Biomedical subjects

C M Lukehart

Publications and source records attributed to C M Lukehart.

11 recordsLinked to original sources

PubMed2004

Preparation of Pt-Re/Vulcan carbon nanocomposites using a single-source molecular precursor and relative performance as a direct methanol fuel cell electrooxidation catalyst.

Pt-Re/Vulcan carbon powder nanocomposites have been prepared with total metal loadings of 18 wt.% and 40 wt.% using a new non-cluster (1:1)-PtRe bimetallic precursor as the source of metal. Pt-Re nanoparticles having an average diameter of ca. 6 nm and atomic stoichiometry near 1:1 are formed. TEM, on-particle HR-EDS, and powder XRD data are consistent with the formation of Pt-Re alloy nanoparticles having a hexagonal unit cell with cell constants of a = 2.77 A and c = 4.47 A. A nanocomposite prepared at higher total metal loading under more rigorous thermal treatment also contains Pt-Re alloy nanoparticles having a fcc unit cell structure (a = 3.95 A). The precise dependence of Pt-Re nanocrystal structure on the thermal history of the nanocomposite specimen has not been investigated in detail. While these Pt-Re/carbon nanocomposites are active as anode catalysts in operating direct methanol fuel cells, the measured performance is less than that of commercial Pt-Ru/carbon catalysts and has marginal practical importance.

Alloys↗

PubMed2004

Carbothermal transformation of a graphitic carbon nanofiber/silica aerogel composite to a SiC/silica nanocomposite.

Carbon nanofiber/silica aerogel composites are prepared by sol-gel processing of surface-enhanced herringbone graphitic carbon nanofibers (GCNF) and Si(OMe)4, followed by supercritical CO2 drying. Heating the resulting GCNF/silica aerogel composites to 1650 degrees C under a partial pressure of Ar gas initiates carbothermal reaction between the silica aerogel matrix and the carbon nanofiber component to form SiC/silica nanocomposites. The SiC phase is present as nearly spherical nanoparticles, having an average diameter of ca. 8 nm. Formation of SiC is confirmed by powder XRD and by Raman spectroscopy.

Carbon↗

PubMed2003

Rapid preparation of Pt-Ru/graphitic carbon nanofiber nanocomposites as DMFC anode catalysts using microwave processing.

Pt-Ru/graphitic carbon nanofiber (GCNF) nanocomposites have been prepared on two different GCNF supports, with the use of a bimetallic precursor as a source of metal and microwave processing for thermal treatments. Pt-Ru nanoparticles appear as the major metal-containing component of these nanocomposites along with variable trace amounts of Ru metal. Use of microwave heating permits rapid preparation of these nanocomposites and affords metal nanoclusters of nearly uniform size. The performance of these nanocomposites as anode electrocatalysts in direct-methanol fuel cells (DMFCs) is compared with that of unsupported Pt-Ru colloid at identical total metal loading. The Pt-Ru/narrow tubular herringbone GCNF nanocomposite shows DMFC performance comparable to that recorded for an unsupported Pt-Ru colloid.

Catalysis↗

PubMed2002

Synthesis and characterization of PtSn/carbon and Pt3Sn/carbon nanocomposites as methanol electrooxidation catalysts.

Two Pt-Sn/vulcan carbon nanocomposites containing nanoclusters of PtSn (niggliite) and Pt3Sn highly dispersed on a carbon powder support have been prepared using Pt(SnPh2Cl)(PPh3)2(Ph) or [Pt3[mu-(PPh2)2CH2]3(mu 3-SnF3) (mu 3-CO)][PF6] as single-source precursors of metal alloy. PtP2 or Pt metal is also present as a secondary phase. Bimetallic Pt-Sn nanoclusters with an average diameter of 5-8 nm are formed at a total metal loading of ca. 15 wt%. Evaluation of both Pt-Sn/C nanocomposites as electrooxidation catalysts in a direct methanol fuel cell gives fuel cell performances comparable to that expected for Pt-Sn catalysts prepared by more conventional methods.

Carbon↗

PubMed2002

Preparation of graphitic carbon nanofibers with the use of water-soluble supports.

Graphitic carbon nanofibers (GCNFs) are prepared from CO/H2 with a nickel-rich Fe-Ni (2:8) growth catalyst supported on three different water-soluble supports (Na4SiO4, Na2SiO3, and Na2CO3). GCNF products are formed with yield and crystallinity comparable to those of GCNF product produced with the same growth catalyst supported on fumed silica. Separation of GCNF product from the solid support is accomplished by aqueous dissolution of the support. This synthetic method extends the convenient isolation of GCNFs formed with supported growth catalysts to a wide variety of potential solid supports.

Carbonates↗

PubMed1985

Particulate oral NMR contrast agents.

Insoluble paramagnetic compounds in suspension can be used to achieve visualization of the gastrointestinal system on magnetic resonance imaging (NMR). Particulate preparations of these agents decrease the T1 and T2 of solutions to which they are added. Gadolinium oxalate, a prototype of these particulate agents, was evaluated in vitro and in vivo (in rabbits) by NMR imaging. The effect of this compound upon T1 and T2 in vitro was also quantitated by NMR spectroscopy. Opacification of the upper gastrointestinal tract was achieved with gadolinium oxalate following oral administration. The colon was visualized following rectal administration.

