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Query: CAS:7782-44-7 (oxygen)
 369,292 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Polyacrylamides (PAAms) were investigated as hydrophilic selectors in non-aqueous capillary electrophoresis (CE). Separation of 10 substituted benzoates and unsubstituted benzoate as model samples was greatly improved by the addition of PAAms in acetonitrile-CE. The migration behavior indicates that the carbonyl moiety of PAAms works as a good hydrogen-accepting site toward hydrogen-donating analytes such as 4-hydroxybenzoate anion (4OH-BA) in acetonitrile. PAAms also serve as electron-accepting agents with its amide proton interacting with the dissociated carboxyl groups of the benzoates. The ion-dipole interaction is useful to control the migration behavior of benzoates without hydrogen-donating substituents. The overall mode of the interaction is similar to that of polyethylene glycol (PEG) 20000 reported previously, but the complex formation constant of poly(N-tert.-butyl)acrylamide (PBAAm) with 40H-BA estimated here was 130-fold larger than that of PEG 20000. This would be ascribed to the strong basicity of the carbonyl oxygen atoms of PBAAm as compared with the ether oxygen atoms of PEG. Furthermore, a copolymer of (N-tert.-butyl)acrylamide-acrylamide [70:30 (in feed)] exhibited a complex formation constant of about fourfold larger toward 4OH-BA than PBAAm, most probably due to decrease in steric hindrance from the tert.-butyl groups. Adrenaline and its six precursors have been separated successfully using the PAAms.
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PMID:Polyacrylamides as hydrophilic selectors in non-aqueous capillary electrophoresis. 1120 96

The fluorescence decay from S2(pi, pi*) state of 2,5-diphenyl-1,6,6a-trithiapentalene (DP-TTP) in cyclohexane, tetrahydrofuran and acetonitrile solutions of a quantum yield of approximately 0.02-0.04 were measured. The results indicate that, the dominant process of radiationless deactivation of the S2 state, is internal conversion to the S1 state. Upon laser pulse excitation (lambda(ex) = 532 nm) from the S1(pi, pi*) state, DP-TTP in deoxygenated benzonitrile, acetonitrile, ethanol and tetrahydrofuran solutions give rise to transient triplet triplet absorption (lambdaTmax = 700-720 nm). Kinetic data are presented for intrinsic triplet lifetimes, self-quenching and quenching by oxygen.
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PMID:Photophysical properties of 2,5-diphenyl-1,6,6a-trithiapentalene revealed by time-resolved spectroscopy. 1120 60

The mechanisms of the Karl Fischer (K.F.) reaction are reviewed and further investigated. Both kinetic measurements of the iodine concentration and chromatographic determinations of the reaction products were performed. In alcoholic solutions mainly alkyl sulfite is oxidized, and a reaction via partial formation of sulfur trioxide is proposed. In methanol an exact 1:1 stoichiometry (H2O:I2) has been verified. In the aprotic, dipolar solvents acetonitrile, DMF and propylene carbonate HSO3- is oxidized by iodine. Based on formation and subsequent hydrolysis of base - SO3 adducts the stoichiometric factor for water is determined by type and concentration of the base, by the concentration of water and by the solvent itself. - In K.F. reagents the oxidation of SO2 by aerial oxygen to sulfate and alkyl sulfate takes place as a side reaction.
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PMID:Kinetics and stoichiometry in the Karl Fischer solution. 1122 May 71

