Search

Complexation of Np4+ and NpO22+ ions was studied in a room temperature ionic liquid (C8mim•NTf2) using two multiple diglycolamide (DGA) ligands with three and four DGA arms tethered to the nitrogen atoms of the aza-9-crown-3 and -12-crown-4 scaffolds termed as LI and LII, respectively. The studies include solvent extraction, UV–visible spectrophotometry, cyclic voltammetry, and density functional theory (DFT). While the extraction of NpO22+ ion, as a function of the nitric acid concentration, resembled that of the ‘solvation’ mechanism, seen in case of neutral donor ligands in molecular diluent, an opposite trend was observed for the Np4+ ion suggesting a ‘cation-exchange’ mechanism often operating in the case of ionic liquid-based solvent systems. Slope analysis suggested formation of Np(NO3)]3+•L and NpO2(NO3)2•L extracted species for the extraction of Np4+ and NpO22+, respectively, in both the ligand systems. The complexation of the metal ions was supported by peak shifts in the UV–visible spectrophotometric as well as cyclic voltammetric studies. DFT studies were carried out to get structural information of the complexes.

Titanium, a high temperature tolerance metal is preferred as neutron targets due to high hydrogen storage capacity. Therefore, there is a need to understand the interaction and dynamical behaviours of hydrogen isotopes with Ti which is investigated by means of linear combination of atomic orbitals (LCAO) and projector augmented wave (PAW) potential within the density functional theoretical framework. The hydrogen isotope is studied by incorporating zero point energy and the harmonic transition state theory (HTST) were used to determine the rate constant. The values of surface adsorption energy of hydrogen isotopes were predicted to follow the trend: Ead(H2) > Ead(D2) > Ead(T2). The activation energy barrier from top to bridge and top to hollow sites was negative for H atom indicating barrier less diffusion. The computed total density of states (TDOS) and partial density of states (PDOS) confirmed that the hollow site offers the most stable site for H atom adsorption than that by bridge and top sites. The calculated barrier height for dissociation was 0.4eV at surface coverage of θH > 0.5ML whereas the barrier height for recombination was found to be much higher than that of dissociation. The calculated dissociation rate constant using HTST was found to be quite fast whereas the rate constant for recombination was determined to be very slow as expected. The ZPE corrected activation heights for bulk diffusion in Ti from one Td void to nearby Td void for H, D and T were computed to be 0.118, 0.126 and 0.129 eV respectively at the PAW level. The calculated diffusivity establishes that the lighter H atom migrates faster than that of heavier D and T atoms. The classical barrier height was observed to be reduced after quantum correction.

Liquid-liquid extraction of several actinide and lanthanide ions, viz., U(vi), Pu(iv), Am(iii) and Eu(iii) was investigated from nitric acid feed solutions employing N,N,N′,N′,N′′,N′′-hexa-n-octyl nitrilotripropamide (HONTP) in 90% n-dodecane + 10% isodecanol. The observed trend of metal ion extraction at 0.5 M HNO3 was Pu(iv) > U(vi) > Eu(iii) ∼ Am(iii). A high distribution ratio was observed for U(vi) at pH 2 using 0.08 M HONTP in 90% n-dodecane + 10% isodecanol. The back extraction study of Pu(iv) and U(vi) using 0.5 M HNO3 + 0.5 M oxalic acid and 1 M Na2CO3, respectively, showed highly efficient stripping (>97%) for both the metal ions from the loaded organic phase. Slope analysis suggested formation of a lower stoichiometry complex of Pu(iv) with HONTP at 3 M HNO3, whereas U(vi) formed 1 : 1 (ML) and 1 : 2 (ML2) species. Temperature variation studies on the extraction of the metal ions showed that complexation of U(vi) with HONTP was not favourable, based on entropy changes. A supported liquid membrane study showed very poor transport of U(vi) using 0.08 M HONTP in 90% n-dodecane + 10% isodecanol, whereas Pu(iv) exhibited significant transport through the membrane. Density functional theoretical (DFT) studies were carried out to corroborate the experimental observations. Comparison of the results with those of hexa-n-octyl nitrilotriacetamide (HONTA) revealed a considerable effect of the spacer length on the binding efficiency, selectivity, and complex stoichiometry.

Considering the beneficial aspects of ZnO doping in silicate and borosilicate glasses for bioactive glass, nuclear waste vitrified glass and many other applications, the combined experiments and molecular dynamics (MD) simulations were performed over wide range of composition. First principles ab-initio MD (AIMD) simulations confirmed the transferability of B-K-S potential model for multi-component glasses. A significant change in glass structure was monitored from short range order parameters: pair correlation function, coordination number, as well as intermediate range order parameters: bond/angle distribution profiles, structure factor and probability of X-O-X\ (X,X\ = Si, B, Zn) connections. Order of connectivity illustrated that hydrolysis of glass will slow down with addition of ZnO in the glass matrix. Successively, the effect of microscopic structure on observable glass properties: chemical durability, mechanical strength, thermal stability and characteristic vibrational spectra was analyzed. Results show good match of MD estimated trend for Young Modulus, glass transition temperature, and leaching data with the experimental observations, hereby, confirm the transferability of applied potential parameters for multi-component (n≥4) glasses. Both the experiments as well as MD simulations report the enhanced chemical durability of glass withZnO addition. Low R (Na2O/B2O3) and high K (SiO2/B2O3) of ZnO doped sodium borosilicate (Zn-NBS) glass surface compared to bare NBS represents the more stable structure of glass surface for Zn-NBS than NBS. During contact with water, Na+ ions were less likely to leach out from glass to aqueous solution for Zn doped glasses. The enhanced chemical resistivity of Zn-NBS was also established from the increasing activation energy for diffusion of Na ions. Likewise, the ring statistics as well as Na cluster size also supported the reduced chemical reactivity of Zn added glasses. The systematic study of linkage between network formers, ring statistics, diffusion dynamics and ion/water migration provides significant understanding of glass dissolution mechanism. Also, results predict the beneficial impact of ZnO doping for improved strength of glass skeleton, which would eventually control the glass degradation due to micro cracking. The combined studies from experiments and MD simulations disclose many interesting microstructure and dynamics due to the presence of ZnO in the glass.

