Scientific Publications 2006
2006. "A High Resolution Study of the Effect of Morphology on the Mass Spectra of Single PSL Particles with Na-Containing Layers and Nodules." Aerosol Science and Technology 40(12):1111-1122. doi:10.1080/02786820601001677 Abstract The interpretation and qualification of measurements of particle composition by laser ablation based single particle mass spectroscopy is complex. Among the most difficult system to quantify are internally mixed particles containing alkali metals. The Alkali atoms in such particles tend to suppress the formation of other ions sometimes to below detection limit. Here we present a study of the behavior of the single particle mass spectral peak intensities as a function of the amount of the sodium containing compounds deposited on the surface of 240 nm PSL spheres. We generate three morphologically distinct and well defined coating types: uniform layer, cubic nodules and rounded nodules, and measure the individual particle mass spectra as a function of the vacuum aerodynamic diameter with nanometer resolution. We find that the probability of detecting the PSL spheres depends on the amount of the alkali metal on the PSL sphere surface and the ablation laser power. We also find that the morphological distribution of the sodium containing coating plays a role in determining mass spectral intensities. The data suggest that PSL spheres with localized Na-containing nodules are easier to detect than those completely encapsulated. We show that 80% of PSL spheres with nodules, whose weight fraction is close to 50%, can be detected at high laser power compared with 60% detection of encapsulated PSL particles with the same amount of coating. At low laser powers these detection limits drop to 35% and ~0% respectively.
2006. "Application of the Accurate Mass and Time Tag Approach to the Proteome Analysis of Sub-cellular Fractions Obtained from Rhodobacter sphaeroides 2.4.1 Aerobic and Photosynthetic Cell Cultures." Journal of Proteome Research 5(8):1940-1947. Abstract Abstract The high-throughput accurate mass and time tag (AMT) proteomic approach was utilized to characterize the proteomes for cytoplasm, cytoplasmic membrane, periplasm, and outer membrane fractions from aerobic and photosynthetic cultures of the gram-nagtive bacterium Rhodobacter sphaeroides 2.4.1. In addition, we analyzed the proteins within purified chromatophore fractions that house the photosynthetic apparatus from photosynthetically grown cells. In total, 8300 peptides were identified with high confidence from at least one sub-cellular fraction from either cell culture. These peptides were derived from 1514 genes or 35% percent of proteins predicted to be encoded by the genome. A significant number of these proteins were detected within a single sub-cellular fraction and their localization was compared to in-silico predictions. However, the majority of proteins were observed in multiple sub-cellular fractions, and the most likely sub-cellular localization for these proteins was investigated using a Z-score analysis of peptide abundance along with clustering techniques. Good (81%) agreement was observed between the experimental results and in-silico predictions. The AMT tag approach provides localization evidence for those proteins that have no predicted localization information, those annotated as putative proteins, and/or for those proteins annotated as hypothetical and conserved hypothetical.
2006. "CrAsH: A Biarsenical Multi-use Affinity Probe with low non-specific fluorescence." Chemical Communications (24):2601-2603. doi:10.1039/b602699k Abstract A biarsenical fluorescent probe 5-carboxy-4’,5’-bis(1,3,2-dithioarsolan-2-yl)fluorescein (CrAsH) was conveniently synthesized from 5-carboxyfluorescein. This probe shows highly selective binding to tetracysteine tags and low hydrophobic non-specific binding in vitro. It provides a potential application for protein labeling and cell imaging.
2006. "Computation of the Redox and Protonation Properties of Quinones: Towards the Prediction of Redox Cycling Natural Products." Phytochemistry 67(16):1781-1788. doi:10.1016/j.phytochem.2006.06.015 Abstract Quinone metabolites perform a variety of key functions in plants, including pathogen protection, oxidative phosphorylation, and redox signaling. Many of these structurally diverse compounds have been shown to exhibit potent antimicrobial, anticancer, and anti-inflammatory properties, although the exact mechanisms of action are far from understood. Redox cycling has been proposed as a possible mechanism of action for many quinine species. Experimental determination of the essential thermodynamic data (i.e. electrochemical and pKa values) required to predict the propensity towards redox cycling is often difficult or impossible to obtain due to the experimental limitations. We demonstrate a practical computational approach to obtain reasonable estimates of these parameters.
