UMLS:C0847097 - FACTA Search

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 present study demonstrated the cytoprotective abilities of low concentrations of ethanol, NaCl and HCl, against the gastric mucosal damage caused by 100% ethanol, and the contributions of the physical and chemical properties of these mild irritants to their protective actions. The results have shown the differential protective effects of ethanol (10-40%), NaCl (2.5-12.5%) and HCl (0.15-0.45M), with the optimal cytoprotective concentrations being 20% ethanol, 5% NaCl and 0.3M HCl, respectively. Solutions of KCl and NaCl with similar osmolarity, and H2SO4 and HCl of similar acidity and osmolarity, all showed similar protective protective potentials as compared to the osmotic agent mannitol, which possessed a concentration- and tonicity-dependent protective action against 100% ethanol-induced mucosal damage. Some concentration of methanol, propan-2-ol and ethanol, having similar osmolarity with deionized water, exerted indifferent protective effects. It is therefore concluded that adaptive cytoprotection induced by low concentrations of NaCl and HCl could depend on their physical properties, while that of ethanol could act through its unique chemical property.
...
PMID:Contributions of physical and chemical properties of mild irritants to gastric cytoprotection in rats. 759 13

A series of sulfate-doped titania-silica mixed oxides have been prepared by immersing titania-silica gel in the required volume of sulfuric acid, followed by drying. The mixed oxide gel is obtained by hydrolyzing an equimolar mixture of tetraethylorthosilicate (TEOS) and tetrabutylorthotitanate (TBOT) at pH 3. The materials, after calcining at 723 K for 4 h, are characterized by XRD, FT-IR, the BET method, and surface acid strength by the Hammett indicator method. The catalytic activity tests are carried in a fixed bed catalytic reactor (i.d. = 10 mm) for alcohol conversion, whereas cumene cracking/dehydrogenation reactions are carried out in a micropulse reactor. XRD results shows that the titania-silica mixture is amorphous and the crystallization starts with sulfation. The surface of the mixed oxide contains both bridged and normal hydroxyl groups, as observed from FT-IR data. The surface area of the material is not much altered by sulfation and lies within 50 m2/g. The acid strength of 4 wt% SO2-4/TiO2-SiO2 is found to be stronger than that of 100% concentrated H2SO4. In the case of 2-propanol conversion, low acetone selectivity indicates the presence of weak basic sites, whereas methanol conversion over all solids shows that dehydration follows a parallel and consecutive pathway. A good correlation is found between the cumene cracking and the acidity of the catalysts. Copyright 1999 Academic Press.
...
PMID:SO2-4/TiO2-SiO2 Mixed Oxide Catalyst, I: Synthesis, Characterization, and Acidic Properties. 1039 70

This work deals with the preparation of SiO(2)-AlPO(4)-B(2)O(3) ternary systems from impregation of a SiO(2)-AlPO(4) solid previously synthesized with B(OH)(3) (0-10% B(OH)(3), by weight). Characterization of the resulting solids has been carried out from adsorption-desorption isotherms of nitrogen, DRIFT, FT-Raman, pyridine adsorption, and (1)H, (11)B, (27)Al, and (31)P MAS NMR. The textural properties are scarcely changed by the impregnation and calcination steps. Moreover, the MAS NMR experiments indicated that the components of the solids do not interact among them. The solids were tested in the dehydration-dehydrogenation of propan-2-ol, widely used to correlate catalytic activity with the surface acid-base properties of the solids. The catalytic results indicate that the effect of boron dopping is an increase in the overall acidity of the solids. Copyright 1999 Academic Press.
...
PMID:MAS NMR, DRIFT, and FT-Raman Characterization of SiO(2)-AlPO(4)-B(2)O(3) Ternary Catalytic Systems. 1044 28

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.
...
PMID:Effects of organic modifiers on retention mechanism and selectivity in micellar electrokinetic capillary chromatography studied by linear solvation energy relationships. 1059 65