Two diglycolamide (DGA) functionalized poly(propylene imine)diaminobutane dendrimers, first generation (Gen I) and second generation (Gen II), termed as LI and LII, were used for the extraction of the tetravalent actinide ions Np4+ and Pu4+ from nitric acid medium. The metal ion extraction followed a ‘solvation’ type mechanism showing increasing metal ion extraction with increasing nitric acid concentration with species of the type: M(NO3)4·L (M = Np or Pu) with some contribution of M(NO3)4·2L for Pu. Pu4+ formed much stronger complexes with both DGA-dendrimer ligands as compared with Np4+, as reflected in their two-phase extraction constants and higher ΔH values, attributed to its higher ionic potential. Binding of the metal ions was to one ‘DGA pocket’ in each of the dendrimers. The structure and bonding analysis was done on the basis of DFT studies.

A series of four N-pivot tripodal diglycolamide (DGA) ligands, where three DGA moieties are attached to the central N atom via spacers of different lengths and with varying alkyl substituents on the amidic nitrogen of DGA (LI-LIV), were studied for their extraction and complexation ability toward trivalent lanthanide/actinide ions, including solvent extraction, complexation using spectrophotometric titrations, and luminescence spectroscopic studies. Introduction of a methyl group on the amidic nitrogen atom gives rise to a 400 fold increase of the Eu distribution ( D) value [LIII (NMe) vs LII (NH)] at 1 M HNO3. Enlargement of the spacer length between the pivotal N atom and the DGA moieties with one carbon atom results in a 14 times higher DEu value [LI (C3) vs LII (C2)]. Slope analyses showed that Eu3+ was extracted as a bis-solvated species with all four ligands. The compositions of the Eu3+/L complexes were further confirmed by spectroscopic measurements, its formation constants following the order: LIII > LIV > LI > LII. Luminescence spectroscopy and electrospray ionization mass spectrometry revealed that all four ligands form [Eu(L)2(NO3)3] complexes. Density functional theory and thermodynamic parameters corroborated the existence of [Eu(L)2(NO3)3] complexes.

Selection of suitable glass composition for vitrification of high-level radioactive wastes (HLWs) is one of the major challenges in nuclear waste reprocessing. Atomic and molecular level understand...

The Mulliken charge embedded newly developed OPLS force field has been applied for computation of various structural and dynamical properties of water–dodecane biphasic system. The interface thickness has been investigated in the presence of finite concentration of third component, a lipophilic ligand, tri-isoamyl phosphate (TiAP) and acid employing molecular dynamics simulation. The physical properties at the interface like interface structure, interfacial tension, interface thickness have been studied for a wide range of mole fraction of TiAP and with various aqueous phase acidity. The interfacial tension is found to be decreased with increasing mole fraction of TiAP whereas increased with the acid concentration. The inverse relation between interface thickness and interfacial tension has been established. The surface tension computed from pressure tensor was found to be in excellent agreement with the experimental results, which is then used to determine the interface thickness employing capillary wave theory (CWT) using a simple scheme of finding the bulk correlation length by adopting conductor like screening model for real solvents. Furthermore, a simple equation has been obtained by fitting the MD results of total interface thickness for a wide range of composition of third component. The value of interface thickness calculated from the model equation was found to be in good agreement with the available experimental and MD results for a wide variety of oil-water biphasic systems. Additionally, the stability of the dimer of TiAP with different orientation was established by computing the dimerization energy using DFT which was also captured in the MD simulation. Furthermore, the present MD data shows that the water extraction is enhanced at higher mole fraction of TiAP because of wider interface thickness at higher composition of TiAP which induced the water transport to the organic phase. Again, the calculated values reveal that the water extractability is decreased with increasing aqueous phase acidity as the interface thickness is reduced at higher acidity. The present results might be useful in the frontier area of interfacial science and engineering as well as in partitioning of drug molecules at the biological interfaces.

An attempt was made to understand the sorption behaviour of UO22+, Th4+ and Eu3+ on novel hybrid metal-organic framework composites, FeBDC@CoBDC. The XRD pattern revealed the composite nature of the hybrid MOF materials, while FTIR and Raman spectroscopic analyses evidenced the presence of different functional moieties. The thermal stability of the hybrid MOF composites was investigated through thermogravimetric analysis. The sorption predominantly followed Langmuir isotherm with sorption capacity of 189 mg g−1, 224 mg g−1 and 205 mg g−1 for UO22+, Th4+ and Eu3+ respectively. The sorption proceeded through chemisorption following pseudo 2nd order rate kinetics. The processes were found to be thermodynamically favourable and endothermic in nature. However, they were entropically driven. Multiple contacts of complexing agents were necessary for quantitative elution of f-elements from loaded MOF. The MOF showed moderate stability towards radiation exposure. DFT calculation was used for the optimization of structures, estimation of bond length and estimation of binding energy. In hybrid MOF composites, the Fe atom was having six coordination with 4 O atoms of BDC moieties and 2 O atoms of –OH groups. The O atoms of BDC and –OH groups were coordinated to Eu, Th and U atoms during their sorption.

