38 results on '"Benjamin W. Stein"'
Search Results
2. Synthesis and Characterization of the Actinium Aquo Ion
- Author
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Maryline G. Ferrier, Benjamin W. Stein, Enrique R. Batista, John M. Berg, Eva R. Birnbaum, Jonathan W. Engle, Kevin D. John, Stosh A. Kozimor, Juan S. Lezama Pacheco, and Lindsay N. Redman
- Subjects
Chemistry ,QD1-999 - Published
- 2017
- Full Text
- View/download PDF
3. Spectroscopic and computational investigation of actinium coordination chemistry
- Author
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Maryline G. Ferrier, Enrique R. Batista, John M. Berg, Eva R. Birnbaum, Justin N. Cross, Jonathan W. Engle, Henry S. La Pierre, Stosh A. Kozimor, Juan S. Lezama Pacheco, Benjamin W. Stein, S. Chantal E. Stieber, and Justin J. Wilson
- Subjects
Science - Abstract
Actinium-225 is a promising isotope for α-therapy but progress in developing its chemistry is hindered by its high radioactivity and short supply. Here, the authors characterize actinium coordination in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory.
- Published
- 2016
- Full Text
- View/download PDF
4. Exploring how exposure to radiolysis and harsh chemical reagents impact americium-241 extraction chromatography
- Author
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Brian T. Arko, David Dan, Sara Adelman, David B. Kimball, Stosh A. Kozimor, Marki M. Martinez, Tara Mastren, Daniel L. Huber, Veronika Mocko, Jung Rim, Jenifer C. Shafer, Benjamin W. Stein, and E. Miller Wylie
- Subjects
Chemistry (miscellaneous) ,General Materials Science - Abstract
Improving control over radiolysis would advance nuclear technologies, spanning from radiotherapeutics to national security. Herein, we studied the effects of radiolysis on large-scale production of Am-241.
- Published
- 2023
5. Whispering gallery mode resonators in continuous flow: spectral assignments and sensing with monodisperse microspheres
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Bryan C. Paulus, Jenny K. Banh, Kirk D. Rector, Benjamin W. Stein, and Laura M. Lilley
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Refractometry ,General Chemical Engineering ,General Engineering ,Microspheres ,Analytical Chemistry - Abstract
Whispering gallery mode resonator (WGMR) microspheres yield highly structured optical spectra that are extremely sensitive to their environment and are of intense interest for use in a variety of sensing applications. Many efforts to leverage the unique sensitivities of WGMRs have relied on stringent experimental requirements to correlate specific spectral shifts/changes to an analyte/stimulus such as (1) precise positional knowledge, (2) reference spectra for each microsphere, and (3) high mechanical stability. Consequently, these factors can hinder adequate mixing or incorporation of analytes and can create challenges for remote sensing. This work describes a continuous flow technique for measuring whispering gallery mode (WGM) spectra of dye-doped microspheres suspended in solution and an accompanying analysis scheme that can extract the local refractive index without
- Published
- 2022
6. Hyperspectral X-Ray Imaging: Progress Towards Chemical Analysis in the SEM
- Author
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Ping Yang, Katrina Koehler, Eric G. Bowes, Enrique R. Batista, Gene C. Hilton, M. H. Carpenter, Carl D. Reintsema, Douglas A. Bennett, Daikang Yan, Johnathon D. Gard, Zachary K. Baker, Daniel S. Swetz, Michael W. Rabin, M. P. Croce, Katherine A. Schreiber, Gregory L. Wagner, Joel C. Weber, Daniel T. Becker, Daniel Schmidt, Benjamin W. Stein, Chandler M. Smith, Christopher J. Fontes, Galen C. O'Neil, Abigail L. Wessels, Joel N. Ullom, Matthew L. Handley, J. Imrek, Kelsey M. Morgan, John A. B. Mates, and Daniel G. McNeel
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Cryostat ,Materials science ,Pixel ,Scanning electron microscope ,business.industry ,Detector ,Hyperspectral imaging ,Condensed Matter Physics ,01 natural sciences ,Sample (graphics) ,Electronic, Optical and Magnetic Materials ,Chemical species ,Optics ,0103 physical sciences ,Electrical and Electronic Engineering ,010306 general physics ,business ,Microwave - Abstract
The Hyperspectral X-ray Imaging (HXI) project will enable non-destructive chemical-state determination of nano-scale samples in the electron microscope for nuclear safeguards applications. To efficiently measure chemical state through electron-excited X-ray emission requires a combination of wide spectral bandwidth, high resolution, and high count rate capability. We are building a next-generation X-ray detector based on an array of transition edge sensors (TESs) to make these measurements possible and routine in the scanning electron microscope (SEM). Leveraging the large pixel densities afforded by microwave multiplexing readout and continuous, uninterrupted operation of a cryogen-free dilution refrigerator, this instrument will have efficiency to allow chemical species identification of nano-scale samples in hours instead of days to weeks. We describe prototype pixel designs for this HXI instrument, comprising three pixel types that will make up the hybrid TES array. Engineering design of the integrated HXI cryostat and SEM system is in progress, with full detector commissioning expected in Spring 2021 followed closely by full-scale integration with the SEM. We also report on the commissioning of a complementary TES-based X-ray emission spectroscopy platform for bulk samples to build a spectral library for HXI sample identification.
