Peter J Bonitatibus Jr | Rensselaer Polytechnic Institute (original) (raw)
Papers by Peter J Bonitatibus Jr
Silicon, Nov 22, 2023
One of four possible stereoisomers of a methyl(trifluoropropyl)siloxane cyclic tetramer was isola... more One of four possible stereoisomers of a methyl(trifluoropropyl)siloxane cyclic tetramer was isolated from low molecular weight volatiles, formed in a reaction mixture during ring-opening/equilibration polymerization of methyl(3,3,3-trifluoropropyl)cyclotrisiloxane (D3F). The crystalline solid was recognized as resembling a previously isolated cyclic siloxane with undetermined stereochemistry, assigned as a cyclotetrasiloxane by IR spectroscopy, and then further characterized by multinuclear (1H, 13C, 19F, and 29Si) NMR spectroscopy as a relatively high symmetry species with respect to the potential cis-trans relationships of the methyl and 3,3,3-trifluoropropyl substituents at Si. Unambiguous characterization and assignment of the stereochemistry was accomplished by a single crystal X-ray diffraction study, which revealed the compound was the trans, trans, trans-isomer, one species in these equilibration polymerization mixtures. The single crystal X-ray structure of the related, com...
Radiology, Mar 1, 2016
To quantify the computed tomographic (CT) image contrast produced by potentially useful contrast ... more 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-mmthick 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 averagesized 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.
Dalton Transactions, 2022
Hyperfine coupling constants predicted by DFT in the most highly distorted four-coordinate d3 (VI... more Hyperfine coupling constants predicted by DFT in the most highly distorted four-coordinate d3 (VII) ion exhibit exceptional agreement with EPR.
Journal of Analytical Atomic Spectrometry, 2016
Materials and reagents Optima grade concentrated nitric (HNO 3) and hydrofluoric (HF) acids from ... more Materials and reagents Optima grade concentrated nitric (HNO 3) and hydrofluoric (HF) acids from Fisher Scientific (Pittsburgh, PA, USA) as well as Ultrex II ultrapure reagent hydrogen peroxide, 30%, (H 2 O 2) and concentrated sulfuric acid (H 2 SO 4) from J.T. Baker Avantor (Center Valley, PA, USA) were used throughout. All dilutions and solutions were prepared using deionized water (18.2 MΩ/cm) produced with a Milli-Q water purification system (Millipore, Bedford, MA, USA). Metals-free 15 and 50 mL polypropylene centrifuge tubes (VWR, Radnor, PA, USA) were used throughout. Single-element 1000 µg/mL Ta was obtained from High-Purity Standards (Charleston, SC, USA) for the preparation of intermediate stock solutions of 50 and 1 µg/mL Ta in 1% HNO 3. The intermediate stock solutions and the 1000 µg/mL Ta stock standard were used to prepare 21 working calibration standards (0.001-40 µg/mL Ta) containing the acid matrix corresponding to the samples prepared by microwave digestion or open-beaker digestion methods. Twenty-three working calibration standards (0.001-100 µg/mL Ta) were prepared in the acid matrix corresponding to the samples prepared by the dry-ash digestion method. A 100 µg/mL Nb solution was prepared in 1% HNO 3 and 0.1% HF from a 10000 µg/mL Nb stock solution (High-Purity Standards) for use as an internal standard reference added to all sample dilution and working calibration solutions. Addition of the 100 μg/mL Nb solution was performed with an accurate and precise manual digital pipette; the volume added was 1 mL, 2 mL, or 5 mL for solutions diluted to a final volume of 10 mL, 20 mL, or 50 mL respectively. SPEX CertiPrep (Metuchen, NJ, USA) 10 µg/mL multi-element solution CLMS-4 and Inorganic Ventures (Christiansburg, VA, USA) 100 µg/mL multi-element solution CCS-5 control materials were used to verify the accuracy of the prepared calibration curves. TaO NP agent solution digestion Microwave-assisted acid digestion of Ta 2 O 5 and NP agent stock. Tantalum (V) oxide powder (Ta 2 O 5 , Puratronic, 99.993% pure on metals basis excluding Nb, 50 ppm Nb maximum) purchased from Alfa Aesar (Ward Hill, MA, USA) was used asreceived as a reference material for the determination of Ta content in CZ3-TaO NP agent