WATLab and Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
J Am Chem Soc. 2014 Dec 3;136(48):16909-18. doi: 10.1021/ja509264t. Epub 2014 Nov 18.
Surface functionalization of an inorganic surface with bio-organic molecules is often aimed at creating a "permanent" bio-organic surface with receptor functional groups. We show here that L-cysteine can be used to transform a highly reactive Si(111)7×7 surface to not just a permanent bio-organic surface but also a semipermanent (or renewable) and a temporary bio-organic surfaces by manipulating the exposure. In the early growth stage, the strong bonding between the first cysteine adlayer and the Si substrate through Si-N or Si-S linkages in unidentate or bidentate arrangement provides permanent biofunctionalization by this interfacial layer. This interfacial layer can be used to build a transitional layer (second adlayer) mediated by interlayer vertical hydrogen bonding between an amino group and a carboxylic acid group. Further exposure of cysteine eventually leads to a zwitterionic multilayer film involving electrostatic interactions between cation (-NH3(+)) and anion moieties (-COO(-)). The interlayer hydrogen bonding therefore provides temporary trapping of bio-organic molecules as the second transitional layer that is stable up to 175 °C. This transitional layer can be easily removed by annealing above this temperature and then regenerated with the same molecular layer or a different one by "renewing" the interlayer hydrogen bonds. We also illustrate coverage-dependent adsorption structures of cysteine, from bidentate to unidentate attachments and to self-assembled multimers, involving formation of intralayer horizontal N···H-O hydrogen bonds, by combining our X-ray photoemission data with the local density-of-state images obtained by scanning tunnelling microscopy.
将生物有机分子的表面功能化到无机表面上通常旨在创建具有受体官能团的“永久性”生物有机表面。我们在这里展示，通过操纵暴露，可以将 L-半胱氨酸用于将高度反应性的 Si(111)7×7 表面转化为不仅是永久性的生物有机表面，而且是半永久性（或可再生）和临时性的生物有机表面。在早期生长阶段，由于第一个半胱氨酸单层通过 Si-N 或 Si-S 键以单齿或双齿排列与 Si 衬底之间的强键合，通过该界面层提供永久性生物官能化。该界面层可用于通过氨基和羧基之间的层间垂直氢键来构建过渡层（第二层）。进一步的半胱氨酸暴露最终导致涉及阳离子（-NH3(+)）和阴离子部分（-COO(-)）之间静电相互作用的两性离子多层膜。因此，层间氢键提供了作为第二层的临时捕获生物有机分子，其在高达 175°C 的温度下稳定。通过在高于此温度下退火，可以很容易地去除这种过渡层，然后通过“更新”层间氢键，可以用相同的分子层或不同的分子层再生。我们还通过将我们的 X 射线光电子能谱数据与通过扫描隧道显微镜获得的局部态密度图像相结合，说明了胱氨酸的覆盖依赖性吸附结构，从双齿到单齿附着和自组装多聚体，涉及形成层内水平 N···H-O 氢键。
