Partitioning behavior of amino acids in aqueous two-phase systems containing polyethylene glycol and phosphate buffer

The partitioning behavior of four amino acids, cysteine, phenylalanine, methionine, and lysine in 15 aqueous two-phase systems (ATPSs) with different polyethylene glycol (PEG) molecular weights and phosphate buffers has been studied in the present paper. The phase diagrams of the systems are investigated together with the effect of the PEG molecular weight and pH of the phosphate solutions. The composition of these systems and some parameters such as density and refractive index are determined. The influences of salts in ATPSs, side chain structure of the amino acids, pH of ATPSs, and the PEG molecular weight on the distribution ratios of the amino acids have been studied. This work is useful for the purification of amino acids and the separation of some proteins whose main surface exposed amino acid residues are these four amino acids, respectively.

Enzymatic degradation of poly(epsilon-caprolactone)/poly(DL-lactide) blends in phosphate buffer solution

Blend films of poly(epsilon-caprolactone) (PCL) and poly(DL-lactide) (PDLLA) with 0.5 weight fraction of PCL were prepared by means of solution casting and their degradation behavior was studied in phosphate buffer solution containing Pseudomonas (PS) lipase. Enzymatic degradation of the blend films occurred continuously within the first 6 days and finally stopped when the film weight loss reached 50%, showing that only PCL in the blends degraded under the action of PS lipase in the buffer solution. These results indicate the selectivity of PS lipase on the promotion of degradation for PCL and PDLLA. The thermal properties and morphology of the blend films were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and scanning electron microscopy (SEM). The morphology resulting from aggregate structures of PCL in the blends was destroyed in the enzymatic degradation process, as observed by SEM. These results confirm again the enzymatic degradation of PCL in the blends in the presence of PS lipase. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Enzymatic degradation of poly(epsilon-caprolactone) film in phosphate buffer solution containing lipases

The enzymatic degradation of poly(epsilon-caprolactone) (PCL) films in phosphate buffer solution containing lipases has been studied by DSC, WAXD and SEM. Three lipases, pseudomonas lipase (PS), porcine pancreatic lipase (PP), and candida cylindracea lipase (AY), were used. The results showed that the degradation of PCL films in phosphate buffer solution containing PP or AY was very slow: no weight loss could be found within 1 week. However, PCL film could degrade rapidly and completely within 4 days in phosphate buffer solution containing PS lipase. (C) 1997 Elsevier Science Limited.

Effect of citrate ions on the electrochemical behaviour of low-carbon steel in borate buffer solutions

The electrochemical behaviour of cold-rolled low carbon steel was studied on both active and passive potential regions in borate buffer solutions with and without the addition of sodium citrate (NaCit). In the active region anodic charges increased significantly and RCT values decreased with citrate, due to the formation of soluble complexes. In the passive potential region the film formed at +0.4 V in borate buffer solution with and without 0.010 M NaCit is probably enriched by Fe3O4 oxide, while films formed at +0.8 V are probably enriched by gamma-Fe2O3. The equivalent circuit [R-s(R(CT)Q)] fitted all experimental impedance data. (C) 2003 Elsevier Ltd. All rights reserved.

In vivo biological behavior of calcium phosphate cements with different Ca/P ratio

Bioceramics with different Ca/P ratio were prepared from a mechanical mixture of NaPO3, CaCO3, Ca(OH)2 and phosphate buffer solution and implanted in rats subcutaneous tissues. The cements were characterized by Thermo gravimetric analysis (TG-TDA), X-ray diffraction and 31P-NMR. The implant sites were excised after 1, 4 and 16 weeks, fixed, dehydrated, included in paraffin wax for serial cutting and examined under the light transmitted microscope. They were biocompatible and biodegradable when implanted in rat subcutaneous. None of the materials induced ectopic osteogenesis. According to the results, the studied materials seem to be able for manufacturing reabsorbable bone implants.

High Catalytic Activity of Amorphous Ir-Pi for Oxygen Evolution Reaction

Large-scale production of hydrogen gas by water electrolysis is hindered by the sluggish kinetics of oxygen evolution reaction (OER) at the anode. The development of a highly active and stable catalyst for OER is a challenging task. Electrochemically prepared amorphous metal-based catalysts have gained wide attention after the recent discovery of a cnbalt-phosphate (Co-Pi) catalyst: Herein, an amorphous iridium-phosphate (Ir-Pi) is investigated as an oxygen evolution catalyst. The catalyst is prepared by the anodic polarization of carbon paper electrodes in neutral phosphate buffer solutions containing IrCl3. The Ir-Pi film deposited on the substrate has significant amounts of phosphate and It centers in an oxidation state higher than +4. Phosphate plays a significant role in the deposition of the catalyst and also in its activity toward OER. The onset potential of OER on the Ir-Pi is about 150 mV lower in comparison with the Co-Pi under identical experimental conditions. Thus, Ir-Pi is a promising catalyst for electrochemical oxidation of water.