- Published
- 2021
7. Photochemical separation of plutonium from uranium
- Author
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Ida M. DiMucci, Harrison D. Root, Zachary R. Jones, Stosh A. Kozimor, Molly M. MacInnes, Jeffrey L. Miller, Veronika Mocko, Warren J. Oldham, and Benjamin W. Stein
- Subjects
Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Plutonium-based technologies would benefit if chemical hazards for purifying plutonium were reduced. One critical processing step where improvements could be impactful is the adjustment of plutonium oxidation-states during separations. This transformation often requires addition of redox agents. Unfortunately, many of the redox agents used previously cannot be used today because their properties are deemed incompatible with modern day processing facilities and waste stream safety requirements. We demonstrated herein that photochemistry can be used as an alternative to those chemical agents. We observed that (1) Pu
- Published
- 2022
8. High Resolution X-Ray Spectra for Chemical Speciation in the SEM
- Author
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Eric G. Bowes, Lei Xu, Chandler M. Smith, Michael W. Rabin, Enrique R. Batista, Benjamin W. Stein, M. P. Croce, Katherine A. Schreiber, M. H. Carpenter, Christopher J. Fontes, Katrina Koehler, Daniel G. McNeel, Gregory L. Wagner, and Ping Yang
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Materials science ,Chemical speciation ,Analytical chemistry ,High resolution ,Instrumentation ,X ray spectra - Published
- 2021
9. Synthesis, solid-state, solution, and theoretical characterization of an 'in-cage' scandium-NOTA complex
- Author
-
Kelly E. Aldrich, Ivan A. Popov, Harrison D. Root, Enrique R. Batista, Samuel M. Greer, Stosh A. Kozimor, Laura M. Lilley, Maksim Y. Livshits, Veronika Mocko, Michael T. Janicke, Brian L. Scott, Benjamin W. Stein, and Ping Yang
- Subjects
Inorganic Chemistry ,Heterocyclic Compounds, 1-Ring ,Ligands ,Scandium ,Chelating Agents - Abstract
Developing chelators that strongly and selectively bind rare-earth elements (Sc, Y, La, and lanthanides) represents a longstanding fundamental challenge in inorganic chemistry. Solving these challenges is becoming more important because of increasing use of rare-earth elements in numerous technologies, ranging from paramagnets to luminescent materials. Within this context, we interrogated the complexation chemistry of the scandium(III) (Sc
- Published
- 2022
10. Advancing understanding of actinide(iii) (Ac, Am, Cm) aqueous complexation chemistry†
- Author
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Laura M. Lilley, Jennifer N. Wacker, Karah E. Knope, Veronika Mocko, Maryline G. Ferrier, Zachary R. Jones, Frankie D. White, Stosh A. Kozimor, David H. Woen, Maksim Y. Livshits, Benjamin W. Stein, Brian L. Scott, and Elodie Dalodière
- Subjects
Aqueous solution ,Inorganic chemistry ,General Chemistry ,Actinide ,Inner sphere electron transfer ,Metal ,Acetic acid ,chemistry.chemical_compound ,Chemistry ,chemistry ,visual_art ,Chemical Sciences ,visual_art.visual_art_medium ,Chelation ,Reactivity (chemistry) ,Absorption (chemistry) - Abstract
The positive impact of having access to well-defined starting materials for applied actinide technologies – and for technologies based on other elements – cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac3+ and Cm3+ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H2O)6(1)(O2CMe)3(1) compound was the major species in solution for the large Ac3+. In contrast, smaller Cm3+ preferred forming an anion. There were approximately four bound O2CMe1− ligands and one to two inner sphere H2O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH4)2M(O2CMe)5 (M = Eu3+, Am3+ and Cm3+) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements)., Actinide complexation from aqueous acetic acid/acetate buffered solutions is described. The number of water ligands was directly correlated with the acetate concentration and characterized by X-ray absorption and optical spectroscopy.
- Published
- 2021
11. Low-spin 1,1′-diphosphametallocenates of chromium and iron
- Author
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Conrad A. P. Goodwin, Benjamin W. Stein, Jaqueline L. Kiplinger, Ökten Üngör, Ross James Beattie, Brian L. Scott, and Samuel M. Greer
- Subjects
Quantum chemical ,Ligand field theory ,Squid ,Materials science ,biology ,Magnetometer ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Chromium ,Crystallography ,chemistry ,law ,biology.animal ,Materials Chemistry ,Ceramics and Composites ,Spin (physics) ,Electron paramagnetic resonance - Abstract
We report two anionic diphosphametallocenates, [K(2.2.2-crypt)][M(PC4Me4)2] (M = Cr, 2-Cr; Fe, 2-Fe). Both are low-spin (S = ½) by EPR spectroscopy and SQUID magnetometry. This contrasts the high-spin (S = 3/2) ferrocenate, [K(2.2.2-crypt)][Fe(C5H2-1,2,4-tBu)2] (4-Fe). Quantum chemical calculations suggest this is due to significant differences in ligand field splitting of the d-orbitals which also explain structural features in the 2-M complexes.
- Published
- 2021
12. Large-Scale Production of 119mTe and 119Sb for Radiopharmaceutical Applications
- Author
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Scott R. Daly, Kevin T. Bennett, Francois M. Nortier, Sharon E. Bone, Laura M. Lilley, C. Vermeulen, Veronika Mocko, Anastasia V. Blake, Benjamin W. Stein, Eva R. Birnbaum, Sara L. Thiemann, Christopher A. Martinez, Michael E. Fassbender, Maryline G. Ferrier, Jonathan W. Engle, Mark Brugh, Andrew C. Akin, and Stosh A. Kozimor
- Subjects
010405 organic chemistry ,business.industry ,Process development ,Computer science ,General Chemical Engineering ,Scale (chemistry) ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,High flux ,Chemistry ,Production (economics) ,Process engineering ,business ,QD1-999 ,Research Article - Abstract
Radionuclides find widespread use in medical technologies for treating and diagnosing disease. Among successful and emerging radiotherapeutics, 119Sb has unique potential in targeted therapeutic applications for low-energy electron-emitting isotopes. Unfortunately, developing 119Sb-based drugs has been slow in comparison to other radionuclides, primarily due to limited accessibility. Herein is a production method that overcomes this challenge and expands the available time for large-scale distribution and use. Our approach exploits high flux and fluence from high-energy proton sources to produce longer lived 119mTe. This parent isotope slowly decays to 119Sb, which in turn provides access to 119Sb for longer time periods (in comparison to direct 119Sb production routes). We contribute the target design, irradiation conditions, and a rapid procedure for isolating the 119mTe/119Sb pair. To guide process development and to understand why the procedure was successful, we characterized the Te/Sb separation using Te and Sb K-edge X-ray absorption spectroscopy. The procedure provides low-volume aqueous solutions that have high 119mTe—and consequently 119Sb—specific activity in a chemically pure form. This procedure has been demonstrated at large-scale (production-sized, Ci quantities), and the product has potential to meet stringent Food and Drug Administration requirements for a 119mTe/119Sb active pharmaceutical ingredient., A large-scale production method for 119mTe and 119Sb from an Sb target is described, with X-ray absorption spectroscopy measurements providing insight into the success of the chemical separations.
- Published
- 2019
13. Total Moisture Analysis of Salts by Dissolution
- Author
-
Benjamin W. Stein and Nhu Lam
- Subjects
Moisture analysis ,Chemistry ,Environmental chemistry ,Dissolution - Published
- 2021
14. Preparation of an Actinium-228 Generator
- Author
-
Laura M. Lilley, Benjamin W. Stein, Stosh A. Kozimor, Veronika Mocko, Kelly E. Aldrich, Cecilia Eiroa-Lledo, and Mila Nhu Lam
- Subjects
Inorganic Chemistry ,Actinium ,Generator (computer programming) ,High specific activity ,Chemistry ,Radiochemistry ,Nuclear spectroscopy ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Volume concentration - Abstract
Advances in targeted α-therapies have increased the interest in actinium (Ac), whose chemistry is poorly defined due to scarcity and radiological hazards. Challenges associated with characterizing Ac3+ chemistry are magnified by its 5f06d0 electronic configuration, which precludes the use of many spectroscopic methods amenable to small amounts of material and low concentrations (like EPR, UV-vis, fluorescence). In terms of nuclear spectroscopy, many actinium isotopes (225Ac and 227Ac) are equally "unfriendly" because the actinium α-, β-, and γ-emissions are difficult to resolve from the actinium daughters. To address these issues, we developed a method for isolating an actinium isotope (228Ac) whose nuclear properties are well-suited for γ-spectroscopy. This four-step procedure isolates 228Ra from naturally occurring 232Th. The relatively long-lived 228Ra (t1/2 = 5.75(3) years) radioisotope subsequently decays to 228Ac. Because the 228Ac decay rate [t1/2 = 6.15(2) h] is fast, 228Ac rapidly regenerates after being harvested from the 228Ra parent. The resulting 228Ac generator provides frequent and long-term access (of many years) to the spectroscopically "friendly" 228Ac radionuclide. We have demonstrated that the 228Ac product can be routinely "milked" from this generator on a daily basis, in chemically pure form, with high specific activity and in excellent yield (∼95%). Hence, in the same way that developing synthesis routes to new starting materials has advanced coordination chemistry for many metals by broadening access, this 228Ac generator has the potential to broaden actinium access for the inorganic community, facilitating the characterization of actinium chemical behavior.
