Publications by authors named "Sk Musharaf Ali"

32 Publications

Characterization of Thorium-Pyrazinoic acid complexation and its decorporation efficacy in human cells and blood.

Chemosphere 2021 May 4;271:129547. Epub 2021 Jan 4.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400094, India.

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 ML (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.
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http://dx.doi.org/10.1016/j.chemosphere.2021.129547DOI Listing
May 2021

Aquatic interaction of uranium with two naturally ubiquitous pyrazine compounds: Speciation studies by experiment and theory.

Chemosphere 2020 Jun 6;249:126116. Epub 2020 Feb 6.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.

The present studies interpret the speciation of uranyl (UO) 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. UO forms ML and ML kind of species with a qualitative detection of ML species, while the ESI-MS identified the formation of all the complexes including ML. Both the ligands act as bidentate chelators with a difference in ring size and coordinating atoms in the complex formed. The ML complexes involve the third ligand participation as monodentate via carboxylate only due to the restricted coordination number and space around the UO 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 ML formation. The UO ion redox properties are used to explore the redox potential and heterogeneous electron-transfer kinetic parameters as a function of pH and concentration of UO 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 UO with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylates.
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http://dx.doi.org/10.1016/j.chemosphere.2020.126116DOI Listing
June 2020

Insight into Speciation and Electrochemistry of Uranyl Ions in Deep Eutectic Solvents.

J Phys Chem B 2020 Jan 19;124(1):181-189. Epub 2019 Dec 19.

Homi Bhabha National Institute , Anushaktinagar, Mumbai 400 096 , India.

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) in DES consisting of choline chloride (ChCl) and urea as the hydrogen-bond donor. Electrochemical and spectroscopic techniques along with molecular dynamics (MD) simulations have provided a microscopic insight into the solvation and speciation of the UO ion in DES and also on associated changes in physical composition of the DES. The hydrogen-bonded structure of DES plays an important role in the redox behavior of the UO ion because of its strong complexation with DES components. X-ray absorption spectroscopy and MD simulations showed strong covalent interactions of uranyl ions with the constituents of DES, which led to rearrangement of the hydrogen-bonding network in it without formation of any clusters or aggregations. This, in turn, stabilizes the most unstable pentavalent uranium (UO) in the DES. MD analysis also highlights the fact that the number of H-bonds is reduced in the presence of uranyl nitrate irrespective of the presence of water with respect to pristine reline, which suggests high stability of the formed complexed species. The effect of added water up to 20 v/v % on speciation is insignificant for DES, but the presence of water influences the redox chemistry of UO ions considerably. The fundamental findings of the present work would have far reaching consequences on understanding DES, particularly for application in the field of nuclear fuel reprocessing.
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http://dx.doi.org/10.1021/acs.jpcb.9b08197DOI Listing
January 2020

Breakdown of continuum model for water transport and desalination through ultrathin graphene nanopores: insights from molecular dynamics simulations.

Phys Chem Chem Phys 2019 Oct 18;21(38):21389-21406. Epub 2019 Sep 18.

Bhabha Atomic Research Center, Mumbai 400085, Maharashtra, India. and Homi Bhabha National Institute, Mumbai 400094, Maharashtra, India.

In the quest for identifying a graphene membrane for efficient water desalination, molecular dynamics simulations were performed for the pressure-driven flow of salty water across a multilayer graphene membrane. Water transport through the graphene membranes was tuned as a function of pore size, external pressure, and salt concentration. The results predicted that water permeability through the graphene channel (width of h = 7 Å) is two orders of magnitude higher than that through the conventional thin film membranes. The breaking of continuum assumption in graphene nanopores was captured by the appearance of a layered water structure and plug-like velocity profiles. Furthermore, the fluidity under nano confinement of graphene was examined in terms of shear viscosity, friction coefficient, and slip length, which were found to depend on the separation of the confining graphene walls and the external pressure. Furthermore, the MD results revealed that the macroscopic water flux through the graphene nanopores can be linked to the microscopic diffusion of water. The calculated viscosity and diffusion coefficient under the graphene pores did not follow the Stokes-Einstein relation, indicating the failure of the hydrodynamic theory. The confined state of water in the graphene pores was also explored via the translational density of states (TDOS) and entropy, which displayed a significant change in the translational entropy with change in the pore size and applied pressure and thus revealed the interconnectivity of the structure, dynamics, thermodynamics, and hydrodynamics of water in the graphene nanopores. Such a linking of the microscopic parameters with the macroscopic profiles provides direct evidence to the experiments of pressure-driven flow through the graphene membranes and might be helpful in examining the performance of graphene membranes for the factors that have large implications on their application in the reverse osmosis (RO) process and other biological channels.
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http://dx.doi.org/10.1039/c9cp04364kDOI Listing
October 2019

Role of Ligand Straining in Complexation of Eu-Am Ions by TPEN and PPDEN, Scalar Relativistic DFT Exploration in Conjunction with COSMO-RS.

