Isotope effects on the 17O, 1H coupling constant and the 17O-{1H} nuclear Overhauser effect in water

The NMR spectra of solutions of 30% O-17-enriched H2O and D2O in nitromethane display the resonances of the three isotopomers H2O, HDO, and D2O. All O-17, H-1 and O-17, H-2 coupling constants and the primary and secondary isotope effects on J(O-17, H-1) have been determined. The primary effect is -1.0 +/- 0.2 Hz and the secondary effect is -0.07 +/- 0.04 Hz. Using integrated intensities in the O-17 NMR spectra, the equilibrium constant for the reaction H2O + D2O reversible arrow 2HDO is found to be 3.68 +/- 0.2 at 343 K. From the relative integrated intensities of proton-coupled and -decoupled spectra the O-17-{H-1} NOE is estimated for the first time, resulting in values of 0.908 and 0.945 for H2O and HDO, respectively. This means that dipole-dipole interactions contribute about 2.5% to the overall O-17 relaxation rate in H2O dissolved in nitromethane. (C) 1999 Academic Press.