CROSS-POLARIZATION IN N-14 OVERTONE NMR-SPECTROSCOPY OF SOLIDS

Several versions of cross-polarization (CP) sequences are analyzed in order to improve the sensitivity of N-14 overtone NMR of biological so lids. Optimum conditions are determined from experiments on a single c rystalline sample of a model peptide, N-acetyl-D,L-valine, for an effi cient CP from H-1 to N-14 overtone frequency. Experimental results inf er that a CP sequence consisting of an amplitude modulated spin-lockin g of N-14 overtone frequency during the CP period followed by a compos ite 90 degrees postpulse is efficient in transferring the proton dipol ar order to the observable overtone signal. (C) 1998 Elsevier Science B.V.