- Published
- 2020
15. Advancing Chelation Chemistry for Actinium and Other +3 f-Elements, Am, Cm, and La
- Author
-
Eva R. Birnbaum, Stosh A. Kozimor, Brian L. Scott, Veronika Mocko, Samantha K. Cary, Ping Yang, Kevin D. John, Amanda Morgenstern, Benjamin W. Stein, Maryline G. Ferrier, Enrique R. Batista, Sharon E. Bone, and Juan S. Lezama Pacheco
- Subjects
Actinium ,Inorganic chemistry ,Binding pocket ,chemistry.chemical_element ,010402 general chemistry ,Ligands ,01 natural sciences ,Biochemistry ,Catalysis ,Coordination complex ,Colloid and Surface Chemistry ,Organophosphorus Compounds ,Coordination Complexes ,Lanthanum ,Molecule ,Chelation ,Chelating Agents ,chemistry.chemical_classification ,Americium ,Extended X-ray absorption fine structure ,Molecular Structure ,Extramural ,General Chemistry ,0104 chemical sciences ,chemistry ,Curium ,Radiopharmaceuticals - Abstract
A major chemical challenge facing implementation of 225Ac in targeted alpha therapy-an emerging technology that has potential for treatment of disease-is identifying an 225Ac chelator that is compatible with in vivo applications. It is unclear how to tailor a chelator for Ac binding because Ac coordination chemistry is poorly defined. Most Ac chemistry is inferred from radiochemical experiments carried out on microscopic scales. Of the few Ac compounds that have been characterized spectroscopically, success has only been reported for simple inorganic ligands. Toward advancing understanding in Ac chelation chemistry, we have developed a method for characterizing Ac complexes that contain highly complex chelating agents using small quantities (μg) of 227Ac. We successfully characterized the chelation of Ac3+ by DOTP8- using EXAFS, NMR, and DFT techniques. To develop confidence and credibility in the Ac results, comparisons with +3 cations (Am, Cm, and La) that could be handled on the mg scale were carried out. We discovered that all M3+ cations (M = Ac, Am, Cm, La) were completely encapsulated within the binding pocket of the DOTP8- macrocycle. The computational results highlighted the stability of the M(DOTP)5- complexes.
- Published
- 2019
16. Long-range spin dependent delocalization promoted by the pseudo Jahn-Teller effect
- Author
-
Diane A. Dickie, Benjamin W. Stein, David A. Shultz, Martin L. Kirk, David J. R. Brook, and Sachin Nedungadi
- Subjects
Physics ,010304 chemical physics ,Spins ,General Physics and Astronomy ,Triad (anatomy) ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Delocalized electron ,Crystallography ,medicine.anatomical_structure ,Ferromagnetism ,0103 physical sciences ,medicine ,Single bond ,Diamagnetism ,Antiferromagnetism ,Physical and Theoretical Chemistry ,Spin (physics) - Abstract
Strong spin-dependent delocalization (double exchange) was previously demonstrated for the complexes, NN-Bridge-SQ-Coiii(py)2Cat-Bridge-NN (where NN = S = 12 nitronylnitroxide, Bridge = 1,4-phenylene and single bond, SQ = S = 12 orthobenzosemiquinone, Coiii = low-spin d6 cobalt 3+, and Cat = diamagnetic catecholate). The mixed-valent S = 12 SQ-Coiii-Cat triad results in ferromagnetic alignment of localized (pinned) NN spins which are ∼22 A apart (Bridge = Ph). Herein, we report similar ferromagnetic coupling of localized verdazyl (Vdz) radical spins. The origin of the magnetic exchange results from a second order vibronic effect (pseudo Jahn-Teller effect) in [Vdz-diox-Ru(py)2-diox-Vdz]0, which possesses a diamagnetic [diox-Ru-diox]0 triad by virtue of strong antiferromagnetic SQ-Ruiii exchange.
- Published
- 2019
17. Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA–); Synthesis and Structure of MIVTTA4 (MIV = Zr, Hf, Ce, Th, U, Np, Pu) and MIII(TTA)4– (MIII = Ce, Nd, Sm, Yb)
- Author
-
Samantha K. Cary, Benjamin W. Stein, Maksim Y. Livshits, Brian L. Scott, Stosh A. Kozimor, Veronika Mocko, Jeffrey J. Rack, Justin N. Cross, and Maryline G. Ferrier
- Subjects
Highly skilled ,010405 organic chemistry ,Extraction (chemistry) ,chemistry.chemical_element ,Actinide ,Uranium ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Physical chemistry ,Physical and Theoretical Chemistry ,Thenoyltrifluoroacetone - Abstract
Thenoyltrifluoroacetone (HTTA)-based extractions represent popular methods for separating microscopic amounts of transuranic actinides (i.e., Np and Pu) from macroscopic actinide matrixes (e.g. bulk uranium). It is well-established that this procedure enables +4 actinides to be selectively removed from +3, + 5, and +6 f-elements. However, even highly skilled and well-trained researchers find this process complicated and (at times) unpredictable. It is difficult to improve the HTTA extraction—or find alternatives—because little is understood about why this separation works. Even the identities of the extracted species are unknown. In addressing this knowledge gap, we report here advances in fundamental understanding of the HTTA-based extraction. This effort included comparatively evaluating HTTA complexation with +4 and +3 metals (MIV = Zr, Hf, Ce, Th, U, Np, and Pu vs MIII = Ce, Nd, Sm, and Yb). We observed +4 metals formed neutral complexes of the general formula MIV(TTA)4. Meanwhile, +3 metals formed an...
