Laura Galicia

Spectroscopy study of 5-amino-1,10-phenanthroline

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.

Diffusion coefficients and electrode kinetic parameters of different Fe(III)-sulfate complexes

Abstract The kinetics of the Fe(III)/Fe(II) redox reaction were studied in solutions with different total sulfate concentration in all forms (pSO′ 4 ) and pH values. The variation found in the values of the kinetic parameters and diffusion coefficient is explained through the influence of the different Fe(III)-sulfate complexes predominant in the solution: Fe(SO 4 ) 2 − , FeSO 4 + and FeHSO 4 2+ .

Evidence of Ternary Inclusion Complexes Formation Using Factorial Design and Determination of Their Formation Constant

Evidence of the interaction among the [PbAc]+ and[PbEDTA]-2 with the β-cyclodextrin (β-CD)is shown, using a 24 factorial design. The factors used werethe [Pb(II)], [β-CD], [Ac-] and [EDTA] concentrationsat pH = 6.2. The statistical results indicate that the changes inchemical response for these species are associated to theinteraction among these factors. Spectrophotometric andelectrochemical studies were undertaken to assess the interactions.The equilibrium constants for inclusion complexes were determinedFor β-CD-[PbAc]+ and β-CD-[PbEDTA]-2.

Electronic structure and conformation of aniline and meta-chloroaniline dimers

Poly(aniline) is a subject of considerable scientific and technological interest. Its homologs such as poly(m-chloroaniline) potentially offer similar physical-chemical properties. In this work we present a comparative theoretical study between aniline and the m-chloroaniline species at several levels of theory. To envisage the possible mechanism of polymerization, we have obtained geometries and electronic structures for the monomers and dimers as well as the corresponding cations and dications. Based on the monomer-optimized geometries, atomic charges, bond orders, and spin densities, a head-to-tail coupling in the electrochemical polymerization is suggested. We have also calculated band gaps and ionization potentials. For the cationic dimers of aniline and m-chloroaniline, the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy difference has a smaller value, and oxidation at specific sites may be observed.

Pourbaix-type diagram of Fe(III) and Fe(II) phenanthroline complexes

Abstract A potential ( E h )—pH diagram has been derived for the Fe(III)—Fe(II)—1, 10-phenanthroline system in sulphuric acid medium. The stability of [Fe(III)—1, 10-phenanthroline], [Fe(II)—1, 10-phenanthroline] [Fe(III)—sulphate] and [Fe(II)—sulphate] complexes discussed. With the aid of this diagram, several experimental results obtained here and others published elsewhere are analysed.

Diagramme potentiel-pH pour le système Fe(III)-Fe(II)/H2O en présence de 1,10 phénanthroline

Resume Le diagramme potential (Eh—pH pour le systeme Fe(III)Fe(II)/H2O a ete construit pour une concentration de 1,10 phenanthroline total de 10−1 mole l−1 et a 298 K. La stabilite des complexes [Fe(III)—1,10 phenanthroline] et [Fe(II)—1,10 phenanthroline] en milieu acide est discutee.

Electrocatalytic effect of iron sulfates on oxygen reduction. Influence of the solvation sphere of the mediator

The redox catalysis of oxygen reduction was performed on a platinum rotating disk electrode. The Fe(III)/Fe(II)/H2SO4 system at different pHs was used as a MEDIATOR. The catalytic effect of mediator was directly related to the solvation sphere of Fe(III) and Fe(II). Only the redox couple FeHSO42+/FeHSO4+ (pH<0) showed a catalytic effect on oxygen reduction.

Electrocatalytic effect of phenanthroline iron complexes on oxygen reduction in sulfuric acid media

The study of oxygen reduction on a platinum rotating disk was performed at different pHs in 1 M H2SO4. An increase in the velocity of this reaction with the addition of 2×10−3M Fe(II) and 0.1 M 1,10-phenanthroline was observed. This increase depends on the solution pH, i.e. at pH<0.5, it is about 100-fold, whereas for pH>0.5, it is greater than by a factor of 600. This change at pH=0.5 can be explained by a change in the coordination sphere of electrogenerated Fe(II). The complex species Fe(II)−SO4 at pH<0.5 changes to [Fephen3]2+ at pH>0.5.AbstractИсследования восстановления кислорода на платиновом вращающемся диске проводили при различных pH в 1M H2SO4. При добавлении 2·10−3M Fe(II) и 0,1M 1,10-фенантролина скорость этой реакции повьшается. Это повышение зависит от pH раствора, а именно при pH<0,5 оно равно приблизительно 100, а при pH>0,5 уже возрастает более чем в 600 раз. Этот перелом при pH=0,5 объясняют изменением координационной сферы электрогенерированного Fe(II). Комплекс Fe(II)−SO4 при pH<0,5 изменяется до [Fephen3]2+ при pH>0,5.