Zeinab M. Anwar

Synthesis and fluorescence properties of Eu-anthracene-9-carboxylic acid towards N-acetyl amino acids and nucleotides in different solvents

Europium (III) complex with anthracene-9-carboxylic acid (9-AA) has been synthesized and characterized by elemental analysis, FT-IR, and TG-DTG techniques. The results indicated that the composition of this complex is Eu (9-AA)(3). The luminescence properties of the complex in different solvents and at different pH values have been investigated. The results show that the complex exhibits more efficient luminescence in THF and ethyl acetate. The interactions of Eu-complex with different N-acetyl amino acids and nucleotides in different solvents have been investigated by fluorescence measurements. Enhancement of the fluorescence intensities has been observed in cyclohexane, acetone, acetonitrile, and tetrahydrofuran whereas the fluorescence intensities of the investigated complex in ethanol, water, and ethyl acetate exhibit relatively low intensity.

Luminescence recognition of different organophosphorus pesticides by the luminescent Eu(III)–pyridine-2,6-dicarboxylic acid probe

Luminescence quenching of a novel long lived Eu(III)-pyridine-2,6-dicarboxylic acid probe of 1:2 stoichiometric ratio has been studied in 0.10 volume fraction ethanol-water mixture at pH 7.5 (HEPES buffer) in the presence of the organophosphorus pesticides chlorfenvinphos (P1), malathion (P2), azinphos (P3), and paraxon ethyl (P4). The luminescence intensity of Eu(III)-(PDCA)(2) probe decreases as the concentration of the pesticide increases. It was observed that the quenching due to P3 and P4 proceeds via both diffusional and static quenching processes. Direct methods for the determination of the pesticides under investigation have been developed using the luminescence quenching of Eu(III)-pyridine-2,6-dicarboxylic acid probe in solution. The linear range for determination of the selected pesticides is 1.0-35.0 μM. The detection limits were 0.24-0.55 μM for P3, P4, and P1 and 2.5 μM for P2, respectively. The binding constants (K), and thermodynamic parameters of the OPs with Eu(III)-(PDCA)(2) were evaluated. Positive and negative values of entropy (ΔS) and enthalpy (ΔH) changes for Eu(III)-(PDCA)(2)-P1 ternary complex were calculated. As the waters in this study do not contain the above mentioned OPs over the limit detectable by the method, a recovery study was carried out after the addition of the adequate amounts of the organophosphorus pesticides under investigation.

High-throughput sensing microtiter plate for determination of biogenic amines in seafood using fluorescence or eye-vision

A new optical sensing microplate was developed for rapid screening for the presence of biogenic amines (BAs) in seafood samples with high sensitivity. The deposition of a sensing spot (containing a chameleon dye (Py-1) in a polymeric cocktail) on the bottom of the wells of a standard microplate renders the plate a new sensing tool for a rapid and parallel detection of up to 96 (real) samples. This sensing microplate enables (1) a semi-quantitative readout of analyte concentration by eye-vision, (2) a rapid fluorescence readout of 96 samples with standard instrumentation in less than two minutes (unlike chromatographic and electrophoretic methods), (3) a statistically robust data evaluation (with 8-12 replicates) and (4) a rapid parallel sample preparation with standard 8 or 12-channel micropipettes. On reaction with biogenic amines, the dye shows a significant visible color change from blue over green to red color. The appearance of red color favorably coincides with the concentration of BAs that can induce symptoms of poisoning. The linear ranges of fluorescence calibration data for six biogenic amines cover the clinical toxicological relevant range of BAs that is too low to be detected by the human nose. The LODs range from 0.16 to 0.56 μg mL(-1), with correlation coefficients (r(2)) between 0.985 and 0.999. Finally, the evolution of spoilage of four fish samples (monitored by determination of their BA status) and the increase of their total amine content were found to agree well with previous data on time-dependent evolution of BAs in fish.

Electrochemical determination of gatifloxacin, moxifloxacin and sparfloxacin fluoroquinolonic antibiotics on glassy carbon electrode in pharmaceutical formulations.

Three fluoroquinolones; gatifloxacin (GAT), moxifloxacin (MOX) and sparfloxacin (SPAR) were electrochemically studied in various buffer systems at different pH values, using a glassy carbon electrode. The three fluoroquinolones were electrochemically oxidized at potential range (0.65-1.1 V) vs Ag-AgCl-KCl. The oxidation was irreversible and exhibited adsorption-controlled process behavior at all pH values and buffers studied. An electroanalytical methodology based on the adsorptive behavior of fluoroquinolones on glassy carbon electrode (GCE) and according to the linear relation between peak current and concentration using differential pulse voltammetry (DPV) method was successfully applied to the determination of the three fluoroquinolones in bulk and tablets. The proposed methods were statistically in agreement with that obtained by spectrophotometric comparison method.

Analytical studies of the interaction of Tb(III)-2-{[(4-methoxy benzoyl) oxy]} methyl benzoic acid binary complex with nucleosides

The interaction of Tb(III)-2-{[(4-methoxy benzoyl) oxy]} methyl benzoic acid binary complex with nucleosides (adenosine, cytidine, guanosine and inosine) was investigated using UV and fluorescence methods. The reaction of Tb-complex with cytidine, guanosine and adenosine is accompanied by shift to longer wavelength in the absorption band, while there is a blue shift in the absorption band with an enhancement in the molar absorptivity upon the reaction with inosine. The fluorescence intensity of Tb(III)-2-{[(4- methoxy benzoyl) oxy]} methyl benzoic acid binary complex at λ = 545 nm (5D4 → 7F5) was decreased with the addition of the nucleoside molecule following the order: cytidine > inosine > guanosine > adenosine.