Limitations of some esterification techniques in structural studies of kerogen-derived acids

Oxidative degradation techniques for characterizing kerogens in oil shales often lead to major yields of precipitated acids (PA), which are less amenable than soluble acid products to analysis by gas chromatography/mass spectrometry (g.c./m.s.). A PA complex produced by oxidation of a Julia Creek (Queensland) kerogen was studied by applying four different esterification techniques before g.c./m.s. Methods based on reaction with diazomethane or boron trifluoride/methanol were of limited effectiveness. Reaction with dimethyl sulphate in acetone with potassium carbonate catalyst led to the detection of by far the widest range of components in the PA complex. This method is recommended for esterifying acid products derived from kerogen, especially in comparative characterization studies of kerogens.     

Physical properties of some low polymer content radiation-grafted wool copolymers

Wool copolymers with low polymer content (6–18%) have been prepared by radiation grafting techniques. Supercontraction, density, and formic acid vapor sorption measurements have been used to assess changes in the keratin structure produced by the grafting processes. Kinetic studies of the contractile forces developed in the first (reversible) stage of the supercontraction of wool in lithium bromide showed that grafting with poly(N-methylol acrylamide) or polyacrylonitrile has a “repairing” action which offsets changes in the wool structure produced by the small radiation dose (2 Mrad) used for the grafting process. By contrast, grafting with poly(vinyl acetate) had no repairing effect. The bonds formed by grafting of poly(N-methylol acrylamide) or polyacrylonitrile to keratin do not reduce swelling of the wool by formic acid, which is a measure of effective crosslink density. Grafting with poly(vinyl acetate) led to increased swelling by formic acid, indicating some disruption of the keratin structure during polymerization. It is suggested that the role of the grafted polymer is mainly to stabilize the hydrogen-bonded secondary network by interaction between the polypeptide and polymer chains.     

Apparent spin polarization decay in Cu-dusted Co/Al2O3/Co tunnel junctions

Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with xi approximately 0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond approximately 5 ML it becomes vanishingly small.     

Internal kink instability during off-axis electron cyclotron current drive in the DIII-D tokamak

Experimental evidence is reported of an internal kink instability driven by a new mechanism: barely trapped suprathermal electrons produced by off-axis electron cyclotron heating on the DIII-D tokamak. It occurs in plasmas with an evolving safety factor profile q(r) when q(min) approaches 1. This instability is most active when ECCD is applied on the high field side of the flux surface. It has a bursting behavior with poloidal/toroidal mode number = m/n = 1/1. In positive magnetic shear plasmas, this mode becomes the fishbone instability. This observation can be qualitatively explained by the drift reversal of the barely trapped suprathermal electrons.     

Fourier Transform Spectroscopy of the A'(1)Pi-X(1)Sigma(+) System of CaO

The A'(1)Pi-X(1)Sigma(+) near-infrared system of CaO was observed for the first time at high resolution using a Fourier transform spectrometer. The A'(1)Pi-X(1)Sigma(+) chemiluminescence was excited in a Ca + N(2)O flame produced in a Broida-type oven. More than 3000 rotational lines, classified into 19 bands involving the A'(1)Pi 0 /= 2) levels with the nearby b(3)Sigma(+) (v-2) levels has been detected. An extended set of A'(1)Pi (v = 0-3) data has been obtained which is suitable for use in a future multistate deperturbation analysis of the a(3)Pi approximately A'(1)Pi approximately b(3)Sigma(+) approximately A(1)Sigma(+) complex of excited states. The new near-infrared spectra of the A'(1)Pi-X(1)Sigma(+) transition of CaO also permits the first direct high-resolution linkage between the orange and green systems and the near-infrared bands. Copyright 2000 Academic Press.     

Improved Parameterization for Combined Isotopomer Analysis of Diatomic Spectra and Its Application to HF and DF

A new way of representing vibration-rotation term values for multiple isotopomers of a given electronic state of a diatomic molecule is presented which resolves problems associated with the way the conventional combined isotopomer expansion represents the atomic mass-dependent JWKB and Born-Oppenheimer breakdown correction terms. Its application to infrared and microwave data for HF and DF yields new Dunham expansion coefficients and Born-Oppenheimer breakdown correction terms for this species. This procedure is implemented in a generally available computer program for fitting to various types of data involving one or several electronic states of multiple isotopomers of a diatomic molecule. Copyright 1999 Academic Press.     

