Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The objective of the present study was to evaluate the gastric cytoprotective activity of the methanol extract of aerial parts of the plant Barleria lupulina Lindl (Acanthaceae) in albino rats using various models of ulcers such as drug induced ulcers, restraint ulcers, duodenal ulcers and pylorus ligated ulcers. The effect of the extract on gastric secretion and lipid peroxidation (thiobarbituric acid reacting substances TBARS) was also studied in rats. The extract at the tested dose of 200 mg/kg significantly reduced the volume of gastric juice, total acidity and the ulcer index in pylorus ligated rats. It also afforded significant protection against alcohol and indomethacin induced ulcer as well as stress induced ulceration. TBARS in the stomach of indomethacin treated rats was also reduced. In addition, it gave protection against duodenal ulcers. The study suggests that the methanol extract of aerial parts of Barleria lupulina Lindl. has a protective effect against experimental gastric and duodenal ulcers.
 ...
PMID:Antiulcer activity of methanol fraction of Barleria lupulina Lindl. in animal models. 1559 9

The spectroscopic properties of enoxacin (ENO), oxolinic acid (OXO) and nalidixic acid (NAL) were studied in various H2O-CH3OH and H2O-CH3CN mixed solvents because these solvents were thought to behave as a biological mimetic system. ENO has piperazinyl group, but OXO and NAL do not have this substituent. The fluorescence emission spectra of ENO were very sensitive to the composition of the solvents. In the Lippert-Mataga analysis of the steady-state fluorescence data, clear reverse solvatochromism was exhibited for ENO in both mixed solvents. This observation can be explained using the excited state twisted intramolecular charge transfer (TICT) from the nitrogen of the piperazinyl group to the keto oxygen. Theoretical calculations further support this observation. The nonradiative and radiative rate constants of these molecules were analyzed as a function of dipolarity-polarizability (pi*) and hydrogen bond donor acidity (alpha) of the mixed solvents. These results for ENO were consistent with the suggested mechanism of the TICT very well. The influence of bulk dielectric effect was more significant relative to the specific hydrogen bonding interactions. The emission spectra of OXO and NAL do not exhibit any characteristic responses to the properties of the solvent.
 ...
PMID:Spectroscopic properties of various quinolone antibiotics in aqueous-organic solvent mixtures. 1562 43

The acid ionization constants of some pyrimidine bases of nucleic acids were determined pH-metrically at 25 degrees C and at the constant ionic strength I = 0.10 mol l(-1) (KNO3) in pure water as well as in aqueous media containing variable mole percentages (5-30%) of organic solvents. The organic solvents used were methanol, ethanol, N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile, acetone and dioxane. The results obtained indicated that the acidity constants are generally decreased as the content of an organic solvent in the medium is increased. It was deduced that the hydrogen bonding interactions and the solvent basicity in addition to the electrostatic effect are the major effects influencing significantly the acid ionization process of pyrimidine bases in the different water-organic solvent media. Some thermodynamic parameters (deltaH, deltaG degrees, deltaS degrees) of the ionization process over the temperature range 5-45 degrees C in pure water were also determined and discussed.
 ...
PMID:The acidity constants of some pyrimidine bases in various water-organic solvent media. 1562 45

The residual silanol acidity and activity of several microparticulate and monolithic C18 columns has been measured from the retention of LiNO3 in the columns with a methanol/buffer (1 mM in Na+) (60:40 v/v) mobile phase buffered to different pH values. For Luna C18 (2) and LiChrospher RP-18 columns, at least two different types of silanols with different acidity for each packing, were observed. Purospher RP-18e and Chromolith RP-18e packings present evidence of some active silanols only at pH values close to their basic pH stability limit or higher. The results obtained have been compared with those obtained previously for Resolve C18, Resolve Silica, Symmetry C18, Symmetry Silica, XTerra MSC18 and Underivatized XTerra. A modification of an equation previously proposed has been applied to all columns studied and the results obtained have been used to classify the columns according to their silanol acidity and activity. The method allows the prediction of the extent of the silanol activity of the columns studied at a particular mobile phase pH.
 ...
PMID:Characterization of the acidity of residual silanol groups in microparticulate and monolithic reversed-phase columns. 1562 56

