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

Thirty-two hormonal polypeptides and nine proteins (8-65 kD) have been used to evaluate the potential of high-performance liquid chromatography on alkylsilane-bonded silica for separating and recovering biologically active compounds of this type. The basic method used was gradient elution with acetonitrile in an acid phosphate buffer. Variation of key chromatographic parameters demonstrated that low pH (less than 4.0) and high buffer molarity (greater than 0.1 M) are mandatory for reproducible high efficiency polypeptide chromatography. Simple NaCl-HCl mixtures of appropriate acidity and molarity could be substituted for the acid phosphate buffer, with the advantage of minimising non-physiological ion contributions to eluted materials. Minor selective effects were noted with different organic modifiers, but variation of other parameters, including choice of specific alkylsilane packings, did not materially influence separations. Under optimal conditions all of the polypeptides tested could be efficiently chromatographed, and many simultaneously resolved, as could most of the proteins tested. Three of the more hydrophobic proteins could not, however, be eluted from the alkylsilane packings. Retention orders of smaller compounds (less than 15 residues) generally correlated with the sum of the Rekker fragmental constants of their strongly hydrophobic residues. Larger polypeptides showed numerous anomalies when ranked by this means, however, limiting its predictive value. The separation of at least eighteen discrete components from a partially-purified posterior pituitary extract has demonstrated the capability of alkylsilane-type reversed-phase packings for the hydrophobic high-performance liquid chromatography of complex biological mixtures.
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PMID:Hydrophobic high-performance liquid chromatography of hormonal polypeptides and proteins on alkylsilane-bonded silica. 4 7

A series of small peptides including clusters of glutamyl residues, synthesized to study the site specificity of rat liver (L-CK2) and yeast (Y-CK2) casein kinase-2, are analytically characterized by ion-pair high-performance liquid chromatography using tetrabutylammonium as counter-ion and acetonitrile as modifier of the aqueous phase. Under these conditions peptides of slightly different acidity can be separated and the elution order parallels the hydrophobicity of the ion-pair-peptide complexes, which increases with the number of the acidic functions present in the sequence.
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PMID:Separation of acidic peptides by reversed-phase ion-pair chromatography. Analytical application to a series of acidic substrates of casein kinases. 193 31

Prostaglandins, leukotrienes, and other metabolites of arachidonic acid can be conveniently and efficiently extracted from biological media using a precolumn containing octadecylsilyl silica connected to a 6-port switching valve that is in line with an analytical HPLC column. This procedure makes it possible to extract complex mixtures of eicosanoids and to analyze them by reversed-phase HPLC in a single step. The requirement to evaporate solvents from extracts prior to HPLC is therefore eliminated, saving time and reducing the possibilities for loss and contamination. The effects on recoveries of various media for loading the sample onto the precolumn were investigated, and it was concluded that 15% methanol at neutral pH gives the best overall results. It is therefore not necessary to acidity the sample prior to extraction, which simplifies the procedure and improves the recoveries of acid-labile eicosanoids. Following extraction, eicosanoids can be introduced onto the HPLC column by changing the position of the 6-port switching valve. We have investigated several approaches to the analysis of complex mixtures of these products by reversed-phase HPLC. The best results were obtained using a ternary gradient with a non-end-capped column of octadecylsilyl silica. Metabolites of arachidonic acid other than peptido-leukotrienes were first eluted by increasing the concentrations of acetonitrile and methanol in the mobile phase, which contained a constant concentration of trifluoroacetic acid (0.001%). Peptido-leukotrienes were then eluted with a second gradient, in which the concentrations of acetonitrile and methanol were kept constant, but the concentration of trifluoroacetic acid was increased to 0.0091%. Leukotrienes C4, D4, and E4 appear as sharp peaks at the end of the chromatogram and are completely separated from other types of arachidonic acid metabolites.
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PMID:Precolumn extraction and reversed-phase high-pressure liquid chromatography of prostaglandins and leukotrienes. 282 29

