Showing papers on "Buffer solution published in 1991"

Calcium phosphate formation at the surface of bioactive glass in vitro

Abstract: The calcium phosphate formation at the surface of bioactive glass was studied in vitro. Glass rods and grains were immersed in different aqueous solutions and studied by means of scanning electron microscopy and energy dispersive x-ray analysis. Surface morphological changes and weight loss of corroded grains were monitored. In-depth compositional profiles were determined for rods immersed in the different solutions. The solutions used were tris-buffer (tris-hydroxymethylaminomethane + HCl), tris-buffer prepared using citric acid (tris-hydroxymethylaminomethane + C6H8O7.H2O), and a simulated body fluid, SBF, containing inorganic ions close in concentration to those in human blood plasma. It was found that the calcium phosphate formation at the surface of bioactive glass in vitro proceeds in two stages. When immersing the glass in tris or in SBF a Ca,P-rich surface layer forms. This accumulation takes place within the silica structure. Later, apatite crystals forming spherulites appear on the surface. The Ca/P-ratio of initially formed calcium phosphate was found to be about unity. It is proposed that this is due to bonding of phosphate to a silica gel. The surface is stabilized, i.e., leaching is retarded, by the rapid Ca,P-accumulation within the silica structure before apatite crystals are observed on the surface. It is proposed that the initially formed calcium phosphate is initiated within the silica gel. The crystallizing surface provides nucleation sites for extensive apatite formation on the glass surface. In the presence of citrate no Ca,P-accumulation occur at the glass surface, but soluble Ca-citrate complexes form. By comparing the weight loss during corrosion in tris with that in the calcium and phosphate containing SBF, it is possible to establish whether the glass can induce apatite formation at its surface or not.

The effect of electric field strength, buffer type and concentration on separation parameters in capillary zone electrophoresis

Abstract: Probe solutes were used to investigate the effect of buffer type, concentration and applied voltage on solute mobility, column efficiency and resolution in capillary zone electrophoresis. With low conductivity buffers higher concentrations and/or higher voltages could be used to improve column efficiency and resolution. Doubling the concentration of the buffer doubles the amount of heat generated inside the column while doubling the applied voltage cause a 4-fold increase. Solute migration time is approximately an inverse function of the charge density of the buffer's cation. Analysis time is increased by about 30% if the buffer concentration is doubled while it is cut in half if the applied voltage is doubled. Column efficiency is improved (higher theoretical plate count) with increasing buffer concentration and/or applied voltage as long as the heat generated is efficiently dissipated. The separation factor is directly related to analysis time and, therefore, selectivity improves with increasing buffer concentration but decreases with increasing applied voltage. Hence, resolution is optimized by increasing buffer concentration at a moderate applied voltage.

Kinetics and mechanisms of water sorption in hydrophobic, ionizable copolymer gels

Abstract: The aqueous kinetic swelling properties of a class of cross-linked hydrophobic polyamine copolymer gels based on n-alkyl esters of methacrylic acid (nAMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been studied as a function of solution ionic composition (pH, ionic strength, and buffer content), gel composition, and temperature. Water uptake and swelling in these gels are driven by ionization of the DMA amine groups, which overcomes the hydrophobic tendency of these gels to exclude water in the unionized state. Sorption kinetics in initially glassy gel disks are generally biphasic, characterized by an initial phase of relatively slow water uptake followed by an accelerated phase during which significant volume expansion of the gel occurs. This sorption/swelling behavior strongly suggests a moving penetrant front mechanism. The initial rate of water sorption increases markedly as (1) solution pH decreases, (2) gel nAMA comonomer content decreases, (3) gel nAMA side-chain length decreases, and (4) temperature increases. Furthermore, the initial phase of sorption in initially glassy gels is generally non-Fickian and approaches zero-order behavior as (1) pH increases, (2) nAMA content increases, and (3) temperature decreases. In direct contrast, sorption in initially dry, rubbery gels is monophasic, but non-Fickian, and approaches zero-order behavior as temperature increases. This behavior is contrary to the Fickian sorption behavior normally observed in polymers above their glass transition temperatures. Finally, sorption kinetics critically depend upon the nature of the ions in solution: Kinetics are significantly faster in the presence of weak electrolytes than that of strong electrolytes. We discuss the importance of the rate of ion transport in determining the overall sorption kinetics and how sorption kinetics can be non-Fickian in rubbery gels. Also, we propose a mechanism for the observed enhanced kinetics in the presence of weak electrolytes.

