Speciation of ternary complexes of lead(II), cadmium(II) and mercury(II) with L-dopa and phenanthroline in propanediol-water mixtures

Abstract

The formation constants of ternary complexes of title systems have been determined pH-metrically in biologically relevant conditions at an ionic strength of 0.16 mol dm -3 and 303 K. The overall stability constants have been evaluated using MINIQUAD75 computer program. The complexation equilibria have been derived on the basis of species distribution diagram. In the present study L-Dopa and 1, 10-phenanthroline are found to be compatible ligands, proving greater stability of ternary complexes as compared to binary ones. The trend in variation of stability constants with change in dielectric constant of medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of the species with pH at different compositions of propanediol-water mixtures are also presented. The factors responsible for the compatibility of both the ligands have also been discussed.

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

“…A combined glass electrode of aqueous range conjugated with Metrohm 877 Titrino plus Auto-titrator (Switzerland, readability 0.001) was used to carry out electrometric titrations. Data acquisition was carried out at an ionic strength of 0.16 mol dm − 3 and temperature of 298 K. The steady ow of puri ed nitrogen gas was applied through the titration mixture [21,26,31]. Periodic calibration of the electrode was done to ensure reliable measurement under stable and reproducible response.…”

“…The rigid framework of Phen and the relative stability of the ve member L-ornithine ring complexes with central metal ion could also be considered as contributors to the stability of the synthesized complexes. Considering these, the following most likely octahedral structures [21], corresponding to the MLX, MLXH, ML 2 X and MLX 2 H chemical models, are proposed for all the metal ions but Cu(II) complexes have also Jahn-Teller distorted structure [26] (Fig. 3).…”

“…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.…”

“…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.…”

Study on mixed ligand complexes of Pb(II) with EDTA and dietary ligands to investigate the applicability on chelation therapy

“…Though quantitative studies and stability constants of mixed ligand complexes of Pb(II) with some ligands have been reported (Gupta and Sharma,1982;Joshaghani et al, 2008;Padmaja & Rao, 2012;Thanavelan et al, 2014), the information related to the quantitative investigations on mixed ligand complexes of Pb(II) with biologically important molecules is scarce, especially under the physiological conditions (Chandrathilaka et al, 2013). Thus, the present work was mainly undertaken to study the stability of mixed ligand complexes of EDTA with biologically significant molecules entering into our body via common drugs and food, as an attempt to introduce more effective and less toxic mixed ligand systems for the use in chelation therapy of Pb(II).…”