Authors:
Sk Musharaf Ali

ACS Omega 2018 Oct 12;3(10):13104-13116. Epub 2018 Oct 12.

Chemical Engineering Division, Bhabha Atomic Research Centre, HBNI, Mumbai 40085, India.

To search for new ligands suitable for the separation of minor actinides (MA) from lanthanides (Ln) in nuclear waste reprocessing, theoretical (density functional theory) studies were carried out on the complexation (structures, bonding, and thermodynamics) of La, Sm, Eu, and Am complexes with moderately soft donor ligands TPEN [,,','-tetrakis(2-pyridylmethyl)ethylenediamine] and PPDEN [,,',″,″-pentakis(2-pyridylmethyl) diethylenetriamine] in aqueous and nitrobenzene solutions. B3LYP level of theory was used in conjunction with the conductor-like screening model for real systems (COSMO-RS). The metal ions in [M(NO)(TPEN)]NO and [M(NO)(PPDEN)](NO) complexes were deca-coordinated with both TPEN and PPDEN. The enthalpy of the complexation with TPEN in an aqueous solution was found to be negative, indicating the exothermic nature of the reaction as observed in the experiments. The calculated values of free energy of complexation follow the experimental trend: Am > Sm > La. Furthermore, the calculated free energy with PPDEN is reduced compared to that with TPEN, which may be attributed to the ligand straining during complex formation, which is also reflected in greater residual charges on both the Eu and Am central ions in the complexes of octadentate PPDEN compared to hexadentate TPEN. The experimental complexation selectivity of Am over Eu with TPEN is established by employing COSMO-RS. Furthermore, TPEN is Am-selective, whereas PPDEN is Eu-selective, which could be exploited for the efficient separation of MA from Ln.
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http://dx.doi.org/10.1021/acsomega.8b00933DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6644696PMC
October 2018

Reduction in Coordination Number of Eu(III) on Complexation with Pyrazine Mono- and Di-Carboxylates in Aqueous Medium.

Inorg Chem 2019 Aug 31;58(16):11180-11194. Epub 2019 Jul 31.

Chemical Engineering Division , Bhabha Atomic Research Centre , Mumbai 400085 , India.

The denticity, flexibility, and steric hindrance of the ligand are key factors in deciding the mode and number of coordination around a metal ion on complex formation. The thermodynamic aspects of lanthanide complexation with various multidentate ligands provides a significant insight into understand the coordination chemistry of lanthanides in framing the relevant metal organic networks for the applications in biological, biochemical and medical aspects. The pyrazine carboxylic acids are known to form many structurally important complexes and further can form chelates with coordination number of eight for europium in which more water molecules can be knocked out from the primary coordination sphere than demanded by denticity of the ligand. The present studies aimed at ESI-MS characterization and determination of the thermodynamic parameters (log β, Δ, Δ, and Δ), luminescence properties of europium complexes with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylate in aqueous solutions by experiment as well as theory. Time resolved luminescence spectroscopy supported by DFT calculations are carried out to optimize the stable geometries of the complexes with various modes of binding and coordination. Furthermore, the thermodynamic parameters estimated theoretically have been used to trace the path of complex formation.
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http://dx.doi.org/10.1021/acs.inorgchem.9b01772DOI Listing
August 2019

Molecular Dynamics Simulation of Amorphous SiO, BO, NaO-SiO, NaO-BO, and NaO-BO-SiO Glasses with Variable Compositions and with CsO and SrO Dopants.

J Phys Chem B 2019 Jul 11;123(29):6290-6302. Epub 2019 Jul 11.

Homi Bhabha National Institute , Mumbai 400094 , Maharashtra , India.

