Can Functionalized Cucurbituril Bind Actinyl Cations Efficiently? A Density Functional Theory Based Investigation

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study

Hydroxycarboxylic acids, viz., α-hydroxyisobutyric acid (HIBA) and mandelic acid (MA), have been widely employed as eluents for inner transition metal separation studies. Both extractants have identical functional groups (OH and COOH) with different side-chains. Despite their similarities in binding motifs, they show different retention behaviors for thorium and uranium in liquid chromatography. To understand the mechanism behind the trend, a detailed study on the aqueous phase interaction of thorium with both extractants is carried out by speciation, spectroscopy, and density functional theory-based calculations. Potentiometric titration experiments are carried out to reveal the stability and species formed. Electrospray ionization mass spectrometry is performed to identify the formation of different species by Th with both HIBA and MA. It is seen that for Th-HIBA and Th-MA, the dominating species are ML3 and ML4, respectively. A similar pattern observed in potentiometric speciation analysis supports the tendency of Th to form higher stoichiometric species with MA than with HIBA. The difference in the dominating species thus helps in explaining the reversal in the retention behavior of uranium and thorium in the reverse-phase liquid chromatographic separation. The results obtained are corroborated with extended X-ray absorption fine structure spectroscopic measurements and density functional theory (DFT) calculations.

Density functional theory study of crown ether-magnesium complexes: from a solvated ion to an ion trap

Metal ion detection rests on host-guest recognition. We propose a theoretical protocol for designing an optimal trap for a desired metal cation. A host for magnesium ions was sought for among derivatives of crown ethers 12-crown-4, 15-crown-5, and 18-crown-6. Mg-crown complexes and their hydrated counterparts with water molecules bound to the cation were optimized using density functional theory. Based on specific geometric criteria, Interacting quantum atoms analysis and density functional theory-based molecular dynamics of Mg-crown complexes immersed in water, crown ethers for optimal accommodation of Mg2+ in aqueous solution were identified. Selectivity of the chosen crowns towards Na+, K+, and Ca2+ ions is addressed.

Redox Potentials of Uranyl Ions in Macrocyclic Complexes: Quantifying the Role of Counter-Ions

Several uranyl ions strapped with Schiff-base ligands in the presence of redox-innocent metal ions are synthesized, and their reduction potentials are recently estimated. The change in Lewis acidity of the redox-innocent metal ions contributes to ∼60 mV/pK_a unit quantified which is intriguing. Upon increasing the Lewis acidity of metal ions, the number of triflate molecules found near the metal ions also increases whose contributions toward the redox potentials remain poorly understood and not quantified until now. Most importantly, to ease the computational burden, triflate anions are often neglected in quantum chemical models due to their larger size and weak coordination to metal ions. Herein, we have quantified and dissected the individual contributions that arise alone from Lewis acid metal ions and from triflate anions with electronic structure calculations. The triflate anion contributions are large, in particular, for divalent and trivalent anions that cannot be neglected. It was presumed to be innocent, but we here show that they can contribute more than 50% to the predicted redox potentials, suggesting that their vital role in the overall reduction processes cannot be neglected.

Binding of toluidine blue-myristic acid derivative to cucurbit[7]uril and human serum albumin: computational and biophysical insights towards a biosupramolecular assembly

A new toluidine blue-myristic acid photosensitizer derivate (TBOMyr) was investigated as a design molecule to bind simultaneously to cucurbit[7]uril (CB[7]) and human serum albumin (HSA) with the aim of constructing a biosupramolecular assembly. Molecular docking and dynamics calculations revealed the main supramolecular and bio-molecular interactions of TBOMyr with the macrocycle or the protein, respectively. The addition of the negatively charged myristic acid-like tail resulted in a unique conformation of the CB[7] complex where the phenothiazine core was included in the cavity of CB[7], leaving the fatty acid portion free to interact with the protein. A favorable ternary interaction between TBOMyr, CB[7] and HSA was suggested by the calculations, and an experimental binding affinity in the order of 10⁵ M^-1 was determined for the TBOMyr@CB[7] complex with HSA. The new TBOMyr derivative could find applications in photodynamic therapy benefiting from the biosupramolecular interactions as a transport system.

