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Thermodynamic and Kinetic Aspects of the Binding Reaction of Molecular Oxygen on Co(II) Complexes in Aqueous Solution
No full textA short survey is given of the main characteristics of the reaction of uptake of molecular oxygen by biological dioxygen carriers. Co(II) complexes able to bind dioxygen are then examined in order to determine whether the type and features of the peroxocomplexes formed are related to the nature of the ligand and the solvent. The thermodynamic and kinetic data relative to the formation in aqueous solution of peroxocompounds starting from Co(II) complexes with ligands belonging to three families (open-chain, macrocyclic and macropolytopic) of saturated polyamines are also examined in greater detail
Thermodynamic studies on the addition of molecular oxygen to cobalt(II)-1,4,8,12-tetraazacyclopentadecane in aqueous solution at 25°C
No full textAqueous solutions containing Co2+ and the macrocyclic ligand 1,4,8,12-tetraazacyclopentadecane (L) are able to bind reversibly molecular oxygen to form the species Co2L2O24+ between pH 5 and 7. This species at pH greater than 8 is replaced by the complex Co2L2O2 (OH)22+ whose concentration in the solution increases to about pH 10.5. At pH greater than 10.5, Co(II) exists totally in this μ-peroxobisydroxo complex. Both the above mentioned oxygenated forms suffer a relatively slow irreversible oxidation to Co(III). From oxygen binding curves, approximate values of the equilibrium constants were calculated for the addition of oxygen to CoL2+ to form the μ-peroxo and the μ-peroxo-bishydroxo complexes. The enthalpies of formation of this latter complex starting from both Co2+ or CoL2+ have been obtained by means of calorimetric measurements. The effects of the size of the macrocyclic ligand on the affinity and the enthalpy of oxygen binding have been considered. © 1986 Plenum Publishing Corporation
Calorimetric Study on Oxygen Addition to Cobalt(II) Complexes with Tris-(2-aminoethyl)amine and 3,7-Diazanonane-1,9-diamine
No full textThrough spectrophotometric and potentiometric measurements it has been verified that in aerated aqueous solutions of CoII containing tris(2-aminoethyl)amine (tren) as ligand, the doubly bridged μ-peroxo-μ-hydroxo dicobalt ion [Co2L2(O2)(OH)]3+ (L = tren) is totally formed at pH > 6.5. In aerated aqueous solutions of CoII and 3,7-diazanonane-1,9-diamine (dadn) at pH 6.5 only the singly bridged μ-peroxo dicobalt ion [Co2L2(O2)]4+ (L = dadn) is present. This complex at higher pH adds OH- ions in its axial positions; at pH > 10.5 the singly bridged μ-peroxo-dihydroxo dicobalt ion [Co2L2(O2)(OH)2]2+ is totally formed. The singly bridged complex [Co2L2(O2)]4+, after several hours, converts irreversibly into the doubly bridged μ-peroxo-μ-hydroxo ion [Co2L2(O2)(OH)]3+, while the single bridged [Co2L2(O2)(OH)2]2+ ion slowly autoxidizes to CoIII. By means of calorimetric measurements, usually carried out at constant pH, the enthalpies of formation of [Co2L2(O2)]4+ and [Co2L2(O2)(OH)2]2+ (L = dadn) and [Co2L2(O2)(OH)]3+ (L = tren) have been obtained. These results are compared with the enthalpies relative to the oxygen addition to [Co(trien)]2+ ion (trien = triethylenetetra-amine), and the enthalpy effects, connected with the change from a linear amine (trien) to its branched isomer (tren) and from the sequence 5,5,5 (trien) to the sequence 5,6,5 (dadn) of the chelate rings, are discussed
Thermodynamic and kinetic studies on the addition of dioxygen to Co(II) complexes with open-chain saturated polyamines
No full textThe systems Co(II)/N,N'-bis(3-aminopropyl)ethylenediamine, NH2(CH2)3NH(CH2)2NH (CH2)3NH2 (3,2,3-TET) and Co(II)/N,N'-bis(3-aminopropyl)propylenediamine, NH2(CH2)3NH(CH2)3NH (CH2)3NH2 (3,3,3-TET), have been investigated in aqueous solutions at 25-degrees-C, both under anaerobic and aerobic conditions, by means of potentiometric, spectrophotometric, calorimetric and dioxygen measurements carried out over a wide range of pH, in some cases at variable temperature. Under anaerobic conditions, at ligand-to-cobalt molar ratio C(L)o/C(Co)o of 1 and cobalt concentrations C(Co)o > 5 x 10(-3) M, the formation of cobalt(II) complexes with 3,2,3-TET and with 3,3,3-TET is complete at pH > 8.5 and at pH > 10, respectively. Under aerobic conditions, in the pH range from 6.5 to 8, the monobridged dicobalt mu-peroxo monohydroxo 3,2,3-TET complex is suggested to be formed which, in about thirty minutes, converts extensively to the dibridged mu-peroxo mu-hydroxo (olate) species. When Co(II) is added to aerated solutions of 3,2,3-TET at pH > 10.5, only the monobridged dicobalt-mu-peroxo dihydroxo complex is formed. This complex may also be slowly produced by increasing the pH of solutions containing the dibridged olate species to a value higher than 10.5. The three dioxygen adducts are also obtained in aerated solutions of Co(II) and 3,3,3-TET at different pH's. The thermodynamic standard functions DELTAX(o) (X = G, H, S) for the formation of the Co(II) complexes in anaerobic conditions are reported; kinetic and thermodynamic data concerning the dioxygen addition reactions, the isomerization of the monobridged mu-peroxo monohydroxo complexes to the debridged olate form, the conversion of the dibridged olate complex into the monobridged dicobalt mu-peroxo dihydroxo complex, and the irreversible oxidation of the Co(II) dioxygen adducts to Co(III) complexes have been evaluated. Finally, a comprehensive analysis has been carried out of the thermodynamic and kinetic features exhibited by the reaction of addition of dioxygen to Co(II) complexes with open-chain saturated tetraamines with ethylenic and/or propylenic chains
Liquid-vapor equilibrium. Pyrrolidine-cyclohexane system
No full textA data table and correlation equations are presented for the binary Pyrrolidine-cyclohexane system, single-phase liq. in equil. with vapor, pure components liq. in equil. with vapor at 298.15 K
Liquid-vapor equilibrium. N-methylpiperidine-cyclohexane system
No full textA data table and correlation equations are presented for the binary N-methylpiperidine-cyclohexane system, single-phase liq. in equil. with vapor, pure components liq. in equil. with vapor at 298.15 K
Excess enthalpy. Oxane-cyclohexane system
No full textA data table and a correlation equation are presented for the excess enthalpies of the oxane-cyclohexane system, single-phase, both components liq. at 298.15 K
Excess enthalpy. Pyrrolidine-cyclohexane system
No full textA data table and a correlation equation are presented for the excess enthalpies of the pyrrolidine-cyclohexane system, single-phase, both components liq. at 298.15 K
Excess Gibbs energy. Azetidine-cyclohexane system
No full textA data table and a correlation equation are presented for the excess free energy of the azetidine-cyclohexane system at 298.15 K
Excess Gibbs energy. Aziridine-cyclohexane system
No full textA data table and a correlation equation are presented for the excess free energy of the aziridine-cyclohexane system at 298.15 K
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