- Published
- 2018
18. A series of F-Element chelators; diaza crown ethers functionalized with catecholate binding substituents
- Author
-
Samantha K. Cary, Eva R. Birnbaum, Benjamin W. Stein, Stosh A. Kozimor, Brian L. Scott, Veronika Mocko, and John M. Berg
- Subjects
Catechol ,Semiquinone ,010405 organic chemistry ,Chemistry ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Combinatorial chemistry ,Redox ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Elemental analysis ,Materials Chemistry ,Cluster (physics) ,Physical and Theoretical Chemistry ,Spectroscopy ,Single crystal ,Mannich reaction - Abstract
Reported here is the preparation of azacrown ethers functionalized with catechol groups. The synthetic approach was (1st) novel in that it made use of the Mannich reaction and (2nd) valuable in that it provided an improved synthesis (in terms of practical deployment) of the known N,N′-bis(2,3-dihydroxybenzyl)-4,13-diaza-18-crown-6, H4ChaCha. Moreover, it demonstrated potential application of the synthetic method for accommodating a wide range of catecholate functionalities by using the synthetic strategy to prepare N,N′-bis(2,3-dihydroxy-5-tert-butylbenzyl)-4,13-diaza-18-crown-6 (H4tBu2ChaCha) for the first time. These H4ChaCha and H4tBu2ChaCha macrocycles offer exciting opportunity to expand redox chemistry for the f-elements. As “proof-of-principle,” we isolated the unusual tetrameric cluster [La2(tBuChaCha)2]2 from reactions between H4tBu2ChaCha and La[N(SiMe3)2]3. Characterization of [La2(tBuChaCha)2]2 by elemental analysis, single crystal X-ray diffraction, IR, and UV–vis–NIR spectroscopy suggested that the complex represented a rare example of an f-element semiquinone. It further demonstrated that the combination of La3+ and H4tBu2ChaCha provided access to one-electron oxidation chemistry within redox potential windows that were amenable to mild reaction conditions.
- Published
- 2018
19. The coordination chemistry of CmIII, AmIII, and AcIIIin nitrate solutions: an actinide L3-edge EXAFS study
- Author
-
Gerald T. Seidler, Stosh A. Kozimor, Veronika Mocko, Sharon E. Bone, Juan S. Lezama Pacheco, Maryline G. Ferrier, Alexander S. Ditter, Samantha K. Cary, and Benjamin W. Stein
- Subjects
chemistry.chemical_classification ,X-ray absorption spectroscopy ,Aqueous solution ,Extended X-ray absorption fine structure ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Analytical chemistry ,General Chemistry ,Actinide ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Coordination complex ,chemistry.chemical_compound ,Nitric acid ,Stoichiometry - Abstract
Understanding actinide(III) (AnIII = CmIII, AmIII, AcIII) solution-phase speciation is critical for controlling many actinide processing schemes, ranging from medical applications to reprocessing of spent nuclear fuel. Unfortunately, in comparison to most elements in the periodic table, AnIII speciation is often poorly defined in complexing aqueous solutions and in organic media. This neglect – in large part – is a direct result of the radioactive properties of these elements, which make them difficult to handle and acquire. Herein, we surmounted some of the handling challenges associated with these exotic 5f-elements and characterized CmIII, AmIII, and AcIII using AnIII L3-edge X-ray absorption spectroscopy (XAS) as a function of increasing nitric acid (HNO3) concentration. Our results revealed that actinide aquo ions, An(H2O)x3+ (x = 9.6 ± 0.7, 8.9 ± 0.8, and 10.0 ± 0.9 for CmIII, AmIII, and AcIII), were the dominant species in dilute HNO3 (0.05 M). In concentrated HNO3 (16 M), shell-by-shell fitting of the extended X-ray fine structure (EXAFS) data showed the nitrate complexation increased, such that the average stoichiometries of Cm(NO3)4.1±0.7(H2O)5.7±1.3(1.1±0.2)−, Am(NO3)3.4±0.7(H2O)5.4±0.5(0.4±0.1)−, and Ac(NO3)2.3±1.7(H2O)8.3±5.2(0.7±0.5)+ were observed. Data obtained at the intermediate HNO3 concentration (4 M) were modeled as a linear combination of the 0.05 and 16 M spectra. For all three metals, the intermediate models showed larger contributions from the 0.05 M HNO3 spectra than from the 16 M HNO3 spectra. Additionally, these efforts enabled the Cm–NO3 and Ac–NO3 distances to be measured for the first time. Moreover, the AnIII L3-edge EXAFS results, contribute to the growing body of knowledge associated with CmIII, AmIII, and AcIII coordination chemistry, in particular toward advancing understanding of AnIII solution phase speciation.
- Published
- 2018
20. Measurement of 227Ac impurity in 225Ac using decay energy spectroscopy
- Author
-
Michael Yoho, Ellen M. O'Brien, Laura M. Lilley, Joel N. Ullom, M. H. Carpenter, Katrina Koehler, Benjamin W. Stein, M. P. Croce, Chandler M. Smith, David J. Mercer, A.D. Tollefson, Michael E. Fassbender, and Daniel Schmidt
- Subjects
Superconductivity ,Phase transition ,Radiation ,Materials science ,Analytical chemistry ,chemistry.chemical_element ,010403 inorganic & nuclear chemistry ,01 natural sciences ,Spectral line ,030218 nuclear medicine & medical imaging ,0104 chemical sciences ,03 medical and health sciences ,Actinium ,0302 clinical medicine ,chemistry ,Decay energy ,Impurity ,Transition edge sensor ,Spectroscopy - Abstract
225 Ac is a valuable medical radionuclide for targeted α therapy, but 227 Ac is an undesirable byproduct of an accelerator-based synthesis method under investigation. Sufficient detector sensitivity is critical for quantifying the trace impurity of 227 Ac , with the 227 Ac / 225 Ac activity ratio predicted to be approximately 0.15% by end-of-bombardment (EOB). Superconducting transition edge sensor (TES) microcalorimeters offer high resolution energy spectroscopy using the normal-to-superconducting phase transition to measure small changes in temperature. By embedding 225 Ac production samples in a gold foil thermally coupled to a TES microcalorimeter we can measure the decay energies of the radionuclides embedded with high resolution and 100% detection efficiency. This technique, known as decay energy spectroscopy (DES), collapses several peaks from α decays into single Q-value peaks. In practice there are more complex factors in the interpretation of data using DES, which we will discuss herein. Using this technique we measured the EOB 227 Ac impurity to be (0.142 ± 0.005)% for a single production sample. This demonstration has shown that DES is a useful tool for quantitative measurements of complicated spectra.
