【作者】 徐振；

【导师】 刘成卜；

【作者基本信息】 山东大学 ， 理论与计算化学， 2011， 博士

【摘要】 随着固体表面吸附研究理论的深入和界面科学的发展,致力于固体表面选择性吸附的实验研究引起了人们的极大兴趣。尤其是通过多样化的实验手段,如电泳沉积法(electrophoretic deposition)、模具胶体溶液流程法(flow of colloidal solution through a mold with micro drains)、三层技术(a three-layer technique)和紫外线照射方法(UV irradiation)等方法对固体表面进行修饰和改性可以形成具有特殊选择性吸附区域的功能材料。这些功能材料对多种领域如金属表面防腐蚀、生物仿生材料的制备、微触点印制技术、生物传感技术、气相敏感元件的制造等都产生了革命性的影响,推动了相关技术的飞速发展。在人们不断改进实验方法制备新型选择性吸附功能固体材料的同时,越来越多的科学工作者致力于采用理论计算的方法研究固体表面选择性吸附。与传统的实验研究手段相比,应用包括量子化学和分子动力学模拟等方法的理论计算可大大减少实验的盲目性和重复试验的耗时性,同时帮助人们全面了解固体材料选择性吸附机理和微观吸附模型,对实验设计和开发新型选择性吸附材料具有重要的指导意义。本文围绕实验研究中最新报道的几种具有选择性吸附能力的固体材料进行了系列理论研究工作。一方面借助分子动力学和量子化学相结合的方法研究了以Si和Si02为基底的两种典型自组装单分子膜(SAMs)的选择性吸附,探讨了不同头基与不同烷烃链在基底上的组装密度对SAM选择性吸附的影响,提出了较为合理的选择性吸附机理,为实验设计和改良这两种SAM的选择吸附提供了有价值的信息。另一方面运用分子动力学方法验证了Au(111)表面选择性吸附组氨酸类氨基酸分子的实验报道,从微观层面上给出了吸附模型,揭示了Au(111)面选择性吸附组氨酸类氨基酸分子的本质,总结出组氨酸类分子的构型变化对选择性吸附的影响,为定向设计、合成相关功能生物材料的研究起到了积极的理论指导。本文主要研究内容和创新性成果归纳如下：(1)修饰SAM的表面头基对SAM内部结构及表面润湿性的影响应用分子动力学方法研究了六种不同头基(-CH3,-C=C,-OCH3,-CN,-NH2,-COOH)烷烃链在H-终止Si(111)表面的自组装行为。讨论了不同头基对SAM内部结构与表面平整度的影响,结果发现三种亲水头基(-CN,-NH2,-COOH)通过彼此之间形成的分子间氢键,对SAM内部结构的影响明显大于三种疏水头基(-CH3,-C=C,-OCH3),这主要体现在对烷烃链与Si(111)表面的夹角和SAM膜厚度方面。并且由于亲水头基之间的氢键相互作用,使得含有三种亲水头基(-CN,-NH2,-COOH)的SAM的表面更加光滑、平整。借助分子动力学模拟和量子化学相结合的方法研究了上述六种头基修饰的SAM表面的润湿性(对水分子的选择性吸附能力)。所得结果与Faucheuxa N教授等人报道(J. Am. Chem. Soc.120,14,1998)的测定这六种SAMs的表面润湿角的结果完全一致,并从分子层面给出了三种亲水性(-CN,-NH2,-COOH) SAM表面在部分润湿和完全润湿后的水分子的排列构型：在三种亲水SAM表面低度润湿后, CN-与COOH-SAM表面上通过分子间氢键形成了单个水分子与相邻两个碳链头基之间的“桥”式结构；而在表面润湿程度持续增加后, NH2-与COOH-SAM的表面首先会通过分子间H键形成两个水分子的二聚体,然后再与相邻的含有亲水头基的烷烃链通过这个二聚体形成“桥”式结构。通过量子化学的计算与氢键的分析证明了SAM表面选择性吸附水分子能力的强弱取决于表面头基基团与水分子形成氢键的数目、以及氢键的强弱。该模拟工作对实验上设计和制备特殊润湿性表面的生物敏感材料具有重要的指导意义。(2)具有不同密度的复合自组装膜选择性吸附荧光有机分子的理论研究实验报道通过Langmuir-B lodgett方法可以得到液体扩展相(liquid expanded(LE))和液体压缩相(liquid condensed (LC))交替排列的二棕榈酰磷脂酰胆碱膜(L-a-dipalmitoyl-phosphatidylcholine (DPPC)),这种单分子膜是一种良好的固体模版,具有选择性吸附微小纳米晶体颗粒的能力。我们根据实验现象设计出与之结构相似,疏密相间的条形自组装膜结构,并通过分子动力学方法研究了不同烷烃链疏密相间的自组装膜(SAMs)对有机荧光分子3(5)-(9-葸基)吡唑(3(5)-(9-anthryl) pyrazole (ANP))和苝(perylene)的选择性吸附。我们的模拟结果表明：烷烃链疏密相间排列的SAM对有机荧光分子具有选择性吸附的能力,荧光分子会优先吸附在SAM烷烃链较稀疏的区域,当表面吸附的荧光分子数目逐渐增加至该区域接近饱和时,才会有少量荧光分子吸附在SAM烷烃链较密集区域。通过对两种有机荧光分子ANP和perylene在SAM不同烷烃链疏密区间的扩散系数以及与固体基底间的均力势(PMF),从分子尺度上揭示了这类构型的自组装膜选择性吸附有机荧光分子的机理。该项工作对相关领域科研人员设计和研发新型选择性吸附荧光分子的功能材料具有重要的指导意义。(3)Au(111)表面对组氨酸类分子的选择性吸附作用应用分子动力学方法研究了组氨酸(Histidine(His))以及三种组氨酸衍生的氨基酸分子——甘-组氨酸(glycyl-histidine (Gly-His)),甘-组-甘氨酸(glycyl-histidine-glycine (Gly-His-Gly))和甘-甘-组氨酸(glycyl-glycyl-histidine (Gly-Gly-His))在Au(111)面的吸附行为。该模拟工作基于Feyer等人对组氨酸类分子在Au(111)表面选择性吸附现象的相关实验报道。模拟结果证实了实验结论：Au(111)表面确实对组氨酸类氨基酸分子具有优先吸附作用,通过模拟方法得到的最终吸附构型与Feyer等人推测的构型非常一致。模拟结果从分子层面上证明了组氨酸及其三种衍生的氨基酸分子是通过咪唑环(imidazole (IM) ring)上的亚氨基氮和羧酸基团与Au原子的相互作用而吸附在Au(111)面的。此外,我们通过比较四种组氨酸类氨基酸分子在溶液中向Au(111)面的吸附速率和单分子表面吸附能,发现在这四种氨基酸分子中,Au(111)表面优先吸附Gly-His分子；而对于两种含组氨酸的三肽分子(Gly-Gly-His与Gly-His-Gly)而言,残基的排列顺序对两种三肽氨基酸分子在Au(111)表面的最终吸附构型有着明显的影响,而对于二者的吸附速率几乎没有影响。我们的模拟结论不但从微观层面上印证了实验结果,同时给出了实验上通过宏观观测手段难以获得的信息,更加完善了该领域的研究工作,这对通过Au表面定点选择性吸附生物小分子而设计新型功能生物材料具有重要的指导意义。更多还原

