Bromoperoxidases and functional enzyme mimics as catalysts for oxidative bromination—A sustainable synthetic approach

 Reactive halogen species (RHS), such as X·, X2 and HOX containing X = chlorine and/or bromine, are released by various sources like photo-activated sea-salt aerosol or from salt pans, and salt lakes Despite many studies of RHS reactions, the potential of RHS reacting with secondary organic aerosol (SOA) and organic aerosol derived from biomass-burning (BBOA) has been neglected Such reactions can constitute sources of gaseous organohalogen compounds or halogenated organic matter in the tropospheric boundary layer and can influence physicochemical properties of atmospheric aerosols Model SOA from α-pinene, catechol, and guaiacol was used to study heterogeneous interactions with RHS Particles were exposed to molecular chlorine and bromine in an aerosol smog-chamber in the presence of UV/VIS irradiation and to RHS, released from simulated natural halogen sources like salt pans Subsequently, the aerosol was characterized in detail using a variety of physicochemical and spectroscopic methods Fundamental features were correlated with heterogeneous halogenation, which results in new functional groups (FTIR spectroscopy), changes UV/VIS absorption, chemical composition (ultrahigh resolution mass spectroscopy (ICR-FT/MS)), or aerosol size distribution However, the halogen release mechanisms were also found to be affected by the presence of organic aerosol Those interaction processes, changing chemical and physical properties of the aerosol are likely to influence eg the ability of the aerosol to act as cloud condensation nuclei, its potential to adsorb other gases with low-volatility, or its contribution to radiative forcing and ultimately the Earth's radiation balance

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Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms

Bromination of phenols in bromoperoxidase-catalyzed oxidations

Bromoperoxidases from the brown alga Ascophyllum nodosum, abbreviated as VBrPO(AnI) and VBrPO(AnII), show 41% sequence homology and differ by a factor of two in the percentage of α-helical secondary structures. Protein monomers organize into homodimers for VBrPO(AnI) and hexamers for VBrPO(AnII). Bromoperoxidase II binds hydrogen peroxide and bromide by approximately one order of magnitude stronger than VBrPO(AnI). In oxidation catalysis, bromoperoxidases I and II turn over hydrogen peroxide and bromide similarly fast, yielding in morpholine-4-ethanesulfonic acid (MES)-buffered aqueous tert-butanol (pH 6.2) molecular bromine as reagent for electrophilic hydrocarbon bromination. Alternative compounds, such as tribromide and hypobromous acid are not sufficiently electrophilic for being directly involved in carbon–bromine bond formation. A decrease in electrophilicity from bromine via hypobromous acid to tribromide correlates in a frontier molecular orbital (FMO) analysis with larger energy gaps between the π-type HOMO of, for example, an alkene and the σ*Br,X-type LUMO of the bromination reagent. By using this approach, the reactivity of substrates and selectivity for carbon–bromine bond formation in reactions mediated by vanadate-dependent bromoperoxidases become predictable, as exemplified by the synthesis of bromopyrroles occurring naturally in marine sponges of the genera Agelas, Acanthella, and Axinella.

Vanadate-dependent bromoperoxidases from Ascophyllum nodosum in the synthesis of brominated phenols and pyrroles

Oxidation of some organic compounds by aqueous bromine solutions

A spectrophotometric determination of the equilibrium constant for the hydrolysis of bromine in water is described.

Spectrophotometric determination of the hydrolysis constant of bromine at 25 °C

The oxidative pattern of α-hydroxy acids by acidic bromine water is shown to be similar to the oxalic acid – bromine water reaction. In both cases HOBr is the oxidant and the undissociated form of ...

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part II. Oxidation in Acidic Medium. A Comparison with the HOBr – Oxalic Acid Reaction

A kinetic study of the oxidative decarboxylation of α-hydroxy acids by bromine water shows that above pH 6 Br2 is a much more significant oxidant for these compounds than is HOBr, and that OBr− is ...

Judith M. Pink

Papers

Spectrophotometric determination of the hydrolysis constant of bromine at 25 °C

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part II. Oxidation in Acidic Medium. A Comparison with the HOBr – Oxalic Acid Reaction

Mechanism of Oxidative Decarboxylation of α-Hydroxy Acids by Bromine Water. Part I. Oxidation in Neutral and Alkaline Medium