Exploring the catalytic activity of new water soluble dinuclear copper(ii) complexes towards the glycoside hydrolysis

Abstract

Two water soluble dinuclear copper(II) complexes of a new dinucleating ligand, H₃phpda [H₃phpda = N,N′-bis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid] have been synthesized and characterized for the investigation of catalytic hydrolysis of glycosides. In methanol, the reaction of stoichiometric amounts of Cu(OAc)₂·H₂O and the ligand H₃phpda in the presence of NaOH, produced a new water soluble dinuclear copper(II) complex, [Cu₂(phpda)(μ-OAc)] (1). Similarly, the reaction of stoichiometric amounts of Cu(ClO₄)₂·6H₂O and the ligand H₃phpda in the presence of NaOH, in methanol, afforded a new water soluble dinuclear copper(II) complex, [Cu₂(phpda) (H₂O)₂](ClO₄) (2). Characterizations of the complexes have been performed using various analytical techniques including DFT calculation. The DFT optimized structure of complex 1 shows that two copper(II) centers are in a distorted square pyramidal geometry with Cu⋯Cu separation of 3.677 Å. On the other hand, the DFT optimized structure of complex 2 reveals that one copper(II) center adopts a five-coordinate distorted square pyramidal geometry and the other copper(II) center is in a distorted square planar geometry with Cu⋯Cu separation of 3.553 Å. Further, the mass spectroscopic analyses of complexes 1 and 2 reconfirm their dimeric nature, even in solution. Glycosidase-like activity of complexes 1 and 2 has been evaluated in aqueous solution at pH ∼ 10.5 by UV-vis spectrophotometric techniques using p-nitrophenyl-α-D-glucopyranoside and p-nitrophenyl-β-D-glucopyranoside as the model substrates. Both complexes are active in catalyzing the hydrolysis of glycosides. DFT calculation has been performed to find the Fukui functions at the metal centers in complexes 1 and 2 to predict the possible metal sites involved in the binding process with substrates during the catalytic hydrolysis reactions.