【Abstract】 With the development of the theory on solid surface adsorption and the interfacial science, it has aroused people’s enormous interest in the experimental study of the selective adsorption of solid surface. Especially through diverse experimental methods, such as electrophoretic deposition, flow of colloidal solution through a mold with micro drains, a three-layer technique and UV irradiation, some functional materials are modified to form special selective region on the surface. These functional materials are widely used in many fields, such as corrosion preventing of metal surface, preparation of bio-materials, micro electronic contact print technology, biological sensing technology, and gas phase sensitive unit. It has promoted the development of the correlation technique.Recent years, more and more scientific workers devote in the research to the solid surface selectivity adsorption through theoretical calculation, as well as improving the experimental technique of new functional solid materials of selective adsorption. Compared with the traditional experimental study method, the application of theoretical calculations, including quantum chemistry and molecular dynamics simulation, may reduce the blindness of experiments and revision test time-consuming greatly. Simultaneously, the theoretical calculations can provide a detailed, atomistic level insight into the three-dimensional structure of the studied model system. These kinds of studies allow us to extract information about dynamic and structural properties at a microscopic level which is not easy to get from experiments.In this dissertation, a series of theoretical studies have been carried out for several kinds of several kinds of solid state materials newly reported in experiments. On the one hand, by performing density functional theory (DFT) calculations and MD simulations, we have studied the ability of selective adsorption of two typical self-assembled monolayers (SAMs) forming in Si or SiO2 substrate, and focused on the influence of different end groups and different alkyl chains in packing density to the selectivity adsorptive capacity of SAMs, meanwhile a reasonable selective adsorption mechanism was proposed. These theoretical research results supply some valuable information for designing and improving the selective adsorption ability of the two kinds of SAM. On the other hand, we have studied the selective adsorption behavior of Histidine (His) and three His-derived peptides on Au(111) reported recently in the experiments through MD simulations. We have given the adsorption configuration from the microscopic level, and gave a possible mechanism of the histidine selective adsorption onto Au(111). We have summarized the influence of configuration changing of the histidine class amino to their capacity of selective adsorption onto Au(111).The important and valuable results in this dissertation can be summarized as follows:(1) The influence of changing SAM with different end groups to the internal structure and superficial wettability of SAM.The morphology of alkyl monolayers with different end groups (-CH3,-C=C,-OCH3,-CN,-NH2,-COOH) on the H-terminated Si(111) surface was investigated by molecular simulation method. We focus on the influence of different end groups on the internal structure and superficial smoothness of SAM. We have found that three hydrophilic end groups (-CN,-NH2,-COOH) has the huge influence to the internal structure of SAM, and make the surface smoother, mainly due to the interaction of hydrogen bonds in the hydrophilic SAM surface.We have studied the wetting ability of SAMs with the different end groups (-CH3,-C=C,-OCH3,-CN,-NH2,-COOH) through a combined molecular dynamics and quantum mechanics method. The obtained results is constant with the contact angle of the six SAMs after surface wetted reported by Faucheuxa N. in experiments. We