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At least 199 records · Page 11Linked to original sources
PubMed1983

Effects of thyrotropin, acetazolamide, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, perchlorate, ouabain and furosemide on pH and HCO3- concentrations in cells and luminal fluid of turtle thyroid as calculated from the distribution of [14C]dimethyloxazolidine-2,4-dione.

[14C]Dimethyloxazolidine-2,4-dione was used to determine the pH and bicarbonate concentration ([HCO3-]) in follicular cells and luminal fluid (LF) of turtle thyroids. Values of cellular and luminal pH and [HCO3-] were derived from the steady-state [14C]dimethyloxazolidine-2,4-dione values in whole gland and in the follicular LF sampled by micropipettes inserted into the follicular lumen and by resolution of the [14C]dimethyloxazolidine-2,4-dione uptake curve into its components by a computer program. In extracellular fluid of control turtles at 24 degrees C, the pH was 7.66, [HCO3-] was 33.1 mmol/l and pCO2 was 33.6 mm Hg. In thyroidal follicular cells, pH was 7.26 and [HCO3-] was 14.3 mmol/l; and in LF, pH was 7.32 and [HCO3-] was 16.5 mmol/l. These data provide evidence that H+ and HCO3- do not distribute according to their electrochemical gradients across both the basal and apical membranes of thyroid. Thyrotropin increased cell pH to 7.70 and [HCO3-] to 39.8 mmol/l; luminal pH and [HCO3-] were also markedly increased. Acetazolamide reduced [HCO3-] in both cells and LF. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid increased cellular pH and [HCO3-] but did not alter these parameters in LF. Both ouabain and furosemide increased cellular pH and [HCO3-] and decreased luminal pH and [HCO3-]. Methimazole increased cellular pH and [HCO3-], decreased LF [HCO3-] and did not affect the LF pH.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1986

Seasonal variations in the stability of monoamines and their metabolites in perchloric acid as measured by high-performance liquid chromatography.

The stability in acid medium of dopamine, dihydroxyphenylacetic acid (DO-PAC), homovanillic acid (HVA), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) was investigated. The stability of 5-HT and 5-HIAA was poor, but could greatly be improved by the addition of sodium bisulphite and disodium edetate. Under these conditions, dopamine, DOPAC, HVA, 5-HT and 5-HIAA showed good stability over 24 h at room temperature throughout the year when stored in capped vials. In uncapped vials, the stability of 5-HT and 5-HIAA was reasonable during the winter months, but was poor during the summer months.

Biogenic Amines↗
PubMed1990

On the mechanism of hydrogen peroxide formation during precipitation of hemoglobin with perchloric acid.

During acid precipitation of hemoglobin, hydrogen peroxide is formed. The oxidant is generated from hemoglobin-bound as well as from physically dissolved oxygen, provided divalent hemoglobin-iron is present. The extent of hydrogen peroxide formation seems to be dependent on the precipitating reagent. From experiments on GSH oxidation during precipitation of red cells and from a literature survey formation of at least one second reactive oxygen species has to be assumed. Different reaction pathways for generating these oxidants during acid precipitation are discussed: Hydroperoxide which is probably liberated by proton catalysis may contribute to the observed oxidation reactions. At pH approximately 1 it rapidly disproportionates yielding oxygen and hydrogen peroxide, which might produce reactive oxidants with hemoglobin intermediates formed during precipitation. In addition a new hypothesis is presented explaining the ability of N-ethylmaleimide to inhibit GSH oxidation during precipitation of red cells. Accordingly, the SH-reagent rapidly penetrates the cell membrane and reacts with GSH before access of protons prevents alkylation.

Chemical Precipitation↗
PubMed1998

Pattern recognition analysis of 1H NMR spectra from perchloric acid extracts of human brain tumor biopsies.

Pattern recognition techniques (factor analysis and neural networks) were used to investigate and classify human brain tumors based on the 1H NMR spectra of chemically extracted biopsies (n = 118). After removing information from lactate (because of variable ischemia times), unsupervised learning suggested that the spectra separated naturally into two groups: meningiomas and other tumors. Principal component analysis reduced the dimensionality of the data. A back-propagation neural network using the first 30 principal components gave 85% correct classification of meningiomas and nonmeningiomas. Simplification by vector rotation gave vectors that could be assigned to various metabolites, making it possible to use or to reject their information for neural network classification. Using scores calculated from the four rotated vectors due to creatine and glutamine gave the best classification into meningiomas and nonmeningiomas (89% correct). Classification of gliomas (n = 47) gave 62% correct within one grade. Only inositol showed a significant correlation with glioma grade.

