Reliability of protonation constants of vildagliptin dimers by the regression analysis of pH-titration data |
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| Authors: | Milan Meloun Zuzana Ferenčíková Irena Niesnerová Tomáš Pekárek |
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| Affiliation: | 1244. Department of Analytical Chemistry, University of Pardubice, 532 10, Pardubice, Czech Republic
2244. Zentiva k.s., 102 37, Prague 10, Czech Republic
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| Abstract: | Protonation constants of protonated monomers and dimers of the vildagliptin are determined potentiometrically. For the low concentration c L = 3.3 mmol dm?3 the monomers L and LH dominate, while for a higher concentration c L = 6.3 mmol dm?3 the dimers L2H2, L2H3, L2H4 and L2H are mainly present. The algorithm used has little influence on the precision of the formation constants in comparison with the reproducibility of the titration. The mixed protonation constants of vildagliptin dimers L q H r at various temperatures are determined using FBSTAC4 and HYPERQUAD regression analysis of the potentiometric titration data. The accuracy of the protonation constants log10 β qr depends on the accuracy of the group parameters. As two group parameters L 0, H T are ill conditioned in a model, their determination is therefore uncertain; both can significantly cause a systematic error in the estimated common parameters log10 β qr . Using various regression diagnostics the goodness-of-fit proves the reliability of all parameter estimates. A rough estimation of thermodynamic enthalpies ΔH 0 (kJ mol?1) and entropies ΔS 0 (J K?1 mol?1) is determined from the temperature variation of protonation constants. The enthalpy shows the protonation process is exothermic, and the entropy indicates that it is spontaneous.  | |
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