Polymer Dots as Photoactive Membrane Vesicles for [FeFe]-Hydrogenase Self-Assembly and Solar-Driven Hydrogen Evolution

Abstract

A semiartificial photosynthesis approach that utilizes enzymes for solar fuel production relies on efficient photosensitizers that should match the enzyme activity and enable long-term stability. Polymer dots (Pdots) are biocompatible photosensitizers that are stable at pH 7 and have a readily modifiable surface morphology. Therefore, Pdots can be considered potential photosensitizers to drive such enzyme-based systems for solar fuel formation. This work introduces and unveils in detail the interaction within the biohybrid assembly composed of binary Pdots and the HydA1 [FeFe]-hydrogenase from Chlamydomonas reinhardtii. The direct attachment of hydrogenase on the surface of toroid-shaped Pdots was confirmed by agarose gel electrophoresis, cryogenic transmission electron microscopy (Cryo-TEM), and cryogenic electron tomography (Cryo-ET). Ultrafast transient spectroscopic techniques were used to characterize photoinduced excitation and dissociation into charges within Pdots. The study reveals that implementation of a donor−acceptor architecture for heterojunction Pdots leads to efficient subpicosecond charge separation and thus enhances hydrogen evolution (88 460 μmol H2 •g H2ase −1•h −1 ). Adsorption of [FeFe]-hydrogenase onto Pdots resulted in a stable biohybrid assembly, where hydrogen production persisted for days, reaching a TON of 37 500 ± 1290 in the presence of a redox mediator. This work represents an example of a homogeneous biohybrid system combining polymer nanoparticles and an enzyme. Detailed spectroscopic studies provide a mechanistic understanding of light harvesting, charge separation, and transport studied, which is essential for building semiartificial photosynthetic systems with efficiencies beyond natural and artificial systems.

Preparation, characterization, evaluation and mechanistic study of organic polymer nano-photocatalysts for solar fuel production

“…Recently, Pavliuk et al reported well resolved attenuated total reflection ATR-FTIR spectra of aqueous Pdots solutions. 48 To achieve fine spectral resolution of Pdots in their unperturbed state a custom-made gas titration cell was utilized. 71 In this case, Pdots solutions were at first concentrated to remove B60% of water under the stream of dry N 2 gas, and then ATR-FTIR spectra were recorded for the rehydrated samples by purging ''wet'' aerosol that formed hydroscopic Pdots films.…”

“…Addition of one of fresh components such as PNP or co-catalyst to the reaction mixture, is a way to check which component is essentially unstable and if solar fuel formation can be reinitiated. 48 Gradually increased concentration of product in the solution can also slack the photocatalytic process. Therefore, removing product and checking if the photocatalytic process can be reinitiated is an effective method to verify this.…”

“…Using methacrylate-based copolymer as a building block, Pavliuk et al synthesized hollow Pdots with donut-like morphology following a self-assembly approach. 48 Pdots with the porous polymer shell that allowed fast proton diffusion were synthesized by introducing ultrasonication in pair with argon stripping during mixing of a solvent and an anti-solvent. 16 2.4.2.…”

“…Resulting intimate interaction within the biohybrid assembly showed a positive impact on overall photocatalytic performance. 48 (d) Surface permeability. Permeability of the nanoparticles surface towards reactants, e.g.…”

“…In order to minimize the electron diffusion distance, Pavliuk et al co-adsorbed proton reduction catalyst, namely [FeFe]-hydrogenase enzyme, via suitable surface groups. 48 (ii) Covalent linking of the cocatalyst. Using covalent linking method (ii) Tseng et al prepared a series of Pdots with a presynthesized platinum complex unit as a comonomer.…”