Anti-Stokes Luminescence in Multi-Resonance-Type Thermally-Activated Delayed Fluorescence Molecules

Photon-upconversion in organic molecular systems is one of the promising technologies for future energy harvesting systems because these systems can generate excitons that possess higher energy than excitation energy. The photon-upconversion caused by absorbing ambient heat as additional energy is particularly interesting because it could ideally provide a light-driving cooling system. However, only a few organic molecular systems have been reported. Here, we report the anti-Stokes photoluminescence (ASPL) derived from hot-band absorption in a series of multi-resonance-type thermally-activated delayed fluorescence (MR-TADF) molecules. The MR-TADF molecules exhibited an anti-Stokes shift of approximately 0.1 eV with a high PL quantum yield in the solution state. The anti-Stokes shift corresponded well to the 1–0 vibration transition from the ground state to the excited singlet state, and we further evaluated a correlation between the activation energy for the ASPL intensity and the TADF process. Our demonstration underlines that MR-TADF molecules have become a novel class of ASPL materials for various future applications, such as light-driving cooling systems.     

Localized surface plasmon enhanced microcrystalline–silicon solar cells

A novel type of substrate named “Ag–SP substrate”, in which silver nanoparticles are incorporated, is introduced and utilized as a back reflector for hydrogenated microcrystalline-silicon solar cell in a substrate-type (n-i-p) configuration. Optical and morphological analyses of Ag–SP substrates fabricated with various sizes of silver nanoparticles are systematically performed. It is shown that silver nanoparticles in Ag–SP substrate structure can lead to significant scattering of light when their diameter increases up to 300 nm. Furthermore, the photocurrent of the solar cell fabricated on an Ag–SP substrate with RMS roughness as small as 16.5 nm and a proper lateral diameter (approximately 300 nm) of silver nanoparticles is improved as compared to that of the solar cell prepared on reference textured substrate with RMS roughness of 25.3 nm, owing to strong scattering of light by silver nanoparticles in the red-infrared region.     

Control Mechanism for cis Double‐Bond Formation by Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final‐product profiles are still obscure. In this study, the FabA‐type dehydratase domain (DH_FabA) in the C‐subunit and the polyketide synthase‐type dehydratase domain (DH_PKS) in the B‐subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C₄‐ to C₈‐acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DH_PKS and DH_FabA, depending on the carbon‐chain length, to introduce either saturation or cis double bonds to growing acyl chains.     

Molecular imprinting on amphiphilic folded polymers for selective molecular recognition in water

We report amphiphilic folded polymers with imprinted nanocavities for selective molecular recognition in water. For this, a molecular imprinting technique is applied to the polymer synthesis: amphiphilic polymer micelles interacting with template molecules are crosslinked in water to fix the folded architecture and memorize the template structure within the polymers; the removal of the templates provides imprint polymers bearing template-specific nanospaces. Here, a hydrophilic dye bearing two anionic groups, Orange G (OG), is used as a model template. For the imprinting, we design amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) chains, hydrophobic olefin groups, and quaternary ammonium groups that can interact with the template. The copolymers were prepared by living radical polymerization and post functionalization. In the presence of OG and methyl blue (MB), the imprinted nanocavity polymers simultaneously capture both of the dyes in water. The total number of encapsulated dyes increased with increasing the number of polymer-bound quaternary ammonium groups. The selectivity of OG against MB increased with the crosslinking density, while imprint polymers encapsulated OG more efficiently than nonimprint polymers. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 215–224     

Control Mechanism for Carbon‐Chain Length in Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are essential fatty acids. PUFA synthases are composed of three to four subunits and each create a specific PUFA without undesirable byproducts. However, detailed biosynthetic mechanisms for controlling final product profiles have been obscure. Here, the bacterial DHA and EPA synthases were carefully dissected by in vivo and in vitro experiments. In vitro analysis with two KS domains (KS_A and KS_C) and acyl‐acyl carrier protein (ACP) substrates showed that KS_A accepted short‐ to medium‐chain substrates while KS_C accepted medium‐ to long‐chain substrates. Unexpectedly, condensation from C₁₈ to C₂₀, the last elongation step in EPA biosynthesis, was catalyzed by KS_A domains in both EPA and DHA synthases. Conversely, condensation from C₂₀ to C₂₂, the last elongation step for DHA biosynthesis, was catalyzed by the KS_C domain in DHA synthase. KS_C domains therefore determine the chain lengths.     

Monodispersed molecularly imprinted polymer for creatinine by modified precipitation polymerization

A monodispersed molecularly imprinted polymer (MIP) for creatinine was prepared by modified precipitation polymerization. The retention and molecular-recognition properties of the prepared MIP were evaluated by the hydrophilic interaction chromatography mode using a mixture of ammonium acetate buffer and acetonitrile as a mobile phase in liquid chromatography. The MIP had a specific recognition ability for creatinine, while other structurally related compounds, such as hydantoin, 1-methylhydantoin, 2-pyrrolidone, N-hydroxysuccinimide and creatine, could not be recognized on the MIP. In addition to shape recognition, hydrophilic interactions could work for the recognition of creatinine on the MIP.     

Synthetic inhibitors of proline-rich ligand-mediated protein-protein interaction: potent analogs of UCS15A

The proline-rich motif in proteins is known to function as a ligand sequence that binds to protein modules such as SH3, WW, and several other protein interaction domains. These proline-rich ligand-mediated protein-protein interactions (abbreviated PLPI) are important in many signaling pathways that are involved in various diseases. Our previous studies showed that UCS15A, produced by Streptomyces species, inhibited PLPI. Here we report on synthetic analogs of UCS15A that show more potent activity than UCS15A in inhibiting PLPI. A synthetic analog, compound 2c, blocked in vitro PLPI of Sam68-Fyn-SH3 as well as in vivo PLPI of Grb2-Sam68 and Grb2-Sos1. Activation of MEK was also inhibited by compound 2c. Unlike UCS15A, compound 2c was an order of magnitude less cytotoxic and did not cause morphological changes in treated cells.     

A pulse radiolysis study of oil/water microemulsions

Absorption spectrum and the yield of e_aq⁻ determined in quaternary benzene/water and dodecane/water microemulsions were found to be identical with those in pure water. This indicates that the excess electrons produced in the oil droplets cross the oil/water interface and appear in the aqueous phase as hydrated electrons. On the contrary, it was found that the OH radical yield measured by converting into (SCN)₂^.− was directly proportional to the water content and there was no contribution from the oil phase. The e_aq⁻ decay in aerated microemulsion showed that the [O₂] in the aqueous phase was decreasing with continuous pulse irradiation and the estimated G(–O₂) in the oil was higher than in water. However, peroxides were predominantly formed in the aqueous phase and almost not in the oil. Rate constants for the addition of e_aq⁻ and OH to benzene in the benzene/water microemulsion and the following bimolecular decay of cyclohexadienyl and hydroxycyclohexadienyl radicals agree well with those reported in aqueous solutions.