Radiolysis of aqueous solutions of cobalt(II) and cobalt(III)

Radiolysis of aqueous solution of di and trivalent cobalt with 1:2 (bis) carboxymethylaminodiethyltetraacetic acid (EGTA) was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed. It has been shown that the degradation at the ligand of the chelate is due to OH only.     

Solvent and chelation effects on the photoreduction of cobalt(III)–amine complexes in aqueous–organic solvent media

The photoreduction of trans-[Co(NH₃)₄Cl₂]⁺, trans-[Co(en)₂Cl₂]⁺, [Co(dien)Cl₃], [Co(trien)Cl₂]⁺, and [Co(tetren)Cl]²⁺, ions has been studied using a low pressure Hg vapour lamp as light source (254 nm) in aqueous–organic solvents [0–30% (v/v) MeOH or 1,4-dioxane]. Quantum yields for Co^II production by redox decomposition have been determined in all the cases, and increase considerably with the increase in concentration of MeOH or 1,4-dioxane in the binary solvent mixtures under investigation. A plot of log(quantum yield) versus the Grunwald–Winstein Parameter, Y, which is a measure of solvent ionizing power, shows that a different blend of general and specific solvent interacts with the solute. This kind of specific solvent interaction on the reactant/excited state has been analysed using multiple regression: viz. Krygowski–Fawcett and Kamlet–Taft equations. Reasons for the difference in reactivity with chelation are also discussed.     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs [Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of [Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.     

Gold(III) amine complexes in aqueous alkali solutions

The gold(III) 1,3-diaminopropane complex [Au(1,3-pn)(1,3-pn-H)]Cl₂ has been synthesized. Its dissociation constant has been determined: Au(1,3-pn)₂³⁺ = Au(1,3-pn-H)²⁺ + H⁺, logK _a1 = −7.03 ± 0.05 (I = 0.1 mol/L NaClO₄). Considerable spectral changes are observed for strong alkali solutions (pH 11–14) containing the monoamido forms of the gold(III) ethylenediamine, 1,3-diaminopropane, and diethylenetriamine complexes (Au(en)(en-H)²⁺, Au(1,3-pn)(1,3-pn-H)²⁺, Au(dien-H)OH⁺). These changes are attributed to the formation of the diamido species Au(en-H)₂⁺, Au(1,3-pn-H)₂⁺, and Au(dien-2H)OH⁰. The dissociation constants of the monoamido complexes have been determined: Au(en)(en-H)²⁺ (logK _a2 = −10.9 ± 0.1 at I = 0.001–0.01 mol/L NaCl); Au(1,3-pn)(1,3-pn-H)²⁺ (logK _a2 = −11.3 ± 0.1 at I = 0.1 mol/L NaCl); Au(dien-H)OH⁺ (logK _a2 = −12.4 ± 0.1 at I = 0.1 mol/L NaCl).     

Convolution-deconvolution cyclic voltammetric equilibria study on cadmium(II)-L-histidinate in aqueous solutions

POLAG computer programme was employed for processing convoluted-deconvoluted cyclic voltammetric data to study cadmium(II)-L-histidinate system. This was performed in 0.1 mol/dm(3) NAClO(4) aqueous solution at different pH's at 298K. The results show that the reduction of cadmium(II) and its complexes proceeds via a reversible and diffusion-controlled wave of two electrons at the entire range of pH. The system was studied at two ranges of pH (6.73-7.44 and 8.53-8.92). It was evident that the system at the first range of pH is well described by the presence of a mixture of binary complexes, [Cd(HisO.H)], [Cd(HisO.H(2))(2)] and a ternary one [Cd(HisO.H)(HisO.H(2))]. For the second pH range, it was revealed that the most likely model corresponds to the presence of a mixture of [Cd(HisO)(2)] and [Cd(OH)] species. The overall stability constants were computed. The structure of the detected complexes was discussed on the basis of ligating sites of histidine.     

Enthalpy of solution of CO2 in aqueous solutions of 2-amino-2-methyl-1-propanol

The enthalpies of solution of CO₂ in aqueous solution of 2-amino-2-methyl-1-propanol (AMP) 15 wt% and 30 wt% were measured at 322.5 K and pressures range from (0.2 to 5) MPa using a flow calorimetric technique. The gas solubilities were simultaneously determined from the calorimetric data. The solubilities were compared to available literature values obtained by direct measurements. The experimental enthalpies of solution were compared to the values derived from the literature vapor liquid equilibrium data. This work provides calorimetric data that will be used later for the development of a thermodynamic model to predict both solubilities and enthalpies of solution of acid gases in aqueous amine solutions.     

