Effect of film ageing on the surface properties of lactoglobulin and lactoglobulin+sucrose stearate monolayers

The change in β-lactoglobulin and β-lactoglobulin+sucrose stearate spread monolayers over time (ageing effect) at room temperature was studied. Measurements of the surface pressure π-mean area per molecule A isotherms of the monolayers were used to probe any time dependent changes. The increase of the protein film area with time was attributed to protein unfolding. At certain ratios of surfactant to protein, a higher film area increase was observed. This correlated well with the excess film areas of 45 h aged films. The excess film areas for newly spread films of the same composition seemed to follow the opposite trend indicating that the protein–surfactant interactions change as the conformational changes of the protein molecules progress.     

Evaluation of molecular structure in Langmuir monolayers of zinc stearate and zinc 12-hydroxystearate by IR external reflection spectroscopy

 In situ polarized Fourier transform IR external reflection spectra of Langmuir monolayers of zinc stearate and zinc 12-hydroxystearate on a water surface were recorded for various surface areas, and their molecular structures were estimated. In the zinc stearate monolayer, the wavenumbers and the absorbances of the antisymmetric and symmetric methylene stretching bands did not change during monolayer compression, which means that orientational and conformational changes of the hydrocarbon chain did not occur. However, wavenumber changes of the antisymmetric and symmetric carboxylate stretching bands were observed during surface compression. The change in the binding nature of the zinc cation to the carboxylate group was speculated. Moreover, it was elucidated that the structure of the hydrocarbon chain in the zinc 12-hydroxystearate monolayer was different from that in the zinc stearate monolayer. Received: 21 March 2001 Accepted: 6 July 2001     

Molecular organization in protein-lipid film on the water surface studied by x-ray standing wave measurements under total external reflection

The x-ray standing wave method has been applied to study self-assembling processes in a protein-lipid film formed by injecting the protein-lipid mixture of alkaline phosphatase and phosphatidylinositol under the phospholipid monolayer preliminarily deposited on the water subphase by Langmuir method. X-ray standing wave measurements allowed to determine the composition of the protein-lipid film and to locate ions position in the direction normal to the film surface. The presence of trace Ni contamination incorporated in the protein-lipid film from the water subphase has been established. Numerical analysis of the X-ray standing wave fluorescence data revealed that after injection under the phospholipid monolayer, the protein-lipid mixture separated in a self-assembled manner to layered structure, molecules of alkaline phosphatase arranged themselves into a pure protein layer containing no phospholipid molecules.     

铕对磷脂酰胆碱LB单分子膜结构影响的原子力显微镜观察

用原子力显微镜观察到亚相中Eu^3^+诱导二棕榈酰磷脂酰胆碱Langmuir-Blodgett(LB)单分子膜出现有规则周期性条纹结构。     

水对SBA-15负载的钴基费-托合成催化剂催化性能的影响

以SBA-15分子筛为载体,采用等体积浸渍法制备了负载量为20%的钴基催化剂,采用TEM、XRD、H2-TPR和N2物理吸附-脱附等方法对催化剂进行了表征,并在浆态床反应器中考察了水的加入对费-托合成反应性能的影响.结果表明,金属钴物种进入到SBA-15载体的孔道中;产物在孔道中的滞留以及水促进的金属钴物种的团聚,引起了催化剂活性的降低;水的加入有利于反应物和产物在孔道中的传输,增加CO的转化率;在SBA-15负载的钴基催化剂中,产物在孔道中的滞留对催化剂活性影响较大,引起的扩散限制是催化剂活性降低的重要原因.     

Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film

Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co²⁺ concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO₃)₂, possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L⁻¹. The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method.     

Preparation and micro-mechanical studies of polysiloxane-containing dual-layer film on Au surface

A novel polysiloxane-containing self-assembled dual-layer film was grafted onto Au surface with a simple three-step method. Firstly, (3-mercaptopropyl)trimethoxysilane (MPTMS) molecules were self-assembled on Au surfaces through S–Au bond followed by hydrolysis and condensation, then the octadecyltrichlorosilane molecules were attached to the resultant hydroxyl terminated surface via the Si–O–Si bonds. The structure and morphology of the film were characterized by means of contact angle measurement, ellipsometry, attenuated total reflectance Fourier transformed infrared spectra, and atomic force microscopy. The resistant ability of charge transfer in the film forming process was detected by electrochemical techniques. Using force–volume technique, we investigated how the different surface chemical groups influence the surface adhesion properties. The nano-friction properties of the as-prepared films were investigated by frictional force microscopy. The results indicated that the dual-layer film fabricated via the hydrolyzation of MPTMS underlayer had significantly less friction. Moreover, compared to the self-assembled monolayer of octadecane thiol, the resultant dual-layer film showed much less wear. This improvement was mainly ascribed to the existence of the network of lateral cross-linked polysiloxane layer within the film which can enhance the stability of the film.     

