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Metal ion coordination chemistry of medicinal interest Saatchi, Katayoun (Seraji-Bozorgzad)

Abstract

Basic coordination chemistry of metal ions of medicinal interest is investigated and reported. The syntheses of vanadium complexes are reported using the naturally occurring ligating moieties isomaltolate (ima⁻) and allomaltolate (ama⁻), as well as a newly synthesized, potentially tetradentate diaminodipyrone [en(ama)₂]²⁻. Complete characterization of the resulting compounds (trans-VO(ima)₂(H₂O), VO(ama)₂, V(ima)₃, V(ama)₃ and VO(en(ama)₂), including X-ray crystallography analyses for trans- VO(ima)₂(H₂O) and V(ima)₃, are presented herein. The crystal structure of trans- VO(ima)₂(H₂O) shows a coordinated water trans to vanadyl. Potentiometric titrations (25°C, 1= 0.16 M NaCl) were used to measure stability constants in the V(IV)- ima⁻, V(IV)- ama⁻ and V(V)- ama⁻ systems; these data were compared to previous data collected on the V-maltolate system. In vivo efficacy of these compounds to normalize the blood glucose levels of STZ diabetic rats was tested; all but VO(en(ama)₂) produced significant decreases in plasma glucose levels. The results were compared to those of the benchmark compound BMOV (VO(ma)₂, bis(maltolato)oxovanadium(IV)), a proven insulin-enhancing agent. Rhenium complexation to [en(ama)₂]²⁻ is also investigated. The resulting complex ReO(en(ama)₂)Cl was characterized by a variety of techniques including ID and 2D NMR spectroscopy. These results clearly point to asymmetric binding of the ligand to the metal centre, leaving O = Re - CI in a cis configuration. Novel complexes of Ga and In were synthesized with a group of hetero donor phosphinophenolate ligands (PO⁻, (orthohydroxophenyl)diphenylphosphine; MePO⁻, (2- hydroxo-5-methylphenyl)diphenylphosphine). The two metal ions interestingly show diversity in their chelation to phosphinophenolates. The RPO⁻ (R = H, Me) heterodonor ligand binds in a bidentate fashion through both the hard and the soft donor atoms to In; whereas, it only chelates Ga through the hard oxygen donor. Electrochemical synthesis proved to be a practical synthetic approach. In₂(PO)₃Cl₃, In(PO)₃ and In(MePO)₃ were synthesized by electrolysis. [In(MePO)(H₂O)Cl₂]₂ and Ga(HPO)Cl₃ were synthesized using MCI₃ (M = In and Ga respectively). Both dimetallic indium complexes, [In(MePO)(H₂O)Cl₂]₂ and In₂(PO)₃Cl₃, show the phenolate oxygens bridging between the two metal ions. All four In atoms are in a distorted octahedral geometry in both complexes with the former having a coordination sphere of PO₃CI₂ for both indium metal ions and the latter showing a coordination sphere of PO₃CI₂ for one indium and P₂O₃CI for the other. Ga(HPO)Cl₃ is a zwitterionic complex, with Ga having a OCI₃ coordination core. All these complexes were fully characterized including X-ray crystallography.

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