- Published
- 2021
21. Covalency in Americium(III) Hexachloride
- Author
-
Stosh A. Kozimor, Justin N. Cross, Brian L. Scott, Samantha K. Cary, Ping Yang, Enrique R. Batista, Cory J. Windorff, Benjamin W. Stein, William J. Evans, Jing Su, and Veronika Mocko
- Subjects
X-ray absorption spectroscopy ,Americium ,Absorption spectroscopy ,010405 organic chemistry ,Chemistry ,Extramural ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Chlorides ,Chemical physics ,Computational chemistry ,Mixing (physics) - Abstract
Developing a better understanding of covalency (or orbital mixing) is of fundamental importance. Covalency occupies a central role in directing chemical and physical properties for almost any given compound or material. Hence, the concept of covalency has potential to generate broad and substantial scientific advances, ranging from biological applications to condensed matter physics. Given the importance of orbital mixing combined with the difficultly in measuring covalency, estimating or inferring covalency often leads to fiery debate. Consider the 60-year controversy sparked by Seaborg and co-workers ( Diamond, R. M.; Street, K., Jr.; Seaborg, G. T. J. Am. Chem. Soc. 1954 , 76 , 1461 ) when it was proposed that covalency from 5f-orbitals contributed to the unique behavior of americium in chloride matrixes. Herein, we describe the use of ligand K-edge X-ray absorption spectroscopy (XAS) and electronic structure calculations to quantify the extent of covalent bonding in-arguably-one of the most difficult systems to study, the Am-Cl interaction within AmCl
- Published
- 2017
22. Synthesis and Characterization of the Actinium Aquo Ion
- Author
-
Kevin D. John, Maryline G. Ferrier, John M. Berg, Lindsay N. Redman, Benjamin W. Stein, Juan S. Lezama Pacheco, Eva R. Birnbaum, Stosh A. Kozimor, Jonathan W. Engle, and Enrique R. Batista
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Chemistry ,General Chemical Engineering ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,3. Good health ,0104 chemical sciences ,Characterization (materials science) ,Coordination complex ,Ion ,Metal ,lcsh:Chemistry ,Actinium ,lcsh:QD1-999 ,visual_art ,visual_art.visual_art_medium ,Molecule ,Absorption (chemistry) ,Metal aquo complex ,Research Article - Abstract
Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H2O)x3+) is critical for current efforts to develop 225Ac [t1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity, many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived 227Ac [t1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the AcIII cation with an Ac–OH2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that AcIII was coordinated by 9 water molecules with Ac–OH2O distances ranging from 2.61 to 2.76 Å. The data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large AcIII coordination numbers and long Ac–OH2O bond distances., The actinium aquo complex has been characterized using Ac L3-edge X-ray absorption spectroscopy and molecular dynamics density functional theory.
- Published
- 2017
23. Evaluating the electronic structure of formal LnIIions in LnII(C5H4SiMe3)31−using XANES spectroscopy and DFT calculations
- Author
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Juan S. Lezama Pacheco, Gregory L. Wagner, Enrique R. Batista, David H. Woen, Jing Su, Austin J. Ryan, Maryline G. Ferrier, Stosh A. Kozimor, Samantha K. Cary, Jonathan W. Engle, Tonya Vitova, Benjamin W. Stein, Ping Yang, Angela C. Olson, William J. Evans, and Megan E. Fieser
- Subjects
Lanthanide ,010405 organic chemistry ,Chemistry ,Transition dipole moment ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,XANES ,0104 chemical sciences ,Ion ,Computational chemistry ,Physical chemistry ,Density functional theory ,Electron configuration ,Spectroscopy - Abstract
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f n 5d1 configurations (not 4f n+1 5d0). In these 4f n 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration.
- Published
- 2017
24. Comparing the 2,2′‐Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium
- Author
-
Justin N. Cross, Joseph A. Macor, Jeffery A. Bertke, Maryline G. Ferrier, Gregory S. Girolami, Stosh A. Kozimor, Joel R. Maassen, Brian L. Scott, David K. Shuh, Benjamin W. Stein, and S. Chantal E. Stieber
- Subjects
010405 organic chemistry ,General Medicine ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences - Abstract
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4)Am[S2P(tBu2C12H6)]4and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., NdIII) and an isoelectronic one (EuIII). The results include the first measurement of an Am−S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the EuIIIand NdIIIcomplexes revealed subtle electronic differences between the complexes of AmIIIand the lanthanides.
- Published
- 2016
25. Vibrational Control of Covalency Effects Related to the Active Sites of Molybdenum Enzymes
- Author
-
Benjamin W. Stein, Nicholas J. Wiebelhaus, Martin L. Kirk, John H. Enemark, Jing Yang, Dennis L. Lichtenberger, Regina P. Mtei, Dominic K. Kersi, and Jesse LePluart
- Subjects
chemistry.chemical_element ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Vibration ,Catalysis ,Article ,Electron Transport ,Electron transfer ,Colloid and Surface Chemistry ,Transition metal ,Oxidation state ,Catalytic Domain ,Organometallic Compounds ,Molecular orbital ,Sulfhydryl Compounds ,Molybdenum ,Valence (chemistry) ,Molecular Structure ,Chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,Electron transport chain ,0104 chemical sciences ,Crystallography ,sense organs ,0210 nano-technology - Abstract
A multi-technique spectroscopic and theoretical study of the Cp(2)M(benzenedithiolato) (M=Ti,V,Mo; Cp = η(5)-C(5)H(5)) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin molybdenum enzymes. This work explains the magnitude of the dithiolene folding distortion, and the concomitant changes in metal-ligand covalency, that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn-Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arise from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance Raman, magnetic circular dichroism, electron paramagnetic resonance, and UV photoelectron spectroscopies to explore the electronic states involved in the vibronic coupling mechanism. Comparison between the UV photoelectron spectroscopy (UPS) of the d(2) M=Mo complex and the resonance Raman spectra of the d(1) M=V complex reveals the power of this combined spectroscopic approach. Here, we observe that the UPS spectrum of Cp(2)Mo(bdt) contains an intriguing vibronic progession that is dominated by a “missing-mode” that is comprised of PJT active distortions. We discuss the relationship of the PJT distortions to facile electron transfer in molybdenum enzymes.
- Published
- 2018
26. The coordination chemistry of Cm
- Author
-
Maryline G, Ferrier, Benjamin W, Stein, Sharon E, Bone, Samantha K, Cary, Alexander S, Ditter, Stosh A, Kozimor, Juan S, Lezama Pacheco, Veronika, Mocko, and Gerald T, Seidler
- Subjects
Chemistry - Abstract
CmIII, AmIII, and AcIII have been characterized by solution L3-edge X-ray absorption spectroscopy as a function of nitric acid concentration. This enabled the first experimental determination of Cm and Ac nitrate distances., Understanding actinide(iii) (AnIII = CmIII, AmIII, AcIII) solution-phase speciation is critical for controlling many actinide processing schemes, ranging from medical applications to reprocessing of spent nuclear fuel. Unfortunately, in comparison to most elements in the periodic table, AnIII speciation is often poorly defined in complexing aqueous solutions and in organic media. This neglect – in large part – is a direct result of the radioactive properties of these elements, which make them difficult to handle and acquire. Herein, we surmounted some of the handling challenges associated with these exotic 5f-elements and characterized CmIII, AmIII, and AcIII using AnIII L3-edge X-ray absorption spectroscopy (XAS) as a function of increasing nitric acid (HNO3) concentration. Our results revealed that actinide aquo ions, An(H2O)x3+ (x = 9.6 ± 0.7, 8.9 ± 0.8, and 10.0 ± 0.9 for CmIII, AmIII, and AcIII), were the dominant species in dilute HNO3 (0.05 M). In concentrated HNO3 (16 M), shell-by-shell fitting of the extended X-ray fine structure (EXAFS) data showed the nitrate complexation increased, such that the average stoichiometries of Cm(NO3)4.1±0.7(H2O)5.7±1.3(1.1±0.2)–, Am(NO3)3.4±0.7(H2O)5.4±0.5(0.4±0.1)–, and Ac(NO3)2.3±1.7(H2O)8.3±5.2(0.7±0.5)+ were observed. Data obtained at the intermediate HNO3 concentration (4 M) were modeled as a linear combination of the 0.05 and 16 M spectra. For all three metals, the intermediate models showed larger contributions from the 0.05 M HNO3 spectra than from the 16 M HNO3 spectra. Additionally, these efforts enabled the Cm–NO3 and Ac–NO3 distances to be measured for the first time. Moreover, the AnIII L3-edge EXAFS results, contribute to the growing body of knowledge associated with CmIII, AmIII, and AcIII coordination chemistry, in particular toward advancing understanding of AnIII solution phase speciation.