Administration, Oral↗

PubMed1984

Contrast enhancement of magnetic resonance images by chromium EDTA: an experimental study.

Chromium EDTA was evaluated as an intravenous contrast agent for magnetic resonance (MR) imaging in vitro and in vivo in rabbits and rats. The effect of Cr EDTA on T1 and T2 values in vitro was first quantitated by spectroscopy at 2.5 MHz, followed by animal trials in which the effects of intravenous injection of Cr EDTA on calculated T1 MR images (obtained by the spin- warp technique at 1.7 MHz) were determined. Following administration of chromium EDTA, differences in T1 values between normal and abnormal kidneys were noted, renal hydronephrosis and renal ischemia were readily identified by the pattern of change in T1, and changes were observed in the normal rabbit brain and in tumors implanted in rats. It is concluded that the use of stable paramagnetic metal ion chelates, such as Cr EDTA, as intravenous contrast agents in MR imaging is feasible and that such agents would make possible the observation of tissue vascularity, breakdown of the blood-brain barrier, and renal function.

Animals↗

PubMed1984

Paramagnetic contrast agents in magnetic resonance imaging: research at Vanderbilt University.

Experimental studies in animals have demonstrated the application of particulate and chelated paramagnetic oral contrast agents in magnetic resonance imaging (at 0.5 tesla). The ability of a soluble paramagnetic species, ferrous gluconate, to improve imaging studies of the pancreas presently is being evaluated in clinical trials. Two paramagnetic metal ion chelates, Cr EDTA and Gd DTPA, have been evaluated extensively as potential intravascular contrast agents. Renal function, tissue vascularity, abnormalities of the blood-brain barrier, and infarction of myocardial tissue may all be assessed with IV contrast enhanced magnetic resonance imaging. The contrast materials tested all represent first generation compounds. Improved relaxation characteristics, toxicity, distribution, and flexibility will result from development of second generation agents, primarily within the particulate and chelate classes.

Animals↗

PubMed1983

Work in progress: potential oral and intravenous paramagnetic NMR contrast agents.

The potential use of paramagnetic compounds as nuclear magnetic resonance (NMR) contrast agents was examined in vitro. The T1 relaxation times for serial dilutions of Cu2+, Cr3+, Fe3+, and Mn2+ ions in saline, gadolinium oxalate (a potential oral contrast agent) in suspension, and chromium EDTA (a potential intravenous contrast agent) in solution were determined. The effect on T1 of increasing the concentration of oxygen in solution was also examined. The relative magnitude of the decrease in T1 was, as expected, proportional to both the concentration of the paramagnetic substance and its effective magnetic moment. Thus NMR has the potential to detect differences in tissue oxygenation. By incorporating paramagnetic metal ions into insoluble compounds or stable complexes, toxicity can be dramatically reduced while maintaining a significant paramagnetic effect. Highly insoluble paramagnetic compounds or stable paramagnetic ion complexes can thus be utilized as effective NMR contrast agents with significantly diminished toxicity.

Administration, Oral↗

PubMed1983

Paramagnetic agents for contrast-enhanced NMR imaging: a review.

The use of paramagnetic agents for contrast enhancement may extend the diagnostic potential of nuclear magnetic resonance (NMR) imaging. Proton relaxation is enhanced in targeted organ systems after either oral or intravenous administration of suitable paramagnetic agents. A decrease in T1 and T2, the spin-lattice and spin-spin relaxation times, can then be observed as an increase in signal intensity on NMR imaging. Initial investigations have focused on development of agents incorporating either paramagnetic ions or stable free radicals. Principles in development and application are illustrated with examples from experiments using the Vanderbilt Technicare 0.5 T NMR imager.

Animals↗

PubMedDate not supplied

Paramagnetic NMR contrast agents. Development and evaluation.

Paramagnetic ions could be theoretically used as NMR contrast agents because of their effect upon T1. However, the toxicity of these ions prevents their application. By the formation of appropriate chemical complexes with these ions, the toxicity of these agents can be substantially reduced while maintaining the paramagnetic effect. Two potential NMR contrast agents, one for oral use and one for intravenous administration, were developed and evaluated both in vitro and in vivo. The effect upon T1 in vitro of these paramagnetic compounds was determined using a JEOL FX-90Q NMR spectrometer. These agents were evaluated in vivo in dogs with a Technicare 0.3 tesla superconducting magnet system and in rabbits with the Aberdeen 0.04 tesla resistive NMR imager. Using calculated T1 NMR images, a nontoxic dose of gadolinium oxalate provided visualization of the gastrointestinal tract. Intravenous administration of chromium EDTA provided enhancement of the kidneys, ureters, and bladder, thereby potentially allowing for the evaluation of renal function with magnetic resonance imaging. Stable paramagnetic complexes can serve as effective, nontoxic, oral and intravenous NMR contrast agents.

Administration, Oral↗