Reactivity of methane mono-oxygenase, insights from quantum mechanic studies on synthetic iron model complexex

Methane mono-oxygenase (MMO) and deoxyhemerythrin (DHr) are examples of di-iron enzymes that catalyze the dissociative and non-dissociative binding of molecular oxygen. To mimic the MMO active site with a finite cluster, we chose to study the binuclear heptapodate coordinated iron(III)-complexes of N,N,N,N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diamino-propane (HPTB) and N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diamino-propane (HPTP). These have active sites of the form [Fez (HPTP)(mu -OH)](4+) (1) and [Fe-2(HPTB)(mu -OH)](4+) (2). Quantum mechanics structures are compared with the experimental data obtained from the EXAFS analysis. For the O-2 binding on the reduced active site. the mu-eta (1):eta (1)-O-2 mode seems the slightly more stable precursor to the O=Fe-O-Fe=O bis-ferryl (re)active site. The nature of the ferryl groups are these of a reactive two center three electron bond. (C) 2001 Elsevier Science B.V. All rights reserved

Layered double hydroxides exchanged with tungstate as biomimetic catalysts for mild oxidative bromination

The manufacture of a range of bulk and fine chemicals, including flame retardants, disinfectants and antibacterial and antiviral drugs, involves bromination1. Conventional bromination methods typically use elemental bromine, a pollutant and a safety and health hazard. Attempts to develop alternative and more benign strategies have been inspired by haloperoxidase enzymes, which achieve selective halogenation at room temperature and nearly neutral pH by oxidizing inorganic halides with hydrogen peroxide2,3. The enzyme vanadium bromoperoxidase has attracted particular interest4,5 in this regard, and several homogeneous inorganic catalysts mimicking its activity are available6, 7, 8, 9, 10, 11, although they are limited by the requirement for strongly acidic reaction media. A heterogenous mimic operating at neutral pH has also been reported12, but shows only modest catalytic activity. Here we describe a tungstate-exchanged layered double hydroxide that catalyses oxidative bromination and bromide-assisted epoxidation reactions in a selective manner. We find that the catalyst is over 100 times more active than its homogeneous analogue. The low cost and heterogeneous character of this system, together with its ability to operate efficiently under mild conditions using bromides rather than elemental bromine, raise the prospect of being able to develop a clean and efficient industrial route to brominated chemicals and drugs and epoxide intermediates.info:eu-repo/semantics/publishe