Peptide Hydrogels—A Tissue Engineering Strategy for the Prevention of Oesophageal Strictures

Endoscopic treatment of Barrett's oesophagus often leads to further damage of healthy tissue causing fibrotic tissue formation termed as strictures. This study shows that synthetic, self‐assembling peptide hydrogels (PeptiGelDesign) support the activity and function of primary oesophageal cells, leading to epithelialization and stratification during in vitro 3D co‐culture. Following buffering in culture media, rat oesophageal stromal fibroblasts (rOSFs) are incorporated into a library of peptide hydrogels, whereas mouse oesophageal epithelial cells (mOECs) are seeded on the surface. Optimal hydrogels (PGD‐AlphaProC and PGD‐CGD2) support mOEC viability (>95%), typical cell morphology (cobblestone‐like), and slower migration over a shorter distance compared to a collagen control, at 48 h. Positive expression of typical epithelial markers (ZO‐1 and cytokeratins) is detected using immunocytochemistry at day 3 in culture. Furthermore, optimal hydrogels are identified which support rOSF viability (>95%) with homogeneous distribution when incorporated into the hydrogels and also promote the secretion of collagen type I detected using an enzyme linked immunosorbent assay (ELISA), at day 7. A 3D co‐culture model using optimal hydrogels for both cell types supports a stratified epithelial layer (expressing involucrin and AE1/AE3 markers). Findings from this study could lead to the use of peptide hydrogels as a minimally invasive endoscopic therapy to manage oesophageal strictures.     

A microenvironmental redox shift at a charged surface detected by papain activity

The relative activity of an SH-enzyme, papain, is decreased by increasing the mole ratio of oxidizing disulfide to reducing thiol in solution. The same inverse relationship applies to papain adsorbed on charged clay particles, but electrostatic interactions among the charged particles and charged disulfides and thiols significantly shift the dependence. Papain activity thus reflects the microenvironmental redox potential in the vicinity of the charged particles. The redox pairs cystine dimethylester-cysteine ethylester, dithiodiglycolic acidmercaptoacetic acid, and dithiodiglycol-mercaptoethanol were used in the assays. A special form of the Boltzmann distribution must be used to calculate mole ratios of ions of different charge near a charged interface.     

Physico-chemical characterization of metal binding proteins using HPLC-ICP-MS, HPLC-MA-AAS and electrospray-MS

A size exclusion HPLC method was developed and interfaced with ICP-MS detection for determining the metal profiles of commercially available rabbit liver metallothioneins (MT) and metallothionein-like proteins (MLP) extracted from fresh water mussels and hemolyzed osprey blood. The redox state of the cysteine residues was indirectly evaluated via a cadmium saturation approach in the presence or absence of a reducing agent, followed by HPLC-microatomization (MA)-AAS and HPLC-ICP-MS analyses. An electrospray-MS protocol was also developed to accurately measure the molecular weight of rabbit MT isoform II. Nanogram quantities of Cd-MT/MLP were poorly chromatographed on silica based supports. A copolymeric styrene-divinylbenzene size exclusion support provided a symmetrical peak (rabbit MT standard) and linear HPLC-MA-AAS calibration curves [r=0.9988; from the LOD (27 ng, as protein) to about 300×LOD], indicating negligible losses of Cd during the chromatography of trace quantities. Co-injection of Cd²⁺ saturated samples with beta-mercaptoethanol (BMSH) was essential to repress Cd²⁺-support interactions which otherwise induced an undesirable metalaffinity retention mechanism. In the presence of added Cd²⁺, 22 mmol/L BMSH did not significantly compete for Cd²⁺ specifically bound to MT, while preventing non-specific binding to non-thiolic complexing sites. Crude mussel and osprey blood MLP extracts (in cold, deoxygenated Tris-HCl buffer) were obtained by ultracentrifugation (145,000 g) and thermocoagulation/centrifugation, respectively. Incubation with BMSH was prerequisite to obtain a maximum saturation of mussel and osprey blood MLP by Cd²⁺, even for samples conserved (–80° C) in the presence of BMSH (22 mmol/L). These observations indicated that a major proportion of the cysteine residues present in these MLP were oxidized. The assumption of a fully reduced MT/MLP pool binding metals in a definite stoichiometry has been the basis of several quantitative metal binding assays involving the saturation of the thiolic complexing sites with a metallic marker (Ag+, Cd²⁺, or Hg²⁺). Since thiolic agents may interfere, the metal saturation protocols do not include a reducing step to ensure that all cysteines in a MT/MLP extract are available for co-ordination. Given that variations in the redox state of crude MT/MLP extracts may compromise the accuracy of metal saturation assays, it is concluded that the preparation of reference samples certified for total metallothionein content would be desirable.