Shift in pKa of 1,10-Phenanthroline in TBAB and PEG-400 Micellar Media: A Potentiometric Study

Abstract

The acid-base equilibrium of 1,10-phenanthroline (1,10-phen) in the presence of polyethylene glycol 400 (PEG-400, non-ionic) and tetrabutylammonium bromide (TBAB, ionic) micellar media has been studied by Calvin-Wilson titration technique at different mole fractions (0.5%-2.5%) of PEG-400 and TBAB micellar solutions at an ionic strength of 0.16 mol dm −3 NaCl and at a temperature of 298 K. The pH metric data were subjected to SCPHD program to obtain correction factor and K w which were given as initial inputs for MINIQUAD75 program to refine protonation constants. HySS program was then used to generate the species distribution diagrams versus pH using the results obtained from the MINIQUAD75 program and SIM run data. The difference in values of protonation constants in aqueous medium (logβ 1 = 4.93 & logβ 2 = 6.22) and in the micellar media (PEG-400, logβ 1 = 4.89 & logβ 2 = 5.91 and TBAB, logβ 1 = 4.84 & logβ 2 = 5.73) is attributed to different intrinsic solvent characteristics of micelles. In case of ionic surfactants, the electrostatic micellar surface is an additional contributing factor.

Electrometric Investigation of the Nature and Stability of Mixed Ligand Complexes of L-Ornithine and 1,10-Phenanthroline With Some Essential Metal Ions in Aqua-TBAB or PEG-400 Surfactant

“…For a reliable determination of stability constants corresponding to mixed ligand model complexes, pooled data re nement of all the experimental trial using MINIQUAD75 computer program was chosen. The results of the free acid correction factor, values of Kw, protonation constants of the ligands [22] and binary M-L complex constants [26] were xed and used as initial imputes in the analysis of the mixed ligand complexes using MINIQUAD75 program [33][34] with inbuilt statistical parameters of chemical model re nement tools.…”

“…1,10-Phenanthroline (Phen) is bidentate hetrocyclic ligand having two electron donor N-atoms to the vacant shell of transition metal ions [19,20]. Studies have also revealed that Phen forms both binary and mixed ligand complexes with a number of metal ions in wide pH ranges [6,[19][20][21][22]. It is capable of forming stable metal complexes of even lower oxidation states [10,23,24] in mixed ligand system.…”

“…For example, copper complexes of Phen inhibit the proteasome activity housed into tumor cells [25]. Phen complexes of metals were not only synthesized in aqueous solvent, but also in aqua-organic solvents and used as potent photodynamic herbicide modulators [6,19,22]. L-Ornithine (Orn), a tridentate ligand having two associable amino protons and one dissociable carboxylate proton, is capable of forming stable non-protonated metal-ligand complexes with many metal ions in various solvents [26].…”

“…Phen as bidentate and Orn as tridentate ligands play prominent roles in maintaining the stability of complexes in various solvents [6,21]. Despite the availability of information on the effect of aqua-surfactants on the stability of binary complexes [19,22,26], data related to mixed ligand complexes of Phen and Orn with essential metals in aqua-surfactant medium is scarce. The aim of this study was, therefore, to determine the stabilities of the mixed ligand complexes of some essential metal ions (Co 2+ , Ni 2+ , Cu 2+ ) with Phen and Orn in aqua-TBAB and PEG-400 surfactant media with an eye on the prediction of the bioavailability the metal complexes.…”

Mononuclear Binary Complex Formation Equilibria of L-Ornithine with Biologically Essential Metals in TBAB Micellar Media

“…nature and extent of formation of species as a function of pH can be obtained from speciation study [7,8].…”