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At least 631 records · Page 35Linked to original sources

PubMed1979

[Effect of tin on rats. 1. Inverse voltammetric determination of tin in the presence of lead in biological material after extraction].

By means of inverse polarography, the authors determined tin selectively after double extraction with diethylammonium diethyl dithiocarbamate (DADDTC) in perchloric solution. The recovery rates were: in potatoes, 91.7 +/- 5.8%; in beef kidney, 85.0 +/- 22.7%; in beef liver 79.9 +/- 13.8%; and in milk, 69.8 +/- 11.4%. Possible interferences from other elements with the tin determination are discussed.

Animals↗

PubMed2005

New method of dynamic color doppler signal quantification in metastatic lymph nodes compared to direct polarographic measurements of tissue oxygenation.

Tumor growth depends on sufficient blood and oxygen supply. Hypoxia stimulates neovascularization and is a known cause for radio- and chemoresistance. The objective of this study was to investigate the use of a novel ultrasound technique for the dynamic assessment of vascularization and oxygenation in metastatic lymph nodes. Twenty-four patients (age 44-78 years) with cervical lymph node metastases of squamous cell head and neck cancer were investigated by color duplex sonography and 17 (age 46-78 years) were investigated additionally with polarography. Sonography was performed after contrast enhancer infusion under defined conditions. Intranodal perfusion data (color hue, colored area) were measured automatically by a novel software technique. This allows an evaluation of blood flow dynamics by calculating perfusion intensity--velocity, perfused area, as well as the novel parameters tissue resistance index (TRI) and tissue pulsatility index (TPI)--for each point of a complete heart cycle. Tumor tissue pO(2) was measured by means of polarographic needle electrodes placed intranodally. The sonographic and polarographic data were correlated using Pearson's test. Sonography demonstrated a statistically significant inverse correlation between hypoxia and perfusion and significant TPI and TRI changes with different N-stages. The percentage of nodal fraction with less than 10 mmHg oxygen saturation was significantly inversely correlated with lymph node perfusion (r = -0.551; p = 0.021). Nodes with a perfusion of less than 0.05 cm/sec flow velocity showed significantly larger hypoxic areas (p = 0.006). Significant differences of TPI and TRI existed between nodes in stage N(1) and N(2)/N(3) (p = 0.028 and 0.048, respectively). This new method of dynamic signal quantification allows a noninvasive and quantitative assessment of tumor and metastatic lymph node perfusion by means of commonly available ultrasound equipment.

Adult↗

PubMed1984

In vivo metal-ion release from porous titanium-fiber material.

Dense and porous Ti, Ti-alloy, and stainless steel specimens were implanted in canine trabecular bone. After 6 and 12 months the specimens were retrieved together with bone tissue immediately adjacent. The trace metal content in the tissue samples was determined using neutron activation analysis, differential pulse polarography, graphite furnace atomic-absorption spectrophotometry, electron microprobe analysis, and laser microprobe analysis. The results are discussed in view of (i) the release of Ti ions, which is larger for porous than for bulk specimens, (ii) the various artifacts arising in electron microprobe (EMP) and laser microprobe mass analysis (LAMMA) determination of compositional gradients of trace metal-ion content in bone tissue, (iii) the absence of measurable quantities of V in bone tissue, and (iv) the difference in local tissue accumulation between Ti, released from Ti specimens, and Ni, released from stainless steel specimens.

Alloys↗

PubMed2003

Adsorptive stripping voltammetric determination of cefepime at the mercury electrode in human urine and cerebrospinal fluid, and differential pulse polarographic determination in serum.

The cephalosporin cefepime has been studied by adsorptive stripping voltammetric on the hanging mercury drop electrode, followed by linear sweep voltammetry (staircase). The adsorptive stripping response was evaluated with respect to preconcentration dependence and other variables. The drug is strongly adsorbed in acid media, with maximum adsorption at pH 5.8. The detection limit found was 4.8 x 10(-10) M, with 120-s preconcentration. The relative standard deviation at the 10(-7) M level was 0.93%. This method was applied to the determination of cefepime in human urine and cerebrospinal fluid. Differential pulse polarography has been applied to determination in human serum.