Thorium (Th) exposure to the human beings is a radiochemical hazard and the chelation therapy by suitable drugs is the major prevention approach to deal with. The present studies aimed at usage of pyrazinoic acid (PCA), which is a prodrug to treat tuberculosis, for its usage as decorporating agent for thorium from human body. The present studies provide a comprehensive knowledge on the chemical interaction and biological efficacy of pyrazinoic acid (PCA) for decorporation of Thorium from the human body. The thermodynamic parameters for Th-PCA speciation are determined by both experiment and theory. The potentiometric data analysis and Electro-Spray Ionization Mass Spectrometry (ESI-MS) studies revealed the formation of MLi (i = 1–4) species with the decrease in stepwise stability constants. All the species formations are endothermic reactions and are predominantly entropy-driven. Biological experiments using human erythrocytes, whole blood and normal human lung cells showed cytocompatibility and decorporation ability of PCA for Thorium. Density functional calculations have been carried out to get insights on interaction process at molecular level. The experimental results and theoretical predictions found to be in line with each other. Present findings on complexation of Th by PCA and its evaluation in human cells and blood would further motivate determination of its safety levels and decorporation efficacy in animal models.

The structure, energetic and quantum chemical descriptors of Cs+ complexes of calix[4]arene-crown-6 (C4C6) and substituted C4C6 i.e 1,3 alternate-diethoxy C4C6 are reported here based on the analysis of results using density functional theory. Substitution of benzo group to both C4C6 and 1,3 alternate-diethoxy C4C6 resulted in reduction of binding energy (BE). Further substitution on benzo group with methyl, methoxy and amino groups leads to increase in BE and nitro substitution leads to decrease in BE for C4C6, whereas in the case of 1,3 alternate-diethoxy calix[4]arenebenzocrown-6, methoxy substitution leads to highest BE compared to other complexes. The calculated Gibbs free energy, ΔGgas also followed the same order as BE in the case of 1,3 alternate-diethoxy C4C6 and their substituted ligands. Furthermore, the ΔG of complexation were computed using thermodynamic cycle with conductor like screening model (COSMO) in different solvents: toluene, chloroform, octanol and nitrobenzene. The values of ΔGext are found to be increased with increase in the dielectric constant of the solvent and found to be highest in the nitrobenzene. The Atoms in Molecule (AIM) analysis reveals partial ionic character in Cs-O bond. Among all the studied complexes, 1,3 alternate-diethoxy calix[4]arene 3’-methoxy benzo crown-6 displays highest ΔGext in nitrobenzene. The calculated value of ∆∆Gext (∆∆G= ∆GCs+-∆GNa+) is found to be -41.82 kcal/mol with 1,3 alternate-diethoxy calix[4]arene 3’-methoxy benzocrown-6 which is higher than that obtained with calix [4] bis-crown-6 (-5.24 kcal/mol). The newly designed ligand might be suitable for the selective extraction of Cs+ over Na+ in the reprocessing of nuclear waste and thus invites the experimentalists for testing this DFT finding in the laboratory.

The Cu complex, which is the key chemical species in well-known Cu–Cl hybrid thermochemical cycles and also in numerous metal hydrometallurgical and sedimentary deposit processes, displays a wide variety of structural and dynamical characteristics that are further complicated by the presence of multiple oxidation states of Cu ions with different coordination chemistries, therefore they are difficult to explore from experiments alone. In this article, an attempt has been made to understand the coordination behavior of the Cu complex using MD simulations. The study provides compelling evidence of the experimentally observed multiple stoichiometries of Cu ions, i.e., 1:6:0, 1:5:1, and 1:4:2 for Cu+:H2O:Cl– and 1:6:0 for Cu2+:H2O:Cl–. The presence of the anionic Cu complex, [Cu+Cl2]−·2H2O, [Cu+Cl2]−·3H2O, [Cu2+Cl3]−·H2O, and [Cu2+Cl3]−·2H2O, was captured in the presence of excess chloride ions. Furthermore, the probability distribution profiles have been estimated to determine the most possible complex in the...

Graphical abstract, Highlights • Thermodynamics of Th(IV)-PCNO complexes are studied for the first time. • All Th(IV)-PCNO complexes are endothermic and entropy driven reactions. • Th(IV) forms six membered chelate complexes with PANO. • The dehydration of ligand played a key role on complexation thermodynamics., The feed wastes and waste water treatment plants are the major sources for the entry of N-oxides into the soils then to aquatic life. The complexation of actinides with potentially stable anthropogenic ligands facilitate the transportation and migration of the actinides from the source confinement. The present study describes the determination of thermodynamic parameters for the complexation of Th(IV) with the three isomeric pyridine monocarboxylates (PCNO) namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO). The potentiometric and isothermal calorimetric titrations were carried out to determine the stability and enthalpy of the formations for all the Th(IV)-PCNO complexes. Th-PANO complexes are more stable than Th-NANO and Th-IANO complexes which can be attributed to chelate formation in the former complexes. Formation of all the Th-PCNO complexes are endothermic and are entropy driven. The geometries for all the predicted complexes are optimized the energies, bond distances and charges on individual atoms are obtained using TURBOMOLE software. The theoretical calculation corroborated the experimental determinations.

