Electrochemical reduction of ciprofloxacin at the mercury electrode and its voltammetric determination in tablet and urine

In this study a reduction square wave voltammetric method was developed and validated for the direct determination of ciprofloxacin (CIP) in pharmaceutical formulation and biological fluid using hanging mercury dropping electrode (HMDE) surface. Best results were obtained for the quantitative determination of CIP in 0.02 M Britton-Robinson buffer at pH 2.5 and at a potential of ?1300 mV vs. Ag/AgCl reference electrode. Various experimental and instrumental parameters affecting the peak current and potential of CIP electrochemical reduction were investigated and optimized. The monitored peak current was directly proportional to the concentration of CIP, where it exhibited a linear response in the range 3.0 × 10^?7–2 × 10^?6 M (r = 0.99). The accuracy of the proposed method was concluded based on the value of mean recovery of 98 ± 0.72 % with RSD of 0.181 % at a detection limit of 7 × 10^?9 M. Possible interferences by various substances usually present in pharmaceutical formulations have been also evaluated. After validating the proposed method, the applicability of this voltammetric method was demonstrated by estimating CIP in its pharmaceutical formulation and spiked human urine, where values of mean recoveries of 97 ± 1.0% and 108.0 ± 2.0% were obtained, respectively.     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.     

Spectrofluorimetric study on the interaction between antimicrobial drug sulfamethazine and bovine serum albumin

The interaction between the antimicrobial drug sulfamethazine (STM) and bovine serum albumin (BSA) has been studied using steady state and synchronous fluorescence spectroscopy. Fluorescence emission data revealed that BSA (2×10⁻⁶ M) fluorescence was statically quenched by STM at various concentrations, which implies that STM-BSA complex has been formed. The fluorescence emission data was analyzed via applying the Stern-Volmer analysis in combination with thermodynamic investigation, where obtained results revealed that quenching is static with quenching constants of 2.371, 1.658, and 0.916×10⁵ M⁻¹ at 298, 304, and 310 K, respectively. Binding constants and number of binding sites at different temperatures were also determined by applying the Scatchard method, which in turn were used to construct the van't Hoff plot in order to estimate the enthalpy (ΔH) and entropy changes (ΔS) for the complexation process. An average of 1.00±0.17 was estimated for the number of sites of BSA, which indicated that STM binds to BSA with stoichiometric ratio of 1:1. The values that were estimated from the van't Hoff plot for ΔH and (ΔS) were −36.8 kJ mol⁻¹ and −14.9 J mol⁻¹ K⁻¹, respectively, which indicate that the STM-BSA complex is stabilized with hydrogen bonds and van der Waals interactions. Synchronous fluorescence data was obtained at Δλ of 15 and 60 nm, where obtained results confirmed that STM binds to BSA at the tryptophan residue (Trp. 213). In addition, the distance between STM and the Trp. 213 was estimated via employing the Förster's non-radiative energy-transfer theory, and was found to be 2.73 nm, which in turn indicated that STM can bind to BSA with high probability.     

Influence of inclusion complexation with β-cyclodextrin on the photostability of selected imidazoline-derived drugs

In this paper, the influence of inclusion complexation with β-cyclodextrin (β-CD) on the photostability of antazoline, xylometazoline, and naphazoline in aqueous media was investigated. The photodegradation reaction of these drugs molecules was explored using UV–vis spectrophotometery-based kinetic analysis and high performance liquid chromatography (HPLC). Quantitative evaluation of the influence of β-CD was judged based on the observed rate constant (k _obs), half-life time (t _0.5) and t _0.1 of the photodegradation reaction and the peak area of the corresponding analyte after photodegradation using HPLC separation. It has been demonstrated that the photostability of these selected imidazoline-based drugs has been enhanced upon forming inclusion complexes with β-CD in aqueous media. Moreover, high consistency regarding the photostability enhancement was obtained using both techniques. Hypothetical structure for 1:1 inclusion complexes was proposed based on molecular mechanics calculations, which in turn provide an insight for the energetically preferential structure of the inclusion complexes. The results obtained demonstrate that β-CD can be utilized as photostabilizer additive for enhancing the photostability of imidazoline-derived drugs molecules.     

Integrated microfluidic device for the separation and electrochemical detection of catechol estrogen-derived DNA adducts

Catechol estrogen-derived DNA adducts are formed as a result of the reaction of catechol estrogen metabolites (e.g., catechol estrogen quinones) with DNA to form depurinating adducts. Developing a new methodology for the detection of various DNA adducts is essential for medical diagnostics, and to this end, we demonstrate the applicability of on-chip capillary electrophoresis with an integrated electrochemical system for the separation and amperometric detection of various catechol estrogen-derived DNA adducts. A hybrid PDMS/glass microchip with in-channel amperometric detection interfaced with in situ palladium decoupler is utilized and presented. The influence of buffer additives along with the effect of the separation voltage on the resolving power of the microchip is discussed. Calibration plots were constructed in the range 0.4–10 μM with r ² ≥ 0.999, and detection limits in the attomole range are reported. These results suggest that on-chip analysis is applicable for analyzing various DNA adducts as potential biomarkers for future medical diagnostics.