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PubMed2003

Colorimetric determination of gabapentin in pharmaceutical formulation.

Three accurate, simple and precise colorimetric methods for the determination of gabapentin in capsules are developed. The first method is based on the reaction of gabapentin with vanillin (Duquenois reagent) in the presence of McIlvain buffer pH 7.5 and the color developed was measured at 376 nm. The linearity range was found to be 80-360 microg ml(-1). The second is based on the reaction of the primary amino group of gabapentin with ninhydrin reagent in N,N'-dimethylformamide (DMF) medium producing a colored product which absorbs maximally at 569 nm. Beer's law is obeyed in the concentration range 40-280 microg ml(-1) of gabapentin. The third method is based on the reaction of gabapentin with p-benzoquinone (PBQ) to form a colored product with lambda(max) at 369 nm. The products of the reaction were stable for 2 h at 30 degrees C, shifts of the wavelength of maximum absorbance were not observed for up to 24 h after starting the reaction. The absorbance is proportional to gabapentin concentration in the range 80-320 microg ml(-1). The optimum experimental parameters for the reactions have been studied. The validity of the described procedures was assessed. Statistical analysis of the results has been carried out revealing high accuracy and good precision. The suggested procedures could be used for the determination of gabapentin in capsules. The procedures were rapid, simple and suitable for quality control application.

Acetates↗

PubMed2003

Validated spectrophotometric methods for the determination of amlodipine besylate in drug formulations using 2,3-dichloro 5,6-dicyano 1,4-benzoquinone and ascorbic acid.

Two simple and sensitive spectrophotometric methods have been proposed for the determination of amlodipine besylate either in pure form or in pharmaceutical formulations. The first method is based on the charge transfer complexation reaction of the drug with 2,3-dichloro 5,6-dicyano 1,4-benzoquinone (DDQ) to give coloured product having maximum absorbance at 580 nm. The second procedure depends on the measurement of purple red colour produced by the interaction of drug with ascorbic acid in N,N-dimethylformamide medium (DMF) which absorbed maximally at 530 nm. Under the optimized experimental conditions, Beer's law was obeyed in the concentration ranges of 1-125 and 10-140 microg ml(-1) with DDQ and ascorbic acid, respectively. Both the methods were applied successfully for the analysis of amlodipine besylate in dosage forms. Results of analyses were validated statistically and through recovery studies.

Amlodipine↗

PubMed1997

Determination of glafenine in dosage forms and serum by thin layer densitometry and high performance liquid chromatography.

New thin layer densitometry and high performance liquid chromatography (HPLC) methods are described for quantitative determination of glafenine in dosage forms in the presence of its photo-degradation products and in serum in the presence of its metabolites. Mobile phases consisting of toluene-isopropyl alcohol-dimethylformamide-water (18:3:1:0.5) and methanol-water-phosphoric acid (80:120:0.5) are found to be efficient for reasonable separation and adequate resolution of glafenine from associated substances by thin layer chromatography (TLC) and HPLC techniques, respectively. The methods are used for the study of glafenine purity, stability, bioavailability, bioequivalence and tablet dissolution rate. The results obtained by TLC and HPLC techniques are in good agreement and offer the advantages of reproducibility and accuracy.

Analgesics, Non-Narcotic↗

PubMed1998

A high-performance liquid-chromatographic assay for amphotericin B in a hydrophilic colloidal paste base.

A stability-indicating high-performance liquid-chromatographic (HPLC) assay has been developed for amphotericin B (AmB) in a paste, containing AmB, tobramycin (or gentamicin) sulphate, colistin sulphate, liquid paraffin and Orabase. Extraction of AmB was performed by partitioning the antibiotic between N,N-dimethylformamide (DMF) and cyclohexane, which led to precipitation of the polymeric materials and extraction of the liquid paraffin into the cyclohexane and AmB into the DMF. Analysis by HPLC of the latter layer gave a linear relationship between concentration and peak area response for the AmB over the range 5.0 x 10(-4) to 7.5 x 10(-3)% (w/v) (r = 0.9995) with a relative standard deviation of +/- 1.46% (n = 8). The efficiency of extraction was 1006 +/- 2.4% (n = 5).