The acceptance of nuclear energy is due to the safe and clean operation of the reactor along with the proper reprocessing of the aqueous nuclear waste. In that context, extraction of uranyl ion form aqueous solution has an immense importance in the field of fuel reprocessing. The extraction of uranyl ion is the key step on which the efficiency of the reprocessing depends. Tri-isoamyl phosphate (TiAP) is proven to be a potential alternative of Tri-butyl phosphate (TBP) in the Plutonium Uranium Extraction (PUREX) process. Therefore, understanding of PUREX process at the atomistic level using molecular dynamics simulations is of immense practical significance. Therefore, extensive molecular dynamics simulations have been conducted using calibrated all-atom optimized potentials. The simulation studies have been performed for a wide range of nitric acid concentration from 1 M to 8 M. MD studies reveal the importance of interfacial properties on the extraction of uranyl ions. The predicted interface thickness is seen to be increased with acidity whereas the calculated interfacial tension shows the opposite behavior. From the calculated results, it is observed that the capillary part of the total interface thickness is suppressed whereas the intrinsic part is expanded due to the packing of uranyl ions. The uranyl complexes remain adsorbed at the close proximity of the aqueous-organic interface. The predicted distribution constant of uranyl ion with increasing acidity exhibits a “curved profile“ as observed in the experiment. The computed interaction energy using DFT displays that the TiAP-UO22+ interaction energy is much higher compared to the TiAP-HNO3 and TiAP-H2O interaction energies thus support the higher distribution constant of uranyl ion. The high value of negative free energy difference, ΔΔG (ΔGSolvation - ΔGHydration) of uranyl ion in the organic and aqueous phase confirms that the partitioning of uranyl ion to the organic phase through complexation reaction is thermodynamically feasible process.

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd3+) and uranium dioxide (UO2) with dibenzo crown ether (DBCE) in nitrobenzene (NB) and octanol (OCT) solvents. The effect of polystyrene graft length, on DBCE, on the binding behavior of Gd3+ and UO22+ is investigated for the first time. Our simulation results demonstrate that the binding of Gd and UO2 on to the oxygens of crown ethers is favorable for polystyrene grafted crown ether in the organic solvents OCT and NB. The metal ion binding free-energy (ΔGBinding) in different solvent environment is calculated using thermodynamic integration (TI) method. ΔGBinding becomes more favorable in both solvents, NB and OCT, with an increase in the polystyrene monomer length. The metal ion transferability from an aqueous phase to an organic phase is estimated by calculating transfer free-energy calculations (ΔGTransfer). ΔGTransfer is significantly favorabl...

We report the molecular dynamics studies on the interfacial behavior of cesium (Cs + ) extraction by bis(2-propyloxy)calix [4]crown-6 (BPC6) and dicyclohexano-18-crown-6 (DCH18C6). For the benchmarking study, the phase separation for [BMIM][Tf 2 N]-water was validated. Thereafter, to understand the mechanism of complexation and the behavior of the crown ether ligand, crown ether (CE) molecules and Cs + NO 3 − ions were inserted randomly in the ionic liquid (IL)–water biphasic system. It was observed that the 2:1 Cs + -BPC6 complex formed during the simulation was more stable at the interface and was found to diffuse slowly to the IL side of the interface. On the contrary the 1:1 Cs + -DCH18C6 complex was found to be fully solvated in the bulk IL phase. The [BMIM] + cation was found to partition to the aqueous phase and exchange with Cs + ion in presence or absence of CE. The solubility, density plots and the snapshots of the [BMIM] + cation at the IL–water interface indicates the dual cationic exchange. A comparison of the interfacial behavior of Cs + -BPC6 complex and Cs + -DCH18C6 complex in IL–water preformed interface system, depicted that the Cs + -BPC6 complex was stable at the interface till the end of the simulation. One the other hand, the uncomplexed DCH18C6 resided at the interface, while the Cs + ion diffused to the bulk aqueous phase. The calculated interaction energy of Cs + -BPC6 was found to higher as compared to Cs + -DCH18C6. These results display the importance of the dual cationic exchange properties of IL and the extraction efficiency of CE for extraction of metal ions.

Amidoamine functionalized multi-walled carbon nanotubes (MWCNT-AA) have been prepared and characterized. Separation of mercury(II) ions from aqueous solution by solid-liquid extraction has been investigated using the synthesized material as an adsorbent. Batch adsorption studies as a function of pH, contact time, initial metal ion concentration, and temperature have been carried out. The best fit for the adsorption equilibrium data was observed with Redlich-Peterson isotherm model and the kinetics data showed superior fitting for pseudo second order model, signifying chemisorption. The adsorbent showed superior selectivity with high adsorption capacity towards mercury as compared to other metal ions present in industrial waste water containing mercury. The MWCNT-AA was successfully used for six adsorption-desorption cycles without significant loss of uptake using 0.05 M EDTA as desorbing agent. A small scale fixed bed column study was demonstrated to test the scale up application. DFT theoretical calculations establish the bi-dentate mode of complexation and correlate the experimental selectivity.

Extraction of actinide (Pu4+, UO2 2+, Am3+) and lanthanide (Eu3+) ions was carried out using different diglycolamide (DGA) ligands with systematic increase in the alkyl chain length from n-pentyl to n-dodecyl. The results show a monotonous reduction in the metal ion extraction efficiency with increasing alkyl chain length and this reduction becomes even more prominent in case of the branched alkyl (2-ethylhexyl) substituted DGA (T2EHDGA) for all the metal ions studied. Steric hindrance provided by the alkyl groups has a strong influence in controlling the extraction behavior of the DGAs. The distribution ratio reduction factor, defined as the ratio of the distribution ratio values of different DGAs to that of T2EHDGA, in n-dodecane follows the order UO2 2+ > Pu4+ > Eu3+ > Am3+. Complexation of Nd3+ was carried out with the DGAs in methanol by carrying out UV-vis spectrophotometric titrations. The results indicate a significant enhancement in the complexation constants upon going from methyl to n-pentyl substituted DGAs. They decreased significantly for DGAs containing alkyl substituents beyond the n-pentyl group, which corresponds to the observed trend from the solvent extraction studies. DFT-based calculations were performed on the free and the Nd3+ complexes of the DGAs both in the gas and the solvent (methanol) phase and the results were compared the experimental observations. Luminescence spectroscopic investigations were carried out to understand the complexation of Eu3+ with the DGA ligands and to correlate the nature of the alkyl substituents on the photophysical properties of the Eu(III)-DGA complexes. The monoexponential nature of the decay profiles of the complex revealed the predominant presence of single species, while no water molecules were present in the inner coordination sphere of the Eu3+ ion.