Achieving highly efficient and selective cesium extraction using 1,3-di-octyloxycalix[4]arene-crown-6 in n-octanol based solvent system: experimental and DFT investigation

Due to the long half-life of ¹³⁷Cs (t_1/2 ∼ 30 years), the selective extraction of cesium (Cs) from high level liquid waste is of paramount importance in the back end of the nuclear fuel cycle to avoid long term surveillance of high radiotoxic waste. As 1,3-di-octyloxycalix[4]arene-crown-6 (CC6) is suggested to be a promising candidate for selective Cs extraction, the improvement in the Cs extraction efficiency by CC6 has been investigated through the optimization of the effect of dielectric media on the extraction process. The effects of the feed acid (HNO₃, HCl, and HClO₄) and the composition of the diluents for the ligand in the organic phase on the extraction efficiency of Cs have been investigated systematically. In 100% n-octanol medium, Cs is found to form a 1 : 1 ion-pair complex with CC6 (0.03 M) providing a very high distribution ratio of D_Cs ∼ 22, suggesting n-octanol as the most suitable diluent for Cs extraction. No significant interference of other relevant cations such as Na, Mg and Sr was observed on the D_Cs value in the optimized solvent system. Density functional theory (DFT) based calculations have been carried out to elucidate the reason of ionic selectivity and enhanced Cs extraction efficiency of CC6 in the studied diluent systems. In addition to the ionic size-based selectivity of the crown-6 cavity, the polarity of the organic solvent system, the hydration energy of the ion, and the relative reorganization of CC6 upon complexation with Cs are understood to have roles in achieving the enhanced efficiency for the extraction of Cs by the CC6 extractant in nitrobenzene medium.

Separation scheme was developed for selective extraction of long-lived fission product ¹³⁷Cs using substituted calix crown 6 ether from aqueous acidic solution.

Computational Study of Actinyl Ion Complexation with Dipyriamethyrin Macrocyclic Ligands

Relativistic density functional theory has been employed to characterize [AnO₂(L)]^0/-1 complexes, where An = U, Np, Pu, and Am, and L is the recently reported hexa-aza porphyrin analogue, termed dipyriamethyrin, which contains six nitrogen donor atoms (four pyrrolic and two pyridine rings). Shorter axial (An═O) and longer equatorial (An-N) bond lengths are observed when going from An^VI to An^V. The actinide to pyrrole nitrogen bonds are shorter as compared to the bonds to the pyridine nitrogens; the former also play a dominant role in the formation of the actinyl (VI and V) complexes. Natural population analysis shows that the pyrrole nitrogen atoms in all the complexes carry higher negative charges than the pyridine nitrogens. Upon binding actinyl ions with the ligand a significant ligand-to-metal charge transfer takes place in all the actinyl (VI and V) complexes. The formation energy of the actinyl(VI,V) complexes in the gas-phase is found to decrease in the order of UO₂L > PuO₂L > NpO₂L > AmO₂L. This trend is consistent with results for the formation of complexes in dichloromethane solution. The calculated ΔG and ΔH values are negative for all the complexes. Energy decomposition analysis (EDA) indicates that the interactions between actinyl(V/VI) and ligand are mainly controlled by electrostatic components over covalent orbital interactions, and the covalent character gradually decreases from U to Am for both pentavalent and hexavalent actinyl complexes.