Amphotericin B↗

PubMed1999

PH-metric log P 11. pKa determination of water-insoluble drugs in organic solvent-water mixtures.

The apparent acid dissociation constants (p(s)Ka) of two water-insoluble drugs, ibuprofen and quinine, were determined pH-metrically in acetonitrile water, dimethylformamide water, dimethylsulfoxide water, 1,4-dioxane-water, ethanol water, ethylene glycol-water, methanol water and tetrahydrofuran water mixtures. A glass electrode calibration procedure based on a four-parameter equation (pH = alpha + SpcH + jH[H+]+jOH[OH-]) was used to obtain pH readings based on the concentration scale (pcH). We have called this four-parameter method the Four-Plus technique. The Yasuda Shedlovsky extrapolation (p(s)Ka + log [H2O] = A/epsilon + B) was used to derive acid dissociation constants in aqueous solution (pKa). It has been demonstrated that the pKa values extrapolated from such solvent water mixtures are consistent with each other and with previously reported measurements. The suggested method has also been applied with success to determine the pKa values of two pyridine derivatives of pharmaceutical interest.

Analgesics, Non-Narcotic↗

PubMedDate not supplied

Prioritization of NTP reproductive toxicants for field studies.

Population studies that evaluate human reproductive impairment are time consuming, expensive, logistically difficult, and with limited resources must be prioritized to effectively prevent the adverse health effects in humans. Interactions among health scientists, unions, and industry can serve to identify populations exposed to potential hazards and develop strategies to evaluate and apply appropriate controls. This report describes a systematic method for prioritizing chemicals that may need human reproductive health field studies. Rodent reproductive toxicants identified from the National Toxicology Program (NTP) Reproductive Assessment by Continuous Breeding (RACB) protocol were prioritized on the basis of potency of toxic effect and population at risk. This model for prioritization links NTP findings with data from the National Occupational Exposure Survey (NOES) and the Hazardous Substance Data Base (HSDB) or the High Production Volume Chemical Database (HPVC) to prioritize chemicals for their potential impact on worker populations. The chemicals with the highest priority for field study were: dibutyl phthalate, boric acid, tricresyl phosphate, and N, N-dimethylformamide.

Animals↗

PubMed1990

A highly specific and quantitative method for determining type III/I collagen ratios in tissues.

The distribution of type I and type III collagens in rat, bovine and human skin were examined by a quantitative 2-D CNBr peptide mapping method. The procedure involved the solubilization of tissues by digestion with CNBr, radioactive labeling in vitro by [3H]-NaBH4 in dimethylformamide, reduction by mercaptoethanol, a second CNBr digestion and 2-D (isoelectric focusing and NaDodSO4 electrophoresis) mapping. The amounts of type I and type III collagen peptide spots in the fluorographs of 2-D maps were analyzed by 2-D scanning densitometer/analyzer. Mixtures containing various ratios of purified type I and type III collagen were used to obtain a standard curve. Using this procedure we were able to determine that in adult human skin (age range 35-65 years) 22% (+1.3%) of the labelled collagen is type III. This value is significantly higher than that was previously estimated by less accurate methods.

Adult↗

PubMed1990

Alteration of collagen composition and cross-linking in keloid tissues.

