Department of Chemistry, Sookmyung Women's University, Cheongpa-dong 2-ga, Yongsan-gu, Seoul, 140-742, Korea.
Chem Asian J. 2011 Sep 5;6(9):2362-7. doi: 10.1002/asia.201100004. Epub 2011 May 17.
The adsorption configurations of methionine molecules on the Ge(100) surface have been studied by using DFT calculations, core-level photoemission spectroscopy (CLPES), and low-energy electron diffraction (LEED) to scrutinize the adsorption structure as a function of coverage. At first, we obtained two important and stable structures. One is the most stable structure between these structures described as an "O-H dissociated-N dative-S dative-bonded structure" and the other is a less stable adsorption structure of these indicating an "O-H dissociated-S dative-bonded structure" by using DFT calculations. We also performed CLPES to clarify our DFT calculation results. Through the spectral analysis of the S 2p, C 1s, N 1s, and O 1s core-level spectra, we acquired the reasonable results that also revealed quite different bonding configurations depending on the methionine coverage. At low coverage (ca. 0.30 ML), a single type of sulfur and charged nitrogen peaks, which indicate an "O-H dissociated-N dative-S dative-bonded structure", were observed. On the other hand, two types of sulfur peaks with thiol formation and two nitrogen peaks with neutralized and charged characteristics were monitored at a higher coverage (0.60 ML and above), which can be described as an "O-H dissociated-S dative-bonded structure". Hence, we can clearly demonstrate that our results obtained from CLPES spectra and DFT calculations are matched well with each other. Moreover, we additionally confirmed that the relative population of the two types of thiols and amines being included in methionine in between half monolayer induces a surface reorientation in the ordering from 2×1 to 1×1 employing LEED. This interesting variation of the methionine adsorbed on the Ge(100) surface by coverage dependence will be precisely discussed by using DFT calculations, CLPES, and LEED.
采用密度泛函理论（DFT）计算、芯层光电子能谱（CLPES）和低能电子衍射（LEED）研究了甲硫氨酸分子在 Ge（100）表面的吸附构型，以研究覆盖率对吸附结构的影响。首先，我们得到了两种重要且稳定的结构。一种是这些结构中最稳定的结构，描述为“O-H 离解-N 配位-S 配位键结构”，另一种是这些结构中不太稳定的吸附结构，描述为“O-H 离解-S 配位键结构”。我们还进行了 CLPES 以澄清我们的 DFT 计算结果。通过对 S 2p、C 1s、N 1s 和 O 1s 芯层谱的谱分析，我们获得了合理的结果，也揭示了不同的键合构型，这取决于甲硫氨酸的覆盖率。在低覆盖率（约 0.30 ML）下，观察到单个类型的硫和带电荷的氮峰，表明“O-H 离解-N 配位-S 配位键结构”。另一方面，在更高的覆盖率（0.60 ML 及以上）下，监测到两种硫峰和两种具有中和和带电荷特性的氮峰，这可以描述为“O-H 离解-S 配位键结构”。因此，我们可以清楚地证明我们从 CLPES 谱和 DFT 计算中获得的结果相互匹配。此外，我们还通过 LEED 进一步证实，半单层之间甲硫氨酸中两种硫醇和胺的相对比例会导致表面重新定向，从 2×1 到 1×1。通过覆盖率依赖关系吸附在 Ge（100）表面上的甲硫氨酸的这种有趣变化将通过 DFT 计算、CLPES 和 LEED 进行精确讨论。