Density functional theory study on carbon dioxide absorption into aqueous solutions of 2-amino-2-methyl-1-propanol using a continuum solvation model

We used density functional theory (DFT) calculations with the latest continuum solvation model (SMD/IEF-PCM) to determine the mechanism of CO(2) absorption into aqueous solutions of 2-amino-2-methyl-1-propanol (AMP). Possible absorption process reactions were investigated by transition-state optimization and intrinsic reaction coordinate (IRC) calculations in the aqueous solution at the SMD/IEF-PCM/B3LYP/6-31G(d) and SMD/IEF-PCM/B3LYP/6-311++G(d,p) levels of theory to determine the absorption pathways. We show that the carbamate anion forms by a two-step reaction via a zwitterion intermediate, and this occurs faster than the formation of the bicarbonate anion. However, we also predict that the carbamate readily decomposes by a reverse reaction rather than by hydrolysis. As a result, the final product is dominated by the thermodynamically stable bicarbonate anion that forms from AMP, H(2)O, and CO(2) in a single-step termolecular reaction.     

Mechanism of hexacyanoferrate(III) oxidation of 1-propanol and 2-propanol in aqueous alkaline medium

Kinetic studies of the hexacyanoferrate(III) oxidation of 1-propanol and 2-propanol have been carried out in aqueous alkaline medium. The reaction velocity is of first order with respect to alcohols, alkali and hexacyanoferrate(III). The kinetic data suggest that the oxidation involves the formation of an anion of the substrate undergoes oxidation with hexacyanoferrate(III) via charge transfer process. The free radical thus produced is further oxidised to form the final products.

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Der Mechanismus der Hexacyanoferrat(III)-Oxidation von 1-Propanol und 2-Propanol in alkalischem, wäßrigen Milieu

Zusammenfassung Kinetische Studien ergaben für die Oxidation Abhängigkeiten erster Ordnung sowohl für die Alkohole, als auch für OH- und Hexacyanoferrat(III). Die Daten legen nahe, daß das Substrat-Anion zunächst unter einfacher Ladungsübertragung oxidiert wird, wobei das gebildete freie Radikal weiterer Oxidation zu den endgültigen Reaktionsprodukten unterliegt.

     

Ion-pair interactions of lanthanide(III) complexes in aqueous solutions

The formation of ion-pair adducts between the cationic complex La(THP)3+ (THP = 1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane) and the anionic complexes Tm(DOTA)- (DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetate), Tm(DTPA)2- (DTPA = diethylenetriamine-N,N,N',N",N"-pentaacetate), Tm(TTHA)3- (TTHA = triethylenetetraamine-N,N,N',N",N"',N"'-hexaacetate), and Tm(DOTP)5- (DOTP = 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetrakis(methylenephosphonate)) is examined by 13C NMR spectroscopy. The induced 13C shifts of the La(THP)3+ complex are followed by titration of the Tm(III) complexes of DOTA, DTPA, and TTHA at pH 7. From these data, the stability constants are calculated to be beta 1 = 64 M-1 (1:1), beta 1 = 296 M-1 (1:1), and beta 2 = 26,000 M-2 (2:1) for the ion pairs of La(THP)3+, with Tm(DOTA)-, Tm(DTPA)2-, and Tm(TTHA)3-, respectively. The La(THP)3+,Tm(DOTP)5- system elicits chiral resolution of the rapidly interconverting Tm(DOTP)5- isomers.     

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

Reactions of e_aq⁻, H-atoms, OH, (CH₃)₂COH, and CO₂⁻ radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.     

Gas solubility of CO2 in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol

Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO₂ against its mole ratio α (mol CO₂/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO₂ in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO₂ at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO₂ has been calculated from the experimental solubility data.     

Kinetics of aquation of cis-aquabromo-bis(ethylenediamine) complexes of cobalt(III) and chromium(III) in binary aqueous mixtures

Summary The kinetics of aquation of cis-[Co(en)₂(H₂O)Br]²⁺ and cis-[Cr(en)₂(H₂O)Br]²⁺ (en = ethylenediamine) were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH. The values of transfer functions corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from solubilities of the complex salt. Analysis of the solvent effect confirmed a common I_d mechanism for the aquation of the Co^III and Cr^III complexes.     