Collagen composition and cross-linking in human keloid and normal skin tissues were analyzed biochemically. CNBr peptides were separated by 2-dimensional (2-D) mapping and high performance liquid chromatography (HPLC). The amounts of type I and type III collagen was quantified by 2-D scanning densitometry of fluorographs of 2-D maps derived from samples radioactively labelled in vitro by [3H]-NaBH4 in dimethylformamide. Keloid tissues contained 31.6 +/- 2.2 percent type III collagen as compared to 21.4 +/- 2.7 percent type III present in normal human skin dermis. HPLC profiles of CNBr peptides showed that approximately 5 percent of the high molecular weight material in keloids is mercaptoethanol reducible, compared to insignificant amounts in normal skin. 2-D maps derived from CNBr peptides of keloid collagen demonstrated thiol reduction sensitive alpha 1(III)-CB9 dimer as well as 24,000- and 32,000-dalton CNBr peptides, which were not mercaptoethanol reduction sensitive in normal skin due to cross-linking via the lysyl oxidase pathway. Also, a group of 20,000- to 25,000-dalton CNBr peptides, in the alpha 1(I)-CB6 cross-linking region were prominent in keloid tissues.

Adult↗

PubMed1998

Synthesis of 3-substituted benzamides and 5-substituted isoquinolin-1(2H)-ones and preliminary evaluation as inhibitors of poly(ADP-ribose)polymerase (PARP).

Inhibitors of poly(ADP-ribose)polymerase (PARP) inhibit repair of damaged DNA and thus potentiate radiotherapy and chemotherapy of cancer. 3-Substituted benzamides and 5-substituted isoquinolin-1-ones have been synthesised and evaluated for inhibition of PARP. Reduction of 3-(bromoacetyl)benzamide, followed by treatment with base, gave RS-3-oxiranylbenzamide. Reduction of 3-(hydroxyacetyl)benzonitrile with bakers' yeast gave the R-diol which was converted to R-3-(1,2-dihydroxyethyl)benzamide. Similar reduction of 3-(acetoxyacetyl)benzonitrile led towards the S-diol which was converted to its cyclic acetonide. E-2-(2,6-Dicyanophenyl)-N,N-dimethylethenamine was formed by condensation of 2,6-dicyanotoluene with dimethylformamide dimethyl acetal (DMFDMA); cyclisation under acidic conditions afforded 5-cyanoisoquinolin-1-one. Heck coupling of 5-iodoisoquinolin-1-one with propenoic acid formed E-3-(1-oxoisoquinolin-5-yl)propenoic acid. 3-Oxiranylbenzamide, 5-bromoisoquinolin-1-one and 5-iodoisoquinolin-1-one were among the most potent inhibitors of PARP activity in a preliminary screen in vitro.

Animals↗

PubMed2001

Gas-phase SN2 reactivity of dicoordinated borinium cations using pentaquadrupole mass spectrometry.

We report gas phase ion/molecule reactions between dialkoxyborinium cations (RO-B+-OR) and small organic amides, such as N,N-dimethylformamide and N,N-diethylpropionamide. Besides direct addition at boron, the results show efficient SN2 methyl transfer from the borinium ion to the amide. Isotopic labeling and collision-induced dissociation (CID) of the methyl transfer products demonstrate O-methylation of the amide. Methyl substitution at the alpha-carbon of the amide affects the degree of alkylation and adduct formation. Direct proton abstraction via beta-elimination is a major competitive reaction for substituents other than methyl. Ab initio calculations at the B3LYP/6-31G(d) level indicate that SN2 transmethylation is highly exothermic with O-methylation favored over N-methylation by 14.8 kcal/mol.

Journal Article↗

PubMed2002

Proton bound homodimers and heterodimers of amides and amines in the gas phase. Equilibrium studies by Fourier transform ion cyclotron resonance spectrometry.

