Nonequilibrium Spin States Research Articles

Bridging the Gap: From Homogeneous to Heterogeneous Parahydrogen-induced Hyperpolarization and Beyond.

Demonstration of parahydrogen-induced polarization effects in hydrogenations catalyzed by heterogeneous catalysts instead of metal complexes in a homogeneous solution has opened an entirely new dimension for parahydrogen-based research, demonstrating its applicability not only for the production of catalyst-free hyperpolarized liquids and gases and long-lived non-equilibrium spin states for potential biomedical applications, but also for addressing challenges of modern fundamental and industrial catalysis including advanced mechanistic studies of catalytic reactions and operando NMR and MRI of reactors. This essay summarizes the progress achieved in this field by highlighting the research contributed to it by our colleague and friend Kirill V. Kovtunov whose scientific career ended unexpectedly and tragically at the age of 37. His role in this research was certainly crucial, further enhanced by a vast network of his contacts and collaborations at the national and international level.

Multiple Quantum Coherences Hyperpolarized at Ultra-Low Fields.

The development of hyperpolarization technologies enabled several yet exotic NMR applications at low and ultra‐low fields (ULF), where without hyperpolarization even the detection of a signal from analytes is a challenge. Herein, we present a method for the simultaneous excitation and observation of homo‐ and heteronuclear multiple quantum coherences (from zero up to the third‐order), which give an additional degree of freedom for ULF NMR experiments, where the chemical shift variation is negligible. The approach is based on heteronuclear correlated spectroscopy (COSY); its combination with a phase‐cycling scheme allows the selective observation of multiple quantum coherences of different orders. The nonequilibrium spin state and multiple spin orders are generated by signal amplification by reversible exchange (SABRE) and detected at ULF with a superconducting quantum interference device (SQUID)‐based NMR system.

Sharp increase of microwave absorption in nonequilibrium MnZn- and NiZn-nanoferrites

We study microwave electromagnetic absorption in films containing (Mn,Zn)Fe2O4 and (Ni,Zn)Fe2O4 spinel nanoparticles in equilibrium and nonequilibrium spin states. The nonequilibrium spin state has been formed by the action of the alternating magnetic field with the frequency of 1 Hz. It is found that in the nonequilibrium state the microwave absorption is strongly enhanced. The microwave losses are increased by 78 times for the film with MnZn-spinel nanoparticles and by 12 times for the film containing NiZn-nanoferrite. The microwave-absorption-increase effect is observed in the central part of the ferromagnetic resonance frequency band. This frequency band of the microwave absorption enhancement is narrower than the ferromagnetic linewidth in the equilibrium state.

Polarization Transfer from Ligands Hyperpolarized by Dissolution Dynamic Nuclear Polarization for Screening in Drug Discovery.

Nuclear magnetic resonance (NMR) spectroscopy is a valuable technique for ligand screening, because it exhibits high specificity toward chemical structure and interactions. Dissolution dynamic nuclear polarization (DNP) is a recent advance in NMR methodology that enables the creation of non-equilibrium spin states, which can dramatically increase NMR sensitivity. Here, the transfer of such spin polarization from hyperpolarized ligand to protein is observed. Mixing hyperpolarized benzamidine with the serine protease trypsin, a "fingerprint" of enhanced protein signals is observed, which shows a different intensity profile than the equilibrium NMR spectrum of the protein, but coincides closely to the frequency profile of a saturation transfer difference (STD) NMR experiment. The DNP experiment benefits from hyperpolarization and enables observation of all frequencies in a single, rapid experiment. Based on these merits, it is an interesting alternative to the widely used STD experiment for identification of protein-ligand interactions.

Spin injection induced phase transition in YBa2Cu3O7−δ/Nd0.35Sr0.65MnO3 bilayer

The spin injection effects from C-type antiferromagnetic Nd0.35Sr0.65MnO3 (NSMO) to superconductor YBa2Cu3O7−δ (YBCO) are investigated via the measurement of temperature dependent resistivity with input current from 10−2 mA to 90 mA. The superconducting transition temperature (Tco) of YBCO decreases with increasing current but at a higher rate with larger thickness of NSMO. Two spin states below Tco are identified as non-equilibrium spin-state and pair-breaking state judging from the width of transition. In particular, the transition from former to later one is observed with NSMO = 30 nm at the current of 30 mA.

