Peter John Bonitatibus

Reversible catalytic dehydrogenation of alcohols for energy storage

Significance Catalytic hydrogenation and dehydrogenation reactions are extremely important in organic chemistry and recently for energy storage in the form of chemical bonds. Although catalysts are known which catalyze both reactions, the rates and conditions required for the two are frequently very different due to the differences associated with the bonds to be activated (C–H/O–H/N–H and C = O/C = N/H–H). The use of a bifunctional catalyst would substantially simplify the design of processes related to energy storage. In this work, organometallic complexes of iron and iridium are shown to act as catalysts for reversible dehydrogenation of alcohols to carbonyl compounds. This finding opens a pathway to the development of catalysts for direct reversible electrochemical dehydrogenation of organic fuels in energy generation and storage reactions. Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.

Preclinical assessment of a zwitterionic tantalum oxide nanoparticle X-ray contrast agent.

Tantalum oxide nanoparticles show great potential as the next generation of X-ray contrast media. Recently, we reported advances in tantalum oxide nanoparticles and identified improvements that were required for such particles to progress further. Namely, the viscosity of concentrated particles, the amount of retention in reticuloendothelial (RES) tissues, and the effect of large quantities of particles on the kidneys after administration were all identified as critical factors which needed further study, understanding, and development. Here, we report on a zwitterionic siloxane polymer nanoparticle coating that reduced the viscosity of concentrated solutions of particles by a factor of 5, decreased tissue retention of injected particles by a factor of 10, and, importantly, did not induce pathological responses in the kidneys.

Biological performance of a size-fractionated core-shell tantalum oxide nanoparticle x-ray contrast agent.

ObjectivesMetal-containing nanoparticles show great promise as x-ray contrast media and could enable reduced radiation dose, increased contrast, and the visualization of smaller anatomic features. In this study, we report progress toward these goals using a size-fractionated core-shell tantalum oxide nanoparticle contrast agent. Materials and MethodsA core-shell tantalum oxide nanoparticle contrast agent was synthesized and size fractionated for preclinical investigation of biodistribution, blood half-life, organ retention, and histopathology. Fractionated agent was injected at anticipated clinical dose and at 3 times the anticipated clinical dose to evaluate biological performance. Computed tomography (CT) imaging studies were also performed to evaluate short-term clearance kinetics and new imaging applications. ResultsImproved control of 2-diethylphosphatoethylsilane-TaO nanoparticle size resulted in significantly reduced retention of injected tantalum. In vivo and in vitro CT imaging studies demonstrated short-term biodistribution differences in the kidney between small-molecule iodinated contrast media and fractionated 2-diethylphosphatoethylsilane-TaO, as well as preliminary data about new “Ta-only” imaging applications using multienergy CT image acquisition. ConclusionsSize-fractionated core-shell tantalum oxide nanoparticles with a well-defined particle size distribution have several key features required of clinically viable vascular imaging compounds and may be used in developing multienergy CT imaging applications.

CT Image Contrast of High-Z Elements: Phantom Imaging Studies and Clinical Implications

PURPOSE To quantify the computed tomographic (CT) image contrast produced by potentially useful contrast material elements in clinically relevant imaging conditions. MATERIALS AND METHODS Equal mass concentrations (grams of active element per milliliter of solution) of seven radiodense elements, including iodine, barium, gadolinium, tantalum, ytterbium, gold, and bismuth, were formulated as compounds in aqueous solutions. The compounds were chosen such that the active element dominated the x-ray attenuation of the solution. The solutions were imaged within a modified 32-cm CT dose index phantom at 80, 100, 120, and 140 kVp at CT. To simulate larger body sizes, 0.2-, 0.5-, and 1.0-mm-thick copper filters were applied. CT image contrast was measured and corrected for measured concentrations and presence of chlorine in some compounds. RESULTS Each element tested provided higher image contrast than iodine at some tube potential levels. Over the range of tube potentials that are clinically practical for average-sized and larger adults-that is, 100 kVp and higher-barium, gadolinium, ytterbium, and tantalum provided consistently increased image contrast compared with iodine, respectively demonstrating 39%, 56%, 34%, and 24% increases at 100 kVp; 39%, 66%, 53%, and 46% increases at 120 kVp; and 40%, 72%, 65%, and 60% increases at 140 kVp, with no added x-ray filter. CONCLUSION The consistently high image contrast produced with 100-140 kVp by tantalum compared with bismuth and iodine at equal mass concentration suggests that tantalum could potentially be favorable for use as a clinical CT contrast agent.

