Association between ammonium monovanadate and β-cyclodextrin as seen by NMR and transport techniques |
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Authors: | ACF Ribeiro VMM Lobo AJM Valente SMN Simes AJFN Sobral ML Ramos HD Burrows |
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Institution: | aDepartment of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal |
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Abstract: | The interaction between vanadium (V) and the carbohydrate β-cyclodextrin (β-CD) has been studied in aqueous solutions (pH ≈ 7.5, 298.15 K) using multinuclear NMR spectroscopy, coupled with measurements of diffusion coefficients and electrical conductivity. The transport properties of vanadate ion solutions are markedly influenced by the presence of β-CD. Data from 51V, 1H and 13C NMR spectroscopy show that these effects are due to strong interactions between this carbohydrate and vanadate due to formation of 2:1 (β-CD:vanadate) complexes. The formation of such 2:1 complexes is also supported by molecular mechanics calculations. Complexation is seen by conductometric and diffusion techniques to lead to a significant decrease in the molar conductivity and diffusion coefficient of vanadate solutions in the presence of β-CD. Using the above stoichiometry, it has been possible to calculate the association constant, leading to the value K = 4.3 × 104 M−2 from the analysis of the conductivity data. |
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Keywords: | Carbohydrates β-Cyclodextrin Vanadium Diffusion NMR Conductivity |
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