solutions. NP agent stock (0.1 g) or Ta 2 O 5 reference material (3-6 mg) was digested with 4 mL HF plus 1 mL HNO 3 in TFM vessels from CEM Corporation (Matthews, NC, USA) using a CEM Mars X-Press microwave digestion unit. The microwave digestion operating parameters were ramp to temperature (220 °C) in 25 min followed by a 30 min hold at temperature. The maximum permitted pressure was 600 psi and the maximum power output was 1600 W. The vessels cooled to less than 50 °C before depressurization. The dissolution solutions were transferred to polypropylene tubes and diluted to 50 g with deionized water. Four-fold secondary dilutions were prepared to contain 4% HF, 1% HNO 3 , and 10 µg/mL Nb. Procedural blanks were carried through the digestion process alongside sample unknowns. Acid dissolution of NP agent stock and dilute solutions. NP agent stock (0.1 g) was digested with 2 mL HF plus 0.5 mL HNO 3 in 50 mL polypropylene tubes using 1 hour of sonication at 50 °C (Branson Ultrasonic Cleaner 2510, Danbury, CT, USA). NP agent dilute solutions (0.2-2 g) were digested with 0.4 mL HF plus 0.1 mL HNO 3 in 15 mL polypropylene tubes following the same procedure as for agent stock. Niobium internal standard stock solution was added and the solutions diluted with deionized water to contain 4% HF, 1% HNO 3 , and 10 µg/mL Nb. Procedural blanks were carried through the digestion process alongside sample unknowns.
Journal of Computer Assisted Tomography, 2017
Objectives-To assess whether the low-to high-kVp CT number ratio at dual-energy CT (DECT) is affe... more Objectives-To assess whether the low-to high-kVp CT number ratio at dual-energy CT (DECT) 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 45 cm. The phantom was scanned using single-energy CT (SECT) at tube potentials of 80 and 140 kVp, and rapid-kVp-switching DECT. 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 dualenergy ratios for each contrast element. For 17/21 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.
Chemical Communications, 2013
A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxyb... more A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.
Zeitschrift Fur Kristallographie-new Crystal Structures, Nov 6, 2020
RöFo - Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren
Zeitschrift für Kristallographie - New Crystal Structures, 2020
C18H20Cl4N2OZr, monoclinic, Pnma (no. 62), a = 12.457(3) Å, b = 22.806(8) Å, c = 7.398(2) Å, V = ... more C18H20Cl4N2OZr, monoclinic, Pnma (no. 62), a = 12.457(3) Å, b = 22.806(8) Å, c = 7.398(2) Å, V = 2101.7(11) Å3, Z = 4, Rgt(F) = 0.0291, wRref(F2) = 0.0685, T = 110 K.
Journal of the American Chemical Society, 1999
Small peptide catalysts containing modified histidine residues are reported that effect enantiose... more Small peptide catalysts containing modified histidine residues are reported that effect enantioselective acylation reactions. The catalysts described include octapeptide-hairpins (e.g., 11) that exhibit high selectivities (up to k rel) 51), tetrapeptide-turns (e.g., 7) that afford moderate selectivities (up to k rel) 28), and several simple derivatives of the modified histidine amino acid that do not exhibit appreciable enantioselectivity. Supporting structural studies (1 H NMR and X-ray) are presented which lead to the proposal of a model in which catalyst rigidity and structural complexity contribute to higher degrees of enantioselection. A covalently rigidified octapeptide (20) is prepared through solid-phase Ru-catalyzed ring-closing metathesis; kinetic evaluation of this peptide reveals that substituents along the peptide backbone may be more important than covalent stabilization of a structural motif. Detailed kinetics studies on the most selective peptide catalysts are presented that suggest the reactions are first order in catalyst and substrate. Additional kinetic studies indicate unambiguously that enantioselectivities are due to specific acceleration of reaction for one substrate enantiomer, rather than the deceleration of the reaction for the other. The results are presented in the context of a possible enantiomer-specific hydrogen-bonding interaction in the stereochemistry-determining step for these processes.
