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Reliability of protonation constants of vildagliptin dimers by the regression analysis of pH-titration data

100%

Meloun M., Ferenčíková Z., Niesnerová I., Pekárek T.

Open Chemistry

2013

vol. 11

issue 7

1101-1111

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 Lq Hr at various temperatures are determined using FBSTAC4 and HYPERQUAD regression analysis of the potentiometric titration data. The accuracy of the protonation constants log10 βqr 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 βqr . 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. [...]

Oligomers-model building in protonation equilibria of sitagliptin

86%

Meloun M., Ferenčíková Z., Niesnerová I., Pekárek T.

Open Chemistry

2013

vol. 11

issue 11

1799-1807

Mixed protonation constants of sitagliptin phosphate at various ionic strengths I (mol kg−1) in range 0.01 and 0.50 and at 298.15 K are determined using FBSTAC4 and HYPERQUAD nonlinear regression analyses of the potentiometric titration curve. At a low concentration c L = 1.1 mmol kg−1 the monomers L, LH, LH2, LH3 and LH4 dominate, while for a concentration range from c L = 13.7 to 24.7 mmol kg−1 dimers L2H2, L2H3, L2H4 and L2H are mainly present. The regression programme has almost no influence on the precision of the protonation constants. The accuracy of the protonation constants log βqr depends on the accuracy of the group parameters. As two group parameters c L,0, c 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 log10βqr . Fitness tests using regression diagnostics have proven the reliability of the parameter estimates. [...]

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Reliability of protonation constants of vildagliptin dimers by the regression analysis of pH-titration data

Oligomers-model building in protonation equilibria of sitagliptin