Seragakinone A, a new pentacyclic metabolite from a marine-derived fungus

A new anthracycline-derived pentacyclic metabolite, seragakinone A (1), was isolated from the mycelium of an unidentified fungus, which was separated from the Okinawan marine rhodophyta Ceralodictyon spongiosum, and the structure was elucidated by spectroscopic data.     

Influence of grafting solvents on the properties of polymer electrolyte membranes prepared by γ-ray preirradiation method

The effect of grafting solvents, such as isopropanol (iPrOH), tetrachloroethane (TCE), tetrahydrofuran (THF), and toluene, on the preparation of poly(ethylene-co-tetrafluoroethylene)-graft-poly(styrene sulfonic acid) (ETFE-g-PSSA) electrolyte membranes by the γ-ray preirradiation grafting method was investigated. It was found that the iPrOH can drastically accelerate the grafting, resulting in a higher degree of grafting. However, for an appropriate degree of grafting of about 50%, the sulfonic acid groups in the ETFE-g-PSSA membrane prepared with the iPrOH were mainly distributed near the membrane surface, as shown by low proton conductivity in the membrane thickness direction. In contrast to this result, the ETFE-g-PSSA membranes prepared with the THF, toluene and TCE exhibited uniform distribution of the sulfonic acid groups in the membrane. Especially, in the case of the TCE grafting solvent, the chemical stability of the resultant electrolyte membrane was clearly higher than those prepared with the other grafting solvents.     

Convectional, sedimentary, and drying dissipative patterns of colloidal suspensions of polymer complexes of poly(acrylic acid) with poly(ethylene glycol) and poly(vinyl pyrrolidone)

Convectional, sedimentary, and drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri dish during the course of dryness of aqueous suspensions of colloidal polymer complexes of poly(acrylic acid) (HPAA) with poly(ethylene glycol) (PEG) and poly(vinyl pyrrolidone) (PVP). With increase in the molecular weight of the polymer component, the complexes showed from transparent solution stable colloidal dispersion and the sticky aggregates. HPAA25K + PVP25K complex showed bluish colors and the colloidal crystal suspension. Size of the macroscopic broad rings of HPAA25K + PEG decreased as molecular weight of PEG increased. Furthermore, the size increased sharply as the polymer concentration increased in the complex systems HPAA25K + PVP25K. Characteristic microscopic patterns appeared for HPAA + PEG and HPAA + PVP complexes.     

Fluorescence spectroscopy of fulvic acids’ interaction with surfactants

Fluorescence spectra of two fulvic acid (FA) samples, FA0 from underground water and FA1 from forest soil, were recorded in various surfactant solutions. Alkyltrimethylammonium ions with different alkyl chain lengths induced a decrease in the fluorescence intensity for both FAs at concentrations below the critical micelle concentration (cmc) and an enhancement above the cmc. The intensity minimum thus obtained at the cmc was deeper for surfactants with longer alkyl chains. This effect was attributable to the formation of insoluble FA–surfactant complexes below the cmc and to the solubilization of the complex into micelles above the cmc. Dodecylpyridinium chloride caused a monotonic decrease in the FA fluorescence even far above the cmc. This was attributable to the quenching of FA fluorescence by the positioning of the pyridinium head group near the FA fluorophore. Anionic and nonionic surfactants showed little to no effect on the FA fluorescence.     

Determination of traces of palladium in stream sediment and auto catalyst by FI-ICP-OES using on-line separation and preconcentration with QuadraSil TA

A flow injection analysis (FIA) method using on-line separation and preconcentration with a novel metal scavenger beads, QuadraSil™ TA, has been developed for the ICP-OES determination of traces of palladium. QuadraSil TA contains diethylenetriamine as a functional group on spherical silica beads and shows the highest selectivity for Pd(II) at pH 1 (0.1 mol l⁻¹ hydrochloric acid) solution. An aliquot of the sample solution prepared as 0.1 mol l⁻¹ in hydrochloric acid was passed through the QuadraSil TA column. After washing the column with the carrier solution, the Pd(II) retained on the column was eluted with 0.05 mol l⁻¹ thiourea solution and the eluate was directly introduced into an ICP-OES. The proposed method was successfully applied to the determination of traces of palladium in JSd-2 stream sediment certified reference material [0.019 ± 0.001 μg g⁻¹ (n = 3); provisional value: 0.0212 μg g⁻¹] and SRM 2556 used auto catalyst certified reference material [315 ± 4 μg g⁻¹ (n = 4); certified value: 326 μg g⁻¹]. The detection limit (3σ) of 0.28 ng ml⁻¹ was obtained for 5 ml of sample solution. The sample throughputs for 5 ml and 100 μl of the sample solutions were 10 and 15 h⁻¹, respectively.     