pH gradient high-performance liquid chromatography (HPLC) is a method of reversed-phase high-performance liquid chromatography suitable for ionogenic substances. It consists in programmed increase during the chromatographic process of the eluting strength of eluent with respect to the analytes separated. On the analogy of the conventional organic modifier gradient reversed-phase HPLC, in the pH gradient approach the eluting strength of the mobile phase increases due to its changing pH: increasing in case of acids or decreasing in case of bases. At the same time the content of organic modifier remains constant. A theory of the pH gradient HPLC has been elaborated. The resulting mathematical model is easily manageable. Its ability to predict changes in retention and separation of analytes following the changes in chromatographic conditions is demonstrated. The pH gradient method is uniquely suitable to determine pKa values of analytes. An equation is presented allowing to calculate pKa values basing on appropriate retention data. The effects on pKa are discussed of the concentration of methanol in the mobile phase. The RP HPLC-derived pKa data correlate to the reference pKa values (w(w)pKa) but are not identical. That may be explained by the effects on the chromatographically determined pKa of the specific interactions of analytes with stationary phases. The proposed pH gradient RP HPLC procedure offers a fast and convenient means to get comparable acidity parameters for larger series of compounds, like drug candidates, also when the analytes are available only in minute amounts and/or as complex mixtures.
 ...
PMID:pH gradient high-performance liquid chromatography: theory and applications. 1562 59

Synergi Hydro-RP is a new type of polar-endcapped, octadecylsiloxane-bonded silica packing for reversed-phase liquid chromatography. Its retention properties as a function of solvent strength and temperature are evaluated from the change in retention factors over the composition range (0-70% v/v methanol) and temperature range (25-65 degrees C) using the solvation parameter model and response surface methodologies. The main factors that affect retention are solute size and hydrogen-bond basicity, with minor contributions from solute hydrogen-bond acidity, dipole-type and electron lone pair interactions. Within the easily accessible range for both temperature and solvent strength, the ability to change selectivity is much greater for solvent strength than temperature. Also, a significant portion of the effect of increasing temperature is to reduce retention without changing selectivity. Response surfaces for the system constants are smooth and non-linear, except for cavity formation and dispersion interactions (v system constant), which is linear. Modeling of the response surfaces suggests that solvent strength and temperature are not independent factors for the b, s and e system constants and for the model intercept (c term).
 ...
PMID:Effect of solvent strength and temperature on retention for a polar-endcapped, octadecylsiloxane-bonded silica stationary phase with methanol-water mobile phases. 1562 60

The purpose of the work presented here was to evaluate the influence of solution composition and analyte characteristics on responsiveness to analysis with negative ion electrospray ionization mass spectrometry. The responses of a series of structurally diverse acidic molecules were compared in various solvents. Response was generally observed to be higher in methanol than acetonitrile and response for all analytes was poorer when water was mixed with the organic solvent. A positive correlation between negative ion ESI-MS response and log P was observed when either acetonitrile or methanol was used as the electrospray solvent. This result was expected because analytes with significant nonpolar character should be particularly responsive to ESI-MS analysis due to their higher affinity for electrospray droplet surfaces. It was also predicted that highly acidic analytes would be most responsive to analysis with negative ion ESI-MS due to their tendency to form negative ions. However, for the analytes studied here, acidity was found not to have a consistent influence on ESI-MS response. Many of the highly acidic molecules were quite polar and, consequently, were poorly responsive. Furthermore, the deprotonated molecular ion was detected for a number of molecules with very high pKa values, which would not be expected to form negative ions in the bulk solution. Ultimately, these results indicate that acidity is not a conclusive parameter for prediction of the relative magnitudes of negative ion ESI-MS response among a diverse series of analytes. Analyte polarity does; however, appear to be useful for this purpose.
 ...
PMID:The relative influences of acidity and polarity on responsiveness of small organic molecules to analysis with negative ion electrospray ionization mass spectrometry (ESI-MS). 1579 13

