Proton spinT1relaxation dispersion in liquid H2O by slow protonhyphen;exchange

摘要

We have measured the longitudinal proton spin relaxation timeT1in pure water as a function of temperature (10, 37, 80deg;C) and Larmor frequency (50 Hzles;ngr;0les;50 kHz) by means of fieldhyphen;cycling techniques.T1becomes frequency dependent below ngr;0ap;5 kHz due to the slow protonhyphen;exchange between different oxygen environments (16O,17O,18O), which modulates the magnetic1Hndash;17O interaction. The protonhyphen;exchange time tgr;ewas found to be Arrheniushyphen;like with activation energy 13.4 kJ/mol and prehyphen;exponential 1.5times;10minus;6thinsp;s (37thinsp;deg;C:tgr;e=2.6times;10minus;4thinsp;s). This is in fairly good agreement with results obtained previously in the literature by more indirect NMR methods. The new access to protonhyphen;exchange reduces the experiemtnal error limits and allows measurements at extremely small frequencies, where the familiarT1rgr;technique no longer works.