By injection of the proton bound homodimer [DMF.H+.DMF] of N,N-dimethylformamide (DMF) generated in an external ion source into a mixture of DMF and a second base within the cell of a Fourier transform ion cyclotron resonance (FT-ICR) spectrometer the equilibria between [DMF.H+.DMF] and the other possible proton bound dimers [DMF.H+.base] and [base.H+.base] have been studied for 13 different bases. Strongly polar bases like aliphatic amides and dimethyl sulfoxide (DMSO) exchange both DMF in [DMF.H+.DMF] by a two step process, while the almost non-polar amines exchange only one DMF. If the base is a primary or secondary amine, the proton bound heterodimer [DMF.H+.amine] reacts further by the addition of one DMF to create a proton bound trimer [(DMF)2.H+.amine]. The affinity deltaG(DMFH+) of the bases towards protonated DMF relative to neutral DMF depends linearly on the difference deltaGB of the gas phase basicity of DMF and the other base, but different correlation lines are obtained for polar and non-polar ligands (deltaGDMFH+ = 0.44GB(base)-375 [kJ/mol] (r = 0.97) and deltaGDMFH+ = 0.46GB(base)-397 [kJ/mol] (r = 0.99), respectively). This different behavior is explained by a different character of the proton bridge in the heterodimers containing only polar ligands and those incorporating a non-polar ligand besides DMF. The former dimers contain a more or less symmetric proton bridge while the latter can be viewed as a protonated base solvated by DMF. The available data have been used to calculate the molecular pair gas phase basicity of DMF and the 13 bases used and to estimate the dissociation energies of the bonds of the proton bridge in various proton bound heterodimers.

Algorithms↗

PubMed1997

Conformational transitions provoked by organic solvents in beta-lactoglobulin: can a molten globule like intermediate be induced by the decrease in dielectric constant?

BACKGROUND: It is known that nonnative states of protein molecules can exist in living cells and can be involved in a number of physiological processes. It has also been established that the membrane surface can be responsible for the partial denaturation of proteins due to negative charges on it. The local decrease in the effective dielectric constant of water near the organic surface has been suggested to be an additional driving force for protein denaturation in the membrane field, but data to confirm this suggestion were lacking. RESULTS: Conformational transitions induced in beta-lactoglobulin by methanol, ethanol, isopropanol, dimethylformamide and dioxane were studied by near and far UV circular dichroism, steady-state tryptophan fluorescence and fluorescence decay of 8-anilinonaphthalene-1-sulfonate (8-ANS). The existence of at least two noncoinciding cooperative transitions has been established in all solvent systems studied. The first of these transitions describes the disruption of rigid tertiary structure in protein molecules, while the second reflects the formation of an expanded helical conformation typical of proteins in concentrated organic solvents. This means that the organic solvents provoke the formation of a denatured intermediate state with pronounced secondary structure and native-like compactness. We show that the positions of maxima in fI versus dielectric constant dependence virtually coincide for all five solvent systems studied. CONCLUSIONS: The decrease in the dielectric constant of the solvent induces in beta-lactoglobulin an equilibrium intermediate state. This state, being denatured, is relatively compact and has pronounced secondary structure and high affinity for the hydrophobic fluorescent probe 8-ANS, i.e. possesses all the properties of the molten globule intermediate state.

Anilino Naphthalenesulfonates↗

PubMed2000

The synthetic rate of dipeptide catalyzed by organic solvent-stable protease from Pseudomonas aeruginosa PST-01 in the presence of water-soluble organic solvents.

The initial synthetic rates of peptide Cbz-Arg-Leu-NH(2) from Cbz-Arg and Leu-NH(2) using PST-01 protease in the presence and absence of organic solvents were investigated under various conditions. The synthetic rates of Cbz-Arg-Leu-NH(2) in the presence of 50% (v/v) methanol, 50% (v/v) N,N-dimethylformamide (DMF) and 60% (v/v) dimethyl sulfoxide (DMSO) were 1.6-, 2.4-, and 5.1-times higher than that in the absence of organic solvent, respectively. The PST-01 protease was not only stable in the presence of organic solvents but also exhibited high reaction rates in the presence of methanol, DMF, and DMSO. When the Cbz-Arg concentration was lower than 60mM or the Leu-NH(2) concentration was lower than 400mM, the initial rates increased lineally with increase in their concentrations. However, the rates did not increase when the Leu-NH(2) concentration was more than 500mM. The optimum temperature and pH of the reaction were 40 degrees C and 7.0, respectively.