Chemical Communications, 2013
A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxyb... more A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.
IUCrData
The title compound, C16H14, an asymmetric naphthyl-/methyl-substituted cyclopentadiene was synthe... more The title compound, C16H14, an asymmetric naphthyl-/methyl-substituted cyclopentadiene was synthesized and one isomer of five accessible through sigmatropic rearrangement was isolated and characterized by 1H NMR and X-ray diffraction. The crystal packing features an intermolecular C—H...π interaction.
Investigative radiology, Dec 25, 2016
The aim of this study was to produce and evaluate a proposed computed tomography (CT) contrast ag... more The aim of this study was to produce and evaluate a proposed computed tomography (CT) contrast agent based on carboxybetaine zwitterionic (CZ)-coated soluble tantalum oxide (TaO) nanoparticles (NPs). We chose tantalum to provide superior imaging performance compared with current iodine-based clinical CT contrast agents. We developed the CZ coating to provide biological and physical performance similar to that of current iodinated contrast agents. In addition, the aim of this study was to evaluate the imaging, biological, and physicochemical performance of this proposed contrast agent compared with clinically used iodinated agents. We evaluated CT imaging performance of our CZ-TaO NPs compared with that of an iodinated agent in live rats, imaged centrally located within a tissue-equivalent plastic phantom that simulated a large patient. To evaluate vascular contrast enhancement, we scanned the rats' great vessels at high temporal resolution during and after contrast agent injecti...
Chemical Communications, 2010
Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solut... more Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solution using HPLC-ICP, DLS, and multinuclear NMR. Nanoparticle formulation permitted intravenous injection, in vivo imaging, and subsequent renal clearance. A clinical CT scanner provided excellent resolution following agent injection, and distribution to the arterial system was visualized. In vitro CT imaging studies indicated that at equal molar concentration of tantalum and iodine, tantalum produced greater image contrast than iodine across the diagnostic X-ray spectrum with contrast benefit increasing with peak X-ray energy.
ACS Nano, 2012
For elemental composition, samples were prepared for analysis according to the following procedur... more For elemental composition, samples were prepared for analysis according to the following procedure: Two replicates per sample of 0.2 g were weighed into plastic, metal-free, 50 mL, screw-cap tubes and exact sample weights recorded. A mix of concentrated HF and HNO 3 was prepared at a ratio of 2:1 and then diluted to 12% with DI water. All acid used was Ultrex II grade from J.T. Baker. Then 2.5 mL of dilute acid mix were added to each tube and the samples were sonicated for 30 minutes in a Branson 2510 ultrasonic water bath. After sonication, DI water was added to each tube to the 40 mL fiducial mark followed by 5 mL of CFA-C (a proprietary aqueous solution of tertiary amines from Spectrasol, Inc.). A Finnpipette was used to add 5 mL to each tube of an aqueous solution of 10 ppm Sc and 40 ppm Zr as the ICP internal drift correct standard. The tubes were capped and solutions well mixed prior to analysis. The final concentration of each reagent in solution was 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. A sample preparation blank and two sample spikes were carried through the preparation procedure with the samples. A series of aqueous calibration standards containing Ta and Si were prepared in plastic, metal-free, 50 mL, screw-cap tubes from certified, 1000 ppm, single-element solutions from High Purity. The Ta concentrations ranged from 0.1 ppm to 100 ppm and the Si concentrations ranged from 0.05 ppm to 20 ppm. HF, HNO 3 , CFA-C, and internal drift standard were added to each calibration standard for 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. Secondary-source calibration check standards of 1 ppm were prepared from 10 ppm Spex Certiprep Assurance Mixed Calibration Standard 2 or 2A and 4 with 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. Wavelengths 240.063, 251.611, 343.823, and 361.383 nm were monitored for Ta, Si, Zr, and Sc, respectively, and linear calibration curves were generated from the ratio of analyte peak area to internal standard peak area and the known standard concentrations. Quantitative concentrations of Ta and Si in each sample were calculated by comparing the ratio of analyte peak area to internal standard peak area measured in the
Zeitschrift für Kristallographie - New Crystal Structures
C34H57BBr6N6O4V2, orthorhombic, Pna21 (no. 33), a = 17.198(2) Å, b = 12.9497(11) Å, c = 20.496(2)... more C34H57BBr6N6O4V2, orthorhombic, Pna21 (no. 33), a = 17.198(2) Å, b = 12.9497(11) Å, c = 20.496(2) Å, V = 4564.8(9) Å3, Z = 4, Rgt(F) = 0.0441, wRref(F2) = 0.1093, T = 183(2) K.
