Showing papers on "Buffer solution published in 1994"

Sequence-specific gene detection with a gold electrode modified with DNA probes and an electrochemically active dye.

Abstract: A synthesized 20-mer DNA probe complementary to a part of an oncogene v-myc region having a mercaptohexyl group at the 5'-phosphate end was immobilized on a gold electrode by chemisorption. The immobilized DNA was detected voltammetrically using Hoechst 33258 with a DNA minor groove binder and an electrochemically active dye. The modified electrode was immersed into a 100 mumol/L Hoechst 33258 solution and washed with a phosphate buffer (pH 7.0). The anodic peak current (ipa) of Hoechst 33258 on the modified electrode was higher than that on a bare gold electrode (128 and 75 nA, respectively). It was considered that Hoechst 33258 was concentrated on the electrode surface due to its association with DNA. When the modified electrode was hybridized in a solution of a model targeted gene (10(-7) g/mL), single-stranded pVM623 containing the PstI fragment of a 1.5-kilobase pair of oncogene v-myc, the ipa was 192 nA. On the other hand, the ipa was 128 nA when the modified electrode was reacted in a solution of single-stranded pUC119 without a region complementary to v-myc in pVM623. The ipa was related to the concentration of the targeted DNA in the hybridization reaction. The use of Hoechst 33258 resulted in a sequence-specific detection of the targeted DNA quantitatively ranging from 10(-7) to 10(-13) g/mL in a buffer solution.

Characterization of poly-L-lysine adsorption onto alkanethiol-modified gold surfaces with polarization-modulation Fourier transform infrared spectroscopy and surface plasmon resonance measurements

Abstract: The electrostatic adsorption of poly-L-lysine molecules onto a vapor-deposited gold film modified with a carboxylic acid-terminated alkanethiol monolayer is monitored with the spectroscopic techniques of polarization-modulation Fourier transform infrared (PM-FTIR) spectroscopy and surface plasmon resonance (SPR). The PM-ITIR spectrum of a monolayer of poly-L-lysine (PL) adsorbed onto a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) indicates that the lysine residues and the MUA carboxylic acid moieties form ammonium-carboxylate ion pairs which electrostatically bind the polypeptide to the surface. The PL molecules can be desorbed from the surface by rinsing with a buffer solution at a pH that destroys the ion pairing (pH 12). Measurements of the shift in the SPR angle upon adsorption were used to determine the thicknesses of the adsorbed monolayers; the MUA and PL monolayers were found to be 17.0 and 10.5 A thick, respectively. These thickness results suggest that the poly-L-lysine monolayer adsorbs onto the packed MUA surface in an extended conformation with the PL backbone lying parallel to the surface. Subsequent exposure ofthe PL monolayer to a solution ofiron phthalocyanine tetracarboxylic acid (FePc) resulted in the adsorption of a third layer onto the surface. The ability of the adsorbed PL molecules to interact with FePc indicates the presence of free lysine residues available for interaction with molecules other than the MUA monolayer.

Activated carbon catalyzes reactions of phenolics during liquid‐phase adsorption

Abstract: Various phenolic compounds in aqueous buffer solutions were contacted batchwise with powdered activated carbon. Relatively slow, but continual, decreases in the solution phenolic concentrations were measured over a period of several weeks. The decreases were due to oxidative coupling reactions of the phenolics which occurred on the carbon surface subsequent to adsorption. The effects of time, pH, dissolved oxygen, and the molecular nature of the phenolic were determined.

Electrocatalysis of nitric oxide reduction by water-soluble cobalt porphyrin. spectral and electrochemical studies

Abstract: Water-soluble cobalt tetrakis(N-methyl-2-pyridy1)porphine (Co(2-TMPyP)) has been investigated for their catalytic behavior toward nitric oxide reduction. The acid dissociation constants (p&) for [CoIn(2-TMPyP)(H2O)2l5+ are 5.5 and 9.6. Nitrite anion coordinates to the Co(II1) center in pH 4-12 buffer solutions. The nitrite complex [CO~~I (~ -TMP~P) (NO~) ]~+ exhibits IR bands at 1401, 1306 and 830 cm-', indicating a cobalt-nitro complex. The 5-coordinated cobaltous porphyrin, [CO~I(~-TMP~P)(H~O)]~+, has been identified by ESR and has pKa = 13.0. This is the first case that the pKa of a Co(I1) porphyrin is presented. Nitric oxide from the disproportionation of nitrite anion in acidic solution can coordinate to the Co(I1) center. Resonance Raman spectrum of [CoI1(2TMPyP)(N0)l4+ exhibits a peak at 1722 cm-', which disappears upon exposure to air. Electrocatalytic reduction of [Con(2-TMPyP)(N0)l4+ at -0.3 V in pH 4.0 buffer solution generates nitrous oxide in a slow rate. Bulk electrolysis was also conducted at -0.7 V, at which [Co1(2-TMPyP)I3+ reacts with nitrite anion and nitric oxide. The reduction products are mainly ammonia and hydroxylamine.

Kinetic studies of the urease-catalyzed hydrolysis of urea in a buffer-free system

Abstract: The kinetics of urea hydrolysis catalyzed by urease, mainly in the absence of buffers by use of the self-buffer effect of the products, was investigated. The effect of pH, temperature, and concentration of enzyme, substrate, product, salt ions, and buffers on the kinetic behavior of urease was examined. A kinetic model of a modified Michaelis-Menten form, incorporating substrate and product inhibition, pH dependence, and temperature effect, was developed to describe the reaction rate. Experimental data indicated that urease in a buffer-free solution was less susceptible to the inhibition of substrate product. The Michaelis constant keeps almost constant with the variation of pH and temperature, and increases with the addition of buffers and salts. The data also suggested that the noncompetitive pattern of the product inhibition, which is not significantly affected by temperature, increases gently with increasing pH. A Monod form rate expression was proposed to analyze the pH effect on the maximum rate. The proposed kinetic model was also examined by the long-time experiments in which pH, substrate, and product concentration varied obviously during the reaction course.

