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.

Dissolution Kinetics of Synthetic Amorphous Silica in Biological-Like Media and Its Theoretical Description

Abstract: Different types of synthetic amorphous silica have been dissolved under biological-like conditions in a buffer system. The buffer solution named TRIS buffer provides a system with comparable pH value, buffer capacity, and osmotic pressure as it can be found in extracellular fluid. Additionally, the phospholipid l-α-dipalmitoylphosphatidylcholine (DPPC) has been used in several dissolution experiments to simulate conditions which are found in extracellular lung fluid. The molybdic acid method (used as standard procedure) and partly ICP−OES have been applied to determine the total amount of silica dissolved. The dissolution of nanodisperse silica shows a strong size effect, which leads to a significant higher silica concentration when compared with the bulk phase. At longer dissolution time a slight decrease of solubility can be observed. The Gibbs free energy of cluster formation is calculated numerically for the dissolution process to predict the temporal development of silica concentration. Theoretical c...

Kinetics of enzymatic synthesis of peptides in aqueous/organic biphasic systems. Thermolysin-catalyzed synthesis of N-(benzyloxycarbonyl)-L-phenylalanyl-L-phenylalanine methyl ester.

Abstract: We studied kinetics of thermolysin-catalyzed peptide synthesis in an aqueous/organic biphasic system theoretically and experimentally. As a model reaction producing a condensation product having no dissociating groups, we used the synthesis of N-(benzyloxycarbonyl)-l-phenylalanine methyl ester (Z-Phe2 OMe) from N-(benzyloxycarbonyl)-l-phenylalanine (Z-Phe) and l-phenylalanine methyl ester (PheOMe). Usually, ethyl acetate was used as the organic solvent. First we studied the kinetics of the synthesis of Z-Phe2OMe in a buffer solution saturated with ethyl acetate. Then, factors that may affect the kinetics in the biphasic system were examined. The course of Z-Phe2OMe synthesis in the biphasic system was explained by the rate equations obtained, using the partitions of substrate and product and non-enzymatic decomposition of PheOMe. In the biphasic reaction syste, the rate of synthesis was lower for a wide range of pH due to the unfavorable partition of PheOMe in the aqueous phase, but yields were higher than in the buffer solution. The effects of the organic solvents on the rate of synthesis could also be explained by variations in the partition coefficient of PheOMe. Finally, we gave a way to predict the aqueous-phase pH change caused by partitioning of the substrate. The significance of the pH change was shown in connection with the reaction using the immobilized enzyme in an organic solvent.

Hydrolysis of some N-alkylmaleimides

Abstract: The kinetics of the hydrolysis of maleimide (MI), N-methylmaleimide (MMI), N-ethylamleimide (EMI), and N-hydroxymethylmaleimide (HMMI) were studied spectrophotometrically in pH-controlled buffer solution over the temperature range 10–50 °C. The rate of hydrolysis is proportional to both the concentration of N-alkylmaleimide and that of hydroxide ion in the pH region between 7 and 9, and is independent of pH below pH 4. The catalytic rate constants for alkaline hydrolysis increase in the order: HMMI > MI > MMI > EMI. The entropies of activation for the hydrolysis at pH 7–9 are large and negative ranging from –132 to –162 J mol–1 K–1 and both the enthalpies and the entropies of activation increase in the order: EMI > MMI > MI > HMMI. The effect of substituent on nitrogen on the rate of hydrolysis is explained satisfactorily by Taft's ρ*σ* relationship, with a value of ρ* of 0.05 at 30 °C. The experimental results can be explained by a bimolecular mechanism, in which nucleophilic attack by hydroxide ion on N-alkylmaleimide is the rate-determining step. The hydrolysis products are N-alkyl-maleamic acids.