The effect of hydrogen chemisorption on titanium surface bonding

The effect of hydrogen chemisorption on the strength of Ti-Ti bonds is studied byab initio configuration interaction techniques using an embedding theory to describe the electronic structure. A Ti adatom on Ti(0001) is modelled by a Ti₂₀H cluster with boundary potentials determined from the embedding treatment. Hydrogen atom chemisorption is highly exothermic for adsorption atop the adatom, a three-fold site formed by the adatom and in the interstitial site below the adatom. Compared to the planar Ti(0001) surface the adatom region binds hydrogen much more strongly. Removal of Ti from the surface is energetically much more favorable if H remains on the surface as opposed to the removal of TiH. The exchange reaction Ti₂₀+HTi₁₉H+Ti is endothermic by 0.3 eV. These results suggest high reactivity of the adatom region on Ti(0001) but not such that the surface is more easily fragmented by removal of Ti or TiH.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Comparative study of adsorption and heats of adsorption on planar and particulate polymer surfaces

The adsorption and heats of adsorption of Lewis acidic-basicprobes on planar and particulate surfaces of polyimide/siloxane, 6F photoimagable fluorinated polyimide and 6F polyimide have been studied by flow microcalorimetric, ellipsometric, and contact angle techniques. The heats of adsotption obtained by these techniques are in good agreement. It is noted that the ellipsometric method based on an analysis of adsorption kinetics has advantages over the contact angle technique and may be used for the study of the interface on planar polymer surfaces. The acidic-basic properties of polymers were approximately estimated by using the DragoE andC constants.     

Theoretical study of NO adsorption on gold surfaces

The activities of neutral,anionic,and cationic Au(111),Au(100),and Au(310) surfaces,as well as an Au adatom on Au(111) surface towards NO adsorption have been studied by performing density functional theory calculations.It was found that the activity of gold increases as the coordination number of the gold atoms decreases,and that the cationic surfaces are generally more active than the neutral and anionic surfaces.The activity of Au surfaces towards NO adsorption is attributable to the presence of low coor...     

Vapour adsorption and contact angles on hydrophobic solid surfaces

To test the effects of vapour adsorption on contact angle measurements, contact angles of high-vapour-pressure liquids and low-vapour-pressure liquids on a hydrophobic solid surface (FC721) were measured by using the axisymmetric drop shape analysis-profile (ADSA-P) technique. Details of the surface preparation and the experiments are presented. By plotting the experimental data in terms of _1v cos vs. _1v, this study shows that the vapour adsorption on a fluorocarbon surface, FC721, is negligible.     

Albumin adsorption on unmodified and sulfonated polystyrene surfaces, in relation to cell-substratum adhesion

Albumin is commonly applied for blocking the adsorption of other proteins and to prevent the nonspecific adhesion of cells to diverse artificial substrata. Here we address the question of how effective these albumin properties are--by investigating unmodified and sulfonated polystyrene substrata with distinctly different wettabilities. As clearly shown with (125)I-radioisotopic assays, above a concentration of 10-20 μg/mL, the efficiency of bovine serum albumin (BSA) adsorption became markedly higher on the sulfonated surface than on the unmodified one. This study was assisted with the atomic force microscopy. On the unmodified surface, BSA, adsorbed from sufficiently concentrated solutions, formed a monolayer, with occasional intrusions of multilayered patches. Conversely, the arrangement of BSA on the sulfonated surface was chaotic; the height of individual molecules was lower than on the unmodified polystyrene. Importantly, the adhesion study of LNCaP and DU145 cells indicated that both surfaces, subjected to the prior BSA adsorption, did not completely loose their cell-adhesive properties. However, the level of adhesion and the pattern of F-actin organization in adhering cells have shown that cells interacted with unmodified and sulfonated surfaces differently, depending on the arrangement of adsorbed albumin. These results suggest the presence of some bare substratum area accessible for cells after the albumin adsorption to both types of investigated surfaces.     