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 and BO; binary glass mixtures-SiO-BO, NaO-SiO, and NaO-BO; ternary glass-NaO-SiO-BO; and also the CsO- and SrO-doped matrix of sodium borosilicate. Most importantly, the MD results have been validated with those of in-house synthesized glasses. The effect of alkali addition on the density and network connectivity of the glass matrix has been explored. The results capture well the boron anomalies for varied concentrations of network formers and network modifiers. The intermediate structural ordering in glasses has been explored by calculating the partial and total structure factors. Further, the characteristic vibration density of states of constituent atoms in the glass matrix is determined. In addition, the glass structures with the addition of dopant oxides CsO and SrO have been examined as they are known to be prime heat-generating agents in HLWs. The results establish the structure and dynamics of the doped glass matrix to be a complex nature of the dopant's mass, concentration, charge, and ionic radius. The present MD results might be of great academic and technological significance for further studies in the field of vitrification and prediction of effects associated with the dopant's nature and concentration.
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http://dx.doi.org/10.1021/acs.jpcb.9b03026DOI Listing
July 2019

Highly Efficient N-Pivot Tripodal Diglycolamide Ligands for Trivalent f-Cations: Synthesis, Extraction, Spectroscopy, and Density Functional Theory Studies.

Inorg Chem 2019 Jul 10;58(13):8633-8644. Epub 2019 Jun 10.

Laboratory of Molecular Nanofabrication, MESA+ Institute for Nanotechnology , University of Twente , P.O. Box 217, 7500 AE Enschede , The Netherlands.

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 (L-L), 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 [L (NMe) vs L (NH)] at 1 M HNO. Enlargement of the spacer length between the pivotal N atom and the DGA moieties with one carbon atom results in a 14 times higher D value [L (C3) vs L (C2)]. Slope analyses showed that Eu was extracted as a bis-solvated species with all four ligands. The compositions of the Eu/L complexes were further confirmed by spectroscopic measurements, its formation constants following the order: L > L > L > L. Luminescence spectroscopy and electrospray ionization mass spectrometry revealed that all four ligands form [Eu(L)(NO)] complexes. Density functional theory and thermodynamic parameters corroborated the existence of [Eu(L)(NO)] complexes.
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http://dx.doi.org/10.1021/acs.inorgchem.9b00985DOI Listing
July 2019

Molecular Dynamics Simulation Studies on Structure, Dynamics, and Thermodynamics of Uranyl Nitrate Solution at Various Acid Concentrations.

J Phys Chem B 2019 05 17;123(21):4571-4586. Epub 2019 May 17.

Chemical Engineering Division , Bhabha Atomic Research Centre , Mumbai 400085 , India.

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.
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http://dx.doi.org/10.1021/acs.jpcb.9b01498DOI Listing
May 2019

Nanoscopic insights of saline water in carbon nanotube appended filters using molecular dynamics simulations.

Phys Chem Chem Phys 2019 Apr;21(16):8529-8542

Chemical Engineering Division, Bhabha Atomic Research Center, Mumbai, Maharashtra 400085, India.

Nanotube appended membranes are shown to be very promising due to their ultrafast water transport and very high salt rejection ability. Using classical molecular dynamics, the present study reports the nanoscopic assessment of various molecular events for nanotube-based desalination, which might be useful for nanoscale devices during process operation at the macroscopic scale. The characteristics of water and ion flow are discussed with varied strength of pressure gradient and salt concentration for different scales of confinement. The results revealed that the membranes comprising nanotubes of 1.0-1.1 nm diameter can be optimized for efficient water desalination with more than >95% salt rejection. Furthermore, the anomalies in water flux through nanotubes are linked with the hydration characteristics of ions inside CNTs. The results show the maximum hydration of confined ions inside the nanotubes, which indicated the minimum permeability of water due to freezing effects. Furthermore, the MD results revealed that akin to bulk phases, the mass transport through nanotubes can be linked with the component diffusivity in the medium. It has been demonstrated that not only the diffusivities of water and ions, but even the gradient of water to ion diffusivity might be utilized to predict and explore the experimental observations, which might be helpful in optimizing the operational regime in nanotube-based filtrations. Moreover, the thermodynamic characteristics of the flow are discussed in terms of the entropy of water and ions using the robust two-phase thermodynamic (2PT) method. The results reflect that the entropy of water is linked to the distortion of the hydrogen bond network inside the nanotube confinement, at the nanotube-water interface and at the bulk solution, whereas the entropy of ions seems to be majorly dominated by their oscillation. Also, the interconnection of hydration structure, mass flux and the diffusivity of water and ions along with their thermodynamic origin are discussed.
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http://dx.doi.org/10.1039/c9cp00648fDOI Listing
April 2019

Complexation of thorium with pyridine monocarboxylate-N-oxides: Thermodynamic and computational studies.