Biomarkers, Tumor↗
PubMed1996

Quantitative and qualitative characterization of 1H NMR spectra of colon tumors, normal mucosa and their perchloric acid extracts: decreased levels of myo-inositol in tumours can be detected in intact biopsies.

Sixteen colonic tumours and 10 normal mucosa biopsies have been examined by 1H NMR spectroscopy at 9.4 T. A complete characterization and quantification of the aliphatic region of PCA extract spectra and the analysis of the two-dimensional COSY spectra of five pairs of intact biopsies (tumor and control mucosa) has been carried out. The analysis of the PCA extracts demonstrated a significant increase in the concentration of the endogenous compounds: lactate, glutamate, aspartate, taurine, spermine, glutathione and glycerophosphoethanolamine, and a significant decrease of myo- and scyllo-inositol, in tumours with respect to mucosae. Among these metabolites, the high myo-inositol and taurine levels and the reciprocal changes found between them in tumours and mucosae make their resonances interesting as possible malignancy markers if they are detectable in vivo. In contrast to the easy observation of taurine in one-dimensional spectra of intact biopsies, the difficulty of observing myo-inositol prompted us to use two-dimensional COSY spectra for the detection and quantification of both these metabolites. In the two-dimensional spectra, the use of a ratio between the cross-peak volumes of both metabolites permits an excellent differentiation between tumours and normal mucosa and suggests its potential to detect malignant changes in the healthy tissue, provided a two-dimensional approach is used.

Biopsy↗
PubMed2005

Ground and excited states proton transfer reactions of 1,8-diaminonaphthalene in perchloric acid solutions.

The proton-transfer reaction of 1,8-diaminonaphthalene (1,8-DAN) in acidic medium was studied by means of fluorescence and picosecond spectroscopic techniques. It has been found that there are three different forms of 1,8-DAN in the ground state, but only two different forms in the excited state. The absorption of the mono-cation form of 1,8-DAN is found to be a mixture of the neutral form and the di-cation form. However, the emission is found to be the same as the neutral form, due to the fast dissociation of the mono-cation form once it is excited. The fluorescence of the mono-cation form of 1,8-DAN shows a small shift under different excitation wavelengths. The di-cation form only fluoresces if no free water cluster is available as a proton acceptor. The reaction in the excited state is shown to be a diabatic quenching reaction. With the help of quantum yields and fluorescence lifetime measurements these results are interpreted in terms of a new photochemical scheme. All dissociation and quenching rate constants, pKa and kq, have been determined.

Journal Article↗
PubMed2002

Acid washing and stabilization of an artificial arsenic-contaminated soil.

An acid-washing process was studied on a laboratory scale to extract the bulk of arsenic(V) from a highly contaminated Kuroboku soil (Andosol) so as to minimize the risk of arsenic to human health and the environment. The sorption and desorption behavior of arsenic in the soil suggested the possibility of arsenic leaching under acidic conditions. Artificially contaminated Kuroboku soil (2830 mg As/kg soil) was washed with different concentrations of hydrogen fluoride, phosphoric acid, sulfuric acid, hydrogen chloride, nitric acid, perchloric acid, hydrogen bromide, acetic acid, hydrogen peroxide, 3:1 hydrogen chloride-nitric acid, or 2:1 nitric acid-perchloric acid. Phosphoric acid proved to be most promising as an extractant, attaining 99.9% arsenic extraction at 9.4% acid concentration in 6 h. Sulfuric acid also attained high percentage extraction. The arsenic extraction by these acids reached equilibrium within 2 h. Elovich-type equation best described most of the kinetic data for dissolution of soil components as well as for extraction of arsenic. Dissolution of the soil components could be minimized by ceasing acid washing in 2 h. The acid-washed soil was further stabilized by the addition of lanthanum, cerium, and iron(III) salts or their oxides or hydroxides which form insoluble complex with arsenic. Both salts and oxides of lanthanum and cerium were effective in immobilizing arsenic in the soil attaining less than 0.01 mg/l As in the leaching test.