have shown the hydrogen bonding patterns between adsorbed water molecules and the three hydrophilic (-CN,-NH2,-COOH) surface groups:at a very low level of hydration, the structure of one water molecule "bridging" between two hydrophilic group-terminated chains was formed in the surfaces of CN- and COOH-SAM; As the level of hydration increases, the predominant pattern is "bridging" two chains by water dimer in the surfaces of CN2- and COOH-SAM. Through hydrogen bonding analysis and QM calculation, our data suggests that the wetting ability of a SAM surface depends mainly on the type, quantity and strength of hydrogen bonds formed between polar head groups and water molecules. The results of this investigation provide a microscopic perspective on the wetting properties of different organic surfaces (from hydrophobic to hydrophilic) that could be helpful in developing models to describe the wetting behavior of organic materials in a biological environment.(2) Selective Deposition of Organic Molecules onto Different Densely Packed Self-Assembled MonolayersA series of MD simulations were conducted towards the selective deposition of organic luminescent molecules 3(5)-(9-anthryl) pyrazole (ANP) and perylene onto different densely packed organosilane self-assembled monolayers (SAMs). Our simulations indicated that the packing density of alkyl chains on SAM may directly control the site-selective deposition of organic molecules. Additionally we propose a possible mechanism for this phenomenon, which can also explain the experimental findings of the selective deposition of organic molecules onto template structures, made of L-a-dipalmitoyl-phosphatidylcholine (DPPC) in alternating liquid expanded (LE) and liquid condensed (LC) states. As expected, the organic molecules firstly deposit exclusively onto the less alkyl chains densely packed area of SAM.The difference in diffusion as well as the different interfacial energy can reasonably explain preferred deposition of organic molecules onto the alkyl chains expanded area of SAM, and it is certainly guiding and helpful to the synthesis of new functional materials in experiments.(3) The selective adsorption of Histidine and Histidine-Containing Peptides on Au(111)The adsorption behavior of Histidine (His) and three His-derived peptides, glycyl-histidine (Gly-His), glycyl-histidine-glycine (Gly-His-Gly), and glycyl-glycyl-histidine (Gly-Gly-His) on the Au(111) surface (reported by Feyer et al.) has been studied using molecular dynamics simulations. Our results have proven that His and His-derived peptides adsorbed on Au(111) via the imino nitrogen in the imidazole (IM) ring and the carboxylic acid group at the molecular level, and it agrees well with available experimental data.In additional, many statistical properties of His and His-derived peptides, like the interaction energy of adsorption, were analyzed after the systems reaching equilibrium. We conclude that:(ⅰ) Au(111) surface first adsorb the dipeptide Gly-His among the four amino acids. (ⅱ) The sequence of residues in a peptide can significantly influence adsorption geometry of amino acids rather than the adsorption rate. Our work agrees well with available experimental data and shows a clear insight into the interaction between His-containing amino acids and Au(111) surface at a microscopic level, which is helpful to future rational design efforts of gold-binding polypeptides.更多还原