J Chem Thermodyn 2018 Jul 8;122:13-22. Epub 2018 Mar 8.

Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India.

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.
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http://dx.doi.org/10.1016/j.jct.2018.02.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7094258PMC
July 2018

Structure, Dynamics, and Adsorption of Charged Guest within the Nanocavity of Polymer-Functionalized Neutral Macrocyclic Host.

ACS Appl Mater Interfaces 2018 Jun 11;10(24):20968-20982. Epub 2018 Jun 11.

Bhabha Atomic Research Center , Mumbai 400085 , Maharashtra , India.

Host-guest encapsulation has been widely applied for purification and seizing of the metal ions. Macrocyclic crown ethers are one of the most popular hosts in the field of host-guest chemistry, which on functionalization with polymers are employed as an effective adsorbent. In spite of their vast applications, the microscopic information about their sensing mechanism toward cations/molecules is very scarce. Therefore, the present study is focused on the molecular insights of ion-exchange mechanism within the cavity of crown ether-functionalized polymers using molecular dynamics (MD) simulations. This present study investigates the molecular-level events of chloromethylated polystyrene (CMPS) bearing dibenzo-18-crown-6 (DB18C6) in the aqueous and acidic environment, which has been found to be particularly successful in sensing of various alkali and alkali earth metal ions. A strategy has been envisaged to design a crown ether-based functionalized polymeric resin, which exhibits good match of properties with the in-house-synthesized resin. The MD studies well capture the experimentally observed Langmuir-type adsorption isotherms of Li ions on crown ether-grafted polymer resins. The presence of acid reduces the adsorption of Li ions due to the competition with HO ions. In addition, the results revealed that the "adsorption in crown cavity" follows a dual residence time function. To the best of our knowledge, this is the first report on the adsorption isotherm of functionalized crown ether using MD simulations. The structure and dynamics of binding sites were explored using radial distribution functions and diffusion coefficients. All of these effects have been studied for different Li-ion concentrations, acid concentrations, and counterions as well as different lengths of polymer chains and degrees of polymerization. Overall, the present study provides insights into and quantitative information about adsorption on the CMPS-DB18C6 resin, which might be useful in myriads of host-guest-based adsorption experiments.
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http://dx.doi.org/10.1021/acsami.8b03874DOI Listing
June 2018

Molecular Facts on the Structure and Dynamics of Electrolyte Species in Cu-Cl Cycle for Hydrogen Generation: An Insight from Molecular Dynamic Simulations.

J Phys Chem B 2018 04 28;122(14):4115-4130. Epub 2018 Mar 28.

Chemical Engineering Division , Bhabha Atomic Research Center , Mumbai , Maharashtra 400085 , India.

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:HO:Cl and 1:6:0 for Cu:HO:Cl. The presence of the anionic Cu complex, [CuCl]·2HO, [CuCl]·3HO, [CuCl]·HO, and [CuCl]·2HO, 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 considered systems. The results establish structural and dynamical reformation of the Cu complex with change in the salt concentration or variation in the solvent medium in which they are dissolved. Moreover, the structure and kinetics of the Cu ions in the Cu-Cl electrolyzer have been explored over a large range of the electric field by extending the simulated systems for varied strengths of the electric fields. It has been observed that with an increase in the strength of the electric field, the water molecules lose their coordination strength with central Cu ions, which, on the other hand, results in a significant change in the structure of the captured complex. The diffusion dynamics of the ions is altered while applying the electric field, which is furthermore modified while increasing the strength of electric field beyond a critical limit. In fact, the diffusion mechanism of the ions was seen to be transformed from Brownian-like to linear motion and then to hopping diffusion with the increasing strength of the electric field. To the best of our knowledge, this is the first time when the multiple oxidation states of the Cu ion are explored using MD simulations, and the coexisting pictures of the multiple coordinations and the solvent effects have been clearly revealed. Also to date, the present article is the first one to report the insights of the structure and the dynamics of the ions in the Cu-Cl electrolyzer over a wide range of the electric field. The present studies will be very helpful in understanding the mechanism involved in numerous metal hydrometallurgical and sedimentary deposit processes and to comprehend the analogies involved in the electrode reactions of the Cu-Cl cycle for hydrogen generation.
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http://dx.doi.org/10.1021/acs.jpcb.8b01650DOI Listing
April 2018

Molecular dynamics simulation for the test of calibrated OPLS-AA force field for binary liquid mixture of tri-iso-amyl phosphate and n-dodecane.