Kinetics and equilibrium of multicomponent adsorption on chiraly templated surfaces

In this contribution we propose a simple model of adsorption of a binary (racemic) mixture on a chiraly templated surface. As an example, the adsorption of a liquid mixture of enantiomers on a chiral stationary phase (CSP) is considered. In particular, we study the effect of the lateral interactions in the adsorbed phase on the kinetic and equilibrium isotherms of the enantiomers. Additionally, we investigate the influence of the composition of the surface on the performance of the CSP in the presence of the lateral interactions. To that end, the adsorption of the mixture is modeled by using Monte Carlo simulations as well as by applying an analytical approach involving rate equations coupled with the Mean Field Approximation (MFA). The predictions of the theory are found to be in good agreement with the results of the simulations.     

Nonrandom adsorption of polyelectrolyte chains on finite regularly charged surfaces

Adsorption phenomena are relevant in a wide variety of subjects, from biophysics to technological applications. Different aspects, such as molecular recognition, multilayer deposition, and dynamics of polymer adsorption have been addressed. The methodologies used range from analytical and numerical methods to molecular dynamics or Monte Carlo simulations. In this work, a coarse‐grained model is used to explore the adsorption of charged backbones to oppositely charged regions of a surface. These regions encompass those small enough to prevent complete adsorption, but extend to surfaces sufficiently large to promote adsorption with minimal effect on the three‐dimensional conformation in bulk. Apart from the different surface areas explored, variations on the surface charge density, polyelectrolyte chain length, and chain stiffness were also considered. The degree of compaction of the polyelectrolyte, on adsorption, is different from that found in the bulk. Also, results indicate an nonuniform adsorption pattern on regularly charged surfaces. © 2013 Wiley Periodicals, Inc.     

A study of the effect of the synthesis conditions of titanium dioxide on its morphology and cell toxicity properties

In this study, titanium dioxide nanoparticles (NPs) were synthesized using the home microwave method, and the effect of the microwave irradiation time on the structure of NPs was investigated. In addition, the morphological effect of these NPs on the toxicity of HDMSCs cells was investigated. The crystalline structure and morphology of the NPs were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM); the cytotoxicity was determined by the methyl thiazolyl tetrazolium (MTT) assay. X-ray diffraction analysis revealed that all thin films had a polycrystalline nature with an anatase phase of TiO₂. It was also found that the crystallite size increased with increasing microwave radiation time. The FTIR spectrum showed Ti-O-Ti properties by the peak in the range between 527 and 580 cm^?1. Further, the FE-SEM images showed that the grain size increased with increasing irradiation time. The MTT assay results showed that the accumulation of NPs leads to toxicity.     

Nitrogen oxide activation on the surfaces of titanium carbide and titanium nitride

The mechanism of NO activation on the surfaces of crystalline titanium monocarbide and titanium mononitride has been studied within the framework of semiempirical SCF LCAO NDDO method. The adsorption has been shown to be accompanied by electron density transfer from the crystal surface to the adsorbate molecule. Stronger activation of the NO molecule is observed on the TiC surface as compared with that on TiN surface.     

Protein adsorption and cell adhesion on RGD-functionalized silicon substrate surfaces

A method was developed to modify silicon surfaces with good protein resistance and specific cell attachment. A silicon surface was initially deposited using a block copolymer of N-vinylpyrrolidone (NVP) and 2-hydroxyethyl methacrylate (HEMA) (PVP-b-PHEMA) film through surface-initiated atom transfer radical polymerization and then further immobilized using a short arginine-glycine-aspartate (RGD) peptide. Our results demonstrate that the RGD-modified surfaces (Si-RGD) can suppress non-specific adsorption of proteins and induce the adhesion of L929 cells. The Si-RGD surface exhibited higher cell proliferation rates than the unmodified silicon surface. This research established a simple method for the fabrication of dual-functional silicon surface that combines antifouling and cell attachment promotion.     

