Masuki Kawamoto

Toward renewable energy for global leveling, compounds that can store ammonia (NH₃), a carbon-free energy carrier of hydrogen, will be of great value. Here, we report an organic-inorganic halide perovskite compound that can chemically store NH₃ through dynamic structural transformation. Upon NH₃ uptake, a chemical structure change occurs from a one-dimensional columnar structure to a two-dimensional layered structure by addition reaction. NH₃ uptake is estimated to be 10.2 mmol g^-1 at 1 bar and 25 °C. In addition, NH₃ extraction can be performed by a condensation reaction at 50 °C under vacuum. X-ray diffraction analysis reveals that reversible NH₃ uptake/extraction originates from a cation/anion exchange reaction. This structural transformation shows the potential to integrate efficient uptake and extraction in a hybrid perovskite compound through chemical reaction. These findings will pave the way for further exploration of dynamic, reversible, and functionally useful compounds for chemical storage of NH₃.

Proton exchange membrane (PEM) electrolyzers are used for hydrogen (H₂) production by water electrolysis. The commercial cathodic electrocatalyst for this process is typically mechanically mixed platinum on carbon (Pt/C). However, aggregation of the platinum (Pt) makes high loading of the catalyst difficult. Therefore, a method for the homogeneous combination of Pt and carbon materials is required. Herein, the first example of a highly efficient single‐walled carbon nanotube (SWCNT) cathodic H₂‐production electrocatalyst that is loaded with platinum nanoparticles (PtNPs) using a newly developed suspension method is reported. Combining SWCNTs lapped with a water‐soluble, thiol‐functionalized polymer with PtNPs in water yields a PtNP‐conjugated SWCNT suspension. The electrocatalyst exhibits a low overpotential of 47 mV at a current density of 10 mA cm⁻² toward H₂ evolution in 0.5 m sulfuric acid. A PEM electrolyzer fabricated using the optimally prepared electrocatalyst with the low loading of 15 µg_Pt cm⁻² shows a high mass activity of 27 200 A g_Pt⁻¹, which is 80 times that of Pt/C with a loading amount of 2.8 mg_Pt cm⁻² (324 A g_Pt⁻¹). In addition, the PEM electrolyzer produces H₂ at a Faradaic efficiency of 97% and operates stably for 150 h at 100 mA cm⁻².

Hydrogels show great potential as soft materials for biomedical applications and flexible devices. However, conventional hydrogels exhibit poor mechanical strengths owing to the presence of water in their polymer networks. Therefore, improving the mechanical properties of hydrogels by controlling the chemical and physical structures that affect their macroscopic behaviors is a challenging issue. In this study, we developed a nanocomposite (NC) hydrogel that harbors exfoliated few-layer graphene sheets through noncovalent interactions. The bifunctional polymer PImQ, which contains both aromatic and cationic groups, was found to enable the direct exfoliation of graphite to few-layer graphene through π–π interactions in 2.7% yield. The poly(acrylamide)-based NC hydrogel containing the PImQ/graphene composite as a nanofiller shows a 3.4-fold increase in tensile stress compared with the hydrogel without the nanofiller. The introduction of the PImQ/graphene nanocomposite also increases the fracture stress of the NC hydrogel through cation–π and π–π interactions. The improved mechanical properties of the NC hydrogel result from the synergistic effects of the chemical crosslinking of the polymer network and the physical crosslinking of the polymer/graphene nanofiller.

Single-walled carbon nanotubes (SWCNTs) have received extensive research attention owing to their extraordinary optical, electrical, and mechanical properties, which make them particularly attractive for application in optoelectronic devices. However, SWCNTs are insoluble in almost all solvents. Therefore, developing methods to solubilize SWCNTs is crucial for their use in solution-based processes. In this study, we developed a photocleavable polythiophene-derivative polymer dispersant for SWCNTs. The noncovalent surface functionalization of SWCNTs with a polymer allows their dispersal in tetrahydrofuran. The resultant solution-processed polymer/SWCNT composite film undergoes a hydrophobic-to-hydrophilic change in surface properties upon light irradiation (313 nm) because hydrophilic carboxyl groups are formed upon photocleavage of the hydrophobic solubilizing units in the polymer. Furthermore, the photocleaved composite film displays a 38-fold increase in electrical conductivity. This is due to the removal of the solubilizing unit, which is electrically insulating.

Monoclonal antibodies have been developed as anticancer agents to block immune checkpoint pathways associated with programmed cell death 1 (PD-1) and its ligand PD-L1. However, the high cost of antibodies has encouraged researchers to develop other inhibitor types. Here, biphenyl compounds were conjugated with poly(ethylene glycol) (PEG) to enhance the activity of small molecular inhibitors. Immunoassay results revealed the decrease in the inhibition activity following conjugation with linear PEG, suggesting that the PEG moiety reduced the interaction between the biphenyl structure and PD-L1. However, the inhibitory effect on PD-1/PD-L1 interaction was further enhanced by using branched PEG conjugates. The increase in the number of conjugated biphenyl compounds resulted in increased inhibitory activity. The highest IC₅₀ value was 0.33 μM, which was about 5 times higher than that observed for a non-conjugated monovalent compound. The inhibitory activity was more than 20 times the activity reported for the starting compound. Considering the increase in the inhibition activity, this multivalent strategy can be useful in the design of new immune checkpoint inhibitors.

Photoreactive polymers that generate active species upon irradiation with light are very useful for modifying the surfaces of substrates. However, water solubility decreases as the number of photoreactive functional groups on the polymer increases because most photoreactive functional groups are hydrophobic. In order to improve the hydrophilicity of the polymer, we synthesized polyethylene-glycol-based photoreactive polymers bearing hydrophobic azidophenyl groups on their side chains. Due to the hydrophilicity of the ethylene glycol main chain, polymers with large numbers of azidophenyl groups were solubilized in protic solvents. Polymers were immobilized on various substrates by irradiation with UV light and were shown to suppress non-specific interactions between proteins and cells on the substrate. We conclude that such polymers are useful, highly water soluble, antifouling agents.

Cancer immunotherapy has been revolutionized by the development of monoclonal antibodies (mAbs) that inhibit interactions between immune checkpoint molecules, such as programmed cell-death 1 (PD-1), and its ligand PD-L1. However, mAb-based drugs have some drawbacks, including poor tumor penetration and high production costs, which could potentially be overcome by small molecule drugs. BMS-8, one of the potent small molecule drugs, induces homodimerization of PD-L1, thereby inhibiting its binding to PD-1. Our assay system revealed that BMS-8 inhibited the PD-1/PD-L1 interaction with IC₅₀ of 7.2 μM. To improve the IC₅₀ value, we designed and synthesized a small molecule based on the molecular structure of BMS-8 by in silico simulation. As a result, we successfully prepared a biphenyl-conjugated bromotyrosine (X) with IC₅₀ of 1.5 μM, which was about five times improved from BMS-8. We further prepared amino acid conjugates of X (amino-X), to elucidate a correlation between the docking modes of the amino-Xs and IC₅₀ values. The results suggested that the displacement of amino-Xs from the BMS-8 in the pocket of PD-L1 homodimer correlated with IC₅₀ values. This observation provides us a further insight how to derivatize X for better inhibitory effect.