Electrochemistry of Microperoxidase-11 (MP-11) on Glassy Carbon Electrode Modified with Chitosan

In this paper, microperoxidase-11 (MP-11) was immobilized on glassy carbon electrode surface modified with chitosan by physical adsorption. The direct electrochemistry and the electrocatalytic behaviours to O-2 and the H2O2 of MP-11 on glassy carbon electrode modified with chitosan were characterized by cyclic voltammetry. The results indicate that MP-11 on modified electrode displays a quasi-reversible electrochemical process coupled with proton transfer in the phosphate buffer solutions(pH = 7.12). Direct electrochemical reaction of MP-11 on modified electrode has been realized. MP-11 on modified electrode can catalyze reduction for O-2 and H2O2. Both of the catalytic reductions are surface-controlled electrochemical process.

Silver(I) ions-enhanced electrochemiluminescence of tris(2,2-bipyridyl)ruthenium(II)

In this paper. we demonstrate an clectrochemiluminescence (ECL) enhancement of tris(2,2-bipyridyl)rutheniuin(II) (Ru(bpy)(3)(2+)) by the addition of silver(l) ions. The maximum enhancement factor of about 5 was obtained on a glassy carbon electrode in the absence of co-reactant. The enhancement of ECL intensity was possibly attributed to the unique catalytic activity of Ag+ for reactions between Ru(bpy)(3)(3+) with OR The higher enhancement was observed in phosphate buffer solutions compared with that from borate buffer solutions. This resulted from the fact that formation of nanoparticles with large surface area in the phosphate buffer solution exhibited high catalytic activity. The amount of Ag+, solution pH and working electrode materials played important roles for the ECL enhancement. We also studied the effects of Ag+ on Ru(bpy)(3)(2+)/tripropylamine and Ru(bpy)(3)(2+)/C2O42- ECL systems.

Anodic voltammetric behavior of medecamycin at a glassy carbon electrode

The anodic voltammetric behavior of medecamycin (MD) in the presence of various electrolytes was studied by linearsweep voltammetry, differential-pulse voltammetry and cyclic voltammetry at a glassy carbon electrode. In phosphate buffer solutions (pH = 9.4), MD is oxidized irreversibly. The peak potential is at about +0.75 V (vs.Ag/AgCl). The height of the peak is linearly increased with the concentration of MD over the range of 5 x 10(-5) similar to 1 x 10(-1) g/L. The method has been used for the direct determination of MD in tablets. The relative standard deviation (n = 10) is 1.8%. The recoveries of MD in urine samples are in the range of 95% similar to 115%.

Ac voltammetric and square wave voltammetric study of the self-assembled monolayers of thiol-functionalized viologen derivative

Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium (i.e. a viologen group), onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated ty Ac voltammetry and square wave voltammetry, which have the high sensitivity against background charging. The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are -360 mV and -750 mV (vs. Ag/AgCl) in 0.1 mol/L phosphate buffer solutions (pH 6.96) respectively, and the standard electron transfer rate constant is 9.0 s(-1). The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.

Studies on the hemolytic activity of tentacle extracts of jellyfish Rhopilema esculentum Kishinouye: Application of orthogonal test

The present work is first reporting the hemolytic activity of venom from jellyfish Rhopilema esculentum Kishinouye extracted by different phosphate buffer solutions and incubated at different temperature according to the orthogonal test L6(1) x 3(6). Of the seven controllable independent variables, incubated temperature and phenylmethylsulfonyl fluoride (PMSF) had strongest effect on the hemolytic activity. (c) 2006 Elsevier B.V. All rights reserved.