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide-Extraction Properties and Metal Ion Speciation in Bis-1,2,4-Triazine Ligands

The synthesis and evaluation of three novel bis-1,2,4-triazine ligands containing five-membered aliphatic rings are reported. Compared to the more hydrophobic ligands 1-3 containing six-membered aliphatic rings, the distribution ratios for relevant f-block metal ions were approximately one order of magnitude lower in each case. Ligand 10 showed an efficient, selective and rapid separation of Am^III and Cm^III from nitric acid. The speciation of the ligands with trivalent f-block metal ions was probed using NMR titrations and competition experiments, time-resolved laser fluorescence spectroscopy and X-ray crystallography. While the tetradentate ligands 8 and 10 formed Ln^III complexes of the same stoichiometry as their more hydrophobic analogues 2 and 3, significant differences in speciation were observed between the two classes of ligand, with a lower percentage of the extracted 1:2 complexes being formed for ligands 8 and 10. The structures of the solid state 1:1 and 1:2 complexes formed by 8 and 10 with Y^III , Lu^III and Pr^III are very similar to those formed by 2 and 3 with Ln^III . Ligand 10 forms Cm^III and Eu^III 1:2 complexes that are thermodynamically less stable than those formed by ligand 3, suggesting that less hydrophobic ligands form less stable An^III complexes. Thus, it has been shown for the first time how tuning the cyclic aliphatic part of these ligands leads to subtle changes in their metal ion speciation, complex stability and metal extraction affinity.

Binding of Cm(III) and Th(IV) with Human Transferrin at Serum pH: Combined QM and MD Investigations

Human serum transferrin (sTf) can also function as a noniron metal transporter since only 30% of it is typically saturated with a ferric ion. While this function of sTf can be fruitfully utilized for targeted delivery of certain metal therapeutics, it also runs the risk of trafficking the lethal radionuclides into cells. A large number of actinide (An) ions are known to bind to the iron sites of sTf although molecular-level understanding of their binding is unclear. Understanding the radionuclide interaction with sTf is a primary step toward future design of their decorporating agents since irrespective of the means of contamination, the radionuclides are absorbed and transported by blood before depositing into target organs. Here, we report an extensive multiscale modeling approach of two An (curium(III) and thorium(IV)) ions' binding with sTf at serum physiological pH. We find that sTf binds both the heavy ions in a closed conformation with carbonate as synergistic anions and the An-loaded sTf maintains its closed conformation even after 100 ns of equilibrium molecular dynamics (MD) simulations. MD simulations are performed in a polarizable water environment, which also incorporates electronic continuum corrections for ions via charge rescaling. The molecular details of the An coordination and An exchange free energies with iron in the interdomain cleft of the protein are evaluated through a combination of quantum mechanical (QM) and MD studies. In line with reported experimental observations, well-tempered metadynamics results of the ions' binding energetics show that An-sTf complexes are less stable than Fe-sTf. Additionally, curium(III) is found to bind more weakly than thorium(IV). The latter result might suggest relative attenuation of thorium(IV) cytotoxicity when compared with curium(III).

Complexation of U(VI) with Cucurbit[5]uril: Thermodynamic and Structural investigation in aqueous medium

The assessment of cucurbituril (CBn) for selective removal of actinides from nuclear waste streams requires comprehensive understanding of binding parameters and coordination of these complexes. The present work is the first experimental report on complexation of actinide ion with Cucurbit[5]uril (CB5) in solution. The thermodynamic parameters (ΔG, ΔH and ΔS) for complexation of CB5 with U(VI) in formic acid water medium were determined using microcalorimetry and UV-Vis spectroscopy. The enthalpy and entropy of complexation revealed the partial binding of U(VI) to CB5 portal. The partial binding was confirmed by spectroscopic techniques viz. extended X absorption fine structure spectroscopy (EXAFS), ¹H and ¹³C NMR. The EXAFS χ(r) versus r spectra for U-CB5 complex has been fitted from 1.4 to 3.5 Å with two oxygen shells and a carbon shell. The presence of three carbon atom in secondary shell shows the involvement of only three carbonyl oxygens directly bonding to U(VI) which is in contrast to that calculated from gas phase DFT calculation of unhydrated system. The combined effect of hydration and formic acid encapsulation led to the enhanced stability of partially bound U(VI) to CB5. In the present work the binding of formic acid has also been studied by fluorescence spectroscopy. ESI-MS data shows the unusual stabilization of U(VI) by CB5 in gas phase.

