Theoretical Studies On Selective Adsorption And Accumulation Behavior Of Several Solid Surfaces

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:(?) Au(111) surface first adsorb the dipeptide Gly-His among the four amino acids. (?) 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.