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Fe(III) protoporphyrin IX encapsulated in a zinc metal–organic framework shows dramatically enhanced peroxidatic activity

DOI: 10.1021/acs.inorgchem.7b02612 DOI Help

Authors: Nicola A. Dare (University of Cape Town) , Lee Brammer (University of Sheffield) , Susan A. Bourne (University of Cape Town) , Timothy J. Egan (University of Cape Town)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: January 2018
Diamond Proposal Number(s): 15787

Abstract: Two MOFs, [H2N(CH3)2][Zn3(TATB)2(HCOO)]·HN(CH3)2·DMF·6H2O (1) and Zn-HKUST-1 (2), were investigated as potential hosts to encapsulate Fe(III) heme (Fe(III) protoporphyrin IX = Fe(III)PPIX). Methyl orange (MO) adsorption was used as an initial model for substrate uptake. MOF 1 showed good adsorption of MO (10.3 ± 0.8 mg g–1) which could undergo in situ protonation upon exposure to aqueous HCl vapor. By contrast, MO uptake by 2 was much lower (2 ± 1 mg g–1), and PXRD indicated that structural instability on exposure to water was the likely cause. Two methods for Fe(III)PPIX-1 preparation were investigated: soaking and encapsulation. Encapsulation was verified by SEM-EDS and showed comparable concentrations of Fe(III)PPIX on exposed interior surfaces and on the original surface of fractured crystals. SEM-EDS results were consistent with ICP-OES data on bulk material (1.2 ± 0.1 mass % Fe). PXRD data showed that the framework in 1 was unchanged after encapsulation of Fe(III)PPIX. MO adsorption (5.8 ± 1.2 mg g–1) by Fe(III)PPIX-1 confirmed there is space for substrate diffusion into the framework, while the UV–vis spectrum of solubilized crystals confirmed that Fe(III)PPIX retained its integrity. A solid-state UV–vis spectrum of Fe(III)PPIX-1 indicated that Fe(III)PPIX was not in a μ-oxo dimeric form. Although single-crystal XRD data did not allow for full refinement of the encapsulated Fe(III)PPIX molecule owing to disorder of the metalloporphyrin, the Fe atom and pyrrole N atoms were located, enabling rigid-body modeling of the porphine core. Reaction of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) with H2O2, catalyzed by Fe(III)PPIX-1 and -2, showed that Fe(III)PPIX-1 is significantly more efficient than Fe(III)PPIX-2 and is superior to solid Fe(III)PPIX-Cl. Fe(III)PPIX-1 was used to catalyze the oxidation of hydroquinone, thymol, benzyl alcohol, and phenyl ethanol by tert-butyl-hydroperoxide with t1/2 values that increase with increasing substrate molecular volume.

Subject Areas: Chemistry, Materials

Instruments: I19-Small Molecule Single Crystal Diffraction

Added On: 15/01/2018 11:30

Discipline Tags:

Catalysis Physical Chemistry Materials Science Metallurgy Metal-Organic Frameworks Chemistry Organometallic Chemistry

Technical Tags:

Diffraction Single Crystal X-ray Diffraction (SXRD)