Gas Phase NMR
Chapter 9: High-resolution Spectra in PHIP
Published:09 Feb 2016
This chapter reviews the recent development of an NMR method to obtain information on site selective hyperpolarized samples by Parahydrogen Induced Polarization (PHIP) where the chemical reaction is carried out at high magnetic fields (PASADENA). The method relies on the acquisition of J-spectra in PHIP, which differ from J-spectra for thermally polarized species due to different evolution in the time domain during application of a Carr–Purcell–Meiboom–Gill (CPMG) sequence. PHIP and thermal polarizations give rise to signals which are centered in spectral positions shifted by half of the spectral width, giving rise to two useful results. On one hand, the antiphase character of PASADENA spectra implies a partial peak cancellation, as J-couplings introduce a splitting in the signal of a few Hz. The acquisition of J-spectra renders line width typically of 0.1 Hz, avoiding cancellation. A second aspect to be considered in PHIP is the suppression of antiphase signals due to overlap with ones steaming from thermal polarization at the same frequency. The frequency discrimination of the method enables the detection of hydrogenation even for very low reaction rates. Thus, the method is referred to as Parahydrogen Discriminated PHIP (PhD-PHIP). Simulations of PhD-PHIP with gas phase NMR are presented.