Retention data for a set of 69 compounds using rapid gradient elution are obtained on a wide range of reversed-phase stationary phases and organic modifiers. The chromatographic stationary phases studied are Inertsil (IN)-ODS, pentafluorophenyl, fluoro-octyl, n-propylcyano, Polymer (PLRP-S 100), and hexylphenyl. The organic solvent modifiers are 2,2,2-trifluoroethanol (TFE); 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP); isopropanol; methanol (MeOH); acetonitrile (AcN); tetrahydrofuran; 1,4-dioxane; N,N-dimethylformamide; and mixed solvents of dimethylsulfoxide (DMSO) with AcN and DMSO with MeOH (1:1). A total of 25 chromatographic systems are analyzed using a solvation equation. In general, most of the systems give reasonable statistics. The selectivity of the reversed phase-high-performance liquid chromatographic (HPLC) systems with respect to the solute's dipolarity-polarity, hydrogen-bond acidity, and basicity are reflected in correspondingly large coefficients in the solvation equation. We wanted to find the most orthogonal HPLC systems, showing the highest possible selectivity difference in order to derive molecular descriptors using the gradient retention times of a compound. We selected eight chromatographic systems that have a large range of coefficients of interest (s, a, and b) similar to those found in water-solvent partitions used previously to derive molecular descriptors. The systems selected are IN-ODS phases with AcN, MeOH, TFE, and HFIP as mobile phase, PLRP-S 100 phase with AcN, propylcyano phase with AcN and MeOH, and fluorooctyl phase with TFE. Using the retention data obtained for a compound in the selected chromatographic systems, we can estimate the molecular descriptors with the faster and simpler gradient elution method.
...
PMID:Characterizing the selectivity of stationary phases and organic modifiers in reversed-phase high-performance liquid chromatographic systems by a general solvation equation using gradient elution. 1110 74

5,5-Dimethyl-1,4,2-dioxazoles are readily installed by transketalization of 2,2-diethoxypropane, where both the NH and OH moieties are protected in a nonprotic form. The dioxazoles are stable to a wide variety of reaction conditions and readily revert back to the hydroxamic acid by treatment with Nafion-H in 2-propanol. The method is applicable to primary, secondary, tertiary, and aromatic hydroxamic acids, and the acidity of the protons adjacent to the dioxazole allows alpha-functionalization.
...
PMID:5,5-Dimethyl-1,4,2-dioxazoles as versatile aprotic hydroxamic acid protecting groups. 1209 95

