【摘要】 利用原子力显微镜(AFM)成像技术来观察DL-缬氨酸晶体表面分子的规则排列,研究表明对映体分子在DL-缬氨酸晶体中相互配对排列,每个晶胞单元中包含两个对映体分子,属于具有中心对称结构P1群,整个晶体是消旋的.通过原子力显微镜对DL-缬氨酸晶体表面重复单元的测量结果与X衍射数据对比,发现用AFM观察到的DL-缬氨酸晶体中分子表面形貌的规整排列的距离,同X衍射得出的三斜晶系晶胞参数数据基本一致,由此判定该晶体属于三斜晶系而不是单斜晶系.探讨了利用纳米技术的研究手段在分子水平研究生命起源中的手性问题,在确定的晶面上通过分子周期性结构排列规律,对DL-缬氨酸晶体表面分子进行手性识别.更多还原

【Abstract】 Atomic force microscopy(AFM) has been used to image arrays of molecules at the surface of DL-valinecrystals. AFM images of DL-valine show that D- and L- molecular pairs formed from a DL-racemic mixture are exclu-sively homochiral. There are two different conclusions about the crystal structure of DL-valine with the data of X-raycrystallography. First, the structure of DL-valine was solved in the monoclinic space group P21/c. Second, the crystalstructure of DL-valine has been refined in the centrosymmetric space group P1 and indicated a triclinic rather than amonoclinic space group. The present work emphasizes to solve the contradicting observations of space group and toprovide direct evidence for chiral recognition at molecular level. DL-valine molecules ｛001｝ are all in zwitterionic formwith the isopropyl groups close to the surface and methyl groups on the top site, showing an ordered molecular mor-phology of triclinic unit cells, which are in fair agreement with the X-ray diffraction data. The application of AFM tothe investigation of protein′s origins and a molecular-level illustration of chiral recognition at a periodic 2D surfacestructure of racemic crystals is discussed.更多还原