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Reactions of a Sulfonamide Antimicrobial with Model Humic Constituents: Assessing Pathways and Stability of Covalent Bonding
journal contribution
posted on 2012-02-21, 00:00 authored by Anna Gulkowska, Martin Krauss, Daniel Rentsch, Juliane HollenderThe mechanism of covalent bond formation of the model
sulfonamide
sulfathiazole (STZ) and the stronger nucleophile para-ethoxyaniline was studied in reactions with model humic acid constituents
(quinones and other carbonyl compounds) in the absence and presence
of laccase. As revealed by high resolution mass spectrometry, the
initial bonding of STZ occurred by 1,2- and 1,4-nucleophilic additions
of the aromatic amino group to quinones resulting in imine and anilinoquinone
formation, respectively. Experiments using the radical scavenger tert-butyl-alcohol provided the same products and similar
formation rates as those without scavenger indicating that probably
not radical coupling reactions were responsible for the initial covalent
bond formation. No addition with nonquinone carbonyl compounds occurred
within 76 days except for a slow 1,4-addition to the β-unsaturated
carbonyl 1-penten-3-one. The stability of covalent bonds against desorption
and pressurized liquid extraction (PLE) was assessed. The recovery
rates showed no systematic differences in STZ extractability between
the two product types. This suggests that the strength of bonding
is not controlled by the initial type of bond, but by the extent of
subsequent incorporation of the reaction product into the formed polymer.
This incorporation was monitored for 15N aniline by 1H–15N HMBC NMR spectroscopy. The initial
1,2- and 1,4-addition bonds were replaced by stronger heterocyclic
forms with increasing incubation time. These processes could also
hold true for soils, and a slow nonextractable residue formation with
time could be related to a slow increase of the amount of covalently
bound sulfonamide and the strength of bonding.
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15 N aniline76 daysnonquinone carbonyl compoundsnonextractable residue formationmodel humic acid constituentsmodel sulfonamide sulfathiazoleNMRreaction productincubation timeCovalent BondingThe mechanismAssessing PathwaysSulfonamide AntimicrobialSTZ extractabilityheterocyclic formsModel Humic ConstituentsHMBCcovalent bond formationincorporationanilinoquinone formationPLEscavengerproduct typesstrengthresolution mass spectrometryrecovery ratescovalent bondsformation ratescarbonyl compounds
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