Acids↗
PubMed2004

Mechanism of four-electron reduction of dioxygen to water by ferrocene derivatives in the presence of perchloric acid in benzonitrile, catalyzed by cofacial dicobalt porphyrins.

The selective two-electron reduction of dioxygen occurs in the case of a monocobalt porphyrin [Co(OEP)], whereas the selective four-electron reduction of dioxygen occurs in the case of a cofacial dicobalt porphyrin [Co(2)(DPX)]. The other cofacial dicobalt porphyrins [Co(2)(DPA), Co(2)(DPB), and Co(2)(DPD)] also catalyze the two-electron reduction of dioxygen, but the four-electron reduction is not as efficient as in the case of Co(2)(DPX). The micro-superoxo species of cofacial dicobalt porphyrins were produced by the reactions of cofacial dicobalt(II) porphyrins with dioxygen in the presence of a bulky base and the subsequent one-electron oxidation of the resulting micro-peroxo species by iodine. The superhyperfine structure due to two equivalent cobalt nuclei was observed at room temperature in the ESR spectra of the micro-superoxo species. The superhyperfine coupling constant of the micro-superoxo species of Co(2)(DPX) is the largest among those of cofacial dicobalt porphyrins. This indicates that the efficient catalysis by Co(2)(DPX) for the four-electron reduction of dioxygen by Fe(C(5)H(4)Me)(2) results from the strong binding of the reduced oxygen with Co(2)(DPX) which has a subtle distance between two cobalt nuclei for the oxygen binding. Mechanisms of the catalytic two-electron and four-electron reduction of dioxygen by ferrocene derivatives will be discussed on the basis of detailed kinetics studies on the overall catalytic reactions as well as on each redox reaction in the catalytic cycle. The turnover-determining step in the Co(OEP)-catalyzed two-electron reduction of dioxygen is an electron transfer from ferrocene derivatives to Co(OEP)(+), whereas the turnover-determining step in the Co(2)(DPX)-catalyzed four-electron reduction of dioxygen changes from the electron transfer to the O-O bond cleavage of the peroxo species of Co(2)(DPX), depending on the electron donor ability of ferrocene derivatives.

Journal Article↗
PubMed1981

Sampling procedure and determination of lead in canned foods.

A method is presented for improving within-can homogeneity and simplifying the determination of lead in canned foods. The entire content of a canned food product is blended with 2N HNO3 and allowed to stand 16 h; then the sample is again blended and a subsample is taken. The subsample is digested by wet ashing using nitric acid-perchloric acid or nitric acid-sulfuric acid-hydrogen peroxide. The pH of the sample is adjusted with ammonium hydroxide, and the lead is extracted into butyl acetate as the pyrrolidinecarbodithioate complex. Lead concentration is determined by flame atomic absorption spectrometry. Recoveries of lead ranged from 92 to 104% for added 100-mesh lead particulate. Within-sample variability for green beans was reduced from 37% obtained with blending alone to 3.7% using the proposed procedure at the 3.1 micrograms/g added lead level. Variability was 7.6% at the 0.68 microgram/g level and 16.4% at the 0.20 microgram/g level of added lead. The use of nitric acid-sulfuric acid-hydrogen peroxide for digestion has the advantage of not forming a precipitate during the neutralization step, as occurs when nitric acid-perchloric acid is used for dissolution.

Food Contamination↗
PubMed1981

A specific method of high sensitivity for the determination of adenosine in the incubation medium of fat tissue.

A suitable method for the measurement of adenosine in the incubation medium of fat tissue (200-500 mg) has been developed. The method is based on the specificity of the adenosine deaminase reaction and on the high sensitivity of a fluorescent method for adenine derivatives. The decrease of fluorescence in a sample after treatment with this enzyme is used for measuring adenosine in the range of 50-500 pmoles/tube. This method is highly specific and is not affected by other adenine derivatives present in the sample. Instead of acetic acid, perchloric acid was used in the fluorescent reaction, thus increasing the amount of adenosine dependent fluorescence. With this modification of the original fluorescent method, perchloric acid extracts can be used without further processing after deproteinization of the samples. Using this method, we could measure the adenosine release of fat pads of Wistar rats incubated in Krebs-Ringer-albumin buffer without concentration or purification procedures.

Adenosine↗