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The use of 1Hâ??31P GHMBC and covariance NMR to unambiguously determine phosphate ester linkages in complex polysaccharide mixtures
The use of 1Hâ??31P GHMBC and covariance NMR to unambiguously determine phosphate ester linkages in complex polysaccharide mixtures
Abstract Poly- and oligo-saccharides are commonly employed as antigens in many vaccines. These antigens contain phosphoester structural elements that are crucial to the antigenicity, and hence the effectiveness of the vaccine. Nuclear Magnetic Resonance (NMR) is a powerful tool for the site-specific identification of phosphoesters in saccharides. We describe here two advances in the characterization of phosphoesters in saccharides: (1) the use of 1Hâ??31P GHMBC to determine the site-specific identity of phosphoester moieties in heterogeneous mixtures and (2) the use of Unsymmetrical/Generalized Indirect Covariance (U/GIC) to calculate a carbon-phosphorus 2D spectrum. The sensitivity of the 1Hâ??31P GHMBC is far greater than the â??standardâ?? 1Hâ??31P GHSQC and allows long-range 3â??5JHP couplings to be readily detected. This is the first example to be reported of using U/GIC to calculate a carbon-phosphorus spectrum. The U/GIC processing affords, in many cases, a fivefold to tenfold or greater increase in signal-to-noise ratios in the calculated spectrum. When coupled with the high sensitivity of 1Hâ??31P HMBC, U/GIC processing allows the complete and unambiguous assignments of phosphoester moieties present in heterogeneous samples at levels of ~5% (or less) of the total sample, expanding the breadth of samples that NMR can be used to analyze. This new analytical technique is generally applicable to any NMR-observable phosphoester.
Source: Journal of Biomolecular NMR |
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