Catalysts
The catalytic tetranuclear manganese-calcium-oxo cluster in the photosynthetic reaction center, p... more The catalytic tetranuclear manganese-calcium-oxo cluster in the photosynthetic reaction center, photosystem II, provides an excellent blueprint for light-driven water oxidation in nature. The water oxidation reaction has attracted intense interest due to its potential as a renewable, clean, and environmentally benign source of energy production. Inspired by the oxygen-evolving complex of photosystem II, a large of number of highly innovative synthetic bio-inspired molecular catalysts are being developed that incorporate relatively cheap and abundant metals such as Mn, Fe, Co, Ni, and Cu, as well as Ru and Ir, in their design. In this review, we briefly discuss the historic milestones that have been achieved in the development of transition metal catalysts and focus on a detailed description of recent progress in the field.
Silicon, Nov 22, 2023
One of four possible stereoisomers of a methyl(trifluoropropyl)siloxane cyclic tetramer was isola... more One of four possible stereoisomers of a methyl(trifluoropropyl)siloxane cyclic tetramer was isolated from low molecular weight volatiles, formed in a reaction mixture during ring-opening/equilibration polymerization of methyl(3,3,3-trifluoropropyl)cyclotrisiloxane (D3F). The crystalline solid was recognized as resembling a previously isolated cyclic siloxane with undetermined stereochemistry, assigned as a cyclotetrasiloxane by IR spectroscopy, and then further characterized by multinuclear (1H, 13C, 19F, and 29Si) NMR spectroscopy as a relatively high symmetry species with respect to the potential cis-trans relationships of the methyl and 3,3,3-trifluoropropyl substituents at Si. Unambiguous characterization and assignment of the stereochemistry was accomplished by a single crystal X-ray diffraction study, which revealed the compound was the trans, trans, trans-isomer, one species in these equilibration polymerization mixtures. The single crystal X-ray structure of the related, com...
Radiology, Mar 1, 2016
To quantify the computed tomographic (CT) image contrast produced by potentially useful contrast ... more 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-mmthick 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 averagesized 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.
Dalton Transactions, 2022
Hyperfine coupling constants predicted by DFT in the most highly distorted four-coordinate d3 (VI... more Hyperfine coupling constants predicted by DFT in the most highly distorted four-coordinate d3 (VII) ion exhibit exceptional agreement with EPR.
