Reaction monitoring using hyperpolarized NMR with scaling of heteronuclear couplings by optimal tracking.
Off-resonance decoupling using the method of Scaling of Heteronuclear Couplings by Optimal Tracking (SHOT) enables determination of heteronuclear correlations of chemical shifts in single scan NMR spectra. Through modulation of J-coupling evolution by shaped radio frequency pulses, off resonance decoupling using SHOT pulses causes a user-defined dependence of the observed J-splitting, such as the splitting of13C peaks, on the chemical shift offset of coupled nuclei, such as1H. Because a decoupling experiment requires only a single scan, this method is suitable for characterizing on-going chemical reactions using hyperpolarization by dissolution dynamic nuclear polarization (D-DNP). We demonstrate the calculation of [13C,1H] chemical shift correlations of the carbanionic active sites from hyperpolarized styrene polymerized using sodium naphthalene as an initiator. While off resonance decoupling by SHOT pulses does not enhance the resolution in the same way as a 2D NMR spectrum would, the ability to obtain the correlations in single scans makes this method ideal for determination of chemical shifts in on-going reactions on the second time scale. In addition, we present a novel SHOT pulse that allows to scale J-splittings 50% larger than the respective J-coupling constant. This feature can be used to enhance the resolution of the indirectly detected chemical shift and reduce peak overlap, as demonstrated in a model reaction between p-anisaldehyde and isobutylamine. For both pulses, the accuracy is evaluated under changing signal-to-noise ratios (SNR) of the peaks from reactants and reaction products, with an overall standard deviation of chemical shift differences compared to reference spectra of 0.02ppm when measured on a 400MHz NMR spectrometer. Notably, the appearance of decoupling side-bands, which scale with peak intensity, appears to be of secondary importance.
Chemistry Department, Texas A&M University, 3255 TAMU, College Station, TX 77843, USA.
Guannan
G
Zhang
Cancer Research UK Cambridge Institute, University of Cambridge, Li Ka Shing Centre, Cambridge CB2 0RE, United Kingdom.
Franz
F
Schilling
Department of Chemistry, Technische Universität München, 85747 Garching, Germany. Electronic address: glaser@tum.de.
Steffen J
SJ
Glaser
Chemistry Department, Texas A&M University, 3255 TAMU, College Station, TX 77843, USA. Electronic address: chilty@tamu.edu.
Christian
C
Hilty
Correlation spectroscopy; Dissolution dynamic nuclear polarization; Nuclear magnetic resonance; Optimal control methods