Are cucurbiturils better drug carriers for bent metallocenes? Insights from theory

Bent metallocenes (BM) have anti-tumor properties but they face a serious drug efficacy problem due to poor aqueous solubility and rapid hydrolysis under physiological conditions. These two problems can be fixed by encapsulating them in host molecules such as cyclodextrin (CD), cucurbituril (CB) etc. Experimentally, CD-BM, CB-BM host-guest complexes have been investigated to check the efficiency of the drug delivery and efficiency of the encapsulated drug. CB has been reported to be a better host than CD but the reasons for this has not been figured out. This can be done by finding out the mechanism of binding and the nature of the binding forces in both the inclusion complexes. This is exactly done here by performing a DFT study at BP86/TZP level on CB-BM host-guest systems. For comparison CD-BM with β-cyclodextrin as host have been studied. Four BMs (Cp₂MCl₂, M=Ti, V, Nb, Mo) and their corresponding cations (Cp₂MCl⁺, Cp₂M²⁺) are chosen as guests and they are encapsulated into cucurbit-[6]-uril (CB[6]) and cucurbit-[7]-uril(CB[7]) host systems. Computations reveal that CB[7] accommodates well the BMs over CB[6] due to their larger cavity size and also CB[7] is found to be a better host than β-cyclodextrin. BMs enter vertically rather than horizontally into the CB cavity. The reversible binding of BMs within CB[7] is controlled by various non-bonding interactions and mainly by hydrogen bonding between the portal oxygen atoms and Cp protons as revealed by QTAIM analysis. On the other hand, the interaction between the wall nitrogen atoms in CB[7] and chlorine atoms attached to the metal in BM strengthens the M-Cl bonds that prevents rapid hydrolysis of M-Cl and M-Cp bonds saving the drug. Comparatively, BMs experience less electrostatic attraction and more Pauli repulsion within β-cyclodextrin cavity and this affects the drug binding with CD. This makes β-cyclodextrin a less suitable drug carrier for BMs than CBs. Among the four BMs, niobocene binds strongly and titanocene binds weakly with CBs. EDA clearly shows that all the interactions between the guest and host are non-covalent in nature and electrostatic interactions outperform high-repulsion resulting in stable complexes. Cations form stronger complexes than neutral BMs. FMO analysis reveals that neutral BMs are less reactive compared to their cations and complexes are more reactive in CB[6] environment due to excess strain. QTAIM analysis helps to bring out the newer insights in these types of host-guest systems.

Stability, speciation and spectral properties of NpO2+ complexes with pyridine monocarboxylates in aqueous solution

Neptunyl ion as NpO₂⁺ is the least reacting and most mobile radioactive species among all the actinides. The picolinic acid used for decontamination is co-disposed along with the radioactive waste. Thus, in long term storage of HLW, there is high possibility of interaction of actinides and long lived fission products with the picolinate and can cause migration. The complexation of NpO₂⁺ with the three structural isomers of pyridine monocarboxylates provides an insight to explore the role of hetero atom (nitrogen) with respect to key binding moiety (carboxylate). In the present study, the log β values, speciation and spectral properties of NpO₂⁺ complexes with pyridine monocarboxylates viz. picolinate, nicotinate and isonicotinate, have been studied at 298K in 0.1M NaClO₄ medium using spectrophotometry. The complexation reactions involving protonated ligands are always accompanied by protonation/deprotonation process; thus, the protonation constants of all the three pyridine monocarboxylates under same conditions were also determined by potentiometry. The spectrophotometric data analysis for complexation of NpO₂⁺ with pyridine monocarboxylates indicated the presence of ML and ML₂ complexes with log β values of 2.96±0.04, 5.67±0.08 for picolinate, 1.34±0.09, 1.65±0.12 for nicotinate and 1.52±0.04, 2.39±0.06 for isonicotinate. The higher values of log β for picolinate were attributed to chelation while in other two isomers, the binding is through carboxylate group only. Density Functional Theory (DFT) calculations were carried out to get optimized geometries and electrostatic charges on various atoms of the complexes and free pyridine monocarboxylates to support the experimental data. The higher stability of NpO₂⁺ nicotinate and isonicotinate complexes compared to simple carboxylates and the difference in log β between the two is due to the charge polarization from unbound nitrogen to the bound carboxylate oxygen atoms.

