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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Experimental Evidence of Differences in the Hydrogen-Bonded Structure of Concentrated Aqueous Solutions Involving DL-and L-Alanine Molecules
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Experimental Evidence of Differences in the Hydrogen-Bonded Structure of Concentrated Aqueous Solutions Involving DL-and L-Alanine Molecules

机译：涉及DL-和L-丙氨酸分子的浓缩水溶液的氢键结构差异的实验证据

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Time-of-Flight(TOF)and steady state reactor neutron diffraction measurements have been carried out for aqueous 2.5 mol% DL-and L-alanine solutions in order to investigate the differences in intermolecular hydrogen-bonded structure between solutions involving amino acid molecules with different optical activities.The observed difference functions,DELTAi(Q)and DELTAi~(inter)(Q),between observed scattering cross sections for DL-and L-alanine solutions with a D content of 96.1% exhibit the first peak located at Q = 2 A"1 followed by oscillatory features extending up to the higher-Q region.The difference distribution function,Ag(r),obtained from the Fourier transform of Ai(Q),clearly indicates negative peaks at r = 2 and 2.5 A and a positive one at r = 3.5 A.Partial structure factors,a_(HH)(Q),a_(XH)(Q)and a_(xx)(Q)(X:O,N,C,H_M,and H_M',where H_M and H_M'denote methyl and methine hydrogen atoms within the alanine molecule,respectively)for 2.5 mol% DL-alanine solutions are successfully determined from combined analyses of intermolecular interference terms observed for solutions with 96.1,66.0,and 35.9% exchangeable deuterium content.The nearest neighbor O…H_(ex)and H_(ex)…H_(ex)(H_(ex):exchangeable hydrogen atom)distances are determined from the least squares fit of the observed partial structure factors,1.90(1)and 2.48(1)A,respectively.These values correspond to the positions of negative peaks observed in the present Ag(r)function.The least squares fitting analysis of the observed Ai(Q)revealed that the difference in the coordination number of the nearest neighbor O…H_(ex)and H_(ex)…H_(ex)interactions between the DL-and L-alanine solutions are-0.031(5)and-0.072(5),respectively.It is concluded that the intermolecular hydrogen bonds among solvent water molecules in the DL-alanine solution are ca.2% weaker than those in the L-alanine solution.
机译：为了研究2.5％摩尔浓度的DL-丙氨酸和L-丙氨酸水溶液的飞行时间（TOF）和稳态反应堆中子衍射测量，以研究涉及氨基酸分子的溶液之间分子间氢键结构的差异。 D含量为96.1％的DL-丙氨酸溶液和L-丙氨酸溶液的散射截面之间观察到的差异函数DELi（Q）和DELTAi（inter）（Q）表现出位于Q的第一个峰= 2 A“ 1，然后是振荡特征，一直延伸到较高的Q区域。从Ai（Q）的傅里叶变换获得的差分分布函数Ag（r）清楚地表明在r = 2和2.5 A处出现负峰且在r = 3.5 A时为正数。部分结构因子a_（HH）（Q），a_（XH）（Q）和a_（xx）（Q）（X：O，N，C，H_M和H_M '，其中H_M和H_M'分别表示丙氨酸分子中的甲基和次甲基氢原子）成功地阻止了2.5 mol％的DL-丙氨酸溶液从分子间干扰项的组合分析中提取，观察到的分子中具有96.1、66.0和35.9％的可交换氘含量的溶液。最近邻O…H_（ex）和H_（ex）…H_（ex）（H_（ex）：可交换氢原子距离是分别由观察到的部分结构因子的最小二乘拟合确定的1.90（1）和2.48（1）A。这些值对应于当前Ag（r）函数中观察到的负峰位置。对观测到的Ai（Q）的最小二乘拟合分析表明，DL-和L-丙氨酸溶液之间最近邻O…H_（ex）和H_（ex）…H_（ex）相互作用的配位数差是得出的结论是，DL-丙氨酸溶液中溶剂水分子之间的分子间氢键比L-丙氨酸溶液中的分子间氢键弱约2％.- 0.031（5）和-0.072（5）。

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