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Abstract instrumentations used in the present measurements, which cover the diverse electrochemical tools: a) Phase sensitive a.c voltammetry . b) Cyclic voltammetry. c) Differential pulse cathodic adsorptive stripping voltammetry. 3- In chapter III, the surface activity of difloxacin was studied at the hanging mercury DROP electrode by phase sensitive a.c voltammetry. In acidic, neutral and alkaline solutions and at relatively low bulk concentrations of difloxacin, the out-of-phase a.c. current indicates a progressive decrease of the capacitive current around the electrocapillary point of zero charge of the pure supporting electrolyte. The decrease of a.c current corresponds to a progressive coverage of .the electrode surface by a.dilute adsorption layer. The adsorption layer reflects a flat orientation of the adsorbed species of difloxacin at the electrode surface i.e with the plane of the ring atom parallel to the electrode surface. The adsorption parameters of the investigated compound were computed at different pH values. The surface activity and the redox behaviour of the biological compound under investigation were studied at different pH values using cyclic voltammetry at HMDE. Over the investigated pH range the surface redox reaction shows a one cathodic peak and the corresponding oxidation process. The morphology and position of these redox peaks are mainly dependent on the solution and operational conditions (e.g. the pH, the adsorption time and potential, and the scan rate).The cathodic peak was attributed to the reduction of the C=O group and the process of reduction was irreversible and fundamentally controlled by adsorption. The surface concentration was obtained as 8.70x10-10 mol.cm-2 and each adsorbed difloxacin molecule therefore occupied an area of 0.20 nm2 . A simple, rapid, reliable and fully validated differential pulse cathodic adsorptive stripping voltammetry (DPCASV) was applied for the determination of the antibiotic difloxacin drug. To obtain a good sensitivity, the solution conditions and instrumental parameters were studied using DPCASV. Applicability to measurement of difloxacin at submicrmolar levels in urine sample was illustrated. The limits of detection (LOD) and quantition (LOQ) for the determination of difloxacin were computed. The degree of interference from coexisting metal ions and some organic compounds on the DPCASV signal for difloxacin was evaluated. The interaction of difloxacin, an antibacterial drug with ds-DNA, β-cyclodextrin and hemoglobin in aqueous solutions was studied by DPCASV and cyclic voltammetry as well as UV-Vis spectroscopy. The nature of the process, taking place at the hanging mercury DROP electrode, was clarified. The measurements show that the difloxacin, acting as an intercalator, is inserted into the cavity of β-cyclodextrin as well as into the base- stacking domain of the ds-DNA double helix. The binding constant was calculated from the absorption spectra and the decrease in cathodic peak current of difloxacin upon the addition of the host molecules. Calculations of the thermodynamic parameters of dix- DNA, dix-β-CD and dix- β-CD-DNA systems including Gibbs free energy change, Helmholz free energy and entropy change show that the complexation is spontaneous process of association. Furthermore , the calibration graph for the determination of DNA or β-CD or hemoglobin was obtained by the decrease in DPCASV peak current of difloxacin in the presence of the host molecules. 4-In chapter IV, the out-of-phase a.c current of danofloxacin recorded as a function of potential in solutions of varying pH was studied. It has found that the experimental data fit well a Frumkin adsorption isotherm. At the optimal adsorption potential of danofloxacin the values of adsorption parameters were calculated and showed significant dependence on the pH values. The interfacial accumulation of danofloxacin on HDME was also studied by cyclic voltammetry. On plotting log ip versus logυ , straight line with slope value of 0.983 was obtained, indicating an adsorption-controlled process. The value of surface concentration Гm was computed using Koryts Equation as 5.23 x 10-10 mol.cm-2 and each adsorbed danofloxacin therefore occupied an surface area of 0.317 nm2. The value of the surface area reflects that the orientation of danofloxacin in the adsorbed layer is characterized by a planar position with respect to the surface of the electrode. The aforementioned results of a.c. and cyclic voltammetry indicate the adsorption character of danofloxacin on the electrode surface. This phenomenon is exploited for the electroanalytical determination of danofloxacin with the aid of differential pulse cathodic adsorptive stripping voltammetry. The DPCASV behaviour of danofloxacin was investigated in solutions of varying pH. Danofloxacin gave rise to a single well-defined reduction peak which is due to a 2e-/2H+ reduction of C=O double bond. Under the optimum conditions and over a concentration range of 9.9x10-9 -6.54x10-8 M of danofloxacin, the DPCASV peak height varied linearly with the concentration of investigated compound. The calibration data, the limit of detection and limit of quantitation for the trace determination of danofloxacin were given. Applicability to measurement of danofloxacin at submicromolar levels in urine was illustrated. The interaction of danofloxacin, a fluoroquinolone antimicrobial drug with ds-DNA and β-cyclodextrin was testified by voltammetry and spectroscopy. The interaction of the inclusion complex of danofloxacin-β-CD with ds-DNA was also investigated. It was found that the interaction of danofloxacin with DNA is more favored and thus the β-CD is replaced by DNA to form intercalate with danofloxacin. In this context the binding affinity increases in the sequence: Dano-DNA ≅ Dano- β-CDDNA > Dano- β-CD which reveals that the existence of β-CD did not affect in the interaction of danofloxacin with DNA. On comparison the change in Gibbs energy values (ΔGo) enthalpy and entropy for the binding of danofloxacin complexes we observed that different values of thermodynamic parameters decrease in the same order. An electrochemical investigation of the interaction between danofloxacin and hemoglobin is reported. An addition of hemoglobin to danofloxacin solution and subsequent scanning over the potential range -0.6 to -1.6 V produced no new waves but only a decrease peak current for the reduction of danofloxacin. We assume that danofloxacin interacting with hemoglobin produces an electrochemically inactive supramolecular complex via intercalation. 5- In chapter V, the phase-sensitive a.c voltammetry corresponding to the out-of-phase component of the total a.c response provides an overall pattern on the adsorption behaviour of orbifloxacin at different pH values. The calculated values of the adsorption parameters of orbifloxacin including the interaction coefficient, adsorption coefficient and adsorption energy are given. The surface activity and redox behaviour of orbifloxacin were also studied by cyclic voltammetry at the charged interface. The aforementioned results of a.c. and cyclic voltammetry supported the adsorption of orbifloxacin at the Hg surface, which is a prerequisite step for application of the DPCASV technique to ultra-trace determination of biologically important compound orbifloxacin. To obtain a good sensitivity, the solution conditions and instrumental parameters were studied. After being validated, the proposed procedure was successfully applied for the determination of the investigated compound in human urine and serum. The interaction of orbifloxacin with ds-DNA, β-CD and hemoglobin was studied using spectroscopic and voltammetric methods. The binding constant and thermodynamic parameters for the interaction of orbifloxacin with host molecules were computed. Structural effects of the investigated fluoroquinolones on their binding to DNA, β-CD and hemoglobin were discussed. |