The concerned azo ligands are 2-(phenylazo)pyridine (HL) and 2-((p-chlorophenyl)azo)pyridine (ClL). The reaction of KReO4 with HL in hot concentrated HCl is attended with metal reduction and ligand chlorination affording the oxo complex ReVOCl3(ClL), 2, which furnishes ReIII(OPPh3)Cl3(ClL), 3, upon treatment with PPh3. Aromatic amines, ArNH2, convert 2 to the imido complex ReV(NAr)Cl3(ClL), 5, and the unusual oxo-imido dimer (ClL)-Cl2(O)ReVOReV(NAr)Cl2(ClL), 7. The complex ReIII(OPPh3)Cl3(HL), 4, has been generated from ReVOCl3(PPh3)2 and HL. Reaction of 4 with HL has yielded ReV(NPh)Cl3(HL), 6, via azo splitting. The complexes have been characterized with the help spectral, magnetic, and X-ray structural data (2, 3, 5c (Ar = pClC6H4) and 7.CH2Cl2 (Ar = pMeC6H4)). In 2, 3, and 5c the ReCl3 fragment is meridionally disposed, and in 7 the ReCl2 fragments have a trans configuration. The Re-O(oxo) bond, 1.663(6) A, in 2 and Re-N(imido) bond, 1.719(5) A, in 5c are triple bonds. The corresponding bonds are slightly longer in 7 wherein the (O)Re(1)-O(2)-Re(2)(NAr) bridge is angular (151.0(5) degrees) and unsymmetrical, the Re(1)-O(2) bond, 1.849(7) A, having a large double-bond character (Re(2)-O(2), 1.954(7) A). In effect, cis-ReVO2 acts as a monodentate oxygen ligand toward ReVNAr in 7. In all cases the pyridine nitrogen binds trans to the oxo, OPPh3, or NAr donor. Bond length data are consistent with the presence of substantial d(Re)-pi*(azo) back-bonding. In acetonitrile solution the complexes display electrochemical one-electron metal (ReVI/ReV or ReIV/ReIII) and azo redox. The imido ligand in 5 stabilizes the ReVI state (E1/2 approximately 1.4 V) better than the oxo ligand in 2 (approximately 1.9 V). Parallely it is more difficult to reduce the azo group in 5 (approximately -0.4 V) than in 2 (approximately 0.0 V). In 7 the metal (approximately 1.0 V) and azo (approximately -0.4 V) couples correspond to the imido and oxo halves, respectively. The significantly higher (by 0.2-0.6 V) metal reduction potentials of the azopyridine compared to pyridine-2-aldimine complexes is ascribed to the superior pi-acidity and electron-withdrawing character of the azo function relative to the aldimine function. This also makes the transfer of the ReVO oxygen function much more facile under azopyridine chelation as in 2. For the same reason, ReOCl3(PPh3)2 reacts with HL affording only 4 while it reacts with pyridine-2-aldimines furnishing oxo species. Crystal data for the complexes are as follows: 2, empirical formula C11H8Cl4N3ORe, crystal system triclinic, space group P1, a = 7.118(4) A, b = 8.537(4) A, c = 13.231(9) A, alpha = 79.16(5) degrees, beta = 78.03(5) degrees, gamma = 70.96(4) degrees, V = 737.2(7) A3, Z = 2; 3, empirical formula C29H23Cl4N3OPRe, crystal system monoclinic, space group P2(1)/n, a = 11.264(2) A, b = 15.221(3) A, c = 17.628(4) A, beta = 94.21(3) degrees, V = 3014(1) A3, Z = 4; 5c, empirical formula C17H12Cl5N4Re, crystal system triclinic, space group P1, a = 9.683(3) A, b = 10.898(3) A, c = 11.522(3) A, alpha = 63.67(2) degrees, beta = 71.24(2) degrees, gamma = 86.79(2) degrees, V = 1026(1) A3, Z = 2; 7.CH2Cl2, empirical formula C30H25Cl8N7O2Re2, crystal system triclinic, space group P1, a = 12.522(6) A, b = 12.857(8) A, c = 13.182(7) A, alpha = 67.75(4) degrees, beta = 88.30(4) degrees, gamma = 82.09(4) degrees, V = 1945(2) A3, Z = 2.
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PMID:Chemistry of the rhenium-azopyridine family: an oxo parent and derivatives thereof including a novel oxo-imido dimer. 1122 35

