Effects of salts, acids, and phenols on the hydrogen-bonding structure of water-ethanol mixtures
Effects of salts, acids, and phenols on the hydrogen-bonding structure of water-ethanol mixtures
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DOI：
10.1021/jp0308312
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发表时间：
2004-01-15
影响因子：
3.3
通讯作者：
Ueda, T
中科院分区：
文献类型：
--
作者：
Nose, A;Hojo, M;Ueda, T
根据水和乙醇的OH的H-1 NMR化学位移，研究了盐、酸和酚类对20%（v/v）EtOH-H_2 O溶液中水的氢键结构的影响。结果表明，多种盐类对水的结构有破坏作用，而MgCl_2、KF等金属盐类对水的结构有强化作用。碱金属和碱土金属离子或强酸阴离子（卤化物、NO_3 ~-、ClO_4 ~-、SO_4 ~（2-））的存在引起的OH质子化学位移与离子的大小和电荷有关。不仅酸（H+和HA，未解离的酸），而且碱（OH-和A（-），来自弱酸的共轭碱阴离子）具有增强水结构的效果;效果的程度取决于酸强度（pK（a））。根据水和乙醇两个信号峰的合并以及H-1 NMR谱随溶质浓度增加而进一步低场移动的规律，研究了60%（v/v）EtOH-H_2 O溶液中水和乙醇分子间的质子交换。虽然已经报道了强酸和强碱促进水和乙醇分子之间的质子交换，但在中性溶液中也观察到明显的质子交换，即，通过加入磷酸盐pH缓冲溶液（pH 6.86）。NaCl在20%（v/v）EtOH-H_2 O溶液中具有破坏水结构的作用;而在60%（v/v）EtOH-H_2 O溶液中，同一种盐在较低浓度下强化了水-乙醇结构，促进了水和乙醇分子之间的质子交换。氢键供体以及受体似乎导致密切（或紧密）之间的相互作用H2O和乙醇分子，即使在酒精饮料。
The effects of salts, acids, and phenols on the hydrogen-bonding structure of water in 20% (v/v) EtOH-H2O solution were investigated on the basis of H-1 NMR chemical shifts of the OH of water and ethanol. It was found that many salts caused structure breaking of water while a few metal salts, such as MgCl2 and KF, had a strengthening effect. The OH proton chemical shifts caused by the presence of alkali-metal and alkaline-earth-metal ions or anions (halides, NO3-, ClO4-, SO42-) from strong acids were related to the sizes and charges of the ions. Not only acids (H+ and HA, undissociated acids) but also bases (OH- and A(-), conjugate-base anions from weak acids) had the effect of strengthening the structure of water; the degree of the effect was dependent on the acid strength (pK(a)). The proton exchange between water and ethanol molecules in 60% (v/v) EtOH-H2O solution was examined, on the basis of the coalescence of two signal peaks of water and ethanol as well as the further low-field shift in H-1 NMR spectra with increasing concentration of solutes. Although it has been already reported that the proton exchange between water and ethanol molecules is promoted by strong acids and bases, a distinct proton exchange was also observed in the neutral solution, i.e., by the addition of phosphate pH buffer solution (pH 6.86). It was also discovered that NaCl had the effect of breaking the structure of water in 20% (v/v) EtOH-H2O solution; however, in 60% (v/v) EtOH-H2O solution the same salt at lower concentrations strengthened the water-ethanol structure, promoting the proton exchange between water and ethanol molecules. Hydrogen bond donors as well as acceptors seemed to cause the intimate (or tight) interaction between H2O and EtOH molecules even in alcoholic beverages.