J Chem Phys 2018 Feb;148(7):074502

Homi Bhabha National Institute, Mumbai 400094, India.

Tri-isoamyl phosphate (TiAP) has been proposed to be an alternative for tri-butyl phosphate (TBP) in the Plutonium Uranium Extraction (PUREX) process. Recently, we have successfully calibrated and tested all-atom optimized potentials for liquid simulations using Mulliken partial charges for pure TiAP, TBP, and dodecane by performing molecular dynamics (MD) simulation. It is of immense importance to extend this potential for the various molecular properties of TiAP and TiAP/n-dodecane binary mixtures using MD simulation. Earlier, efforts were devoted to find out a suitable force field which can explain both structural and dynamical properties by empirical parameterization. Therefore, the present MD study reports the structural, dynamical, and thermodynamical properties with different mole fractions of TiAP-dodecane mixtures at the entire range of mole fraction of 0-1 employing our calibrated Mulliken embedded optimized potentials for liquid simulation (OPLS) force field. The calculated electric dipole moment of TiAP was seen to be almost unaffected by the TiAP concentration in the dodecane diluent. The calculated liquid densities of the TiAP-dodecane mixture are in good agreement with the experimental data. The mixture densities at different temperatures are also studied which was found to be reduced with temperature as expected. The plot of diffusivities for TiAP and dodecane against mole fraction in the binary mixture intersects at a composition in the range of 25%-30% of TiAP in dodecane, which is very much closer to the TBP/n-dodecane composition used in the PUREX process. The excess volume of mixing was found to be positive for the entire range of mole fraction and the excess enthalpy of mixing was shown to be endothermic for the TBP/n-dodecane mixture as well as TiAP/n-dodecane mixture as reported experimentally. The spatial pair correlation functions are evaluated between TiAP-TiAP and TiAP-dodecane molecules. Further, shear viscosity has been computed by performing the non-equilibrium molecular dynamics employing the periodic perturbation method. The calculated shear viscosity of the binary mixture is found to be in excellent agreement with the experimental values. The use of the newly calibrated OPLS force field embedding Mulliken charges is shown to be equally reliable in predicting the structural and dynamical properties for the mixture without incorporating any arbitrary scaling in the force field or Lennard-Jones parameters. Further, the present MD simulation results demonstrate that the Stokes-Einstein relation breaks down at the molecular level. The present methodology might be adopted to evaluate the liquid state properties of an aqueous-organic biphasic system, which is of great significance in the interfacial science and technology.
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http://dx.doi.org/10.1063/1.5009900DOI Listing
February 2018

Interfacial Behavior of Cs, K, Na, and Rb Extraction in the Presence of Dibenzo-18-Crown-6 from the Nitrobenzene-Water Biphasic System: Experimental, Quantum Chemical, and Molecular Dynamic Studies.

ACS Omega 2018 Feb 8;3(2):1663-1674. Epub 2018 Feb 8.

Bhabha Atomic Research Center, Chemical Engineering Division, Mumbai, 400085 Maharashtra, India.

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 () 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 (i.e., 0.059, 0.060, and 0.056) were found to be very large as compared to the values of (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 CsNO 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).
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http://dx.doi.org/10.1021/acsomega.7b01828DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6641252PMC
February 2018

Alkali Metal Ion Partitioning with Calix[4]arene-benzo-crown-6 Ionophore in Acidic Medium: Insights from Experiments, Statistical Mechanical Framework, and Molecular Dynamics Simulations.

J Phys Chem B 2018 02 13;122(7):2102-2112. Epub 2018 Feb 13.

Chemical Engineering Division, Bhabha Atomic Research Center , Mumbai 400085, India.

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 HNO 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 energies of the extraction were found to increase with the dielectric constant of the organic solvents, namely, nitrobenzene > o-nitrophenyl hexyl ether > 1-octanol > chloroform. Overall, a higher selectivity of Cs ion over that of other metal ions (K, Na, and Rb) was obtained for the newly synthesized CBCBGA ionophore in a radioactive waste solution.
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http://dx.doi.org/10.1021/acs.jpcb.7b10632DOI Listing
February 2018

Extraction of Gd and UO Ions Using Polystyrene Grafted Dibenzo Crown Ether (DB18C6) with Octanol and Nitrobenzene: A Molecular Dynamics Study.

