INFLUENCE OF pH WATER ON THE LIPOPHILICITY OF NICOTINIC ACID AND ITS DERIVATIVES INVESTIGATED BY RP-TLC

Abstract

Nicotinic acid (1) and its derivatives, namely methyl nicotinate (2), ethyl nicotinate (3), isopropyl nicotinate (4), butyl nicotinate (5), hexyl nicotinate (6), benzyl nicotinate (7), nicotinamide (8), N-methylnicotinamide (9), N,N-diethylnicotinamide (10), 3-pyridinecarboaldehyde (11), 3-pyridinecarbonitrile (12), 3-pyridylmethanol (13), and methyl 3-pyridyl ketone (14) were investigated with the use reversed-phase thin layer chromatography on RP-2 plates (Kieselgel 60 F₂₅₄ silanisiert, E. Merck), and methanol – water (pH_water = 2.53; 5.88; 8.11) in different volume compositions as a mobile phase. The chromatographic parameters of lipophilicity (R_{MW(pH = 2.53)}; R_{MW(pH = 5.88)}; R_{MW(pH = 8.11)}) of the studied compounds were determined and compared with both measured (logP_exp), and calculated partition coefficients (AlogPs, IAlogP, ClogP, logP_Kowwin, xlogP, and miLogP). The lipophilicity R_MW values correlate well with experimental partition coefficients (logP_exp) for the compounds investigated. Best agreement was obtained with the experimental partition coefficients (logP_exp) and the chromatographic parameter of lipophilicity R_{MW(pH = 5.88)} for compounds investigated on RP-2 plates and by use of methanol + water (pH_water = 5.88) mobile phase. Chromatographic parameters of the lipophilicity correlated best with AlogPs. Moreover, ClogP correlated best with experimental partition coefficients (logP_exp) of the compounds studied.

Keywords:

• densitometry
• experimental n-octanol-water partition coefficient
• lipophilicity parameter R_MW
• nicotinic acid
• nicotinic acid derivative
• RP-TLC
• theoretical partition coefficient

ACKNOWLEDGMENT

This research was financed by the Ministry of Science and Information Society Technologies, as research project No. 3 T09A 155 29, by resources reserved for science in the years 2005–2008.

Notes

Where: SE – standard error; n – number of points to drive the particular regression equation; r – correlation coefficient; SEE – standard error of the estimation; F – the values of the Fisher test; for all regression equation the significance level (p) is p < 0.01.

Where: SE – standard error; n – number of points to drive the particular regression equation; r – correlation coefficient; SEE – standard error of the estimation; F – the values of the Fisher test; for all regression equation the significance level (p) is p < 0.01.

Where: SE – standard error; n – number of points to drive the particular regression equation; r – correlation coefficient; SEE – standard error of the estimation; F – the values of the Fisher test; for all regression equation the significance level (p) is p < 0.001.