2006. "Understanding the Cytochrome bc Complexes By What They Don't Do. The Q-cycle at 30. ." Trends in Plant Science 11(1):46-55. Abstract The cytochrome (cyt) bc1 and b6f complexes are central components of the respiratory and photosynthetic electron transport chains. These complexes carry out an extraordinary sequence of electron and proton transfer reactions that conserve redox energy in the form of a trans-membrane proton motive force for use in synthesizing ATP and other processes. Thirty years ago, Peter Mitchell proposed a general turnover mechanism for these complexes, which he called the Q-cycle. Since that time, many opposing schemes have challenged the Q-cycle, but with the accumulation of large amounts of biochemical, kinetic, thermodynamic and high-resolution structural data, the Q-cycle has triumphed as the accepted model although some of the intermediate steps are poorly understood and still controversial. Perhaps the major research questions concerning the cyt bc1 and b6f complexes now surround how the enzymes suppress deleterious and dissipative side reactions. In particular, most Q-cycle models involve reactive semiquinone radical intermediates which can reduce O2 to superoxide, and can lead to cellular oxidative stress. Interestingly, each of the current models to explain the avoidance of side reactions involves unprecedented or unusual enzyme mechanisms the testing of which will involve cutting edge theory and experimental approaches.
2006. "The Lipid-Droplet Proteome Reveals that Droplets Are a Protein-Storage Depot ." Current Biology 16(18):1783-1795. doi:10.1016/j.cub.2006.07.062 Abstract Lipid droplets are ubiquitous organelles that are among the basic building blocks of eukaryotic cells. Despite central roles for cholesterol homeostasis and lipid metabolism, their function and protein composition are poorly understood. Results: We purified lipid droplets from Drosophila embryos and analyzed the associated proteins by capillary LC-MS-MS. Important functional groups include enzymes involved in lipid metabolism, signaling molecules, and proteins related to membrane trafficking. Unexpectedly, histones H2A, H2Av, and H2B were present. Using biochemistry, genetics, real-time imaging, and cell biology, we confirm that roughly 50% of certain embryonic histones are physically attached to lipid droplets, a localization conserved in other fly species. Histone association with droplets starts during oogenesis and is prominent in early embryos, but it is undetectable in later stages or in cultured cells. Histones on droplets are not irreversibly trapped; quantitation of droplet histone levels and transplantation experiments suggest that histones are transferred from droplets to nuclei as development proceeds. When this maternal store of histones is unavailable because lipid droplets are mislocalized, zygotic histone production starts prematurely. Conclusions: Because we uncover a striking proteomic similarity of Drosophila droplets to mammalian lipid droplets, Drosophila likely provides a good model for understanding droplet function in general. Our analysis also reveals a new function for these organelles; the massive nature of histone association with droplets and its developmental time-course suggest that droplets sequester maternally provided proteins until they are needed. We propose that lipid droplets can serve as transient storage depots for proteins that lack appropriate binding partners in the cell. Such sequestrationmay provide a general cellular strategy for handling excess proteins.
2006. "Ferromagnetism in Oxide Semiconductors ." Materials Today 9(11):28-35. Abstract In order to become a practical technology, semiconductor spintronics requires the discovery and utilization of ferromagnetic semiconductors which exhibit spin polarization in the majority carrier band at and above room temperature. Intrinsic remanent magnetization would allow spin polarized currents to be propagated in such materials without the need for a continuous magnetic field. However, the discovery and understanding of such materials is proving to be a grand challenge in solid-state science. Indeed, one of the 125 critical unanswered scientific questions recently posed in Science magazine asks, “Is it possible to create magnetic semiconductors that work at room temperature?”
2006. "High-Field NMR Studies of Molecular Recognition and Structure-FunctionRelationships in Antimicrobial Piscidins at the Water-Lipid Bilayer Interface." Journal of the American Chemical Society 128(16):5308-5309. doi:10.1021/ja058385e Abstract Piscidins are the first amphipathic, cationic, antimicrobial peptides (ACAPs) to be found in the mast cells of fish, and they are believed to play a crucial role in the fight against many aquatic infections.1 Many ACAPs have been characterized functionally, and some models for their mechanism of action exist, including the barrel-stave model, the wormhole model, the carpet mechanism, and the intracellular activation of fatal pathways.2-9 Much information remains to be learned about the details of their structure, initial interactions with membranes, and the ultimate mechanism for disrupting cellular function. To this end, we employed solid-state NMR (ssNMR) to probe the structure and topology of isotopically labeled piscidins in the membrane-bound state.
2006. "Effects of Dimerization of Serratia marcescens Endonuclease on Water Dynamics." Biopolymers 85(3):241-252. doi:10.1002/bip.20641 Abstract An abstract for this article is not available at this time.
