Vinyl polymerization. 422. Initiation mechanism of uncatalyzed polymerization by polyethyleneglycol

The initiation mechanism on the radical polymerization of vinyl monomers by polyethyleneglycol (PEG-300) in aqueous solution was studied. The initiating radical species were determined by means of the spin trapping technique. They were concluded to be generated by the hydrogen atom transfer from the monomer adsorbed at the ether group of PEG-300 to the free monomer.     

Structure of amauromine,a new alkaloid with vasodilating activity produced by amauroascus sp.

Structure of amauromine (1a), a novel alkaloid with potent vasodilating activity has been established by chemical and spectroscopic evidences.     

Dielectric loss of high-density polyethylene below 4.2°K

Drawing of oxidized high-density polyethylene (HDPE) and subsequent annealing greatly reduce the low-temperature dielectric loss when the electric field is applied perpendicular to the draw direction. This supports our model (J. Polym. Sci. Polym. Phys. Ed., 15 , 43 (1977)) of the proton moving parallel to the c axis of the PE crystal. A particular antioxidant (Ionox 330) in unoxidized HDPE induces a dielectric loss with a frequency and temperature dependence which differs from that for the loss in oxidized HDPE. The antioxidant loss seems to be an overlapping of tunneling and a thermal activation process. The possibility that the hydroperoxide group in the PE crystal is the origin of the loss in oxidized HDPE was theoretically examined in a manner similar to that used for the hydroxyl group in the previous paper. Results suggest that the hydroperoxide group is less probable than hydroxyl as the origin of the low-frequency loss in HDPE.     

Late-stage functionalisation of alkyne-modified phospha-xanthene dyes: lysosomal imaging using an off–on–off type of pH probe

Near-infrared (NIR) fluorescent molecules are of great importance for the visualisation of biological processes. Among the most promising dye scaffolds for this purpose are P O-substituted phospha-xanthene (POX) dyes, which show NIR emission with high photostability. Their practical utility for in vitro and in vivo imaging has recently been demonstrated. Although classical modification methods have been used to produce POX-based fluorescent probes, it is still a challenge to introduce additional functional groups to control the localisation of the probe in cells. Herein, we report on the development of POXs that bear a 4-ethynylphenyl group on the phosphorus atom. These dyes can subsequently be functionalised with azide-tagged biomolecules via a late-stage Cu-catalysed azide/alkyne cycloaddition (CuAAC) reaction, thus achieving target-selective labelling. To demonstrate the practical utility of the functionalised POXs, we designed a sophisticated NIR probe that exhibits a bell-shaped off–on–off pH-response and is able to assess the degree of endosomal maturation.

A series of NIR-emissive phospha-xanthene dyes bearing an ethynyl group are reported. The late-stage functionalisation of the NIR dyes enables creation of multi-functionalised fluorescent probes that can be designed to target organelles of interest.     

Dibenzoborole-containing pi-electron systems: remarkable fluorescence change based on the "on/off" control of the p(pi)-pi* conjugation

A series of dibenzoborole derivatives with various groups such as (N,N-diphenylamino)phenyl, thienyl, and bithienyl groups at the 3,7-positions have been synthesized and their photophysical properties studied. These new pi-electron systems show significant solvatochromism in the fluorescence spectra. Thus, about 100-140 nm blue shifts in the emission maxima and 20-30-fold increments in the quantum yields are observed upon changing the solvent from THF to DMF. Similar fluorescence changes are observed upon the addition of n-Bu4NF to their THF solutions, demonstrating their sensing abilities toward a fluoride ion. These fluorescence changes result from the "on/off" control of the ppi-pi* conjugation in their LUMO by the coordination of donor solvents or fluoride ion to the boron atom in the dibenzoborole skeleton.     

Silver(I) compounds consisting of [2.2]paracyclophane: reversible guest-driven solid-state transformation and incorporation behavior

Reaction of [2.2]paracyclophane with silver(I) heptafluorobutyrate (AgC3F7CO2) has isolated three novel networks: [Ag4(pcp)(C3F7CO2)4] x pyrene (1), [Ag4(pcp)(C3F7CO2)4] x phen (phen = phenanthrene) (2), and [Ag4(pcp)(C3F7CO2)4] x fluorene (3), and an intercalation compound [Ag4(pcp)(C3F7CO2)4] x 2benzene (4). All the four complexes exhibit two-dimensional (2D) sheet structures in which AgC3F7CO2 form an infinite chain and pcp acts as linkage. 1, 2, and 3 show 2D flat sheets with cavities in which guest molecules are situated, whereas 4 exhibits 2D zigzag layers between which guest benzene molecules are intercalated. Pcp shows mu-di-eta1-eta2 coordination mode in 1, mu-tetra-eta1 coordination mode in 2 and 3, and mu-tetra-eta2 coordination mode in 4. The reversible guest exchanges were observed between complex 1, 2, or 3 and intercalation compound 4. It is unprecedented for metal-organic inclusion complexes that the guest exchange occurs where the guest is the solute molecule. Furthermore, 4 can release the guest, and the original framework was completely recovered after reincorporation of benzene. It should be noted that 4 can incorporate pyrene, phen, and fluorene to give 1, 2, and 3, respectively, after desorption.