- Published
- 2018
27. Separation of Protactinium Employing Sulfur-Based Extraction Chromatographic Resins
- Author
-
Lance E. Wyant, Eva R. Birnbaum, Michael E. Fassbender, Roy Copping, Stosh A. Kozimor, Mark Brugh, Allison Owens, T. Gannon Parker, Tara Mastren, Valery Radchenko, F. Meiring Nortier, Benjamin W. Stein, and Kevin D. John
- Subjects
Fission products ,Chromatography ,Molecular Structure ,010405 organic chemistry ,Surface Properties ,Extraction (chemistry) ,Protactinium ,Thorium ,chemistry.chemical_element ,Uranium ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,Radium ,Actinium ,Resins, Synthetic ,chemistry ,Yield (chemistry) ,Thymidine - Abstract
Protactinium-230 (t1/2 = 17.4 d) is the parent isotope of 230U (t1/2 = 20.8 d), a radionuclide of interest for targeted alpha therapy (TAT). Column chromatographic methods have been developed to separate no-carrier-added 230Pa from proton irradiated thorium targets and accompanying fission products. Results reported within demonstrate the use of novel sulfur bearing chromatographic extraction resins for the selective separation of protactinium. The recovery yield of 230Pa was 93 ± 4% employing a R3P═S type commercially available resin and 88 ± 4% employing a DGTA (diglycothioamide) containing custom synthesized extraction chromatographic resin. The radiochemical purity of the recovered 230Pa was measured via high purity germanium γ-ray spectroscopy to be >99.5% with the remaining radioactive contaminant being 95Nb due to its similar chemistry to protactinium. Measured equilibrium distribution coefficients for protactinium, thorium, uranium, niobium, radium, and actinium on both the R3P═S type and the DGTA...
- Published
- 2018
28. Electronic structure contributions to reactivity in xanthine oxidase family enzymes
- Author
-
Martin L. Kirk and Benjamin W. Stein
- Subjects
Models, Molecular ,Xanthine Oxidase ,Protein Conformation ,Stereochemistry ,chemistry.chemical_element ,Electrons ,Crystallography, X-Ray ,Xanthine ,Biochemistry ,Aldehyde ,Article ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Multienzyme Complexes ,Organic chemistry ,Reactivity (chemistry) ,Xanthine oxidase ,Molybdenum ,chemistry.chemical_classification ,biology ,Electron Spin Resonance Spectroscopy ,Active site ,Aldehyde Oxidoreductases ,chemistry ,Xanthine dehydrogenase ,biology.protein ,Oxidation-Reduction ,Carbon monoxide dehydrogenase - Abstract
We review the xanthine oxidase (XO) family of pyranopterin molybdenum enzymes with a specific emphasis on electronic structure contributions to reactivity. In addition to xanthine and aldehyde oxidoreductases, which catalyze the two-electron oxidation of aromatic heterocycles and aldehyde substrates, this mini-review highlights recent work on the closely related carbon monoxide dehydrogenase (CODH) that catalyzes the oxidation of CO using a unique Mo-Cu heterobimetallic active site. A primary focus of this mini-review relates to how spectroscopy and computational methods have been used to develop an understanding of critical relationships between geometric structure, electronic structure, and catalytic function.
- Published
- 2014
29. Evaluating the electronic structure of formal Ln
- Author
-
Megan E, Fieser, Maryline G, Ferrier, Jing, Su, Enrique, Batista, Samantha K, Cary, Jonathan W, Engle, William J, Evans, Juan S, Lezama Pacheco, Stosh A, Kozimor, Angela C, Olson, Austin J, Ryan, Benjamin W, Stein, Gregory L, Wagner, David H, Woen, Tonya, Vitova, and Ping, Yang
- Subjects
Chemistry - Abstract
LnII(C5H4SiMe3)1– have been characterized by XANES and DFT., The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)3 1– (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)3 1– (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)3 1– (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4fn 5d1 configurations (not 4fn+1 5d0). In these 4fn 5d1 complexes, the C 3h-symmetric ligand environment provides a highly shielded 5d-orbital of a′ symmetry that made the 4fn 5d1 electronic configurations lower in energy than the more typical 4fn+1 5d0 configuration.
- Published
- 2017
30. EPR, ENDOR, and Electronic Structure Studies of the Jahn–Teller Distortion in an FeV Nitride
- Author
-
Jeremy M. Smith, Brian M. Hoffman, Martin L. Kirk, Benjamin W. Stein, Deepak Subedi, and George E. Cutsail
- Subjects
Models, Molecular ,Jahn–Teller effect ,Electrons ,Electronic structure ,Nitride ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Molecular physics ,Catalysis ,Article ,law.invention ,Coordination complex ,Colloid and Surface Chemistry ,law ,Distortion ,Molecular symmetry ,Electron paramagnetic resonance ,chemistry.chemical_classification ,Condensed matter physics ,Molecular Structure ,010405 organic chemistry ,Chemistry ,Electron Spin Resonance Spectroscopy ,General Chemistry ,3. Good health ,0104 chemical sciences ,Ground state ,Iron Compounds - Abstract
The recently synthesized and isolated low-coordinate Fe(V) nitride complex has numerous implications as a model for high-oxidation states in biological and industrial systems. The trigonal [PhB((t)BuIm)3Fe(V)≡N](+) (where (PhB((t)BuIm)3(-) = phenyltris(3-tert-butylimidazol-2-ylidene)), (1) low-spin d(3) (S = 1/2) coordination compound is subject to a Jahn-Teller (JT) distortion of its doubly degenerate (2)E ground state. The electronic structure of this complex is analyzed by a combination of extended versions of the formal two-orbital pseudo Jahn-Teller (PJT) treatment and of quantum chemical computations of the PJT effect. The formal treatment is extended to incorporate mixing of the two e orbital doublets (30%) that results from a lowering of the idealized molecular symmetry from D3h to C3v through strong "doming" of the Fe-C3 core. Correspondingly we introduce novel DFT/CASSCF computational methods in the computation of electronic structure, which reveal a quadratic JT distortion and significant e-e mixing, thus reaching a new level of synergism between computational and formal treatments. Hyperfine and quadrupole tensors are obtained by pulsed 35 GHz ENDOR measurements for the (14/15)N-nitride and the (11)B axial ligands, and spectra are obtained from the imidazole-2-ylidene (13)C atoms that are not bound to Fe. Analysis of the nitride ENDOR tensors surprisingly reveals an essentially spherical nitride trianion bound to Fe, with negative spin density and minimal charge density anisotropy. The four-coordinate (11)B, as expected, exhibits negligible bonding to Fe. A detailed analysis of the frontier orbitals provided by the electronic structure calculations provides insight into the reactivity of 1: JT-induced symmetry lowering provides an orbital selection mechanism for proton or H atom transfer reactivity.