2006. "Solvent Participation in Serratia marcescens Endonuclease Complexes." Proteins. Structure, Function, and Bioinformatics 62(4):982-995. Abstract An abstract for this article is not available at this time.
2006. "Microchip Capillary Electrophoresis with Electrochemical Detection for Monitoring Environmental Pollutants." Current Analytical Chemistry 2(1):43-50. Abstract This invited paper reviews recent advances and the key strategies in microchip capillary electrophoresis (CE) with electrochemical detection (ECD) for separating and detecting a variety of environmental pollutants. The subjects covered include the fabrication of microfluidic chips, sample pretreatments, ECD, typical applications of microchip CE with ECD in environmental analysis, and future prospects. It is expected that microchip CE-ECD will become a powerful tool in the environmental field and will lead to the creation of truly portable devices.
2006. "Monitoring environmental pollutants by microchip capillary electrophoresis with electrochemical detection ." Talanta 68(3):497-503. Abstract This is a review article. During the past decade, significant progress in the development of miniaturized rnicrofluidic systems has Occurred due to the numerous advantages of microchip analysis. This review focuses on recent advances and the key strategies in microchip capillary electrophoresis (CE) with electrochemical detection (ECD) for separating and detecting a variety of environmental pollutants. The subjects covered include the fabrication of ruicrofluidic chips, ECD, typical applications of microchip CE with ECD in environmental analysis, and future prospects. It is expected that microchip CE-ECD will become a powerful tool in the environmental field and will lead to the creation of truly portable devices.
2006. "Growth of aligned carbon nanotubes on carbon microfibers by dc plasma-enhanced chemical vapor deposition." Applied Physics Letters 88:033103. doi:10.1063/1.2166472 Abstract It is shown that unidirectionally aligned carbon nanotubes can be grown on electrically conductive network of carbon microfibers via control of buffer layer material and applied electric field during dc plasma chemical vapor deposition growth. Ni catalyst deposition on carbon microfiber produces relatively poorly aligned nanotubes with significantly varying diameters and lengths obtained. The insertion of Ti 5 nm thick underlayer between Ni catalyst layer and C microfiber substrate significantly alters the morphology of nanotubes, resulting in much better aligned, finer diameter, and longer array of nanotubes. This beneficial effect is attributed to the reduced reaction between Ni and carbon paper, as well as prevention of plasma etching of carbon paper by inserting a Ti buffer layer. Such a unidirectionally aligned nanotube structure on an open-pore conductive substrate structure may conveniently be utilized as a high-surface-area base electrodes for fuel cells, batteries, and other electrochemical and catalytic reactions.
2006. "The Origin of X-ray Luminescence from CdTe Nanoparticles in CdTe/BaFBr:Eu2+ Nanocomposite Phosphors." Journal of Applied Physics 99(3):Art. No. 034302. Abstract Intense X-ray luminescence from CdTe nanoparticles is observed when CdTe particles are encapsulated into BaFBr:Eu2+ phosphors. In contrast, negligible X-ray luminescence is observed from the unencapsulated nanoparticles, either in solution or in solid form. The origin of the X-ray luminescence is attributed to the effective energy transfer from Eu2+ ions to CdTe nanoparticles in the nanocomposite materials. The X-ray luminescence of these nanocomposites is dose dependent and the emission wavelength is size-adjustable which may allow use as a new type of dosimeter for both in vitro and in vivo applications.
2006. "Utilizing Nanofabrication to Construct Strong, Luminescent Materials." Nanotechnology 17(10):2595-2601. doi:10.1088/0957-4484/17/10/025 Abstract Luminescent materials have been utilized widely in applications from lighting to sensing. The new development of technologies based on luminescence properties requires the materials to have high luminescence efficiency and mechanical strength. In this article, we report the fabrication of luminescent materials possessing high mechanical strength by nanofabrication with polyvinyl alcohol used as a stabilizer or coupling agent. X-ray diffraction and high resolution transmission microscope observations reveal that the nanocomposite sample contains ZnS and ZnO nanoparticles as well as kozoite and sodium nitrate. The mechanical strength and hardness of these nanocomposite materials are higher than polycarbonate and some carbon nanotube reinforced nanocomposites. Strong luminescence is observed in the new nanocomposites and the luminescence intensity does not degrade following up to 30 minutes of X-ray irradiation. Our results indicate that nanofabrication may provide a good method to improve the mechanical strength of luminescent materials for some applications in which high strength luminescent materials are needed.
