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Hay, Benjamin P.

Publications and source records attributed to Hay, Benjamin P..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores

Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. Finally, this is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.

58 GEOSCIENCES↗
DOE OSTI2018

Pyrrole- and Naphthobipyrrole-Strapped Calix[4]pyrroles as Azide Anion Receptors

Here, the binding interactions between the azide anion (N 3 – ) and the strapped calix[4]pyrroles 2 and 3 bearing auxiliary hydrogen bonding donors on the bridging moieties, as well as of normal calix[4]pyrrole 1, were investigated via 1 H NMR spectroscopic and isothermal titration calorimetry analyses. The resulting data revealed that receptors 2 and 3 have significantly higher affinities for the azide anion in organic media as compared with the unfunctionalized calix[4]pyrrole 1 and other azide receptors reported to date. Single crystal X-ray diffraction analyses and calculations using density functional theory revealed that receptor 2 binds CsN 3 in two distinct structural forms. As judged from the metric parameters, in the resulting complexes one limiting azide anion resonance contributor is favored over the other, with the specifics depending on the binding mode. In contrast to what is seen for 2, receptor 3 forms a CsN 3 complex in 20% CD 3 OD in CDCl 3 , wherein the azide anion is bound only vertically to the NH protons of the calix[4]pyrrole and the cesium cation is complexed within the cone shaped-calix[4]pyrrole bowl. The bound cesium cation is also in close proximity to a naphthobipyrrole subunit present in a different molecule, forming an apparent cation-π complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Computer-Aided Molecular Design of Bis-phosphine Oxide Lanthanide Extractants

Computer-aided molecular design and high-throughput screening of viable host architectures can significantly reduce the efforts in the design of novel ligands for efficient extraction of rare earth elements. This paper presents a computational approach to the deliberate design of bis-phosphine oxide host architectures that are structurally organized for complexation of trivalent lanthanides. Molecule building software, HostDesigner, was interfaced with molecular mechanics software, PCModel, providing a tool for generating and screening millions of potential R 2 (O)P-link-P(O)R 2 ligand geometries. The molecular mechanics ranking of ligand structures is consistent with both the solution-phase free energies of complexation obtained with density functional theory and the performance of known bis-phosphine oxide extractants. For the case where link is -CH 2 -, evaluation of the ligand geometry provides the first characterization of a steric origin for the ‘anomalous aryl strengthening’ effect. The design approach has identified a number of novel bis-phosphine oxide ligands that are better organized for lanthanide complexation than previously studied examples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis of Naphthalimidedioxime Ligand-Containing Fibers for Uranium Adsorption from Seawater

Uranium exists as uranyl carbonates (primarily as [UO2(CO3)3]4-) at a low concentration of 3.3 ppb, in seawater. Due to the ocean's vast volume, the total amount of uranium in seawater has been estimated at 4.5 billion tons or nearly 1000 times more than land-based resources. This large surplus provides attractive solution to supply nuclear fuel feeds in future. However, the presence of a variety of competing metal ions and the low concentration of uranium in seawater make the extraction of uranium from seawater challenging. The goal of this work is to develop adsorbent fibers that can recover uranium from the slightly alkaline (pH 8.0 - 8.3) seawater. In this process, radiation-induced graft polymerization (RIGP) is used where fibers are prepared by irradiating and treating polyethylene (PE) with different bulk ratios of vinyl benzyl chloride (VBC) and methacrylic acid (MAA) or itaconic acid. Furthermore, chemical modifications of these fibers were performed via two step processes, where novel bisimidoxime ligands are incorporated into fibers. These ligands contain imidedioxime, which is known to be a uranium-philic functionality. Also, the core structures of these ligands containing three donor atoms facilitate the formation of chelates with uranyl ion in seawater. Density functional theory (DFT) calculations were performed to quantify the binding strength with the uranyl ion. The adsorbent showed moderate to high uranium (~35-50 g-U/kg adsorbent) adsorption capacity in a model seawater with a uranium concentration of 6 ppm at pH 8.0 8.3.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Conformations of organophosphine oxides

