Abstract

M. Zaky²* M. M. Moawad¹ and Shaker Labib Stefan³

The complexation of nicotinic (niacin) and quinaldic acid ( 2-quinoline carboxylic acid ) with some metal ions of biological interest, such as Au (III), Pt (II), Zr (IV), U (VI), Cr (III), Cu (II), Zn (II) and Mn (II), has been studied potentiometrically using the Calvin-Bjerum titration technique as employed by Irving and Rossotti. The protonation constants of two ligands and the stability constants of the respective metal complexes have been determined at constant temperature (25°C) and ionic strength (0 .1)μ . The overall stability constant values for nicotinic acid complexes have been found in the order. log β2 Au3+ > Pt2+ > ZrO2+ > UO2 2 > Cr3+ > Cu2+ > Zn2+ > Mn2+ and for quinaldic acid complexes: log β2 Au2 > ZrO2+ > Pt2+ > UO2 2 + > Cr3+ > Zn2+ > Mn2+ The formation of 1:1, 1:2, and 1:3 (metal: ligand) complexes have been established by conductometric measurements. I. R spectra of Cu (II) ion with nicotinic acid and quinaldic acid were investigate as an example and the obsetvations indicate that nicotinic acid is coardinated to Cu (II) ion via the heterocyclic nitrogen atom only while quinaldic acid is coordinated via the heterocyclic nitrogen atom and oxygen atom in carboxylic group.

Nicotinic; Bioloical; Interest

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