Journal of Analytical Atomic Spectrometry, 2016
Materials and reagents Optima grade concentrated nitric (HNO 3) and hydrofluoric (HF) acids from ... more Materials and reagents Optima grade concentrated nitric (HNO 3) and hydrofluoric (HF) acids from Fisher Scientific (Pittsburgh, PA, USA) as well as Ultrex II ultrapure reagent hydrogen peroxide, 30%, (H 2 O 2) and concentrated sulfuric acid (H 2 SO 4) from J.T. Baker Avantor (Center Valley, PA, USA) were used throughout. All dilutions and solutions were prepared using deionized water (18.2 MΩ/cm) produced with a Milli-Q water purification system (Millipore, Bedford, MA, USA). Metals-free 15 and 50 mL polypropylene centrifuge tubes (VWR, Radnor, PA, USA) were used throughout. Single-element 1000 µg/mL Ta was obtained from High-Purity Standards (Charleston, SC, USA) for the preparation of intermediate stock solutions of 50 and 1 µg/mL Ta in 1% HNO 3. The intermediate stock solutions and the 1000 µg/mL Ta stock standard were used to prepare 21 working calibration standards (0.001-40 µg/mL Ta) containing the acid matrix corresponding to the samples prepared by microwave digestion or open-beaker digestion methods. Twenty-three working calibration standards (0.001-100 µg/mL Ta) were prepared in the acid matrix corresponding to the samples prepared by the dry-ash digestion method. A 100 µg/mL Nb solution was prepared in 1% HNO 3 and 0.1% HF from a 10000 µg/mL Nb stock solution (High-Purity Standards) for use as an internal standard reference added to all sample dilution and working calibration solutions. Addition of the 100 μg/mL Nb solution was performed with an accurate and precise manual digital pipette; the volume added was 1 mL, 2 mL, or 5 mL for solutions diluted to a final volume of 10 mL, 20 mL, or 50 mL respectively. SPEX CertiPrep (Metuchen, NJ, USA) 10 µg/mL multi-element solution CLMS-4 and Inorganic Ventures (Christiansburg, VA, USA) 100 µg/mL multi-element solution CCS-5 control materials were used to verify the accuracy of the prepared calibration curves. TaO NP agent solution digestion Microwave-assisted acid digestion of Ta 2 O 5 and NP agent stock. Tantalum (V) oxide powder (Ta 2 O 5 , Puratronic, 99.993% pure on metals basis excluding Nb, 50 ppm Nb maximum) purchased from Alfa Aesar (Ward Hill, MA, USA) was used asreceived as a reference material for the determination of Ta content in CZ3-TaO NP agent solutions. NP agent stock (0.1 g) or Ta 2 O 5 reference material (3-6 mg) was digested with 4 mL HF plus 1 mL HNO 3 in TFM vessels from CEM Corporation (Matthews, NC, USA) using a CEM Mars X-Press microwave digestion unit. The microwave digestion operating parameters were ramp to temperature (220 °C) in 25 min followed by a 30 min hold at temperature. The maximum permitted pressure was 600 psi and the maximum power output was 1600 W. The vessels cooled to less than 50 °C before depressurization. The dissolution solutions were transferred to polypropylene tubes and diluted to 50 g with deionized water. Four-fold secondary dilutions were prepared to contain 4% HF, 1% HNO 3 , and 10 µg/mL Nb. Procedural blanks were carried through the digestion process alongside sample unknowns. Acid dissolution of NP agent stock and dilute solutions. NP agent stock (0.1 g) was digested with 2 mL HF plus 0.5 mL HNO 3 in 50 mL polypropylene tubes using 1 hour of sonication at 50 °C (Branson Ultrasonic Cleaner 2510, Danbury, CT, USA). NP agent dilute solutions (0.2-2 g) were digested with 0.4 mL HF plus 0.1 mL HNO 3 in 15 mL polypropylene tubes following the same procedure as for agent stock. Niobium internal standard stock solution was added and the solutions diluted with deionized water to contain 4% HF, 1% HNO 3 , and 10 µg/mL Nb. Procedural blanks were carried through the digestion process alongside sample unknowns.
