Atsushi Hirano

Carbon nanotubes (CNTs) exhibit exceptional properties, including high thermal conductivity, mechanical flexibility, and near-infrared luminescence. These properties can be further tuned through CNT surface functionalization. Aryl diazonium salts are widely used for such functionalization because they react under mild conditions. Although the CNT functionalization efficiency depends on the solvent, the factors contributing to these solvent effects remain insufficiently understood. This study systematically investigated the effect of five representative organic solvents—dimethylformamide, isopropyl alcohol, tetrahydrofuran, N-methyl-2-pyrrolidone, and dimethyl sulfoxide (DMSO)—on the degree of CNT functionalization using aryl diazonium reagents. The degree of functionalization was evaluated using photoluminescence spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The solvent effect on CNT functionalization was attributable to three factors: CNT dispersibility, the chemical stability of the aryl diazonium reagent, and the binding affinity of the reagent to CNTs; the relative contributions depend on the reagent concentration. Among the solvents tested, DMSO was the most effective for CNT functionalization over a wide range of reagent concentrations. Furthermore, a homogeneous CNT–protein composite film exhibiting near-infrared photoluminescence was fabricated using DMSO. These findings provide mechanistic insights into solvent effects in diazonium-based CNT functionalization and offer guidelines for solvent selection in CNT functionalization and CNT-based composite fabrication.

PFAS（per- and polyfluoroalkyl substances）は有機フッ素化合物の総称であり，優れた耐熱性・耐薬品性・撥水撥油性を有する．そのため，工業プロセスのほか，日用品や食品包装材，泡消火器など，幅広く利用されている．しかしながら，PFASは極めて難分解性で環境中に長期間残留しやすく，近年では腎臓がんや免疫障害，発達毒性などの健康被害との関連も報告されている．現在，浄水処理ではPFASの除去に活性炭が用いられているが，その除去性能は十分とはいえない．したがって，より高性能な除去材料の開発が急務となっている．本研究では，ジルコニア粒子を用いたPFAS除去の可能性を検討した．その結果，ジルコニアは特定のPFAS分子に対して結合能を示すことが明らかになった．結合機構は主として静電相互作用に基づくものであることが示唆された．吸着はpHによって制御することが可能であった．ジルコニアは地殻中に豊富に存在する資源であり，化学的安定性や機械的強度，安全性にも優れることから，浄水処理プロセスに利用可能なPFAS除去材として期待される．

Carbon nanotubes (CNTs) exhibit exceptional properties, including high thermal conductivity and flexibility, and biologically transparent near-infrared luminescence. These properties can be further tuned by introducing functional groups onto CNT surfaces. Aryl diazonium salts are widely used for such functionalization because they react under mild conditions, typically in organic solvents. However, the effect of solvent on the efficiency of CNT functionalization remains unclear. This study systematically investigated the effect of organic solvents on the degree of CNT functionalization using 4-carboxybenzenediazonium tetrafluoroborate as the aryl diazonium reagent. The solvents tested were dimethylformamide (DMF), isopropyl alcohol (IPA), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and 1-methyl-2-pyrrolidone (NMP). The degree of functionalization was found to depend on the solvent type, reflecting their combined effects on CNT dispersion and aryl diazonium salt stability. These insights enabled the fabrication of a CNT–protein composite film that exhibited near-infrared emission derived from CNT functional groups under white LED irradiation. The present findings provide general guidelines for CNT surface modification and interface design in CNT-based applications.

Immunoglobulin A (IgA) is the most abundant antibody in the human body and plays a critical role in defending against bacteria and viruses that invade through mucosal surfaces. Leveraging this property, recombinant IgA has been developed as a preventive drug for infectious diseases such as COVID-19, influenza, and tuberculosis. Recombinant IgA is typically purified using columns packed with protein-immobilized resins, such as jacalin, Protein L, or nanobody-based materials. However, these methods have several drawbacks, including high costs due to expensive resins and mobile phases, the need for multiple purification steps, and the potential leakage of immobilized proteins. To address these issues, the present study proposes an alternative IgA purification method using zirconia (ZrO₂) particles. Purification was performed for three forms of IgA─monomeric, dimeric, and secretory component-bound IgA─using both batch adsorption and chromatography. All three forms were successfully purified with high purity. The method employs phosphate buffers at mildly acidic and neutral pH as the mobile phase, which helps preserve the structure of IgA. Because ZrO₂ particles are both cost-effective and chemically and mechanically robust, the proposed method overcomes the limitations associated with conventional protein-immobilized resins in IgA purification.

The affinity between carbon nanotubes (CNTs) and organic compounds is of substantial importance since it strongly relates to the dispersibility of CNTs in those compounds. Several affinity evaluation methods have been developed so far, and the concept of the Hansen solubility parameter is a representative method widely used in the field of nanocarbon materials. Here, we demonstrate that CNT-loaded silica columns can effectively assess the affinity of organic compounds for CNT surface by exploiting the chromatographic retention time as a criterion. Obtained trends of the affinity of organic compounds for CNT were compared to those based on Hansen solubility parameter distance values. Most organic compounds showed similar trends, but one exceptional compound was observed. Simple CNT dispersion tests were conducted with these organic compounds to demonstrate the advantage of the chromatographic assessment. Further, we conducted comparison experiments using a pyrene-functionalized column and other CNT-loaded columns to elucidate the characteristics of each CNT column. The chromatographic approaches using CNT columns would be beneficial for realizing CNT suspensions with improved CNT dispersibility.

Polyphosphate (polyP) is one of the most conserved biomacromolecules and can form aggregates, such as polyP granules in bacteria, which are generated through liquid–liquid phase separation (LLPS). Studies have examined the mechanism of polyP aggregation using LLPS systems containing artificial polyP molecules as aggregation system models, where LLPS is typically induced by multivalent salts and polyelectrolytes. Although the typical concentrations of monovalent ions in living cells are approximately 100 times higher than those of divalent ions, the effects of monovalent ions on the LLPS of polyP solutions are little known. This study demonstrated that submolar NaCl induces LLPS of polyP solutions, whereas other monovalent salts did not at the same concentrations. Small-angle X-ray scattering measurements revealed that NaCl significantly stabilizes the intermolecular association of polyP, inducing LLPS. These findings suggest that the modulation of monovalent ion concentrations is an underlying mechanism of polyP aggregate formation/deformation within living cells. TOC GRAPHIC: