methods has already been performed, and it demonstrated several peculiarities [14,15]. The ratio of the observed CIDNP coefficients of the SS and (RS, SR) configurations is 9.8, instead of 2, detected for dyads I and II.…”

“…An analysis of the CIDNP effects allows one to obtain a portrait of the radical precursors of polarized products (hyperfine interaction constants (HFI), g-factors, etc.) [15]. Today, CIDNP is one of the most informative, albeit indirect, methods for identifying short-lived radical particles [15].…”

“…[15]. Today, CIDNP is one of the most informative, albeit indirect, methods for identifying short-lived radical particles [15]. Two peculiarities of CIDNP effects in PET in chiral linked systems have been established [11][12][13].…”

Recent advances in the application of parahydrogen in catalysis and biochemistry

“…Konstantin Ivanov proposed, in analogy to the well-known spincorrelated radical pair model from Spin Chemistry 88 explaining the origin of the chemically induced dynamic nuclear polarization (CIDNP), [89][90][91][92] a pictorial description of the spin-dynamics of the spin-pair (see in Fig. 3).…”