Elimination of phosphathes by ion-exchange in the systematic analysis of cations

J. Chem. Educ

FORMATION OF COBALT(III) COMPOUNDS WITH SOME PEPTIDES

The complexes formed from cobalt(III) and dipeptides such as glycylglycine, glycylaspartic acid, glycylthreonine, glycyltyrosine and glycylproline were studied. The formation process of cobalt(III)-dipeptide species was investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The formation of the cobalt(III) complexes occurs through an oxointermediate, as shown by the spectral behaviour, and depends on the pH of the solutions. Complex stoichiometries, molar absorptivities and concentration ratios at the equilibrium of the cobalt(III)- dipeptide complexes were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes

FORMATION AND DISSOCIATION EQUILIBRIA OF INTERMEDIATE SPECIES IN THE OXIDATION OF COBALT(II)-DIPEPTIDE COMPLEXES

The oxidation of various cobalt(II)-dipeptide complexes in the presence of both molecular oxygen and hydrogen peroxide is examined. The nature of the oxidant exercises a marked influence on the reaction path. The oxointermediate species formed apparently possesses different structures, depending on the oxidant. Moreover, when molecular oxygen is employed, the inertness of the resulting cobalt(III)-dipeptide complexes is much higher, suggesting a different degree of protonation. The effect of the ligand structure on the oxidative process is considered; the reaction rate is found to be strongly influenced by the hydrophobicity of the substituent group and by the presence of amidic hydrogen

Complex formation between copper(II) and several b-amino alcohols in aqueous solution: a potentiometric and spectrophotometric study

The behaviour of solutions containing copper(II) and several b-amino alcohols was examined by potentiometric and spectrophotometric techniques. The potentiometric results at 258C and KNO 0.5 M, indicates in all the examined systems the formation of four 3 main species with M:L:H stoichiometry 1:1:0, 1:1:21, 1:2:21 and 1:2:22, respectively. The deprotonated species have been demonstrated to be alkoxo chelates formed by the loss of alcoholic hydrogen. No evidence of formation of ternary hydroxy or polynuclear complexes have been found in the examined experimental conditions, and the absence of dimeric alkoxo-bridged species have been confirmed by the analysis of the UV charge-transfer bands. The dependence of complex stability on the ligand structure is discussed with particular regard to the influence exherted by the number of hydroxyl groups. Also, the comparison with the behaviour of other metal ions is discussed