Stable aqueous dispersions of fullerenes, C60 and C70, were prepared by simply injecting into water a saturated solution of fullerene in tetrahydofuran (THF), followed by THF removal by purging gaseous nitrogen. To our knowledge, this is the first report of the stable dispersion of C70 in water. Fullerenes are dispersed as monodisperse clusters in water, 60 nm in diameter. High resolution transmission electron microscopy revealed the polycrystalline nature of the cluster. The preparation of the dispersion is very easy to perform, and the dispersions thus obtained are of excellent colloidal stability even though no stabilizing agent is used. It was found that the surface of the cluster is negatively charged and the electrostatic repulsion between the negatively charged cluster surfaces is important for the stability of the dispersions.
Solution properties in water of hydrophobized pullulan containing 1.6 cholesterol groups per 100 glucose units (CHP-55-1.6) were studied by size exclusion column chromatography (SEC), dynamic (DLS) and static light scattering (SLS) methods, electron microscopy, lH NMR, and fluorescence spectroscopy.SEC measurementsshow that CHP (l.Omg/mL, 0.lOwt %) intermolecularly aggregates and providesrelatively monodispersive particles upon ultrasonication. Spherical particles with relatively uniform size (the diameter, 25 * 5 nm) were observed in the negatively stained electron microscopy of the aqueous CHP solution. The hydrodynamic radius of the CHP self-aggregate determined by DLS was approximately 13 nm, and the aggregation number determined by SLS was approximately 13; the weight averaged molecular weight of the self-aggregate was 7.6 X lo5, the root mean-square radius of gyration (Re) was 16.8 nm, and the second virial coefficient (Az) was 2.60 X 10-4 (mol mL)/g2. The critical concentration of the self-aggregate formation determined fluorometrically was 0.01 mg/mL. In addition, they showed no surface activity at all up to the concentration of 0.145 mg/mL. Existence of microdomains which consist of both the rigid core of hydrophobic cholesterol and the relatively hydrophilic polysaccharide shell was auggested on the basis of both the line broadening of the proton signal of the cholesterol moiety of CHP(8 = 0.6-2.4 ppm) in the 'H NMR spectrum and the incorporation of several hydrophobic fluorescent probes in the CHP self-aggregates. The CHP self-aggregates strongly complexed with hydrophobic and less hydrophilic fluorescent probes similarly to the case of cyclodextrin.
Various cholesterol-bearing pullulans (CHPs) with different molecular weights of the parent pullulan and degrees of substitution (DS) of the cholesteryl moiety were synthesized. The structural characteristics of CHPs in water were studied by static (SLS) and dynamic light scattering (DLS) and the fluorescence probe method. Irrespective of the molecular weight of the parent pullulan and the DS, all of CHPs provided unimodal and monodisperse self-aggregates in water. The size of the self-aggregate decreased with an increase in the DS of the cholesteryl moiety (hydrodynamic radius, 8.4−13.7 nm). However, the aggregation number of CHP in one nanoparticle was almost independent of the DS. The polysaccharide density within the self-aggregate (0.13−0.50 g/mL) was affected by both the molecular weight and the DS of CHPs. The mean aggregation number of the cholesteryl moiety (3.5−5.7), which was estimated by the fluorescence quenching method using pyrene and cetylpyridinium chloride, was almost same for all the CHP self-aggregates. The CHP self-aggregate is regarded as a hydrogel nanoparticle, in which pullulan chains are cross-linked noncovalently by associating cholesteryl moieties. The microenvironment inside or the structural characteristic of the self-aggregate was spectrometrically studied using a fluorescence probe, ANS. The characteristic temperature to cause a structural change of the nanoparticle (T*) decreased with an increase in the DS of CHP and the ionic strength of the medium. The thermoresponsiveness of the nanoparticle hydrogel is related to the partial dehydration of the hydrophobized pullulan upon heating.
Colloidal dispersions of C60 and C70 were prepared by simply mixing a fullerene solution in a good solvent with a poor polar organic solvent for fullerenes. The process was very easy and fast and the formation of particles with average diameter in the colloidal range was detected immediately after the components were mixed. The formation and the properties of the fullerene particles were studied mainly with dynamic light scattering and high-resolution transmission electron microscopy. The most interesting findings are the long-term colloid stability of the samples in the absence of any stabilizers, the relatively narrow size distribution, and the different average sizes of the particles formed by C60, C70, and their mixtures. The influence of various factors such as fullerene concentration, mixing procedure, solvent properties, and C60/C70 ratio was investigated. It is shown that the smaller particles are formed when the total fullerene concentration in the good solvent is decreased and that the fullerene particles have crystalline structure. The measured negative values for the electrophoretic mobility of the particles suggest that fullerene dispersions in polar organic solvents are stabilized by repulsive electrostatic interactions.
The study of extracellular DNA viral particles in the ocean is currently one of the most advanced fields of research in viral metagenomic analysis. However, even though the intracellular viruses of marine microorganisms might be the major source of extracellular virus particles in the ocean, the diversity of these intracellular viruses is not well understood. Here, our newly developed method, referred to herein as fragmented and primer ligated dsRNA sequencing (flds) version 2, identified considerable genetic diversity of marine RNA viruses in cell fractions obtained from surface seawater. The RNA virus community appears to cover genome sequences related to more than half of the established positive-sense ssRNA and dsRNA virus families, in addition to a number of unidentified viral lineages, and such diversity had not been previously observed in floating viral particles. In this study, more dsRNA viral contigs were detected in host cells than in extracellular viral particles. This illustrates the magnitude of the previously unknown marine RNA virus population in cell fractions, which has only been partially assessed by cellular metatranscriptomics and not by contemporary viral metagenomic studies. These results reveal the importance of studying cell fractions to illuminate the full spectrum of viral diversity on Earth.
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