Highly efficient phosphodiester hydrolysis promoted by a dinuclear copper(II) complex

The interaction of Cu-II with the ligand tdci (1,3,5-trideoxy-1,3,5-tris(di methylamino)-cis-inositol) was studied both in the solid state and in solut ion. The complexes that were formed were also tested for phosphoesterase ac tivity. The pentanuclear complex [Cu-5(tdciH(-2))(tdci)(2)(OH)(2)(NO3)(2)]( NO3)(4). 6H(2)O consists of two dinuclear units and one trinuclear unit, ha ving two shared copper(II) ions. The metal centers within the pentanuclear structure have three distinct coordination environments. All five copper(II ) ions are linked by hydroxo/alkoxo bridges forming a CU5O6 cage. The Cu-Cu separations of the bridged centers are between 2.916 and 3.782 Angstrom, w hile those of the nonbridged metal ions are 5.455-5.712 Angstrom. The solut ion equilibria in the Cu-II-tdci system proved to be extremely complicated. Depending on the pH and metal-to-ligand ratio, several differently deproto nated mono-, di-, and trinuclear complexes are formed. Their presence in so lution was supported by mass, CW, and pulse EPR spectroscopic study, too. I n these complexes, the metal ions are presumed to occupy tridentate {O-ax,N -eq,O-ax} coordination sites and the O-donors of tdci may serve as bridging units between two metal ions. Additionally, deprotonation of the metal-bou nd water molecules may occur. The dinuclear Cu2LH-3 species, formed around pH 8.5, provides outstanding rate acceleration for the hydrolysis of the ac tivated phosphodiester bis(4-nitrophenyl)phosphate (BNPP). The second-order rate constant of BNPP hydrolysis promoted by the dinuclear complex (T = 29 8 K) is 0.95 M-1 s(-1), which is ca. 47600-fold higher than that of the hyd roxide ion catalyzed hydrolysis (k(OH))Its activity is selective for the ph osphodiester, and the hydrolysis was proved to be catalytic. The proposed b ifunctional mechanism of the hydrolysis includes double Lewis acid activati on and intramolecular nucleophilic catalysis.