Supramolecular structures of enzyme clusters

The structural characterization of subtilisin mesoscale clusters, which were previously shown to induce supramolecular order in biocatalytic self-assembly of Fmocdipeptides, was carried out by synchrotron small-angle X-ray, dynamic, and static light scattering measurements. Subtilisin molecules self-assemble to form supramolecular structures in phosphate buffer solutions. Structural arrangement of subtilisin clusters at 55 degrees Centigrade was found to vary systematically with increasing enzyme concentration. Static light scattering measurements showed the cluster structure to be consistent with a fractal-like arrangement, with fractal dimension varying from 1.8 to 2.6 with increasing concentration for low to moderate enzyme concentrations. This was followed by a structural transition around the enzyme concentration of 0.5 mg mL-1 to more compact structures with significantly slower relaxation dynamics, as evidenced by dynamic light scattering measurements. These concentration-dependent supramolecular enzyme clusters provide tunable templates for biocatalytic self-assembly.

Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution

Pyrolytic graphite electrodes (PGE) were modified into dopamine solutions using phosphate buffer solutions, pH 10 and 6.5, as supporting electrolyte. The modification process involved a previous anodization of the working electrode at +1. 5 V into 0. 1 mol-L-1 NaOH followed by other anodization step, in the same experimental conditions, into dopamine (DA) solutions. pH of the supporting electrolyte performed an important role in the production of a superficial melanin polymeric film, which permitted the simultaneous detection of ascorbic acid (AA), (DA) and uric acid (UA), Delta EAA-DA = 222 mV-, Delta EAA-UA = 360 mV and Delta EDA-UA=138mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4 x 10(-6) mol L-1 for uric acid, 1.3x10-(5) molL(-1) for ascorbic acid and 1.1 X 10(-7) mol L-1 for dopamine, with sensitivities of (7.7 +/- 0.5), (0.061 +/- 0.001) and (9.5 +/- 0.05)A mol(-1) cm(-2), respectively, with no mutual interference. Uric acid was determined in urine, blood and serum human samples after dilution in phosphate buffer and no additional sample pre-treatment was necessary. The concentration of uric acid in urine was higher than the values found in blood and serum and the recovery tests (92-102%) indicated that no matrix effects were observed. (C) 2008 Elsevier B.V. All rights reserved.

Determination of carbaryl in tomato ""in natura"" using an amperometric biosensor based on the inhibition of acetylcholinesterase activity

This work reports the utilization of two methodologies for carbaryl determination in tomatoes. The measurements were carried out using an amperometric biosensor technique based on the inhibition of acetylcholinesterase activity due to carbaryl adsorption and a HPLC procedure. The electrochemical experiments were performed in 0.1 mol L-1 phosphate buffer solutions at pH 7.4 with an incubation time of 8 min. The analytical curve obtained in pure solutions showed excellent linearity in the 5.0 x 10(-5) to 75 x 10(-5) mol L-1 range, with the limit of detection at 0.4 x 10(-3) gL(-1). The application of such a methodology in tomato samples involved solely liquidising the samples, which were spiked with 6.0 x 10(-6) and 5.0 x 10(-5) mol L-1 carbaryl. Recovery in such samples presented values of 99.0 and 92.4%, respectively. In order to obtain a comparison, HPLC experiments were also conducted under similar conditions. However, the tomato samples have to be manipulated by an extraction procedure (MSPD), which yielded much lower recovery values (78.3 and 84.8%, respectively). On the other hand, the detection limit obtained was much lower than that for the biosensor, i.e., 3.2 x 10(-6) g L-1. Finally, the biosensor methodology was employed to analyze carbaryl directly inside the tomato, without any previous manipulation. In this case, the biosensor was immersed in the tomato pulp, which had previously been spiked with the pesticide for 8 min, removed and inserted in the electrochemical cell. A recovery of 83.4% was obtained, showing very low interference of the matrix constituents. (C) 2007 Elsevier B.V. All rights reserved.

Determination of cinnamic acid in human urine by differential-pulse polarography

The differential pulse polarographic behaviour of cinnamic acid was studied in acetate and phosphate buffer solutions (pH 3.5-7.5). The reduction mechanism is discussed. The drug can be determined at pH 5.0 over the concentration range 5 X 10(-5)-1 X 10(-3) mol l(-1). The effect of tetraalkylammonium salts on the electroanalytical determination of cinnamic acid was investigated, the direct determination of the drug (0.7-5.5 mu g ml(-1)) in urine samples diluted with acetate buffer (pH 5.0) can be effected in the presence of 1 x 10(-3) mol l(-1) cetyldimethylethylammonium bromide solution. The detection limit was found to be 0.1 mu g ml(-1). The relative standard deviation from six determinations at the 5.5 mu g ml(-1) level was 1%.