Improved separation of diastereomeric derivatives of enantiomers by a physical network of linear polyvinylpyrrolidone applied as pseudophase in capillary zone electrophoresis

Abstract: Diastereomeric analytes were separated using capillary zone electrophoresis with polyvinylpyrrolidone as polymeric additive to the buffer solution. As test substances derivatives of D- and L- alpha-amino and alpha-hydroxy acids formed by reaction with (+)-O,O'-diacetyl- and (+)-O,O'-dibenzoyl-L-tartaric anhydride, respectively, were used. The physical network formed by the linear polymer is supposed to act as a kind of pseudophase. It was found that the network affects the mobility of diastereomeric compounds to a different extent, enhancing the selectivity of the system. In nearly all cases of aromatic acids the diastereomer carrying the D-amino acid was more strongly retained than the L-isomer, as opposed to the situation with aliphatic acids.

A chronoamperometric sensor for hydrogen peroxide based on electron transfer between immobilized horseradish peroxidase on a glassy carbon electrode and a diffusing ferrocene mediator

Abstract: A sensor has been constructed by adsorptive immobilization of horseradish peroxidase onto a glassy carbon electrode, thus permitting a sensitive chronoamperometric determination of low micromolar levels of hydrogen peroxide. The method is based on enzymatic reduction of the substrate (H 2 O 2 by peroxidase and subsequent electron transfer from the glassy carbon electrode to the enzyme, via a redox mediator. To a mediator solution (0.5 mM of ferocene monocarboxylic acid in a 0.05 M buffer solution of phosphate at pH=7.20, 0.05 ml volume) 50 γl of the sample of H 2 O 2 is injected and the current-time response is recorded with an applied potential of +50 mV. The peak height of the obtained chronoamperogram varies linearly with the final H 2 O 2 concentration in the range 0.5×10 t -7-5×10−6-5×10−6 M. The attained detection limit of the enzyme electrode is 4×10 −8 M (1.4 ng ml −1 ) in the final solution. The lifetime of the sensor is at least one week about 120–160 analyses are carried out in this time). The effects of possible interferences of uric acid, ascorbic acid, haemoglobin, riboflavin, bilirubin, albumin, gluthaioine, d + glucose, pyruvic acid and lactate have also been studied. The use of the sensor to determine hdyrogen peroxide in samples of bovine serum, heparinezed blood and water is also shown.

Enantiomeric separation of drugs by affinity electrokinetic chromatography using dextran sulfate

Abstract: Dextran sulfate (sodium salt), which is a mixture of a linear alpha-(1,6)-linked D-glucose polymer having a sulfate group in the molecule, has been employed as a chiral selector in affinity electrokinetic chromatography (EKC) for the separation of enantiomers of drugs. Enantiomers of trimetoquinol hydrochloride and its positional isomer have been successfully separated by the method using a 3-5% dextran sulfate buffer solution of pH 5.5 within 20 min. The effects of buffer pH, concentration of dextran sulfate, and additives (such as an organic solvent, urea and a surfactant) on the enantioselectivity were investigated. The choice of pH and the concentration of dextran sulfate has been important for the improvement in selectivity.

Capillary zone electrophoresis of neutral organic molecules in organic – aqueous solution

Abstract: Very good separations of non-ionic organic compounds have been achieved by capillary zone electrophoresis (CZE) using a tetrahep-tylammonium salt as an additive in aqueous acetonitrile as solvent. A systematic study was undertaken to determine the effect of experimental parameters on electroosmotic mobility and electro-phoretic mobility. It was found that pH, acetonitrile concentration, and the type and concentration of quaternary ammonium salt are important experimental variables. Under appropriate conditions, the separation window was enlarged and a broad range of electrically neutral organics, including very hydrophobic compounds (e. g. poly-cyclic aromatic hydrocarbons) and fairly hydrophilic compounds were separated in a relatively short time. By adjusting the separation conditions, high resolution CZE of a specific group of neutral organic compounds could be achieved. A method for calculation of capacity factor was proposed and capacity factors for a variety of non-lonic organic compounds were calculated.

A pitzer mixed electrolyte solution theory approach to assignment of pH to standard buffer solutions

Abstract: The IUPAC recommendations for the pH scale for aqueous solutions are based on the Bates-Guggenheim (B-G) convention (1961) for the single ion activity coefficient of the chloride ion in the standard buffer(s). This convention was adopted as a reasonable estimate based on the Debye-Huckel theory and is limited in its application to ionic strengths less than 0.1 mol-kg−1. This approach ignores the results of many workers over the years on the properties of mixed electrolyte solutions and their prediction on the basis of the theories of Harned, Scatchard, Guggenheim and more recently of Pitzer. The literature data of EMF measurements on appropriate weak acid systems have been reexamined to determine both the pKa values and values of appropriate Pitzer interaction coefficients. The latter are used to calculate single chloride ion activity coefficients for the chosen compositions of pH standard buffers, and compared with the B-G convention values. Calculations were made to check the consistency of the pH values with determined pKa values using the Pitzer treatment for all the required single ion activity coefficients. The overall aim was to remove the ionic strength restriction of the B-G convention and rationalize the approach to pH standardization for such diverse aqueous media as sea water, blood and acid-rain water.