UV-visible spectroscopic and electrochemical methods were used to study the interaction of some fluoroquinolones with calf-thymus DNA. UV-visible spectroscopy was used to evaluate the binding constants of drug-DNA complexes and to elucidate the nature of binding of of these drugs with DNA. The interaction of the studied fluoroquinolones with DNA was investigated by cyclic voltammetry at a glassy carbon electrode with an irreversible electrochemical equation. The diffusion coefficients of both free and bound fluoroquinolones (Df, Db), the binding constant (K), and the binding site size (s) of fluoroquinolone-DNA complexes were obtained simultaneously by non-linear fit analysis of the experimental data. The results suggested that fluoroquinolones bind to DNA through an electrostatic mode of interaction with partial intercalation. DNA-modified glassy carbon electrodes were used for the first time as a biosensor for the determination of the studied compounds. Differential-pulse anodic stripping voltammetry was used for investigating different factors that affect the oxidation of the studied fluoroquinolones at the DNA-biosensor. A method was proposed for the determination of ciprofloxacin concentration both in tablets and in a biological fluid (urine). The method was found to be sensitive, accurate, and inexpensive. Kinetics of osmium tetroxide catalyzed-oxidation of the studied fluoroquinolones by potassium hexacyanoferrate (III) in alkaline medium were studied. The rate was found to be independent on the concentration of hexacyanoferrate (III), and first order with respect to both fluroquinolone and OsO4. An empirical rate law was derived for the reaction, and the effect of various variables on the rate of reaction was studied. Thermodynamic parameters (Ea, ?H*, ?S*, ?G*) were also calculated.
Monday, January 18, 2010
Kinetic Studies of the Hydrolysis of Furfurylidenefuroyl Hydrazone Derivatives, Solvatochromism and Fluorimetric Determination of Iron (III)
Preferential solvation of di-2-pyridylketonebenzoyl hydrazone was investigated in aqueous-ethanol binary mixtures . The kinetics and mechanism of the hydrolysis of a series of substituted furfurylidenefuroyl hydrazones (X-FFH) in 25% (v/v) ethanol-buffer mixtures have been studied by ultraviolet visible spectrophotometry at different temperatures in the range 22-500C. The hydrolysis reactions were found to follow first-order kinetics. The effect of pH, molecular structure and temperature on the rate of hydrolysis have been discussed. A mechanism for the hydrolysis is postulated in which the attack of water on the protonated substrate is subject to general acid-base catalysis using HCl-sodium acetate buffer solution. The hydrolysis of 5-Chlorothiophenylidene salicoyl hydrazone (CTSH) was found to obey specific acid catalysis using HCl-KCl buffer solutions. The observed rate constants and the catalytic rate constants with respect to H+, HC2O4- and H2C2O4 were calculated. Activation energy and thermodynamic parametres for the hydrolysis are evaluated and discussed. A sensitive method for the determination of iron (III) in trace levels using fluorescence spectroscopy was devised. The method is based on the oxidation of di-2-pyridylketonebenzoyl hydrazone by hydrogen peroxide whereby Fe (III) shows an inhibition effect on the emission signal. The detection limit of Fe (III) was found to be 3.0x10-6M. Interference studies and order of addition were also investigated. The method was successfully applied to milk and other medicinal samples.
HPLC Determination of Four Textile Dyes and Studying Their Degradation Using Spectrophotometric Technique
In the present work, a simple and a sensitive HPLC method was developed for quantitative determination of four Direct textile dyes (Direct Red 81, Direct Blue 15, Direct Black 22 and Direct Orange 34). The maximum absorbance value for the above mentioned dyes were found to be at 510 nm, 607 nm, 484 nm and 411 nm, with retention times of 15.4, 8.8, 5.8 and 12.7 min, respectively. The mobile phase used was consisting of acetonitrile: water (60:40, v/v) containing 0.45 M N-cetyl-N,N,N-trimehyl ammonium bromide (CTAB). RP C18 column was used with a flow rate of 0.5ml/min. Calibration graphs were found to be linear over the ranges of 0.3–10ppm, 10–30ppm, 0.5–10ppm and 1–12ppm for Direct Red 81, Direct Blue 15, Direct Black 22 and Direct Orange 34, respectively, with limit of detection 0.3ppm, 10ppm, 0.5ppm and 1ppm. The relative standard deviations (RSD%) were found to be 0.92 %, 0.83 %, 1.13 % and 0.34 %, respectively (n=3) with concentrations of 10ppm of each dye. The effect of pH, CTAB concentration and acetonitrile: water ratios (v/v) in the mobile phase on the determination of the four Direct azo dyes were investigated. The reducing degradation kinetics of the four Direct dyes; Direct Red 81, Direct Blue 15, Direct Black 22 and Direct Orange 34 by zero– valent iron and aluminum metals in aqueous solutions were studied. Effective degradation was achieved when using Al compared to Fe. The results show that the rate of degradation is affected by acidity, amount of iron and aluminum, temperature and speed of solution agitation. The effect of metals nature on degradation of the four Direct azo dyes was studied. The following metals were used in this study (Mn, Ni, Co, Zn, Mg and Cu). The obtained results showed that using Cu do not effects on degradation rate, where using Al, Mg give a higher degradation rate compared to iron.