Redox reactions of cobalt(III) complexes in aqueous organic mixtures effects: of single ion assumptions on initial state-transition state solvation analysis

Summary Solvent effects on the kinetics of redox reactions of cobalt(III) complexes were assessed in aqueous mixtures containing methanol,t-butanol, and acetone according to three different extra-thermodynamic assumptions —Wells, TATB, and TPTB^** — at 298.2 K. The calculated values of transfer functions of individual ions and initial and transition states were often markedly different. In some cases these differences led to different conclusions in the evaluation of the role of solvation in the reactions investigated.     

Fluorescence of lanthanide(III) complexes with aminopolyacetic acids in aqueous solutions

The fluorescence of Eu(III), Gd(III), Tb(III) and Dy(III) ions complexed with aminopolyacetic acids was investigated. The influence of temperature and the dimensions of the ligand molecules and of their electric charge on the intensity of the emission bands is discussed as well as the ratio of the hypersensitive (forbidden) band to the allowed band intensity. On the basis of the fluorescence measurements a simple theoretical model is discussed and certain generalizations concerning the fluorescence of the lanthanides group are derived.

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Fluoreszenz von Lanthaniden(III)-Komplexen mit Aminopolyessigsäuren in wäßrigen Lösungen

Zusammenfassung Die Fluoreszenz von mit Aminopolyessigsäuren komplexierten Eu(III), Gd(III), Tb(III) und Dy(III) Ionen wurde untersucht. Der Einfluß von Temperatur und Größe der Ligandenmoleküle und von deren elektrischer Ladung auf die Intensität der Emissionsbanden wird diskutiert, ebenso das Verhältnis der Intensitäten der hyperempfindlichen und erlaubten Banden. Auf der Basis von Fluoreszenzmessungen wird ein einfaches theoretisches Modell diskutiert und Verallgemeinerungen betreffend der Fluoreszenz der Lanthanidengruppe getroffen.

     

Solvent and substituent effects on the photoreduction of cobalt(III)-aryl amine complexes in an aquo-organic solvent medium

The photoreduction of a series of Co^III complex ions, [Coen₂Cl(RC₆H₄NH₂)]²⁺ where R = p-OMe, p-OEt, p-Me, m-Me, H, and p-F, has been studied using a low pressure Hg vapour lamp as the light source (254 nm) in an aquo-organic solvent [15–40% (v/v) 2-methylpropan-2-ol] medium. Quantum yields for Co^II production by redox decomposition have been determined in all cases. The quantum yield increases considerably with the increase in concentration of the organic co-solvent in the binary solvent mixture under investigation. The Hammett correlation is linear, affording negative reaction constants, which indicate that the excited state is electron deficient. Correlation of the experimental results with Kamlet–Taft's solvatochromic parameters indicates that the solvent hydrogen bond donor acidity plays a dominant role in governing the reactivity.     

Terbium (III) chelate complexes as fluorescence energy transfer donor in the determination of formaldehyde in aqueous solutions

The sensitized fluorescence intensity of the terbium (III) ion can be notably enhanced in the presence of sodium hexametaphosphate (SHMP). Based on this, water-soluble Tb-SHMP chelate complexes were synthesized in aqueous solutions, and characterized by spectrofluorometry. 6-Mercapto-5-triazole[4,3-b]-S-tetrazine was generated by the quantitative reaction of HCHO with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole under alkaline conditions at room temperature. The spectral overlap between the emission of Tb-SHMP chelate complexes and absorption of 6-mercapto-5-triazole[4,3-b]-S-tetrazine meets the prerequisite for fluorescence energy transfer. Based on this, a novel efficient fluorescence energy transfer system between Tb-SHMP chelate complexes as donor and 6-mercapto-5-triazole[4,3-b]-S-tetrazine as acceptor was developed for the determination of HCHO in aqueous solutions. Under the optimal experimental conditions, this method is capable of detecting HCHO concentrations from 2.06×10(-5) to 6.18×10(-3) mg mL(-1) and the limit of detection was 7.11×10(-6) mg mL(-1). Compared with other general methods for the determination of HCHO, the proposed method improved the sensitivity and selectivity. Moreover, the proposed method was successfully applied to the determination of HCHO in water samples.