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At least 1,063 records · Page 59Linked to original sources
PubMed2003

[Preparation of chloro-sparfloxacin and its fluorescence behavior].

Sparfloxacin (SPFX) can be oxidized by nitrous acid then react with chlorohydric acid further to form a strong fluorescence substance in acid media. The molecular structure is identified by elemental analysis, IR, MS and fluorescence spectra. The emission properties of sparfloxacin and chloro-sparfloxacin are greatly distinct, the fluorescence of sparfloxacin is so weak that it can not be determined by means of fluorescence spectra, but the fluorescence intensity of the new substance is 110 fold more than that of sparfloxacin itself. With quinine sulfate (0.05 mol.L-1 of H2SO4, phi f = 0.55) as standard solution, the fluorescence quantum production rate of SPFX and this new fluorescence were determined as 0.0072 and 0.1539, respectively. By this, a new sensitive method for the determination of SPFX tablets by fluorescence spectroscopy is presented with good result. The recovery of method is 97.2%. RSD is 1.6%. Finally, the fluorescence self quenching and chloro-sparfloxacin enhancement mechanism of sparfloxacin are explored in detail.

Anti-Infective Agents↗
PubMed1976

[Ultrastructure of the particles reconstituted by complementation of extracts from chl-r mutants of Escherichia coli K 12].

By freeze-fracturing it is shown that the vesicles reconstituted by complementation of the chlA and chlB mutants of E. coli K 12 extracts are characterized by an asymmetric membrane bilayer. In a feature quite similar to the original intact plasma membranes, the membrane splits in two halves and the intramembranous particles are asymmetrically distributed on the two facture faces. It is proposed that the process of membrane reconstitution, which is also associated with the restoration of nitrate-reductase activity, relies on a sequence of increasing complexity of the molecular organisation.

Adenosine Triphosphatases↗
PubMed2006

[Influence of gastric juice pH on the metabolism of vitamin C in gastric mucosa and juice].

UNLABELLED: Vitamin C is present as ascorbic acid (Asc) with antioxidative properties and as its oxidation product dehydroascorbic acid (dAsc). Asc is actively transported from blood to gastric juice where it prevents formation of carcinogenic nitrosamines and protects mucosa from reactive oxygen species. Another important function of gastric mucosa is proton pump-dependent secretion of hydrochloric acid. The pump maintains high pH gradient between gastric juice and plasma. The aim of the work was to analyse relations between gastric juice pH and concentrations of Asc and dAsc in plasma, gastric mucosa and juice as well as other factors modifying metabolism of vitamin C and function of gastric mucosa. MATERIALS AND METHODS: 31 patients were subjected to diagnostic endoscopy due to dyspepsia. Concentrations of Asc and dAsc were measured in plasma, gastric mucosa and juice with HPLC method. pH of gastric juice was determined. Histopathology examination of mucosa and urease test for Helicobacter pylori were performed. Data concerning dyspeptic symptoms and used drugs, including vitamin C preparations, were collected. RESULTS: Patients taking vitamin C preparations had significantly lower gastric juice pH values than the others (median 2.2 vs 5.4; p < 0.01). Treatment with vitamin C preparations was also associated with higher Asc concentrations in gastric juice (median 16.6 vs. 1.8 micromol/L; p < 0.09); the difference was statistically significant in the subgroup of patients with gastritis (median 16.6 vs. 0.1 micromol/L; p < 0.04). Strong negative correlations of pH with Asc (Rs = -0.67; p < 0.001) and dAsc (Rs = -0.48; p < 0.01) concentrations were observed in gastric juice. Positive correlation of pH and relative dAsc content expressed as percent of total vitamin C concentration in gastric juice was also statistically significant (Rs = +0.48; p < 0.05). CONCLUSIONS: Performance of the proton pump and vitamin C metabolism in the stomach are closely mutually connected. Modification of hydrochloric acid secretion may affect gastric juice vitamin C concentration. Potentially disadvantageous influence of antisecretory drugs on the mechanisms of antioxidative protection in the stomach needs further investigation.

Ascorbic Acid↗
PubMed1990

[pH gradient support and antacid action of gastroesophageal coating agents. In vitro pharmacologic study using a model of "the artificial stomach"].

The effects of gastroesophageal mucosal coating agents could be related to a) the decrease of aggressive contents of gastric juice and/or b) the presence of a pH gradient between intraluminal (IL) contents and mucosa. Antacid capacities of Gaviscon and Topaal, containing sodium alginate or alginic acid, respectively, were measured using the "artificial stomach" model. This model, reproducing two major gastric dynamic functions, secretion and gastric emptying, allows to evaluate the pH variations in the IL contents and at its surface, by a double pH metric recording. Experiments were performed when drugs to be tested were added either to 100 ml of human gastric juice (100 mmol/l or 88 mmol/l with biliary reflux) or to 100 ml of 0.1 N HCl, without and with 1 percent meat extract. Simulated secretion was represented by a 3 ml/min flux of either 0.1 N HCl or gastric juice and "gastric emptying" fluxes varied from 1.5, 3.0 to 4.5 ml/min. When 0.1 N HCl solution was used, the pH levels at the surface of IL contents were close to pH 3.0 when intragastric pH reached pH 1.0 independently of "gastric" emptying flux variations. In the presence of proteins or biliary reflux material, these pH levels were higher, close to pH 4.5 and persisted for a longer time. Antacid activity was calculated as the resistance to acidification of the IL contents, as the amount of H+ ions consumed after addition of antacid to recover initial pH, i.e. 37 and 22 mmol in human gastric juice, between 37 and 17.5 mmol in 0.1 N HCl for Gaviscon and Topaal, according to emptying fluxes.(ABSTRACT TRUNCATED AT 250 WORDS)

Alginates↗