Direct-determination of 15N- and 19F-NMR correlation times from spin-lattice and spin-spin relaxation times

The NMR rotational correlation equations for dipolar relaxation between H-1 and the nuclei N-15 and F-19 have been solved for viscous solutions using the R-2/R-1 dipolar ratio. The rotational correlation times have been determined over the dipolar R-2/R-1 range 1.1-1200 at field strengths of 4.7, 6.35, 7.05, 9.4, 11.75, and 14.1 T. The calculated correlation times al each field strength have been fitted to pairs of polynomials that reproduce the correlation times from R-2/R-1 values at a given temperature. These polynomials are used to determine correlation times in two studies where molecular rotation is slow (omega tau > 1), The studies include (1) where the N-15-H-1 correlation-time polynomial equations are used to determine the correlation times of the enzyme 4-oxalocrotonate tautomerase and the backbone correlation time of the intestinal fatty acid binding protein and (2) where the F-19-H-1 polynomial equations are used to characterize the rotational mobility of 5-fluorouracil-substituted Escherichia coli tRNA(1)(Val) and to establish the existence of scalar relaxation in the case of an isomer of the peptide complex [Co(benzyloxycarbonyl-cys-pro-leu-cys-gly-NHC6H4-m-F)(2)](2-).