Anil Boda

DFT modeling on the suitable crown ether architecture for complexation with Cs+ and Sr2+ metal ions

Crown ether architectures were explored for the inclusion of Cs+ and Sr2+ ions within nano-cavity of macrocyclic crown ethers using density functional theory (DFT) modeling. The modeling was undertaken to gain insight into the mechanism of the complexation of Cs+ and Sr2+ ion with this ligand experimentally. The selectivity of Cs+ and Sr2+ ions for a particular size of crown ether has been explained based on the fitting and binding interaction of the guest ions in the narrow cavity of crown ethers. Although, Di-Benzo-18-Crown-6 (DB18C6) and Di-Benzo-21-Crown-7 (DB21C7) provide suitable host architecture for Sr2+ and Cs+ ions respectively as the ion size match with the cavity of the host, but consideration of binding interaction along with the cavity matching both DB18C6 and DB21C7 prefers Sr2+ ion. The calculated values of binding enthalpy of Cs metal ion with the crown ethers were found to be in good agreement with the experimental results. The gas phase binding enthalpy for Sr2+ ion with crown ether was higher than Cs metal ion. The ion exchange reaction between Sr and Cs always favors the selection of Sr metal ion both in the gas and in micro-solvated systems. The gas phase selectivity remains unchanged in micro-solvated phase. We have demonstrated the effect of micro-solvation on the binding interaction between the metal ions (Cs+ and Sr2+) and the macrocyclic crown ethers by considering micro-solvated metal ions up to eight water molecules directly attached to the metal ion and also by considering two water molecules attached to metal-ion-crown ether complexes. A metal ion exchange reaction involving the replacement of strontium ion in metal ion-crown ether complexes with cesium ion contained within a metal ion-water cluster serves as the basis for modeling binding preferences in solution. The calculated O-H stretching frequency of H2O molecule in micro-solvated metal ion-crown complexes is more red-shifted in comparison to hydrated metal ions. The calculated IR spectra can be compared with an experimental spectrum to determine the presence of micro-solvated metal ion–crown ether complexes in extractant phase.

Ab initio and density functional theoretical design and screening of model crown ether based ligand (host) for extraction of lithium metal ion (guest): effect of donor and electronic induction

AbstractThe structures, energetic and thermodynamic parameters of model crown ethers with different donor, cavity and electron donating/ withdrawing functional group have been determined with ab initio MP2 and density functional theory in gas and solvent phase. The calculated values of binding energy/ enthalpy for lithium ion complexation are marginally higher for hard donor based aza and oxa crown compared to soft donor based thia and phospha crown. The calculated values of binding enthalpy for lithium metal ion with 12C4 at MP2 level of theory is in good agreement with the available experimental result. The binding energy is altered due to the inductive effect imparted by the electron donating/ withdrawing group in crown ether, which is well correlated with the values of electron transfer. The role of entropy for extraction of hydrated lithium metal ion by different donor and functional group based ligand has been demonstrated. The HOMO-LUMO gap is decreased and dipole moment of the ligand is increased from gas phase to organic phase because of the dielectric constant of the solvent. The gas phase binding energy is reduced in solvent phase as the solvent molecules weaken the metal-ligand binding. The theoretical values of extraction energy for LiCl salt from aqueous solution in different organic solvent is validated by the experimental trend. The study presented here should contribute to the design of model host ligand and screening of solvent for metal ion recognition and thus can contribute in planning the experiments. FigureAb initio modeling for extraction of Li ion from aqueous medium to nitrobenzene by B12C4-CH3 crown ether

Oxidation state selective sorption behavior of plutonium using N,N-dialkylamide functionalized carbon nanotubes: experimental study and DFT calculation

Selective phase separation of Pu4+ and PuO22+ was performed using N,N-dialkylamide functionalized multi-walled carbon nanotubes (AFMWCNTs). To understand the sorption kinetics, three widely accepted kinetic models (Lagergren first order kinetics, intra particle diffusion model and pseudo second order kinetics) were investigated. The sorption kinetics followed a pseudo second order kinetics with rate constants of 2.50 × 10−5 g mg−1 min−1 and 4.30 × 10−5 g mg−1 min−1 for Pu4+ and PuO22+ respectively. The analysis of the sorption mechanism through Langmuir, Freundlich, Dubinin–Rodushkevich (D–R) and Temkin isotherms revealed that the sorption proceeds via heterogeneous, non-ideal multi-layer adsorption following the Freundlich isotherm. The radiolytic stability of the AFMWCNTs and the stripping behavior of plutonium from the loaded AFMWCNTs were also investigated and finally AFMWCNTs were employed for the processing of simulated high level waste solutions originating from Research Reactors (RRs) and Fast Breeder Reactors (FBRs). Density functional theory calculation was used to understand the higher selectivity of tetra valent plutonium over hexa valent plutonium. The structural parameters of the AFMWCNT and its complexes of Pu4+ and PuO22+ were optimized along with the evaluation of their binding energy in the gas phase as well as solution phase. Orbital bonding analysis was carried out to rationalize the selectivity of Pu4+ions over PuO22+ with AFMWCNTs.