Use of cellulose derivatives on gold surfaces for reduced nonspecific adsorption of immunoglobulin G

This study addresses the design of protein-repellent gold surfaces using hydroxyethyl- and ethyl(hydroxyethyl) cellulose (HEC and EHEC) and hydrophobically modified analogues of these polymers (HM-HEC and HM-EHEC). Adsorption behavior of the protein immunoglobulin G (IgG) onto pure gold and gold surfaces coated with cellulose polymers was investigated and described by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and contact angle measurements (CAM). Surfaces coated with the hydrophobically modified cellulose derivatives were found to significantly outperform a reference poly(ethylene glycol) (PEG) coating, which in turn prevented 90% of non-specific protein adsorption as compared to adsorption onto pure gold. HEC and EHEC prevented around 30% and 60% of the IgG adsorption observed on pure gold, while HM-HEC and HM-EHEC were both found to completely hinder biofouling when deposited on the gold substrates. Adsorption behavior of IgG has been discussed in terms of polymer surface coverage and roughness of the applied surfaces, together with hydrophobic interactions between protein and gold, and also polymer-protein interactions.     

The cell effect in adamantane adsorption on graphitized thermal carbon black

Nonequivalence of the nodal and bridging carbon atoms of the adamantane molecule during adsorption on graphitized thermal carbon black was shown. The nonequivalence is related to a special type of intermolecular interaction, the cell effect. Based on the experimental data and the molecular statistical calculations of Henry's constants, the parameters of atomatom potentials for the nodal carbon atoms in the adamantane molecule were found. This atom-atom potential differs from that known for the carbon atom in the sp³-hybridization. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 849–853, May, 2000.     

Spreading of proteins and its effect on adsorption and desorption kinetics

The kinetics of adsorption of lysozyme and alpha-lactalbumin from aqueous solution on silica and hydrophobized silica has been studied. The initial rate of adsorption of lysozyme at the hydrophilic surface is comparable with the limiting flux. For lysozyme at the hydrophobic surface and alpha-lactalbumin on both surfaces, the rate of adsorption is lower than the limiting flux, but the adsorption proceeds cooperatively, as manifested by an increase in the adsorption rate after the first protein molecules are adsorbed. At the hydrophilic surface, adsorption saturation (reflected in a steady-state value of the adsorbed amount) of both proteins strongly depends on the rate of adsorption, but for the hydrophobic surface no such dependency is observed. It points to structural relaxation ("spreading") of the adsorbed protein molecules, which occurs at the hydrophobic surface faster than at the hydrophilic one. For lysozyme, desorption has been studied as well. It is found that the desorbable fraction decreases after longer residence time of the protein at the interface.     

A comparative DFT study of Fe3+ and Fe2+ ions adsorption on (100) and (110) surfaces of pyrite: An electrochemical point of view

Pyrite acts as a catalyst in the mineral processing, and the speed of ferric ion reduction and mineral decomposition increases with increasing cathodic points. In this study, the ferric ion interaction on the (100) and (110) surfaces of pyrite was studied using the density functional theory calculations. The analysis of stability, density of states, and electron density were performed to understand the interaction between the ferric ion and pyrite surfaces. The results showed that pyrite surface is chemically active and tends to absorb ferric ion between two surface sulfur atoms. The hyperconjugation between the 3d orbital of ferric ion and the 3p or 3d orbitals of surface atoms provides the conditions for the Fe³⁺ ion adsorption. The molecular orbital (MO) and electron density analyses indicate that the 3p orbitals of S atoms play a more important role in bonds formations relative to the 3d orbitals. The (110) surface is more active, and the adsorption energy is larger than that of surface (100), which is the result of decreased cation coordination and the presence of sulfur at the surface. Subsequently, the interaction of the Fe²⁺ ion, as product of Fe³⁺ ion reduction and its competitor for adsorption, on the surfaces was studied. The Fe^{2 +} ion adsorbs stronger at the surface of (110), and the adsorption energies at (100) and (110) surfaces were obtained as −24 and −47 kcal/mol, respectively. In general, the Fe³⁺ ion is a stronger oxidizing agent than Fe²⁺ on pyrite surfaces.     

