Excitation of singlet–triplet coherences in pairs of nearly-equivalent spins

We present approaches for an efficient excitation of singlet–triplet coherences in pairs of nearly-equivalent spins. Standard Nuclear Magnetic Resonance (NMR) pulse sequences do not excite these coherences at all or with very low efficiency. The single quantum singlet–triplet coherences, here termed the outer singlet–triplet coherences, correspond to lines of low intensity in the NMR spectrum of a strongly-coupled spin pair (they are sometimes referred to as “forbidden transitions”), whereas the zero-quantum coherences, here termed the inner singlet–triplet coherences, do not have a direct spectral manifestation. In the present study, we investigated singlet–triplet coherences in a pair of …

Geminal Parahydrogen-Induced Polarization: Accumulating Long-Lived Singlet Order on Methylene Proton Pairs

In the majority of hydrogenative parahydrogen-induced polarization (PHIP) experiments, the hydrogen molecule undergoes pairwise cis addition to an unsaturated precursor to occupy vicinal positions on the product molecule. However, some ruthenium-based hydrogenation catalysts induce geminal hydrogenation, leading to a reaction product in which the two hydrogen atoms are transferred to the same carbon centre, forming a methylene (CH2) group. The singlet order of parahydrogen is substantially retained over the geminal hydrogenation reaction, giving rise to a singlet-hyperpolarized CH2 group. Although the T1 relaxation times of the methylene protons are often short, the singlet order has a long…

Singulett‐Kontrast‐Magnetresonanztomographie: Freisetzung der Hyperpolarisation durch den Metabolismus**

Singlet‐Contrast Magnetic Resonance Imaging: Unlocking Hyperpolarization with Metabolism

Abstract Hyperpolarization‐enhanced magnetic resonance imaging can be used to study biomolecular processes in the body, but typically requires nuclei such as 13C, 15N, or 129Xe due to their long spin‐polarization lifetimes and the absence of a proton‐background signal from water and fat in the images. Here we present a novel type of 1H imaging, in which hyperpolarized spin order is locked in a nonmagnetic long‐lived correlated (singlet) state, and is only liberated for imaging by a specific biochemical reaction. In this work we produce hyperpolarized fumarate via chemical reaction of a precursor molecule with para‐enriched hydrogen gas, and the proton singlet order in fumarate is released a…

Polarization transfer via field sweeping in parahydrogen-enhanced nuclear magnetic resonance.

<div><br></div><div><table><tr><td>We show that in a spin system of two magnetically inequivalent protons coupled to a heteronucleus such as 13C, an adiabatic magnetic field sweep, passing through zero field, transfers proton singlet order into magnetization of the coupled heteronucleus. This effect is potentially useful in parahydrogen-enhanced nuclear magnetic resonance, and is demonstrated on singlet-hyperpolarized [1-13C]maleic acid, which is prepared via the reaction between [1-13C]acetylene dicarboxylic acid and para-enriched hydrogen gas. The magnetic field sweeps are of microtesla amplitudes, and have durations on the order of seconds. We sh…

Algorithmic cooling of nuclear spins using long-lived singlet order

Algorithmic cooling methods manipulate an open quantum system in order to lower its temperature below that of the environment. We achieve significant cooling of an ensemble of nuclear spin-pair systems by exploiting the long-lived nuclear singlet state, which is an antisymmetric quantum superposition of the "up" and "down" Zeeman states. The effect is demonstrated by nuclear magnetic resonance (NMR) experiments on a molecular system containing a coupled pair of near-equivalent 13C nuclei. The populations of the system are subjected to a repeating sequence of cyclic permutations separated by relaxation intervals. The long-lived nuclear singlet order is pumped well beyond the unitary limit. T…

<i>Geminal</i> Parahydrogen-Induced Polarization: Accumulating Long-Lived Singlet Order on Methylene Proton Pairs

Abstract. In the majority of hydrogenative PHIP (Parahydrogen Induced Polarization) experiments, the hydrogen molecule undergoes pairwise cis-addition to an unsaturated precursor to occupy vicinal positions on the product molecule. However, some ruthenium-based hydrogenation catalysts induce geminal hydrogenation, leading to a reaction product in which the twohydrogen atoms are transferred to the same carbon center, forming a methylene (CH2) group. The singlet order of parahydrogen is substantially retained over the geminal hydrogenation reaction, giving rise to a singlet-hyperpolarized CH2 group. Although the T1 relaxation times of the methylene protons are often short, the singlet order h…

Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution

Significance Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by…

Algorithmic Cooling of Nuclear Spin Pairs using a Long-Lived Singlet State

Algorithmic cooling methods manipulate an open quantum system in order to lower its temperature below that of the environment. We show that significant cooling is achieved on an ensemble of spin-pair systems by exploiting the long-lived nuclear singlet state, which is an antisymmetric quantum superposition of the "up" and "down" qubit states. The effect is demonstrated by nuclear magnetic resonance (NMR) experiments on a molecular system containing a coupled pair of near-equivalent 13C nuclei. The populations of the system are subjected to a repeating sequence of cyclic permutations separated by relaxation intervals. The long-lived nuclear singlet order is pumped well beyond the unitary lim…