Journal of Computer Assisted Tomography, 2017
Objectives-To assess whether the low-to high-kVp CT number ratio at dual-energy CT (DECT) is affe... more Objectives-To assess whether the low-to high-kVp CT number ratio at dual-energy CT (DECT) 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 45 cm. The phantom was scanned using single-energy CT (SECT) at tube potentials of 80 and 140 kVp, and rapid-kVp-switching DECT. 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 dualenergy ratios for each contrast element. For 17/21 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.
Chemical Communications, 2013
A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxyb... more A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.
Zeitschrift Fur Kristallographie-new Crystal Structures, Nov 6, 2020
RöFo - Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren
Zeitschrift für Kristallographie - New Crystal Structures, 2020
C18H20Cl4N2OZr, monoclinic, Pnma (no. 62), a = 12.457(3) Å, b = 22.806(8) Å, c = 7.398(2) Å, V = ... more C18H20Cl4N2OZr, monoclinic, Pnma (no. 62), a = 12.457(3) Å, b = 22.806(8) Å, c = 7.398(2) Å, V = 2101.7(11) Å3, Z = 4, Rgt(F) = 0.0291, wRref(F2) = 0.0685, T = 110 K.
Journal of the American Chemical Society, 1999
Small peptide catalysts containing modified histidine residues are reported that effect enantiose... more Small peptide catalysts containing modified histidine residues are reported that effect enantioselective acylation reactions. The catalysts described include octapeptide-hairpins (e.g., 11) that exhibit high selectivities (up to k rel) 51), tetrapeptide-turns (e.g., 7) that afford moderate selectivities (up to k rel) 28), and several simple derivatives of the modified histidine amino acid that do not exhibit appreciable enantioselectivity. Supporting structural studies (1 H NMR and X-ray) are presented which lead to the proposal of a model in which catalyst rigidity and structural complexity contribute to higher degrees of enantioselection. A covalently rigidified octapeptide (20) is prepared through solid-phase Ru-catalyzed ring-closing metathesis; kinetic evaluation of this peptide reveals that substituents along the peptide backbone may be more important than covalent stabilization of a structural motif. Detailed kinetics studies on the most selective peptide catalysts are presented that suggest the reactions are first order in catalyst and substrate. Additional kinetic studies indicate unambiguously that enantioselectivities are due to specific acceleration of reaction for one substrate enantiomer, rather than the deceleration of the reaction for the other. The results are presented in the context of a possible enantiomer-specific hydrogen-bonding interaction in the stereochemistry-determining step for these processes.
Chemical Communications, 2013
A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxyb... more A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.
IUCrData
The title compound, C16H14, an asymmetric naphthyl-/methyl-substituted cyclopentadiene was synthe... more The title compound, C16H14, an asymmetric naphthyl-/methyl-substituted cyclopentadiene was synthesized and one isomer of five accessible through sigmatropic rearrangement was isolated and characterized by 1H NMR and X-ray diffraction. The crystal packing features an intermolecular C—H...π interaction.
Investigative radiology, Dec 25, 2016
The aim of this study was to produce and evaluate a proposed computed tomography (CT) contrast ag... more The aim of this study was to produce and evaluate a proposed computed tomography (CT) contrast agent based on carboxybetaine zwitterionic (CZ)-coated soluble tantalum oxide (TaO) nanoparticles (NPs). We chose tantalum to provide superior imaging performance compared with current iodine-based clinical CT contrast agents. We developed the CZ coating to provide biological and physical performance similar to that of current iodinated contrast agents. In addition, the aim of this study was to evaluate the imaging, biological, and physicochemical performance of this proposed contrast agent compared with clinically used iodinated agents. We evaluated CT imaging performance of our CZ-TaO NPs compared with that of an iodinated agent in live rats, imaged centrally located within a tissue-equivalent plastic phantom that simulated a large patient. To evaluate vascular contrast enhancement, we scanned the rats' great vessels at high temporal resolution during and after contrast agent injecti...