In an effort to understand the mechanism by which dietary indoles inhibit chemically initiated tumorigenesis in experimental animals, we have investigated the potency of 3-substituted and 1,3-disubstituted indoles on the induction of intestinal and hepatic cytochrome P-448-dependent monooxygenases in the rat. Oral intubation with indole-3-carbinol (13C), 1-methoxyindole-3-carbinol (N13C), 1-methoxyindole-3-carboxaldehyde (NCHO), and 3,3'-diindolylmethane (133') at 31 mumol/animal led to significant increases in hepatic ethoxyresorufin O-deethylase activity (EROD; 15, 7, 6, and 5-fold over control, respectively), while intubation with indole (IND), 3-methylindole (3MI), indole-3-carboxaldehyde (13CHO), and indole-3-acetonitrile (IAN) did not increase this monooxygenase activity over control levels. For the eight indoles tested, there was a strong relationship between instability in acidic solution, as indicated by the generation of insoluble products, and capacity to induce hepatic EROD. Further experiments indicated that 13C did not induce hepatic EROD when dosed ip (thus bypassing the acidity of the stomach). Acid treatment of 13C generated a reaction mixture (RXM) that induced EROD after ip or po dosing. Chromatographic fractionation of the RXM indicated that there exist at least four different 13C acid-condensation products in the RXM with the ability to induce EROD. The results presented strongly support the hypothesis that dietary indoles influence the levels of monooxygenase activities via a series of acid-condensation products generated upon introduction of the indole into the acidic environment of the stomach.
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PMID:Structure-activity relationships of dietary indoles: a proposed mechanism of action as modifiers of xenobiotic metabolism. 349 67

Bulk electrolysis of the antioxidant flavonoids quercetin and kaempferol in acetonitrile both yield a single oxidation product in two-electron processes. The oxidation products are more polar than their parent compounds, with an increased molecular weight of 16g/mol, and were identified as 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone and 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone for quercetin and kaempferol, respectively. Two-electron oxidation of the parent flavonoid is suggested to yield a 3,4-flavandione with unchanged substitution pattern in the A- and B-ring, which may rearrange to form the substituted 3(2H)-benzofuranone through the chalcan-trione ring-chain tautomer. The acidity of the 3-OH group is suggested to determine the fate of the flavonoid phenoxyl radical, originally formed by one-electron oxidation, as no well-defined oxidation product of luteolin (lacking the 3-OH group) could be isolated despite rather similar half-peak potentials: Ep/2 = 0.97V, 0.98 V and 1.17 V vs. NHE for quercetin, kaempferol and luteolin, respectively, as measured by cyclic voltammetry in acetonitrile.
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PMID:Two-electron electrochemical oxidation of quercetin and kaempferol changes only the flavonoid C-ring. 986 49

The effect of methanol and acetonitrile, respectively, on the separation of neutral compounds (benzyl alcohol, phenols) is investigated in electrokinetic chromatographic (EKC) systems consisting of polyethyleneimine (PEI) as charged, polymeric, replaceable pseudostationary phase. The separation systems consist of a buffer solution (2-morpholinoethanesulfonic acid, pH 7.0, 20 mM) containing 0.3-0.9% (w/v) PEI as additive and a varying percentage of methanol (0-50%, v/v) or acetonitrile (0-30%, v/v). EKC is carried out in fused-silica capillaries [47.0 cm (effective length 40.3 cm) x 100 microns I.D.]. They are dynamically coated with PEI, resulting in an electroosmotic flow directed towards the anode. The neutral analytes are migrating with the electroosmotic flow, and are retarded by the electrically driven counterflow of PEI. Separation of the analytes follows in the sequence benzyl alcohol, phenol, resorcinol, pyrogallol, reflecting the increasing hydrogen bond acidity and polarity (polarizibility) of the solutes. However, addition of methanol or acetonitrile causes a drastic loss of resolution, whereby the relative retention of the separands (related to benzyl alcohol) indicates a decrease of retardation upon addition of the organic solvents.
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PMID:Capillary electrokinetic chromatography with polyethyleneimine as replaceable cationic pseudostationary phase. Influence of methanol and acetonitrile on separation selectivity. 1048 18