Nuances of multi-quantum excitation in solid state NMR of quadrupolar nuclei

In this article, a simple heuristic approach that is in agreement with the density operator formalism is presented for understanding the mechanism of multi-quantum (MQ) excitation in half-integral quadrupolar systems. Employing the population level diagram of the nuclear spin states, the effect of radio-frequency (RF) pulses on multi-level systems is described. Based on this approach, alternate schemes that involve non-equilibrium spin states are proposed for improving the sensitivity of MQ experiments in spin 3/2 and 5/2 systems. Additionally, the utility of frequency sweep techniques in the excitation of MQ transitions is discussed. The results obtained from the analytic theory are substantiated through numerical simulations.

Hyperpolarized 13C metabolic imaging using dissolution dynamic nuclear polarization

This article describes the basic physics of dissolution dynamic nuclear polarization (dissolution-DNP), and the impact of the resulting highly nonequilibrium spin states, on the physics of magnetic resonance imaging (MRI) detection. The hardware requirements for clinical translation of this technology are also presented. For studies that allow the use of externally administered agents, hyperpolarization offers a way to overcome normal magnetic resonance sensitivity limitations, at least for a brief T(1)-dependent observation window. A 10,000-100,000-fold signal-to-noise advantage provides an avenue for real-time measurement of perfusion, metabolite transport, exchange, and metabolism. The principles behind these measurements, as well as the choice of agent, and progress toward the application of hyperpolarized (13)C metabolic imaging in oncology, cardiology, and neurology are reviewed.

Polarization field in a single-valley strongly-interacting 2D electron system

The magnetic field of complete spin polarization is calculated in a disorderless single-valley strongly-interacting 2D electron system. In the metallic region above the Wigner-Mott transition, non-equilibrium spin states are predicted, which should give rise to hysteresis in the magnetization.

NMR study of transport of nuclear spin polarization in sodium hypophosphite NaH 2PO 2· nH 2O

A process of spin polarization transfer between two groups of protons in sodium hypophosphite NaH 2PO 2· nH 2O, governed by the flip–flop mechanism under resonance conditions, is analyzed in this work. Phenomenological description is obtained for interpretation of transfer of non-equilibrium spin states from one system to another. Good agreement between our calculations and experiment makes it possible to find characteristic time τ of the process, the best conditions for its registration and time of spin–lattice relaxation T 1 for both spin systems.

Cyclotron resonance of InAs/AlSb single quantum well in high magnetic fields and spin relaxation process

Spin-split cyclotron resonance (CR) of InAs/AlSb single quantum well exhibits a new type hysteresis in strong magnetic fields at low temperature. Pulsed high magnetic fields up to 150T with a duration of 6μs were generated by the single turn coil technique. The hysteresis was observed in the up and down sweep process of the fields with Bmax≳ 60T. This suggests that a non-equilibrium spin-state in the lowest Landau level is induced due to a slow spin reversal rate 1/T1≈107s−1. Two mechanisms for the spin reversal process are proposed: (i) Direct LO–phonon process and (ii) Raman process associated with LO–phonon emission and acoustic phonon absorption. These processes can well explain the characteristic feature of the hysteresis.

Nonequilibrium spin states and tunnel paramagnetic centers in copper oxide CuO

It is shown that the formation of tunnel paramagnetic centers — triplet spin centers with a strongly different adiabatic potential in different spin states — can form in copper oxides based on CuO clusters. The results of measurements of the magnetization and magnetostriction of CuO single crystals are reported. They attest to the presence of nonequilibrium spin states and confirm the results obtained in the model of tunnel paramagnetic centers.

Three-quantum nuclear magnetic resonance spectroscopy of liquid water: Intermolecular multiple-quantum coherence generated by spin–cavity coupling

We show experimentally and theoretically that coupling between a spin system and the NMR probe, which is responsible for radiation damping, can also act to generate multiple-quantum coherences, even in molecules such as water which ordinarily have no multiple-quantum spectrum. We discuss the implications of this observation for solvent suppression sequences and for preparing nonequilibrium spin states.