关键词: 单晶表面手性识别, 空间群, DL-缬氨酸, 原子力显微镜, X射线衍射

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

Key words: Single crystal surface chiral recognition, Space group, DL-valine, AFM, X-ray diffraction