Metallo-β-lactamase and phosphotriesterase activities of some zinc(II) complexes
摘要:
Metallo-beta-lactamases (m beta l) and phosphotriesterase (PTE) are zinc(II) enzymes, which hydrolyze the beta-lactam antibiotics and toxic organophosphotriesters, respectively. In the present work, we have synthesized a few asymmetric phenolate-based ligands by sequential Mannich reaction and their corresponding zinc(II) complexes. These zinc(II) complexes were studied for their m beta l and PTE activities. It is shown that the zinc(II) complexes can hydrolyze oxacillin, the beta-lactam antibiotic, at much higher rates as compared to the hydrolysis of p-nitrophenyl diphenylphosphate (PNPDPP), the phosphotriester. Among the complexes studied, the binuclear asymmetric complex 1 having a water molecule coordinated to one of the zinc(II) ions exhibits much better mbl activity than the mononuclear complexes. However, the mononuclear zinc(II) complexes having labile chloride ions exhibit significant PTE activity, which can be ascribed to the replacement of chloride ions by hydroxide ions during hydrolysis reactions. (C) 2011 Elsevier B.V. All rights reserved.
phenols were prepared and investigated by 1H and 13C NMR spectroscopy in chloroform-d1 solution. The chemical shifts of intramolecular hydrogen-bonded protons in Mannich bases depend on the pKa of the parent phenols. A correlation between Hammett's constants, σp, and 13C NMR chemical shifts of para carbon atoms has been found. All the results obtained from 1H and 13C NMR spectra show that in the case
Eleven mono- and diaurates of 2,6-bis((diethylamino)methyl)-4-R-phenols were studied in CD2Cl2 solutions using H-1 NMR spectroscopy. With the monoaurates a collective proton fluctuation occurs in the intramolecular hydrogen-bonded system as known from IR results. With increasing acidity of the phenolic group a low field shift of the sipal of the hydrogen-bonded protons is found, indicating increasing deshielding. The protons arc most strongly deshielded in the R = Cl system, from which it is known that it shows the largest proton polarizability. With further increasing acidity the protons are more and more shielded by the N atoms. When the proton limiting structure in which the hydrogen-bonded protons are preferentially present at the N atoms becomes realized, the signals of the Ph-CH2 and the N-CH2 protons are strongly broadened. When the protons are almost localized at these N atoms, a doublet and an octet, respectively. are observed. These effects arise due to spin-spin coupling between the methylene protons and the NH+ protons.