Speciation of uranium-mandelic acid complexes using electrospray ionization mass spectrometry and density functional theory

RATIONALE

Mandelic acid is a complexing agent employed for the liquid chromatographic separation of actinides. However, the types of species and the structural details of the uranyl-mandelate complexes are still unknown. Understanding the nature of these complex species would provide better insight into the mechanism of their separation in liquid chromatography.

METHODS

Formation of different species of the uranyl ion (UO₂ ) with mandelic acid was studied using electrospray ionization mass spectrometry (ESI-MS) with a quadrupole time-of-flight analyzer. The different species of uranyl nitrate with mandelic acid (MA) at ligand (L) to metal ratios in the range 1-10 were examined in both positive and negative ion modes. The stability of different species with the possible pathways of formation was scrutinized using density functional theory (DFT) calculations.

RESULTS

In negative ion mode, nitrate-containing UO₂ (MA)₁ , UO₂ (MA)₂ and UO₂ (MA)₃ species were found in good abundance. In positive ion mode, under-coordinated uranyl-mandelate species, and solvated (S) species of types UO₂ (MA)₁ (S), UO₂ (MA)₁ (S)₂ and UO₂ (MA)₂ (S), were observed whereas nitrate-containing species were absent. Interestingly, doubly and singly charged dimeric species were also identified in positive ion mode. The theoretically computed energetics of the various species are in close agreement with their experimentally observed intensities in ESI-MS.

CONCLUSIONS

The most intense peak observed in ESI-MS, UO₂ (MA)₃ , was found to be the energetically most favorable amongst different UO₂ (MA)_n type species. Metal-ligand equilibria studied in the two modes yielded similar results. The combined experimental and quantum chemical investigations predict that T-shape complexes may be formed even in the gas phase. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis, structural and theoretical studies of dithiodiglycolamide compounds of palladium(II)

The reaction of palladium(ii) halide with dithiodiglycolamide ligands yielded compounds of the type [PdX2L] (where X = Cl, L = (CH2SCH2CON(i)Pr2)2 (1); L = (CH2SCH2CON(i)Bu2)2 (2); L = (CH2SCH2CONBu2)2 (3); L = C7H6(SCH2CON(i)Bu2)2 (4); X = Br, L = (CH2SCH2CON(i)Bu2)2 (5); X = I, L = (CH2SCH2CON(i)Bu2)2 (6)), whereas palladium(ii) nitrate yielded compounds of the type [PdL2](NO3)2 (where L = (CH2SCH2CON(i)Pr2)2 (7); L = (CH2SCH2CON(i)Bu2)2 (8)). All compounds were characterized by using IR, (1)H NMR spectral techniques and CHN analyses. The structures of compounds 4, 5 and 7 have been determined by using X-ray diffraction methods. The structures show that the ligands bond through the thioether group to the metal centre in all compounds. They show further that the palladium(ii) ion is surrounded by four atoms (two halogens and two thio groups in 4 and 5 and four thio groups in 7) in a square planar arrangement. The dithiodiglycolamide ligand acts as a bidentate chelating ligand and bonds through both the thioether groups to the metal centre, leaving the carbamoyl groups uncoordinated. Theoretical studies reveal that the 1 : 2 compound is energetically more stable and nicely correlates with the IR carbamoyl stretching frequencies as compared to the 1 : 1 compound in which the ligand acts as a tetradentate ligand.