The complexes trans-RuH(Cl)(tmen)(R-binap) (1) and (OC-6-43)-RuH(Cl)(tmen)(PPh(3))(2) (2) are prepared by the reaction of the diamine NH(2)CMe(2)CMe(2)NH(2) (tmen) with RuH(Cl)(PPh(3))(R-binap) and RuH(Cl)(PPh(3))(3), respectively. Reaction of KHB(sec)Bu(3) with 1 yields trans-Ru(H)(2)(R-binap)(tmen) (5) while reaction of KHB(sec)Bu(3) or KO(t)Bu with 2 under Ar yields the new hydridoamido complex RuH(PPh(3))(2)(NH(2)CMe(2)CMe(2)NH) (4). Complex 4 has a distorted trigonal bipyramidal geometry with the amido nitrogen in the equatorial plane. Loss of H(2) from 5 results in the related complex RuH(R-binap)(NH(2)CMe(2)CMe(2)NH) (3). Reaction of H(2) with 4 yields the trans-dihydride (OC-6-22)-Ru(H)(2)(PPh(3))(2)(tmen)(6). Calculations support the assignment of the structures. The hydrogenation of acetophenone is catalyzed by 5 or 4 in benzene or 2-propanol without the need for added base. For 5 in benzene at 293 K over the ranges of concentrations [5] = 10(-)(4) to 10(-)(3) M, [ketone] = 0.1 to 0.5 M, and of pressures of H(2) = 8 to 23 atm, the rate law is rate = k[5][H(2)] with k = 3.3 M(-1) s(1), DeltaH++ = 8.5 +/- 0.5 kcal mol(-1), DeltaS++ = -28 +/- 2 cal mol(-1) K(-1). For 4 in benzene at 293 K over the ranges of concentrations [4] = 10(-4) to 10(-3) M, [ketone] 0.1 to 0.7 M, and of pressures of H(2) = 1 to 6 atm, the preliminary rate law is rate = k[4][H(2)] with k = 1.1 x 10(2) M(-1) s(-1), DeltaH++ = 7.6 +/- 0.3 kcal mol(-1), DeltaS++ = -23 +/- 1 cal mol(-1) K(-1). Both theory and experiment suggest that the intramolecular heterolytic splitting of dihydrogen across the polar Ru=N bond of the amido complexes 3 and 4 is the turn-over limiting step. A transition state structure and reaction energy profile is calculated. The transfer of H(delta+)/H(delta-) to the ketone from the RuH and NH groups of 5 in a Noyori metal-ligand bifunctional mechanism is a fast process and it sets the chirality as (R)-1-phenylethanol (62-68% ee) in the hydrogenation of acetophenone. The rate of hydrogenation of acetophenone catalyzed by 5 is slower and the ee of the product is low (14% S) when 2-propanol is used as the solvent, but both the rate and ee (up to 55% R) increase when excess KO(t)Bu is added. The formation of ruthenium alkoxide complexes in 2-propanol might explain these observations. Alkoxide complexes [RuP(2)]H(OR)(tmen), [RuP(2)] = Ru(R-binap) or Ru(PPh(3))(2), R= (i) Pr, CHPhMe, (t)Bu, are observed by reacting the alcohols (i)PrOH, phenylethanol, and (t)BuOH with the dihydrides 5 and 6, respectively, under Ar. In the absence of H(2), the amido complexes 3 and 4 react with acetophenone to give the ketone adducts [RuP(2)]H(O=CPhMe)(NH(2)CMe(2)CMe(2)NH) in equilibrium with the enolate complexes trans- [RuP(2)](H)(OCPh=CH(2))(tmen) and eventually the decomposition products [RuP(2)]H(eta(5)-CH(2)CPhCHCPhO), with the binap complex characterized crystallographically. In general, proton transfer from the weakly acidic molecules dihydrogen, alcohol, or acetophenone to the amido nitrogen of complexes 3 and 4 is favored in two ways when the molecule coordinates to ruthenium: (1) an increase in acidity of the molecule by the Lewis acidic metal and (2) an increase in the basicity of the amido nitrogen caused by its pyramidalization. The formato complexes trans-[RuP(2)]H(OCHO)(tmen) were prepared by reacting the respective complex 4 or 5 with formic acid. The crystal structure of RuH(OCHO)(PPh(3))(2)(tmen) displays similar features to the calculated transition state for H(delta+)/H(delta-) transfer to the ketone in the catalytic cycle.
...
PMID:Mechanism of the hydrogenation of ketones catalyzed by trans-dihydrido(diamine)ruthenium II complexes. 1247 57