J Phys Chem B 2018 01 16;122(3):1334-1344. Epub 2018 Jan 16.

Computational Nano Science Laboratory, Department of Chemical Engineering, Indian Institute of Technology (IIT) Kanpur , Kanpur 208016, India.

Atomistic molecular dynamics (MD) simulations are performed in order to derive thermodynamic properties important to understand the extraction of gadolinium (Gd) and uranium dioxide (UO) 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 Gd and UO is investigated for the first time. Our simulation results demonstrate that the binding of Gd and UO onto 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 (ΔG) in different solvent environments is calculated using the thermodynamic integration (TI) method. ΔG 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 (ΔG). ΔG is significantly favorable for both Gd and UO for the transfer from the aqueous phase to the organic phase (i.e., NB and OCT) via ion-complexation to DBCE with an increase in polystyrene length. The partition coefficient (log P) values for Gd and UO show a 5-fold increase in separation capacity with polystyrene grafted DBCE. We corroborate the observed behavior by further analyzing the structural and dynamical properties of the ions in different phases.
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http://dx.doi.org/10.1021/acs.jpcb.7b11384DOI Listing
January 2018

Unusual extraction of trivalent f-cations using diglycolamide dendrimers in a room temperature ionic liquid: extraction, spectroscopic and DFT studies.

Dalton Trans 2017 Dec 20;46(47):16541-16550. Epub 2017 Nov 20.

Molecular Nanofabrication Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.

The complexation of Am and Eu 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 ([Cmim][TfN]). The extraction of trivalent f-cations was found to increase with decreasing HNO concentrations conforming to a cation exchange mechanism with the extraction of Eu being higher than that of Am in the acid concentration range of 0.01-6.0 M HNO. The nature of the extracted species showed unusual trends compared to those reported previously in molecular diluents. Fluorescence lifetime data suggested the absence of HO in the extracted complexes meaning strong inner-sphere complexes. The nature of the extracted complexes predicted by solvent extraction was supported by DFT computations.
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http://dx.doi.org/10.1039/c7dt03831cDOI Listing
December 2017

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

Spectrochim Acta A Mol Biomol Spectrosc 2018 Feb 9;190:150-163. Epub 2017 Sep 9.

Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.

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 (ML, i=1-4) are formed by Eu(III) with PANO while non chelating ML and ML 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.
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http://dx.doi.org/10.1016/j.saa.2017.09.013DOI Listing
February 2018

Enhanced free energy of extraction of Eu and Am ions towards diglycolamide appended calix[4]arene: insights from DFT-D3 and COSMO-RS solvation models.

Authors:
Sk Musharaf Ali

Dalton Trans 2017 Aug;46(33):10886-10898

Chemical Engineering Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India.

Density functional theory in conjunction with COSMO and COSMO-RS solvation models employing dispersion correction (DFT-D3) has been applied to gain an insight into the complexation of Eu/Am with diglycolamide (DGA) and calix[4]arene appended diglycolamide (CAL4DGA) in ionic liquids by studying structures, energetics, thermodynamics and population analysis. The calculated Gibbs free energy for both Eu and Am ions with DGA was found to be smaller than that with CAL4DGA. The entropy of complexation was also found to be reduced to a large extent with DGA compared to complexation with CAL4DGA. The solution phase free energy was found to be negative and was higher for Eu ion. The entropy of complexation was not only found to be further reduced but also became negative in the case of DGA alone. Though the entropy was found to be negative it could not outweigh the high negative enthalpic contribution. The same trend was observed in the solution where the free energy of extraction, ΔG, for Eu ions was shown to be higher than that for Am ions towards free DGA. But the values of ΔG and ΔΔG(= ΔG-ΔG) were found to be much higher with CAL4DGA (-12.58 kcal mol) in the presence of nitrate ions compared to DGA (-1.69 kcal mol) due to enhanced electronic interaction and positive entropic contribution. Furthermore, both the COSMO and COSMO-RS models predict very close values of ΔΔΔG (= ΔΔG - ΔΔG), indicating that both solvation models could be applied for evaluating the metal ion selectivity. The value of the reaction free energy was found to be higher after dispersion correction. The charge on the Eu and Am atoms for the complexes with DGA and CAL4DGA indicates the charge-dipole type interaction leading to strong binding energy. The present theoretical results support the experimental findings and thus might be of importance in the design of functionalized ligands.
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http://dx.doi.org/10.1039/c7dt01949aDOI Listing
August 2017

Insight into the Complexation of Actinides and Lanthanides with Diglycolamide Derivatives: Experimental and Density Functional Theoretical Studies.

