Spectrophotometric and electrophoretic studies on character of interactions between iron(II)-(α-diimine) chelates and (anionic, neutral, cationic) micelles

Interactions between Fe(II) chelates with 1,10-phenanthroline (phen) or its derivatives: 5-nitro-1,10-phenanthroline (NO2phen), 4,7-diphenyl-1,10-phenanthroline (Ph2phen), 4,7-diphenyl-1,10-phenanthrolinedisulfonic acid, disodium salt (SO3Ph)2phen and surfactant micelles were investigated. By means of spectrophotometry it was proved, that solvent parameters (dielectric constant, ionic strength and ion-pair formation) did not influence the position of absorption λmax of MLCT band (metal-to-ligand charge transfer) transition of Fe(NN) chelates (NN=phen, NO2phen, Ph2phen, (SO3Ph)2phen). Shift in λmax of MLCT band of Fe(NN) chelates (NN=phen, NO2phen, Ph2phen) towards lower wavelength was obtained in anionic surfactant solution and exclusively for NN=Ph2phen in cationic surfactant solution. No shift in λmax of MLCT band of Fe(SO3Ph)2phen) chelate was noticed in all examined micellar media. It was indicated that both hydrophobic and electrostatic interactions between chelate and charged micelle influence the position of λmax of MLCT band. The former interaction is found to be responsible for the chelate positioning in micellar structure, under the actual micellar electrostatic potential and the latest one directly affects the position of λmax. The nature of the Fe(NN) chelate–micelle interaction was further investigated by the micellar ion-exchange mechanism using: Li+, Na+ and tetraalkylammonium (R4N+, R=C1–C4) salts, also exploiting some micellar effects (addition of C1–C5 alcohols, urine, effect of temperature and formation of mixed micelles). In order to explain the character of binding of Fe(NN) chelates to micelle additional measurements (liquid chromatography, capillary electrophoresis) were performed and the obtained data for ligands and their chelates (log Pow, distribution constant octanol/water and Kmw, binding constant) were examined to rationalize observed effects.