Understanding the speciation of metal ions in heterogeneous hydrogen-bonded deep eutectic solvents (DES) has immense importance for their wide range of applications in green technology, environmental remediation, and nuclear industry. Unfortunately, the fundamental nature of the interaction between DES and actinide ions is almost completely unknown. In the present work, we outline the speciation, solvation mechanism, and redox chemistry of uranyl ion (UO

Selection of suitable glass composition for vitrification of high-level radioactive wastes (HLWs) is one of the major challenges in nuclear waste reprocessing. Atomic and molecular level understanding of various structural, thermodynamical, and dynamical properties of a glass matrix can help in preliminary screening and thus reduce the dependency to some extent on tedious experimental procedures. In that context, extensive molecular dynamics (MD) simulations have been performed to calculate various microscopic properties of the glass matrix. The present article demonstrates that the "Buckingham potential-included long-ranged Coulomb interaction" can be utilized to simulate the glasses of varied compositions. The proposed simulation model has been validated for a wide range of glass compositions: pure glass matrix-SiO

The structural and dynamical characteristics of uranyl ions in an aqueous acidic environment are of immense importance in the field of nuclear fuel reprocessing. In view of that, the structural and dynamical behavior of the uranyl ion in water has been investigated by performing molecular dynamics (MD) simulations using different force fields. All the force fields have depicted similar structural and dynamical properties except the free energy of hydration where the Guilbaud-Wipff (GW) model performs well over the others. The calculated density using MD simulations is found to be in excellent agreement with the measured experimental density, which ensures the accuracy of the adopted GW force field. The calculated surface tension and shear viscosity are seen to be increased with uranyl nitrate concentrations. At a higher concentration of about 4.0 mol/L, the supersaturation effect has been captured by an inflection in the plot of surface tension and shear viscosity against concentration because of the solution heterogeneity, which was correlated by an inflection in the scattering intensity observed by performing the dynamic light scattering experiment. The binding mode of nitrate ions with the uranyl ion is found to be concentration-dependent, and at higher concentration, it is predominantly monodentate.

In addition to solvent extraction experiments, the extensive molecular dynamics simulations have been performed for aqueous (water + uranyl ion + nitrate ion + nitric acid) organic (tributyl phosphate (TBP) + dodecane) biphasic systems in order to gain molecular insights of uranium extraction process. The simulation results well corroborate with the experimental observations. An attempt has been made to uncover the location of uranyl-TBP complexation by systematically studying the distribution of the complexes at the interface, mixed phase and the bulk phases. From the distribution constant profile, the extraction of UO2+2 ions to the organic phase was predicted to increase with increase in UO2+2 ion concentration. The experimentally observed bell shaped profile of distribution constant for uranyl extraction vs. acid concentration was first time captured by the MD simulations. The interface thickness was seen to be increased with increase in uranyl concentration. On the other hand, the inverse bell-shaped curve of interfacial thickness was noticed with increasing acid concentration. The extraction of uranyl ions was predicted to be proportional to the interface thickness. Finally, the stoichiometry distribution of UO2+2ions and UO2+2-TBP complex, their hydration characteristics, and structural orientation was explored in the different zones of biphasic system. The MD results show that the UO2+2-TBP complexation happens at the interface not in the organic phase as recently reported by the vibrational sum frequency generation experiment. However, reorganization of UO2+2-TBP complex was observed while migration from interface to the bulk organic phase. More, simulations and experimental studies are needed further to resolve the issue of uranyl ion complexation at the interface.

Cesium is a major fission product in spent nuclear wastes. Crown ethers are used as extracting agent for the removal of cesium ions from aqueous media. We report the interaction energies between the individual complexing species i.e. crown ether and Cs + metal ion. In order to understand the mechanism of complexation and the behavior of crown ether ligand, crown ether (CE) molecules and Cs + NO 3 − ions were inserted randomly in the Ionic Liquid-water/methanol biphasic system, where Ionic Liquid is carrier solvent for CE. It was observed that the interaction energies which comprised of the non-bonded interaction during initial stages of the simulation have a value close to zero. This suggests that the Cs + cation is not present in the crown ether. After the formation of Cs + –CE complex, it is very clear that the electrostatic interactions are particularly attractive in nature and are crucial in realizing complexation.

A comparative evaluation was carried out for the extraction of Sr2+ using novel calix crown ether in molecular diluent and in ionic liquid. Though the trend in extraction profiles was found to be similar for both the systems, still, almost 5 times higher distribution ratio (D) values were observed in ionic liquid. The speciation studies revealed that; neutral Sr (NO3)2. DHCC species was formed in dodecane and the extraction followed through ‘solvation’ mechanism. However, ionic liquid medium (IL), anionic species, [Sr(NO3)3. DHCC]− was found to be predominating indicating ‘anion exchange’ mechanism. The slower kinetics of extraction in IL was attributed to the high viscosity of IL. The extraction process was found to be spontaneous, endothermic and entropy driven.IL based system was found to be radiolytically more stable compared to the molecular diluent (Mol dil) based system. The electron paramagnetic resonance (EPR) spectroscopic investigation revealed the formation of oxygen centered radical with orthorhombic symmetry (gx = 2.00105, gy = 2.00475, gz = 2.00835) in irradiated ligand. The density functional theoretical (DFT) calculation was utilized to investigate the complexation and speciation in detail in microscopic level.

