الفهرس 
Acknowledgments
THE AIM OF INVESTIGATIONOnly 14 pages are availabe for public view
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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.