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Nano Lett. 2018 Jun 13;18(6):4015-4022. doi: 10.1021/acs.nanolett.8b01522. Epub 2018 May 18.

Catalyzed and Electrocatalyzed Oxidation of l-Tyrosine and l-Phenylalanine to Dopachrome by Nanozymes.

Author information

1
Institute of Chemistry, The Center for Nanoscience and Nanotechnology , The Hebrew University of Jerusalem , Jerusalem 91904 , Israel.
2
Department of Chemistry , Bar-Ilan University , Ramat Gan 52 900 , Israel.

Abstract

Catalyzed oxygen insertion into C-H bonds represents a continuous challenge in chemistry. Particularly, driving this process at ambient temperature and aqueous media represents a "holy grail" in catalysis. We report on the catalyzed cascade transformations of l-tyrosine or l-phenylalanine to dopachrome in the presence of l-ascorbic acid/H2O2 as oxidizing mixture and CuFe-Prussian Blue-like nanoparticles, Fe3O4 nanoparticles or Au nanoparticles as catalysts. The process involves the primary transformation of l-tyrosine to l-DOPA that is further oxidized to dopachrome. The transformation of l-phenylalanine to dopachrome in the presence of CuFe-Prussian Blue-like nanoparticles and l-ascorbic acid/H2O2 involves in the first step the formation of l-tyrosine and, subsequently, the operation of the catalytic oxidation cascade of l-tyrosine to l-DOPA and dopachrome. Electron spin resonance experiments demonstrate that ascorbate radicals and hydroxyl radicals play cooperative functions in driving the different oxygen-insertion processes. In addition, the aerobic elecrocatalyzed oxidation of l-tyrosine to dopachrome in the presence of naphthoquinone-modified Fe3O4 nanoparticles and l-ascorbic acid is demonstrated. In this system, magnetic-field attraction of the naphthoquinone-modified Fe3O4 nanoparticles onto the electrode allows the quinone-mediated electrocatalyzed reduction of O2 to H2O2 (bias potential -0.5 V vs SCE). The electrogenerated H2O2 is then utilized to promote the transformation of l-tyrosine to dopachrome in the presence of l-ascorbic acid and Fe3O4 catalyst.

KEYWORDS:

Fe3O4; Prussian Blue; catalysis; enzyme model; iron oxide; surface modification

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