Journal Article↗

PubMed2002

Chemical models for cytochrome P450 as a biomimetic metabolic activation system in mutation assays.

DNA damage is a critical factor in carcinogenesis. The Ames assay is a short-term test that screens for DNA-damaging agents. To be detected in the assay, most carcinogens require oxidation by cytochrome P450, a component of the liver homogenate preparation (S9 mix) that is traditionally used to metabolize promutagens to an active form in vitro. A combination of iron(III) porphyrin plus an oxidant activates many promutagens by mimicking cytochrome P450 metabolism. We previously reported that the mutagenicity of the N-nitrosodialkylamines was detected following reaction with tetrakis(pentafluorophenyl)porphyrinatoiron(III) chloride (Fe(F(5)P)Cl) plus tert-butyl hydroperoxide (t-BuOOH), which yielded the same alcohols and aldehydes as the enzymatic reaction. In the present study, to extend the scope of biomimetic models, we tested the mutagenicity of other carcinogens exposed to chemical oxidation systems.We investigated the optimal assay conditions for the models in Salmonella typhimurium TA1538, a strain sensitive to frame-shift mutagens. We activated 2-aminofluorene (AF), benzo[a]pyrene (B[a]P), a tryptophane pyrolysate 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), and 2-acetylaminofluorene (AAF) with Fe(F(5)P)Cl plus an oxidant-t-BuOOH, m-chloroperoxybenzoic acid (mCPBA), or magnesium monoperoxyphthalate (MPPT)-and we noted the effect of three solvents-acetonitrile (CH(3)CN),1,4-dioxane, and N,N-dimethylformamide (DMF)-on AF activation. All the promutagens became mutagenic in the presence of Fe(F(5)P)Cl plus an oxidant, with the effectiveness of the oxidant varying with the chemical. Aromatic amines, for example, showed the strongest mutagenicity with t-BuOOH whereas polycyclic hydrocarbons showed the strongest mutagenicity with mCPBA. All the promutagens were mutagenic in the presence of Fe(F(5)P)Cl plus MPPT. For AF activation, the order of effectiveness of the solvents was CH(3)CN>1,4-dioxane>DMF. The results suggested that these systems would serve as useful models for microsomal activating systems.

2-Acetylaminofluorene↗

PubMed1999

The frequency of induced premature centromere division in human populations occupationally exposed to genotoxic chemicals.

Premature (early) centromere division (PCD, i.e., the separation of centromeres during the prometaphase/metaphase of the mitotic cycle) seems to be a possible manifestation of chromosome instability in human chromosome-breakage syndromes. Chromosome instability also frequently occurs in the peripheral blood lymphocytes (PBL) of humans occupationally exposed to clastogenic agents, and is considered an etiologic factor of neoplastic diseases. In order to investigate the importance of PCD in cancer risk assessment, we studied the frequency of PCDs in PBL of 400 Hungarian subjects. The various groups comprised 188 control donors and 212 subjects occupationally exposed to different genotoxic chemicals, such as acrylonitrile (ACN) and/or dimethylformamide (DMF), benzene, cytostatic drugs, ethylene oxide (ETO), mixed exposure in the rubber industry, mixed organic solvents including CCl4, hot oil-mist, bitumen, and polychlorinated biphenyls (PCB). Data were compared with chromosomal aberration frequencies determined in the same samples. PCD yields are significantly higher in populations exposed to mixed chemicals, crude oil and cytostatic drugs, compared with controls. PCDs involving more than three chromosomes are also more frequent in ETO- and oil mist-exposed groups than in the others. The results indicate that the induction of PCDs is neither incidental nor artificial. As a consequence, we suggest that PCD can be developed into a new, exposure-related cytogenetic biomarker for a more adequate occupational cancer risk assessment. A further, follow-up epidemiological and cytogenetic investigation of PCD is in progress.

