Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl₂O₄) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.     

石墨炉原子吸收光谱法测定 北美自然铜矿中的铅

采用石墨炉原子吸收光谱法对北美多个自然铜矿区的55个样品进行了铅含量分析,在制作校准曲线时加入高纯铜溶液以消除基体效应影响,高纯铜及样品加标回收率分别为104.0%和111.0%,表明该方法具有较高的可信度.分析结果表明,北美自然铜中铅含量极低,多数含量低于1μg/g,少数介于1-10μg/g之间.     

Perturbed kernel approximation on homogeneous manifolds

Current methods for interpolation and approximation within a native space rely heavily on the strict positive-definiteness of the underlying kernels. If the domains of approximation are the unit spheres in euclidean spaces, then zonal kernels (kernels that are invariant under the orthogonal group action) are strongly favored. In the implementation of these methods to handle real world problems, however, some or all of the symmetries and positive-definiteness may be lost in digitalization due to small random errors that occur unpredictably during various stages of the execution. Perturbation analysis is therefore needed to address the stability problem encountered. In this paper we study two kinds of perturbations of positive-definite kernels: small random perturbations and perturbations by Dunkl's intertwining operators [C. Dunkl, Y. Xu, Orthogonal polynomials of several variables, Encyclopedia of Mathematics and Its Applications, vol. 81, Cambridge University Press, Cambridge, 2001]. We show that with some reasonable assumptions, a small random perturbation of a strictly positive-definite kernel can still provide vehicles for interpolation and enjoy the same error estimates. We examine the actions of the Dunkl intertwining operators on zonal (strictly) positive-definite kernels on spheres. We show that the resulted kernels are (strictly) positive-definite on spheres of lower dimensions.     

Study into the shape of oxide lines formed by LAO - Influence of an oxidized material

Linear oxide patterns were formed by local anodic oxidation (LAO) using an atomic force microscope (AFM) on an n-doped GaAs substrate, a 10-nm-thick titanium layer, and on shallow GaAs/AlGaAs-based heterostructures capped either with a 5-nm-thick undoped GaAs layer or a 2-nm-thick undoped InGaP layer. Each heterostructures had a 2DEG buried at a specific depth between 22 and 45 nm. LAO was performed in contact and non-contact AFM modes with the aim to explain the phenomenon of single and double line formation depending on material oxidized. The occurrence of the phenomenon was also simulated. The results showed that the occurrence of the double lines is linked with the thickness of native oxides.     

Loss of PEG chain in routine SDS‐PAGE analysis of PEG‐maleimide modified protein

SDS‐PAGE represents a quick and simple method for qualitative and quantitative analysis of protein and protein‐containing conjugates, mostly pegylated proteins. PEG‐maleimide (MAL) is frequently used to site‐specifically pegylate therapeutic proteins via free cysteine residue by forming a thiosuccinimide structure for pursuing homogeneous products. The C–S linkage between protein and PEG‐MAL is generally thought to be relatively stable. However, loss of intact PEG chain in routine SDS‐PAGE analysis of PEG‐maleimide modified protein was observed. It is a thiol‐independent thioether cleavage and the shedding of PEG chain exclusively happens to PEG‐MAL modified conjugates although PEG‐vinylsulfone conjugates to thiol‐containing proteins also through a C–S linkage. Cleavage kinetics of PEG40k‐MAL modified ciliary neurotrophic factor showed this kind of degradation could immediately happen even in 1 min incubation at high temperature and could be detected at physiological temperature and pH, although the rate was relatively slow. This may provide another degradation route for maleimide‐thiol conjugate irrespective of reactive thiol, although the specific mechanism is still not very clear for us. It would also offer a basis for accurate characterization of PEG‐MAL modified protein/peptide by SDS‐PAGE analysis.     

Proteomic analysis of cellular soluble proteins from human bronchial smooth muscle cells by combining nondenaturing micro 2DE and quantitative LC‐MS/MS. 2. Similarity search between protein maps for the analysis of protein complexes

Human bronchial smooth muscle cell soluble proteins were analyzed by a combined method of nondenaturing micro 2DE, grid gel‐cutting, and quantitative LC‐MS/MS and a native protein map was prepared for each of the identified 4323 proteins [1]. A method to evaluate the degree of similarity between the protein maps was developed since we expected the proteins comprising a protein complex would be separated together under nondenaturing conditions. The following procedure was employed using Excel macros; (i) maps that have three or more squares with protein quantity data were selected (2328 maps), (ii) within each map, the quantity values of the squares were normalized setting the highest value to be 1.0, (iii) in comparing a map with another map, the smaller normalized quantity in two corresponding squares was taken and summed throughout the map to give an “overlap score,” (iv) each map was compared against all the 2328 maps and the largest overlap score, obtained when a map was compared with itself, was set to be 1.0 thus providing 2328 “overlap factors,” (v) step (iv) was repeated for all maps providing 2328 × 2328 matrix of overlap factors. From the matrix, protein pairs that showed overlap factors above 0.65 from both protein sides were selected (431 protein pairs). Each protein pair was searched in a database (UniProtKB) on complex formation and 301 protein pairs, which comprise 35 protein complexes, were found to be documented. These results demonstrated that native protein maps and their similarity search would enable simultaneous analysis of multiple protein complexes in cells.     

Oxidative Deselenization of Selenocysteine: Applications for Programmed Ligation at Serine

Despite the unique chemical properties of selenocysteine (Sec), ligation at Sec is an under‐utilized methodology for protein synthesis. We describe herein an unprecedented protocol for the conversion of Sec to serine (Ser) in a single, high‐yielding step. When coupled with ligation at Sec, this transformation provides a new approach to programmed ligations at Ser residues. This new reaction is compatible with a wide range of functionality, including the presence of unprotected amino acid side chains and appended glycans. The utility of the methodology is demonstrated in the rapid synthesis of complex glycopeptide fragments of the epithelial glycoproteins MUC5AC and MUC4 and through the total synthesis of the structured, cysteine (Cys)‐free protein eglin C.     

Synthesis of an O-acyl isopeptide by using native chemical ligation to efficiently construct a hydrophobic polypeptide

By using dimethylformamide to suppress the O-to-N acyl migration, we efficiently synthesized an O-acyl isopeptide by native chemical ligation of a peptide-thioester and a Cys-O-acyl isopeptide. The reaction mixture was then loaded onto an octadecylsilane reverse-phase HPLC column, and the isopeptide was purified by using a linear gradient of CH₃CN in 0.1% aqueous trifluoroacetic acid. The recovery rate of the O-acyl isopeptide was considerably higher than that of the corresponding native polypeptide. Synthesis of O-acyl isopeptides via native chemical ligation, with O-to-N acyl migration as the final step to give the native form, has potential as an efficient method of constructing hydrophobic polypeptides.