Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridinecatalyzed O−H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C−H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase−acridine−cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.

Some of us have previously reported the preparation of a dimeric form of the iron storage protein, bacterioferritin (Bfr), in which the native heme b is substituted with the photosensitizer, Zn(II)-protoporphyrin IX (ZnPP-Bfr dimer). We further showed that the ZnPP-Bfr dimer can serve as a photosensitizer for platinum-catalyzed H 2 generation in aqueous solution without the usually added electron relay between photosensitizer and platinum (Clark, E. R., et al. Inorg. Chem. 2017, 56, 4584−4593). We proposed reductive or oxidative quenching pathways involving the ZnPP anion radical (ZnPP •− ) or the ZnPP cation radical, (ZnPP •+ ), respectively. The present report describes structural, photophysical, and photochemical properties of the ZnPP in the ZnPP-Bfr dimer. X-ray absorption spectroscopic studies at 10 K showed a mixture of fiveand six-coordinated Zn centers with axial coordination by one long Zn−SγMet distance of ∼2.8 Å and ∼40% having an additional shorter Zn−S distance of ∼2.4 Å, in addition to the expected 4 nitrogen atom coordination from the porphyrin. The ZnPP in ZnPP-Bfr dimer was prone to photosensitized oxidation to ZnPP •+ . The ZnPP •+ was rapidly reduced by ascorbic acid, which we previously determined was essential for photosensitized H 2 production in this system. These results are consistent with an oxidative quenching pathway involving electron transfer from 3 ZnPP* to platinum, which may be assisted by a flexible ZnPP axial coordination sphere. However, the low quantum yield for H 2 production (∼1%) in this system could make reductive quenching difficult to detect, and can, therefore, not be completely ruled out. The ZnPP-Bfr dimer provides a simple but versatile framework for mechanistic assessment and optimization of porphyrin-photosensitized H 2 generation without an electron relay between porphyrin and the platinum catalyst.

The synthesis, characterization and redox properties of the first single crystal X-ray characterized, water soluble bis-gluconato-tetra-iron(iii) containing complex has been reported.

The iron storage protein bacterioferritin (Bfr) binds up to 12 hemes b at specific sites in its protein shell. The heme b can be substituted with the photosensitizer Zn(II)-protoporphyrin IX (ZnPP), and photosensitized reductive iron release from the ferric oxyhydroxide {[FeO(OH)] n } core inside the ZnPP-Bfr protein shell was demonstrated [Cioloboc, D., et al. (2018) Biomacromolecules 19, 178−187]. This report describes the X-ray crystal structure of ZnPP-Bfr and the effects of loaded iron on the photophysical properties of the ZnPP. The crystal structure of ZnPP-Bfr shows a unique six-coordinate zinc in the ZnPP with two axial methionine sulfur ligands. Steady state and transient ultraviolet−visible absorption and luminescence spectroscopies show that irradiation with light overlapping the Soret absorption causes oxidation of ZnPP to the cation radical ZnPP •+ only when the ZnPP-Bfr is loaded with [FeO(OH)] n . Femtosecond transient absorption spectroscopy shows that this photooxidation occurs from the singlet excited state ( 1 ZnPP*) on the picosecond time scale and is consistent with two oxidizing populations of Fe 3+ , which do not appear to involve the ferroxidase center iron. We propose that [FeO(OH)] n clusters at or near the inner surface of the protein shell are responsible for ZnPP photooxidation. Hopping of the photoinjected electrons through the [FeO(OH)] n would effectively cause migration of Fe 2+ through the inner cavity to pores where it exits the protein. Reductive iron mobilization is presumed to be a physiological function of Bfrs. The phototriggered Fe 3+ reduction could be used to identify the sites of iron mobilization within the Bfr protein shell.

An assembly of platinum nanoparticles produced by Fe(ii) reduction of Pt(ii) and stabilized by human heavy chain ferritin's native catalysis of Fe(ii)(aq) autoxidation functions as an efficient photosensitized H2 evolution catalyst.