Intermolecular hydrogen-bonded structure in aqueous solutions involving amino acid molecules with different optical activities

用中子衍射和x射线衍射测量了含有不同光学活性氨基酸分子的2.5 mol% DL-和l -丙氨酸水溶液在D_2O中的分子间氢键结构。DL-和l -丙氨酸溶液分子间中子干涉差函数Δi(Q)的傅里叶变换得到的差分布函数Δg(r)在r = 2和2.5处出现负峰Å，这些位置分别对应O-H和H-H分子间氢键距离。采用最小二乘拟合方法对观测值Δi(Q)进行定量分析。得到的分子间距离r(O-H)=1.99(3)Å， r(H-H)=2.54Å， Δn(O-H)=-0.031(5)， Δn(H-H)=-0.072(5)。Δn（O-H）和Δn（H-H）的现值表明，l -丙氨酸溶液中水分子间的氢键比dl -丙氨酸溶液中水分子间的氢键强约2%。对2.5 mol%和1 mol% DL-和l -丙氨酸重水溶液进行了分子动力学模拟。在1 mol% DL-和l -丙氨酸溶液中，水-水相互作用的偏分布函数g_<HH>(r)、g_<OH>(r)和g_<OO>(r)没有差异，这表明在稀释条件下DL-和l -丙氨酸溶液的分子间氢键结构不存在差异。另一方面，得到的描述水-水相互作用的偏分布函数g_<HH>(r)、g_<OH>(r)和g_<OO>(r)表明，l -丙氨酸溶液中的分子间氢键比DL-丙氨酸溶液中的分子间氢键强约1%。为了研究丙氨酸分子内的氨基和最邻近的水分子之间的氢键差异，对^<14>N/^<15>N同位素取代的3mol % DL-和l -丙氨酸重水水溶液进行了飞行时间中子衍射测量。数据分析正在进行中。少

Neutron and X-ray diffraction measurements were carried out on aqueous 2.5 mol% DL- and L-alanine solutions in D_2O in order to investigate the difference in intermolecular hydrogen-bonded structure between these solutions involving amino acid molecules with different optical activities. The difference distribution functions Δg(r) derived from the Fourier transform of the difference neutron intermolecular interference function Δi(Q) between DL- and L-alanine solutions exhibited negative peaks at r = 2 and 2.5 Å, these positions correspond to O-H and H-H intermolecular hydrogen-bonded distances, respectively. Quantitative analysis was carried out by means of the least squares fitting analysis of observed Δi(Q). Intermolecular distances and difference coordination numbers obtained were r(O-H)=1.99(3)Å, r(H-H)=2.54Å, Δn(O-H)=-0.031(5), and Δn(H-H)=-0.072(5), respectively. The present values of Δn(O-H) and Δn(H-H) indicate that the intermolecular hydrogen bonds between water molecules in t … More he L-alanine solution are ca.2% stronger than those in the DL-alanine solution. The molecular dynamics simulation was adopted for 2.5 mol% and 1 mol% DL- and L-alanine heavy water solutions. Difference in partial distribution functions for water-water interaction, g_<HH>(r), g_<OH>(r), and g_<OO>(r) does not observed between 1 mol% DL- and L-alanine solutions, implying that the difference in the intermolecular hydrogen-bonded structure between DL- and L-alanine solutions is not present in the diluted condition. On the other hand, the partial distribution functions describing water-water interaction, g_<HH>(r), g_<OH>(r), and g_<OO>(r), obtained for 2.5 mol% DL- and L-alanine solutions indicated that the intermolecular hydrogen bonds in L-alanine solution are ca.1% stronger than that in the DL-alanine solutions. Time-of-flight neutron diffraction measurements on ^<14>N/^<15>N isotopically substituted aqueous 3 mol% DL- and L-alanine heavy water solutions were carried out in order to investigate the difference in hydrogen-bonds between the amino group within the alanine molecule and the nearest neighbor water molecules. The data analysis is in progress. Less