A Straightforward Method for the Generation of Hyperpolarized Orthohydrogen with a Partially Negative Line.

The hydrogen molecule, which exists in two spin isomers (ortho- and parahydrogen), is a highly studied system due to its fundamental properties and practical applications. Parahydrogen is used for Nuclear Magnetic Resonance signal enhancement, which is hyperpolarization of other molecules, including biorelevant ones. Hyperpolarization can be achieved by using Signal Amplification by Reversible Exchange (SABRE). SABRE can also convert parahydrogen into orthohydrogen, and surprisingly, in some cases, it has been discovered that orthohydrogen's resonance has the Partially Negative Line (PNL) pattern. Here, an approach for obtaining orthohydrogen with a PNL signal is presented for two catalysts: Ir-IMes, and Ir-IMesBn. The type of solvent in which SABRE is conducted is crucial for the observation of PNL. Specifically, a PNL signal can be easily generated in benzene using both catalysts, but it is more intense for Ir-IMesBn. In acetone, PNL is observed only for Ir-IMesBn. In methanol, no PNL is detected. The PNL effect is only detectable during the initial steps of pre-catalyst activation, and disappears as the activation process progresses. We have proposed a working hypothesis that explains our results. The presented data may facilitate the further investigation of PNL and its applications in material science and catalysis.

Two fields are better than one - A multifunctional (semi)automated setup for quantitative measurements of parahydrogen-induced signal enhancement at low and high fields.

The rapid advancement of parahydrogen-induced hyperpolarization (PHIP) and its diverse array of applications highlights the critical need for enhanced signals in both 1H NMR and heteronuclear NMR spectroscopy. Simultaneously, there is an increasing interest in utilizing benchtop NMR analysis across various laboratory settings. However, due to their lower magnetic fields, benchtop NMR spectrometers inherently produce weaker signal intensities. Here, PHIP is a well-established solution to this challenge. Consequently, we are expanding our cost-effective PHIP setup from a high-field NMR spectrometer (11.7 T) to include an additional benchtop NMR spectrometer (1.4 T), thereby enabling concurrent execution of PHIP experiments and measurements. Through the implementation of automated experimental protocols, we aim to minimize experiment time while increasing reproducibility. In this work, a non-isotope labelled propargyl alcohol sample is used at low concentrations to demonstrate our setup's capabilities. It could be shown that single-scan PASADENA experiments can be run with comparable signal enhancements at the benchtop as well as the high-field spectrometer. At 1.4 T, fully automated PHIP pseudo-2D measurements will also be demonstrated. Additionally, two different field profiles for the spin-order transfer of p-H2 to 13C at zero- to ultralow fields are elaborated upon. The setup facilitates the measurement of carbon signal enhancement of more than 2000 on the benchtop NMR spectrometer, employing a straightforward one-pulse, one-scan experiment.

Parahydrogen-induced polarization enables the single-scan NMR detection of a 236 kDa biopolymer at nanomolar concentrations.

Nuclear magnetic resonance (NMR) experiments utilizing parahydrogen-induced polarization (PHIP) were performed to elucidate the PHIP activity of the synthetic 236 kDa biopolymer poly-γ-(4-propargyloxy)-benzyl-L-glutamate) (PPOBLG). The homopolypeptide was successfully hyperpolarized and the enhanced signals were detected in 11.7 T solution NMR as a function of the PPOBLG concentration. The hydrogenation with parahydrogen caused signal enhancements of 800 and more for the vinyl protons of the side chain at low substrate concentration. As a result of this high enhancement factor, even at 13 nM of PPOBLG, a single scan 1H-NMR detection of the hyperpolarized protons was possible, owing to the combination of hyperpolarization and density of PHIP active sites.

Parahydrogen-induced polarization allows 2000-fold signal enhancement in biologically active derivatives of the peptide-based drug octreotide.

Octreotide, a somatostatin analogue, has shown its efficacy for the diagnostics and treatment of various types of cancer, i.e., in octreotide scan, as radio-marker after labelling with a radiopharmaceutical. To avoid toxicity of radio-labeling, octreotide-based assays can be implemented into magnetic resonance techniques, such as MRI and NMR. Here we used a Parahydrogen-Induced Polarization (PHIP) approach as a cheap, fast and straightforward method. Introduction of L-propargyl tyrosine as a PHIP marker at different positions of octreotide by manual Solid-Phase Peptide Synthesis (SPPS) led to up to 2000-fold proton signal enhancement (SE). Cell binding studies confirmed that all octreotide variants retained strong binding affinity to the surface of human-derived cancer cells expressing somatostatin receptor 2. The hydrogenation reactions were successfully performed in methanol and under physiologically compatible mixtures of water with methanol or ethanol. The presented results open up new application areas of biochemical and pharmacological studies with octreotide.

Recent advances in the application of parahydrogen in catalysis and biochemistry.

Nuclear Magnetic Resonance (NMR) spectroscopy and Magnetic Resonance Imaging (MRI) are analytical and diagnostic tools that are essential for a very broad field of applications, ranging from chemical analytics, to non-destructive testing of materials and the investigation of molecular dynamics, to in vivo medical diagnostics and drug research. One of the major challenges in their application to many problems is the inherent low sensitivity of magnetic resonance, which results from the small energy-differences of the nuclear spin-states. At thermal equilibrium at room temperature the normalized population difference of the spin-states, called the Boltzmann polarization, is only on the order of 10-5. Parahydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, which has widespread applications in Chemistry, Physics, Biochemistry, Biophysics, and Medical Imaging. PHIP creates its signal-enhancements by means of a reversible (SABRE) or irreversible (classic PHIP) chemical reaction between the parahydrogen, a catalyst, and a substrate. Here, we first give a short overview about parahydrogen-based hyperpolarization techniques and then review the current literature on method developments and applications of various flavors of the PHIP experiment.

A disintegrin derivative as a case study for PHIP labeling of disulfide bridged biomolecules.

A specific labeling strategy for bioactive molecules is presented for eptifibatide (integrilin) an antiplatelet aggregation inhibitor, which derives from the disintegrin protein barbourin in the venom of certain rattlesnakes. By specifically labeling the disulfide bridge this molecule becomes accessible for the nuclear spin hyperpolarization method of parahydrogen induced polarization (PHIP). The PHIP-label was synthesized and inserted into the disulfide bridge of eptifibatide via reduction of the peptide and insertion by a double Michael addition under physiological conditions. This procedure is universally applicable for disulfide-containing biomolecules and preserves their tertiary structure with a minimum of change. HPLC and MS spectra prove the successful insertion of the label. 1H-PHIP-NMR experiments yield a factor of over 1000 as lower limit for the enhancement factor. These results demonstrate the high potential of the labeling strategy for the introduction of site selective PHIP-labels into biomolecules' disulfide bonds.