The present studies interpret the speciation of uranyl (UO22+) with the most ubiquitous class of natural species named pyrazines in terms of stability, speciation and its identification, thermodynamics, spectral properties determined by a range of experimental techniques and further evidenced by theoretical insights. UO22+ forms ML and ML2 kind of species with a qualitative detection of ML3 species, while the ESI-MS identified the formation of all the complexes including ML3. Both the ligands act as bidentate chelators with a difference in ring size and coordinating atoms in the complex formed. The ML3 complexes involve the third ligand participation as monodentate via carboxylate only due to the restricted coordination number and space around the UO22+ ion to accommodate three ligand molecules in its primary coordination sphere. All the complexes are found to be endothermic and purely entropy driven formations. The complex formations showed redshift in the absorption spectra and the shift was further enhanced from ML to ML2 formation. The UO22+ ion redox properties are used to explore the redox potential and heterogeneous electron-transfer kinetic parameters as a function of pH and concentration of UO22+ in presence of pyrazine carboxylates. Interestingly, the cyclic voltammograms identified the ligands also as redox sensitive. The theoretical calculation gave inputs to understand the complex formation at the molecular level with major emphasis on geometry optimization, energetics, bonding parameters, molecular orbital diagrams and bond critical point analyses. The experimental observations in combination with theoretical addendum provided detailed knowledge on the interaction of UO22+ with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylates.

The current work reports the experimental and predicted interfacial behavior of metal ion extraction from aqueous phase-diluent system using a newly synthesized calix-benzo-crown-6 (CBCBGA) ionophore. Conductor-like screening model for real solvents was used to predict the selectivity at infinite dilution for the metal ion complexes in both aqueous and diluent phases. The selectivity for Cs+-CBCBGA extraction was found to be higher than that of other metal ions, namely, K+, Na+, and Rb+. This was confirmed by the experimental distribution coefficients obtained in the diluents system at 3 M HNO3 along with 0.01 M CBCBGA/organic solvents. The high selectivity of Cs+–CBCBGA complex over other complexes (K+, Rb+, and Na+) in nitrobenzene was also confirmed and validated by the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap (i.e., 0.13114 > 0.12411 > 0.11719 > 0.11561 eV) and interaction energy (i.e., −68.25 > −57.11 > −55.52 > −52.37 kcal/mol). The interaction and free energ...

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.

Amido amine-functionalized multi-walled carbon nanotubes (MWCNT-AA) were used for efficient and selective solid phase separation of plutonium(IV) and plutonium(VI). Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Tempkin isotherms were employed for understanding the sorption mechanism and Lagergren first order kinetics, an intra-particle diffusion model, and pseudo second order kinetics were applied to understand the sorption kinetics. The sorption proceeded through monolayer coverage of MWCNT-AA with capacities of 91.2 mg g−1 and 89.4 mg g−1 for Pu4+ and PuO22+, respectively following a Langmuir isotherm while the sorption kinetics followed a pseudo second order reaction with rate constants of 3.86 × 10−5 and 3.19 × 10−5 g mg−1 min−1 for Pu4+ and PuO22+ respectively. This MWCNT-AA showed high radiolytic stability and a method was developed for almost quantitative back extraction of plutonium in both the oxidation states from MWCNT-AA. Finally, the sorbent MWCNT-AA was employed for processing synthetic high level waste solution obtained from a research reactor origin. Moreover, density functional theory calculation was performed to examine the coordination and interaction behaviour of Pu4+ and PuO22+ ions towards MWCNT-AA. The present DFT study reveals that Pu is deca-coordinated (two from each of four nitrates and one AA) in the case of Pu4+ and octa-coordinated (two from each of two nitrates and one AA, and one from each of two oxo groups) in PuO22+. The calculated free energy of complexation was found to be almost three times higher for Pu4+ than PuO22+ both in the gas and aqueous phase, which thus confirms the experimentally observed higher sorption of Pu4+ compared to PuO22+ by MWCNT-AA.

A new bisglycolamide substituted calix-benzo-crown-6 (CBCBGA) ionophore has been synthesized and characterized by using 1H, 13C NMR, ESI-MS and elemental analysis. Detailed investigations on the effect of various parameters such as the aqueous phase acidity, ionophore concentration and nitrate ion concentration on extraction of cesium have been carried out. The new ionophore is found to be highly selective for Cs over other metal ions present in the simulated high level liquid waste solution. The complexing ability of this novel ionophore towards Cs+ and Na+ metal ions was further complimented by predicting the structure, extraction free energy and fraction of charge transfer using the B3LYP density functional employing a split-valence plus polarization (SVP) basis set in conjunction with the conductor like screening model. The unusually high selectivity of CBCBGA for Cs+ ion over Na+ ion was established by the calculated value of difference in the free energy, ΔΔG (ΔGext,Cs+ − ΔGext,Na+), −9.46 kcal mol−1, which is in good agreement with the experimentally determined value of −5.59 kcal mol−1. The calculated values of ρ and ∇2ρ at the bond critical point for the hydrated Na+ ion are found to be reduced during complexation with the CBCBGA, whereas for the hydrated Cs+ ion, though ρ remains same, the value of ∇2ρ is increased which seems to play a decisive role in the higher selectivity to Cs+ ion over Na+ ion of CBCBGA. The new CBCBGA ionophore shows promise for the selective removal of Cs+ ion over other metal ions present in the simulated high level liquid waste solution.

