Potential-assisted deposition of mixed alkanethiol self-assembled monolayers

Preparation of self-assembled monolayers (SAMs) usually involves passive incubation. The recently developed potential-assisted deposition is indeed more selective as well as 100-fold faster than passive adsorption, thereby enhancing the reproducibility of the monolayer deposition.This article aims to identify the electrodeposition conditions necessary to prepare mixed alkanethiol SAMs on gold surface. Parameters such as concentrations in solution, electrode polarization and deposition time were examined for two chain lengths, C₃ (mercaptopropionic acid, MPA) and C₁₈ (octadecanethiol, ODT). The kinetics and composition of the SAMs were systematically characterized by reductive stripping analysis and by surface plasmon enhanced ellipsometry. Control of the surface concentration of the stable binary SAM was achieved by carefully adjusting the MPA fraction at between 70% and 95% in the deposition solution. Three theoretical models were developed. For MPA or ODT SAMs, whatever the adsorbate and the time period, the second order model gives the best fit. For the binary monolayer (MPA-ODT), a co-adsorption model was developed to describe the kinetics before 10 s.     

Adsorption of mercaptopropionic acid onto Au(1 1 1): Part I. Adlayer formation, structure and electrochemistry

The adsorption of 3-mercaptopropionic acid (MPA) on Au(1 1 1) in 0.1 M H₂SO₄ was studied by cyclic voltammetry, capacitance measurements and in situ scanning tunneling microscopy (STM). The formation of a self-assembled monolayer under electrochemically controlled conditions was monitored for the first time with an STM. A two-step adsorption process has been found, beginning with the adsorption of MPA to form a disordered film, which lifts the () reconstruction of Au(1 1 1), followed by an ordering of the MPA adlayer into two different dense structures. Concomitantly with the second step, formation of the well-known vacancy islands is observed. This formation is explained by an adsorbate-induced compression of the gold substrate. Two distinctly different structures of the dense MPA monolayer on Au(1 1 1) were observed. One () structure with p=3.6-4.8 and a second structure consisting of two unit cells of () and () symmetry. In part II, the effect of the MPA on the copper electrodeposition onto Au(1 1 1) is discussed.     

Surface modification of gold electrode with gold nanoparticles and mixed self-assembled monolayers for enzyme biosensors

This paper describes the development and evaluation of a generic method for the immobilization of enzymes onto a gold electrode and its application to amperometric biosensors. The surface of the gold electrode was modified with gold nano-particles (AuNP) and mixed self-assembled monolayers (SAMs) to form an enzyme biosensor matrix. Horseradish peroxidase (HRP) was immobilized on the modified surface to form a biosensor matrix on a gold electrode. After the deposition of gold nano-particles on a bare gold surface, the AuNP-deposited gold electrode and a bare electrode were compared for the surface area and electric current using AFM and cyclic voltammetry (CV). The AuNP strongly adhered to the surface of the gold electrode, had uniform distribution and was very stable. A mixed SAM, composed of two different monolayer molecules, dithiobis-N-succinimidyl propionate (DTSP) and inert tetradecane-1-thiol (TDT), was formed using reductive desorption technique and cyclic voltammetry was used to verify the formation of mixed deposition. First, 3-mercaptopropionic acid (MPA) and TDT were deposited with a specified deposition ratio between the two components. Then, MPA was desorbed by applying electric potential to the surface. Finally, DTSP was deposited where MPA was. The ratios of 20: 80 and 50: 50 between MPA and TDT were examined, and differences in the CV responses were discussed. HRP was immobilized on the mixed SAM surface. The investigated method is regarded as an effective way for stable enzyme attachment, while the presence of gold nanoparticles provides enhanced electrochemical activity; it needs very small amounts of samples and enzymes and the SAM matrix helps avoid enzyme leaking. It is interesting that the mixed SAM shows unique CV characteristics compared to the uni-molecular SAMs. The reaction kinetics of the SAM-immobilized enzyme is discussed with the CV results and is observed to obey the Michaelis-Menten equation.     