Systematic structural studies on cobalt(II) complexes of tricyclohexylphosphine oxide and related ligands

The new cobalt(II) phosphine oxide complexes Co(Cy₃PO)₂Cl₂ (1), Co(Cy₃PO)₂Br₂ (2), Co(Cy₃PO)₂I₂ (3), Co(Ph₂CyPO)₂Cl₂ (4), Co(Ph₂CyPO)₂Br₂ (5), Co(Ph₂CyPO)₂I₂ (6), Co(Ph₂EtPO)₂Br₂ (7), Co(Cy₃PO)₂(NCS)₂ (8) and Co(Cy₃PO)₂(NO₃)₂ (9) have been prepared mainly by the reaction of anhydrous CoX₂ (X = Cl, Br, I, NCS, NO₃) with the appropriate phosphine oxide. The complexes were characterised by single-crystal X-ray crystallography supported by IR and UV-Vis absorption spectroscopy. The structural analyses show that the cobalt(II) centre adopts a distorted tetrahedral coordination geometry except for 9 which displays an octahedral geometry. Systematic structural features of these complexes are explained within this paper.     

Thermal curing and water re‐exposure of silane–PVA/PVAc complex film on glass fiber surface

Because glass fiber reinforced composites are in industrial demand, chemistry and topography of the glass fiber sizing are of interest. Silane–PVA/PVAc (polyvinyl alcohol/polyvinyl acetate) complex film on the glass fiber surface is studied during thermal curing and water re‐exposure by using atomic force microscopy. The complex film consists of silane with the honeycomb structure film and PVA/PVAc with the hexagonal close pack structure of ellipsoidal shaped microspheres (270 × 620 nm). The thermal curing at 100 °C is leading to the evaporation of water contained in the microspheres. Because of water evaporation, the average roughness value of 1‐min thermal curing decreases from initial 7.3 to only 2.7 nm. Such a collapse of microsphere is followed by an intermixing between silane film and PVA/PVAc microspheres leading to a change of silane honeycomb structure along with silane tips. The average value of the silane honeycomb structure wall width decreases from 144 nm to 54 nm, for curing times of 15 and 30 min, respectively. A re‐exposure to an aqueous environment after 100 °C curing leads to almost completely restored microspheres regarding shape and size. The average complex film thickness increases from 180 nm for thermal curing for 30 min to 225 nm for water re‐exposed film. Interestingly, the pits in the microsphere structure are observed presumably because of the tips from intermixing. The thermal curing at 200 °C enhances the intermixing, and after 15 min, an intramixing is suggested to occur between PVAc core and PVA shell of the microsphere. The water re‐exposure after 15 min of 200 °C curing leads to a re‐containing of water but without restored microsphere structure; Because of the intramixing, leaving the silane–PVA/PVAc film is not complex anymore. Copyright © 2014 John Wiley & Sons, Ltd.     

Synergistic effect of combination of Irganox 1010 and zinc stearate on thermal stabilization of electron beam irradiated HDPE/EVA both in hot water and oven

Thermo-oxidative stability of HDPE/EVA blends can be considerably increased by combination of a high-molecular weight phenolic antioxidant and zinc stearate. In this work, the post-irradiation thermal stability of HDPE/EVA blends has been studied. High-density polyethylene and its blends with ethylene-vinylacetate copolymer in both pure form and mixed with Irganox 1010 and zinc stearate were exposed to electron beam radiation at doses between 80 and 150 kGy, at room temperature, in air. In order to evaluate the thermal stability of the samples, post-irradiation heat treatments were done in both hot water bath at 95 °C and in an oven at 140 °C. The mechanical properties and changes in the chemical structure were determined during thermal aging in hot water and oven. The gel content was enhanced by increasing EVA concentration in all applied doses. The stabilized blends have lower gel content than the unstabilized samples. From the results of heat aging treatments it was observed that the thermal stability of the unstabilized blend samples was lower than HDPE. Thermal stability of the samples has been improved by incorporation of Irganox 1010 and zinc stearate. Formation of hydroxyl group was insignificant for stabilized samples during heat aging in both conditions. Also, the changes in the value of oxidation induction time (OIT) for the stabilized samples were negligible after prolonged immersion in hot water.     