This report covers initial studies in the coaggregation of nickel (Ni2+) and lanthanide (Ln3+) metal ions to form complexes with interesting structural and magnetic properties. The tripodal amine phenol ligand H3tam (1,1,1-tris(((2-hydroxybenzyl)amino)methyl)ethane) is shown to be particularly accommodating with respect to the geometric constraints of both transition and lanthanide metal ions, forming isolable complexes with both of these ion types. In the solid-state structure of [Ni(H2tam)(CH3CN)]PF6.2.5CH3CN.0.5CH3OH (1), the Ni(II) center has a distorted octahedral geometry, with an N3O2 donor set from the [H2tam]- ligand and a coordinated solvent (acetonitrile) occupying the sixth site. The reaction of stoichiometric amounts of H3tam with the Ni(II) ion in the presence of lanthanide(III) ions provides [LnNi2(tam)2]+ cationic complexes which contain coaggregated metal ions. These complexes are isolable and have been characterized by a variety of analytical techniques, with mass spectrometry proving to be particularly diagnostic. The solid-state structures of [LaNi2(tam)2(CH3OH)1/2(CH3CH2OH)1/2(H2O)]ClO4.0.5CH3OH.0.5CH3CH2OH.4H2O (2), [DyNi2(tam)2(CH3OH)(H2O)]ClO4.CH3OH. H2O(6), and [YbNi2(tam)2(H2O)]ClO4.2.58H2O(9) have been determined. Each complex contains two octahedral Ni(II) ions, each of which is encapsulated by the ligand tam3- in an N3O3 coordination sphere; each [Ni(tam)]-unit caps the lanthanide(III) ion via bridging phenoxy oxygen donor atoms. In 2, La3+ is eight-coordinated, while in 6, Dy(III) is seven- (to "weakly eight-") coordinated, and Yb(III) in 9 has a six-coordination environment. The complexes are symmetrically different, 2 possessing C2 symmetry and 6 and 9 having C1 symmetry. Magnetic studies of 2, 6, and 9 indicate that antiferromagnetic exchange coupling between the Ni(II) and Ln(III) ions increases with decreasing ionic radius of Ln(III).
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PMID:Coaggregation of paramagnetic d- and f-block metal ions with a podand-framework amine phenol ligand. 1122 70

The activities of pyrroloquinoline quinone (PQQ), a coenzyme of methanol dehydrogenase and amine oxidase, and its reduced form pyrroloquinoline quinol (PQQH2) as an antioxidant have been measured in solution. PQQH2 was stable in the absence of oxygen but rapidly auto-oxidized to PQQ in the presence of oxygen in water. PQQH2 was stable in an aprotic solvent such as acetonitrile, even in air. PQQ did not exert appreciable antioxidant activity, whereas PQQH2 exerted higher reactivity than alpha-tocopherol toward galvinoxyl radical and peroxyl radical. PQQH2 acted as a potent antioxidant against the oxidation of methyl linoleate in acetonitrile induced by azo compound and produced a clear induction period, from which the apparent stoichiometric number was obtained as 1.1. PQQH2 reduced the alpha-tocopheroxyl radical and spared alpha-tocopherol in the oxidation of methyl linoleate. These results suggest that PQQH2 may act as a potent antioxidant, particularly in combination with alpha-tocopherol.
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PMID:Action of pyrroloquinolinequinol as an antioxidant against lipid peroxidation in solution. 1123 51

Binuclear [FeIIFeIII(BMDP)(O2CPh)3](BF4) (1) was obtained by treating an acetonitrile solution of the fully reduced [FeIIFeII(BMDP)(O2CPh)(MeOH)1.5(H2O)0.5](BF4)2 with 5 equiv of benzoate and then exposing the mixture to oxygen. Examination of [FeIIFeIII(BMDP)(O2CPh)3](BF4) by X-ray crystallography reveals the localized, mixed oxidation state nature of the cation in the solid state. 1H NMR and magnetic susceptibility data for the new complex are also reported. In the absence of dioxygen and other oxidants, treatment of FeIIFeII(BMDP)(O2CPh)(MeOH)1.5(H2O)0.5](BF4)2 with excess benzoate results in the formation of [FeIIFeII(BMDP)(O2CPh)2](BF4)2, which has also been characterized by X-ray diffraction.
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PMID:A mixed oxidation state, binuclear iron complex containing an unsymmetrically coordinating ligand. A ligand-induced switch in redox behavior. 1126 50

The potentially pentadentate, chiral ligand N,N-bis(1-propan-2-onyl oxime)-L-methionine N'-methylamide (L-MABO) shows remarkable versatility in its coordination chemistry with Ni(II) and Zn(II). In the crystal structure of the ZnCl2 complex of L-MABO, the ligand coordinates to the metal only through its three nitrogen donor groups (one amine and two oximes), with two chloride anions completing the distorted trigonal bipyramidal coordination sphere. In the NiCl2 complex, the three nitrogen donors and the thioether sulfur coordinate, along with two chlorides. The crystal structure of the Ni(NO3)2 complex contains two independent molecules, one of which coordinates the three nitrogens, the thioether sulfur, and the amide oxygen of L-MABO in addition to one nitrate anion. The second molecule coordinates the three nitrogen donors, the amide oxygen, one nitrate anion, and a methanol molecule. Thus, in only three crystal structures, L-MABO demonstrates its ability to provide N3, N3S, N3O, and N3OS donor sets. The thioether-bound complexes are unusual in that they have a predominantly nitrogen environment with a nickel-thioether bond that is not constrained by surrounding donor groups in a macrocyclic or linear polydentate motif. Comparison of the thioether-coordinated and methanol-coordinated molecules in the Ni(NO3) salt of L-MABO demonstrate the effect of the thioether bond on the relative "hardness" of the nickel. The electronic absorption and circular dichroism spectra of the aqueous solutions of the nickel complexes are interpreted in terms of a "descent in symmetry" model based on successive C3v and Cs distortions from octahedral geometry. These ligand field spectra indicate that in aqueous solution all ligand groups except for the three nitrogens of L-MABO are displaced by water. In acetonitrile, the non-nitrogen donors in the nitrate salt may also be displaced, while the chlorides remain coordinated.
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PMID:Structural and spectroscopic studies of the versatile coordination chemistry of the chiral ligand N,N-bis(1-propan-2-onyl oxime)-L-methionine N'-methylamide with Ni(II) and Zn(II). 1126 71

