Showing papers on "Buffer solution published in 1996"

Application of Molecular Imprinting to the Development of Aqueous Buffer and Organic Solvent Based Radioligand Binding Assays for (S)-Propranolol

Abstract: Antibody mimics have been prepared by molecular imprinting of (S)-propranolol and applied in the development of radioligand binding assays for the imprint species. In the assays, polymer particles, radioligand, and analyte were incubated either in an organic solvent or an aqueous buffer, with similarly high sensitivity under both set of conditions. Optimization of the assay conditions led to 100-1000-fold improvements in the limit of determination and 100-1000-fold reductions of the amount of imprinted polymer used, compared with previous studies of this novel type of assay. The present assay uses only 10-50 μg of polymer, and the limit of determination is about 6 nM. The toluene-based assay showed excellent enantioselectivity, the cross-reactivity of the R enantiomer being only 1%, which is better than that demonstrated by biological antibodies. The aqueous buffer based assay showed high substrate selectivity for propranolol in the presence of structurally similar β-blockers. The different selectivity profiles obtained are due to a different balance between hydrophobic and polar interactions in toluene and water, since polar interactions, such as hydrogen bonds, are strong in apolar solvents and hydrophobic interactions are strong in water.

Electrochemical Oxidation of Glucose on Single Crystal and Polycrystalline Gold Surfaces in Phosphate Buffer

Abstract: The electrochemical oxidation of glucose has been studied in phosphate buffer (pH = 7.4) on single crystal and polycrystalline gold electrodes using electrochemical techniques, ex situ NMR, in situ FTIR spectroscopy, and isotope labeling. Under these conditions, the results indicate that the rate determining step for the electro-oxidation of glucose is bond breaking between the hydrogen atom and the C 1 carbon atom. Gluconolactone appears to be an intermediate and sodium gluconate is the reaction product. First order kinetics with respect to glucose were also found. Gold would be a useful electrode for sensor applications, if the inhibition of the glucose oxidation by the adsorption of Cl - could be avoided

Glucose-sensing electrode coated with polymer complex gel containing phenylboronic Acid.

Abstract: We have prepared a copolymer containing both phenylboronic acid and tertiary amine moieties. The copolymer forms a stable complex with poly(vinyl alcohol) (PVA) since boronate moieties interact with PVA hydroxyl groups. The polymer−polymer complex changes its swelling degree with glucose concentration in Dulbecco's phosphate-buffered saline solution (PBS) at pH 7.4, due to the higher complex formation of boronic acid moieties with glucose hydroxyl groups over those in PVA. Glucose-responsive swelling changes of a membrane complex were then utilized to control glucose-responsive current changes with a membrane-coated platinum electrode. Glucose addition to PBS induces swelling of the cast gel membrane, leading to increased diffusion of ion species and thus increased measurable current changes. Since the addition of methyl α-d-glucoside has little influence on the current changes, the current change by the addition of glucose is indicative of the high selectivity of this system for glucose and its cis-hydro...

Synthesis and swelling characteristics of pH and thermoresponsive interpenetrating polymer network hydrogel composed of poly(vinyl alcohol) and poly(acrylic acid)

Abstract: The swelling behavior of novel pH- and temperature-sensitive interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) in water was investigated. The PVA/PAAc IPN hydrogels were synthesized by UV irradiation, followed by a repetitive freezing and thawing process by which PVA hydrogel networks were formed inside of cross-linked PAAc chains. The swelling behaviors of these IPNs were analyzed in buffer solution at various pH and temperature ranges. Swelling ratios of all IPNs were relatively high, and they showed reasonable sensitivity to both pH and temperature. Hydrogels showed both the positive and negative swelling behaviors depending on PAAc content. IPN46 showed the positive temperature-sensitive swelling behaviors and its stepwise changes in swelling ratio was about 1.8 and 2.0 obtained between 25 and 45°C at pH 7, and between pH 4 and 7 at 35°C, respectively. The positive temperature dependence is attributed to the formation and dissociation of hydrogen bonding complexes between PVA and PAAc. These IPNs are expected to show a pH- and temperature-sensitive drug release according to the stepwise behavior at this temperature region. © 1996 John Wiley & Sons, Inc.

Mixed potential response mechanism of cobalt electrodes toward inorganic phosphate

Abstract: The potentiometric response mechanism of a previously reported phosphate ion-sensitive electrode based on a surface-oxidized cobalt metal is examined. Beyond response to phosphate, the cobalt electrode is found to respond to changes in the partial pressure of oxygen in the sample solution. The potentiometric response toward phosphate ions and molecular oxygen is shown to depend on the sample stirring rate as well as the pH, ionic strength, and nature of the buffer salts present within the test solution. X-ray photoelectron spectroscopy studies of the cobalt electrodes, in conjunction with cyclic voltammetric measurements, suggest that the potentiometric response originates from a mixed potential resulting from the slow oxidation of cobalt and simultaneous reduction of both oxygen and Co2+ at the surface of the electrode. In contrast to an originally proposed host−guest mechanism, the present mixed potential mechanism more accurately explains behavior of oxidized cobalt electrodes in the presence of phosph...

