Thermodynamic, Structural, and Computational Investigation on the Complexation between UO22+ and Amine-Functionalized Diacetamide Ligands in Aqueous Solution

Complexation of Hexavalent Neptunium(VI) with Oxydiacetic Acid and Its Amide Derivatives in Aqueous Solution: Spectrophotometry and DFT Calculations

Unfolding the solution coordination chemistry of high-valent transuranium elements with the "CHON"-type ligands is important to understand the fundamental chemistry of actinides and to design more efficient extractants for partitioning of transuranium elements in advanced nuclear fuel cycles. Here, the complexation of a hexavalent neptunyl ion (NpO22+ or Np(VI)) with oxydiacetic acid (ODA) has been systematically investigated in comparison with its amide analogues N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) and N,N,N',N'-tetramethyl-3-oxa-glutaramide (TMOGA) both experimentally and computationally. The formation of both 1:1 and 1:2 complexes between Np(VI) and the three ligands was identified by spectrophotometry, and their stability constants were obtained and compared with those of hexavalent U(VI) and Pu(VI). The corresponding bonding nature is elucidated by using energy decomposition analysis (EDA), electrostatic potential (ESP), ELF contours, and natural orbitals for chemical valence (NOCV) methods, which shows that the Np-O bonds are essentially ionic in character and the unoccupied 6d orbitals of Np play a key role in enhancing the covalent interactions between Np(VI) and the three ligands.

Understanding the Interaction of Uranyl Cation with Two C-Pivot Tripodal Amides: Synthesis, Complexation, Microcalorimetry, and DFT Studies

Complexation of uranyl ions with two structurally related C-pivotal tripodal amides with varying spacer lengths, synthesized for the first time, was studied by optical spectroscopy. In the tripodal amides, the coordination was through the carbonyl O atoms where the carbonyl groups were away from the central C-atom by three spacer atoms (LI) and four spacer atoms (LII), respectively. Increasing the spacer atoms going from LI to LII favors the complexation with the linear uranyl cations and results in stronger complex formation. The complexation heat between the uranyl cations and the two amide ligands was directly measured by microcalorimetric titrations. The complexation with both the ligands was driven by exothermic enthalpy and positive entropy changes. Formation of the complex proceeded by the replacement of water molecules from the primary coordination sphere of the uranyl cation. Both ligands formed bisolvated (ML2-type) complexes in which one unit of the ligand binds in a monodentate manner and the other in a bidentate mode. Density functional theory calculations further supported our experimental observations.

Entropy and Enthalpy Effects on Metal Complex Formation in Non-Aqueous Solvents: The Case of Silver(I) and Monoamines

Access to the enthalpy and entropy of the formation of metal complexes in solution is essential for understanding the factors determining their thermodynamic stability and speciation. As a case study, in this report we systematically examine the complexation of silver(I) in acetonitrile (AN) with the following monoamines: n-propylamine (n-pr), n-butylamine (n-but), hexylamine (hexyl), diethylamine (di-et), dipropylamine (di-pr), dibutylamine (di-but), triethylamine (tri-et) and tripropylamine (tri-pr). The study shows that the complex stabilities are quite independent of the length of the substitution chain on the N atom and demonstrates that, in general, the overall enthalpy terms associated with the complex formation are strongly exothermic, whereas the entropy values oppose the complex formations. In addition, we examined the similarity of the formation constants of AgL complexes of the primary monoamines in AN, dimethylsulfoxide (DMSO) and water, which were unexpected on the basis of the difference between the donor properties of solvents.

