A novel salt of antidiabetic drug metformin resulting from a proton transfer reaction: Synthesis, characterization, crystal structure and solution studies

Reaction between N,N-dimethylebiguanidine, Met = Metformin, and 4-hydroxy-2,6-pyridinedicarboxylic acid, HO-dipicH(2), results in the formation of a novel proton transfer compound, [MetH(2)][HO-dipicH](2 center dot)H2O, 1. The characterization was performed using FI'IR, UV-Vis, H-1 and C-13 NMR spectroscopy and X-ray crystallography. The crystal system is triclinic with space group P (1) over bar and two molecules per unit cell. The protonation constants of O-dipic and Met, in all of probability protonated forms, and the equilibrium constants for the O-dipic-Met proton transfer system were investigated by the potentiometric pH titration method using the Hyperquad2008 program. The stoichiometry of the proton transfer species in solution were in agreement with the solid state result. (C) 2016 Elsevier B.V. All rights reserved.