Asymmetric catalytic cycloetherification mediated by bifunctional organocatalysts

Oxacyclic structures such as tetrahydrofuran (THF) rings are commonly found in many bioactive compounds, and this has led to several efforts toward their stereoselective syntheses. However, the process of catalytic asymmetric cycloetherification for their straightforward synthesis has remained a challenge. In this study, we demonstrate a novel asymmetric synthesis method for THF via the catalytic cycloetherification of ε-hydroxy-α,β-unsaturated ketones mediated by cinchona-alkaloid-thiourea-based bifunctional organocatalysts. This catalytic process represents a highly practical cycloetherification method that provides excellent enantioselectivities, even with low catalyst loadings at ambient temperature.     

In vivo fluorescence imaging of bone-resorbing osteoclasts

Osteoclasts are giant polykaryons responsible for bone resorption. Because an enhancement or loss of osteoclast function leads to bone diseases such as osteoporosis and osteopetrosis, real-time imaging of osteoclast activity in vivo can be of great help for the evaluation of drugs. Herein, pH-activatable chemical probes BAp-M and BAp-E have been developed for the detection of bone-resorbing osteoclasts in vivo. Their acid dissociation constants (pK(a)) were determined as 4.5 and 6.2 by fluorometry in various pH solutions. These pK(a) values should be appropriate to perform selective imaging of bone-resorbing osteoclasts, because synthesized probes cannot fluoresce intrinsically at physiological pH and the pH in the resorption pit is lowered to about 4.5. Furthermore, BAp-M and BAp-E have a bisphosphonate moiety that enabled the probes to localize on bone tissues. The hydroxyapatite (HA) binding assay in vitro was, therefore, performed to confirm the tight binding of the probes to the bone tissues. Our probes showed intense fluorescence at low pH values but no fluorescence signal under physiological pH conditions on HA. Finally, we applied the probes to in vivo imaging of osteoclasts by using intravital two-photon microscopy. As expected, the fluorescence signals of the probes were locally observed between the osteoclasts and bone tissues, that is, in resorption pits. These results indicate that our pH-activatable probes will prove to be a powerful tool for the selective detection of bone-resorbing osteoclasts in vivo, because this is the first instance where in vivo imaging has been conducted in a low-pH region created by bone-resorbing osteoclasts.     

Spectrophotometric determination of cobalt(II) and cyanocobalamin with vanillilfluorone and its applications

Spectrophotometric determination of cobalt(II) was accomplished with vanillilfluorone (VF) in the presence of dimethylbenzyltetradecylammonium chloride (Zephiramine, Zep). In the determination of cobalt(II), Beer's law was obeyed in the range of 24-470 ng/ml, with an effective molar absorption coefficient (at 575 nm) and relative standard deviation of 1.35×10(5) l mol(-1) cm(-1) and 0.66% (n=5), respectively. The composition ratio of the colored complex was determined by the mole ratio and continuous variation methods, and it was found to be Co(II) : VF : Zep=1 : 2 : 4. Analysis of cyanocobalamin by the same procedure showed that cyanocobalamin could be determined in the concentration range of 0.5-0.11 μg/ml using the proposed method.     

π‐Electron‐System‐Layered Polymer: Through‐Space Conjugation and Properties as a Single Molecular Wire

[2.2]Paracyclophane‐based through‐space conjugated oligomers and polymers were prepared, in which poly(p‐arylene–ethynylene) (PAE) units were partially π‐stacked and layered, and their properties in the ground state and excited state were investigated in detail. Electronic interactions among PAE units were effective through at least ten units in the ground state. Photoexcited energy transfer occurred from the stacked PAE units to the end‐capping PAE moieties. The electrical conductivity of the polymers was estimated using the flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC) method and investigated together with time‐dependent density functional theory (TD‐DFT) calculations, showing that intramolecular charge carrier mobility through the stacked PAE units was a few tens of percentage larger than through the twisted PAE units.     

Photoreversible Supramolecular Polymerisation and Hierarchical Organization of Hydrogen‐Bonded Supramolecular Co‐polymers Composed of Diarylethenes and Oligothiophenes

Diarylethene 1 equipped with two monotopic melamine hydrogen‐bonding sites and oligothiophene‐functionalized ditopic cyanurate (OTCA) were mixed in a nonpolar solvent to form AA‐BB‐type supramolecular co‐polymers (SCPs) bearing photoswitchable moieties in their main chains and extended π systems as side chains. UV/Vis, fluorescence, dynamic light scattering (DLS), TEM, and AFM studies revealed that the two functional co‐monomers formed flexible quasi‐one‐dimensional SCPs in solution that hierarchically self‐organized into helical nanofibers through H‐aggregation of the oligothiophene side chains. Upon irradiating the SCPs with UV light, a transition occurred from the H‐aggregated state to non‐aggregated monomeric oligothiophene side chains, as shown by spectroscopic studies, which indicates the formation of small oligomeric species held together only by hydrogen‐bonding interactions. TEM and AFM visualized unfolded fibrils corresponding to elongated single SCP chains formed upon removal of solvent. The helical nanofibers were regenerated upon irradiating the UVirradiated solution with visible light. These results demonstrated that the supramolecular polymerisation followed by hierarchical organization can be effectively controlled by proper supramolecular designs using diarylethenes and π‐conjugated oligomers.