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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Proton and carbon-13 NMR spectra of eight 2-substituted imidazolines of pharmaceutical interest are presented as solutes in DMSO-d6 together with certain protonation effects. The acidity of the linking methylene group and hydrogen bonding phenomena of the compounds have been also investigated. The data are analysed in terms of analytical utility and the detection of electronic perturbation around specific hydrogen and carbon atoms.
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PMID:An analytical study of eight medicinal 2-imidazolines by 1H and 13C nuclear magnetic resonance spectroscopy. 337 96

Copper complexes of phenols related to salicylic acid were prepared in DMSO and applied to the shaved dorsal skin of rats. The following activities were assayed: (i) suppression of the carrageenan or hydroxylapatite paw oedemas; (ii) reduction of chronic inflammation in established adjuvant arthritis; (iii) local skin toxicity. Cu(II) was an essential component. Some limited structure-activity correlations were made among alternative cupriphores. DMSO solutions of copper complexes were more potent than their solutions in ethanol. Glycerol was a beneficial additive. Reducing the acidity of some copper salicylate formulations also reduced their potency. Niflumic acid and phenylbutazone were effective non-salicylate transcutaneous cupriphores.
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PMID:Lipophilic copper(II) formulations: some correlations between their composition and anti-inflammatory/anti-arthritic activity when applied to the skin of rats. 708 Sep 60

An NMR titration method has been developed to simultaneously measure the difference in acid dissociation constants (delta pKa) of two or more compounds with high precision and accuracy. The delta pKa between the conjugate acids of the two stereoisomers of 4-tert-butylcyclohexylamine 1 was determined in a single 1H NMR titration experiment. A mixture of the two stereoisomers was titrated with DCI in a 3:1 (v/v) mixture of CD3OD/D2O. From the variations of the H1 chemical shifts the ratio of the acidity constants was determined. The trans stereoisomer 1t was found to be the more basic by 0.121 +/- 0.002 pK unit. A repeat titration in DMSO-d6 also found 1t to be the more basic, by 0.217 +/- 0.003 pK unit. The delta pKa between the two stereoisomers of 4-tert-butylcyclohexanecarboxylic acid 2 was determined in both of these solvents using 1H and 13C NMR. Thermodynamic parameters delta delta H degree and delta delta S degree were evaluated from the temperature dependence of delta pKa. To further demonstrate the utility of this method, the delta pKas of the conjugate acids of the four stereoisomers of 2-decalylamine 3 were determined in a single 1H NMR titration experiment. The cis,cis stereoisomer (3cc) was found to be the most basic, with the cis,trans (3ct), trans,cis (3tc), and trans,trans (3tt) less basic by 0.012 +/- 0.003, 0.037 +/- 0.004, and 0.141 +/- 0.005 pK unit, respectively. A second four-component titration was also performed with the two 4-tert-butylcyclohexylamines (1) and the two trans-2-decalylamines (3tc, 3tt).
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PMID:Multicomponent NMR titration for simultaneous measurement of relative pKaS. 902 28

In this paper, we demonstrate the spreading pressure and interfacial film pressure to be profoundly relevant to interfacial tension, miscibility of liquids, and the Lewis acid-base approach. For immiscible liquid-solid and liquid-liquid systems, we prefer to employ Harkins' spreading model containing the equilibrium spreading pressure pie. With the inclusion of pie, we can also improve the Lewis acid-base approach for hydrogen-bonding, proposed by van Oss, Chaudhury, and Good. We establish an acidity-basicity scale for the initial surface tension by taking pie into account, and we further calculate interfacial tensions for liquid pairs containing formamide or dimethyl sulfoxide (DMSO) with dispersion components cited in Fowkes et al.'s later publication. However, for initially immiscible liquid-liquid systems, the Harkins model does not apply, and we propose, instead, an adsorption model, which requires the interfacial tension to be varying and surface tensions of the bulk liquids at a distance from the interface to remain unchanged. Thus, the difference between the initial and equilibrium interfacial spreading coefficients (Si) equals the equilibrium interfacial film pressure (pii)e, and that difference also equals that of the two interfacial tensions. For liquid-liquid systems, we can choose either of these two models depending on the miscibility of liquids. According to our adsorption model, there should be two interfacial tensions. The initial (or calculated) interfacial tension can be positive or negative, while the equilibrium (experimental) interfacial tension can reach zero. The former has more predictive value than the latter. A negative, initial interfacial tension is delineated to favor miscibility or spontaneous emulsification, but it tends to revert to zero instantaneously. Furthermore, a slightly positive, initial interfacial tension can also lead to miscibility, if (pii)e can help reduce it to a zero equilibrium interfacial tension. We have also found a new important relationship between (pii)e and pie on the basis of the Laplace equation. We also attempt to calculate with our model the (pii)e's for at least 34 liquid pairs, by assuming the published interfacial tensions to be reasonable equilibrium values. Finally, the equilibrium spreading pressure pie for the liquid-solid interface, or the (pii)e for the liquid-liquid interface, appears to be the missing link between the wetting thermodynamics and linear free energy solvatochromic relationship (LFER). We have shown the pie or (pii)e of the former to be the equivalent of the Pi*, polarity/dipolarity parameter, of the latter. Our findings about the correlation between the surface tension component (STC) concept and LFER have provided a new support for the STC theory. Copyright 1999 Academic Press.
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PMID:Relevance of Film Pressures to Interfacial Tension, Miscibility of Liquids, and Lewis Acid-Base Approach. 1032 97

The hydrogen bonding properties of 1-methylcytosine (1-MeC) with the following guanine base derivatives have been studied in DMSO-d6, applying concentration-dependent 1H NMR spectroscopy: 9-ethylguanine, 7,9-dimethylguanine (7,9-DimeGH+), and 7,8-dihydro-8-oxo-9-methylguanine (8-O-9-MeGH), as well as three 9-ethylguanine complexes carrying different Pt(II) moieties at the N7 position. The association constants K for the Watson-Crick pairing schemes are by a factor 2-3 higher in the cases of platinated guanine complexes compared to the Watson-Crick pair between 9-ethylguanine and 1-methylcytosine (K = 6.9 +/- 1.3 M(-1)). Similar enhanced stabilities are observed for the pairs formed between 1-MeC and 7,9-DimeGH+ or 8-O-9-MeGH. The increase in N1H acidity of the guanine derivative upon modification at the N7 or C8 positions can be correlated with the association constants K; the result is a bell-shaped curve meaning that acidification initially stabilizes hydrogen bond formation up to a certain maximum; further acidification then leads to a destabilization. For two of the examples studied in solution, hydrogen bonding according to Watson-Crick between N7-platinated 9-ethylguanine and 1-methylcytosine has also been established by X-ray crystallography.
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PMID:Effects of N7-methylation, N7-platination, and C8-hydroxylation of guanine on H-bond formation with cytosine: platinum coordination strengthens the Watson-Crick pair. 1090 39

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.
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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

9,10-Phenanthrenequinone and acenaphthenequinone are shown to act as simple redox-dependent receptors toward aromatic ureas in CH(2)Cl(2) and DMF. Reduction of the o-quinones to their radical anions greatly increases the strength of hydrogen bonding between the quinone carbonyl oxygens and the urea N-hydrogens. This is detected by large positive shifts in the redox potential of the quinones with no change in electrochemical reversibility upon addition of urea guests. Cyclic voltammetric studies with a variety of possible guests show that the effect is quite selective. Only guests with two strong hydrogen donors, such as O-H bonds or amide N-H bonds, that are capable of simultaneously interacting with both carbonyl oxygens give large shifts in the redox potential of the quinones. The electronic character and conformational preference of the guest are also shown to significantly affect the magnitude of the observed potential shift. In the presence of strong proton donors the electrochemistry of the quinone becomes irreversible indicating that proton transfer has taken place. Experiments with compounds of different acidity show that the pK(a) of the protonated quinone radical is about 15 on the DMSO scale, >4 pK(a) units smaller than that of 1,3-diphenylurea. This is further proof that hydrogen bonding and not proton transfer is responsible for the large potential shifts observed with this and similar guests.
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PMID:Electrochemically controlled hydrogen bonding. o-Quinones as simple redox-dependent receptors for arylureas. 1114 23