An amide functionalized task specific carbon nanotube for the sorption of tetra and hexa valent actinides: experimental and theoretical insight

An amide functionalized multiwalled carbon nanotube (CNT-DHA) was used for efficient and selective solid phase separation of tetravalent (Th4+) and hexavalent (UO22+) actinides. Langmuir, Freundlich, Dubinin–Rodushkevich (D–R) and Tempkin isotherms were employed for understanding the sorption mechanism while various models (Lagergren first order kinetics, intra particle diffusion model and pseudo second order kinetics) were applied to understand the sorption kinetics. The sorption proceeded via monolayer coverage of CNT-DHA with capacities of 32 mg g−1 and 47 mg g−1 for UO22+ and Th4+, respectively following a Langmuir isotherm while the sorption kinetics followed a pseudo second order reaction with rate constants of 0.044 and 0.095 g mg−1 min−1 for UO22+ and Th4+, respectively. The CNT-DHA was found to have high radiolytic stability up to 1000 kGy gamma exposure. The stripping study revealed that oxalic acid can be used for almost quantitative back extraction of Th4+ and for UO22+ sodium carbonate can be effectively used. DFT calculations were performed to understand the complexation of Th4+ and UO22+ with CNT-DHA. The structural parameters of UO22+ and Th4+ ions with CNT-DHA, and the large ion–ligand interaction energy were correlated with the higher selectivity of Th4+ ions over UO22+ ions.

Dual mode of extraction for Cs+ and Na+ ions with dicyclohexano-18-crown-6 and bis(2-propyloxy)calix[4]crown-6 in ionic liquids: density functional theoretical investigation

The unusually high selectivity of the Cs+ ion over the Na+ ion with bis(2-propyloxy)calix[4]crown-6 (BPC6) compared to dicyclohexano-18-crown-6 (DCH18C6) has been investigated using generalized gradient approximated (GGA) BP86, hybrid B3LYP and meta hybrid TPSSH density functionals, employing split valence plus polarization (SVP) and triple zeta valence plus polarization (TZVP) basis sets in conjunction with the COSMO (conductor like screening model) solvation approach. The calculated theoretical selectivity of the Cs+ ion over the Na+ ion was found to be in accordance with the experimental selectivity obtained using solvent extraction experiments in ionic liquids (IL) and octanol. The distribution constant of the Cs+ ion, DCs with DCH18C6 in the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTF2N) IL phase was found to be significantly large than that in octanol. The experimentally measured DCs value was found to be very large compared to the value of DNa in the IL phase. The presence of the BMIM cation in the recorded UV-visible spectra of the raffinate phase with and without DCH18C6 indicates the BMIM cation exchange with Cs+ and Na+ ions, thus supporting the dual mode of extraction. The dual mode of metal ion extraction observed in the experimental study was complemented by density functional theoretical study. The calculated free energy of extraction, ΔGext, for the metal ion was found to be higher in IL compared to octanol. Further, preferential selectivity of the Cs+ ion over the Na+ ion was established from the free energy difference, ΔΔGext, between the two competing metal ions. The unusually high selectivity of Cs+ over the Na+ ion by BPC6 in IL compared to DCH18C6 is also demonstrated by the free energy difference, ΔΔΔGext, between the two competing ligands which was shown to be free from the complicated metal ion solvation energy.

Density functional theoretical analysis of structure, bonding, interaction and thermodynamic selectivity of hexavalent uranium (UO22+) and tetravalent plutonium (Pu4+) ion complexes of tetramethyl diglycolamide (TMDGA)

Abstract In the well-known PUREX process, tertiary butyl phosphate shows preferential extraction of UO22+ over Pu4+, whereas tetraoctyl diglycolamide (TODGA) displays the reverse selectivity. The reversal of selectivity toward diglycolamide has been investigated here theoretically by considering shorter analogue of TODGA, tetramethyl diglycolamide (TMDGA). Structure, bonding, energetic parameter and thermodynamic parameters of UO22+ and Pu4+ ions with TMDGA in the gas and solvent phase have been reported in order to understand their complexation and extraction behavior. The calculation has been performed with generalized gradient approximated BP86 density functional and hybrid B3LYP functional employing SVP and TZVP basis set. The calculated structure obtained at BP86/SVP level of optimization is found to be in close agreement with the reported experimental data. The free energy of extraction, ΔGext, of UO22+ and Pu4+ ions from aqueous phase to the dodecane phase has been computed using the Born-Haber thermodynamic cycle in conjunction with COSMO (conductor like screening model) solvation approach. The free energy of extraction is predicted to be exergonic for explicit monomer water model. The free energy of extraction for Pu4+ ion is shown to be higher than that of UO22+ as observed in the reported solvent extraction experiment. Further, the suitability of non-polar solvents as organic diluents has been confirmed by the decreased free energy of extraction with increasing dielectric constant of the solvents. Natural population and orbital analysis indicate the electrostatic and small covalent nature of interactions between the metal ions and the tridentate TMDGA chelating ligand. The results presented here might be helpful in designing new ligands for efficient extraction of actinides.

