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PubMed2004

Polarographic behaviors of diclofenac sodium in the presence of dissolved oxygen and its analytical application.

The polarographic response characteristics of diclofenac sodium were investigated in 0.25 M HAc-NaAc (pH 5.0) supporting electrolyte in the absence and the presence of dissolved oxygen. The results demonstrate that the reduction peak at ca. -1.10 V is a catalytic hydrogen wave after deaeration, and the reduction peak in the presence of dissolved oxygen is a so-called parallel catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave, a novel method has been proposed for the determination of diclofenac sodium by single-sweep polarography. The calibration curve is linear in the range 1.2 x 10(-7)-2.6 x 10(-6)M and the detection limit is 6.0 x 10(-8)M. The proposed method is applied to the direct determination of diclofenac sodium in tablet forms and biological samples.

Buffers↗

PubMed2005

Identification of heavy metal complexes of a hexapeptide inhibitor of the human immunodeficiency virus integrase protein by using a voltammetric approach.

Complexation of the hexapeptide Hys-Cys-Lys-Phe-Trp-Trp, inhibitor of the human immunodeficiency virus integrase protein, with the heavy metal ions Cd2+, Pb2+, and Zn2+ has been investigated using differential pulse polarography. In the case of Pb2+, no significant complexation is detected, whereas in the cases of Cd2+ and Zn2+, strong and electrochemically inert ML2 complexes predominate. In contrast, ML complexes are present in a low proportion or are absent. When possible, the corresponding conditional stability constants have been determined at both pH 7.0 and pH 7.5, showing that Zn2+ complexes are slightly more stable than Cd2+ complexes.

Cadmium↗

PubMed2006

Myocardial oxygen tension during surgical revascularization. A clinical comparison between blood cardioplegia and crystalloid cardioplegia.

OBJECTIVE: The aim of this study was to assess the effect of cardioplegic solutions on myocardial oxygenation during surgical revascularization. METHODS: In 30 patients, randomized to receive crystalloid (CC) or blood (BC) cardioplegia, myocardial oxygen tension was measured continuously by polarography. RESULTS: The two groups were comparable in terms of patients' age, sex, pre-operative ejection fraction, coronary disease, perfusion time, and aorta cross-clamping time. However, the BC group required 22% more of cardioplegic solution to stop electrical activity of the heart. Throughout the pre- and post-cardiac arrest periods, oxygen tension between the two groups was similar. At the end of the observation (4th day), myocardial oxygenation increased over 200% in relation to the values before revascularization. During the first infusion of cardioplegia, oxygen tension in the CC group was lower compared to the BC group (0.1 mmHg vs 1.3 mmHg; P<0.05) being the only significant difference between the two groups during cardiac arrest. Throughout the cardiac arrest, myocardial oxygen tension was close to zero regardless of the type of cardioplegia used. Post-operatively, addition of oxygen to the respiratory air increased myocardial oxygenation by over 17% resulting in a positive correlation (r=0.94; P<0.05) between myocardial oxygen tension and peripheral saturation. CONCLUSIONS: In conclusion, the differences in myocardial oxygen tension between the CC and BC groups are trivial. Thus, any potential beneficial effect of blood cardioplegia compared to crystalloid cardioplegia must be due to other circumstances than its oxygen carrying capacity. An important observation is a significant increase in myocardial oxygenation during oxygen supplement to the respiratory air.

Aged↗

PubMed2005

Mixed-valence Cu(II)/Cu(I) complex of quinolone ciprofloxacin isolated by a hydrothermal reaction in the presence of L-histidine: comparison of biological activities of various copper-ciprofloxacin compounds.

A new quinolone-metal complex was prepared by a hydrothermal reaction in the presence of L-histidine that served as a reducing agent for a metal. The title compound [Cu(II)(cfH)(2)(Cu(I)Cl(2))(2)] (1) is a mixed-valence Cu(II)-Cu(I) complex, which contains two ciprofloxacin (cfH) molecules bonded to the central copper(II) atom and two almost planar [Cu(I)Cl(2)](-) moieties. Both metal centers are connected through two bridging atoms (chloride and quinolone oxygen). The electrochemical methods (differential-pulse polarography and cyclovoltammetric measurements) confirmed the presence of various copper-ciprofloxacin complex species in aqueous solution at low concentrations used in biological activity tests and also indicated that the equilibria in this system are very complex. The biological properties of the title compound and some previously isolated copper-ciprofloxacin complexes ([Cu(cfH)(2)Cl(2)].6H(2)O (2) and [CuCl(cfH)(phen)]Cl.2H(2)O (3)) (phen=1, 10-phenantroline) were determined and compared. The DNA gyrase inhibition tests and antibacterial activity tests have shown that the effect of copper complexes is comparable to that of free quinolone. Additionally, an interesting DNA cleavage activity of the title compound was also discovered.

