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Complex formation in aqueous solution and in the solid state of the potent insulin-enhancing VIVO2+ compounds formed by picolinate and quinolinate derivatives

Lodyga-Chruscinska, Elzbieta and Micera, Giovanni and Garribba, Eugenio (2011) Complex formation in aqueous solution and in the solid state of the potent insulin-enhancing VIVO2+ compounds formed by picolinate and quinolinate derivatives. Inorganic Chemistry, Vol. 50 (3), p. 883-899. eISSN 1520-510X. Article.

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DOI: 10.1021/ic101475x

Abstract

The complexation of VIVO2+ ion with 10 picolinate and quinolinate derivatives, provided with the donor set (N, COO), was studied in aqueous solution and in the solid state through the combined application of potentiometric (pH-titrations), spectroscopic (EPR, UV/vis and IR spectroscopy), and computational (density functional theory (DFT) calculations) methods. Such derivatives, that form potent insulin-enhancing VIVO2+ compounds, are picolinic (picH), 6-methylpicolinic (6-mepicH), 3-methylpicolinic (3-mepicH), 5-butylpicolinic or fusaric (fusarH), 6-methyl-2,3-pyridindicarboxylic (6-me-2,3-pdcH2), 2-pyridylacetic (2-pyacH), 2-quinolinecarboxylic or quinaldic (quinH), 4-hydroxyquinoline-2-carboxylic or kynurenic (kynurH), 1-isoquinolinecarboxylic (1-iqcH) and 3-isoquinolinecarboxylic (3-iqcH) acid. On the basis of the potentiometric, spectroscopic, and DFT results, they were divided into the classes A, B, and C. The ligands belonging to class A (3-mepicH, 1-iqcH, 2-pyacH) form square pyramidal complexes in aqueous solution and in the solid state, and those belonging to class B (picH, fusarH, 3-iqcH) form cis-octahedral species, in which the two ligands adopt an (equatorial-equatorial) and an (equatorial-axial) arrangement and one water molecule occupies an equatorial site in cis position with respect to the V═O bond. Class C ligands (6-mepicH, 6-me-2,3-pdcH2, quinH, kynurH) yield bis chelated species, that in water are in equilibrium between the square pyramidal and trans-octahedral form, where both the ligand molecules adopt an (equatorial-equatorial) arrangement and one water is in trans position with respect to the V═O group. The trans-octahedral compounds are characterized by an anomalous electron paramagnetic resonance (EPR) response, with Az value being reduced by about 10% with respect to the prediction of the “additivity rule”. DFT methods allow to calculate the structure, 51V hyperfine coupling constant (Az), the stretching frequency of V═O bond (νV═O), the relative stability in aqueous solution, and the electronic structure and molecular orbital composition of bis chelated complexes. The results were used to explain the biotransformation of these potent insulin-enhancing compounds in blood serum.

Item Type:Article
ID Code:5776
Status:Published
Refereed:Yes
Uncontrolled Keywords:Picolinate derivatives, quinolinate derivatives, VIVO2+ compounds
Subjects:Area 03 - Scienze chimiche > CHIM/03 Chimica generale e inorganica
Divisions:001 Università di Sassari > 02 Centri > Centro di eccellenza interdisc. sviluppo ricerca biotecnologica e studio biodiversità della Sardegna e dell'area mediterranea
001 Università di Sassari > 01 Dipartimenti > Chimica
Publisher:American Chemical Society
eISSN:1520-510X
Deposited On:10 May 2011 17:22

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