Density functional theoretical study on the preferential selectivity of macrocyclic dicyclohexano-18-crown-6 for Sr+2 ion over Th+4 ion during extraction from an aqueous phase to organic phases with different dielectric constants

AbstractThe preferential selectivity of dicyclohexano-18-crown-6 (DCH18C6) for bivalent Sr+2 ion over tetravalent Th+4 ion was investigated using generalized gradient approximated (GGA) BP86 and the hybrid B3LYP density functional, employing split valence plus polarization (SV(P)) and triple-zeta valence plus polarization (TZVP) basis sets in conjunction with the COSMO (conductor-like screening model) solvation approach. The calculated theoretical selectivity of DCH18C6 for Sr+2 ion over Th+4 ion was found to be in accord with the selectivity for Sr+2 ion over Th+4 ion observed when performing liquid–liquid extraction experiments in different organic solvents. While 1:1(M:L) stoichiometric complexation reactions can be used to predict the preferential selectivity of Sr2+ ion over Th4+ ion, the results obtained are not consistent with the experimental results observed upon increasing the dielectric constant of the solvent. The calculated theoretical gas-phase data for the free energy of complexation, ∆G, fail to explain the selectivity for Sr+2 ion over Th+4 ion. However, when 1:2 (M:L) stoichiometric complexation reactions (reported in previous X-ray crystallography studies) are considered, correct and consistent results for the selectivity for Sr+2 ion over a wide range of dielectric constants are predicted. The distribution constant for Sr2+ and Th4+ ions was found to gradually increase with increasing dielectric constant of the organic solvent, and was found to be highest in nitrobenzene. The selectivity data calculated from ∆∆Gext are in excellent agreement with the results obtained from solvent extraction experiments. FigureExperimentally observed separation factors and theoretically predicted values of ΔΔGext for Sr2+ ion over Th4+ ion with DCH18C6 in a nitrate medium. Solvent extraction with DCH18C6/nitrobenzene shows high selectivity and a high separation factor for Sr2+ over Th4+. DFT was successfully adopted to model the extraction mechanism of Sr2+/Th4+. The free energy of extraction ΔΔGext failed to predict the experimental selectivity of Sr2+ over Th4+ for 1:1 stoichiometric complexation, but was able to predict this selectivity for 1:2 stoichiometric complexation with Th4+ ion. The ΔΔGext values for the preferential selection of Sr2+ over Th4+ increase with increasing dielectric constant of the solvent

Ionic liquid as a novel partitioning media

ABSTRACT The partition coefficients of large number of organic solute including macrocyclic crown ethers in different water-ionic liquid (IL) bi-phasic systems based on Hartree-Fock (HF) and density functional theory (DFT) are presented here. The structure of imidazolium cation based ILs were optimized at HF-6-311G (d,p) level of theory and then surface charge density were calculated at BP-TZVP level of theory using novel conductor like screening model for real solvents (COSMORS) approach. The calculated value of density is decreased with increasing alkyl chain length for all the ILs considered here. The calculated values of partition coefficient for various organic solutes obtained from the first principle based COSMO-RS theory are reasonably in good agreement with the available experimental results. The predicted values of partition coefficient will help in the screening and thus selection and design of suitable ILs prior to solvent extraction experiments.

Molecular modeling guided isotope separation of gadolinium with strong cation exchange resin using displacement chromatography

ABSTRACT Molecular modeling was carried out using DFT to identify the suitable displacing agent for carrying out Gd isotope separation using displacement chromatography. EDTA was identified as the best eluting agent among EDTA, malic acid and citric acid. Displacement chromatography of Gd adsorption band in cation exchange resin was performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagent – EDTA. The heavier isotope of 160Gd was found to be enriched at the front boundary of Gd adsorption band, while the lighter isotopes of 155Gd and 157Gd were enriched at the rear boundary.

Structural, luminescence, thermodynamic and theoretical studies on mononuclear complexes of Eu(III) with pyridine monocarboxylate-N-oxides in aqueous solution

The mononuclear complexes formed by Eu(III) with three isomeric pyridine monocarboxylate-N-oxides namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO) in aqueous solutions were studied by potentiometry, luminescence spectroscopy and isothermal titration calorimetry (ITC) to determine the speciation, coordination, luminescence properties and thermodynamic parameters of the complexes formed during the course of the reaction. More stable six membered chelate complexes with stoichiometry (MLi, i=1-4) are formed by Eu(III) with PANO while non chelating ML and ML2 complexes are formed by NANO and IANO. The stability of Eu(III) complexes follow the order PANO>IANO>NANO. The ITC studies inferred an endothermic and innersphere complex formation of Eu(III)-PANO and Eu(III)-IANO whereas an exothermic and outer-sphere complex formation for Eu(III)-NANO. The luminescence life time data further supported the ITC results. Density functional theoretical calculations were carried out to optimize geometries of the complexes and to estimate the energies, structural parameters (bond distances, bond angles) and charges on individual atoms of the same. Theoretical approximations are found to be in good agreement with the experimental observations.