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Complexation Studies of Pyridyl Sulfonamide Ligands for Sensing Zinc and Copper Ions

Research paper by Ritu Kataky, Mark A. Knell

Indexed on: 20 Oct '09Published on: 20 Oct '09Published in: Journal of Solution Chemistry



Abstract

Ligand protonation and stepwise dissociation constants, formation constants and speciation of four pyridyl sulfonamide ligands (Congreeve et al., New J. Chem. 27:98–106, 2003) were assessed, using potentiometric and UV/Visible spectrophotometric pH titrations (in 80% MeOH − 20% H2O). The suitability of these ligands as Cu(II) and Zn(II) sensors for physiological applications was assessed. Two ligands L1 and L4 were p-toluenesulfonamide derivatives while L2 and L3 were triflurosulfonamide derivatives. Additionally L3 and L4 were appended with α-methyl groups. The most stable complex was formed by L1 with Cu(II) owing to the fact that this complex was square planar (log 10  K1=12.15±0.004 and log 10  β2=15.42±0.006). The rest of the complexes invariably formed distorted tetrahedron geometry and complexation was weaker. Speciation diagrams show the effect of ligand to metal concentration, revealing that the L2 and L3 ligands are the most suitable for forming ML2 complexes at physiological pH.