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.

A thiourea functionalized polystyrene adsorbent (TPS-DVB) is theoretically and experimentally investigated for selective sorption of antimony from acidic aqueous mixtures with CoCl2 and ZrOCl2. The optimal uptake of 35.6 and 24.2 mg g−1, respectively, was obtained for antimony(III) and antimony(V), at pH 1. The isotherm data could be well explained by the Langmuir model and the adsorption kinetics was successfully fitted in the pseudo first-order kinetics. Very high separation factors of 1129 and 918 were achieved for the Sb(III)/Co(II) and Sb(V)/Co(II) mixtures, respectively. The adsorption of Sb(III) and Sb(V) ions onto the TPS-DVB adsorbent was explored using the Density Functional Theory (DFT). These theoretical studies of metal coordination with the sulfur atom in the isothiourea group of the adsorbent showed stronger interaction of Sb(III) and Sb(V) ions over Co(II) and ZrO(II) ions. The inclusion of solvation model in the theoretical calculations improved the agreement between the experimental and the calculated metal–sulphur bond distances.

The hybrid B3LYP density functional and TZVP basis set in conjunction with COSMO solvation approach have been used successfully to predict the free energy of adsorption for Th4+ ions with pristine CNTs, oxidized CNTs (CNT–COOH) and diglycolamic acid functionalized CNTs (CNT–DGA). Experimentally reported values of adsorption capacities of Th4+ by the above three types of CNT indicate that CNT–COOH has the strongest binding with Th4+, whereas p-CNT has the lowest; CNT–DGA shows less adsorption than CNT–COOH, although the former has tridentate ligands on CNTs' surfaces. This experimental observation has been demonstrated by DFT theoretical studies: gas phase calculation does not match with the above experimental fact, whereas, solvent phase calculation in the presence of nitrate ions, a more realistic approach, is able to explain. Free energy of complexation between Th4+ and CNT–COOH is higher than that of CNT–DGA in all available models of complexation reaction viz. bare Th4+ in aqueous nitrate medium, octahydrated Th4+ in nitrate and thorium nitrate ion pair in aqueous solution. The experimental fact that the presence of oxidized fullerene C60 enhances the Th4+ adsorption by oxidized CNT has also been theoretically corroborated as oxidized C60 has a quite high binding energy for Th4+. Present computational calculation in the search for the best nano carbon based Th4+ adsorbent parallel with experimental verification might be helpful for the design of effective nanomaterials to be used in the treatment of radioactive liquid waste.

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd

The complexation of Am3+ and Eu3+ was studied with three generations of diglycolamide (DGA)-functionalized poly(propylene imine) diaminobutane dendrimers (DGA-Den) with two, four and eight DGA moieties by solvent extraction and luminescence spectroscopy in a room temperature ionic liquid, viz. 3-butyl-1-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]). The extraction of trivalent f-cations was found to increase with decreasing HNO3 concentrations conforming to a cation exchange mechanism with the extraction of Eu3+ being higher than that of Am3+ in the acid concentration range of 0.01-6.0 M HNO3. The nature of the extracted species showed unusual trends compared to those reported previously in molecular diluents. Fluorescence lifetime data suggested the absence of H2O in the extracted complexes meaning strong inner-sphere complexes. The nature of the extracted complexes predicted by solvent extraction was supported by DFT computations.

Extraction of metal ions (i.e., Cs+, K+, Na+, and Rb+) in the presence of ionophore such as dibenzo-18-crown-6 (DB18C6) from the nitrobenzene–water biphasic system is reported by COSMO-RS (conductor-like screening model for real solvents) predictions, molecular dynamics simulation, along with experimental validation. The predicted values of selectivity as obtained for the Na+–DB18C6 complex were 4.571, 4.877, and 4.947 at 298.15, 308.15, and 318.15 K, respectively. This was then confirmed by the experimental distribution coefficient (D) as obtained in the diluent systems along with by varying the metal ion to crown ether ligand (M–L) mole ratios: 10:1 (0.1 M M+ and 0.01 M DB18C6), 1:1 (0.01 M M+ and 0.01 M DB18C6), and 1:10 (0.001 M M+ and 0.01 M DB18C6). The experimentally determined values of DNa (i.e., 0.059, 0.060, and 0.056) were found to be very large as compared to the values of DCs (i.e., 0.001, 0.010, and 0.024) in the nitrobenzene phase. It indicates an excellent extraction ability of DB18C6 for Na+. The rate of phase separation for the Cs+NO3– system was slow as compared to other metal ion systems. The binding energies, free energies, and nonbonded interaction energies of the complexed metal ion in solution were calculated with both explicit and implicit solvent models. A higher interaction energy between Na+–DB18C6 complex and nitrobenzene was observed (i.e., −289.92 in the explicit model and −143.12 kcal/mol in the implicit model) when compared with other metal ions (i.e., Cs+, K+, and Rb+).