The effects of six organic modifiers (urea, methanol, dioxane, tetrahydrofuran, acetonitrile and 2-propanol) on the retention mechanism and separation selectivity of the bulk buffer in micellar electrokinetic capillary chromatography (MECC) with sodium dodecyl sulfate (SDS) micelles as pseudo-stationary phase have been investigated through linear solvation energy relationships (LSERs). It is found that the retention value in MECC systems with or without organic modifier is primarily dependent on the solvophobic interaction and the hydrogen bonding interaction with the solute as proton acceptor, while the dipolar interaction and the hydrogen bonding interaction with the solute as proton donor play minor roles. The effects of the organic modifiers on the solvophobic, dipolar and hydrogen bonding interactions are evaluated in terms of the relationship between regression coefficient of the LSER equations and the modifier concentration. The variations of the solvophobic interaction and the dipolar interaction with change of the modifier concentration can be approximately explained using the solubility parameter and the dipolarity/polarizability parameter of the organic modifier, respectively. However, the relationships between the hydrogen bond acidity and basicity of the bulk buffer and the organic modifiers are rather complicated. Those results may be caused from the displacement of organic modifiers to the water adsorbed on the micellar surface as well as changes in the acidity and basicity of the bulk buffer with the addition of organic modifiers. In addition, it is found that the phase ratio is influenced significantly by the use of organic modifier.
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PMID:Effects of organic modifiers on retention mechanism and selectivity in micellar electrokinetic capillary chromatography studied by linear solvation energy relationships. 1059 65

Through correct pH measurements, pKa and activity coefficient values, a model describing their effect on electrophoretic behaviour of substances is established. The suggested model uses the pH values in the acetonitrile-water mixtures used and takes into account the effect of activity coefficients. The model permits the calculation of acidity constants of analytes in hydro-organic media and also the prediction of the effect of pH on the electrophoretic mobility. The model is tested by determining the dissociation constants of a series of nine quinolones in acetonitrile-water mixtures of 0, 5.5, 10 and 30% (w/w) acetonitrile.
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PMID:Influence of pH and pKa values on electrophoretic behaviour of quinolones in aqueous and hydro-organic media. 1073 18

The solvatochromic comparison method has been used to probe the interactions of solutes with binary solvent mixtures of methanol-water and acetonitrile-water. The solute spectra recorded in these mixtures are composed of the additive spectral contributions of the different solvated species of the solute, i.e., the water-solvated species, the cosolvent-solvated species, and the species solvated by water-solvent complexes. Multivariate curve resolution-alternating least squares has been used to model the solvation of the solutes as a function of the composition of the binary solvent mixture. Spectra and concentration profiles of the dye surrounded by the different solvation environments have been isolated. For the first time, solute spectra solvated exclusively by methanol-water and acetonitrile-water complexes have been obtained, and the solvatochromic parameters of dipolarity/polarizability and hydrogen-bonding acidity have been estimated for these complex species.
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PMID:Characterization of methanol-water and acetonitrile-water association using multivariate curve resolution methods 1081 51

The decarboxylation rate of the tetramethylguanidinium salt of 3-carboxy-6-nitrobenzisoxazole in 24 pure solvents and 36 dimethyl sulfoxide binary mixtures with diglyme, acetonitrile, benzene, dichloromethane, chloroform, and methanol was analyzed in the light of the SPP, SA, and SB pure solvent scales. The results allow one to rationalize the high sensitivity of this kinetics to the reaction medium and to assess the potential use of this compound as a probe in biochemical environments. The natural environment for comparison of this kinetics was found to be the gas phase rather than the aqueous medium. In the latter, the process is much faster owing to such high polarity, which, however, is strongly diminished by the high acidity of the medium. Based on our calculations, the rate constant for the decarboxylation kinetics in the gas phase must be in the region of 2 x 10(-10) s(-1) (i.e., 3 orders of magnitude smaller than in water).
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PMID:Effects of medium on decarboxylation kinetics: 3-carboxybenzisoxazoles and their potential use as environmental probes in biochemistry. 1084 24


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