UMLS:C0847097 - FACTA Search

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

The use of Bu(3)SnH and Me(3)SnH in the synthesis of HP(CF(3))(2) and HP(C(6)F(5))(2) from the corresponding bromides leads to a high-yield synthesis, which additionally provides these compounds in large quantities. The pentacarbonyl tungsten complexes [W(CO)(5)PH(CF(3))(2)] and [W(CO)(5)PH(C(6)F(5))(2)] were synthesized reacting the corresponding phosphanes with [W(CO)(5)THF] and characterized by X-ray and elemental analysis as well as multinuclear NMR and mass spectroscopy. The vibrational analyses of HP(CF(3))(2) and HP(C(6)F(5))(2) and their tungsten pentacarbonyl complexes were achieved in combination with hybrid DFT calculations. The optimized structures of [W(CO)(5)PH(CF(3))(2)] and [W(CO)(5)PH(C(6)F(5))(2)] at the B3PW91 level of theory using a LanL2DZ basis and ECP at the tungsten atom and a 6-311G(3d,p) and 6-311G(d,p) basis set for the nonmetal atoms, respectively, yield an impressively good agreement between experimental and theoretical geometric parameters. An increased pi-acidity of HP(CF(3))(2) in comparison with HP(C(6)F(5))(2) and HPPh(2) is discussed in the context of vibrational analysis, X-ray structural investigations, and theoretical calculations.
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PMID:Bis(trifluoromethyl)phosphane and bis(pentafluorophenyl)phosphane and their pentacarbonyl tungsten complexes: improved synthesis and an experimental and density functional study. 1276 2

A series of new platinum(II) complexes with diethyl (2-dqmp) and monoethyl (2-Hmqmp) 2-quinolylmethylphosphonates have been prepared and studied. Both organophosphorus ligands by reaction with [PtX(4)](2-) (X=Cl, Br) form either the molecular or ionic complexes depending on the acidity of the reaction solution. Dihalide adducts, trans-[PtL(2)X(2)] (L=2-dqmp, 2-Hmqmp), with N-bonded ligand through the quinoline nitrogen were obtained in the neutral medium, while under acidic conditions at pH<3 were isolated the ion-pair salt complexes, [LH](2)[PtX(4)], containing the protonated quinoline ligand as cation and tetrahaloplatinate complex as anion. In addition, 2-Hmqmp at pH approximately 3.5 forms quinolinium hexahalodiplatinum salt complexes, [2-H(2)mqmp](2)[Pt(2)X(6)], while the chelate complex, [Pt(2-mqmp)(2)].2H(2)O, with N,O-bonded ligand through the quinoline nitrogen and the deprotonated phosphonic acid oxygen was obtained at pH>6. The new complexes were characterized on the basis of elemental and thermogravimetric analyses, conductometric measurements, and by infrared and (1)H NMR spectral studies. As a preliminary assessment of their biological activity, complexes were evaluated for their in vitro cytostatic activity in an epidermoid human carcinoma (KB) and murine leukemia (L1210) cell lines. The results obtained were compared with those obtained for the corresponding Pd(II) complexes.
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PMID:Synthesis, characterization and antitumor activity of platinum(II) complexes with diethyl and monoethyl 2-quinolylmethylphosphonates. 1281 96

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.
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PMID:Synthesis and reactivity of (C6F5)3B-N-heterocycle complexes. 1. Generation of highly acidic sp3 carbons in pyrroles and indoles. 1283 36

