The vanadium bromoperoxidase enzyme (VBPO) is a catalyst for the two electron oxidation of halides, so VBPO has the ability to selectively bromated particular substrates at specific locations on the phenyl ring. A computational study using the B3LYP method was carried out for the mechanism of bromide oxidation by a series of oxoperoxovanadium(V) complexes with tripodal amine ligands (ligands: (1) H3heida=N-(2-hydroxyethyl)iminodiacetic acid, (2) H2ada=N-(2-amidomethyl) iminodiacetic acid, (3) H3nta=nitrilotriacetic acid, (4) H2pda=N-pyridyl methyliminodiacetate, (5) Hbpg=N,N-bis(2-pyridylmethyl)-glycine). The key step of reaction is the direct nucleophilic attack of bromide on a protonated peroxide unit (rate determining step of the catalytic cycle), i.e., the protonated peroxo is an active site. We discuss the possible mechanisms for transition states, with particular focus paid on the activation energy barriers. Hydrogen bond formation ability of peroxo group and basic property of tripodal amine ligands (1-5) are two important factors that affect on the reactivity of peroxo active site. According to the quantum calculations, catalytic activity of the studied functional model compounds (1-5) shows the regularity 1>2>3>4>5, that had been expected from experimental results.

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