Computational and ion mobility MS study of (all-S)-cyclohexylhemicucurbit[6]uril structure and complexes

A computational study of (all-S)-cyclohexylhemicucurbit[6]uril and its complexes with anions (Cl(-), Br(-), I(-) and HCOO(-)), the proton (H(+)) and non-dissociated acid (HCl, HBr, HI and HCOOH) guests was performed. The geometries of guest-host complexes were optimized via density functional theory using the BP86 functional, SV(P) basis set and Stuttgart pseudopotentials for iodide. Binding affinities and their trends were evaluated at the BP86/TZVPD level of theory. In addition, the quantum theory of atoms in molecules was used to gain insight into guest-host interactions. A computational study in the gas phase and ion-mobility mass-spectrometry analysis revealed that the studied macrocycle formed inclusion complexes with anions. Protonation of the macrocycle is preferred at the nitrogen atom pointing inside of the cavity. In the studied conditions, non-dissociated acids formed complexes at the oxygen atom pointing outside of the macrocycle.

Elucidating the structures and cooperative binding mechanism of cesium salts to the multitopic ion-pair receptor through density functional theory calculations

Quantum chemical studies predict the binding of Cesium salts to multitopic ion-pair receptor is through cooperative mechanism.

Theoretical studies on the AnO2n+ (An = U, Np; n = 1, 2) complexes with di-(2-ethylhexyl)phosphoric acid

The AnO₂ⁿ⁺ (An = U, Np; n = 1, 2) extraction complexes with HDEHP (di-(2-ethylhexyl)phosphoric acid) in nitric acid solutions.

Using dispersion-corrected density functional theory to understand supramolecular binding thermodynamics

A recently published theoretical approach employing a nondynamic structure model using dispersion-corrected density functional theory (DFT-D3) to calculate equilibrium free energies of association (Chem. – Eur. J., 2012, 18, 9955–9964) is illustrated by its application to eight supramolecular complexes.

Unanticipated favoured adsorption affinity of Th(iv) ions towards bidentate carboxylate functionalized carbon nanotubes (CNT–COOH) over tridentate diglycolamic acid functionalized CNT: density functional theoretical investigation

CNT–COOH has higher adsorption affinity for Th⁴⁺ in aqueous solution compared to CNT–DGA, whereas pristine CNT has nil.

Effect of successive alkylation of N,N-dialkyl amides on the complexation behavior of uranium and thorium: solvent extraction, small angle neutron scattering, and computational studies

The effect of successive alkylation of the Cα atom adjacent to the carbonyl group in N,N-dialkyl amides (i.e., di(2-ethylhexyl)acetamide (D2EHAA), di(2-ethylhexyl)propionamide (D2EHPRA), di(2-ethylhexyl)isobutyramide (D2EHIBA), and di(2-ethylhexyl)pivalamide (D2EHPVA)) on the extraction behavior of hexavalent uranium (U(VI)) and tetravalent thorium (Th(IV)) ions has been investigated. These studies show that the extraction of Th(IV) is significantly suppressed compared to that of U(VI) with increased branching at the Cα atom adjacent to the carbonyl group. Small angle neutron scattering (SANS) studies showed an increased aggregation tendency in the presence of nitric acid and metal ions. D2EHAA showed more aggregation compared to its branched homologues, which explains its capacity for higher extraction of metal ions. These experimental observations were further supported by density function theory calculations, which provided structural evidence of differential binding affinities of these extractants for uranyl cations. The complexation process is primarily controlled by steric and electronic effects. Quantum chemical calculations showed that local hardness and polarizability can be extremely useful inputs for designing novel extractants relevant to a nuclear fuel cycle.