Highly selective extraction of uranium from wastewater using amine-bridged diacetamide-functionalized silica

A major environmental concern related to nuclear energy is wastewater contaminated with uranium, thus necessitating the development of pollutant-reducing materials with efficiency and effectiveness. Herein, highly selective mesoporous silicas functionalized with amine-bridged diacetamide ligands SBA-15-ABDMA were prepared. Different spectroscopy techniques were used to probe the chemical environment and reactivity of the chelating ligands before and after sorption. The results showed that the functionalized SBA-15-ABDMA had a strong affinity for uranium at low pH (pH = 3) with desirable sorption capacity (68.82 mg/g) and good reusability (> 5). It showed excellent separation performance with a high distribution coefficient (K_d,U > 10⁵ mL/g) and separation factors SF_U/Ln > 1000 at a pH of 3.5 in the presence of lanthanide nuclides, alkaline earth metal and transition metal ions. In particular, SiO₂spheres-ABDMA was used as a column material, which achieved excellent recovery of U(VI) (> 98%) and good reusability for samples of simulated mining and nuclear industries wastewater. XPS and crystallography studies clearly illustrated the tridentate coordination mode of U(VI)/PEABDMA and the mechanism and origin behind the high selectivity for U.

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

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.

Molecular Interpretation of Pharmaceuticals’ Adsorption on Carbon Nanomaterials: Theory Meets Experiments

The ability of carbon-based nanomaterials (CNM) to interact with a variety of pharmaceutical drugs can be exploited in many applications. In particular, they have been studied both as carriers for in vivo drug delivery and as sorbents for the treatment of water polluted by pharmaceuticals. In recent years, the large number of experimental studies was also assisted by computational work as a tool to provide understanding at molecular level of structural and thermodynamic aspects of adsorption processes. Quantum mechanical methods, especially based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were mainly applied to study adsorption/release of various drugs. This review aims to compare results obtained by theory and experiments, focusing on the adsorption of three classes of compounds: (i) simple organic model molecules; (ii) antimicrobials; (iii) cytostatics. Generally, a good agreement between experimental data (e.g. energies of adsorption, spectroscopic properties, adsorption isotherms, type of interactions, emerged from this review) and theoretical results can be reached, provided that a selection of the correct level of theory is performed. Computational studies are shown to be a valuable tool for investigating such systems and ultimately provide useful insights to guide CNMs materials development and design.

Effect of the Counterion on Circularly Polarized Luminescence of Europium(III) and Samarium(III) Complexes

Each enantiopure europium(III) and samarium(III) nitrate and triflate complex of the ligand L, with L = N,N′-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine ([LnL(tta)₂]·NO₃ and [LnL(tta)₂(H₂O)]·CF₃SO₃, where tta = 2-thenoyltrifluoroacetylacetonate) has been synthesized and characterized from a spectroscopic point of view, using a chiroptical technique such as electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). In all cases, both ligands are capable of sensitizing the luminescence of both metal ions upon absorption of light around 280 and 350 nm. Despite small differences in the total luminescence (TL) and ECD spectra, the CPL activity of the complexes is strongly influenced by a concurrent effect of the solvent and counterion. This particularly applies to europium(III) complexes where the CPL spectra in acetonitrile can be described as a weighed linear combination of the CPL spectra in dichloromethane and methanol, which show nearly opposite signatures when their ligand stereochemistries are the same. This phenomenon could be related to the presence of equilibria interconverting solvated, anion-coordinated complexes and isomers differing by the relative orientation of the tta ligands. The difference between some bond lengths (M–N bonds, in particular) in the different species could be at the basis of such an unusual CPL activity.

Triflate ([EuL(tta)₂(H₂O)]·CF₃SO₃) and nitrate ([EuL(tta)₂]·NO₃) complexes, with L = N,N′-bis(2-pyridylmethylidene)-1,2-(R,R or S,S)-cyclohexanediamine, where tta = 2-thenoyltrifluoroacetylacetonate, show nearly opposite circularly polarized luminescence (CPL) signatures when dissolved in dichloromethane (DCM) or methanol (MeOH), even though their ligand stereochemistries remain unchanged. The presence (in DCM) and absence (in MeOH) of the counterion in the inner coordination sphere determine a strong change of the CPL activity of the relative europium(III) complex.