- Published
- 2014
31. Coordination Chemistry of +3 Actinium
- Author
-
Kevin D. John, Benjamin W. Stein, Amanda Morgenstern, Laura M. Lilley, Veronika Mocko, Enrique R. Batista, Stosh A. Kozimor, and Eva R. Birnbaum
- Subjects
chemistry.chemical_classification ,Actinium ,Radiological and Ultrasound Technology ,chemistry ,Computational chemistry ,chemistry.chemical_element ,Radiology, Nuclear Medicine and imaging ,Coordination complex - Published
- 2019
32. Comparing the 2,2'-Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium
- Author
-
Joseph A. Macor, Justin N. Cross, David K. Shuh, Gregory S. Girolami, Benjamin W. Stein, Jeffery A. Bertke, Joel R. Maassen, S. Chantal E. Stieber, Maryline G. Ferrier, Brian L. Scott, and Stosh A. Kozimor
- Subjects
Lanthanide ,Ionic radius ,010405 organic chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Americium ,General Chemistry ,Actinide ,010402 general chemistry ,01 natural sciences ,Neodymium ,Catalysis ,0104 chemical sciences ,Bond length ,Crystallography ,chemistry ,X-ray crystallography ,Europium - Abstract
Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4 )Am[S2 P((t) Bu2 C12 H6 )]4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., Nd(III) ) and an isoelectronic one (Eu(III) ). The results include the first measurement of an Am-S bond length, with a mean value of 2.921(9) A, by single-crystal X-ray diffraction. Comparison with the Eu(III) and Nd(III) complexes revealed subtle electronic differences between the complexes of Am(III) and the lanthanides.
- Published
- 2016
33. Spectroscopic and computational investigation of actinium coordination chemistry
- Author
-
Henry S. La Pierre, Eva R. Birnbaum, Justin N. Cross, Enrique R. Batista, S. Chantal E. Stieber, Juan S. Lezama Pacheco, Justin J. Wilson, Maryline G. Ferrier, Jonathan W. Engle, Stosh A. Kozimor, John M. Berg, and Benjamin W. Stein
- Subjects
Lanthanide ,Actinium ,Models, Molecular ,Absorption spectroscopy ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Coordination complex ,Reactivity (chemistry) ,chemistry.chemical_classification ,Radioisotopes ,X-ray absorption spectroscopy ,Multidisciplinary ,Fourier Analysis ,010405 organic chemistry ,General Chemistry ,Actinide ,3. Good health ,0104 chemical sciences ,Solutions ,X-Ray Absorption Spectroscopy ,chemistry ,Physical chemistry ,Density functional theory - Abstract
Actinium-225 is a promising isotope for targeted-α therapy. Unfortunately, progress in developing chelators for medicinal applications has been hindered by a limited understanding of actinium chemistry. This knowledge gap is primarily associated with handling actinium, as it is highly radioactive and in short supply. Hence, AcIII reactivity is often inferred from the lanthanides and minor actinides (that is, Am, Cm), with limited success. Here we overcome these challenges and characterize actinium in HCl solutions using X-ray absorption spectroscopy and molecular dynamics density functional theory. The Ac–Cl and Ac − O H 2 O distances are measured to be 2.95(3) and 2.59(3) Å, respectively. The X-ray absorption spectroscopy comparisons between AcIII and AmIII in HCl solutions indicate AcIII coordinates more inner-sphere Cl1– ligands (3.2±1.1) than AmIII (0.8±0.3). These results imply diverse reactivity for the +3 actinides and highlight the unexpected and unique AcIII chemical behaviour.
- Published
- 2016
34. Spectroscopic and Electronic Structure Studies Probing Covalency Contributions to C–H Bond Activation and Transition-State Stabilization in Xanthine Oxidase
- Author
-
Martin L. Kirk, Joseph Sempombe, and Benjamin W. Stein
- Subjects
Models, Molecular ,Xanthine Oxidase ,Static Electricity ,Chemistry, Organic ,Electronic structure ,Cleavage (embryo) ,Photochemistry ,Aldehyde ,Article ,law.invention ,Reaction coordinate ,Inorganic Chemistry ,Paramagnetism ,law ,Animals ,Prodrugs ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Hyperfine structure ,Biotransformation ,Molybdenum ,chemistry.chemical_classification ,Aldehydes ,Molecular Structure ,Spectrum Analysis ,Electron Spin Resonance Spectroscopy ,Carbon ,Oxygen ,Solutions ,Crystallography ,chemistry ,Thermodynamics ,Cattle ,Oxidation-Reduction ,Hydrogen ,Natural bond orbital - Abstract
A detailed electron paramagnetic resonance (EPR) and computational study of a key paramagnetic form of xanthine oxidase (XO) has been performed and serves as a basis for developing a valence-bond description of C-H activation and transition-state (TS) stabilization along the reaction coordinate with aldehyde substrates. EPR spectra of aldehyde-inhibited XO have been analyzed in order to provide information regarding the relationship between the g, (95,97)Mo hyperfine (A(Mo)), and (13)C hyperfine (A(C)) tensors. Analysis of the EPR spectra has allowed for greater insight into the electronic origin of key delocalizations within the Mo-O(eq)-C fragment and how these contribute to C-H bond activation/cleavage and TS stabilization. A natural bond orbital analysis of the enzyme reaction coordinate with aldehyde substrates shows that both Mo═S π → C-H σ* (ΔE = 24.3 kcal mol(-1)) and C-H σ → Mo═S π* (ΔE = 20.0 kcal mol(-1)) back-donation are important in activating the substrate C-H bond for cleavage. Additional contributions to C-H activation derive from O(eq) lp → C-H σ* (lp = lone pair; ΔE = 8.2 kcal mol(-1)) and S lp → C-H σ* (ΔE = 13.2 kcal mol(-1)) stabilizing interactions. The O(eq)-donor ligand that derives from water is part of the Mo-O(eq)-C fragment probed in the EPR spectra of inhibited XO, and the observation of O(eq) lp → C-H σ* back-donation indicates a key role for O(eq) in activating the substrate C-H bond for cleavage. We also show that the O(eq) donor plays an even more important role in TS stabilization. We find that O(eq) → Mo + C charge transfer dominantly contributes to stabilization of the TS (ΔE = 89.5 kcal mol(-1)) and the Mo-O(eq)-C delocalization pathway reduces strong electronic repulsions that contribute to the classical TS energy barrier. The Mo-O(eq)-C delocalization at the TS allows for the TS to be described in valence-bond terms as a resonance hybrid of the reactant (R) and product (P) valence-bond wave functions.
