Hiroki Hotta

Objective: The use of traditional hair dyeing agents to dye hair may cause scalp and hair damage, induce melanocyte stem cell depletion, and in some cases trigger allergic reactions. Therefore, we explored a novel hair colouring approach using 5,6‐dihydroxyindole (DHI), a precursor of eumelanin, to dye grey hair. This study aimed to elucidate the mechanism by which cationic polymer pretreatment enhances the dyeability of DHI, focusing on changes in hair surface charge and the dyeing mechanism of DHI. Methods: Dyeability was assessed by UV–Vis spectrophotometry. The degree of cationization at different pH values was determined by colloid titration, and the hair surface potential was measured using a zeta potential analyser. Adsorption and penetration behaviours were evaluated by confocal fluorescence microscopy with ionic fluorescent dyes. Cross‐sections of DHI‐dyed hair were examined by optical microscopy. Results: Pretreatment with a specific cationic polymer increased the dyeability of DHI‐based formulations. A polymer capable of retaining positive charge under alkaline conditions (pH 10) was identified, and its suitability was confirmed by degree of cationization measurements, zeta potential shifts and fluorescence adsorption imaging. Mechanistic analyses indicated that water‐soluble DHI is retained within the δ‐layer of the cell membrane complex in the cuticle region, where it undergoes air oxidation and polymerization, resulting in fixation within the hair. Conclusion: Cationic polymer pretreatment enhances DHI dyeability and may support the development of DHI‐based formulations as potential alternatives to oxidative hair dyes.

This study investigated the effects of incorporating muconic acid-derived amino acid compounds (CM) into a reductive hair-straightening formulation on hair shape stability and surface characteristics. Hair tresses obtained from Brazilian donors with moderately wavy to curly hair were treated with a cysteamine-based straightening system, with or without CM, and evaluated under high-temperature, high-humidity conditions (40 °C, 75% relative humidity). CM-treated hair maintained a straighter configuration after 24 h of humidity exposure, whereas the control groups exhibited partial or complete loss of the straightening effect. The mean hair width significantly decreased in the CM-treated group, indicating improved macroscopic shape stability. Furthermore, the coefficient of friction was significantly reduced following CM treatment, and the combing resistance showed a decreasing trend, although the difference was not statistically significant. Scanning electron microscopy (SEM) observations suggested a tendency toward reduced cuticle lifting after repeated thermal and mechanical stress. These findings suggest that preservation of cuticle morphology together with reduced fiber–fiber friction may contribute to enhanced humidity-resistant straightening and improved hair manageability. Overall, CM enhanced humidity-resistant straightening while improving hair surface characteristics. These findings suggest that CM is a promising additive for the development of humidity-resistant hair-straightening formulations.

This study investigated the effects of incorporating a novel amino acid compound (CM) into a reductive hair-straightening formulation on hair shape stability, mechanical properties, and surface characteristics. Hair trees from Brazilian donors were treated with a cysteamine-based straightening system, with or without CM, and evaluated under high-temperature, high-humidity conditions (40 °C, 75% relative humidity). CM-treated hair remained straight after 24 h of humidity exposure, whereas the control group exhibited partial or complete loss of the straightening effect. The mean hair spread width significantly decreased in the CM-treated group, indicating improved macroscopic shape stability. Mechanical analysis revealed a significant increase in bending rigidity (p < 0.05), whereas torsional rigidity and torsional hysteresis were significantly decreased (p < 0.01), suggesting direction-dependent changes in fiber mechanics. Furthermore, the coefficient of friction was significantly reduced following CM treatment, and the combing resistance tended to decrease. Scanning electron microscopy images revealed suppression of cuticle deterioration induced by repeated thermal and mechanical stress. Collectively, reduced torsion, improved shape retention, increased bending stiffness, and decreased fiber–fiber friction contributed to the improved combability and enhanced durability of straightening performance. Overall, CM enhanced humidity-resistant straightening while improving the surface and mechanical properties of the hair fibers. These findings suggest that CM is a promising additive for the development of humidity-resistant hair-straightening formulations.

DPPH radical (DPPH•) scavenging reactions by antioxidants were monitored using continuous cyclic voltammetry. Electrochemical responses of both DPPH• and the antioxidants were simultaneously recorded, and the reversibility of electron transfer was evaluated from changes in their respective concentrations. In reactions between DPPH• and antioxidants containing a p-dihydroxybenzene moiety, the electrochemical responses of both DPPH• and the antioxidants showed no significant changes over time. This indicates that both species underwent reversible electron transfer accompanied by H+ transfer without side reactions. In contrast, for antioxidants containing an o-dihydroxybenzene moiety, DPPH• consistently showed reversible electron transfer, whereas the electrochemical response of the antioxidants gradually decreased during the reaction. This suggests that DPPH• underwent electron transfer with H+ transfer only, while the antioxidants subsequently participated in chemical reactions after electron transfer, resulting in electrochemical deactivation. Ascorbic acid, cysteine and Trolox exhibited similar behavior. By contrast, reactions involving antioxidants with an m-dihydroxybenzene moiety showed time-dependent electrochemical changes for both DPPH• and the antioxidants, indicating irreversible addition reactions that produced products with redox activities distinct from those of the original reactants. Overall, a clear regularity in the reaction behavior between DPPH• and antioxidants was identified based on their fundamental structural features.