The reaction between CpFe(dppe)H and a number of different proton donors (2-fluoroethanol, MFE; 2,2,2-trifluoroethanol, TFE; hexafluoro-2-propanol, HFIP; perfluoro-tert-butyl alcohol, PFTB; and trifluoroacetic acid, TFA) has been investigated spectroscopically by variable-temperature infrared, UV-visible, and NMR spectroscopy, and has been measured kinetically by the stopped-flow technique with UV-visible detection. The low-temperature IR study shows the establishment of hydrogen-bonding interactions which involve the hydride ligand as the proton accepting site. This investigation quantifies the thermodynamics of the hydrogen-bonding interaction and the basicity factor (E(j)) of the hydride complex. All techniques agree in indicating an equilibration process, after the immediate hydrogen-bond formation, between the hydride complex and an intermediate dihydrogen complex, [CpFe(dppe)(H(2))](+). The equilibrium is shifted toward the dihydrogen complex to a greater extent for the stronger alcohols and for higher alcohol/Fe ratios. The observed equilibration rate constant is linearly dependent on the alcohol concentration, in agreement with the involvement of two alcohol molecules and the formation of a homoconjugate pair. The rate constant increases with the acidity of the proton donor (TFE < HFIP < PFTB < TFA). The rate of the subsequent irreversible isomerization leading to the classical dihydride complex, [CpFe(dppe)H(2)](+), is first order, and the rate constant does not depend on the proton donor nature. The reaction continues, if conducted in CH(2)Cl(2), with a third, slower step leading to the paramagnetic [CpFe(dppe)Cl](+) product. The kinetic data are in accord with an isomerization mechanism consisting of an intramolecular reorganization, leading in one step from the dihydrogen complex to the classical dihydride species, and disagree with the occurrence of a proton-transfer process at the metal site.
...
PMID:Kinetics and mechanism of the proton transfer to CpFe(dppe)H: absence of a direct protonation at the metal site. 1295 93

The Ehrlich reaction was optimized to determine the formation of pyrrolized phospholipids in edible oils in an attempt to understand the color reversion produced during the deodorization of poorly degummed edible oils. The procedure consisted of the treatment of the oil with p-(dimethylamino)benzaldehyde in tetrahydrofuran/2-propanol at a controlled acidity and temperature and the spectrophotometric determination of adducts produced. The extinction coefficient of Ehrlich adducts was calculated by using 1-[1-(2-hydroxyethyl)-1H-pyrrol-2-yl]propan-1-ol (1) as a standard and was 15 300 M(-)(1) cm(-)(1). The response was linear and reproducible within the range of 0.334-48.6 microM of compound 1. When the assay was applied to a soybean oil treated with 100-1000 ppm of phosphatidylethanolamine and submitted to deodorization, the formation of pyrrolized phospholipids was observed at the same time that the disappearance of the phospholipid and the oil darkening were produced. The main changes were observed during the first steps of the deodorization process, when the oil was heated between 80 and 160 degrees C. During the initial heating of the oil until achieving 200 degrees C, oil darkening, phosphatidylethanolamine disappearance, and pyrrolized phospholipid formation were correlated, therefore suggesting a contribution of phospholipid pyrrolization to the oil darkening produced.
...
PMID:Contribution of phospholipid pyrrolization to the color reversion produced during deodorization of poorly degummed vegetable oils. 1521 64

The solution structures of a number of trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) precatalysts [TolBINAP = 2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl; 1,2-diamine==(S,S)- or (R,R)-1,2-diphenylethylenediamine (DPEN), ethylenediamine (EN), and (S)-1,1-di(4-anisyl)-2-isopropylethylenediamine (DAIPEN)] have been determined using 2D NMR ((1)H--(1)H DQF-COSY, (1)H--(13)C HMQC, (1)H--(31)P HSQC, and (1)H--(15)N HSQC), and a double-pulsed field-gradient spin-echo (DPFGSE) NOE technique. All the octahedral Ru complexes adopt a trans configuration with respect to the BH(4) and hydride ligands. Amine protons of trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) complexes undergo H/D exchange in (CD(3))(2)CDOD. This inherent high acidity, coupled with the lability and chemical properties of the BH(4) ligand, allows for precatalyst activation without the need for an added base, in contrast to trans-RuCl(2)[(S)-tolbinap](1,2-diamine) precatalysts, which require a strong base for generation of a catalytic species. The H/BH(4) complex in a 2-propanol solution is converted to catalytically active [trans-RuH{(S)-tolbinap}{(S,S)-dpen}(ROH)](+) [(RO)(ROH)(n)](-) (R = (CH(3))(2)CH), a loosely associated ion pair of the discrete (solvated) cationic fragment and anionic species.
...
PMID:Solution structures and behavior of trans-RuH(eta(1)-BH(4)) (binap)(1,2-diamine) complexes. 1632 88

1 2 3 4 5 Next >>