The actual mobilities and dissociation constants of acidic and basic pharmaceuticals were determined in methanol. Actual mobilities were derived from the dependence of the effective mobilities of the analytes on the pH of the methanolic background electrolyte solution (pH(MeOH)). The pKa values of the pharmaceuticals in methanol (pK(a,MeOH)) were calculated by non-linear curve fitting to the measured mobility values. It was found that the shift in pKa value (when compounds were transferred from water to methanol) increased with the acidity of the analyte. The average pKa shift for compounds exhibiting acidic properties in water was ca. 5.5 units, and the shift for basic compounds about 2 units. As was shown for a mixture of beta-blockers, the calculated actual mobilities and pKa values can be utilised in the optimisation of pH conditions for separation. The practical value of the method was illustrated by the analysis of urine samples.
 ...
PMID:Capillary zone electrophoresis of cationic and anionic drugs in methanol. 1584 46

Soy isoflavones have been correlated with beneficial health effects. The predominant chemical forms of isoflavones present may affect their biological activities. Choosing the solvent system that can accurately quantify the amounts of individual isoflavones present in these products is paramount. Our objectives were to compare frequently used solvent systems and to evaluate the effects of polarity and acidity on the recovery of isoflavones from soybeans. Isoflavones were extracted from pulverized Manokin soybeans using six solvent systems, which are the combinations of three polarity levels (83% acetonitrile, 80% methanol, and 58% acetonitrile) and two acidity levels (nonacidified and acidified). The pulverized soybean was stirred for 2 h in each solvent system before filtration and concentration using rotary evaporation. The extract was resuspended in 16% acetonitrile and analyzed by high-performance liquid chromatography. Recoveries of pure standards were evaluated with all solvent systems. Solvents with a higher polarity extracted a significantly higher amount of total isoflavones. For individual isoflavones, 58% acetonitrile (highest polarity) extracted either the highest amounts or no less than other solvents, while 83% acetonitrile (lowest polarity) extracted either the lowest amounts or no more than other solvents except for the aglycone form. Acidification significantly reduced the recovery of the malonylglucoside form and the total isoflavones. The recovery study revealed that acidification favored the chemical transformations of isoflavones during the extraction. Among the six solvent systems examined, 58% acetonitrile aqueous solution without acid was the best for extraction of isoflavones from soybeans.
 ...
PMID:Effects of solvent polarity and acidity on the extraction efficiency of isoflavones from soybeans (Glycine max). 1588 99

The chromatographic retention and membrane activity relationships of local anesthetics were studied to address the possible mechanisms for structure specificity and inflammation-associated decrease of their effects. Five representative drugs (3 mM for each) were reacted with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposomes in 25 mM potassium phosphate buffer (pH 5.9-7.9, containing 100 mM NaCl and 0.1 mM EDTA) for 10 min at 37 degrees C and the membrane fluidity changes were analyzed by measuring fluorescence polarization with 1,6-diphenyl-1,3,5-hexatriene. Their capacity factors were determined on octadecyl-, octyl- and phenyl-bonded silica columns with a mobile phase consisting of 25 mM potassium phosphate buffer (pH 5.9-7.9, containing 100 mM NaCl and 0.1 mM EDTA)-methanol (30:70, v/v) at a flow rate of 1.0 ml/min and at a column temperature of 37 degrees C and diode-array detection. Mepivacaine, prilocaine, lidocaine, ropivacaine and bupivacaine fluidized membranes in increasing order of intensity, which agreed with their clinical potency. The relative degree of membrane fluidization correlated with that of retention on an octadecyl stationary phase more significantly than the other phases. Both membrane-fluidizing effects and capacity factors decreased by lowering the reaction and mobile phase pH, being consistent with the hypothesis that anesthetic potency is reduced in inflammation because of tissue acidity. Reversed-phase liquid chromatography appears to be useful for estimating the structure-specific and pH-dependent membrane-fluidizing effects of local anesthetics.
 ...
PMID:Reversed-phase liquid chromatographic retention and membrane activity relationships of local anesthetics. 1590 34


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>