Homo- and heteronuclear 2D NMR approaches to analyse a mixture of deuterated unlike/like stereoisomers using weakly ordering chiral liquid crystals
Résumé
We describe several homo- and heteronuclear 2D NMR strategies dedicated to the analysis of anisotropic 2H spectra of a mixture of dideuterated unlike/like stereoisomers with two remote stereogenic centers, using weakly orienting chiral liquid crystals. To this end, we propose various 2D correlation experiments, denoted ‘‘D(H)nD’’ or ‘‘D(H)nC’’ (with n = 1, 2), that involve two heteronuclear polarization transfers of INEPT-type with one or two proton relays. The analytical expressions of correlation signals for four pulse sequences reported here were calculated using the product-operators formalism for spin I = 1 and S = 1/2. The features and advantages of each scheme are presented and discussed. The efficiency of these 2D sequences is illustrated using various deuterated model molecules, dis-solved in organic solutions of polypeptides made of poly-gamma-benzyl-L-glutamate (PBLG) or poly-epslion-carbobenzyloxy-L-lysine (PCBLL) and NMR numerical simulations.