The current study aims to assign and estimate the total creatine (tCr) signal contribution to the Z-spectrum in mouse brain at 11.7 Tesla. Creatine (Cr), phosphocreatine (PCr) and protein phantoms were used to confirm presence of a guanidinium resonance at this field strength. Wild type (WT) and knockout mice with Guanidinoacetate N-Methyltransferase deficiency (GAMT−/−) that have low Cr and PCr concentrations in the brain were used to assign the tCr contribution to the Z-spectrum. To estimate the total guanidinium concentrations, two pools for the Z-spectrum around 2 ppm were assumed: (i) a Lorentzian function representing the guanidinium CEST at 1.95 ppm in the 11.7 T Z-spectrum; (ii) a background signal that can be fitted by a polynomial function. Comparison between the WT and GAMT−/− mice provided strong evidence for three types of contributions to the peak in the Z-spectrum at 1.95 ppm, namely proteins, Cr and PCr, the latter fitted as tCr. A ratio of 20±7% (Protein) and 80±7% tCr was found in brain with 2 μT and 2 s saturation. Based on phantom experiments, the tCr peak was estimated to consist of about 83±5% Cr and 17±5% PCr. Maps for tCr of mouse brain were generated based on the peak at 1.95 ppm after concentration calibration with in vivo MRS.

Fluorine NMR spectroscopy is widely used for detection of protein-ligand interactions in drug discovery because of the simplicity of fluorine spectra combined with a relatively high likelihood for a drug molecule to include at least one fluorine atom. In general, an important limitation of NMR spectroscopy in drug discovery is its sensitivity, which results in the need for unphysiologically high protein concentrations and large ligand:protein ratios. An enhancement in the (19)F signal of several thousand fold by dynamic nuclear polarization allows for the detection of submicromolar concentrations of fluorinated small molecules. Techniques for exploiting this gain in signal to detect ligands in the strong-, intermediate-, and weak-binding regimes are presented. Similar to conventional NMR analysis, dissociation constants are determined. However, the ability to use a low ligand concentration permits the detection of ligands in slow exchange that are not easily amenable to drug screening by traditional NMR methods. The relative speed and additional information gained may make the hyperpolarization-based approach an interesting alternative for use in drug discovery.

Purpose To use the Variable Delay Multi-Pulse (VDMP) CEST approach to obtain clean Amide Proton Transfer (APT) and relayed Nuclear Overhauser (rNOE) Chemical Exchange Saturation Transfer (CEST) images in human brain by suppressing the conventional magnetization transfer contrast (MTC) and reducing the direct water saturation (DS) contribution. Methods The VDMP CEST scheme consists of a train of RF pulses with a specific mixing time. The CEST signal with respect to the mixing time shows distinguishable characteristics for protons with different exchange rates. Exchange rate filtered CEST images are generated by subtracting images acquired at two mixing times at which the MTC signals are equal, while the APT and rNOE-CEST signals differ. Since the subtraction is done at the same frequency offset for each voxel and the CEST signals are broad, no B0 correction is needed. Results MTC-suppressed APT and rNOE-CEST images of human brain were obtained using the VDMP method. The APT-CEST data shows hyper-intensity in gray matter versus white matter while the rNOE-CEST images show negligible contrast between gray and white matter. Conclusion The VDMP approach provides a simple and rapid way of recording MTC-suppressed APT-CEST and rNOE-CEST images without a need for B0 field correction.

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Emerging techniques for hyperpolarization of nuclear spins, foremost dynamic nuclear polarization (DNP), lend unprecedented sensitivity to nuclear magnetic resonance spectroscopy. Sufficient signal can be obtained from a single scan, and reactions even far from equilibrium can be studied in real-time. When following the progress of a reaction by nuclear magnetic resonance, however, spin relaxation occurs concomitantly with the reaction to alter resonance line intensities. Here, we present a model for accounting for spin-relaxation in such reactions studied by hyperpolarized NMR. The model takes into account auto- and cross-relaxation in dipole-dipole coupled spin systems and is therefore applicable to NMR of hyperpolarized protons, the most abundant NMR-active nuclei. Applied to the Diels-Alder reaction of 1,4-dipheneylbutadiene (DPBD) with 4-phenyl-1,2,4-triazole-3,5-dione (PTD), reaction rates could be obtained accurately and reproducibly. Additional parameters available from the same experiment include relaxation rates of the reaction product, which may yield further information about the molecular properties of the product. The method presented is also compatible with an experiment where a single spin in the reactant is labeled in its spin-state by a selective radio frequency pulse for subsequent tracking through the reaction, allowing the unambiguous identification of its position in the product molecule. In this case, the chemical shift specificity of high-resolution NMR can allow for the simultaneous determination of reaction rates and mechanistic information in one experiment.

Intermediates during the anionic polymerization of styrene were observed using hyperpolarized NMR. Dissolution dynamic nuclear polarization (DNP) of monomers provides a sufficient signal-to-noise ratio for detection of (13)C NMR signals in real time as the reaction progresses. Because of its large chemical shift dispersion, (13)C is well-suited to distinguish and characterize the chemical species that arise during the reaction. At the same time, incorporation of hyperpolarized small-molecule monomers is a unique way to generate polymers that exhibit a transient signal enhancement at the active site. This strategy is applicable despite the decay of the hyperpolarization of the polymer due to rapid spin-lattice relaxation. Real-time measurements on polymerization reactions provide both mechanistic and kinetic information without the need for stable isotope labeling of the molecules of interest. These capabilities are orthogonal to currently established methods that separate synthesis and analysis into two steps, making dissolution DNP an attractive method to study polymerization reactions.

The development of biocompatible hyperpolarized media is a crucial step towards application of hyperpolarization in vivo. This article describes the achievement of 1% hyperpolarization of 3-amino-1,2,4-triazine protons in water using the parahydrogen induced polarization technique based on signal amplification by reversible exchange (SABRE). Polarization was achieved in less than 1 min.

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