Selective separation and purification of two lipases from chromobacterium viscosum using AOT reversed micelles

Abstract: Selective separation and purification of two lipases form Chromobacterium viscosum were carried out by liquid-liquid extraction using a reversed micellar system. Optimum parameters for extraction were determined using a 250 mM AOT micellar solution in isooctane. Complete separation of the two lipases was achieved at pH 6.0 with a 50mM potassium phosphate buffer solution containing 50 mM KCI. By adding 2.5% by volume of ethanol to the lipase-loaded micellar solution, 85% of the extracted lipase could be recovered in a new aqueous phase, 50 mM K(2)HPO(4) with 50 mM KCl, at pH 9.0. Lipase A was purified 2.6-fold with a recovery of 86%, and lipase B by 1.5-fold with a recovery of 76%.

Leaching with Penicillium simplicissimum: Influence of Metals and Buffers on Proton Extrusion and Citric Acid Production.

Abstract: In the presence of insoluble metal oxides (industrial filter dust, zinc oxide, synthetic mixture of metal oxides), Penicillium simplicissimum developed the ability to excrete considerable amounts of citric acid (>100 mM). Parallel with the increase of citric acid concentration in the culture broth, zinc was solubilized from zinc oxide. The adsorption of filter dust onto the mycelium (the pellets formed were less than 1 mm in diameter) was required for not only the citric acid excretion but also the leaching of zinc. When the filter dust was replaced with a synthetic mixture of metal oxides or with zinc oxide in combination with trace elements, levels of adsorption and citric acid production were observed to be similar to those in experiments where industrial filter dust was used. The two most important properties of the filter dust were its heavy-metal content and its buffering capacity. These properties were simulated by adding heavy metals in soluble form (as chlorides, sulfates, or nitrates) or soluble buffers to the medium. Both heavy metals and buffers were not able to induce a citric acid efflux. As with citric acid production by Aspergillus niger, the addition of manganese lowered citric acid excretion (by 40% with metal oxide-induced citric acid efflux and by 100% with urea-induced citric acid efflux). Copper antagonized the effect of manganese. The mechanism for the bulk of citric acid excretion by P. simplicissimum, however, seemed to be different from that described for citric acid accumulation by A. niger. Because of the inefficiency of metals in solubilized form and of soluble buffers to induce a strong citric acid efflux, adsorption of an insoluble metal compound (zinc oxide) turned out to be essential. Surface phenomena possibly involving the plasma membrane H+-ATPase are thought to participate in the induction of citric acid excretion by P. simplicissimum in the presence of industrial filter dust.

Calcium buffer solutions and how to make them: A do it yourself guide'

Abstract: In measurements of the intracellular free calcium concentration ([Ca2+]) using either microelectrodes or fluorescent probes, calibration is normally carried out in EGTA calcium buffer solutions. In...

Cell preservative solution

Abstract: An aqueous alcohol buffer solution for substantially ambient, in vitro preservation of mammalian cells for a selected duration. The solution generally contains a water-miscible alcohol in an amount sufficient to fix the sample cells without coagulation, an anti-clumping agent, and a buffer agent to maintain the solution at a pH within a range of four to seven.