2006. "Fluorescence Anisotropy Studies of Molecularly Imprinted Polymers." Luminescence 21(1):7-14. Abstract A molecularly imprinted polymer (MIP) is a biomimetic material that can be used as a biochemical sensing element. We studied the steady-state and time-resolved fluorescence and fluorescence anisotropy of anthracene imprinted polyurethane. We compared MIPs with imprinted analytes present, MIPs with the imprinted analytes extracted, MIPs with rebound analytes, non-imprinted control polymers (non-MIPs), and non-MIPs bound with analytes to understand MIP’s binding behavior. MIPs and non-MIPs had similar steady-state fluorescence anisotropy in the range of 0.11–0.24. Anthracene rebound in MIPs and non-MIPs had a fluorescence lifetime _=0.64 ns and a rotational correlation time _F =1.2–1.5 ns, both of which were shorter than that of MIPs with imprinted analytes present (_=2.03 ns and _F =2.7 ns). The steady-state anisotropy of polymer solutions increased exponentially with polymerization time and might be used to characterize the polymerization extent in-situ.
2006. "Oxidation of Black Carbon by Biotic and Abiotic Processes." Organic Geochemistry 37(11):1477-1488. doi:10.1016/j.orggeochem.2006.06.022 Abstract The objectives of this study were to quantify the relative importance of either biotic or abiotic oxidation of biomass-derived black carbon (BC) and to characterize the surface properties and charge characteristics of oxidized particulate BC. We incubated BC and BC-soil mixtures at two different temperatures (30ºC and 70ºC) with and without microbial inoculation, nutrient additions, or manure amendments for four months. Abiotic processes were more important for oxidation of BC than biotic processes during this short-term incubation, as inoculation with microorganisms did not change any of the measured parameters. Black C incubated at both 30ºC and 70ºC without microbial activity showed dramatic decreases in pH (in water) from 5.4 to 5.2 and 3.4, as well as increases in cation exchange capacity (CEC at pH 7) by 53% and 538% and in oxygen (O) contents by 4% and 38%, respectively. Boehm titration and Fourier transform infrared (FTIR) spectroscopy suggested that the formation of carboxylic functional groups was the reason for the enhanced CEC during oxidation. The analyses of BC surface properties by X-ray photoelectron spectroscopy (XPS) indicated that the oxidation of BC particles initiated on the surface. Incubation at 30ºC only enhanced oxidation on particle surfaces, while oxidation during incubation at 70ºC penetrated into the interior of particles. Such short-term oxidation of BC has great significance for the stability of BC in soils as well as for its effects on soil fertility and biogeochemistry.
2006. "Solution State Structure Determination of Silicate Oligomers by 29Si NMR Spectroscopy and Molecular Modeling." Journal of the American Chemical Society 128(7):2324-2335. doi:10.1021/ja0559202 Abstract Evidence for nine new solution state silicate oligomers has been discovered by 29Si NMR homonuclear correlation experiments of 29Si-enriched samples. In addition to enhancing signal sensitivity, the isotopic enrichment increases the probability of the 29Si–29Si two-bond scalar couplings that are necessary for the observation of internuclear correlations in 2-D experiments. The proposed assignments are validated by comparisons of experimental and simulated crosspeaks obtained with high digital resolution. The internuclear connectivity indicated by the NMR data suggests that several of these oligomers can have multiple stereoisomers, including conformers and/or diastereomers. The stability of these oligomers and their possible stereoisomers have been investigated by electronic structure calculations.
2006. "Enthalpy-Entropy Contributions to the Potential of Mean Force of NanoscopicHydrophobic Solutes." Journal of Physical Chemistry B 110:8459-8463. doi:10.1021/jp056909r Abstract Entropic and enthalpic contributions to the hydrophobic interaction between nanoscopic hydrophobic solutes, modeled as graphene plates in water, have been calculated using molecular dynamics simulations in the isothermal-isobaric (NPT) ensemble with free energy perturbation methodology. We find the stabilizing contribution to the free energy of association (contact pair formation) to be the favorable entropic part, the enthalpic contribution being highly unfavorable. The desolvation barrier is dominated by the unfavorable enthalpic contribution, despite a fairly large favorable entropic compensation. The enthalpic contributions, incorporating the Lennard-Jones solute-solvent terms, largely determine the stability of the solvent separated configuration. We decompose the enthalpy into a direct solute-solute term, the solute-solvent interactions, and the remainder that contains pressure-volume work as well as contributions due to solvent reorganization. The enthalpic contribution due to changes in water-water interactions arising from solvent reorganization around the solute molecules is shown to have major contribution in the solvent induced enthalpy change.
