Self-Assembly of Linear Arrays of Semiconductor Nanoparticles on Carbon Single-Walled Nanotubes †

Ligand-stabilized nanocrystals (NCs) were strongly bound to the nanotube surfaces by simple van der Waals forces. Linear arrays of CdSe and InP quantum dots were formed by self-assembly using the grooves in bundles of carbon single-walled nanotubes (SWNTs) as a one-dimensional template. A simple geometrical model explains the ordering in terms of the anisotropic properties of the nanotube surface. CdSe quantum rods were also observed to self-organize onto SWNTs with their long axis parallel to the nanotube axis. This approach offers a route to the formation of ordered NC/SWNT architectures that avoids problems associated with surface derivatization. Both semiconductor quantum dots (QDs) 1 and carbon singlewalled nanotubes (SWNTs) 2 possess interesting and potentially useful optical and electronic properties due to their nanoscale structures. In the case of QDs, quantum confinement in three dimensions produces a size-dependent modification of the electronic band structure, resulting in the formation of discrete electronic states. QDs exhibit unique behaviors such as efficient photoluminescence and photon up-conversion, slowed relaxation and cooling of hot carriers, enhanced lasing, and carrier multiplication via impact ionization. 3 SWNTs, however, consist of sp 2 -hybridized carbon atoms that form the walls of nanometer-wide, seamless cylinders. Past efforts to attach semiconductor nanocrystals (NCs) to nanotubes have focused on forming chemical attachments between the two different nanostructures. In this approach, defects in the nanotube lattice, i.e., any site where the sp 2 -bonded carbon network is broken, are used as sites for chemical bond formation. Such defects are typically present after acid-based purification methods or may be specifically introduced by chemical derivatization. In this paper, we report the formation of organized, onedimensional (1-D) arrays of semiconductor QDs by van der Waals (vdW) adsorption onto SWNTs. Two representative II-VI and the III-V semiconductor NCs, CdSe and InP, respectively, demonstrated linear ordering when adsorbed from nonaqueous colloidal solutions onto high-purity, low-defectdensity SWNTs. The tendency to form linear arrays was greatest when tube-tube alignment was relatively good within bundles and when the QDs were relatively large. The edge-to-edge (ee) separation distance between QDs in the 1-D arrays was ∼18 Å for both the InP and the CdSe QDs, indicating that QD-QD separation is governed by the thickness of the ligand shells, as is the case in two-and three-dimensional QD arrays

Conditional Myh9 and Myh10 inactivation in adult mouse renal epithelium results in progressive kidney disease

Actin-associated nonmuscle myosin II (NM2) motor proteins play critical roles in a myriad of cellular functions, including endocytosis and organelle transport pathways. Cell type–specific expression and unique subcellular localization of the NM2 proteins, encoded by the Myh9 and Myh10 genes, in the mouse kidney tubules led us to hypothesize that these proteins have specialized functional roles within the renal epithelium. Inducible conditional knockout (cKO) of Myh9 and Myh10 in the renal tubules of adult mice resulted in progressive kidney disease. Prior to overt renal tubular injury, we observed intracellular accumulation of the glycosylphosphatidylinositol-anchored protein uromodulin (UMOD) and gradual loss of Na+ K+ 2Cl– cotransporter from the apical membrane of the thick ascending limb epithelia. The UMOD accumulation coincided with expansion of endoplasmic reticulum (ER) tubules and activation of ER stress and unfolded protein response pathways in Myh9&10-cKO kidneys. We conclude that NM2 proteins are required for localization and transport of UMOD and loss of function results in accumulation of UMOD and ER stress–mediated progressive renal tubulointerstitial disease. These observations establish cell type–specific role(s) for NM2 proteins in regulation of specialized renal epithelial transport pathways and reveal the possibility that human kidney disease associated with MYH9 mutations could be of renal epithelial origin

Synthesis-Dependent Oxidation State of Platinum on TiO₂ and Their Influences on the Solar Simulated Photocatalytic Hydrogen Production from Water

Platinized TiO₂ photocatalysts of different compositions of Pt⁰ and PtO₂ were prepared by modifying the synthesis procedures. The physicochemical properties of the composite materials were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Energy dispersive X-ray spectroscopy measurements confirmed the presence of Pt species existing as PtO₂ and/or mixtures of Pt⁰ and PtO₂. The composite material, Pt–TiO₂–2%H, contained a high amount of metallic Pt⁰ and PtO₂ in close proximity with TiO₂ that promoted an enhanced photocatalytic hydrogen evolution activity under simulated solar light irradiation. Although Pt–TiO₂–2%C and Pt–TiO₂–2%T consisted of similar compositions of PtO₂, these oxidized platinum species seem to appear further apart from TiO₂ in Pt–TiO₂–2%C than Pt–TiO₂–2%T. This caused dramatic variation in their optical behaviors such as strong fluorescence quenching and lower photocatalytic hydrogen evolution activity in the former photocatalyst. A photocatalyst prepared by the conventional photodeposition method was also prepared, characterized, and its photocatalytic activity assessed. This work provides an opportunity to understand the role of PtO₂ for photocatalytic production of hydrogen from platinized TiO₂ composites and the importance of heterojunctions in such photocatalysts for solar energy conversion