Chemical Communications, 2010
Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solut... more Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solution using HPLC-ICP, DLS, and multinuclear NMR. Nanoparticle formulation permitted intravenous injection, in vivo imaging, and subsequent renal clearance. A clinical CT scanner provided excellent resolution following agent injection, and distribution to the arterial system was visualized. In vitro CT imaging studies indicated that at equal molar concentration of tantalum and iodine, tantalum produced greater image contrast than iodine across the diagnostic X-ray spectrum with contrast benefit increasing with peak X-ray energy.
ACS Nano, 2012
For elemental composition, samples were prepared for analysis according to the following procedur... more For elemental composition, samples were prepared for analysis according to the following procedure: Two replicates per sample of 0.2 g were weighed into plastic, metal-free, 50 mL, screw-cap tubes and exact sample weights recorded. A mix of concentrated HF and HNO 3 was prepared at a ratio of 2:1 and then diluted to 12% with DI water. All acid used was Ultrex II grade from J.T. Baker. Then 2.5 mL of dilute acid mix were added to each tube and the samples were sonicated for 30 minutes in a Branson 2510 ultrasonic water bath. After sonication, DI water was added to each tube to the 40 mL fiducial mark followed by 5 mL of CFA-C (a proprietary aqueous solution of tertiary amines from Spectrasol, Inc.). A Finnpipette was used to add 5 mL to each tube of an aqueous solution of 10 ppm Sc and 40 ppm Zr as the ICP internal drift correct standard. The tubes were capped and solutions well mixed prior to analysis. The final concentration of each reagent in solution was 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. A sample preparation blank and two sample spikes were carried through the preparation procedure with the samples. A series of aqueous calibration standards containing Ta and Si were prepared in plastic, metal-free, 50 mL, screw-cap tubes from certified, 1000 ppm, single-element solutions from High Purity. The Ta concentrations ranged from 0.1 ppm to 100 ppm and the Si concentrations ranged from 0.05 ppm to 20 ppm. HF, HNO 3 , CFA-C, and internal drift standard were added to each calibration standard for 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. Secondary-source calibration check standards of 1 ppm were prepared from 10 ppm Spex Certiprep Assurance Mixed Calibration Standard 2 or 2A and 4 with 0.6% 2:1 HF:HNO 3 , 10% CFA-C, 1 ppm Sc, and 4 ppm Zr. Wavelengths 240.063, 251.611, 343.823, and 361.383 nm were monitored for Ta, Si, Zr, and Sc, respectively, and linear calibration curves were generated from the ratio of analyte peak area to internal standard peak area and the known standard concentrations. Quantitative concentrations of Ta and Si in each sample were calculated by comparing the ratio of analyte peak area to internal standard peak area measured in the
Zeitschrift für Kristallographie - New Crystal Structures
C34H57BBr6N6O4V2, orthorhombic, Pna21 (no. 33), a = 17.198(2) Å, b = 12.9497(11) Å, c = 20.496(2)... more C34H57BBr6N6O4V2, orthorhombic, Pna21 (no. 33), a = 17.198(2) Å, b = 12.9497(11) Å, c = 20.496(2) Å, V = 4564.8(9) Å3, Z = 4, Rgt(F) = 0.0441, wRref(F2) = 0.1093, T = 183(2) K.
Catalysts
The catalytic tetranuclear manganese-calcium-oxo cluster in the photosynthetic reaction center, p... more The catalytic tetranuclear manganese-calcium-oxo cluster in the photosynthetic reaction center, photosystem II, provides an excellent blueprint for light-driven water oxidation in nature. The water oxidation reaction has attracted intense interest due to its potential as a renewable, clean, and environmentally benign source of energy production. Inspired by the oxygen-evolving complex of photosystem II, a large of number of highly innovative synthetic bio-inspired molecular catalysts are being developed that incorporate relatively cheap and abundant metals such as Mn, Fe, Co, Ni, and Cu, as well as Ru and Ir, in their design. In this review, we briefly discuss the historic milestones that have been achieved in the development of transition metal catalysts and focus on a detailed description of recent progress in the field.