Anti-Bacterial Agents↗

PubMed2006

Acid decomposition of omeprazole in the absence of thiol: a differential pulse polarographic study at the static mercury drop electrode (SMDE).

The reactions of omeprazole, a potent proton pump inhibitor (PPI), were investigated in the absence of a nucleophile. Reactions were monitored, using differential pulse polarography (DPP) at the static mercury drop electrode (SMDE), in solutions buffered to pH values ranging from 2.0 to 8.0. The fast, sensitive, and selective electrochemical technique facilitated to repeat recordings of successive voltammograms [peak current (nA) vs. peak potential (volts vs. Ag/AgCl saturated with 3.0 M KCl)]. The DPP signals of omeprazole and its degradation products, believed to be due to sulfur functional group (the principal site of electrode reaction), gave advantages over the previously employed UV detection technique. The latter primarily relied on pyridine and benzimidazole analytical signals, which are common reaction products of PPI in aqueous acidic solutions. After peak identification, the resulting current (nA)-time (s) profiles, demonstrated that omeprazole undergoes degradation to form two main stable compounds, the first is the cyclic sulfenamide (D(+)), previously believed to be the active inhibitor of the H(+), K(+)-ATPase, the second is omeprazole dimer. This degradation is highly dependant on pH. Unlike previous studies which reported that the lifetime of D(+) is few seconds, the cyclic sulfenamide (D(+)) was found to be stable for up to 5-20 min. The results further indicated that omeprazole converts into the cyclic sulfenamide in an irreversible reaction, consequently, D(+) and sulfenic acid (an intermediate which rapidly converts into D(+)) were not interconvertable. The present work suggested that the sulfenic acid is the active inhibitor in vivo. In addition, the omeprazole reactions, in the absence of the thiol, were not as complicated as were previously reported.

Acids↗

PubMed2007

Reactions of sulfenic acid with 2-mercaptoethanol: a mechanism for the inhibition of gastric (H+-K+)-adenosine triphosphate by omeprazole.

The reactions of omeprazole, a potent proton pump inhibitor (PPI) were investigated in the presence of 2-mercapotoethanol. Reactions were monitored in solutions buffered to pH values ranging 2.0-8.0 using differential pulse polarography (DPP) at the static mercury drop electrode (SMDE). The fast, sensitive and selective electrochemical technique facilitated successive recordings of voltammograms (peak current (nA) vs. peak potential (volts vs. Ag/AgCl)) for all analytes in situe, including the 2-mercaptoethanol. In acidic solutions and in the presence of 2-mercaptoethanol, omeprazole undergoes degradation into three compounds, the first is a cyclic sulfenamide (D+), previously believed to be the active inhibitor of the H+, K+-ATPase, the second is the omeprazole dimer, and the third is the disulfide believed to be the product of reaction between 2-mercaptoethanol and D+. The cyclic sulfenamide (D+) solution was found to be stable in solutions containing 2-mercaptoethanol having pH values: 2.0, 4.0, and 6.0. This finding proved conclusively that the cyclic sulfenamide is not reactive toward the 2-mercaptoethanol. In contrast to previous reports, the conversion of the sulfenic acid intermediate into D+ was found to be irreversible. Due to this irreversibility, D+ and sulfenic acid were not rapidly interconvertable. The present work suggests that the active inhibitor is the sulfenic acid.

Anti-Ulcer Agents↗

PubMed1977

Electrochemical analysis of the cephalosporin cefamandole nafate.

The polarographic assays for cefamandole sodium and its formyl ester, cefamandole nafate, are described. Controlled potential coulometry is used as an absolute method for the assignment of purity of these compounds without the need for a reference material. The precision, accuracy, and selectivity of these assays were better than for the microbiological autoturbidimetric and automated iodometric assays. NMR, TLC, GC, and polarography are used to detect and quantitate likely impurities and degradation products.