Anti-Bacterial Agents↗

PubMed2005

Voltammetry as a virtual potentiometric sensor in modelling of a metal-ligand system and refinement of stability constants. Part 4. An electrochemical study of NiII complexes with methylene diphosphonic acid.

The Ni(II)-MDP-OH system (MDP=methylene diphosphonic acid) and stability constants of complexes formed at ionic strength 0.15M at 298K were established by direct current polarography (DCP) and glass electrode potentiometry (GEP). The final M-L-OH model could only be arrived to by employing recent concept of virtual potentiometry (VP). VP-data were generated from non-equilibrium and dynamic DC polarographic technique. The VP and GEP data were refined simultaneously by software dedicated to potentiometric studies of metal complexes. Species distribution diagrams that were generated for different experimental conditions employed in this work assisted in making the final choice regarding the metal-ligand model. The model established contains ML, ML(2), ML(OH) and ML(OH)(2) with stability constants, as logbeta, 7.94+/-0.02, 13.75+/-0.02, 12.04 (fixed value), and 16.75+/-0.05, respectively. It has been demonstrated that virtual potential must be used in modelling operations (predictions of species formed) when a polarographic signal decreases significantly due to the formation of polarographically inactive species (or formation of inert complexes). The linear free energy relationships that included stability constant logK(1) for Ni(II)-MDP established in this work together with other available data were used to predict logK(1) values for Sm(III) and Ho(III) with MDP. The logK(1) values for Sm(III)-MDP and Ho(III)-MDP were estimated to be 9.65+/-0.10 and 9.85+/-0.10, respectively.

Bone and Bones↗

PubMed2005

Voltammetric behavior and assay of the antibiotic drug cefazolin sodium in bulk form and pharmaceutical formulation at a mercury electrode.

The electrochemical behavior of the antibiotic drug cefazolin sodium (CFZ) in Britton-Robinson buffers (pH 2-11) at the mercury electrode was studied by means of dc-polarography, cyclic voltammetry, controlled-potential coulometry and square-wave adsorptive stripping voltammetry techniques. A validated square-wave adsorptive cathodic stripping voltammetric procedure was described for the trace determination of cefazolin in bulk form up to limits of detection and quantitation of 2.6 x 10(-10)M and 8.6 x 10(-10)M, respectively. The method was successfully applied for determination of cefazolin in pharmaceutical preparation without the necessity for samples pretreatment or any time-consuming extraction or evaporation steps prior to the analysis.

Anti-Bacterial Agents↗

PubMed2006

Voltammetry and quantification of the contraceptive drug norethisterone in bulk form and pharmaceutical formulation.

The electrochemical behavior of norethisterone at the mercury electrode was studied in the universal buffer of various pH values using dc-polarography, cyclic voltammetry and controlled-potential electrolysis. Norethisterone was reduced at the mercury electrode via the consumption of two electrons corresponding to reduction of the 3-keto-delta-4-group in the A-ring of the molecule. The pK(a) value (8.7) of norethisterone was determined from the polarographic and spectrophotometric measurements. A fully validated, simple, sensitive, precise and inexpensive square-wave adsorptive cathodic stripping (SWAdCS) voltammetry procedure was described for trace quantification of bulk norethisterone. The stripping voltammetry peak current of norethisterone in a universal buffer of pH 5 following its accumulation onto the hanging mercury drop electrode (HMDE) at -0.6 V (versus Ag/AgCl/KCl(s)) for 130 s showed a linear response with the concentration over the range 5 x 10(-9) to 3 x 10(-7)M norethisterone. Detection and quantitation limits of 1.5 x 10(-9) and 5 x 10(-9)M bulk norethisterone, respectively, were achieved. The proposed procedure was successfully applied for the assay of norethisterone in Steronate tablets without interference from excipients.

Buffers↗

PubMed2006

Study of the physicochemical properties in aqueous medium and molecular modeling of tagitinin C/cyclodextrin complexes.

The inclusion complexes of tagitinin C with beta-, 2,6-di-O-methyl-beta- and gamma-cyclodextrin (CyD) was investigated in aqueous medium. The stoichiometric ratios and stability constants (K(f)) which describe the extent of formation of the complexes have been determined by UV spectroscopy and direct current tast polarography (DC(tast)), respectively. For each complex, a 1:1 molar ratio was formed in solution and the trend of stability constants was K(f) (2,6-di-O-methyl-beta-CyD)>K(f) (gamma-CyD)>K(f) (beta-CyD). The effect of molecular encapsulation on the photochemical conversion of tagitinin C was evaluated. No significant protection efficacy was noticed with beta- and gamma-CyD for the complexed drug with the respect to the free one. On the other hand, the photochemical conversion rate was slowed in presence of 2,6-di-O-methyl-beta-CyD. Data from (1)H NMR and ROESY experiments provided a clear evidence of formation of inclusion complexes. The lactone, the ester and the unsaturated ketone parts of tagitinin C inserted into the wide rim of the CyDs torus. These experimental results were confirmed by the molecular modeling using semiempirical Austin Model 1 (AM1) method.

