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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Partial pair correlation functions of highly concentrated aqueous urea solutions determined by neutron diffraction with 14N/15N and H/D isotopic substitution methods
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Partial pair correlation functions of highly concentrated aqueous urea solutions determined by neutron diffraction with 14N/15N and H/D isotopic substitution methods

机译：用14N / 15N和H / D同位素置换法通过中子衍射测定的高浓度尿素水溶液的偏对相关函数

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摘要

Neutron diffraction measurements were carried out on 14N/15N and H/D isotopically substituted aqueous 25 mol% urea (x_(urea) = 0.25) solutions in order to obtaindirect experimental information on the short-range structure on the ureaurea, urea-water, and water-water interactions inhighly concentrated aqueous urea solutions near saturation. Scattering cross sections observed for isotopicallydistinct solutions were successfully combined to derive intermolecular partial structure factors, a_(NN)inter(Q), a _(NH)inter(Q), a_(NO(NC))inter(Q), a_(HH)inter(Q), A_(XH)inter(Q), and a_(XX)inter(Q) (X: O, N, and C), and corresponding intermolecular partial pair correlation functions. The nearest neighbor intermolecular N-O and N-H distances have been obtained as 3.14(1) and 3.42(1) ?, respectively, indicating that the amino group of the urea molecule forms hydrogen bonds with neighboring water molecules in such a highly concentrated solution. The nearest neighbor intermolecular N-N interaction was found at intermolecular distance of 4.71(5) ? with a coordination number of 3.1(5), which evidences that the hydrogen-bonded urea oligomers exist in the present solution. The nearest neighbor intermolecular O-Hdistance has been found to be 1.90(1) ?,which indicates that hydrogen bonds among the solvent water molecules are still preserved in the present solutions. On the other hand, corresponding O...H coordination number 0.83(1) is much smaller than that reported for room temperature liquid water. The nearest neighbor intermolecular H-H and O...O distances were determined to be 2.37(5) and 2.86(2) ?, respectively. The corresponding H...H and O...O coordination numbers were obtained as 2.0(5) and 1.4(1), respectively. These values are also much smaller than those observed for the pure water. The present results suggest that the hydrogen-bonded network among water molecules is considerably modified due to the nearest neighbor urea-water and urea-urea interactions, which can be stronglyrelated with protein denaturation ability of the concentrated aqueous urea solutions.
机译：在14N / 15N和H / D同位素取代的25 mol％尿素水溶液（x_（urea）= 0.25）溶液上进行中子衍射测量，以便获得有关尿素尿素，尿素水，和高浓度尿素水溶液在饱和状态附近的水-水相互作用。成功地将观察到的同位素异解的散射截面组合起来，得出分子间部分结构因子a_（NN）inter（Q），a_（NH）inter（Q），a_（NO（NC））inter（Q），a_（ HH）inter（Q），A_（XH）inter（Q）和a_（XX）inter（Q）（X：O，N和C），以及相应的分子间部分对相关函数。最接近的相邻分子间的N-O和N-H距离分别为3.14（1）和3.42（1）λ，表明在这种高浓度溶液中，尿素分子的氨基与相邻的水分子形成氢键。分子间距离为4.71（5）Ω，发现最近的分子间N-N相互作用。配位数为3.1（5），这表明本溶液中存在氢键结合的尿素低聚物。已经发现最近的相邻分子间的O-H距离为1.90（1）Ω，这表明溶剂水分子之间的氢键仍保留在本溶液中。另一方面，相应的O ... H协调数0.83（1）远小于室温液态水的报告值。确定最近的分子间H-H和O.O距离分别为2.37（5）和2.86（2）θ。相应的H ... H和O ... O配位数分别为2.0（5）和1.4（1）。这些值也比纯水观察到的值小得多。目前的结果表明，由于最邻近的尿素-水和尿素-尿素之间的相互作用，水分子之间的氢键网络发生了很大的变化，这可能与浓缩尿素水溶液的蛋白质变性能力密切相关。

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