Premium
Chemical speciation by selective heteronuclear single‐quantum coherence spectroscopy: determination of double‐bond quantity in unsaturated fatty acid compounds
Author(s) -
Tesiram Yasvir A.,
Saunders Debra,
Towner Rheal A.
Publication year - 2008
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1196
Subject(s) - chemistry , chemical shift , double bond , heteronuclear molecule , heteronuclear single quantum coherence spectroscopy , nuclear magnetic resonance spectroscopy , fatty acid , pulse sequence , unsaturated fatty acid , nmr spectra database , oleic acid , spectroscopy , analytical chemistry (journal) , nuclear magnetic resonance , spectral line , organic chemistry , biochemistry , physics , astronomy , quantum mechanics
A method for identifying fatty acid species based on the number of double bonds contained in a lipid molecule is presented. Common to all polyunsaturated fatty acids are two signature resonances at ∼5.3 and 2.8 ppm in the proton chemical‐shift spectrum of NMR. These resonances are from the vinyl and bis‐allyl protons, respectively, and, although they can be readily observed by NMR from lipid extracts of biological samples, direct speciation has never been demonstrated by NMR. By modifying a conventional HSQC pulse sequence with a J ‐pulse on the spin system of the vinyl group (generalized as an IS spin system) at the beginning of the initial polarization transfer period and selectively inverting the 13 C ( I ) spins with a narrowband sech/tanh inversion pulse, the collection of data in both dimensions can be restricted to a narrow slice of the chemical‐shift range. The resolution is subsequently determined by digitizer efficiency, and spectra can be collected optimally from within a very narrow 1 × 6 ppm window of the respective proton and carbon chemical‐shift ranges. With this modification it is possible to distinguish at least one resonance each from the multiple shifts expected from the indirectly detected nuclei of the fatty acid species, oleic acid, linoleic acid, linolenic acid and arachidonic acid, which contain one, two, three and four double bonds, respectively. This and similar methods of applied selectivity are of potential interest in characterizing speciation in biological samples where mixtures are often encountered and chemical shifts of the same structural group of similar molecules give rise to complicated overlapping resonances but are important for diagnosis of disease processes such as cancer. Copyright © 2007 John Wiley & Sons, Ltd.