Invertase β-fructosidase): Effects of montmorillonite, AL-hydroxide and AL(OH)x-montmorillonite complex on activity and kinetic properties

Abstract: The effects of a montmorillonite (M), a non-crystalline aluminium hydroxide (AL) and an Al(OH)2-montmorillonite complex (a montmorillonite partially coated with OH-Al ions; AM) on the adsorption, residual activity and kinetic properties of invertase were determined. In the range of pH 3.0–9.0 the ability of the clay minerals to adsorb protein molecules was in the order M > AM > AL and was influenced by the nature of the buffer solution. Adsorption resulted in a significant reduction of invertase activity (more than 85% at pH 4.65). the extent of which depended on clay mineral (AL > AM > M) and on pH. The free and immobilized enzyme showed maximum activity in the range of pH 4.5–5.5 and both states obeyed Michaelis-Menten kinetics. The Vmax, and Km values indicated a partial non-competitive inhibition of the clay minerals. Invertase adsorbed on AM and AL was more stable to thermal deactivation than was free enzyme, whereas invertase held on M was much less stable. In contrast, invertase adsorbed on M was more stable to the action of protease than free enzyme or that adsorbed on AM or AL.

In situ laser activation of carbon fiber microdisk electrodes

Abstract: : Carbon Fiber microdisk electrodes (11 microns in diameter) were activated in situ via intense laser pulses produced by a small nitrogen laser. The laser beam was focused down to a small spot size to ensure adequate power density. The laser treatment resulted in more Nernstian voltammetry for dopamine, 4-methylcatechol, and 3, 4-dihydroxyphenylacetate in several different buffer systems over a range of pH. The effect of buffer composition and pH on the apparent electrode kinetics observed both before and after laser treatment was studied. An apparent cleaning of the electrode surface by the laser pulses results in more Nernstian voltammetry; however, voltammograms obtained in some buffer systems, particularly those containing citrate, show anomalous effects after laser treatment. A model of the activation process is presented which might explain the observed phenomenon by surface ablation exposing clean, active carbon, followed by adsorption of solution species. This activation procedure is presented as a simple, fairly inexpensive way to obtain consistent, repetitive voltammetry at carbon fiber microdisk electrodes. (RH)

A kinetic study of the permanganate oxidation of triethylamine. Catalysis by soluble colloids

Abstract: The kinetics of the reaction between permanganate ion and triethylamine in aqueous phosphate buffers (pH 6–8) has been studied The reaction is autocatalytic, a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface having been identified as the autocatalyst The reaction is also catalyzed by gum arabic Mechanisms in agreement with the kinetic data are proposed for the reaction pathways taking place in the bulk solution (for both triethylamine and triethylammonium ion as reductants) and on both the gum arabic and manganese dioxide colloidal particles

Electrophoresis with chemically suppressed detection

Abstract: Improved capillary electrophoresis apparatus of the type that generally includes a capillary tube, the capillary tube having a sample inlet end and an outlet end, a first electrode in electrical communication with the inlet end of the capillary tube, a second electrode in electrical communication with the outlet end of the capillary tube and a high voltage power supply in electrical communication with the first and second electrodes. The improvement is to connect a miniature Ion Chromatography membrane suppressor to the outlet end of the capillary tube, to connect a conductivity detector to the membrane suppressor and to place the second electrode in the regenerant compartment of the membrane suppressor. The method embodiment of the invention for anion analysis includes the steps of: (a) separating anions of interest by capillary electrophoresis in a buffer solution; (b) exchanging cations of the buffer for regenerant cations using an ion chromatography membrane suppressor to reduce the electrical conductivity of the buffer to produce a suppressed buffer; and (c) measuring the electrical conductivity of the suppressed buffer to determine the separated anions. Similarly, the method embodiment of the invention for cation analysis includes the steps of: (a) separating cations of interest by capillary electrophoresis in a buffer solution; (b) exchanging anions of the buffer for regenerant anions using a stationary means for exchanging anions thereby reducing the electrical conductivity of the buffer to produce a suppressed buffer; and (c) measuring the electrical conductivity of the suppressed buffer to determine the separated cations.

