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Coordination chemistry : basics to bioactive molecules

University of British Columbia

The stability constants of bis(maltolato)oxovanadium(IV) (BMOV, or VO(ma)₂) and bis(kojato)oxovanadium(IV) (BKOV, or VO(ka)₂) at 25 °C (0.15 M NaCl) were measured. The former was found to be slightly more stable that the latter system. Since BMOV exhibits favourable chemical and insulin-enhancing properties in streptozotocin(STZ)-diabetic rats, the biodistributions of BMOV and its parent compound, vanadyl sulfate (VOSO₄ or VS), using ⁴⁸V as a tracer via oral or intraperitoneal administration in rats were studied. The data were analyzed using compartmental modeling. The results showed that tissue uptake of ⁴⁸V from an oral dose of ⁴⁸V-BMOV was approximately two to three times greater than that from an equivalent dose of ⁴⁸VS. This is consistent with previous studies in which a two to three times increased acute glucose-lowering potency was seen with BMOV compared with VS. The reactions of potentially hexadentate H₂bbpen (N,N'-bis(2-hydroxybenzyl)-N,N'- bis(2-methylpyridyl)ethylenediamine, H₂LI), H₂Clbbpen (N,N'-bis(5-chloro-2- hydroxybenzyl)-N,N'-bis(2-methylpyridyl)ethylenediamine, H₂L₂), and H₂Brbbpen (N,N'- bis(5-bromo-2-hydroxybenzyl)-N,N' -bis(2-methylpyridyl)ethylenediamine, H₂L₃) with Ln(III) ions in the presence of a base in methanol resulted in three types of complex: neutral mononuclear ([LnL(N0₃)]), monocationic dinuclear ([Ln₂L₂ (N0₃)]+) and monocationic trinuclear ([Ln₃L₂ (X)n(CH₃OH)]+), where X = bridging (CH₃COO⁻) and bidentate ligands (NO₃⁻, CH₃COO⁻, or CIO₄⁻) and n is 4. The formation of a complex depends on the base (hydroxide or acetate) and the size of the respective Ln(III) ion. All complexes were characterized by infrared spectroscopy, mass spectrometry, elemental analyses, and in some cases, by X-ray diffraction studies. The [LnL(N0₃)] or [Ln₂L₂ (N0₃)]+ complexes can be converted to [Ln₃L₂ (X)n(CH₃0H)]+ complexes by addition of one equivalent of a Ln(III) salt, and 2-3 equivalents of sodium acetate in methanol. The trinuclear complexes were found to be surprisingly stable, evinced by the presence of the intact monocationic high molecular weight parent peaks ([Ln₃L₂ (X)n]+) in the mass spectra of all trinuclear complexes, and from the ease of conversion from the mononuclear or dinuclear to the trinuclear species. X-ray crystal structures showed myriad modes of coordination geometry around Ln(III). The incompatibility of the ligand denticity with the coordination requirements of the Ln(III) ions was proven to be a useful tool in the construction of multinuclear Ln(III) metal ion arrays. The complexation of Fe₃+ and [RevO] ₃+ with bbpen²⁻ (LI²⁻) and Clbbpen²⁻ (L₂²⁻) resulted in the formation of monocationic complexes. The X-ray crystal structure of distorted octahedral [Fe(Ll)]N0₃»CH3₃0H showed the same coordination environment as in its previously studied Ga(III) and In(III) congeners. The solid state and solution structures of a monocationic oxorhenium(V) complex with H₂LI ([ReO(Ll)]+) were quite symmetric, with a pentagonal bipyramidal geometry.

Thesis/Dissertation

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2009-07-03

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http://hdl.handle.net/2429/10093

Chemistry

University of British Columbia

UBCV

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