Thiazolocatechol: Electron-Withdrawing Catechol Anchoring Group for Dye-Sensitized Solar Cells

Anchoring groups adopting a five-membered bidentate chelating are attractive to realize high power conversion efficiency (η) and long-term durability in dye-sensitized solar cells (DSSCs). In this regard, we chose catechol as an anchoring group that can adopt the chelating. However, the DSSCs with catechol-based sensitizers have never exceeded an η-value of 2 %. These poor photovoltaic performances may be associated with the electron-donating ability of the hydroxy groups in catechol. Considering these, we envisioned that fusing an electron-withdrawing thiazole moiety with a catechol anchoring group would improve its photovoltaic performance. Herein, we report a push-pull porphyrin sensitizer ZnPTC with a thiazolocatechol anchoring group. The DSSC with ZnPTC exhibited η=4.87 %. This value is the highest ever reported for catechol-anchor based DSSCs. Meanwhile, the long-term cell durability was not improved, although the robust anchoring properties were attained under harsh conditions.     

Fluorescence Quenching‐based Assay for Measuring Golgi endo‐α‐Mannosidase

Golgi endo‐α‐mannosidase (G‐EM) catalyzes an alternative deglucosylation process for N‐glycans and plays important roles in the post‐endoplasmic reticulum (ER) quality control pathway. To understand the post‐ER quality control mechanism, we synthesized a tetrasaccharide probe for the detection of the hydrolytic activity of G‐EM based on a fluorescence quenching assay. The probe was labeled with an N‐methylanthraniloyl group as a reporter dye at the non‐reducing end and a 2,4‐dinitrophenyl group as a quencher at the reducing end. This probe is hydrolyzed to disaccharide derivatives by G‐EM, resulting in increased fluorescence intensity. Thus, the fluorescence signal is directly proportional to the amount of disaccharide derivative present, allowing the G‐EM activity to be evaluated easily and quantitatively.     

Environment-sensitive fluorophores with benzothiadiazole and benzoselenadiazole structures as candidate components of a fluorescent polymeric thermometer

An environment-sensitive fluorophore can change its maximum emission wavelength (λ(em)), fluorescence quantum yield (Φ(f)), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge-transfer-type environment-sensitive fluorophores, DBThD-IA and DBSeD-IA, in which the oxygen atom of a well-established 2,1,3-benzoxadiazole environment-sensitive fluorophore, DBD-IA, has been replaced by a sulfur and selenium atom, respectively. DBThD-IA is highly fluorescent in n-hexane (Φ(f) =0.81, λ(em) =537?nm) with excitation at 449?nm, but is almost nonfluorescent in water (Φ(f) =0.037, λ(em) =616?nm), similarly to DBD-IA (Φ(f) =0.91, λ(em) =520?nm in n-hexane; Φ(f) =0.027, λ(em) =616?nm in water). A similar variation in fluorescence properties was also observed for DBSeD-IA (Φ(f) =0.24, λ(em) =591?nm in n-hexane; Φ(f) =0.0046, λ(em) =672?nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time-resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD-IA and DBSeD-IA. In addition, DBThD-IA exhibits a 10-fold higher photostability in aqueous solution than the original fluorophore DBD-IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry.     

Utilization of photoinduced charge-separated state of donor-acceptor-linked molecules for regulation of cell membrane potential and ion transport

The control of ion transport across cell membranes by light is an attractive strategy that allows targeted, fast control of precisely defined events in the biological membrane. Here we report a novel general strategy for the control of membrane potential and ion transport by using charge-separation molecules and light. Delivery of charge-separation molecules to the plasma membrane of PC12 cells by a membranous nanocarrier and subsequent light irradiation led to depolarization of the membrane potential as well as inhibition of the potassium ion flow across the membrane. Photoregulation of the cell membrane potential and ion transport by using charge-separation molecules is highly promising for control of cell functions.     

Asymmetric Total Synthesis of (−)‐Stenine and 9a‐epi‐Stenine

A route for the asymmetric synthesis of (?)‐stenine, a member of the Stemona alkaloid family used as folk medicine in Asian countries, is described. The key features of the sequence employed include stereoselective transformations on a cyclohexane ring controlled by a chiral auxiliary unit and an intramolecular Mitsunobu reaction to construct the perhydroindole ring system. By using an intermediate in the route to (?)‐stenine, an asymmetric synthesis of 9a‐epi‐stenine was also executed. The C(9a) stereocenter in 9a‐epi‐stenine was installed by using a Staudinger/aza‐Wittig reaction of a keto–azide precursor followed by reduction of the resulting imine. The results of this effort demonstrate the applicability of the chiral auxiliary based strategy to the preparation of naturally occurring alkaloids that contain highly functionalized cyclohexane cores.     