Electrochemical Behavior of Azobenzene Self-Assembled Monolayers on Gold

Abstract: The self-assembly and electrochemical properties of a novel thiol-functionalized azobenzene derivative were studied on gold electrodes by cyclic voltammetry. The compound was 4-ethoxy-4‘-((N-(2‘‘-mercaptoethyl)amino)carbonyl)azobenzene (C2AzoC2SH), which was synthesized using a simple and general technique by our laboratory. The C2AzoC2SH formed uniform and reproducible self-assembled monolayers (SAMs) on gold with a surface coverage of 4.21 × 10-10 mol/cm2. The SAMs showed voltammetric responses in a B-R buffer at a pH range of 3.2−8.6 that corresponded to the two-electron, two-proton reduction−oxidation of azobenzene. The voltammetric behavior was totally irreversible, exhibiting very large peak-to-peak splitting and other distortions. The dependence of apparent surface electrochemical rate constant on pH value has a V-shape, owing to the influence of protonation reactions on the multistepped reduction−oxidation of azobenzene functionality.

Use of vancomycin as chiral selector in capillary electrophoresis. Optimization and quantitation of loxiglumide enantiomers in pharmaceuticals

Abstract: Vancomycin has been used as chiral selector for the enantiomers separation of D, L-loxiglumide, a new drug proposed for the treatment of gastrointestinal pathology. The chiral selector, dissolved at very low concentration in the running buffer, filled only part of the capillary (polyacrylamide coated) and allowed chiral resolution in less than 12 min using a 50 mM phosphate buffer at pH 6. The partial separation technique allowed to obtain a detection limit of 0.5 μg/ml for each enantiomer avoiding the drop in sensitivity due to the strong UV absorption of vancomycin when present in the detector path. The effects of vancomycin concentration and buffer pH on enantiomers resolution have been studied in order to find the optimum experimental conditions for the chiral purity control of drug. The optimized method, using the internal standard, showed good reproducibility for both migration times and normalized peak area ratio and for linearity. Under the studied operating conditions it was possible to detect 0.2 % (w/w) of L-loxiglumide as a chiral impurity. Analysis of pharmaceutical preparations of D-loxiglumide did not reveal the presence of the impurity (L-isomer).

Enantiomeric separation of acidic drugs by capillary electrophoresis using a combination of charged and uncharged β‐cyclodextrins as chiral selectors

Abstract: High resolution could be achieved for the enantiomers of acidic drugs, namely, sulindac, fenoprofen, ketoprofen, warfarin, and hexobarbital, in a buffer of pH 3 by the simultaneous addition of uncharged and charged β-cyclodextrin derivatives. The interaction of the analytes with the anionic sulfobutyl ether β-cyclodextrin provides the analytes with an adequate electrophoretic mobility whereas the interaction with various neutral β-cyclodextrins generates high enantioselectivity. Five neutral cyclodextrins, the native β-cyclodextrin, as well as methyl-, dimethyl-, trimethyl- and hydroxypropyl-β-cyclodextrin, were tested to enhance the enantioselectivity of the electrophoretic system. High resolution values and the shortest analysis times for the five drugs tested were achieved in a buffer made of 100 mM phosphoric acid adjusted to pH 3 with triethanolamine and containing dimethyl- or trimethyl-β-cyclodextrin in addition to sulfobutyl ether β-cyclodextrin.

Temperature dependence of dissociation constants for formic acid and 2,6-dinitrophenol in aqueous solutions up to 175 °C

Abstract: The temperature dependence of the dissociation constants for formic acid and 2,6-dinitrophenol (2,6-DNP) has been determined in aqueous solutions from 25 to 175 °C using spectrophotometric measurements. The optical indicator 2,6-DNP was employed to measure the pH of a buffer solution by deconvolution of absorption spectra of 2,6-DNP at various temperatures. First, using the temperature dependence of pKa for acetic acid, pKi of 2,6-DNP were determined in acetate buffer solutions as a function of temperature. The results were then used to study the ionization reaction of formic acid at elevated temperature. Measured values of pKa for formic acid were fitted to a function of temperature, which was derived by assuming that ΔCop is a non-zero constant. The result for formic acid was given by pKa=– 57.528 + 2773.9/T+ 9.1232 ln T where T is absolute temperature. Additionally, thermodynamic functions of formic acid were determined from the temperature dependence of pKa and compared with those obtained from other methods. The isocoulombic reactions for formic acid and 2,6-DNP were considered to predict the temperature dependence of pKa by the extrapolation of – log KOH values to higher temperatures.