J Phys Chem B 2017 03 16;121(12):2640-2649. Epub 2017 Mar 16.

Radiochemistry Division, Bhabha Atomic Research Centre , Trombay, Mumbai 400085, India.

Extraction of actinide (Pu, UO, Am) and lanthanide (Eu) 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 UO > Pu > Eu > Am. Complexation of Nd 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 Nd 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 Eu 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 Eu ion.
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http://dx.doi.org/10.1021/acs.jpcb.6b11222DOI Listing
March 2017

Surface Engineering of PAMAM-SDB Chelating Resin with Diglycolamic Acid (DGA) Functional Group for Efficient Sorption of U(VI) and Th(IV) from Aqueous Medium.

J Hazard Mater 2017 Apr 3;328:1-11. Epub 2017 Jan 3.

Radiological Safety Division.

A novel chelating resin obtained via growth of PAMAM dendron on surface of styrene divinyl benzene resin beads, followed by diglycolamic acid functionalization of the dendrimer terminal. Batch experiments were conducted to study the effects of pH, nitric acid concentration, amount of adsorbent, shaking time, initial metal ion concentration and temperature on U(VI) and Th(IV) adsorption efficiency. Diglycolamic acid terminated PAMAM dendrimer functionalized styrene divinylbenzene chelating resin (DGA-PAMAM-SDB) is found to be an efficient candidate for the removal of U(VI) and Th(IV) ions from aqueous (pH >4) and nitric acid media (>3M). The sorption equilibrium could be reached within 60min, and the experimental data fits with pseudo-second-order model. Langmuir sorption isotherm model correlates well with sorption equilibrium data. The maximum U(VI) and Th(IV) sorption capacity onto DGA-PAMAMG-SDB was estimated to be about 682 and 544.2mgg respectively at 25°C. The interaction of actinides and chelating resin is reversible and hence, the resin can be regenerated and reused. DFT calculation on the interaction of U(VI) and Th(IV) ions with chelating resin validates the experimental findings.
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http://dx.doi.org/10.1016/j.jhazmat.2017.01.001DOI Listing
April 2017

Passage of TBP-uranyl complexes from aqueous-organic interface to the organic phase: insights from molecular dynamics simulation.

Phys Chem Chem Phys 2016 Aug;18(34):23769-84

Chemical Engineering Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400085, India.

The present study reports molecular dynamics simulations for biphasic systems comprising tributyl phosphate (TBP) in dodecane and uranyl nitrate in the aqueous phase, which are key chemical species in the well-known Pu-U extraction (PUREX) process. An attempt has been made to understand the nature of interface and mechanism of 'TBP associated uranyl' crossing under neutral and acidic conditions. Results show that the solvent density undergoes large fluctuation near the interface depending on the nature of the aqueous-organic phase. The study provides compelling evidence of experimentally observed reorganization of interfacial complexes at the interface and their structural reformation during extraction. It has been observed that the surface active nature of TBP and their interfacial coverage is modulated by the nature of incorporated solute species and their location with respect to the interface. Also, the TBP structuring near the interface is destroyed when an acidic interface is considered rather than a neutral one which favors the uranyl extraction. With an acidic interface, the water humidity of organic phase was observed to be increased in the experiments. Furthermore, the acid/water solubility in the organic phase was observed to be influenced by selection of acid models and their concentration. Simulations with high acid concentration show water pocket formation in the organic phase. However, in the case of dissociated ions or a mixture of both, no such water pool is observed and the extracted water remains dispersed in the organic phase, having the tendency to be replaced by HNO3 because of preferred TBP·HNO3 complexation over TBP·H2O. Most remarkably, the present study makes evident the TBP-induced charge redistribution of uranyl complexes during migration from the interface to the bulk organic phase, which contributes to drive uranyl complexes such as UO2·NO3·4TBP, UO2·5TBP and UO2·NO3·3TBP·HNO3 in the organic phase, and this was reestablished by DFT calculations. Thus, the present study inspires future simulation and experimental investigations on the extraction of species at the liquid-liquid interface.
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http://dx.doi.org/10.1039/c6cp02194hDOI Listing
August 2016

Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions.