Unusual Fluorescence Quenching-Based Al3+ Sensing by an Imidazolylpiperazine Derivative. β-Cyclodextrin Encapsulation-Assisted Augmented Sensing

We report in this paper an unusual β-cyclodextrin mediated-aluminum (III) ion sensing based on augmented quenching of fluorescence. The fluorescent sensing of metal ions by a new ligand prepared (L = 4-[{4-(1H-imidazol-1-yl)phenyl]imino}methyl]piperazine-1-carboxaldehyde) has been investigated as well as the effect of the supramolecular complex formation with β-CD. In aqueous solution, L shows an increase of fluorescence due to the interaction with β-cyclodextrin with a formation constant of 77 (± 12) M^-1. The ROESY NMR spectrum clearly indicates that L is encapsulated by β-CD. Theoretical calculations show the possible structure both of the L-β-CD adduct and of the coordination mode of Al³⁺ ion to L. In the presence of β-CD, the piperazine adopts a distorted conformation. It leads to an enhanced Al³⁺ sensing by the compound in its supramolecular complexed form. The lower limit of detection of Al³⁺ ions is 6.00 × 10^-8 mol L^-1. This detection limit slightly expands for L in the presence of β-CD.

Ligand rigidity and electronic effect on the complexation of hexavalent plutonyl with three dicarboxylic acids: a combined spectrophotometric and computational study

Both the ligands’ rigidity and electronic structure contribute to the stability and coordination mode of Pu(vi) complexes with three dicarboxylic acids.

Complexation of Light Trivalent Lanthanides with N-(2-Hydroxyethyl)ethylenediamine-N,N',N'-triacetic Acid in Aqueous Solutions: Thermodynamic Analysis and Coordination Modes

N-(2-Hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA, denoted as H₃L) is a strong chelating ligand that is widely used in the separation of f elements as relevant to the nuclear fuel cycle. There is much to be known about the structure and composition of the coordination sphere of the complexes of HEDTA with lanthanides. The complexation of HEDTA with light lanthanides (La³⁺, Nd³⁺, and Eu³⁺) was investigated thermodynamically and structurally in aqueous solutions. Potentiometry and microcalorimetry were performed to acquire the complexation constants (25-70 °C) and enthalpies (25 °C), respectively, at I = 1.0 mol·L^-1 NaClO₄. Coordination modes of the complexes were analyzed by luminescence spectroscopy and NMR spectroscopy. The results indicate that there are two successive Ln³⁺/HEDTA complexes, LnL_aq and Ln₂(H_-1L)₂^2- (Ln³⁺ refers to La³⁺, Nd³⁺, and Eu³⁺; H_-1L^4- refers to deprotonation of the hydroxyl group) during titration. The hydroxyl group of HEDTA is coordinated in the Ln³⁺/HEDTA complex. The dinuclear Ln₂(H_-1L)₂^2- complex is present as a carboxyl-bridged centrosymmetric dimer, and two carboxyl groups in bridging positions are coordinated to two adjacent Ln³⁺ cations. Complexation of NdL_aq is exothermic, while formation of the hydrolytic complex Nd₂(H_-1L)₂^2- is endothermic. Both NdL_aq and Nd₂(H_-1L)₂^2- complexes are driven by entropic force. These data will help to predict the behavior of lanthanides in the separation process, where HEDTA is used as the aqueous complexant.

A simple urea-based multianalyte and multichannel chemosensor for the selective detection of F−, Hg2+ and Cu2+ in solution and cells and the extraction of Hg2+ and Cu2+ from real water sources: a logic gate mimic ensemble

Herein, a hydrazine-based chromogenic, fluorogenic and electrochemical chemosensor BCC [1,5-bis(4-cyanophenyl) carbonohydrazide] was reported.

para-Aminosalicylic acid in the treatment of manganese toxicity. Complexation of Mn2+ with 4-amino-2-hydroxybenzoic acid and its N-acetylated metabolite

Manganese excess can induce in humans neurological disorders known as manganism.