Chemical Phenomena↗

PubMed2005

Interactions between different selenium compounds and zinc, cadmium and mercury.

In this paper, we present a polarographic study of systems containing different inorganic and organic selenium compounds (sodium selenite, sodium selenate, seleno-methionine and seleno-urea) and metal ions (Zn2+, Cd2+ Hg2+) of the 12th group of elements in the periodic table. While zinc is a trace element known to be essential for plants and animals, cadmium and mercury are exogenous elements and are harmful pollutants that accumulate during aging; selenium is also recognized as an important micronutrient and is sometimes added to the diet. Experiments investigating the interactions were carried out using polarographic techniques in unbuffered systems. The three metal cations originated complexes with different strength and solubility in the presence of selenite anions; in the presence of selenate, polarography was not able to detect formation of complexes with these metal ions, at least under the experimental conditions used: a decrease of Hg2+ ion concentration was observed. Seleno-methionine did not react with Cd2+; in the presence of Zn2+, a soluble complex with a co-ordination number 1 was formed, while, again, the concentration of Hg2+ decreased in the presence of increasing concentrations of the selenium derivative. Seleno-urea did not react with Zn2+, but formed a complex with Cd2+ with limited solubility. Finally, this ligand could not be studied with Hg2+ because of the overlapping of the reduction potentials of both the ligand and the metal cation. Overall equilibrium constants for complex formation (Kf) and the solubility product (Ksp) for poorly soluble species are also reported.

Cadmium↗

PubMed2001

Heterogeneity of the mechanism of water splitting in photosystem II.

We measured the temperature dependence of oxygen evolution in thylakoids from tobacco using mass spectrometry and high resolution polarography. We determined the initial S-state distribution and the efficiency of the transition between these states including the probability of the O(2) yield through a fast mode. We observed discontinuous changes of the parameters at the temperatures 11 degrees C, 15 degrees C and 21 degrees C. Due to the mass spectroscopy data we think that the irregularity observed at 11 degrees C is due to conformational changes within the water catalytic site. We show that the different contributions of the slow and fast modes of oxygen evolution and of the water molecule exchange are correlated and that their behavior can be explained in terms of the H(2)O accessibility to the water splitting enzyme.

Mass Spectrometry↗

PubMed1972

Oxygen permeability of the limiting layers of the cornea.

Using polarography and suitable mathematical analysis, the oxygen permeability of an individual layer of a bilayered tissue may be determined if the oxygen consumption and permeability of the other layer are known. Results obtained on rabbit cornea indicate that the permeability of the epithelium is about four times that of the endothelium.

Animals↗

PubMed2000

Activities of mitochondrial oxidative phosphorylation enzymes in cultured amniocytes.

Amniocytes represent a population of foetal cells that can be used for prenatal diagnosis in families with suspected mitochondrial oxidative phosphorylation (OXPHOS) defects. In this paper, we present a complex protocol for evaluation of the function of mitochondrial OXPHOS enzymes in cultured amniocytes using three independent and complementary methods: (a) spectrophotometry as a tool for determination of the capacities of mitochondrial respiratory-chain enzymes (NADH ubiquinone oxidoreductase, succinate- and glycerophosphate cytochrome c reductase, cytochrome c oxidase and citrate synthase); (b) polarography as a tool for the evaluation of mitochondrial OXPHOS enzyme functions in situ using digitonin-permeabilised amniocytes (rotenone-sensitive oxidation of pyruvate+malate, antimycin A-sensitive oxidation of succinate, KCN-sensitive oxidation of cytochrome c, ADP-activated substrate oxidation) and (c) cytofluorometric determination of tetramethyl rhodamine methyl ester (TMRM) fluorescence in digitonin-permeabilised amniocytes as a sensitive way to determine the mitochondrial membrane potential under steady-state conditions (state 4 with succinate). These protocols are presented together with reference control values using 9-22 independent cultures of amniocytes.

Adenosine Diphosphate↗

PubMed2002

Sphingomyelin content conditions insertion of daunorubicin within phosphatidylcholine monolayers.

Cell death induced by the chemotherapeutic drug daunorubicin (DNR) implicates an apoptotic pathway originating at the plasma membrane and characterized by sphingomyelin (SM) hydrolysis and ceramide generation. The mechanisms by which such a drug (hypothetically passively diffusing across a structural membrane) can trigger SM hydrolysis is unknown, but raises the question of the precise interaction between DNR and membrane lipid constituents. In this initial study, using alternative current polarography together with voltammetry, we report that after a first step of adsorption, insertion of DNR within a condensed phosphatidylcholine monolayer was significantly facilitated by SM content.

