Ryota Yamasaki

Flattened-Top Domical Water Drops Formed through Self-Organization of Hydrophobin Membranes: A Structural and Mechanistic Study Using Atomic Force Microscopy

The Trichoderma reesei hydrophobin, HFBI, is a unique structural protein. This protein forms membranes by self-organization at air/water or water/solid interfaces. When HFBI forms a membrane at an air/water interface, the top of the water droplet is flattened. The mechanism underlying this phenomenon has not been explored. In this study, this unique phenomenon has been investigated. Self-organized HFBI membranes form a hexagonal structured membrane on the surface of water droplets; the structure was confirmed by atomic force microscopy (AFM) measurement. Assembled hexagons can form a planar sheet or a tube. Self-organized HFBI membranes on water droplets form a sheet with an array of hexagonal structures or a honeycomb structure. This membrane, with its arrayed hexagonal structures, has very high buckling strength. We hypothesized that the high buckling strength is the reason that water droplets containing HFBI form flattened domes. To test this hypothesis, the strength of the self-organized HFBI membranes was analyzed using AFM. The buckling strength of HFBI membranes was measured to be 66.9 mN/m. In contrast, the surface tension of water droplets containing dissolved HFBI is 42 mN/m. Thus, the buckling strength of a self-organized HFBI membrane is higher than the surface tension of water containing dissolved HFBI. This mechanistic study clarifies why the water droplets formed by self-organized HFBI membranes have a flattened top.

Non-catalyzed one-step synthesis of ammonia from atmospheric air and water

It is well known that ammonia is produced through a catalytic reaction at high temperature and pressure from pure nitrogen and hydrogen. This catalytic chemical process is a massive and high-energy-consuming process, but a very important one for nitrogen fixation. Here, we show a non-catalyzed one-step synthesis of ammonia from atmospheric air (nitrogen source) and water (hydrogen source), based on an interfacial reaction between the air plasma gas phase and the water phase, at 25 °C and atmospheric pressure. In the plasma/liquid interfacial reaction (P/L reaction), atomic nitrogen in both air plasma and nitrogen plasma first abstracts hydrogen from the water phase surface at the P/L interface, and then NH is produced without any catalyst. Transiently formed NH is reduced further at the water phase, affording NH3, which then dissolves in the water phase. The P/L reaction may provide an alternative solution that enables both energy conservation and CO2 emission reduction.

Formation Mechanism of Flattened Top HFBI Domical Droplets

A water droplet assumes a spherical shape because of its own surface tension. However, water droplets containing dissolved hydrophobin (HFBI) have flat surfaces. In our previous study, the mechanism of this unique phenomenon was revealed. HFBI forms a self-organized membrane that has a densely packed and honeycomb-like structure. Furthermore, the buckling strength of the membrane is higher than the surface tension of the HFBI droplet. Therefore, an HFBI domical droplet has a flat surface. However, it was not clear why only the top of the domical droplet was flattened while other areas such as the side face were not. In this study, we observed HFBI domical droplets to investigate this phenomenon. The flat top area (self-organized HFBI membrane) remained parallel to the ground even if the substrate was tilted. Therefore, buoyancy was thought to be a factor affecting the HFBI membrane. In addition, the side face of the HFBI domical droplet was analyzed by atomic force microscopy and electrochemical impedance spectroscopy, and it was found that the sides of the HFBI droplet were not composed of densely packed HFBI membranes.

Electrochemical properties of honeycomb-like structured HFBI self-organized membranes on HOPG electrodes

HFBI (derived from Trichoderma sp.) is a unique structural protein, which forms a self-organized monolayer at both air/water interface and water/solid interfaces in accurate two-dimensional ordered structures. We have taken advantage of the unique functionality of HFBI as a molecular carrier for preparation of ordered molecular phase on solid substrate surfaces. The HFBI molecular carrier can easily form ordered structures; however, the dense molecular layers form an electrochemical barrier between the electrode and solution phase. In this study, the electrochemical properties of HFBI self-organized membrane-covered electrodes were investigated. Wild-type HFBI has balanced positive and negative charges on its surface. Highly oriented pyrolytic graphite (HOPG) electrodes coated with HFBI molecules were investigated electrochemically. To improve the electrochemical properties of this HFBI-coated electrode, the two types of HFBI variants, with oppositely charged surfaces, were prepared genetically. All three types of HFBI-coated HOPG electrode perform electron transfer between the electrode and solution phase through the dense HFBI molecular layer. This is because the HFBI self-organized membrane has a honeycomb-like structure, with penetrating holes. In the cases of HFBI variants, the oppositely charged HFBI membrane phases shown opposite electrochemical behaviors in electrochemical impedance spectroscopy. HFBI is a molecule with a unique structure, and can easily form honeycomb-like structures on solid material surfaces such as electrodes. The molecular membrane phase can be used for electrochemical molecular interfaces.

Excitation of H2O at the plasma/water interface by UV irradiation for the elevation of ammonia production

Ammonia is well known to be a very important chemical substance for human life. Simultaneously, the conventional ammonia production process needs pure nitrogen and pure hydrogen. Hydrogen has been produced from either liquid natural gas (LNG) or coal. In this study, water is used as a direct hydrogen source for ammonia production, thereby obviating the need for catalysts or water electrolysis. We have studied and developed a plasma/liquid interfacial reaction (P/L reaction) that can be used to produce ammonia from air (nitrogen) and water at ambient temperature and pressure, without any catalysts. In this study, the P/L reaction entails enhanced ultraviolet (UV) irradiation of the surface of the water phase. The nitrogen plasma/water interface reaction locus can produce ammonia. In contrast, the vacuum ultraviolet (VUV) irradiated interface reaction locus produces increased amounts of ammonia. In a spin trap electron spin resonance (st-ESR) experiment, large amounts of atomic H (H˙) were produced by UV irradiation, especially by VUV irradiation. The derived H˙ effectively enhanced the P/L reaction rate.