Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Hydrogenases (H2ases) are benchmark electrocatalysts for H2 production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and wiring of H2ase through the introduction of a hierarchical inverse opal (IO) TiO2 interlayer. This proton-reducing Si j IO-TiO2 j H2ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias-free) water splitting by wiring Si j IO-TiO2 j H2ase to a modified BiVO4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si j IO-TiO2 j H2ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z-scheme that replaces the non-complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode

Solid-phase growth of nanostructures from amorphous peptide thin film: Effect of water activity and temperature

We report the solid-phase self-assembly of nanostructures from amorphous thin film of aromatic peptides. The thickness of amorphous peptide film could be precisely controlled down to ~50 nm. Aligned nanostructures were grown from the film either by changing water activity in the vapor phase or by applying high thermal energy. The growth of peptide nanorods on solid substrate occurred via a watervapor-mediated self-assembly process. We found that the peptide nanostructures could be "reversibly" dissociated and reassembled depending on the chemical composition of the vapor phase. We also observed that the phase transition of aromatic peptide occurs at extremely high temperatures above 100??C, and the thermal aging of amorphous film resulted in the formation of peptide nanorods. In this work, the formation of peptide nanostructures from amorphous thin film was investigated by multiple analytical tools such as electron and atomic force microscopies, vibrational and diffraction spectroscopies, and differential scanning calorimetry. To the best of our knowledge, this is the first report for the self-assembly of peptides into nanostructures starting from amorphous thin film.close292

High-Temperature Self-Assembly of Peptides into Vertically Well-Aligned Nanowires by Aniline Vapor

A solid-phase growth of crystalline peptide nanowires at high temperatures influenced by aniline vapor under anhydrous conditions was reported. The formation of vertically well-aligned peptide nanowires on a solid surface were investigated through multiple tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and thermal analytical tools like differential scanning calorimeters. The experiments were conducted under strictly anhydrous conditions in a vacuum desiccator to avoid the affect of water vapor in the final surface structure of the peptide thin film. It was found that the self-assembly of peptide nanowires from the film depended on both the aging temperature and the nature of the solvent vapor used. The peptide nanowires were thermally stable up to 200 ??C without any loss in weight or structural integrity.close706

Lignin as a Multifunctional Photocatalyst for Solar-Powered Biocatalytic Oxyfunctionalization of C-H Bonds

Lignin is a key structural material in all terrestrial plants that is responsible for cell wall formation, water transportation, seed protection, and stress adaptation. Each year, pulp and paper industry produces approximately 50 million metric tons of lignin as waste, 95% of which is combusted or abandoned. Here, we report a new multifunctionality of lignin as a photocatalyst (e.g., synergistic formation of H2O2 formation through O2 reduction and H2O oxidation, use of H2O as an electron donor, and OH• -scavenging activity). Our spectroscopic and photoelectrochemical analyses reveal the photophysical characteristics (e.g., light absorption, charge separation/transfer) of lignin models [e.g., lignosulfonate (LS) and kraft lignin (KL)] and their electronic properties [HOMO-LUMO gap: 2.67 eV (LS), 2.95 eV (KL), LUMO: -0.VRHE (LS) and -0.26 VRHE (KL), HOMO: 2.44 VRHE (LS) and 2.69 VRHE (KL)]. We demonstrate lignin-sensitized redox chemistry, such as (i) H2O2 formation through O2 reduction using H2O as an electron donor and (ii) O2 evolution through H2O oxidation, under visible light. Furthermore, the integration of lignin and H2O2-dependent unspecific peroxygenases (UPOs) enables enantiospecific oxyfunctionalization reactions (e.g., benzylic hydroxylation, alkane hydroxylation, styrene epoxidation). Lignin photocatalysts solve existing issues (e.g., requirement of artificial electron donors, H2O2- or OH• -driven inactivation of UPO) related to the sustainable activation of UPO. The lignin/UPO hybrid achieves a total turnover number of enzyme of 81070, the highest value ever recorded for solar-powered biocatalytic oxyfunctionalization in photochemical platforms. This work demonstrates the propriety of lignin in robust photocatalyst/biocatalyst hybrids for artificial photosynthesis