Objective: Hair is a crucial aspect of an individual's physical appearance. Thus, there is always a need for technology to care for curls and undulations. In this study, we found that heat treatment with a mixed aqueous solution of cysteamine (2‐aminoethanethiol) and fumaric acid was highly effective in improving hair quality. The purpose of this study was to scientifically elucidate the effectiveness of this technology by identifying its active ingredients, evaluating their functionality and analysing changes in the internal structure of hair after treatment.Method: We observed changes in hair shape through a hair straightening test, analysed the components using liquid chromatography/mass spectrometry (LC/MS) and investigated the effects on mechanical properties using bending and surface friction measurements. Furthermore, we analysed the hair conditions using small‐angle X‐ray scattering (SAXS) measurements and evaluated water retention using thermal analysis.Results: In the hair straightening test, even extremely strong curls of African human hair improved. The LC/MS results revealed that the active ingredient was 2‐(2‐aminoethylthio) succinic acid (ATS). Furthermore, by treating hair with ATS, decreases in the coefficient of friction and bending stiffness and an increase in moisture content were observed. The SAXS measurements revealed that the treatment widened the distance between the intermediate filaments (IFs) inside the hair and improved the orientation of the IFs.Conclusion: ATS, produced by the thiol–ene reaction between fumaric acid and cysteamine, acts as an active ingredient in hair shape control. ATS reacted within the matrix and increased the IF–IF distance. This suggests that ATS functions as a crosslinker for keratin proteins. ATS is believed to increase the moisture content of hair and improve hair texture.

Muconic acid, a crucial precursor in synthesizing materials like PET bottles and nylon, is pivotal for the anticipated growth in the textiles and plastics industries. This study presents a novel chemical synthesis route for cis,cis-muconic acid (ccMA) using catechol. Biochemical methods face scale-up challenges due to microorganism sensitivity and complex extraction processes, while chemical methods involve environmentally harmful substances and have low yields. Our research introduces a method that enhances ccMA yield to 56% by employing ozonation in the presence of an alkali, significantly simplifying the synthesis process. This one-step synthesis reduces reagent use and labor, aligns with green chemistry principles, and avoids using toxic chemicals. The methodology, involving the low-temperature ozonation of catechol with base addition, reduces ccMA degradation and improves yield, as confirmed by an HPLC analysis and replicated experiments. This promising approach could lead to sustainable industrial synthesis of muconic acid derivatives. Further investigations will focus on refining this method for larger-scale applications and testing its economic viability, aiming to optimize conditions for maximum efficiency and yield.

Muconic acid, a crucial precursor in synthesizing materials like PET bottles and nylon, is pivotal for the anticipated growth in textiles and plastics industries. This study presents a novel chemical synthesis route for cis,cis-muconic acid (ccMA) using catechol. Biochemical methods face scale-up challenges due to microorganism sensitivity and complex extraction processes, while chemical methods involve environmentally harmful substances and have low yields. Our research intro-duces a method that enhances ccMA yield to 56% by employing ozonation in the presence of a hydrophilic base, significantly simplifying the synthesis process. This one-step synthesis reduces reagent use and labor, aligns with green chemistry principles, and avoids using toxic chemicals. The methodology, involving low-temperature ozonation of catechol with base addition, reduces ccMA degradation and improves yield, confirmed by HPLC analysis and replicated experiments. This promising approach could lead to sustainable industrial synthesis of muconic acid deriva-tives. Further investigations will focus on refining this method for larger-scale applications and testing its economic viability, aiming to optimize conditions for maximum efficiency and yield.

天然抗酸化剤は生体の還元剤として，活性酸素の過剰生成による酸化傷害から生体を防御する機能を担っている。抗酸化剤の基本的な物理化学的特性を評価するために，電気化学測定は非常に有効な手段である。電気化学測定によって得られるパラメータのうち，筆者らは特に酸化電子数（n）に注目することで，酸化に伴う多量化反応によってnが増大する反応メカニズムを発見した。これはバルク溶液中での抗酸化活性を非常によく説明することができる特性であった。一方で，生体内での反応を考えるうえで，混じり合わない溶液／溶液または溶液／膜界面での反応を観察することは極めて重要である。液／液界面近傍で起こる電子移動の観察にも着手し，疎水性の度合いにより反応機構が異なることを示した。液膜界面での電子移動を観察するために，筆者らが考案した分光測定法についても紹介する。