Iron chelates such as ethylenediamine-N,N'-bis(2-hydroxyphenyl)acetic acid (EDDHA) and their analogues are the most efficient soil fertilizers to treat iron chlorosis in plants growing in calcareous soils. EDDHA, EDDH4MA (ethylenediamine-N,N'-bis(2-hydroxy-4-methylphenyl)acetic acid), and EDDCHA (ethylenediamine-N,N'-bis(2-hydroxy-5-carboxyphenyl)acetic acid) are allowed by the European directive, but also EDDHSA (ethylenediamine-N,N'-bis(2-hydroxy-5-sulfonylphenyl)acetic acid) and EDDH5MA (ethylenediamine-N,N'-bis(2-hydroxy-5-methylphenyl)acetic acid) are present in several commercial iron chelates. In this study, these chelating agents as well as p,p-EDDHA (ethylenediamine-N,N'-bis(4-hydroxyphenyl)acetic acid) and EDDMtxA (ethylenediamine-N,N'-bis(2-metoxyphenyl)acetic acid) have been obtained following a new synthetic pathway. Their chemical behavior has been studied to predict the effect of the substituents in the benzene ring on their efficacy as iron fertilizers for soils above pH 7. The purity of the chelating agents has been determined using a novel methodology through spectrophotometric titration at 480 nm with Fe(3+) as titrant to evaluate the inorganic impurities. The protonation constants were determined by both spectrophotometric and potentiometric methods, and Ca(2+) and Mg(2+) stability constants were determined from potentiometric titrations. To establish the Fe(3+) and Cu(2+) stability constants, a new spectrophotometric method has been developed, and the results were compared with those reported in the literature for EDDHA and EDDHMA and their meso- and rac-isomers. pM values have been also determined to provide a comparable basis to establish the relative chelating ability of these ligands. The purity obtained for the ligands is higher than 87% in all cases and is comparable with that obtained by (1)H NMR. No significant differences have been found among ligands when their protonation and stability constants were compared. As expected, no Fe(3+) complexation was observed for p,p-EDDHA and EDDMtxA. The presence of sulfonium groups in EDDHSA produces an increase in acidity that affects their protonation and stability constants, although the pFe values suggest that EDDHSA could be also effective to correct iron chlorosis in plants.
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PMID:Chelating agents related to ethylenediamine bis(2-hydroxyphenyl)acetic acid (EDDHA): synthesis, characterization, and equilibrium studies of the free ligands and their Mg2+, Ca2+, Cu2+, and Fe3+ chelates. 1292 15

Binary mixtures of water and acetonitrile (W/AN) were characterized in the light of the pure solvent scales, using suitable probe/homomorph couples. Various thermodynamic (vapour pressure, softness parameter, excess molar Gibbs energy and enthalpy of mixing) properties, surface tension, viscosity, and spectroscopic (IR, Raman and NMR) properties of the mixtures, and the distribution of molecular structures (viz. free CH3CN and CH3CN-H2O complexes) are described in terms of their polarity, acidity and basicity, and the descriptions examined in relation to a potential physical significance.
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PMID:Characterization of binary solvent mixtures: the water-acetonitrile mixture. 1292 61

As part of studies aimed at clarifying conflicting reports concerning the acidifying effects exerted by the SO2CF3 vs. NO2 moieties with respect to carbanion stabilities, we have investigated the ionization equilibria of an extended set of benzyltriflones and have determined both pKa values of the carbon acids and 1H and 13C NMR parameters of the resulting carbanions. Acidities determined in H2O-Me2SO mixtures and in pure Me2SO show a contrasting behaviour between 4-X-substituted benzyl triflones and related arylnitromethanes. While the latter exhibit a decreasing acidity on going from H2O to Me2SO media, the benzyltriflone analogues show in fact increasing acidity in Me2SO. This opposing trend suggests that the exocyclic alpha-SO2CF3 moiety is strongly stabilizing the negative charge of the carbanions through polarizability effects favored by the dipolar aprotic Me2SO solvent. As a result, inversions in the acidity sequences of alpha-NO2 and alpha-SO2CF3 activated carbon acids are observed on going from H2O to Me2SO. 1H and 13C NMR data are in full accord with the conclusion that only little negative charge is transferred to the 4-X-substituted phenyl ring upon ionization. Increasing further the ring substitution by electronegative groups to 2,4- and 2,4,6- patterns, enhances the charge transfer but this nevertheless remains moderate even with the most activated 2,4,6- trinitro or 2,6-dinitro-4-SO2CF3 sequences. Altogether, our results provide convincing evidence of the unusual electron transmission ability of the very strongly acidifying SO2CF3 group.
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PMID:Super acidifiers: the origin of the exceptional electron transmission capability of the SO2CF3 group in carbanion stabilization. 1292 64

