Tao Feng, Bernasek Steven L
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
J Phys Chem B. 2005 Apr 7;109(13):6233-8. doi: 10.1021/jp0452397.
The molecular arrangement and chirality of the self-assembled arachidic anhydride monolayer on graphite were investigated using scanning tunneling microscopy (STM). This molecule has two identical alkyl chains, linked by an anhydride group in the middle. In its extended form, one alkyl chain is shifted, with respect to the other, along the molecular backbone. Upon adsorption on graphite, this achiral anhydride spontaneously forms two types of homogeneous domains (denoted as m and m') with mirror symmetry. The angle from the molecular chain to the row-packing direction is 98.0 degrees +/- 0.5 degrees and 82.0 degrees +/- 0.5 degrees for domains m and m', respectively. Domain m is the mirror image of m'. The molecular arrangement of this self-assembled monolayer shows that domains m and m' are two-dimensional enantiomers with opposite chiralities. This new molecular packing motif is confirmed by line-profile analyses along the molecule-chain and the row-packing directions. This finding demonstrates the spontaneous formation of highly ordered homogeneous enantiomorphous domains on graphite resulting only from weak van der Waals forces between the achiral arachidic anhydride molecules.
利用扫描隧道显微镜（STM）研究了花生酸酐在石墨上自组装单层的分子排列和手性。该分子有两条相同的烷基链，中间由一个酸酐基团相连。在其伸展形式下，一条烷基链相对于另一条沿着分子主链发生了位移。吸附在石墨上时，这种非手性酸酐会自发形成两种具有镜像对称性的均匀畴（分别记为m和m'）。对于畴m和m'，分子链与行堆积方向的夹角分别为98.0度±0.5度和82.0度±0.5度。畴m是m'的镜像。这种自组装单层的分子排列表明，畴m和m'是具有相反手性的二维对映体。通过沿分子链和行堆积方向的线轮廓分析证实了这种新的分子堆积模式。这一发现表明，仅由非手性花生酸酐分子之间的弱范德华力就能在石墨上自发形成高度有序的均匀对映异构畴。
