A thermodynamic study on the complexation between riboflavin and a diaminotriazine derivative mediated by triple hydrogen bonds at water/oil interfaces

Ishizaka, Shoji; Nishijima, Yoshiaki; Kitamura, Noboru
November 2006
Analytical & Bioanalytical Chemistry;Nov2006, Vol. 386 Issue 3, p749
Academic Journal
The changes in Gibbs free energy (Δ G int), enthalpy (Δ H int) and entropy ( TΔ S int) upon complexation between riboflavin (RF) and N,N-dioctadecyl-[1,3,5]triazine-2,4,6-triamine (DTT), mediated by triple hydrogen bonds at water/carbon tetrachloride, trichloroethylene and chloroform interfaces, were determined via temperature-controlled interfacial tension measurements. It was shown that hydrogen bonding interactions between RF and DTT were best characterized by large and negative Δ H int values, unlike those predicted from either the polarity in each phase or the arithmetic average of the polarities in the two phases. Furthermore, the Δ H int values became more positive as the dielectric constant of the oil phase was increased. These results strongly indicate that Δ H int is governed by the dielectric properties of the oil phase. Adsorption of RF, DTT and the RF-DTT complex at the water/oil interface gave rise to restrictions on the translational and rotational motions of these species, as demonstrated by the Δ S int values observed, which is another characteristic of interfacial complexation. The thermodynamic parameters evaluated in the present study revealed the characteristic complexation behavior that occurs at a water/oil interface, as mediated by hydrogen bonding.


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