Zakład Fizyki Wysokich Ciśnień - publikacje

Abstract: Proton spin-lattice relaxation times in the laboratory frame,T1(H),have been measured as a function of frequency and temperature (333K>T > 80 K). The spin-lattice relaxation times in the rotating frame, T1ρ{variant}(H), have been measured at two different rotating fields while M2(H), the proton second moment, has been extracted from the shape of the FID. In addition, T1(31P) and T1(23Na) have been measured as functions of temperature at 81 and 50 MHz, respectively. The results demonstrate clearly that the water content of the compounds influences the results to a large extent. It seems that water molecules at some of the lattice sites can be removed from the structure by evacuation, while others are more tightly bound to the ADP and ATP molecules. The more loosely bound water molecules are very mobile and dominate the relaxation results in the high-temperature region via the spin-rotation and dipolar mechanisms. The more tightly bound water molecules rotate about their twofold axes and this motion, characterized by a distribution of correlation times, results in a T1(H) minimum in the low-temperature region. The results have been interpreted in terms of a Fuoss-Kirkwood distribution function. The 23Na spin-lattice relaxation rates are dominated by the quadrupolar interactions, which provide a dominating relaxation mechanism for the proton spins in the rotating frame. In the case of Na2ATP, T1(P) is independent of the degree of hydration of the sample, but the NaADP T1(H), values are influenced strongly by a change in the water content. An X-ray determination of the lengths of the a axes of the unit cells has provided supporting evidence for the interpretation of the NMR results. © 1987.