Slow-gelling Cr+3/polyacrylamide solutions for reservoir profile modification : dependence of the gelation time on pH

Abstract: Systematic studies of the gelation of both buffered and unbuffered aqueous Cr+3/polyacrylamide solutions show that the gelation time is a strong function of pH, increasing by about one order of magnitude per unit decrease in pH for polyacrylamides less than about 7.5% hydrolyzed. The gelation rate also depends strongly on the Cr+3 concentration, the degree of polymer hydrolysis, and temperature. At 25°C, gelation delays of more than 10 months have been obtained; the maximum delay observed at 60°C is about 1 month and at 90°C 1 d. The resistance of buffered gel solutions to change in pH results in significantly longer gelation times at 90°C and low pH than for identical unbuffered solutions; at lower temperatures, however, the differences are insignificant. Most importantly, the use of low pH to control the gelation time of Cr+3/polymer solutions provides an attractive, inexpensive substitute for the environmentally unacceptable Cr+6/reductant method currently employed for profile modification treatments.

A NEW METHOD OF DETERMINING INTRACELLULAR FREE Ca2+CONCENTRATION USING Quin2-FLUORESCENCE

Abstract: — We determined intracellular free Ca2+ concentration by fluorescence spectroscopy and the time-resolved measurements of 2-[(2-amino-5-methylphenoxy) methyl]-6-methoxy-8-aminoquinoline-N, N, N′, N′-tetraacetic acid, tetrapotassium salt (Quin2) incorporated in suspended mouse leukemia L1210 cells. The paper reports the following two points. (1) Various fluorescence spectrum patterns in cell suspensions dissolved with Quin2 acetoxy methylester were compared with those of the complex in buffer solution containing esterase. (2) The fluorescence lifetime of Quin2 bound to Ca2+ was approx. 4.5–11 times longer (10 ± 1 ns) than that (1.5 ± 0.5 ns) of Quin2. The fraction of the long lifetime component was plotted against the concentration of CaCl2 in buffer solution. From the results obtained, it was found that approx. 35 nM Ca2+ was contained in each L1210 cell.

Urea sensor based on an ammonium-ion-sensitive field-effect transistor

Abstract: A urea sensor based on an ammonium-ion-sensitive field-effect transistor has been realized in combination with an immobilized urease membrane The effect of buffer concentrations on the response characteristics of the sensor is investigated The lower detection limit, as given by the calibration curve, is strongly affected by the concentrations of potassium and sodium ions, while its slope in the appropriate buffer solution is independent of the buffer concentration in a limited urea concentration range Although the slope in physiological saline solution is only 18 mV/dec, the dynamic range of the sensor covers the physiological range of urea in blood The small slope and the narrow dynamic range are found to be due to poor selectivity of the ammonium-ion-selective membrane over sodium and potassium ions It is, therefore, possible to improve the sensor response characteristics by improving the selectivity of the ammonium-ion-selective membrane

Solubilization of Steviolbioside and Steviolmonoside with γ-Cyclodextrin and Its Application to Selective Syntheses of Better Sweet Glycosides from Stevioside and Rubusoside

Abstract: 1, 4-α-Glucosylation at the 13-O-glycosyl moiety of stevioside (S) and rubusoside (RU) results in a significant increase of sweetness. Saponification of the 19-COO-β-glucosyl linkage of S and RU yielded steviolbioside (SB) (=13-O-β-sophorosyl-steviol) and steviolmonoside (SM) (=13-O-β-glucosyl-steviol), respectively, both of which are poorly soluble in an acetate buffer. It was found that the solubilities of SM and SB in the buffer solution were remarkably increased in the presence of γ-cyclodextrin (γ-CD). SB was solubilized in the buffer solution with the aid of γ-CD, and the solution was subjected to 1, 4-α-transglucosylation by using a cyclodextrin glucanotransferase-starch system to give a mixture of products which were glucosylated at the 13-O-glycosyl moiety. This mixture was acetylated, and the acetate was subjected to chemical β-glucosylation of 19-COOH followed by deacetylation to afford compounds which have superior sweetness to S. In the same way, derivatives with superior sweetness were selectively prepared from RU through SM.