Rasha Mohamed El Nashar

Preparation and application of molecularly imprinted polymer for isolation of chicoric acid from Chicorium intybus L. medicinal plant

Molecularly imprinted polymer (MIP) was synthesized and applied for the extraction of chicoric acid from Chicory herb (Chicorium intybus L.). A computational study was developed to find a suitable template to functional monomer molar ratio for MIP preparations. The molar ratio was chosen based on the comparison of the binding energy of the complexes between the template and functional monomers. Based on the computational results, eight different polymers were prepared using chicoric acid as the template. The MIPs were synthesized in a non-covalent approach via thermal free-radical polymerization, using two different polymerization methods, bulk and suspension. Batch rebinding experiments were performed to evaluate the binding properties of the imprinted polymers. The best results were obtained with a MIP prepared using bulk polymerization with 4-vinylpyridine (4-VP) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the crosslinker with a molar ratio of 1:4:20. The best MIP showed selective binding ability toward chicoric acid in the presence of the templates structural analogues, caffeic acid, caftaric acid and chlorogenic acid.

Synthesis and application of a molecularly imprinted polymer for the voltammetric determination of famciclovir.

A molecularly imprinted polymer (MIP) was synthesized and applied as additive within a carbon paste electrode for the cyclic voltammetric determination of famciclovir (FCV). Complementary computational studies were performed to study the intermolecular interactions in the pre-polymerization mixture. Derived from the computational studies, four MIP ratios were synthesized and their performance was evaluated using equilibrium rebinding assays. The MIP with the highest binding capacity was selected. A linear response was obtained in the range of 2.5×10(-6)-1.0×10(-3)M with a limit of detection at 7.5×10(-7)M. Finally, the developed MIP-voltammetry system was successfully applied for the determination of FCV in pure solutions and pharmaceutical preparations.

Flow injection catalase activity measurement based on gold nanoparticles/carbon nanotubes modified glassy carbon electrode.

Amperometric flow injection method of hydrogen peroxide analysis was developed based on catalase enzyme (CAT) immobilization on a glassy carbon electrode (GC) modified with electrochemically deposited gold nanoparticles on a multiwalled carbon nanotubes/chitosan film. The resulting biosensor was applied to detect hydrogen peroxide with a linear response range 1.0×10(-7)-2.5×10(-3)M with a correlation coefficient 0.998 and response time less than 10s. The optimum conditions of film deposition such as potential applied, deposition time and pH were tested and the flow injection conditions were optimized to be: flow rate of 3ml/min, sample volume 75μl and saline phosphate buffer of pH 6.89. Catalase enzyme activity was successfully determined in liver homogenate samples of rats, raised under controlled dietary plan, using a flow injection analysis system involving the developed biosensor simultaneously with spectrophotometric detection, which is the common method of enzymatic assay.

Dissolution testing and potentiometric determination of famciclovir in pure, dosage forms and biological fluids

The performance characteristics of two new plastic membrane ion selective electrodes (ISEs) used for the determination of famciclovir (Fcv) based on the ion associate of Fcv with phosphotungstic acid (PTA) or phosphomolybdic acid (PMA) are described. Different experimental conditions as type of plasticizer to be incorporated in the membrane, life span, effect of soaking, pH, temperature, and interferences were studied. Both electrodes showed similar performance under these conditions, exhibiting Nernstian slopes of S (Fcv-PTA)=58.60±0.84 mV/decade and S (Fcv-PMA)=58.77±0.68 mV/decade within a usable concentration range of 10⁻⁵-10⁻² [Fcv/M] at 298/K. Famciclovir was assayed potentiometrically in its pure solution, pharmaceutical preparations and biological fluids (urine and plasma) using proposed electrodes under batch and flow injection analysis (FIA) conditions with a recovery % ranging between 96.76% and 102.83% having RSD of 0.66%-1.81%. The electrodes were also successfully applied in the determination of the dissolution profile of Fcv tablets and the results came in agreement with the validated results of the HPLC method obtained from the quality control unit of the company producing the tablets.

Potentiometric determination of tolterodine in batch and flow injection conditions.

Two new ion-selective electrodes of the plastic membrane type for the determination of Tolterodine (Tol) were prepared. These electrodes depend on the incorporation of the ion-exchangers of the above mentioned drug with phosphotungestic acid (PTA) or Silicotungestic acid (STA) in a PVC matrix. A comparative study is made between the performance characteristics of electrodes containing ion-exchanger in batch and FIA conditions. The usable concentration range of the electrodes was found to be (1.0×10(-5)-1.0×10(-2) and 5.0×10(-5)-1.0×10(-2)M) in batch and FIA conditions, respectively. The electrodes have nearly the same usable concentration, pH range and exhibited high selectivity toward Tol in the presence of many inorganic cations and can be used in biological fluids such as urine and plasma. The dissolution profile of the investigated drug as well as its assay in pure and pharmaceutical preparations was performed, and the results were relatively accurate and precise as indicated by the recovery values and coefficients of variation.

