RESUMO
Selective 1D COSY can unambiguously identify coupled spins but is often limited both by lack of selectivity, and by unfavourable multiplet lineshapes. Here, ultra-selective GEMSTONE excitation is employed with CLIP-COSY to provide through-bond correlations for nuclei whose NMR signals overlap. The new method is illustrated using the coccidiostat lasalocid and the immunosuppressant cyclosporin.
RESUMO
Pure shift nuclear magnetic resonance (NMR) methods suppress the effect of homonuclear scalar couplings to produce NMR spectra consisting solely of a single signal for each chemically distinct site. They are increasingly relied upon for analysis of complex molecules and mixtures as they overcome the extensive signal overlap that complicates proton NMR spectra of all but the simplest species. Current broadband pure shift methodologies for 1D proton spectra suffer from reduced sensitivity compared with their conventional counterparts and typically require a large amount of instrument time for low concentration samples. In this study, we demonstrate how the sensitivity limitation may be overcome by transiently increasing the bulk polarization using signal amplification by reversible exchange (SABRE) hyperpolarization. We utilize para-enriched dihydrogen to enhance the pure shift NMR resonances of pyridine by up to a factor of 60 in a single-scan experiment and extend this to propose a method to unambiguously determine mixture components based on the enhancement of their pure shift NMR signals.
