Browsing by Author "Kumar, Ish"

Now showing 1 - 5 of 5
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    Aluminum Nanocrystals
    (American Chemical Society, 2015) McClain, Michael J.; Schlather, Andrea E.; Ringe, Emilie; King, Nicholas S.; Liu, Lifei; Manjavacas, Alejandro; Knight, Mark W.; Kumar, Ish; Whitmire, Kenton; Everitt, Henry O.; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 to 220 nm diameter with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral, and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support size-dependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.
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    Facile one-pot synthesis of triphenylbismuth (V) bis(carboxylate) complexes
    (American Chemical Society, 2014) Kumar, Ish; Bhattacharya, Prateek; Whitmire, Kenton H.
    Triphenylbismuth(V) bis(carboxylates), Ph3Bi(O2CR)2 (R = 5-Br-2-OH-C6H3- (1), 2-OH-C6H4-(2), 2,6-(OH)2-C6H3- (3); 3-Me-2-NH2-C6H3- (4); Ph- (5) and Me- (6)) were obtained from the reaction of triphenylbismuth with hydrogen peroxide and excess carboxylic acid in wet 2-propanol. The synthesis avoids the use of halogens as oxidants and the products crystallize directly from the solution as pure compounds. They crystallize from solution without further need of purification. The structures of 1 - 5 were confirmed by single crystal X-ray diffraction. Compounds 2 and 5 exhibit a different polymorph than that previously reported in the literature. While all of the Bi(V) compounds adopt a trans-axial trigonal-bipyramidal configuration with the carboxylates in the axial positions, there is considerable variation in the coordination of the carboxylate that ranges from simple monohapto to the mixture of mono- and bidentate chelating bonding modes.
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    High-Performance Hybrid Bismuth–Carbon Nanotube Based Contrast Agent for X-ray CT Imaging
    (American Chemical Society, 2017) Hernández-Rivera, Mayra; Kumar, Ish; Cho, Stephen Y.; Cheong, Benjamin Y.; Pulikkathara, Merlyn X.; Moghaddam, Sakineh E.; Whitmire, Kenton H.; Wilson, Lon J.
    Carbon nanotubes (CNTs) have been used for a plethora of biomedical applications, including their use as delivery vehicles for drugs, imaging agents, proteins, DNA, and other materials. Here, we describe the synthesis and characterization of a new CNT-based contrast agent (CA) for X-ray computed tomography (CT) imaging. The CA is a hybrid material derived from ultrashort single-walled carbon nanotubes (20–80 nm long, US-tubes) and Bi(III) oxo-salicylate clusters with four Bi(III) ions per cluster (Bi4C). The element bismuth was chosen over iodine, which is the conventional element used for CT CAs in the clinic today due to its high X-ray attenuation capability and its low toxicity, which makes bismuth a more-promising element for new CT CA design. The new CA contains 20% by weight bismuth with no detectable release of bismuth after a 48 h challenge by various biological media at 37 °C, demonstrating the presence of a strong interaction between the two components of the hybrid material. The performance of the new Bi4C@US-tubes solid material as a CT CA has been assessed using a clinical scanner and found to possess an X-ray attenuation ability of >2000 Hounsfield units (HU).
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    Synthesis and structural studies of the simplest bismuth(III) oxo-salicylate complex: [Bi4(m3-O)2(HO-2-C6H4CO2)8]×2 Solv (Solv = MeCN or MeNO2)
    (Royal Society of Chemistry, 2014) Boyd , Tyler D.; Kumar, Ish; Wagner, Eric E.; Whitmire, Kenton H.
    Reaction of BiPh3 with salicylic acid (HO-2-C6H4CO2H, H2Sal) at room temperature in wet acetonitrile or nitromethane leads to the facile formation of an oxo cluster compound with formula [Bi4(m3-O)2(HSal)8] solvated by either MeCN and MeNO2 (1×2MeCN or 1×2MeNO2). This simple procedure affords a convenient, high yield (>80%) synthesis of a single bismuth oxo cluster. Both adducts exhibit a nearly planar Bi4(m3-O)2 core. The solvent ligands are situated in the same coordination sites in both but at long Bi---N and Bi---O distances. The ease of preparation as a pure compound makes this an ideal starting material for study of bismuth oxo-salicylate chemistry.
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    The Unexpected Isolation of Bismuth Tris(carboxylate) Hydrates: Syntheses and Structures of [Bi(Hsal)3(H2O)] and [Bi(Hanth)3(H2O)] (H2sal = 2-OH-C6H4CO2H, Hanth = 2-NH2-C6H4CO2H)
    (Wiley, 2015) Kumar, Ish; Andrews, Phil; Whitmire, Kenton H.
    A complex of the composition [Bi(2-OH-C6H4CO2)3(H2O)] (1) was isolated from the 1:3 reaction of BiPh3 with H2sal (H2sal = salicylic acid = 2-OH-C6H4CO2H) in wet xylene, and the analogous anthranilate compound [Bi(2-NH2-C6H4CO2)3(H2O)] (2) was obtained from the 1:3 reaction of Bi(OtBu)3 with Hanth (Hanth = anthranilic acid = 2-NH2-C6H4CO2H) in tetrahydrofuran. Compounds 1 and 2 were fully characterized spectroscopically and by single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the triclinic space group and display the η2-(O,O′) binding mode for the oxygen atoms of the carboxylate ligands. There are two independent molecules in the asymmetric units of 1 and 2 that are connected by a weak bridging interaction of the OH or NH2 group to an adjacent molecule. Both bismuth atoms are bound to a H2O molecule, but the distances are highly asymmetric, long Bi···O lengths ranging from 2.74 to 2.89 Å.