Protonation of the Os(IV) amido complex TpOs(NHPh)Cl(2) (1) to give the aniline complex [TpOs(NH(2)Ph)Cl(2)]OTf (2) requires excess triflic acid (HOTf). Complex 1 is unreactive with HCl and other moderately strong acids. Consistent with the low basicity of 1, the aniline complex 2 is extremely acidic and is deprotonated by stoichiometric addition of weak bases such as Cl(-) or H(2)O. No reaction is observed between 1 and methyl triflate (CH(3)OTf) at ambient temperatures. Upon heating, CH(3)OTf removes the chloride ligands from 1 to give CH(3)Cl and the amidobis(triflate) complex TpOs(NHPh)(OTf)(2) (3). Attack at the amido nitrogen is not observed. Complex 1 is thus very inert to protonation and electrophilic attack at nitrogen. A deprotonated form of 1, TpOs[NPh(MgBr)]Cl(2) (4), is generated on reaction of PhMgBr with TpOs(N)Cl(2). Complex 4 is extremely basic and will protonate to 1 with weak acids such as CH(3)CN, DMSO, and acetic anhydride. Thus, 1 has a low acidity as well as a low basicity; it is both less acidic and less basic than aniline. The inertness of 1 is ascribed to partial Os-N pi bonding and to the oxidizing nature of the Os(IV) center.
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PMID:Protonation and deprotonation of TpOs(NHPh)Cl(2): an unusually inert amido ligand. 1131 46

Binary mixtures of DMSO with nine different cosolvents were characterized in light of the pure solvent scales, using suitable probe/homomorph couples. Various physical (vapor pressure, surface tension, viscosity, and enthalpy of mixing) and spectroscopic (IR and NMR) properties of the DMSO/water mixtures are described in terms of their polarity, acidity, and basicity, and the descriptions are examined with a view to establishing their potential physical significance.
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PMID:Characterization of binary solvent mixtures of DMSO with water and other cosolvents. 1151 Dec 61

Equilibrium acidities (pK(HA)) of six P-(para-substituted benzyl)triphenylphosphonium (p-GC(6)H(4)CH(2)PPh(3)(+)) cations, P-allyltriphenylphosphonium cation, P-cinnamyltriphenylphosphonium cation, and As-(p-cyanobenzyl)triphenylarsonium cation, together with the oxidation potentials [E(ox)(A(-))] of their conjugate anions (ylides) have been measured in dimethyl sulfoxide (DMSO) solution. The acidifying effects of the alpha-triphenylphosphonium groups on the acidic C-H bonds in toluene and propene were found to be ca 25 pK(HA) units (34 kcal/mol). Introduction of an electron-withdrawing group such as 4-NO(2), 4-CN, or 4-Br into the para position of the benzyl ring in p-GC(6)H(4)CH(2)PPh(3)(+) cations resulted in an additional acidity increase, but introduction of the 4-OEt electron-donating group decreases the acidity. The equilibrium acidities of p-GC(6)H(4)CH(2)PPh(3)(+) cations were nicely linearly correlated with the Hammett sigma(-) constants of the substituents (G) with a slope of 4.78 pK(HA) units (R(2) = 0.992) (Figure 1). Reversible oxidation potentials of the P-(para-substituted benzyl)triphenylphosphonium ylides were obtained by fast scan cyclic voltammetry. The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in these cations, estimated by combining their equilibrium acidities with the oxidation potentials of their corresponding conjugate anions, showed that the alpha-Ph(3)P(+) groups have negligible stabilizing or destabilizing effects on the adjacent radicals. The equilibrium acidity of As-(p-cyanobenzyl)triphenylarsonium cation is 4 pK(HA) units weaker than that of P-(p-cyanobenzyl)triphenylphosphonium cation, but the BDE of the acidic C-H bond in As-(p-cyanobenzyl)triphenylarsonium cation is ca 2 kcal/mol higher than that in P-(p-cyanobenzyl)triphenylphosphonium cation.
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PMID:Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C-H Bonds in P-(Para-substituted benzyl)triphenylphosphonium Cations and Related Cations. 1166 88


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