Hierarchical Supramolecular Spinning of Nanofibers in a Microfluidic Channel: Tuning Nanostructures at a Dynamic Interface

One of the fundamental problems in supramolecular chemistry, as well as in material sciences, is how to control the self‐assembly of polymers on the nanometer scale and how to spontaneously organize them towards the macroscopic scale. To overcome this problem, inspired by the self‐assembly systems in nature, which feature the dynamically controlled self‐assembly of biopolymers, we have previously proposed a self‐assembly system that uses a dynamic liquid/liquid interface with dimensions in the micrometer regime, thereby allowing polymers to self‐assemble under precisely controlled nonequilibrium conditions. Herein, we further extend this system to the creation of hierarchical self‐assembled architectures of polysaccharides. A natural polysaccharide, β‐1,3‐glucan (SPG), and water were injected into opposite “legs” of microfluidic devices that had a Y‐shape junction, so that two solvents would gradually mix in the down stem, thereby causing SPG to spontaneously self‐assemble along the flow in a head‐to‐tail fashion, mainly through hydrophobic interactions. In the initial stage, several SPG nanofibers would self‐assemble at the Y‐junction owing to the shearing force, thereby creating oligomers with a three‐way junction point. This unique structure, which could not be created through conventional mixing procedures, has a divergent self‐assembly capability. The dynamic flow allows the oligomers to interact continuously with SPG nanofibers that are fed into the Y‐junction, thus amplifying the nanostructure along the flow to form SPG networks. Consequently, we were able to create stable, centimeter‐length macroscopic polysaccharide strands under the selected flow conditions, which implies that SPG nanofibers were assembled hierarchically in a supramolecular fashion in the dynamic flow. Microscopic observations, including SEM and AFM analysis, revealed the existence of clear hierarchical structures inside the obtained strand. The network structures self‐assembled to form sub‐micrometer‐sized fibers. The long fibers further entangled with each other to give stable micrometer‐sized fibers, which finally assembled to form the macroscopic strands, in which the final stabilities in the macroscopic regime were governed by that of the network structures in the nanometer regime. Thus, we have exploited this new supramolecular system to create hierarchical polymeric architectures under precisely controlled flow conditions, by combining the conventional supramolecular strategy with microfluidic science.     

Tag‐Convertible Photocrosslinker with Click‐On/Off N‐Acylsulfonamide Linkage for Protein Identification

The N‐acylsulfonamide group, known as a safety‐catch linker, has been applied to photoaffinity labeling (PAL) using a cinnamate‐type photocrosslinker to improve the efficiency of PAL‐based target identification. A bioorthogonal sulfo‐click reaction was used to stably link a photocrosslinker unit with N‐acylsulfonamide linkage to produce a photoactivatable probe without any protection. In addition, the crosslinked protein was selectively isolated with a small cinnamate tag via linkage disruption upon N‐alkylation. Furthermore, the tag moiety was photochemically converted to a stable coumarin derivative by losing a water molecule, which is a useful property in MS‐based identification.     

Direct Dimesitylborylation of Benzofuran Derivatives by an Iridium-Catalyzed C−H Activation with Silyldimesitylborane

Direct dimesitylborylation of benzofuran derivatives by a C−H activation catalyzed by an iridium(I)/N-heterocyclic carbene (NHC) complex in the presence of Ph₂MeSi-BMes₂ afforded the corresponding dimesitylborylation products in good to high yield with excellent regioselectivity. This method provides a straightforward route to donor–(π-spacer)–acceptor systems with intriguing solvatochromic luminescence properties.     

Identification of possible technical problems in determination of the major inorganic constituents of brown-rice flour by evaluating proficiency test results

To support skill upgrading in analysis of inorganic constituents of environmental and food samples, the National Metrology Institute of Japan (NMIJ) and the National Food Research Institute (NFRI) have organized a proficiency test (PT) of determination of Mn, Fe, Cu, Zn, As, and Cd in brown-rice flour based on the international standard (ISO/IEC 17043:2010). One hundred and thirty-three sets of reports were assessed by use of the E _n -number and z-score approaches in accordance with ISO/IEC 17043 and the international harmonized protocol for PT. The PT results and analytical procedures, reported in detail, were reviewed, and possible technical reasons for questionable or unsatisfactory results are discussed.