The conformations of a series of organophosphine oxides, OP(CH 3 ) 2 R, where R = methyl, ethyl, isopropyl, tert-butyl, vinyl, and phenyl, are predicted using the MP2/cc-pVTZ level of theory. Comparison of potential energy surfaces for rotation about P–C bonds with crystal structure data reveals a strong correlation between predicted location and energetics of minima and histograms of dihedral angle distributions observed in the solid state. In addition, the most stable conformers are those that minimize the extent of steric repulsion between adjacent rotor substituents, and the torsional barriers tend to increase with the steric bulk of the rotating alkyl group. MM3 force field parameters were adjusted to fit the MP2 results, providing a fast and accurate model for predicting organophosphine oxides shapes—an essential part of understanding the chemistry of these compounds. As a result, the predictive power of the modified MM3 model was tested against MP2/cc-pVTZ conformations for triethylphosphine oxide, OP(CH 2 CH 3 ) 3 , and triphenylphosphine oxide, OP(Ph) 3 .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Synthesis, selected coordination chemistry and extraction behavior of a (phosphinoylmethyl)pyridyl N-oxide-functionalized ligand based upon a 1,4-diazepane platform

For syntheses of new multidentate chelating ligands ((6,6'4(1,4-diazepane-1,4-diyl)bis(methylene))bis(pyridine-6,2-diyl))bis(methylene))bis(diphenylphosphine oxide) (2) and 6,6'-((1,4-diazepane1,4-diyl)bis(methylene))bis(2-((diphenylphosphoryl)methyl)pyridine 1-oxide) (3), based upon a 1,4-diazepane platform functionalized with 2-(diphenylphosphinoylmethyl)pyridine P-oxide and 2-(diphenylphosphinoylmethyl)pyridine NP-dioxide fragments, respectively, the results are reported. Our results from studies of the coordination chemistry of the ligands with selected lanthanide nitrates and Cu(BF 4 )(2) are outlined, and crystal structures for two complexes, [Cu(2)](BF 4 ) 2 and [Cu(3)](BF 4 ) 2 , are described along with survey Eu(III) and Am(III) solvent extraction analysis, for 3.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Predicting Stability Constants for Uranyl Complexes Using Density Functional Theory

The ability to predict the equilibrium constants for the formation of 1:1 uranyl:ligand complexes (log K 1 values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We also use density functional theory (B3LYP) and the IEFPCM continuum solvation model to compute aqueous stability constants for UO 2 2+ complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K 1 values are significantly overestimated. Accurate predictions of the absolute log K 1 values (root mean square deviation from experiment < 1.0 for log K 1 values ranging from 0 to 16.8) can be obtained by fitting the experimental data for two groups of mono and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelate capability to uranyl.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Theoretical Prediction of Am(III)/Eu(III) Selectivity to Aid the Design of Actinide-Lanthanide Separation Agents

Selective extraction of minor actinides from lanthanides is a critical step in the reduction of radiotoxicity of spent nuclear fuels. However, the design of suitable ligands for separating chemically similar 4f- and 5f-block trivalent metal ions poses a significant challenge. Furthermore, first-principles calculations should play an important role in the design of new separation agents, but their ability to predict metal ion selectivity has not been systematically evaluated. We examine the ability of several density functional theory methods to predict selectivity of Am(III) and Eu(III) with oxygen, mixed oxygen–nitrogen, and sulfur donor ligands. The results establish a computational method capable of predicting the correct order of selectivities obtained from liquid–liquid extraction and aqueous phase complexation studies. To allow reasonably accurate predictions, it was critical to employ sufficiently flexible basis sets and provide proper account of solvation effects. The approach is utilized to estimate the selectivity of novel amide-functionalized diazine and 1,2,3-triazole ligands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