Cephalosporins↗

PubMed1978

Effect of antineoplastic and cytotoxic Mannich Bases derived from conjugated styryl ketones on mitochondrial respiration in rat liver cells.

Five cytotoxic Mannich bases (5-dimethylamino-1-substituted phenyl-1-penten-3-ones), three having antineoplastic activity, were evaluated for respiratory-inhibiting properties in rat liver mitochondria in the presence of four substrates: succinate, glutamate, 3-hydroxybutyrate, and palmitylcarnitine. Four compounds (Ib--Ie) showed significant inhibiting properties which, on occasion, were reversed partially by coenzyme Q10. Evaluation of the spectra of the mitochondrial cytochromes indicated that Ib--Ie blocked the electron transport chain prior to the sequence of cytochromes. Since inhibition occurred when different substrates were used, a common site of action for Ib--Ie is likely; competition of Ib--Ie with coenzyme Q10 probably occurs. Compounds Ia--Ie inhibited RNA polymerase from Swiss mouse kidney cells but were virtually bereft of activity versus RNA polymerase from L-1210 leukemia cells. Polarography of the Mannich bases and the related styryl ketones showed that antineoplastic activity was associated with higher half-wave potentials.

Amines↗

PubMed1979

Differential pulse polarographic analysis of thyroid hormone: determination of iodine, thyroxine, and liothyronine.

A differential pulse polarographic method for the analysis of thyroid and thyroid tablets for total iodine, thyroxine, and liothyronine is described. The procedure for iodine, which is also applicable to individual tablet assay, consists of ashing the sample, coverting iodide to iodate, and analyzing by differential pulse polarography. The procedure for thyroxine and liothyronine involves hydrolysis of the sample with barium hydroxide and isolation and separation of the iodoamino acids using ion exchangers, followed by differential pulse polarographic determination in a supporting electrolyte composed of 0.5 N Na2CO3 in 20% 2-propanol containing 1% tetrabutylammonium bromide. The differential pulse polarographic results for iodine agree with values obtained using the USP XIX procedure, and the quantities of thyroxine and liothyronine found agree with literature values.

Iodine↗

PubMed1980

Polarographic determination of edetate disodium in eyewash and ophthalmic decongestant solutions.

The quantitative analysis of edetate disodium in nonprescription eyewash and ophthalmic solutions is described. The method involves differential pulse polarography using a dropping mercury electrode. A known concentration of cadmium or zinc is added to a buffer in a polarographic cell. The sample solution is incremented into the cell with a micropipet. The peak current decreases because the resulting chelate is not reducible at the potentials used. The quantity of edetate disodium in the sample then is determined graphically. Some contact lens cleaning and wetting solutions containing polymeric compounds are amenable to assay to edetate disodium if extraction, precipitation, centrifugation, or dilution steps minimize the maximum suppressor effect of the additives. These steps are very effective with cellulose ether compounds but are ineffective with polyvinyl alcohol.

Edetic Acid↗

PubMed1980

Differential pulse polarographic determination of colchicine.

A differential pulse polarographic method for the analysis of colchicine-containing dosage forms is described. The reduction of the tropolone carbonyl is useful for quantitative analysis in that the relationship of the colchicine concentration to the current is linear over the concentration range of 0 to approximately 50 micrograms/ml, with a slight negative deviation at higher concentration. The procedure involves no preliminary treatment, is simple and specific, and is applicable to the assay of composite tablets, individual tablets, and injectable solutions. Polarography is conduction on a solution of colchicine in pH 1.81 Britton-Robinson buffer with 0.01% alkylphenoxy polyethoxyethanol. The quantitative analysis is achieved using the method of standard addition. A relative standard deviation of 3.2% was obtained for tablets. The results agree with those obtained using the USP XIX method.

Colchicine↗

PubMed1989

Electrochemical behavior and polarographic determination of auronofin.