Adult↗

PubMed2002

Simple and selective spectrophotometric determination of ruthenium after solid phase extraction with some quinoxaline dyes into microcrystalline p-dichlorobenzene.

A simple selective and highly sensitive extraction method has been developed for the determination of ruthenium spectrophotometrically after extraction of its 2,3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline (I), 2,3-dichloro-6-(2-hydroxy-3,5-dinitrophenylazo)quinoxaline (II) and 2,3-dichloro-6-(2,7-dihydroxy-naphthylazo)quinoxaline (III) complexes into microcrystalline p-dichlorobenzene. The optimization of experimental conditions for the procedure is studied. The solid p-dichlorobenzene containing the ruthenium-reagent (I-III) complexes is separated by filtration and dissolved in N,N-dimethylformamide. The absorbance is measured at lambda(max) 622, 518 and 542 nm against reagents I, II and III, respectively, as blank. Beer's law is obeyed upto 2.5 microg ml(-1) of ruthenium. The molar absorptivity, Sandell sensitivity, detection and quantification limits are calculated, when compared with those parameters without using solid phase extraction method. The interference of various ions has been studied in detail and the statistical evaluation of the experimental results is reported. The proposed methods have been successfully applied for the determination of trace amount of ruthenium in seawater, ore and metallurgy products.

Chlorobenzenes↗

PubMed2003

Spectral studies of safranin-O in different surfactant solutions.

The interaction of Safranin-O (SO), a cationic dye, with various surfactants viz., anionics; Sodiumdodecylsulfate (SDS) and Sodiumdodecylsulfonate (SDSo), nonionics; polyoxyethylenesorbitanmonolaurate (Tween 20) and polyoxyethylenedodecylether (Brij 35), cationic; Dodecyltrimethylammoniumbromide (DTAB) and zwitterionic; Laurylsulfobetaine (LSB) was studied spectrophotometrically as a function of surfactant concentration ranging from premicellar to postmicellar region in aqueous media in the absence and presence of cosolvents. The binding constants (K(b)) and fraction of bound SO to micelles (f), were calculated by means of Benesi-Hildebrand Equation. The binding tendency of SO to micelles followed the order as; Tween 20>Brij 35>SDS>SDSo>LSB. The presence of cosolvents, such as Methanol, Dimethylformamide (DMFA) and 1,4 Dioxan (DX) at various volume percentages, increased the CMC of both SDS and Tween 20 and at a certain concentration totally inhibited the micellization. The binding of SO to micelles decreased as the concentration of the cosolvents increased. This inhibitory effect of cosolvents on binding of SO to micelles followed the order as; Methanol>DMFA>DX.

Cations↗

PubMed1995

Application of capillary electrophoresis with laser-induced fluorescence detection for routine determination of methylmalonic acid in human serum.

Methylmalonic acid (MMA) in serum is an established marker of cobalamin deficiency. MMA and other short-chain dicarboxylic acids react with 1-pyrenyldiazomethane to form stable, highly fluorescent 1-pyrenylmethyl monoesters. We have analyzed these esters in human blood by capillary electrophoresis (CE) combined with laser-induced fluorescence detection, and here we describe our approach to achieve long-term reproducibility, which is a prerequisite for routine clinical application. To stabilize CE performance and to minimize solute adsorption to the capillary wall, we coated capillaries with linear polyacrylamide, used hydroxypropyl methylcellulose and dimethylformamide as buffer additives, and extensively diluted derivatized samples prior to injection. A discontinuous buffer system was used for sample stacking. Separation was performed in Tris-citrate buffer, pH 6.4, under reversed polarity conditions (negative potential at the inlet vial). The assay was linear for serum MMA concentrations in the range 0.1-200 mumol/L, the total run time was 26 min, the sample output was about 50 samples/24 h, and the coefficients of variation ranged between 3 and 12%, depending on the MMA concentration. Comparison of our assay with two established GC/MS methods demonstrated good correlation and measuring agreement.

Electrophoresis↗