Dynamics of hydration of alcohols and diols in aqueous solutions
Dynamics of hydration of alcohols and diols in aqueous solutions
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DOI：
10.1039/a701969f
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发表时间：
1997-09-21
期刊：
影响因子：
--
通讯作者：
Uedaira, H
中科院分区：
文献类型：
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作者：
Ishihara, Y;Okouchi, S;Uedaira, H
测定了9种醇和5种二醇水溶液中溶剂水在25℃时的O-17核磁共振自旋晶格驰豫时间T-1随浓度的变化关系。对于醇溶液，在1-50℃温度范围内测定了T-1的浓度依赖关系。由T-1浓度依赖关系得到的n(H)[(tau(C)(H)/tau(C)(0))-1]被定义为动态水化数(n(Dhn))。根据溶质分子的水可达表面积(ASA)估算了配位数n(H)的值。计算了水分子在溶质分子周围的转动关联时间tau(C)(H)，并与纯水的tau(C)(0)进行了比较。在所研究的溶质中，25℃时(BuOH)-O-t的tau(C)(H)/tau(C)(0)=2.22的值最大。正构醇和二元醇的tau(C)(H)/tau(C)(0)值随ASA的增加而增大并趋于恒定。(BuOH)-O-t的tau(C)(H)/tau(C)(0)值随温度升高而减小，在40℃以上接近恒定值。正构醇的tau(C)(H)活化能在约240埃(2)附近有极大值。在考虑分子尺寸的情况下对这些结果进行了讨论。二醇的tau(C)(H)/tau(C)(0)值小于相应的正醇。这一结果支持了疏水水化是由溶质分子中的羟基分布的概念。正构醇、丁醇异构体和二醇的水合热力学性质与它们的n(Dhn)呈线性关系。
The O-17 NMR spin-lattice relaxation times, T-1, of the solvent water in aqueous solutions of nine alcohols and five diols have been determined as a function of the concentration at 25 degrees C. For the alcohol solutions, the concentration dependence of T-1 has been determined in the temperature range from 1 to 50 degrees C. The value of n(h)[(tau(c)(h)/tau(c)(0))-1] which has been obtained from the concentration dependence of T-1 has been defined as the dynamic hydration number (n(DHN)). The values of the coordination numbers n(h), have been estimated on the basis of the water-accessible surface areas (ASA) of the solute molecules. The rotational correlation times, tau(c)(h), of water molecules around the solute molecules have been estimated and compared with that of pure water tau(c)(0). The value of tau(c)(h)/tau(c)(0) = 2.22 for (BuOH)-O-t at 25 degrees C is the largest among the solutes investigated. The tau(c)(h)/tau(c)(0) values of the n-alcohols and diols increase with increasing ASA and become almost constant. The tau(c)(h)/tau(c)(0) values decrease with increasing temperature and approach constant value above 40 degrees C. The temperature dependence of tau(c)(h)/tau(c)(0) for (BuOH)-O-t is the largest. The activation energy of tau(c)(h) for n-alcohols has the maximum value at ASA approximate to 240 Angstrom(2). These results are discussed bg considering the molecular sizes. The tau(c)(h)/tau(c)(0) value for a diol was smaller than that of the corresponding n-alcohol. This result supports the concept that hydrophobic hydration is distributed by the OH groups of the solute molecules. The thermodynamic properties of hydration for n-alcohols, butanol isomers and diols are linearly dependent on their n(DHN).