SnCl4-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control of the reaction

The SnCl₄-promoted rearrangement of 2,2,3,3-tetrasubstituted-2,3-epoxy-1-alcohol derivatives proceeded in a regio- and stereo-controlled manner to selectively give two types of rearranged products from a single isomer by changing the protecting group of the alcohol.     

Stable molecular configuration in crystalline carboxylic acids

The stable (lower enthalpy) molecular configurations of propionic, butyric, Jeric and lauric acids in the crystalline state have been examined via their atom-atom potentials. It was found that the cis configuration is more stable than the trans configuration for propionic, butyric and valeric acids, and that the trans configuration is more stable than the cis configuration for lauric acid, in accord with a previous IR spectral analysis. The potential energy of benzoic acid was recalculated using the positions of atoms given by Speakman, and indicates that the A form is more stable than the B form, in agreement with the results of previous work.     

Photoinduced increase in vesicle size and role of photoresponsive malachite green leuconitrile derivative in vesicle fusion

The influence of photoirradiation on vesicles containing a Malachite Green leuconitrile derivative carrying a long alkyl chain, affording photogenerated amphiphilicity, was investigated. The photoresponsive Malachite Green leuconitrile derivative was embedded in the vesicle bilayer of two single-tailed amphiphiles with oppositely charged head groups consisting of cetyltrimethylammonium chloride (CTAC) and sodium octyl sulfate (SOS). Transmission electron microscopy, which was used for observing photoinduced structural change in the vesicles, demonstrated that photoirradiation of the vesicles containing the Malachite Green leuconitrile derivative increased the average size of the vesicle diameter from 116 to 243 nm in the [CTAC]/[SOS] = 0.48 system. The mechanism for vesicle enlargement was studied with fluorescent probe molecules. The photoinduced change in the vesicle size can be explained by the destabilization of the vesicle bilayer, which is perturbed by photogenerated amphiphilicity. In addition, it was shown that the fusion process arising from the destabilized bilayer contributed to the increase in vesicle size.     

Subdiffraction imaging through the selective donut-mode depletion of thermally stable photoswitchable fluorophores: numerical analysis and application to the fluorescent protein Dronpa

The fast and reversible on/off switching of the fluorescence emission of the GFP-like fluorescent protein Dronpa has attracted considerable interest for applications in subdiffraction imaging. In this paper we study the use of a donut-mode beam in combination with two more overlapping laser beams to increase the imaging resolution through selective switching to the nonfluorescent photoswitched state. We devise and run a series of numerical simulations to determine suitable photophysical parameters of prospective, thermally stable photoswitchable molecules, in terms of photoswitching quantum yields, fatigue resistance, and possible presence of transient nonfluorescent states. Many of our findings are applicable to other measurements that make use of donut beams, and these guidelines can be used in the synthesis and screening of novel photoswitchable compounds. We experimentally demonstrate the possibility of obtaining increased resolution by making use of the efficient and thermally stable Dronpa photoswitching, using equipment that is commonly available.     

Comprehensive separation of secondary metabolites in natural products by high-speed counter-current chromatography using a three-phase solvent system

High-speed counter-current chromatography (HSCCC) using the three-phase solvent system n-hexane-methyl acetate-acetonitrile-water at a volume ratio of 4:4:3:4 was applied to the comprehensive separation of secondary metabolites in several natural product extracts. A wide variety of secondary metabolites in each natural product was effectively extracted with the three-phase solvent system, and the filtered extract was directly submitted to the HSCCC separation using the same three-phase system. In the HSCCC profiles of crude natural drugs listed in the Japanese Pharmacopoeia, several physiologically active compounds were clearly separated from other components in the extracts. The HSCCC profiles of several tea products, each manufactured by a different process, clearly showed their compositional difference in main compounds such as catechins, caffeine, and pigments. These HSCCC profiles also provide useful information about hydrophobic diversity of whole components present in each natural product.     

Binding of malachite green promotes stability and shows preference for a human telomere DNA G-quadruplex

A single-stranded human telomere DNA sequence can fold into an intramolecular G-quadruplex structure, which has been shown to inhibit telomerase activity. Small molecules that selectively target and stabilise the G-quadruplex structure have been proposed as potential anticancer drugs. In this study, we analysed the properties of binding of malachite green, a cationic triphenylmethane dye, to the G-quadruplex of d[(T₂AG₃)₄] by UV spectroscopy of thermal melting analysis, a competitive equilibrium dialysis assay, and absorption and circular dichroism spectroscopies. When binding to malachite green, the quadruplex structure that formed in the presence of K⁺ ions was stabilised with an increase in melting temperatures by 6 °C. Malachite green showed selective binding to the G-quadruplex in the presence of duplex and single-stranded DNAs, owing to which it presents higher potential for anticancer therapy, compared to other triphenylmethane dyes. The induced signals of circular dichroism indicate that the binding mode of malachite green involves intercalation between adjacent guanine tetrads of the G-quadruplex.     

Dehydrogenative oxidation of alcohols in aqueous media using water-soluble and reusable Cp*Ir catalysts bearing a functional bipyridine ligand

A new catalytic system for the dehydrogenative oxidation of alcohols using a water-soluble Cp*Ir complex bearing a bipyridine-based functional ligand as catalyst has been developed. With this catalytic system, a variety of primary and secondary alcohols have been efficiently converted to aldehydes and ketones, respectively, in aqueous media without using any oxidant. Reuse of the catalyst by a very simple procedure has been also accomplished.     

Size-dependent partitioning of nano/microparticles mediated by membrane lateral heterogeneity

It is important that we understand the physical, chemical, and biological mechanisms that govern the interaction between nanoparticles (NPs) and heterogeneous cellular surfaces because of the possible cytotoxicity of engineered nanomaterials. In this study, we investigated the lateral localization of nano/microparticles within a biomimetic heterogeneous membrane interface using cell-sized two-phase liposomes. We found that lateral heterogeneity in the membrane mediates the partitioning of nano/microparticles in a size-dependent manner: small particles with a diameter of ≤200 nm were localized in an ordered phase, whereas large particles preferred a fluidic disordered phase. This partitioning behavior was verified by temperature-controlled membrane miscibility transition and laser-trapping of associated particles. In terms of the membrane elastic energy, we present a physical model that explains this localization preference of nano/microparticles. The calculated threshold diameter of particles that separates the particle-partitioning phase was 260 nm, which is in close agreement with our observation (200 nm). These findings may lead to a better understanding of the basic mechanisms that underlie the association of nanomaterials within a cell surface.