Molecularly imprinted polymers based biomimetic sensors for mosapride citrate detection in biological fluids

Computational modeling was applied to study the intermolecular interactions in the pre-polymerization mixture and find a suitable functional monomer to use in the design of a new molecularly imprinted polymer (MIP) for mosapride citrate which is considerably a large molecule (as the citrate ion is also included in calculations as it has centers that can take part in interaction with monomer via hydrogen bonding). Based on these calculations, methacyrlic acid (MAA) was selected as a suitable functional monomer. Mosapride citrate selective MIP and a non-imprinted polymer (NIP) were synthesized and characterized using FTIR, TGA and SEM and then incorporated in carbon paste electrodes (CPEs). The designed modified sensor revealed linear responses in the ranges of 1×10-4-8×10-7 and 8×10-7-8×10-8molL-1 with a limit of detection (LOD) of 2.6×10-8molL-1. The results of the sensor exhibited high selectivity over interfering species and could be applied for the determination of mosapride citrate in pure solutions, pharmaceutical preparations, urine and human serum samples.

Isolation of sinapic acid from broccoli using molecularly imprinted polymers

A molecularly imprinted polymer was synthesized for the purpose of sinapic acid isolation from Egyptian nutraceutical Botrytis italica, L. (broccoli) due to its prominent medicinal and wide pharmacological activities. A computational study was first developed to determine the optimal template to functional monomer molar ratio. Based on the computational results, five polymers were synthesized using a bulk polymerization method with sinapic acid as the template molecule. Evaluation of the synthesized polymers binding performance was carried out using batch rebinding assay, which revealed that the molecularly imprinted polymer of molar ratio (1:4:20), template to functional monomer (4-vinyl pyridine) to crosslinker (ethylene glycol dimethacrylate) was of optimum performance, thus, this polymer was applied for sinapic acid isolation from closely related analogues. This represents a more practical approach to isolate sinapic acid from different natural extracts selectively.

Calixarene-doped PVC polymeric films as size-selective optical sensors: Monitoring of salicylate in real samples

Preparation of novel salicylate-selective optical sensors (bulk optodes) was performed and applied successfully for salicylate determination in pharmaceutical formulations, Aspirin® and Aspocid®. t-butyl calix[4]arene ionophore was incorporated in a plasticized poly (vinyl-chloride) membrane containing the chromoionophore ETH5294 (O1) or ETH7075 (O5). The optical response to salicylate was due to size-selective extraction of salicylate from the aqueous solution to the optode bulk through formation of hydrogen bond accompanied by chromoionophore protonation, that resulted in the optical response at 680 or 540 nm for O1 or O5, respectively. Reliable size-selectivity was measured for salicylate over other anions; The calculated selectivity coefficients of O5 optode were found to be: -4.4, -2.0 and - 3.7 for iodide, benzoate and perchlorate, respectively. The hydrogen bonding mechanism and selectivity pattern were ensured and explained by IR and 1H NMR spectroscopy. For the same purpose, a molecular recognition constant of βsal=100.043 was calculated using sandwich membrane method, and its small value ensured that hydrogen bonding interaction is responsible for the optode response. The detection limits of O1 and O5 in salicylate buffered solutions were 9.0 × 10-5 and 8.9 × 10-5 M with response times of 5 and 3 min, respectively, and with very good reversibility. The practical utility of the developed sensors was ensured by salicylate determination in Aspirin® and Aspocid®. Beyond the observed analytical performance, the present work aims not only to effectively apply Calixarene without derivatization, but also to estimate the strength of the size-dependent hydrogen bonding and comprehensively study the interaction mechanism.

Electrochemical Detection of the Different Species of Levofloxacin Using PVC, Carbon Paste and Screen-Printed Electrodes: Effect of pH

The zwitterionic compound, levofloxacin, was determined for the first time at different pH values in pure samples, pharmaceutical preparations and spiked serum and urine samples. Different types of potentiometric sensors including poly (vinyl chloride) membrane electrode, carbon paste electrode and screen printed electrode, containing the ion pair levofloxacinium-phosphomolybdate as the electroactaive species, were used for this purpose. The effect of pH is the key factor in determining the ratio of the different species that can exist in the medium (zwitterionic, monocationic, dicationic, anionic and neutral), and so it is the controller of the electrochemical performance. The different sensors were fully characterized and optimized in terms of composition, pH effect, selectivity, response and lifetimes. The different sensors showed reliable reversibility and could be utilized for the determination of the drug in real spiked physiological fluids with reliable recovery values.