- Published
- 2011
35. Orbital contributions to CO oxidation in Mo–Cu carbon monoxide dehydrogenase
- Author
-
Benjamin W. Stein and Martin L. Kirk
- Subjects
Inorganic chemistry ,Molecular Conformation ,chemistry.chemical_element ,Electronic structure ,Crystallography, X-Ray ,Article ,Catalysis ,Comamonadaceae ,chemistry.chemical_compound ,Multienzyme Complexes ,Catalytic Domain ,Materials Chemistry ,Molecular orbital ,Reactivity (chemistry) ,Molybdenum ,Carbon Monoxide ,biology ,Metals and Alloys ,General Chemistry ,Aldehyde Oxidoreductases ,Copper ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Biocatalysis ,Ceramics and Composites ,biology.protein ,Quantum Theory ,Thermodynamics ,Physical chemistry ,Oxidation-Reduction ,Carbon monoxide ,Carbon monoxide dehydrogenase - Abstract
A molecular orbital analysis provides new insight into the mechanism of Mo/Cu carbon monoxide dehydrogenase, and reveals electronic structure contributions to reactivity that are remarkably similar to the structurally related molybdenum hydroxylases. A calculated reaction barrier of ~12 kcal mol(-1) is in excellent agreement with experiment.
- Published
- 2014
36. Pyranopterin conformation defines the function of molybdenum and tungsten enzymes
- Author
-
Richard A. Rothery, Matthew Solomonson, Joel H. Weiner, Martin L. Kirk, and Benjamin W. Stein
- Subjects
Iron-Sulfur Proteins ,Models, Molecular ,Protein Folding ,Stereochemistry ,Xanthine Dehydrogenase ,chemistry.chemical_element ,Redox ,Cofactor ,Tungsten ,chemistry.chemical_compound ,Protein structure ,Sulfite oxidase ,polycyclic compounds ,Organic chemistry ,heterocyclic compounds ,chemistry.chemical_classification ,Molybdenum ,Multidisciplinary ,Crystallography ,biology ,Molecular Structure ,Chemistry ,Sulfite Oxidase ,Enzymes ,Pterins ,Enzyme ,Xanthine dehydrogenase ,Physical Sciences ,biology.protein ,Protein folding ,Oxidoreductases ,Oxidation-Reduction - Abstract
We have analyzed the conformations of 319 pyranopterins in 102 protein structures of mononuclear molybdenum and tungsten enzymes. These span a continuum between geometries anticipated for quinonoid dihydro, tetrahydro, and dihydro oxidation states. We demonstrate that pyranopterin conformation is correlated with the protein folds defining the three major mononuclear molybdenum and tungsten enzyme families, and that binding-site micro-tuning controls pyranopterin oxidation state. Enzymes belonging to the bacterial dimethyl sulfoxide reductase (DMSOR) family contain a metal-bis-pyranopterin cofactor, the two pyranopterins of which have distinct conformations, with one similar to the predicted tetrahydro form, and the other similar to the predicted dihydro form. Enzymes containing a single pyranopterin belong to either the xanthine dehydrogenase (XDH) or sulfite oxidase (SUOX) families, and these have pyranopterin conformations similar to those predicted for tetrahydro and dihydro forms, respectively. This work provides keen insight into the roles of pyranopterin conformation and oxidation state in catalysis, redox potential modulation of the metal site, and catalytic function.
- Published
- 2012
37. A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum-bis(dithione)
- Author
-
Regina P. Mtei, Partha Basu, Eranda Perera, Benjamin Mogesa, Martin L. Kirk, and Benjamin W. Stein
- Subjects
Chemistry ,Stereochemistry ,Ligand ,chemistry.chemical_element ,Electronic structure ,Ring (chemistry) ,Resonance (chemistry) ,Article ,Inorganic Chemistry ,Crystallography ,Piperazine ,chemistry.chemical_compound ,symbols.namesake ,Molybdenum ,symbols ,Valence bond theory ,Raman spectroscopy - Abstract
Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo(4+)O(i-Pr2Pipdt)2Cl][PF6] (where i-Pr2Pipdt is N,N'-piperazine-2,3-dithione), that possesses a piperazine ring as an integral part of the dithiolene ligand. The title complex displays unusual spectroscopic features for a formally reduced Mo(IV) dithiolene complex, namely a low energy metal-to-ligand charge transfer band with appreciable intensity and C-C and C-S stretching frequencies that are markedly different from those of oxomolydenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene contributing structures.
- Published
- 2011
38. Spectroscopic and electronic structure studies of a dimethyl sulfoxide reductase catalytic intermediate: implications for electron- and atom-transfer reactivity
- Author
-
Nick D. Rubie, Russ Hille, Benjamin W. Stein, Ganna Lyashenko, Regina P. Mtei, and Martin L. Kirk
- Subjects
Iron-Sulfur Proteins ,Molecular Structure ,Chemistry ,Spectrum Analysis ,Electrons ,General Chemistry ,Electronic structure ,Electron ,Photochemistry ,Biochemistry ,Catalysis ,Article ,Paramagnetism ,Colloid and Surface Chemistry ,Biocatalysis ,Atom ,Molecule ,Reactivity (chemistry) ,Oxidoreductases - Abstract
The electronic structure of a genuine paramagnetic des-oxo Mo(V) catalytic intermediate in the reaction of dimethyl sulfoxide reductase (DMSOR) with (CH(3))(3)NO has been probed by electron paramagnetic resonance (EPR), electronic absorption, and magnetic circular dichroism (MCD) spectroscopies. EPR spectroscopy reveals rhombic g- and A-tensors that indicate a low-symmetry geometry for this intermediate and a singly occupied molecular orbital that is dominantly metal centered. The excited-state spectroscopic data were interpreted in the context of electronic structure calculations, and this has resulted in a full assignment of the observed MCD and electronic absorption bands, a detailed understanding of the metal-ligand bonding scheme, and an evaluation of the Mo(V) coordination geometry and Mo(V)-S(dithiolene) covalency as it pertains to the stability of the intermediate and electron-transfer regeneration. Finally, the relationship between des-oxo Mo(V) and des-oxo Mo(IV) geometric and electronic structures is discussed relative to the reaction coordinate in members of the DMSOR enzyme family.
- Published
- 2011
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