2006. "Nitrogen Mineralization and Assimilation at Millimeter Scales." Soil Biology and Biochemistry 39(3):823–826. doi:10.1016/j.soilbio.2006.10.005 Abstract This study used inoculated, artificial soil microcosms containing sand, clay, cellulose, and localized hotspots of highly labile, organic-N containing dead bacteria to study N mineralization and assimilation at submillimeter and centimeter scales. Labeling with 15NH4+ along with measurement of label assimilated into microbial biomass at the bulk scale allowed estimation of gross rates of ammonification and N assimilation using isotope dilution. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of transects of organic-15N across Si wafers in contact with the microcosms indicated strong gradients of 15NH4+ assimilation as a function of proximity to the hotspots that were not apparent using bulk analyses. This combination of bulk and ToF-SIMS analyses represents a powerful approach to explore the physical and biochemical factors that affect N process heterogeneities in soils.
2006. "Characterization of Energy Conservation in Primary Knock-On Atom Cascades: Ballistic Phase Effects on Variable Time Steps." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 250(1-2):6-11. doi:10.1016/j.nimb.2006.04.075 Abstract Non-equilibrium molecular dynamics simulation trajectories must in principle conserve energy along the entire path. Processes exist in high-energy primary knock-on atom cascades that can affect the energy conservation, specifically during the ballistic phase where collisions bring atoms into very close proximities. The solution, in general, is to reduce the time step size of the simulation. This work explores the effects of variable time step algorithms and the effects of specifying a maximum displacement. The period of the ballistic phase can be well characterized by methods developed in this work to monitor the kinetic energy dissipation during a high-energy cascade.
2006. "Analysis of Rotational Structure in the High-Resolution Infrared Spectrum and Assignment of Vibrational Fundamentals of Butadiene-2,3-13C2." Journal of Molecular Spectroscopy 235(2):181-189. Abstract The 2,3-13C2 isotop0omer of butadiene was synthesized and its fundamental vibrational fundamentals were assigned from a study of its IR and Raman spectra aided with quantum chemical predictions of frequencies, intensities, and Raman depolarization ratios. For two C-type bands in the high-resolution (0.002 cm-1) infrared spectrum, the rotational structures was analyzed. These bands are for v11(au) at 907.17 cm-1 and for v12(au) at 523.37 cm-1. Ground state and upper state rotational constants were fitted to Watson-type Hamiltonians with a full quartic set and two sextic centrifugal distortion constants. For the ground state, Ao=1.3545088(7) cm-1, Bo=0.1469404(1) cm-1, and Co=0.1325838(2) cm-1. The small inertia defects of butadiene and two 13C2 isotopomers, as well as for five deuterium isotopomers as previously reported, confirm the planarity of the s-trans rotamer of butadiene.
2006. "Solid-State NMR Identification and Quantification of Newly Formed Aluminosilicate Phases in Weathered Kaolinite Systems." Journal of Physical Chemistry B 110(2):723-732. Abstract The weathering of a specimen kaolinite clay was studied over the course of 369 d via solid-state 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and high-field 27Al MAS NMR. The chosen baseline solution conditions (0.05 mol kg-1 of Al, 2 mol kg-1 of Na+, 1 mol kg-1 of NO3 -, 1 mol kg-1 of OH-, and pH ~13.8) approximate those of solutions leaking from waste tanks at the Hanford Site in Richland, WA. Nonradioactive Cs and Sr cations were added to this synthetic tank waste leachate (STWL) solution at concentrations of 10-3, 10-4, and 10-5 molal (m) to represent their radionuclide counterparts. The transformations of silicon- and aluminum-containing solid phase species were monitored quantitatively by using NMR spectroscopy, with the resulting spectra directly reporting the influence of the initial Cs and Sr on formation and transformation of the neo-formed solids. At the lowest concentration of Cs and Sr employed (10-5 m in each cation) peaks consistent with the formation of zeolite-like minerals were detected via 29Si and 27Al MAS NMR as early as 33 d. At concentrations of 10-3 m in each cation, new silicon species are not detected until 93 d, although neophases containing four-coordinate aluminum were detectable at earlier reaction times via 27Al MAS NMR. At the highest magnetic field strengths employed in this NMR study, deconvolutions of resonances detected in the tetrahedral region of the 27Al MAS spectra yielded multiple components, indicating the existence of at least four new aluminum-containing phases. Two of these phases are identified as sodalite and cancrinite through comparison with diffuse-reflectance infrared (DRIFT) spectra and powder X-ray diffraction (XRD) results, while a third phase may correlate with a previously detected aluminum-rich chabazite phase. All measurable solid reaction products have been quantified via their 27Al MAS resonances acquired at high magnetic field strengths (17.6 T), and the quantitative nature of the 27Al NMR data shows that cancrinite growth increases while sodalite reaches a steady state with respect to total aluminum in the solid phases. The data also relate the coupling of Cs sorption to the ripening of feldspathoid phases in this heterogeneous system as a function of time, and illustrate the important influence of co-contaminants on the environmental reaction kinetics studied here.