The Effect of Patient Diameter on the Dual-Energy Ratio of Selected Contrast-Producing Elements.

Objectives The aim of this study was to assess whether the low- to high-kVp computed tomography (CT) number ratio at dual-energy CT is affected by changes in patient diameter. Methods Seven contrast-producing elements were housed sequentially within an abdomen phantom. Fat rings enlarged the phantom diameter from 26 to 44 cm. The phantom was scanned using single-energy CT at tube potentials of 80 and 140 kVp and rapid-kVp-switching dual-energy CT. Results CT numbers decreased proportionally (∼20% CT number reduction for smallest to largest phantom diameters) for low- and high-energy acquisitions but resulted in consistent dual-energy ratios for each contrast element. For 17 of 21 material pair combinations, the dual-energy ratio ranges of the two elements did not overlap, implying that discrimination should remain possible for these material pairs at all patient sizes. Conclusions The dual-energy ratio for different contrast materials is largely unaffected by changes in phantom diameter. This should allow for robust separation of most contrast material combinations irrespective of patient size.

An Intravascular Tantalum Oxide–based CT Contrast Agent: Preclinical Evaluation Emulating Overweight and Obese Patient Size

Purpose To compare the CT imaging performance of a carboxybetaine zwitterionic-coated tantalum oxide (TaCZ) nanoparticle CT contrast agent with that of a conventional iodinated contrast agent in a swine model meant to simulate overweight and obese patients. Materials and Methods Four swine were evaluated inside three different-sized adipose-equivalent encasements emulating abdominal girths of 102, 119, and 137 cm. Imaging was performed with a 64-detector row CT scanner at six scan delays after intravenous injection of 240 mg element (Ta or I) per kilogram of body weight of TaCZ or iopromide. For each time point, contrast enhancement of the aorta and liver were measured by using regions of interest. Two readers independently recorded the clarity of vasculature using a five-point Likert scale. Findings were compared by using paired t tests and Wilcoxon signed-rank tests. Results Mean peak enhancement was higher for TaCZ than for iopromide in the aorta (270 HU [σ = 24.5] vs 199 HU [σ = 10.2], P < .001) and liver (61.3 HU [σ = 11.7] vs 45.2 HU [σ = 8], P < .001). Vascular clarity was higher for TaCZ than for iopromide in 63% (132 of 208), 82% (170 of 208), and 86% (178 of 208) of the individual vessels at the 102-, 119-, and 137-cm girths, respectively (P < .01). Arterial clarity scores were higher for TaCZ than for iopromide in 62% (208 of 336) of vessels. Venous clarity scores were higher for TaCZ than for iopromide in 89% (128 of 144) of the veins in the venous phase and in 100% (144 of 144) of veins in the delayed phase (P < .01). No vessel showed higher clarity score with iopromide than with TaCZ. Conclusion An experimental tantalum nanoparticle-based contrast agent showed greater contrast enhancement compared with iopromide in swine models meant to simulate overweight and obese patients.

Determination of tantalum from tantalum oxide nanoparticle X-ray/CT contrast agents in rat tissues and bodily fluids by ICP-OES

Accurate and precise means for quantifying Ta in tissues, bodily fluids, and bone is critical in understanding anticipated safety-profiles for tantalum oxide (TaO) nanoparticle-based X-ray/CT diagnostic imaging agents and has prompted the development of three digestion methods which are the focus of this work. Spike recovery studies were employed to evaluate bias, precision, and sample matrix effects in the quantification of Ta in (1) liver, blood and femur by microwave-assisted digestion, (2) urine by open-beaker digestion, and (3) carcass, liver and feces by dry-ash digestion. All analyses were performed with inductively coupled plasma optical emission spectrometry (ICP-OES). Spike recoveries were 98.5–102.3% for all biological matrices except femur (91.6%); however, a modified version of the original microwave digestion procedure improved the recovery of Ta in femur to 103.8%. Precision of spike recovery reported as one standard deviation ranged from 0.1 to 3.8% for within-run and from 0.5 to 3.3% for overall recovery depending on the tissue type and digestion method. Limit of detection (LOD) was 0.006 to 6 μg Ta per g and limit of quantification (LOQ) was 0.02 to 20 μg Ta per g depending on the method. The presented methods were applied to the determination of Ta in liver, kidney, spleen and carcass from an in vivo TaO nanoparticle retention study, and the results for percent injected dose (% ID) of Ta retained are given.