Thermodynamic Study of Oxidovanadium(IV) with Kojic Acid Derivatives: A Multi-Technique Approach

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VIVO2+, constitute the precondition for the development of new insulin-mimetic and anticancer compounds. In the present work, we examined the VIVO2+ complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VIVO2+ ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Deferoxamine B: A Natural, Excellent and Versatile Metal Chelator

Deferoxamine B is an outstanding molecule which has been widely studied in the past decade for its ability to bind iron and many other metal ions. The versatility of this metal chelator makes it suitable for a number of medicinal and analytical applications, from the well-known iron chelation therapy to the most recent use in sensor devices. The three bidentate hydroxamic functional groups of deferoxamine B are the centerpiece of its metal binding ability, which allows the formation of stable complexes with many transition, lanthanoid and actinoid metal ions. In addition to the ferric ion, in fact, more than 20 different metal complexes of deferoxamine b have been characterized in terms of their chemical speciation in solution. In addition, the availability of a terminal amino group, most often not involved in complexation, opens the way to deferoxamine B modification and functionalization. This review aims to collect and summarize the available data concerning the complex-formation equilibria in solutions of deferoxamine B with different metal ions. A general overview of the progress of its applications over the past decade is also discussed, including the treatment of iron overload-associated diseases, its clinical use against cancer and neurodegenerative disorders and its role as a diagnostic tool.

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

Investigation of mononuclear complex of L-ornithine in tetrabutylammonium bromide (TBAB, a cationinc surfactant) micelle media has been made pH metrically at constant temperature and ionic strength in different percentage of micellar solutions (0.0-2.5 %). Stability constants and best fit model for metal complexes were obtained by MINIQUAD75 computer program on the basis of the analysis of residues and other statistical parameters. Accordingly, ML, ML2, MLH and ML2H for both Co(II) and Cu(II) and ML2 and ML2H for Ni(II) mononuclear chemical models were obtained. The stabilization/destabilization equilibria of the binary system for the model species with percentage composition of micelles at constant ionic strength and temperature could be attributed to dielectric constant and other intrinsic interaction properties of tetrabutylammonium bromide micelle with ligands and metal ions. The plot of percentage of species against pH values has been generated from SIM refined data using origin85 software.

A Potentiometric Studies of Ternary Complexes of Co(II), Ni(II), Cu(II) and Zn(II) with Ethylenediaamine-N,N,N1,N1-Tetraacetic Acid and Melonic Acid

Potentiometeric investigation on the complex formation equilibria involving Co(II), Ni(II), Cu(II) & Zn(II) with ethylenediaamine-N,N,N1,N1-tetraacetic acid and melonic acid have been made in solution at three different temps viz. (150, 350, 450C). Important thermodynamic parameters namely, change in Gibb’s free energy (DG0), change in enthalpy (DH0) and change in entropy (DS0) and stability constant have been determined potentiometrically at ionic strength of 0.1 M (KNO3).

Aminobisphosphonates based on cyclohexane backbone as coordinating agents for metal ions. Thermodynamic, spectroscopic and biological studies

Complex formation equilibria of calcium, magnesium, copper and nickel with amino-bisphosphonic ligands are described, together with a speciation study along with calorimetric outcome and cytotoxicity characteristics.