Auronofin in a 50% ethanol:water solution yields, on the dropping mercury electrode, a reduction wave whose E1/2 is a function of pH in the 2 less than pH less than 9 range (E1/2 = -0.036-0.054 pH), and acquires a constant value above pH 9 (E1/2 = -0.50 V, versus saturated calomel electrode). The influence of the variables which affect the reduction process of auronofin in tripotassium phosphate medium was studied. The electrochemical process is reversible and diffusion controlled. Coulometry showed that one electron is involved in the reduction of the drug. Analytical methods are proposed for the determination of auronofin at micromolar levels by DC and DP polarography, with relative standard deviations of 3.2 and 2.4%, respectively.

Auranofin↗

PubMed1994

Photodecomposition of a new 1,4-dihydropyridine: furnidipine.

The photodecomposition of new 1,4-dihydropyridine, furnidipine (CRE-319); [2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester) was studied by voltammetric, UV-vis spectrophotometric, and HPLC technique with three different light conditions (artificial daylight, UV light, and room daylight). The artificial daylight photodecomposition of furnidipine follows 0.5-order kinetics as assessed by the above-mentioned techniques. Furthermore, the daylight photoderivative was isolated and identified by NMR and IR as 2,6-dimethyl-4-(2-nitros-ophenyl)pyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester. Quantitative kinetic data for the UV photodecomposition of furnidipine cannot be obtained due to both the high rate of degradation (< 1 min) and intermediate reactions. However, polarographic, spectroscopic, and chromatographic evidence permits us to identify this photoproduct as 2,6-dimethyl-4-(2-nitrophenyl)pyridine-3,5-dicarboxylic acid 3-tetrahydrofurfuryl 5-methyl diester. Polarography was the most useful technique to assess the photodegradation of this drug from the qualitative point of view, and quantitative kinetic data were similar to those obtained by HPLC and UV-vis spectroscopy.

Calcium Channel Blockers↗

PubMed2000

A study on the reactions of plant copper amine oxidase with C3 and C4 aliphatic diamines.

The paper reports a study on the reactions of grass pea (Lathyrus sativus) amine oxidase (GPAO) with several aliphatic diamines. The influence of the chain length and of unsaturations in the molecules was examined. Kinetic measurements confirmed that trans-, i.e., (E)-2-butene-1,4-diamine (TDABE) and cis-, i.e., (Z)-2-butene-1,4-diamine (CDABE) could be classified as good substrates. Propane-1,3-diamine (DAP) and propene-1,3-diamine (DAPE) were only weakly oxidized, whereas 1,3-diamino-2-propanol (DAPL) was not utilized as a substrate. Contrary to the inactivator 2-butyne-1,4-diamine (DABI), DAPE was shown to be only a competitive inhibitor. DAP itself did not inhibit the catalytic activity. Irreversible inhibition of the activity occurred only after the incubation of GPAO with DABI; other diamines were without this effect. Differential pulse polarography and chromatofocusing confirmed that the aminoaldehyde product of DABI oxidation binds to the enzyme. Activity assay of pea aminoaldehyde dehydrogenase enabled us to detect the products of the oxidation of TDABE, CDABE, and DAP by GPAO. As the product of DAP oxidation, 3-amino-propanal (APAL) was detected by mass spectrometry and confirmed to be a potent noncompetitive inhibitor of GPAO. The absorption changes that occurred in the course of the reaction of GPAO with the diamines were investigated using rapid-scanning spectrophotometry. DABI, TDABE, CDABE, DAP, and DAPE reacted with GPAO providing characteristic maxima of the Cu(I)-semiquinolamine species that is formed in the catalytic cycle. The results presented here confirm that with the exception of DAPL, all the studied diamines could be classified as GPAO substrates, but only DABI can be considered as a mechanism-based inhibitor.

Aldehyde Dehydrogenase↗

PubMed1993

An examination of the reliability of the radiochemical assay for monoamine oxidases A and B.