The influence of gold nanoparticle modified electrode on the structure of mercaptopropionic acid self-assembly monolayer

The comparison of assembly structure and property of mercaptopropionic acid (MPA) self-assembled monolayers (SAMs) on gold nanoparticle modified electrode (nanogold electrode) with that on planar gold electrode was studied by cyclic voltammetry (CV). The electron transfer of through the MPA SAMs and Cu underpotential deposition (UPD) on MPA-covered electrode indicated that MPA molecules assemblied on the planar gold electrode could form a very compact layer, which could surpass the electron transfer K₃Fe(CN)₆ greatly, whereas on the surface on the nanogold, which curvature make the compact packing loose. The reductive desorption in 0.5 M KOH and oxidative desorption in phosphate buffer solution (PBS) (pH 6.8) showed that gold nanoparticles could enhance the Au-S bond and stabilize the MPA molecules.     

Nanopatterning of an organic monolayer covered Si (1 1 1) surfaces by atomic force microscope scratching

In the present work, an atomic force microscope (AFM) mounted with a diamond-coated tip was used to scratch through organic monolayer covered Si surfaces to create nanostructures by electrodeposition. The organic layer (1-octadecene) was covalently attached to a hydrogen-terminated Si (1 1 1) surface. Copper was deposited into the nanostructures either by immersion plating or electrodeposition. The morphology of copper deposits was studied using scanning electron microscope (SEM). The influence of the different types of semiconductor substrates (1-octadecene covered n-type Si and p-type Si) and different parameters such as immersion time on the copper deposition morphology is presented. Auger electron spectroscopy (AES) scans were performed to obtain information of the selectivity and the copper deposition. The results show clearly that under optimized conditions the organic layer can be used as an effective mask for the site selective patterning of copper nanostructures on Si.     

The initial stages of palladium deposition onto Pt(1 1 1)

The electrodeposition of Pd onto Pt(1 1 1) from PdCl₂ and PdSO₄ containing solutions was studied by cyclic voltammetry and in situ scanning tunnelling microscopy. Pd deposition starts by forming a pseudomorphic monolayer in both cases. While in the presence of chloride this monolayer is deposited at underpotentials, its formation in chloride-free solution is kinetically hindered to such an extent that the deposition peak is shifted negative of the equilibrium potential. Detailed structure information has been obtained from STM data about the Pd layer as well as the co-adsorbed anions. Bulk deposition from the chloride-containing solution proceeds via a quasi layer-by-layer fashion. However, the particular electrochemical properties of the first Pd monolayer disappear only after deposition of the equivalent of four more Pd layers. The electrochemical behaviour of such films is similar to that of a rough Pd(1 1 1) surface. Pd bulk deposition from chloride-free solution leads to the formation of three-dimensional clusters from the very beginning. About 10 ML equivalents are needed in that case to completely cover the first Pd monolayer.     

Protein functionalized Pt nanoparticles-conducting polymer nanocomposite film: Characterization and immunosensor application

We report an electrochemically prepared 3-mercaptopropionic acid (MPA) capped Pt nanoparticles-Polypyrrole (PPy) nanocomposite film based bioelectrode for the detection of human C-reactive protein (αCRP). The electrochemical deposition provides homogeneous distribution of ultrafine Pt(MPA)-NPs within the uniform and adherent PPy film with high degree of geometrical conformity and controllable film thickness. Protein antibody, Ab-αCRP, was covalently immobilized through the site specific carboxyl groups of Pt(MPA)-NPs within the polymer nanocomposite film by carbodiimide coupling reaction. The bioelectrode interfacial surface electron transport study towards protein antigen, Ag-αCRP, was carried out by electrochemical impedance spectroscopy (EIS). The value of ‘n’, a Constant Phase Element exponent used as a gauge of the heterogeneity, for Pt(MPA)-PPy nanocomposite film was found to be 0.88∼1 which is indicative of a homogeneous morphology of the composite film with minimal defects. The EIS of the bioelectrode exhibited significant changes in charge transfer resistance (R_et) component at a low ac frequency of <20 Hz towards Ag-αCRP detection over a linear range of 10 ng mL⁻¹–10 μg mL⁻¹ in PBS with a sensitivity of 109.74 Ωcm² per decade.     

Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Fracture Toughness of Chemically Vapor-Deposited Diamond

The fracture toughness of chemically vapor-deposited diamond is estimated by a Vickers indentation method. Freestanding diamond films of 400-μm thickness are produced with plasma-enhanced chemical vapor deposition and highly polished for indentation testing. Indentation testing was performed with a microhardness tester using a load range of 5 to 8 N. The average fracture toughness is estimated as 5.3 ± 1.3 MPA · m^1/2.     

掺杂CdTe量子点的凝胶光子晶体制备

先将单分散的聚苯乙烯微球通过垂直沉积法自组装得到聚苯乙烯光子晶体模板,再将水相合成法制备的巯基丙酸改性CdTe量子点与丙烯酸、丙烯酰胺、过硫酸铵、N,N’-亚甲基双丙烯酰胺等水凝胶前驱液混合填入聚苯乙烯光子晶体模板中,引发交联聚合,得到掺杂CdTe量子点的凝胶光子晶体。分别采用扫描电镜（SEM）、光纤光谱仪、固体荧光分光光度计对材料进行了表征,结果表明该材料既具有光子晶体的三维面心立方结构和光子带隙特征,又具有CdTe量子点荧光性能。     

Absolute Stereochemistry of 1,2-Diols from Lipids of Thermomicrobia

1,2‐Diol based phospholipids are a well‐known feature of bacteria from the class Thermomicrobia. Since these bacteria contain only lipids with an alkyldiol‐1 ‐phosphate backbone instead of sn‐glycero‐3‐phosphate, it is important to elucidate the stereochemistry of the 1,2‐diols. We have studied the absolute stereochemistry of long‐chain 1,2‐diols isolated from Thermorudis pharmacophila (formerly known as Thermomicrobia sp. WKT50.2) by nuclear magnetic resonance (NMR) using α‐methoxyphenylacetic acid (MPA). Low‐temperature (?60 °C) NMR of bis‐(R)‐MPA ester showed (R) stereochemistry of the 1,2‐diols. This is the first report concerning the stereochemistry of natural 1,2‐diols, which replace the glyceride moiety in phospholipids. The (R) stereochemistry of the diols is expected as it is the same configuration as for the common bacterial lipid backbone—sn‐glycero‐3‐phosphate. This is the first application of low‐temperature NMR of a single MPA derivative for assignment of stereochemistry of natural 1,2‐diols. The results were confirmed by the comparison of NMR data with bis‐(R)‐MPA ester of (R) and rac‐1,2‐octanediol.     

醋酸甲羟孕酮诱导结肠癌SW480细胞凋亡及其差异表达蛋白的分析

目的对醋酸甲羟孕酮(Medroxyprogesterone acetate,MPA)诱导结肠癌SW480细胞凋亡时的差异表达蛋白进行分析。方法以不同浓度(25、50、75μmol/L)的MPA作用SW480细胞24、48和72h,MTT法检测细胞增殖水平。以上述浓度的MPA作用SW480细胞48h,流式细胞术分析细胞的凋亡率及细胞周期各时相比例的变化。以50μmol/L MPA作用SW480细胞48h,透射电镜观察细胞结构的变化;应用双向电泳技术分离细胞总蛋白,PDQUEST8.0软件分析凝胶图谱,选择差异表达蛋白,以Agilent1100HPLC-Chip/MS系统进行MS/MS分析,搜索UniProtKB/SWISS-PORT,Homo Sapiens(Human)数据库筛选目标蛋白质。结果透射电镜下观察经MPA作用的SW480细胞可见明显的凋亡形态学变化;不同浓度的MPA对SW480细胞均有明显的抑制增殖和诱导凋亡作用,且呈剂量依赖性,细胞凋亡率最高可达56.15%;细胞周期分析表明,MPA诱导结肠癌细胞凋亡的作用可能与细胞周期的阻滞相关,此阻滞作用具有剂量依赖性;共鉴定出泛素、只含LIM结构域蛋白质3、热休克蛋白10、有机阴离子转运蛋白4、泛素羧基末端水解酶2、核苷二磷酸激酶-A、层黏连蛋白受体1共7种SW480细胞凋亡相关蛋白。结论 MPA具有诱导SW480细胞凋亡的作用,SW480细胞凋亡相关蛋白可能作为MPA抗结肠癌的潜在生物标志物。     

