Jianzhong Yang

Endocytic mechanisms and toxicity of a functionalized fullerene in human cells

Derivatized fullerenes could be used in biomedical applications and be suitable vectors for drug delivery due to their small size, large surface area and solubility. However, the interactions of derivatized fullerenes with biological systems and cells are not well understood. A water-soluble fullerene-substituted phenylalanine (Bucky amino acid, Baa) poly-lysine derivative with a FITC label (Baa-Lys(FITC)-(Lys)(8)-OH) was characterized by dynamic light scattering, transmission electron microscopy with negative staining, gel electrophoresis, zeta-potential, and UV/vis spectroscopy. Viability assays depicted the cytotoxicity was time, concentration and assay dependent. A decrease in ATP and glutathione at the high concentrations suggests that reactive oxygen species may be involved. Baa-Lys(FITC)-(Lys)(8)-OH was present near the cell membrane at 15 min and entered into the cytoplasm by 30 min but did not localize in the lysosomes. Endocytic inhibitors were used to investigate the uptake mechanism. These results showed that the endocytic pathways could be mediated by caveolae/lipid rafts and cytoskeletal components. A scavenger receptor inhibitor completely blocked the uptake of Baa-Lys(FITC)-(Lys)(8)-OH, suggesting a specific endocytic pathway was strongly involved in Baa-Lys(FITC)-(Lys)(8)-OH cellular uptake.

Diels–Alder addition to fluorinated single walled carbon nanotubes

Fluorinated single walled carbon nanotubes (SWNTs) undergo a facile Diels-Alder [4 + 2] cycloaddition with a range of dienes resulting in a C ratio substituent ratio between 20 ratio 1 to 32 ratio 1; IR, Raman, AFM and (13)C NMR characterization are consistent with sidewall functionalization.

Determination of the mode and efficacy of the cross-linking of guar by borate using MAS 11B NMR of borate cross-linked guar in combination with solution 11B NMR of model systemsElectronic supplementary information (ESI) available: Figs. S1?S9. See http://www.rsc.org/suppdata/dt/b4/b406952h/

The reaction product of boric acid and the polysaccharide guaran (the major component of guar gum) has been investigated by 11B NMR spectroscopy. By comparison with the 11B NMR of boric acid and phenylboronic acid complexes of 1,2-diols (HOCMe2CMe2OH, cis-C6H10(OH)2, trans-C6H10(OH)2, o-C6H4(OH)2), 1,3-diols (neol-H2), monosaccharides (L-fucose, mannose and galactose) and disaccharides (cellobiose and sucrose) it is found that the guaran polymer is cross-linked via a borate complex of two 1,2-diols both forming chelate 5-membered ring cycles ([B5(2)]), this contrasts with previous proposals. Based upon steric constraints we propose that preferential cross-linking the guaran polymer occurs via the 3,4-diols of the galactose side chain. The DeltaH and DeltaS for complexation of boric acid to cis- and trans-1,2-cyclohexanediol have been determined, from the temperature dependence of the appropriate equilibrium constants, and used in conjunction with ab initio calculations on model compounds, to understand prior conflicting proposals for guaran-boric acid interactions. 11B NMR derived pH dependent equilibrium constants and ab initio calculations have been used to understand the reasons for the inefficiency of boric acid to cross-link guaran (almost 2 borate ions per 3 monosaccharide repeat units are required for a viscous gel suitable as a fracturing fluid): the most reactive sites on the component saccharides (mannose and galactose) are precluded from reaction by the nature of the guar structure; the comparable acidity (pKa) of the remaining guaran alcohol substituents and the water solvent, results in a competition between cross-linking and borate formation; a significant fraction of the boric acid is ineffective in cross-linking guar due to the modest equilibrium (Keq). In contrast to prior work, we present evidence for the reaction of alcohols with boric acid, rather than the borate anion. Based upon the results obtained for phenylboronic acid, alternative cross-linking agents are proposed.

SiO2 template-derived polyurethane and alumina nanoparticle-polyurethane lithium ion separator membranes

Alumina nanoparticle (alumoxane) doped polyurethane films were prepared by the template directed synthesis method with highly controlled physical dimensions and tested as a Li-ion battery separator. Monodispersed silica spheres are used as a template around which polyurethane monomer is infiltrated and cross-linked by UV light (320 nm). The silica is subsequently removed by etching to leave an alumina NP doped polyurethane membrane. The choice of substitutent on the alumina nanoparticle [methoxy(ethoxyethoxy) acteic acid (MEEA), acetic acid, and lysine] was chosen to alter the surface properties of the polyurethane. The MEEA-alumoxane doped membranes were characterized by SEM, and the conductivity of the electrolyte in the separators was measured using AC impedance spectroscopy. The MacMullin number for all of the template directed polyurethane separators was greater than that of the commercial porous membrane suggesting that despite a high pore volume the conductivity is limited by the size of the interconnects.