It has been discovered that the use of excess zirconium in reactions with 4,4'-biphenyl and 4,4'-terphenylbis(phosphonic acid) in DMSO or DMSO-ethanol mixtures produces microporous inorganic-organic hybrids. Surface areas of 400 m(2)/g and pore sizes in the range of 10-20 A in diameter are routinely obtained. These materials are readily sulfonated with SO(3) under pressure to yield strong Bronsted acids. The acid strength, measured by (13)C NMR shifts of acetone and cyclopentanone in contact with the sulfonates, indicates an acidity close to that of 100% H(2)SO(4). Condensation and cracking reactions were obtained for both ketones under mild conditions. A working hypothesis is presented to account for the high surface area and microporosity. The combination of high surface areas and pore dimensions that are between those of zeolites and mesoporous silicas commends these materials for applications in separations, ion exchange, and catalysis.
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PMID:Sulfonated microporous organic-inorganic hybrids as strong Bronsted acids. 1292 62

The title organo-molybdate derivatives are synthesized and their IR, 1H NMR spectra have been determined and the relations between the structures and the 1H NMR and IR parameters have been studied. The results indicate that the red shift of the IR frequency of Mo-O-Mo in [(n-Bu)4N]2[Mo2O5(OC10H6O)2] (complex I) takes place to compare with that in [(n-Bu)4N]2[Mo4O10 (OC10H6O)2(OCH3)2] (complex II) and lower filed shift of 1H NMR of the aromatic H atoms in complex II occurs as contrasted to that in the complex I. It is found also the organo-molybdate derivatives are very sensitive to the acidity of the chemical system.
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PMID:[The synthesis, 1H NMR and IR study of [(n-Bu)4N]2[Mo2O5(OC10H6O)2] and [(n-Bu)4N]2[Mo4O10 (OC10H6O)2(OCH3)2]]. 1294 21

The N7/O6 equatorial binding interactions of the antitumor active complex Rh(2)(OAc)(4)(H(2)O)(2) (OAc(-) = CH(3)CO(2)(-)) with the DNA fragment d(GpG) have been unambiguously determined by NMR spectroscopy. Previous X-ray crystallographic determinations of the head-to-head (HH) and head-to-tail (HT) adducts of dirhodium tetraacetate with 9-ethylguanine (9-EtGH) revealed unprecedented bridging N7/O6 guanine nucleobases that span the Rh-Rh bond. The absence of N7 protonation at low pH and the notable increase in the acidity of N1-H (pK(a) approximately 5.7 as compared to 8.5 for N7 only bound platinum adducts), suggested by the pH dependence titrations of the purine H8 (1)H NMR resonances for Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2-)[d(GpG)],are consistent with bidentate N7/O6 binding of the guanine nucleobases. The pK(a) values estimated for N1-H (de)protonation, from the pH dependence studies of the C6 and C2 (13)C NMR resonances for the Rh(2)(OAc)(2)(9-EtG)(2) isomers, concur with those derived from the H8 (1)H NMR resonance titrations. Comparison of the (13)C NMR resonances of C6 and C2 for the dirhodium adducts Rh(2)(OAc)(2)(9-EtG)(2) and Rh(2)(OAc)(2)[d(GpG)] with the corresponding resonances of the unbound ligands [at pH 7.0 for 9-EtGH and pH 8.0 for d(GpG)], shows substantial downfield shifts of Deltadelta approximately 11.0 and 6.0 ppm for C6 and C2, respectively; the latter shifts reflect the effect of O6 binding to the dirhodium centers and the ensuing enhancement in the acidity of N1-H. Intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum of Rh(2)(OAc)(2)[d(GpG)] indicate head-to-head arrangement of the guanine bases. The Rh(2)(OAc)(2)[d(GpG)] adduct exhibits two major right-handed conformers, HH1 R and HH2 R, with HH1 R being three times more abundant than the unusual HH2 R. Complete characterization of both adducts revealed repuckering of the 5'-G sugar rings to C3'-endo (N-type), retention of C2'-endo (S-type) conformation for the 3'-G sugar rings, and anti orientation with respect to the glycosyl bonds. The structural features obtained for Rh(2)(OAc)(2))[d(GpG)] by means of NMR spectroscopy are very similar to those for cis-[Pt(NH(3))(2))[d(GpG)]] and corroborate molecular modeling studies.
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PMID:Unprecedented head-to-head conformers of d(GpG) bound to the antitumor active compound tetrakis (mu-carboxylato)dirhodium(II,II). 1294 Jul 56

