Metallohydrolase biomimetics with catalytic and structural flexibility

The structural and functional properties of zinc(II) complexes of two nitrogen rich polydentate ligands, HTPDP = 1,3-bis(bis-pyridin-2-ylmethylamino) propan-2-ol and HTPPNOL = N,N,N'-tris-(2-pyridylmethyl)-1,3- diaminopropan-2-ol, are compared. HTPDP is a hepta-dentate ligand with four pyridyl groups attached to a 1,3- diaminopropan-2-ol backbone while HTPPNOL contains only three pyridyl groups. In reactions with Zn(ClO4)(2),HTPDP forms a dinuclear zinc compound [Zn-2(TPDP)(OAc)](ClO4)(2), 1. On the other hand, mononuclear [Zn(HTPPNOL)](ClO4)(2), 2, and tetranuclear [Zn-4(TPPNOL)(2)(OAc)(3)] (ClO4)(3,) 3, complexes were isolated with the ligand HTPPNOL. Kinetic measurements with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) revealed that compound 1 (k(cat) = 31.4 x 10(-3) min(-1)) is more reactive than 3 (k(cat) = 7.7 x 10(-3) min(-1)) at pH = 8.5, whilst the mononuclear compound 2 is inactive. Compound 1 displays a typical steady-state kinetic behaviour, while compound 3 exhibits steady-state behaviour only similar to 120 s after starting the reaction, preceded by a burst-phase. P-31 NMR studies confirm that 1 can promote the hydrolysis of both ester bonds in BDNPP, generating the monoester DNPP and inorganic phosphate in the process. In contrast, DNPP is not a substrate for 3. The crystal structure of the complex formed by 3 and DNPP reveals the formation of a tetranuclear zinc complex [Zn-4(TPPNOL)(2)(DNPP) 2](ClO4)(2), 4, in which the phosphate moiety of DNPP adopts an unusual tridentate mu-eta(1):eta(1):eta(1)coordination mode