2006. "Pb-12(2-): Plumbaspherene." Journal of Physical Chemistry A 110(34):10169-10172. Abstract Photoelectron spectroscopy and theoretical calculations show that Pb122- is a highly stable icosahedral cage cluster, similar to Sn122-. It is bonded by four delocalized radial bonds and nine delocalized on-sphere bonds from the 6p orbitals of the Pb atoms. Following Sn122- (stannaspherene), we coin a name, plumbaspherene, for the highly stable and nearly spherical Pb122- cluster, which has a diameter of ~6.3 Å with an empty interior volume large enough to host most transition metal atoms and afford a new class of stable endohedral plumbaspherenes similar to the endohedral fullerenes.
2006. "Photoelectron Spectroscopy of AInD-2 (n=3-15): Observation of Chemisorption and Physisorption of Dideuterium on Aluminum Cluster Anions." Journal of Chemical Physics 124(5):article no. 054308. Abstract Photoelectron spectroscopy is used to investigate aluminum dideuteride cluster anions, AlnD2 − _n=3,6–15_, produced by laser vaporization of a pure Al target with a D2-seeded helium carrier gas. Comparison between the well-resolved photoelectron spectra of AlnD2 − and Aln − reveals the nature of interactions between D2 and Aln −. Depending on the size of the Aln − clusters and their electronic structure, three types of AlnD2 − species are observed, dideuteride _dissociative chemisorption_, molecular chemisorption, and physisorption. Striking spectral similarities are observed between photoelectron spectra of AlnD2 − and Aln − for n=9, 11, 13, and 15, suggesting that D2 is physisorbed on these closed-shell Aln − clusters. For AlnD2 − with n=3, 6, 7, and 10, completely different spectra are observed in comparison with the corresponding Aln − clusters, suggesting that the AlnD2 − species may be characterized as dideuterides. For AlnD2 − with n=8, 12, and 14, in which the Aln − clusters are open shell, the D2 is characterized as chemisorption on the basis of spectral shifts and similarities relative to those of the corresponding Aln − clusters. © 2006 American Institute of Physics.
2006. "Sn₁₂²⁻: Stannaspherene." Journal of the American Chemical Society 128(26):8390-8391. doi:10.1021/ja062052f Abstract The Sn₁₂²⁻ cluster is discovered to be a highly stable and highly symmetric icosahedral cage bonded by four delocalized radial π bonds and nine delocalized onsphere bonds from the 5p orbitals of the Sn atoms. It has a diameter of 6.1 Å with a large empty interior volume and can host most transition metal atoms inside, giving rise to a large class of endohedral chemical building blocks for cluster-assembled nanomaterials.
2006. "Preparation, Characterization and Anion Exchange Properties of Polypyrrole/Carbon Nanotube Nanocomposite." Journal of Nanoscience and Nanotechnology 6(2):547-553. Abstract In this study, polypyrrole (PPy) thin film was electrodeposited on carbon nanotube (CNT) backbones by applying a constant deposition potential in solution with 0.1 M pyrrole with different electrolytes such as NaCl, NaNO3, or NaClO4. The hybrid films were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. SEM images revealed the nanostructrure of PPy film generated on CNTs surface. The electrochemical and anion exchange properties of PPy-CNT composite film have been investigated. Nanostructured composite thin films of polypyrrole/CNTs were studied by cyclic votammetry between 0.4 and -0.8 V in aqueous solution to evaluate their cycling stability and capacity for electrically switched anion exchange. It is found that the PPy/CNTs nanocomposites can improve the anion exchange capacity and stability of the PPy-CNTs composite film, which may be attributed to the nanostructure of the polyprrole film, which offer the high aspect ratio of the film and ease of diffusion of anions in the nanostructured film, and the interaction between CNTs and PPy.