Insight into the N7/O6 equatorial binding interactions of the antitumor active complex Rh(2)(OAc)(4)(H(2)O)(2) (OAc(-) = CH(3)CO(2)(-)) with the nucleotide 5'-GMP and the DNA fragment d(pGpG) has been obtained by one- (1D) and two-dimensional (2D) NMR spectroscopy. The lack of N7 protonation at low pH values and the significant increase in the acidity of N1-H (pK(a) approximately 5.6 as compared to 8.5 for N7 only bound platinum adducts), indicated by the pH dependence study of the H8 (1)H NMR resonance for the HT (head-to-tail) isomer of Rh(2)(OAc)(2)(5'-GMP)(2), are consistent with bidentate N7/O6 binding of the guanine. The H8 (1)H NMR resonance of the HH (head-to-head) Rh(2)(OAc)(2)(5'-GMP)(2) isomer, as well as the 5'-G and 3'-G H8 resonances of the Rh(2)(OAc)(2) [d(pGpG)] adduct exhibit pH-independent titration curves, attributable to the added effect of the 5'-phosphate group deprotonation at a pH value similar to that of the N1 site. The enhancement in the acidity of N1-H, with respect to N7 only bound metal adducts, afforded by the O6 binding of the bases to the rhodium centers, has been corroborated by monitoring the pH dependence of the purine C6 and C2 (13)C NMR resonances for Rh(2)(OAc)(2)(5'-GMP)(2) and Rh(2)(OAc)(2) [d(pGpG)]. The latter studies resulted in pK(a) values in good agreement with those derived from the pH-dependent (1)H NMR titrations of the H8 resonances. Comparison of the (13)C NMR resonances of C6 and C2 for the dirhodium adducts Rh(2)(OAc)(2)(5'-GMP)(2) and Rh(2)(OAc)(2) [d(pGpG)] with the corresponding resonances of the unbound ligands at pH 8.0, showed substantial downfield shifts of Deltadelta approximately 11.0 and 6.0 ppm, respectively. The HH arrangement of the bases in the Rh(2)(OAc)(2) [d(pGpG)] adduct is evidenced by intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum. The presence of the terminal 5'-phosphate group in d(pGpG) results in stabilization of one left-handed Rh(2)(OAc)(2) [d(pGpG)] HH1 L conformer, due to the steric effect of the 5'-group, favoring left canting in cisplatin-DNA adducts. Complete characterization of the Rh(2)(OAc)(2[d(pGpG)] adduct revealed notable structural features that resemble those of cis-[Pt(NH(3))(2) [d(pGpG)]]; the latter involve repuckering of the 5'-G sugar ring to C3'-endo (N-type) conformation, retention of C2'-endo (S-type) 3'-G sugar ring conformation, and anti orientation with respect to the glycosyl bonds. The superposition of the low energy Rh(2)(OAc)(2) [d(pGpG)] conformers, generated by simulated annealing calculations, with the crystal structure of cis-[Pt(NH(3))(2) [d(pGpG)]], reveals remarkable similarities between the adducts; not only are the bases almost completely destacked upon coordination to the metal in both cases, but they are favorably poised to accommodate the bidentate N7/O6 binding to the dirhodium unit. Unexpectedly, the two metal-metal bonded rhodium centers are capable of engaging in cis binding to GG intrastrand sites by establishing N7/O6 bridges that span the Rh-Rh bond.
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PMID:Novel binding interactions of the DNA fragment d(pGpG) cross-linked by the antitumor active compound tetrakis(mu-carboxylato)dirhodium(II,II). 1294 Jul 57

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