Effects of compatibilizer precursors on the barrier properties and morphology of polyethylene/polyamide blends

Summary A systematic investigation on the effects of type of compatibilizer precursors (CP) upon the barrier properties and morphology of PE/PA blends was reported. Three alkyl carboxyl-substituted polyolefins were selected to modify PA in a twin screw extruder by reactive extrusion process. The barrier property of the modified PA (MPA) was better than pure PA, and the amount of barrier improvement of the blend of PE and MPA dependended significantly on the barrier property of the MPA prepared. The extent of mixing PE and MPA before blow-molding has a significant effect on its corresponding barrier properties. Further analysis of the fracture surfaces indicated that a more demarcated laminar structure of MPA dispersed in PE matrix is essential for better barrier properties of PE/MPA blends. It is not completely clear how the type of CP added affects the barrier properties of MPAs. However, it is suggested that long PA sequence with shorter grafted CP chain and high normalized grafting efficiency of MPA are essential for preparing a clear laminar structure of MPA, and a good barrier properties of PE/MPA blends.     

Studying the localized deposition of Ag nanoparticles on self-assembled monolayers by scanning electrochemical microscopy (SECM)

The local deposition of Ag nanoparticles (NPs) on ω-mercaptoalkanoic acid, HS(CH₂)_nCO₂H, (n = 2, 10) self-assembled monolayers (SAMs) by scanning electrochemical microscopy (SECM) is reported. We found that the presence of a SAM had a pronounced effect on Ag deposition. Experiments were conducted by applying different potentials to an Au(1 1 1) substrate either in the presence of a constant concentration of Ag⁺ ions in solution (bulk deposition) or by generating a flux of Ag⁺ from an Ag microelectrode that was positioned close to the Au(1 1 1) substrate (SECM deposition). SECM was used for generating a controlled flux of silver ions by anodic dissolution of an Ag microelectrode close to the SAMs modified Au(1 1 1). We found that the shape of the NPs was affected by the length of the carbon-chain of the SAM. Tetrahedral NPs were obtained on bare Au(1 1 1) surfaces while rod like and cubic Ag NPs were deposited onto 3-mercaptopropanoic acid (MPA) and 11-mercaptoundecanoic acid (MUA) SAMs, respectively. The size and shape of the deposited NPs were influenced by the deposition potential.We conclude that the shape and distribution of locally deposited Ag NPs on Au(1 1 1) can be controlled by modification of the substrate with a SAM and through controlling the Ag⁺ flux generated by SECM.     

Functional Characterization of MpaG′, the O‐Methyltransferase Involved in the Biosynthesis of Mycophenolic Acid

Mycophenolic acid (MPA, 1 ) is a clinically important immunosuppressant. In this report, a gene cluster mpa′ responsible for the biosynthesis of 1 was identified from Penicillium brevicompactum NRRL 864. The S‐adenosyl‐L ‐methionine‐dependent (SAM‐dependent) O‐methyltransferase encoded by the mpaG′ gene was functionally and kinetically characterized in vitro. MpaG′ catalyzes the methylation of demethylmycophenolic acid (DMMPA, 6 ) to form 1 . It also showed significant substrate flexibility by methylating two structural derivatives of 6 prepared by organic synthesis.     

改性尼龙6纤维的制备与性能研究

采用MAH-g-PE与增塑剂邻苯二甲酸二辛酯(DOP)对尼龙6进行改性制得了改性尼龙6纤维(MPA),研究了MAH-g-PE和DOP用量对MPA流变性能、热性能、热延伸及比强力性能的影响.结果表明:MPA样品流动性随着DOP含量的增加而增强,说明增塑剂对于尼龙6的增塑效果比较明显.DSC分析表明,MAH-g-PE的加入...     

