Vladimir V. Zhivonitko

arXiv2026

Mechanistic Insights into Chemical Exchange during the Signal Amplification by Reversible Exchange Sensitization of Pyruvate

Signal amplification by reversible exchange (SABRE) is a nuclear spin hyperpolarization technique in which the transient interaction of parahydrogen (pH2) and a target substrate with an iridium complex leads to polarization transfer to the substrate. Here, we use a parahydrogen-enhanced, spin-selective NMR method to investigate pyruvate binding, which is combined with exchange-model fitting and DFT calculations. Our study reveals several key findings that reshape the current understanding of SABRE: (a) intramolecular hydrogen exchange of the hydrides, occurring faster than pyruvate or H2 loss; (b) the discovery of a novel stable [Ir(H)2(IMes)(\k{appa}1-pyr)(DMSO)2] complex; and (c) the potential role of counterions (here Na+) in Ir-pyruvate binding. Previously unknown insights into complex kinetics and distributions as a function of temperature, [DMSO], [pyruvate], and hydrogen pressure are presented. The methods demonstrated here, exemplified by SABRE, provide a framework that is expected to guide future research in the field.

physics.chem-ph↗

arXiv2024

Diversity of Parahydrogen-Induced Hyperpolarization Effects in Chemistry

Nuclear spin hyperpolarization utilizing parahydrogen has the potential for broad applications in chemistry, biochemistry, and medicine. This review examines recent chemical and biochemical insights gained using parahydrogen-induced polarization (PHIP). We begin with photo-induced PHIP, which allows the investigation of short-lived and photo-activated catalysis. Next, we review the partially negative line effect, in which distinctive lineshape helps to reveal information about rapid exchange with parahydrogen and the role of short-lived catalytic species. The NMR signal enhancement of a single proton in oneH-PHIP is discussed, challenging the underpinning concept of the necessity of pairwise hydrogenation. Furthermore, we examine metal-free PHIP facilitated by novel molecular tweezers and radicaloids, demonstrating alternative routes to conventional hydrogenation using metal-based catalysts. Although symmetric molecules incorporating parahydrogen are NMR silent, we showcase methods that reveal hyperpolarized states through post-hydrogenation reactions. We discuss chemical exchange processes that mediate polarization transfer between parahydrogen and a molecular target, expanding the reach of PHIP without synthesizing specialized precursors. We conclude this review by highlighting the role of PHIP in uncovering the H2 activation mechanisms of hydrogenases. By providing a detailed review of these diverse phenomena, we aim to familiarize the reader with the versatility of PHIP and its potential applications for mechanistic studies and chemical analysis.

physics.chem-ph↗