Stabilizing effect of citrate buffer on the photolysis of riboflavin in aqueous solution

Publication date: May 2011 Source:Results in Pharma Sciences, Volume 1, Issue 1 Author(s): Iqbal Ahmad , Muhammad Ali Sheraz , Sofia Ahmed , Sadia Hafeez Kazi , Tania Mirza , Mohammad Aminuddin In the present investigation the photolysis of riboflavin (RF) in the presence of citrate species at pH 4.0–7.0 has been studied. A specific multicomponent spectrophotometric method has been used to assay RF in the presence of photoproducts during the reactions. The overall first-order rate constants (k obs ) for the photolysis of RF range from 0.42 to 1.08×10–2 min−1 in the region. The values of k obs have been found to decrease with an increase in citrate concentration indicating an inhibitory effect of these species on the rate of reaction. The second-order rate constants for the interaction of RF with total citrate species causing inhibition range from 1.79 to 5.65×10–3 M−1 min−1 at pH 4.0–7.0. The log k–pH profiles for the reactions at 0.2–1.0M citrate concentration show a gradual decrease in k obs and the value at 1.0M is more than half compared to that of k 0, i.e., in the absence of buffer, at pH 5.0. Divalent citrate ions cause a decrease in RF fluorescence due to the quenching of the excited singlet state resulting in a decrease in the rate of reaction and consequently leading to the stabilization of RF solutions. The greater quenching of fluorescence at pH 4.0 compared to that of 7.0 is in accordance with the greater concentration of divale...
Source: Results in Pharma Sciences - Category: Drugs & Pharmacology Source Type: research