Buffer solution

About: Buffer solution is a research topic. Over the lifetime, 6948 publications have been published within this topic receiving 112440 citations. The topic is also known as: pH buffer & buffer.

Reversible near-infrared pH probes based on benzo[a]phenoxazine.

Abstract: Several benzo[a]phenoxazine derivatives containing substituted N-aromatic groups are evaluated for their pH-dependent absorption and emission properties. Among the compounds exhibiting optical responses under near-neutral and subacid pH conditions, benzo[a]phenoxazine derivatives with an electron-withdrawing aromatic group attached to nitrogen of the imino group show potential application as near-infrared pH sensors. Three water-soluble pH probes based on benzo[a]phenoxazine with different pyridinium structures are designed and synthesized. Their reversible pH-dependent emissions in buffer solution containing 0.1% dimethyl sulfoxide (DMSO) locate in 625-850 nm with the fluorescent enhancement of 8.2-40.1 times, and their calculated pKa values are 2.7, 5.8, and 7.1, respectively. A composite probe containing the three benzo[a]phenoxazines shows a linear pH-emission relationship in the range of pH 1.9-8.0. Real-time detection of intracellular pH using an in vitro assay with HeLa cells is also reported.

Quantitative analyses of the interaction between calcium ions and human serum albumin

Abstract: We examined the suitability of nine organic buffers for studying calcium binding to albumin by equilibrium dialysis. Results obtained with defatted human serum albumin showed that 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 2-([tris(hydroxymethyl)methyl] amino)ethanesulfonic acid were superior. Scatchard analysis of the experimental data from an extensive study performed in HEPES at pH 7.4 and 20 degrees C revealed (putting n(i) = 1, i = 1-4) k1 = 367 L/mol, k2 = 314 L/mol, k3 = 291 L/mol, and k4 = 179 L/mol. The very weak binding was characterized as n5 = 10 and k5 = 40 L/mol. The results were also analyzed in terms of stoichiometric association constants. The constants K1 and K2 were calculated to be 1513 and 647 L/mol, respectively, whereas the other constants were considered undeterminable. pH studies showed that in the interval 6.8-7.4, binding was not influenced by changes in acidity. Increasing pH to above the physiological value resulted in increased binding. At pH 8.0, k1 was increased almost fourfold, whereas k2 and k3 were approximately doubled. These findings indicate that the neutral to basic transition is important for the calcium-binding properties of albumin. The transition is a reversible, gradual conformational change of the protein at pH 6-9.

Fe3+-Sensitive Carbon Dots for Detection of Fe3+ in Aqueous Solution and Intracellular Imaging of Fe3+ Inside Fungal Cells.

Abstract: In this article, the Fe3+-sensitive carbon dots were obtained by means of a microwave-assisted method using glutamic acid and ethylenediamine as reactants. The carbon dots exhibited selective response to Fe3+ ions in aqueous solution with a turn-off mode, and a good linear relationship was found between (F0-F)/F0 and the concentration of Fe3+ in the range of 8-80 μM. As a result, the as-synthesized carbon dots can be developed as a fluorescent chemosensor for Fe3+ in aqueous solution. Moreover, the carbon dots can be applied as a fluorescent agent for fungal bioimaging since the fungal cells stained by the carbon dots were brightly illuminated on a confocal microscopy excited at 405 nm. Furthermore, an increase in the concentration of intracellular Fe3+ could result in fluorescence quenching of the carbon dots in the fungal cells when incubated in the Tris-HCl buffer solution containing Fe3+. However, due to EDTA might hinder Fe(III) to enter the fungal cells, incubation in Fe(III)-EDTA complex solution exerted negligible effect on the fluorescence of fungal cells labeled by the carbon dots. Therefore, the carbon dots can serve as a potential probe for intracellular imaging of Fe3+ inside fungal cells.

Effects of pH, temperature, and aqueous organic material on the dissolution kinetics of meta-autunite minerals, (Na, Ca)2-1[(UO2)(PO4)]2.3H2O

Abstract: Autunite minerals have been frequently identified in contaminated sediments as the long-term controlling phase of uranium. Under these conditions the mobility of uranium in subsurface pore waters is limited by the rate of dissolution of autunite and meta-autunite group minerals, [(UO2)(PO4)]2 ? xH2O. Single-pass flow-through (SPFT) tests were conducted to quantify the dissolution kinetics of natural calcium meta-autunite, Ca[(UO2)2(PO4)2]2 ? 3H2O, and synthetic sodium meta-autunite, Na2[(UO2)(PO4)]2 ? 3H2O, as a function of pH (7 -10) and temperature (5 ? 70 C) in the presence and absence of aqueous organic material. The data indicate that release of uranium and phosphorus are non-stoichiometric over the range of experimental conditions investigated. In a 0.1 M NH4OH buffer solution, acquisition of valid dissolution rate data was limited by uramphite solubility, NH4[(UO2)(PO4)]2 ? xH2O. Dissolution rates obtained in a 0.01 M TRIS [tris (hydroxymethyl) aminomethane] buffered solution increased by a factor of {approx}100X over the pH interval of 7 to 10 (? = 0.90?0.08), irrespective of temperature. At constant pH the rate data showed a minor increase with temperature. Data from experiments using a more concentrated 0.05 M TRIS buffer exhibited a {approx}35-fold increase in rates compared to those in a 0.01 M TRIS buffermore » at constant temperature and pH. The difference in rate between interlayer cation (Na+ or Ca2+) and uranium release is {approx}10,000 in neutral solutions; however, the difference diminishes to {approx}10 at higher pH values. The combination of structural dissolution and ion exchange explain these trends in interlayer cation behavior. Data presented here illustrate the significance of pH and dissolved organic material on the dissolution of autunite minerals.« less