HOMONUCLEAR AND HETERONUCLEAR MULTIPLE-QUANTUM FILTERS FOR MEASUREMENT OF NMR ISOTOPE SHIFTS

The measurement of NMR isotope shifts as mechanistic probes can be com plicated by mixtures of isotopomers. Homo- and heteronuclear NMR techn iques based on multiple-quantum filtration are presented and shown to be a useful aid in measuring such shifts. The effects of H-1/H-2 subst itution and O-16/O-18 substitution on the nuclear shielding of H-1, C- 13, and P-31 in a multiply labeled phosphoenolpyruvate are measured an d interpreted qualitatively in terms of their rovibrational origins. ( C) 1994 Academic Press, Inc.