三元配合物薄层树脂相光度法测定天然水中痕量钴的研究

在酸性条件下(pH 5), 利用阳离子交换树脂-丁二酮肟-碘-钴四元体系, 在454 nm处具有最大吸收, 确定了借助薄层树脂相光度法测定钴的新方法.本法灵敏度高(ε454=1.7×105 L·mol-1·cm-1), 比水相光度法提高14倍, 精密度高(测定2.0 μg/mL Co(Ⅱ) 6次, RSD=1.3%), 选择性好. 实测天然水中钴,线性范围0.024～2.0 μg/mL, 检出限10.4 ng/mL.     

X-ray structures of cobalt(III) complexes with bio-relevant pyrazolyl thiosemicarbazone: Indication of structural changes on the increasing bulkiness of the alkyl substituents on thiosemicarbazone moiety

X-ray crystallographic studies of cobalt(III) complexes of 5-methyl-3-formylpyrazole-N(4)-diethylthiosemicarbazone (HMP_zNEt₂), [Co(MP _z NEt ₂ ) ₂ ]Br·2H ₂ O, 5-methyl-3-formylpyrazole-N(4)-dipropylthiosemicarbazone (HMP_zNPr ₂ ), [Co(MP _z NPr ₂ ) ₂ ]Br·2H ₂ O and 5-methyl-3formylpyrazole-N(4)-dibutylthiosemicarbazone (HMP_zNBu ₂ ), [Co(MP _z NBu ₂ ) ₂ ]Br·H ₂ O, have been reported. In all the three complex species, X-ray crystallography has authenticated a CoN₄S₂ octahedral coordination with the pair of orthogonally coordinated NNS tridentate ligands in the monodeprotonated form of the ligand. The two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogens and the thiolato sulfurs are in cis positions. A gradual decrease in the dihedral angle between the coordinating ligands has been observed with increase in the bulkiness of the aliphatic side chains of the substituent on the thiosemicarbazone moieties. In all the three complexes, intraligand C–H···S contacts appear to arrest the free rotation of the side chains about the C(6)–N(5) single bond. ^†Deceased     

Voltammetric determination of thiocytosine based on its electrocatalytic oxidation on the surface of carbon-paste electrode modified with cobalt Schiff base complexes

The electrochemical oxidation of thiocytosine on the surface of carbon-paste electrode modified with Schiff base (salophen derivatives) complexes of cobalt is studied. The effect of the substituents in the structure of salophen on the catalytic property of the modified electrode is investigated by using cyclic and differential pulse voltammetry. Cobalt (II)-5-nitrosalophen, because of its electrophilic functional groups, leads to a considerable enhancement in the catalytic activity, sensitivity (peak current), and a marked increase in the anodic potential of the modified electrode. The differential pulse voltammetry is applied as a very sensitive method for the detection of thiocytosine. The linear dynamic range was between 1 × 10⁻³ to 4 × 10⁻⁶ M with a slope of 0.0168 μA/μM, and the detection limit was 1 × 10⁻⁶ M. The modified electrode is successfully applied for the voltammetric detection of thiocytosine in human synthetic serum sample and also pharmaceutical preparations. A linear range from 1 × 10⁻³ to 1 × 10⁻⁵ M with a slope of 0.0175 μA/μM is resulted for the standard addition of thiocytosine spiked to the buffered human serum, which is differing from the curve in buffer solution about 4%. The electrode has a very good reproducibility (relative standard deviation for the slope of the calibration curve is less than 3.5% based on six determinations in a month), high stability in its voltammetric response and low detection limit for thiocytosine, and high electrochemical sensitivity with respect to other biological thiols such as cysteine.     

The critical size of clusters of water molecules on a carbon surface

The experimental adsorption isotherms of water and nitrogen vapors on graphitized carbonaceous adsorbents with large pore size prepared from ultradispersive technical carbon black have been compared with those on the surface of non-porous graphitized carbon black. The saturation value of water vapor adsorption has been shown to be proportional to the concentration of primary adsorption centers. At low concentrations of these centers the saturation value corresponds to the formation of fractions of a dense monolayer on the surface. The maximum size of clusters of water molecules on a carbonaceous adsorbent surface has been estimated.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 54–56, January, 1993.     

Partial stripping of Ag atoms from silver bilayer on a Au(111) surface accompanied with the reductive desorption of hexanethiol SAM

The interfacial structures of Ag bilayer prepared by underpotential deposition on Au(111) (Ag(2ML)/Au(111)) were determined by ex situ scanning tunneling microscopy and in situ surface X-ray scattering measurements before and after oxidative adsorption and after reductive desorption of a self-assembled monolayer (SAM) of hexanethiol (C₆SH) in alkaline ethanol solution. While no structural change was observed after oxidative formation of C₆SH SAM on the Ag(2ML)/Au(111) in an ethanol solution containing 20 mM KOH and 0.1 mM C₆SH, some of the Ag atoms in the bilayer were stripped when the SAM was reductively desorbed. Dedicated to Professor J. O’M. Bockris on the occasion of his 85th birthday.     