The radiochemical assay for MAO A has been compared with the polarographic and alcohol dehydrogenase-coupled assays, using 5-hydroxytryptamine (5-HT) and tyramine and the homogeneous human liver enzyme expressed in yeast, and rat liver mitochondria. Despite efforts to measure true initial rates and to avoid known sources of error in the radiochemical procedure, significantly higher rates (Vmax) and lower Km values for the substrate were obtained with the polarographic than with the radiochemical method for 5-HT and tyramine, using either highly purified enzyme or mitochondria. The rate of tyramine oxidation measured by the polarographic method and the coupled assay agreed well, however. Consequently, for kinetic and inhibition studies we recommend the polarographic method for MAO A substrates. Comparison of the radiochemical, polarographic, spectrophotometric, and coupled assays for MAO B from beef liver (mitochondria and homogeneous enzyme) showed polarography to be the method of choice on all substrates tested, although, if all known sources of error are carefully controlled, the radiochemical assay gives the same Vmax and Km values. We also report that with each substrate studied the apparent Km is much lower when mitochondria are used than when the highly purified, virtually lipid-free preparations of MAO A are studied.

Animals↗

PubMed1993

New spectrophotometric assay for polyphenol oxidase activity.

We describe a convenient and sensitive assay of polyphenol oxidase (PPO, EC 1.14.18.1) consisting of spectrophotometry at 300 nm based on the stoichiometric reaction of cysteine with o-quinones produced during the enzymatic oxidation of phenols. The adduct formed exhibited spectral properties different from those of the parent phenol. PPO activities extracted from apple, pear, and mushroom were assayed. The assay cannot be used with hydroxycinnamoyl derivatives since the cysteinyl adduct compounds exhibited spectral properties similar to those of their parent phenolic substrates. However, the cysteine-coupled method presents several advantages over the measurement of oxygen uptake by polarography or the direct estimation of o-quinone by spectrophotometry. The duration of the linear period was increased, allowing a better estimation of its value. The zone of proportionality between rates and enzyme quantities was enlarged. The difference in molar extinction coefficients between adduct and phenol at 300 nm ranged between 2000 and 2800 M-1.cm-1, i.e., two times higher than those of the corresponding o-quinones. Therefore, this assay improves the sensitivity of polyphenol oxidase detection over that of the direct spectrophotometric assay of quinone formation.

Catechol Oxidase↗

PubMed1996

Application of multivariate curve resolution to voltammetric data. II. Study of metal-binding properties of the peptides.

The complexation of Cd2+ by glutathione (GSH), in 0.13 m borate buffer at pH 9.5, was studied by differential pulse polarography (DPP) and multivariate curve resolution. The Cd-GSH system has been chosen as a model to check the possibilities of this new polarographic approach to the study of metal ion complexation by peptides. Experimental data obtained by DPP for different Cd2+-to-GSH concentration ratios have been analyzed by a procedure which consists of using several chemometrical techniques based on factor analysis: principal component analysis, evolving factor analysis, and multivariate curve resolution with alternating least-squares (ALS) optimization. The use of different constraints during the ALS optimization process, such as nonnegativity and unimodality constraints, yields the optimal sought solution from a chemical point of view. In the present work, a new constraint has been implemented during ALS optimization to take into account the expected peak-shaped signal of DPP. This data treatment allows us to detect simultaneously the formation of 1:1 and 1:2 Cd:GSH complexes which were very difficult to detect by univariate analysis of DPP data. It is concluded that the described multivariate curve resolution method could be a reliable tool for studying metal-binding properties of peptides.

Cadmium↗

PubMed1998

Electrochemical immunoassay based on catalytic conversion of substrate by labeled metal ion and polarographic detection of the product generated.

In a new electrochemical immunoassay based on the conversion of a substrate catalyzed by a labeled metal ion and the polarographic detection of the product generated, metal copper ion was used to label model antigen human serum albumin through the bifunctional chelating agent diethylenetriaminepentaacetic acid. After heterogeneous competitive immunoreaction, the labeled copper ion was released or activated by acidification and chemically catalyzed the conversion of the substrate o-phenylenediamine to the electroactive product 2,3-diaminophenazine (DAP). The DAP was quantified using linear-potential scan polarography. The sensitivity of the proposed assay was 100 times higher than that of the previous methods based on direct detection of the metal ion labels. This immunoassay can be used to detect any protein of interest.

Catalysis↗