5 results on '"Benjamin W. Stein"'
Search Results
2. Synthesis and Characterization of the Actinium Aquo Ion
- Author
-
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. Large-Scale Production of 119mTe and 119Sb for Radiopharmaceutical Applications
- Author
-
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
4. 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
5. 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
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