The present work describes the sorption of Cs+, Sr2+, La3+ and Th4+ on Fe3O4 nanoparticles (NPs). The selection of metal ions was done on the basis of different charges to see its effect on sorption. Experiments were carried out at two different pH, 6 and 9 and in presence of NaCl salt to see the effect of these factors on metal ion removal rate. Interestingly no sorption of metal ions were observed at pH ∼ 6 while at pH ∼ 9 only Sr2+ and La3+ ions can be selectively sorbed on NPs surface. Experiments in presence of high concentration of salt suggest that the presence of salt does not have an appreciable effect on sorption suggesting the formation of an inner sphere complex of these metal ions on NPs surface. Sr2+ and La3+ sorption over NPs surface facilitates the enhancement of settlement of NPs. NPs settlement rate was monitored in presence of different metal ions and interestingly was found to vary with metal ions. The results were explained on the basis of DLVO theory, HSAB (hard soft acid base) principle, hydrogen bonding and different charges on metal ions.

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.

The 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 Sr(2+) ion over Th(4+) 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 Sr(2+) and Th(4+) 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 ∆∆G ext are in excellent agreement with the results obtained from solvent extraction experiments.

The structures, energetics, thermodynamic parameters and vibrational spectrum of hydrated cationic rubidium clusters incorporating a single rubidium ion and up to 32 water molecules using second order Moller–Plesset and hybrid B3LYP density functional are presented. The predicted equilibrium rubidium–oxygen distance of 2.99 A at the present level of theory is in excellent agreement with the diffraction result of 2.98 A for a hydrated rubidium ion cluster. From geometry optimizations it has been found that Rb+ ion has seven water molecules in the first hydration sphere for n ≥ 24 which support the earlier experimental and simulation findings. The number of hydrogen bonds is found to be increased with an increase in the hydrated cluster size. The present calculated values of interaction enthalpies are in good agreement with the reported gas phase experimental results up to n = 5. The hydration number of rubidium metal ion is predicted to be 7 as seven water molecules are directly linked to the metal ion independently for a large cluster (n > 24) having three layer of solvation representing the bulk solvent limit. Calculation of the vibrational frequencies shows that the formation of a Rb+-water cluster induces significant shifts from the normal stretching modes of isolated water. From the ab initio molecular dynamics simulation, the average first shell coordination number was found to be 6.31 at both PW91 and PBE levels of theories, which is in close agreement with the QM predicted value (CN = 7) and experimental results (CN = 6.4–7.4). The average second shell coordination number is found to be ~ 21–25.

Molecular dynamics (MD) simulation was conducted to explore the extraction mechanism of Cs+ and Na+ ions in the octanol–water biphasic system containing the ionophore: dicyclohexano-18-crown-6 (DCH18C6). The rate of phase separation for the Na+NO3− system was rapid as compared to Cs+NO3− and mixed metal ion systems. Further, the binding energy during complexation of Na+ cation is −55.86 kcal/mol which was found to be more than that of Cs+ ion (−31.23 kcal/mol). A large sharp peak height for radial distribution function in both Cs–CE and Na–CE complexes suggests a high stability and a strong interaction. The self-diffusion coefficient of the Cs+–CE complex (0.054 10−9 m2/s) at the octanol–water interface was found to be smaller than that of other species.

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO2(2+) and Pu(4+) ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu(4+) ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (DPu(IV)/DU(VI)) followed a trend as cross-linked poly(EGMP) (0.95)EGMP in solvent methyl isobutyl ketone (1.3)GO-poly(EGMP) (25)GO-EGMP (181); the DPu(IV)/DU(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO2(2+) and Pu(4+) ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu(4+) ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO2(2+) ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.

This paper presents the results of quantum chemical and classical molecular dynamics (MD) simulations of the microhydration states of the Sr 2+ ion. The quantum chemical results strongly suggest a coordination number (CN) of 8 for the first hydration shell of Sr 2+ , which is in quantitative agreement with data available from X-ray absorption fine structure (XAFS) measurements. The calculated theoretical Sr O bond distance of 2.59 A is also in excellent agreement with the XAFS results (2.60 A). Classical MD simulations are conducted on various water models to predict the hydration structure of the Sr 2+ ion. The CN is found to be in the range of 8–9 using SPC, TIP3P, and TIP4P-2005 water models, with the probability more skewed toward 8. MD–EXAFS study and coordination number analyses reveal that TIP4P-2005 is the best model potential for simulating water molecules to reproduce the experimentally observed absorption spectra and coordination numbers.

The 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.

The partition coefficients for a large number of macrocyclic crown ethers in different water–organic bi-phasic systems at BP-SVP-AM1 and BP-TZVP level of theory using novel conductor like screening model for real solvents (COSMO-RS) approach are presented here for the first time. The predicted values of partition coefficient obtained from the present calculation are compared with the available reported experimental results. The calculated values of partition coefficient obtained from the first principle based COSMO-RS theory are in reasonably good agreement with the available experimental results. The present study reveals that the solvents with strong hydrogen bond donating, weak hydrogen bond accepting and high dipolarity/polarizability are the good solvents for partitioning of a neutral organic solute. The partitioning of a neutral solute in a particular solvent is enhanced due to increased hydrophobicity.

We report density functional theory (DFT) based study to predict various conformation of free 12-crown-4 ether and its complexes with alkali metal cations. The optimized geometries, binding energies, and binding enthalpies of crown ether–cation complexes have been determined with a correlated hybrid density functional, namely Becke’s three-parameter functional, B3LYP using split valence basis function, 6-311++G(d, p). Geometry optimizations for all the conformers of free 12-crown-4 ether and its metal cation complexes are carried out with several initial guess structures based on semi-empirical PM3 optimized results. The optimized structure for free 12-crown-4 ether and its metal cation complexes obtained from the present DFT calculation confirmed the experimentally reported structures. The calculated values of the gas phase binding energy for lithium ion is always found to be higher than that of the sodium ion for all the conformers of macrocyclic 12-crown-4 ethers reported in the present study. Expected...