Adsorption of fibrinogen on tantalum oxide, titanium oxide and gold studied by the QCM-D technique

The adsorption of human fibrinogen on tantalum oxide, titanium oxide and gold surfaces has been studied by quartz crystal microbalance with dissipation (QCM-D) at 37 degrees C. Two different protein concentrations have been used, one close to physiological concentration (1 mg/ml) and one significantly lower (0.033 mg/ml). To further characterize the adsorbed fibrinogen layer, the subsequent binding of both polyclonal and monoclonal antibodies of fibrinogen is studied. We found that the viscoelastic properties of the fibrinogen layer depends strongly on the initial protein concentration. The trend is generally seen for all three surfaces. The fibrinogen layer on gold and tantalum oxide is found to have the same viscoelastic properties, which are different from those found for the fibrinogen layer adsorbed on titanium oxide. The dependency of the surface chemistry on the viscoelastic properties of the fibrinogen layer is observed directly for the 0.033 mg/ml solution, and indirectly through the antibody response for the 1 mg/ml solution. From this we conclude that the orientation and/or denaturation of fibrinogen on a surface depends on the surface chemistry and the protein concentration in the solution, and that the binding of antibodies is a useful way to detect this difference.     

ToF‐SIMS study of 1‐dodecanethiol adsorption on Au,Ag, Cu and Pt surfaces

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to perform a chemical analysis of long‐chain thiol (CH₃(CH₂)₁₁SH)‐treated gold, silver, copper and platinum surfaces. All the mass peaks from positive and negative ion spectra within the range m/z = 0–2000 u are studied. ToF‐SIMS data revealed that on gold, silver and copper substrates 1‐dodecanethiol form dense standing‐up phases, but on platinum being a catalytically active substrate, we were able to identify also surface‐aligned parallel lying molecules in addition to a standing thiolate layer. Our study shows that when ToF‐SIMS spectra are analyzed, not only the existence of oligomers but also metal + hydrocarbon fragments give information about the order of SAM. Copyright © 2008 John Wiley & Sons, Ltd.     

Nitrogen-rich plasma-polymerized coatings on PET and PTFE surfaces improve endothelial cell attachment and resistance to shear flow

Low seeding efficiency and poor cell retention under flow-induced shear stress limit the effectiveness of in vitro endothelialization strategies for small-diameter vascular grafts. Primary-amine-rich plasma-polymerized coatings (PPE:N) deposited using low- and atmospheric-pressure plasma discharges on PET and PTFE are evaluated for their ability to improve endothelial cells' kinetics and strength of attachment. PPE:N coatings increase cell adhesion and adhesion rate, spreading, focal adhesion, and resistance to flow-induced shear compared with bare and gelatin-coated PET and PTFE. In particular, about 90% of the cells remain on coated surfaces after 1 h exposure to shear. These coatings, therefore, appear as a promising versatile approach to improve cell seeding strategies for vascular grafts.     

金属前驱体对质子交换膜燃料电池用PtCu/C催化剂性能的影响

采用乙二醇还原法,利用不同金属前驱体(CuSO_4/CuCl_2、K_2PtCl_4/H_2PtCl_6)制备了铂铜总质量分数为20%的四种PtCu/C催化剂,并通过透射电子显微镜(TEM)、X射线衍射(XRD)、循环伏安法(CV)和线性扫描伏安法(LSV)对催化剂进行物相结构表征及电化学性能测试。结果表明,以CuSO_4和K_2PtCl_4为前驱体组合制备出的PtCu/C催化剂性能最优。所制备的PtCu/C催化剂金属颗粒平均粒径为2.3nm,粒径范围窄,在碳载体上负载均匀;电化学活性面积(ECSA)达到73.0m2/gPt,质量比活性(MA)为126.65mA/mgPt,均优于商业Pt/C催化剂。     

MgO缺陷和不规则表面吸附CO的能带和电子结构研究

采用从头算程序优化MgO表面三种不同配位位置吸附CO构型,并用扩展休克尔紧束缚(EHT)晶体轨道方法对MgO的缺陷和不规则表面吸附CO的可能构型进行能带计算,讨论了能带结构及组成,不同构型吸附前后能带和成键性质的变化,以及吸附前后的电荷转移和吸附键的变化规律。研究结果发现,CO的C端更有利于在MgO固体表面的吸附,具有氧缺陷结构的MgO更有利于吸附分解CO。