Collapse and swelling of poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on a flat SiO2 surface

Poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on SiO₂‐coated quartz crystal surface were prepared with a surface‐immobilized initiator. The collapse and swelling of the thermally sensitive copolymer brushes in water were studied with quartz crystal microbalance in situ. The frequency and dissipation changes with the temperature increasing in the range 20–38 °C indicate that the brushes undergo a continuous collapse transition. Our results show that the copolymer brushes collapse to a state where the brushes were prepared. A hysteresis was observed in the cooling process. Fourier transform infrared (FTIR) results revealed that the formation of some additional hydrogen bonds within the copolymer chains at their collapsed state is responsible for the hysteresis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 770–778, 2006     

Determination of ultra trace amounts of cobalt and nickel in water samples by inductively coupled plasma-optical emission spectrometry after preconcentration on modified C18-silica extraction disks

A highly sensitive and accurate method for preconcentration and determination of ultra trace amounts of cobalt and nickel ions in water samples is proposed. The preconcentration is achieved using C₁₈-silica extraction disks modified with 5-(6-methoxy-2-benzothiazoleazo)-8-aminoquinoline (MBTAQ). The retained ions on the prepared solid phase was eluted with 10 ml of 0.01 M nitric acid and measured by inductively coupled plasma-optical emission spectrometry (ICP-OES). The influence of the type and amount of eluent used, pH, sample and eluent flow rates, amount of MBTAQ and the effect of other ions on extraction efficiency were investigated. The limits of detection of the method were 0.08 and 0.06 μg l^− 1 for cobalt and nickel, respectively, and provide an enrichment factor of 100. The results obtained on 10 successive extractions and elution cycles revealed relative standard deviations of 1.5 and 1.0% for cobalt and nickel, respectively. The proposed method has been applied to the determination of ultra trace amounts of cobalt and nickel ions in natural and synthetic water samples with satisfactory results.     

Effects of post-deposition annealing on chemical composition of SiNx film in SiO2/SiNx/SiO2/Si stacked structure

To systematically evaluate the quality of SiN_x films in multi-stacked structures, we investigated the effects of post-deposition annealing (PDA) on the film properties of SiN_x within the SiO₂/SiN_x/SiO₂/Si stacked structure by performing X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier transform infrared (FT-IR) spectroscopy, and scanning transmission electron microscope–electron energy loss spectroscopy (STEM-EELS) analyses. The XPS results showed that PDA induces the oxidation of the SiN_x layer. In particular, new finding is that Si-rich SiN_x in the SiN_x layer is preferentially oxidized by PDA even in multi-stacked structure. The XRR results showed that the SiN_x layer becomes thinner, whereas the interface layer between the SiN_x layer and Si becomes thicker. It is concluded by STEM-EELS and XPS that this interface layer is SiON layer. The density of N–H and Si–H bonding within the stacked structure strongly depends on the PDA temperature. Our study helps elucidate the properties of SiN_x films in stacked structures from various perspectives.     

Evolution of surface topography and optical band gap of ZnO film deposited on NiO/Si(100)

Evolution of surface features and optical band gap of ZnO thin films deposited on different NiO/Si(100) are reported. In order to create different initial microstructure, we first deposited NiO film on Si(100) at 3 different temperatures (400°C, 650°C, and 700°C) by pulsed laser deposition. These NiO/Si(100) films are used as substrate for the deposition of ZnO films. Combining the results obtained from grazing incidence X‐ray diffraction, atomic force microscope, and UV‐Visible characterization, our study indicated that the microstructure of the substrate takes the important role in dictating properties of the film. Our study also indicated that one needs to choose appropriate synthesis condition to achieve good quality ZnO films.     

Analysis of the antitarnish film on a tin surface by x-ray photoelectron spectroscopy and Auger electron spectroscopy

A corrosion-resistant complex film formed in ethylenediaminetetra(methylidenephosphonic acid) (EDTMP) solution was determined by x-ray photoelectron spectroscopy and Auger electron spectroscopy to consist of 48.0% O, 11.7% Sn, 7.7% N, 22.1% C and 10.5% P. From the differences in the binding energies of Sn, N and O before and after film formation and the RPO^2?₃ and SnN vibrations in the Raman spectrum of the film, it was deduced that N and O in EDTMP were coordinated with Sn in the film.