J Phys Chem B 2016 Mar 9;120(11):2942-50. Epub 2016 Mar 9.

Radiochemistry Division, Bhabha Atomic Research Centre Trombay , Mumbai-400 085, India.

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.
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http://dx.doi.org/10.1021/acs.jpcb.5b11293DOI Listing
March 2016

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.

J Mol Model 2012 Aug 10;18(8):3507-22. Epub 2012 Feb 10.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.

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.
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http://dx.doi.org/10.1007/s00894-011-1348-1DOI Listing
August 2012

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

J Mol Model 2011 May 30;17(5):1091-108. Epub 2010 Jul 30.

Chemical Engineering Group, Bhabha Atomic Research center, Mumbai 400085, India.

Crown ether architectures were explored for the inclusion of Cs(+) and Sr(2+) 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 Sr(2+) ion with this ligand experimentally. The selectivity of Cs(+) and Sr(2+) 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 Sr(2+) 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 Sr(2+) 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 Sr(2+) 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 Sr(2+)) 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 H(2)O 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.
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http://dx.doi.org/10.1007/s00894-010-0812-7DOI Listing
May 2011

Micro-solvation of the Zn2+ ion-a case study.

Phys Chem Chem Phys 2009 Oct 1;11(37):8285-94. Epub 2009 Jul 1.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.

The structures and thermodynamic parameters of hydrated zinc ion clusters incorporating a single zinc ion and up to eighteen water molecules have been determined with a quantum mechanical hybrid density functional, namely B3LYP using cc-PVDZ basis functions for H and O and a split valence 6-31G (d, p) basis function for Zn. The geometries for all the zinc ion water clusters are optimized with several initial guess structures and without imposing any initial symmetry restriction. Zinc metal ion is found to be preferably four coordinated for smaller sizes of hydrated cluster but attains an octahedral coordination for larger sizes (n >or= 11) of hydrated cluster. Structures with seven or more than seven water molecules attached directly to the central zinc ion are not found. The calculated gas phase coordination number in the first solvation sphere of a large hydrated zinc metal ion is found to be six and the same is also confirmed in the force field based classical molecular dynamics simulation study for an aqueous zinc ion and thus confirms the experimental findings. The equilibrium zinc-oxygen distance of 2.09328 A at the present B3LYP level of study is in excellent agreement with the X-ray diffraction result of 2.093 +/- 0.002 A for a hexahydrated zinc cluster.
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http://dx.doi.org/10.1039/b902422kDOI Listing
October 2009

Mass dependence of shear viscosity in a binary fluid mixture: mode-coupling theory.

Phys Rev E Stat Nonlin Soft Matter Phys 2006 Nov 3;74(5 Pt 1):051201. Epub 2006 Nov 3.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.

An expression for the shear viscosity of a binary fluid mixture is derived using mode-coupling theory in order to study the mass dependence. The calculated results on shear viscosity for a binary isotopic Lennard-Jones fluid mixture show good agreement with results from molecular dynamics simulation carried out over a wide range of mass ratio at different composition. Also proposed is a new generalized Stokes-Einstein relation connecting the individual diffusivities to shear viscosity.
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http://dx.doi.org/10.1103/PhysRevE.74.051201DOI Listing
November 2006

Retraction: "Scaling law of shear viscosity in atomic liquid and liquid mixtures" [J. Chem. Phys. 124, 144504 (2006)].

Authors:
Sk Musharaf Ali

J Chem Phys 2006 Jul;125(1):019901

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.

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http://dx.doi.org/10.1063/1.2214720DOI Listing
July 2006

Scaling law of shear viscosity in atomic liquid and liquid mixtures.

Authors:
Sk Musharaf Ali

J Chem Phys 2006 Apr;124(14):144504

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.

A scaling law relating the shear viscosity of one and two component liquid mixtures to their excess thermodynamic entropies defined through pair correlation functions is derived by approximating the mode coupling theory expressions of frictions and then combining with the Stokes-Einstein relation. Molecular dynamics simulation has been performed to generate the data of shear viscosity for one and two component liquid mixtures to test the derived scaling law. The derived scaling laws yield numerical results of shear viscosity for one component and two component liquid mixtures, which are in excellent agreement with the molecular dynamics simulation results for a wide range of density and interaction potential.
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http://dx.doi.org/10.1063/1.2186322DOI Listing
April 2006