岸川 圭希

Melanin is a widely occurring biopolymer and has been the subject of much research, especially in dermatology. However, from a resource perspective, melanin is still an unutilized biomass because of its complex three-dimensional cross-linked structure, which makes it challenging to handle. Here, we demonstrate melanin upcycling by decomposing melanin and preparing polymeric materials from its products. A detailed study of the chemical decomposition products of artificial melanin, i.e., polydopamine, reveals that the melanin decomposition products are mainly oligomeric pyrrole derivatives containing carboxylic acids. Furthermore, decomposition experiments using natural melanin extracted from cuttlefish ink revealed that the composition of melanin decomposition products is almost identical regardless of the melanin source. We proposed a melanin decomposition mechanism and demonstrated the preparation of biobased polymer films and particles from melanin decomposition products. The use of melanin decomposition products as building blocks for material preparation is expected to lead to the development of new biodegradable polymers from biomass.

The columnar polarization direction of ferroelectric columnar liquid crystals can be switched by applying an external electric field, and the polarization direction can be maintained, even after the electric field is removed. If the polarization direction of each column in ferroelectric columnar liquid crystals can be switched and maintained, then ultrahigh-density memory devices can be generated. Recently, we found that the columnar phase of N,N′-bis(3,4,5-tri(S)-citronellyloxyphenyl)urea (Urea-(S)-cit) shows ferroelectricity, whereas that of N,N′-bis(3,4,5-tridecyloxyphenyl)urea (Urea-10) does not. However, the mechanisms by which the six chiral alkoxy groups in Urea-(S)-cit generate ferroelectricity have not been determined. In this study, we regioselectively synthesized four diphenylurea compounds containing (S)-citronellyloxy and decyloxy groups, i.e., N,N′-bis(3,5-di((S)-citronellyloxy)-4-decyloxyphenyl)urea (1), N,N′-bis(4-((S)-citronellyloxy)-3,5-didecyloxyphenyl)urea (2), N,N′-bis(3-((S)-citronellyloxy)-4,5-didecyloxyphenyl)urea (3), and N,N′-bis(3,4-di((S)-citronellyloxy)-5-decyloxyphenyl)urea (4), and investigated which chiral alkoxy group at which position is strongly responsible for the ferroelectricity. The chiral alkoxy groups at 3- and 5-positions of the phenyl groups were clarified to play a significant role in the generation of ferroelectricity. Furthermore, a comparison of these four compounds based on circular dichroism spectroscopy and second harmonic generation experiments revealed the relationship between the helical structure order and the stability of the polarized structure.

Abstract Here, an unprecedented phenomenon in which 7‐coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H₂O molecules, form micellar cubic mesophases at room temperature, creating body‐centered cubic (BCC)‐type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self‐assembling behavior of 6‐coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7‐coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

The realization of ferroelectric columnar liquid crystals (FCLCs) capable of axial polarization switching along the column axis at room temperature (RT) is an important breakthrough in the practical application of FCLCs. However, molecules exhibiting FCLC phases generally have low fluidity at RT, which inhibits the response of polar functional groups to an applied external electric field, making changing the direction of the column polarity difficult. Here, we report RT-FCLCs, N,N′-bis(3,4-dialkoxyphenyl)ureas, driven by a low electric field. The introduction of bulky branched alkyl chains lowered the temperature range of the columnar liquid crystal phases, resulting in a fluid-assembled state with moderate hydrogen bonding that allowed polarization switching at RT. Comparison of these synthesized ureas revealed that reductions in the bulk and length of the side chains produced longer retention times of the polarization. Our thermodynamic analyses clarified that these ureas have high enough depolarization activation energy to maintain polarization, despite a low coercive field of a few V μm-1. Furthermore, the retention time of the columnar liquid crystal phase dramatically increased as the temperature neared RT, indicating an increase in the slowness of molecular motion, reminiscent of the vitrification process. We established a methodology to achieve FCLCs with the desired performance by selecting the alkyl chain to be introduced.

In this study, we show that doping lanthanides into lamellar crystals reorganizes the lamellar structure and dramatically changes the crystal morphology. Azo-DA, a compound with azobenzene derivatives and carboxylic acids at both ends of the diacetylene moiety, formed plate-like lamellar crystals. The doping of holmium (Ho), a lanthanide, into the film obtained by stacking Azo-DA lamellar crystals, promoted a dramatic change in crystal morphology, resulting in the formation of an Azo-DA/Ho film with a radial lamellar crystal structure. A detailed investigation of the crystal growth process revealed that Azo-DA/Ho, which is slightly formed in the solution phase during Ho doping, acts as a pseudonucleating agent and dramatically changes the morphology of the lamellar crystals. Additionally, the morphological changes in the lamellar crystal films significantly changed the surface properties of the films, such as their appearance and water repellency. Similar morphological changes in lamellar crystals were induced when other lanthanide elements were used instead of Ho, and the type of lanthanide dopant can affect the magnetic properties of the films.