环保增塑剂马来海松酸三正辛酯的合成及表征

以马来海松酸和正辛醇为原料,对甲苯磺酸为催化剂,正辛烷为带水剂,合成了环保增塑剂马来海松酸三正辛酯。考察了醇酸摩尔比、催化剂用量、反应时间、带水剂用量和反应温度对酯化反应的影响,经单因素实验得到的最佳工艺条件为:n(马来海松酸)∶n(正辛醇)=1∶4.5,催化剂用量为马来海松酸质量的3.6%,带水剂用量为马来海松酸质量的17.5%,反应温度180～200℃,N2保护下反应8.3 h,产物为浅黄色透明油状液体,产率92.3%,经HPLC测定酯色谱纯度为99.24%,1HNMR及FTIR对产物进行了结构表征,元素分析确定了产物分子式为C48H82O6,GPC测得其重均相对分子质量为755。测定了其酸值、加热减量、开口闪点、体积电阻、黏度、热重曲线等,结果表明,马来海松酸三正辛酯符合增塑剂的性能要求。     

Ureidosilanes on E-glass fibres: deposition and surface characteristics

The behaviour of methoxy- and ethoxy-ureidosilanes deposited onto E-glass fibres from both organic and aqueous solutions is reviewed. γ-Ureidopropyltri(m)ethoxysilanes are used as coupling agents for paints to metal surfaces, but they have not found much use as coupling agents for E-glass fibres. On metal surfaces, the silane is deposited with the ureido-functional group outermost, available for reaction with a paint/polymer matrix. On E-glass surfaces, however, unless specific conditions are employed, ureidosilanes tend to deposit with a highly cross-linked siloxane surface. The silanol groups condense not only with silanols of adjacent silanes and the E-glass surface, but also with aluminium hydroxides leached from the E-glass surface. This forms a highly cross-linked aluminosiloxane outer layer. The aluminosiloxane forms at all pHs between 4 and 10, and also when a range of organic deposition solvents is used. ²⁹Si-NMR results are presented which illustrate the high level of condensation; silane to silicate binding via the amino group was not detected. A small proportion of Si—O—Si (silane-glass) bonds was inferred, indicating that a small number of sparsely distributed Si—O—Si links bound the silane to the surface. Electrokinetic analysis of the surfaces confirmed patchy deposition with a siloxane outer surface. Using AFM and ab initio calculations, it was estimated that the patchwise deposition of the silane was in the form of bilayers (or multiples of bilayers). The bilayer structure consisted of siloxane outer layers, with the inner ureido layers forming hydrogen bonds. A graphical fit using the mole and volume fractions of silane and organic solvents confirmed the various types of siloxane surfaces as deposited from different organic solvents. Chlorinated solvents tended to produce a ureido outer surface, which was condensed, but solventswollen; deposition from alcohol and acetone resulted in a siloxane surface. Toluene and THF both produced minimally condensed ureido surfaces, which were easily removed by washing with methylene chloride.     

Potential of zero free charge of Pd overlayers on Pt(1 1 1)

Differential capacitance measurements of Pd overlayers on a Pt(1 1 1) electrode in dilute aqueous NaF solutions have been performed as a function of film thickness in order to determine the potential of zero free charge (pzfc). The pzfc of the first, pseudomorphic Pd monolayer on Pt(1 1 1) is −0.21 V versus SCE. By increasing the amount of deposited Pd, a clear shift of the pzfc to more positive values is observed. After deposition of an equivalent of 10 monolayers, the value approaches that of a massive Pd(1 1 1) electrode (−0.12 V versus SCE). The pzfc's for the various Pd coverages are correlated with surface structure information, derived from STM images (R. Hoyer, L.A. Kibler, D.M. Kolb, Electrochim. Acta 49 (2003) 63). Variations in the pzfc are discussed in the context of an electronic modification by the underlying substrate and are compared with corresponding data for Pd overlayers on Au(1 1 1).