Adsorption↗

PubMed2003

Polarographic behavior and determination of finasteride.

The polarographic behavior of finasteride at the dropping mercury electrode (DME) was studied adopting direct current (DC(t)), alternating current (AC(t)) and differential-pulse polarography (DPP) modes. In Britton-Robinson buffer (BRb), finasteride exhibited cathodic waves over the pH range 6-12. At pH 10, a well-defined cathodic wave was obtained. The latter could be characterized as being irreversible, diffusion-controlled and partially affected by adsorption phenomenon. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented. The current-concentration plots were rectilinear over the ranges 8-40 and 2-30 microg ml(-1) using DC(t) and DPP modes, respectively. The minimum delectability was 0.2 microg ml(-1) (5.4 x 10(-7) M), for the latter. The proposed method was successfully applied to the determination of finasteride in its commercial capsules and the results obtained were in good agreement with those given with a reference method.

Finasteride↗

PubMed2002

Polarographic behaviour of meloxicam and its determination in tablet preparations and spiked plasma.

Meloxicam is a new non-steroidal anti-inflammatory drug (NSAID), which has a higher activity cyclooxygenase-2 (COX-2) than against cyclooxygenase-1 (COX-1), with potentially high anti-inflammatory and analgesic action. The voltammetric behaviour of meloxicam was studied using direct current (DC), differential pulse polarography (DPP) and cyclic voltammetry (CV). The influence of several variables (including nature of the buffer, pH, concentration, modulation amplitude, scan rate, drop size, etc.) was examined in DPP method for meloxicam. The best DPP response was obtained in acetate buffer pH 4.88. The peak currents were measured with a static mercury drop electrode at -1.49 V versus Ag/AgCl. Calibration curve for meloxicam was linear at a concentration range from 0.38 to 15.0 microg ml(-1). The method was validated and applied to the determination of meloxicam in tablets, which were in two different dosage forms. A spectrophotometric method reported in the literature was utilized as a comparison method. There were no significant differences between the results obtained by two methods. DPP method is also available and applicable for the determination of mentioned substance in plasma. Mean recovery was 99.20+/-0.37%. It was concluded that the developed method was accurate, sensitive, precise, reproducible and useful for the quality control of meloxicam in pharmaceuticals and spiked plasma.

Administration, Oral↗

PubMed2003

Polarographic determination of flubendazole in spiked human urine and plasma.

The voltammetric behavior of flubendazole was studied using direct current (DCt), differential pulse (DPP) and alternating current (ACt) polarography. The drug manifests a cathodic wave in 20% v/v formic acid solution. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The diffusion current-concentration relationship was found to be rectilinear over the range 3.2-14.4 microg/ml and 0.1 to 12.8 microg/ml, using DCt and DPP modes, respectively, with minimum detectability of 0.161 microg/ml (5.14 x 10(-7) M) and 0.0.057 microg/ml (1.82 x 10(-8) M) using DCt and DPP modes, respectively. Furthermore, the proposed method was applied to the in-vitro determination of flubendazole in spiked human urine and plasma adopting the DPP technique. The percentage recoveries were 100.20+/-0.62 and 97.42+/-0.95, respectively.

Adsorption↗

PubMed1984

Structural influences on the amperometric detection of opiates in high-performance liquid chromatography.

The oxidation reactions of a series of opiates occurring at a glassy-carbon electrode in amperometric high-performance liquid chromatographic detection has been investigated. A structure-reactivity correlation has been drawn for morphone, morphinan and benzomorphan derivatives. Polarography and hydrodynamic voltammography were used to show the importance of phenolic groups to this reaction. Acyl substitution on the phenol did not prevent amperometric detection.

Chemical Phenomena↗

PubMed2001

Resolution by polarographic techniques of the ternary mixture of captan, captafol and folpet by using PLS calibration and artificial neuronal networks.

The simultaneous polarographic determination of the ternary mixture of captan-captafol and folpet is studied. The polarographic signals of these compounds in their mixture show a high overlapping. For this reason different chemometric methods such as PLS, PCR and artificial neuronal network (ANN) have been utilized for the simultaneous determination of these compounds in mixtures. The calibration model is built from solutions containing river water of known pesticide concentrations and the signals obtained by Sampled DC and DPP (differential pulse polarography) have been used. The analysis of both synthetic and real samples (river water) has been carried out by PLS with satisfactory results in most cases. It is possible to determine 0.25 ppm of each pesticide in river water samples after a preconcentration step by extraction into diethyl ether. ANN has also been applied to improve the results obtained by the PLS tool when the sampled DC current is recorded or when liquid-solid extraction with C18 cartridges is performed.

Calibration↗