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Peptide dendrimer BP1 was obtained by double thioether bond formation between 5,5′-bis(bromomethyl)-2,2′-bipyridine and two equivalents of peptide dendrimer N1 (Ac-Glu-Ser)8(Dap-Glu-Ala)4(Dap-Amb-Tyr)2Dap-Cys-Asp-NH2 (Dap = branching 2,3-diaminopropanoic acid, Amb = 4-aminomethyl-benzoic acid). At pH 4.0 BP1 bound Fe(II) to form the expected tris-coordinated complex [FeII(BP1)3] (Kf = 2.1 × 1015 M−3). At pH 6.5 a monocoordinated complex [FeII(BP1)] was formed instead (Kf = 2.1 × 105 M−1) due to electrostatic repulsion between the polyanionic dendrimer branches, as confirmed by the behavior of three analogues where glutamates were partially or completely replaced by neutral glutamines or positive lysines. [FeII(BP1)] catalyzed the oxidation of o-phenylenediamine with H2O2 with enzyme-like kinetics (kcat = 1.0 min−1, KM = 1.5 mM, kcat/kuncat = 90000) and multiple turnover, while Fe2+ or [Fe(bipy)3]2+ were inactive. The labile coordination positions allowing coordination to H2O2 and to the substrate are likely responsible for the enhanced peroxidase activity of the metallopeptide dendrimer.
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Organic & Biomolecular Chemistry
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