Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique for chemistry and biochemistry. Since an inherent limitation of NMR is a lack of sensitivity, long experimental time with signal averaging or spins with high concentration are often required. An emerging technique, dissolution dynamic nuclear polarization (D-DNP), significantly enhances an NMR signal by several orders of magnitude. The large signal gains enable detection of spins with micromolar concentration and offer opportunities to various fields of applications.
Two dimensional (2D) correlation spectroscopy plays an essential role in identifying molecular structure and dynamics. Because of the non-renewability of the hyperpolarized spin state, this property prevents the application of conventional 2D methods which rely on repetition of the experiment by successive increments of the indirect dimension. Therefore, it is important to find applicable methods to circumvent this problem. The present dissertation is focused on using fast single-scan 2D and pseudo-2D correlation methods to elucidate molecular structures and characterize physical parameters, such as diffusion and spin relaxation, with the goal of investigating reaction kinetics and mechanisms as well as studying membrane transport of metabolite.
Since conventional 2D correlation spectroscopy is not compatible with D-DNP, an alternative way of collecting correlation information without obtaining an indirect spectral dimension is via off-resonance decoupling. Based on this concept, heteronuclear chemical shift correlations were determined in single scan DNP-enhanced NMR spectra under off resonance decoupling by Scaling of Heteronuclear Couplings by Optimal Tracking (SHOT) pulses, with the purpose of determining the identity of transient species and reaction mechanisms.
Physical parameters of molecules, such as diffusion and spin relaxation, can further be characterized with single-scan correlation methods and used to examine membrane transport of metabolite. Ultrafast diffusion-Tv2 correlation Laplace NMR enables one to correlate spin relaxation and diffusion parameters in a single-scan. Diffusion-Tv2 correlation data was acquired by detecting hyperpolarized ^13C /^ 1H signals of small molecules, and maps were generated using inverse Laplace transform. The accurate determination of diffusion and Tv2 relaxation in homogeneous / inhomogeneous magnetic fields demonstrated the robustness of the method.
The usability of hyperpolarized UF-LNMR is then demonstrated in the context of cell metabolism, by investigating the conversion of pyruvate to lactate in the cultures of mouse 4T1 cancer cells. We show that ^13C ultrafast diffusion-Tv2 relaxation correlation measurements, with the sensitivity enhanced by several orders of magnitude by D-DNP, allows the determination of the extra- vs. intracellular location of metabolites in the cells due to their significantly different values of diffusion coefficients and Tv2 relaxation time