The photophysical and photochemical properties of N-phthaloyl-methionine (1), S-methyl-N-phthaloyl-cysteine methyl ester (2) and N-phthaloyltranexamic acid (3) were studied by time-resolved UV/Vis spectroscopy, using laser pulses at 248 or 308 nm. The quantum yield of fluorescence is low (phi(f)< 10(-2)) for 1-3 in fluid and glassy media, whereas that of phosphorescence is large (0.3-0.5) in ethanol at - 196 degrees C. The triplet properties were examined in several solvents, at room temperature and below. The spectra and decay kinetics are similar, but the population of the pi(pi*) triplet state, as measured by T-T absorption, is much lower for 1 and 2 than for 3 or N-methyltrimellitimide (5') at ambient temperatures. The quantum yield (phi(delta)) of singlet molecular oxygen O2(1deltag) formation is substantial for 3 and 5' in several air- or oxygen-saturated solvents at room temperature, but small for 2 and 1. The quantum yield of decomposition is substantial (0.2-0.5) for 3 and small (<0.05) for 2 and 1. It is postulated that photoinduced charge separation in the spectroscopically undetectable 3n,pi* state may account for the cyclization products of 1 and 2. In aqueous solution, this also applies for 3, whereas in organic solvents cyclization involves mainly the lower lying 3pi,(pi*) state. Triplet acetone, acetophenone and xanthone are quenched by 1-3 in acetonitrile; the rate constant is close to the diffusion-controlled limit, but smaller for benzophenone. While the energy transfer from the triplet ketone occurs for 3, a major contribution of electron transfer to the N-phthalimide derivative is suggested for 1 and 2, where the radical anion of benzophenone or 4-carboxybenzophenone is observed in alkaline aqueous solution.
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PMID:Time-resolved spectroscopy of sulfur- and carboxy-substituted N-alkylphthalimides. 1133 Sep 9

A cationic carotenoid derivative (GRP-carotenal) was synthesized by the reaction of Girard's reagent P and beta-apo-8'-carotenal. The singlet-oxygen quenching constants for GRP-carotenal were 1.3 +/- 0.1 x 10(10) and 1.0 +/- 0.1 x 10(10) M-1 s-1 in acetonitrile and in detergent micelles, respectively. Photosensitized damage to K562 leukemia cells from cis-di(4-sulfonatophenyl)diphenylporphine, hypericin and protoporphyrin IX was inhibited by GRP-carotenal under conditions where beta-apo-8'-carotenal, beta-carotene and crocetin were ineffective. The unique cytoprotective properties of GRP-carotenal, relative to the other carotenoids studied, could not be explained by the differences in the cell content of the various carotenoids or by the changes in the cell content of the photosensitizers used. Photosensitizer fluorescence from labeled K562 cells was reduced by GRP-carotenal but not by the other carotenoids studied. The novel photoprotective properties of GRP-carotenal may be due to its subcellular distribution. In photosensitizer-containing detergent micelles, novel properties of GRP-carotenal were not apparent. None of the carotenoids studied reduced photosensitizer fluorescence or singlet-oxygen generation. Singlet-oxygen quenching by GRP-carotenal and by beta-apo-8'-carotenal were roughly the same. Crocetin has a singlet-oxygen quenching constant that is about a factor of five lower. Singlet-oxygen quenching by beta-carotene was limited by its aggregation.
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PMID:Girard's reagent P derivative of beta-Apo-8'-carotenal: a potent photoprotective agent. 1133 29


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