Temperature and Pressure Effects on the Spin-lattice Relaxation Time of Hydrated Water Molecules by NMR

本文用核磁共振谱研究了在碱金属溴化物（LiBr，NaBr，KBr，CsBr）和四烷基溴化铵（Me_4NBr，Et_4NBr，n-Pro_4 NBr，n-Bu_4 NBr）盐稀溶液中水合D_2O分子的自旋-晶格弛豫速率的温度效应。在<17>低于20 ℃的低温下，D_2O分子在四烷基溴化铵D_2O溶液中的D和^0自旋-晶格弛豫速率（R_1）与浓度的关系可用方程R_1/R_R_1 = 1 + Bm + Cm^2（R_1 =纯D_2O，m ; mol kg^<-1>，B和C ;常数）表示。这意味着当较低的温度诱导水的氢键网络结构时，四烷基铵离子的水合球重叠。在溶剂分离的疏水水化模型上分析这些结果，溶剂分离的疏水水化水分子的旋转运动比水化水分子的旋转运动快。在5 ℃ ~ 50 ℃的较宽温度范围内，碱金属溴化物D_2O分子中R_1的浓度依赖关系可用线性方程R_1/R_1 = 1 + Bm表示。随着温度的升高，盐溶液的B系数由负向正逐渐增大。因此，碱金属离子的水合水分子的旋转运动比本体水分子的旋转运动慢。

The temperature effects on the spine-lattice relaxation rates of hydrated D_2O molecules in the dilute solutions of alkali metal bromide (LiBr, NaBr, KBr, and CsBr) and tetraalkylammonium bromide (Me_4NBr, Et_4NBr, n-Pro_4NBr, and n-Bu_4NBr) salts have been studied by NMR spectroscopy, and the high pressure NMR polmer cell has been tested up to 500 bar at room temperature. The concentration dependences of D and ^<17>0 spine-lattice relaxation rates (R_1) of D_2O molecules in D_2O solutions of tetraalkylammonium bromide are repersented by the equation of R_1/R_Rﾟ= 1 + Bm + Cm^2 (R_1ﾟ ; pure D_2O, m ; mol kg^<-1>, B and C ; constants) at lower temperatures below 20 ﾟC. This means the overlap the hydration sphere of tetraalkylammonium ions, when the lower temperature induces the hydrogen bonded network structure of water. Analyzing these results on the model of the solvent-separated hydrophobic hydration, the rotationa motion of the solvent separated hydrophobic hydrated water molecules is faster than those of the hydrated water molecules. The concentration dependences of R_1 in D_2O molecules of alkali metal bromides are represented by the linear equation of R_1/R_1ﾟ = 1 + Bm in the wide range of temperatures of 5 ﾟC to 50 ﾟC. With increasing temperature, the B coefficients of salts solution increase from the negative to positive sign. Therefore, the rotational motion of hydrated water molecules of alkali metal ions is slower than that of the bulk water molecules.