title: A phenoxo-bridged dicopper(ii) complex as a model for phosphatase activity: mechanistic insights from a combined experimental and computational study.
abstract: A μ-phenoxo-bis(μ2-1,3-acetato)-bridged dicopper(ii) complex [Cu(L1)(μ-O2CMe)2][NO3] (1) has been synthesized from the perspective of modeling phosphodiesterase activity. Structural characterization was done initially with 1·3Et2O (vapour diffusion of Et2O into MeOH solution of 1; poor crystal quality) and finally with its perchlorate salt [Cu(L1)(μ-O2CMe)2][ClO4]·1.375MeCN·0.25H2O, crystallized from vapour diffusion of n-pentane into a MeCN-MeOH mixture (comparatively better crystal quality). An asymmetric unit of such a crystal contains two independent molecules of compositions [Cu(L1)(μ-O2CMe)2][ClO4] and [Cu(L1)(μ-O2CMe)2(MeCN)][ClO4] (coordinated MeCN with 0.75 occupancy), and two molecules of MeCN and H2O (each H2O molecule with 0.25 occupancy) as the solvent of crystallization. These two cations, each having five-coordinate (μ-phenoxo)bis(μ-acetato)-bridged CuIIions, differ by only the coordination environment of only one CuIIion, which has a weakly coordinated acetonitrile molecule in its sixth position. Temperature-dependent magnetic studies on 1 reveal that the copper(ii) centres are antiferromagnetically coupled with the exchange-coupling constant J = -124(1) cm-1. Theoretically calculated J = -126.51 cm-1, employing a broken-symmetry DFT approach, is in excellent agreement with the experimental value. The dicopper(ii) complex has been found to be catalytically efficient in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Detailed kinetic experiments and solution studies (potentiometry, species distribution and ESI-MS) were performed to elucidate the reaction mechanism. DFT calculations were performed to discriminate between different possible mechanistic pathways. The free-energy barrier for HPNP hydrolysis catalyzed by 1 is comparable to that obtained from the experimentally-determined value. The involvement of non-covalent (hydrogen-bonding) interaction has also been probed by DFT calculations. The activity of 1 is found to be the highest, compared to the structurally-characterized Mn, Co, Ni and Zn complexes of L1(-) reported earlier, under identical experimental conditions, in which each metal centre is six-coordinate.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India. rnm@iitk.ac.in and Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India.
authors.forename: Suman K
authors.initials: SK
authors.lastname: Barman
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India.
authors.forename: Totan
authors.initials: T
authors.lastname: Mondal
authors.affiliation: Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India.
authors.forename: Debasis
authors.initials: D
authors.lastname: Koley
authors.affiliation: Departament de Química Inorgànica/Fundació General de la Universitat de València (FGUV)/Instituto de Ciencia, Molecular (ICMOL), Universitat de València, Polígono de la Coma, s/n, 46980-Paterna, València, Spain.
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.affiliation: Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India. rnm@iitk.ac.in and Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741 246, India.
authors.forename: Rabindranath
authors.identifier: http://orcid.org/0000-0003-0739-5896
authors.initials: R
authors.lastname: Mukherjee
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D008024:Ligands; D060328:Magnetic Phenomena; D008958:Models, Molecular; D008968:Molecular Conformation; D010710:Phosphates / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D013696:Temperature
chemical_list: D056831:Coordination Complexes; D008024:Ligands; D010710:Phosphates; D003300:Copper; D010744:Phosphoric Monoester Hydrolases