Bio-inspired fabrication of superhydrophobic surfaces through peptide self-assembly

A vertically aligned peptide nanowire film, prepared by the self-assembly of diphenylalanine upon exposure to fluorinated aniline vapor at high temperature, exhibits a superhydrophobic property due to its nanoscale roughness and low surface free energy. We fabricated a self-cleaning, superhydrophobic surface by hierarchically re-organizing peptide nanowires into a hill-and-valley-like structure using capillary force induced by solvent-evaporation. Our approach provides an alternative way of nanofabrication for superhydrophobic materials, which should broaden the spectrum of applications for peptide self-assembly.close353

Inhibition of beta-amyloid peptide aggregation and neurotoxicity by alpha-D-mannosylglycerate, a natural extremolyte

The aggregation of soluble ??-amyloid (A??) peptide into oligomers/fibrils is one of the key pathological features in Alzheimer's disease (AD). The use of naturally occurring small molecules for inhibiting protein aggregation has recently attracted many interests due to their effectiveness for treating protein folding diseases such as AD, Parkinson's, Huntington's disease, and other amyloidosis diseases. ??-d-Mannosylglycerate (MG), a natural extremolyte identified in microorganisms growing under extremely high temperatures up to 100 ??C, had been shown to protect proteins against various stress conditions such as heat, freezing, thawing, and drying. Here, we report the effectiveness of MG on the suppression of Alzheimer's A?? aggregation and neurotoxicity to human neuroblastoma cells. According to our study - carried out by using thioflavin-T induced fluorescence, atomic force microscopy, and cell viability assay - MG had significant inhibitory effect against A?? amyloid formation and could reduce the toxicity of amyloid aggregates to human neuroblastoma cells while MG itself was innocuous to cells. On the other hand, the structural analogs of MG such as ??-d-mannosylglyceramide, mannose, methylmannoside, glycerol, showed negligible effect on A?? aggregate formation. The results suggest that MG could be a potential drug candidate for treating Alzheimer's disease.close141

Bone-like peptide/hydroxyapatite nanocomposites assembled with multi-level hierarchical structures

Inspired by nature's strategy for creating organic/inorganic hybrid composite materials, we developed a simple but powerful method to synthesize bone-like peptide/hydroxyapatite nanocomposites using a mussel-mimetic adhesive, polydopamine. We found that polydopamine was uniformly coated in a graphite-like layered structure on the surface of self-assembled diphenylalanine (Phe-Phe, FF) nanowires and enabled the epitaxial growth of c-axis-oriented hydroxyapatite nanocrystals along the nanowires, which is similar to mineralized collagen nanofibers of natural bone. The mineralized peptide nanowires were further organized in relation to each other and then readily hybridized with osteoblastic cells, resulting in the formation of multi-level hierarchical structures. They were found to be nontoxic and enabled efficient adhesion and proliferation of osteoblastic cells by guiding filopoidal extension.close21

Mussel-inspired functionalization of carbon nanotubes for hydroxyapatite mineralization

Hydroxyapatite (HAp)/carbon nanotubes (CNTs) hybrid composite materials are successfully synthesized via a biomineralization process that employs poly(dopamine) (PDA), a synthetic mimic of mussel adhesive proteins. Creating bio-inorganic composites for regenerative medicine requires appropriate fillers to enhance their mechanical robustness; for example, natural bones are composed mainly of HAp supported by collagen fibers. In this regard, many efforts have been made to harness HAp as a bone substitute through its integration with reinforcing fibrous materials such as CNTs. We found that the formation of a PDA ad-layer on the surface of CNTs changed the hydrophobic CNTs to become bioactive. This enabled efficient interaction between the CNTs and mineral ions (e.g., Ca2+), which facilitated the mineralization of HAp. CNTs functionalized with PDA (CNT-PDA) highly accelerated the formation of HAp when incubated in a simulated body fluid and exhibited a minimal cytotoxic effect on bone osteoblast cells compared to pristine or carboxylated CNTs. Our results show the potential of CNT-PDA as a scaffold material for bone tissue regeneration and implantation.close272