Understanding the interactions of neptunium and plutonium ions with graphene oxide: scalar-relativistic DFT investigations

Due to the vast application potential of graphene oxide (GO)-based materials in nuclear waste processing, it is of pivotal importance to investigate the interaction mechanisms between actinide cations such as Np(V) and Pu(IV, VI) ions and GO. In this work, we have considered four types of GOs modified by hydroxyl, carboxyl, and carbonyl groups at the edge and epoxy group on the surface, respectively. The structures, bonding nature, and binding energies of Np(V) and Pu(IV, VI) complexes with GOs have been investigated systematically using scalar-relativistic density functional theory (DFT). Geometries and harmonic frequencies suggest that Pu(IV) ions coordinate more easily with GOs compared to Np(V) and Pu(VI) ions. NBO and electron density analyses reveal that the coordination bond between Pu(IV) ions and GO possesses more covalency, whereas for Np(V) and Pu(VI) ions electrostatic interaction dominates the An-OG bond. The binding energies in aqueous solution reveal that the adsorption abilities of all GOs for actinide ions follow the order of Pu(IV) > Pu(VI) > Np(V), which is in excellent agreement with experimental observations. It is expected that this study can provide useful information for developing more efficient GO-based materials for radioactive wastewater treatment.

Investigations on preferential Pu(IV) extraction over U(VI) by N,N-dihexyloctanamide versus tri-n-butyl phosphate: evidence through small angle neutron scattering and DFT studies

Straight chain amide N,N-dihexyloctanamide (DHOA) has been found to be a promising alternative extractant to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated uranium- and thorium-based fuels. Unlike TBP, DHOA displays preferential extraction of Pu(IV) over U(VI) at higher acidities (≥3 M HNO3) and poor extraction at lower acidities. Density functional theory (DFT) based calculations have been carried out on the structures and relative binding energies of U(VI) and Pu(IV) with the extractant molecules. These calculations suggest that the differential hardness of the two extractants is responsible for the preferential binding/complexation of TBP to uranyl, whereas the softer DHOA and the bulky nature of the extractant lead to stronger binding/complexation of DHOA to Pu(IV). In conjunction with quantum chemical calculations, small angle neutron scattering (SANS) measurements have also been performed for understanding the stoichiometry of the complex formed that leads to relatively lower extraction of Th(IV) (a model for Pu(IV)) as compared to U(VI) using DHOA and TBP as the extractants. The combined experimental and theoretical studies helped us to understand the superior complexation/extraction behavior of Pu(IV) over U(VI) with DHOA.

Theoretical study of the inclusion complexation of TCDD with cucurbit[n]urils

Cucurbit[n]urils as a host are indicated to be capable of including TCDD guest and the formed inclusion complexes can be detected using IR and Raman techniques.

Theoretical prediction of the complexation behaviors of antitumor platinum drugs with cucurbiturils

The inclusion complex formation ability between CB[n] (n = 6-9) and Pt-drugs (oxaliplatin, nedaplatin, carboplatin, and cisplatin) in gas phase as well as water phases has been investigated using the using density functional theory. The results reveal the existence of several stable inclusion complexes in aqueous solution with high solvation energies compared to the guest and host molecule. It has been shown that the formation of complexes between CB[6] and Pt-drugs resulted in structural change in the CB[6], with the calculated deformation energies being higher for the inclusion complexes. The inclusion complexes are stabilized by the hydrogen bonding and the charge transfer between the Pt-drugs and the CB[n] host. Calculated enthalpy and Gibbs free energy of formation in aqueous solution revels that the formation of CB[7]-oxaliplatin is spontaneous, and hence its experimental synthesis is feasible. Among the CB's studied, CB[8]-Pt-drug inclusion complexes have exothermic enthalpy and low Gibbs free energy of formation. Computed (1)NMR spectra in CB[7]-oxaliplatin showed high chemical shielding for the cyclohexane ring, indicating the existence of charge transfer in the inclusion complex. The amine protons in the guest Pt-drugs are shielded due to the hydrogen bonding interaction with CB's oxygen portal.