Metal Complexes Research Articles

A Comparative Study of Green and Conventional Synthesis of Schiff Base And its Metal Complexes from 3, 5-Dichloro Aniline And 3-Chloro-4 Fluroaniline

A Comparative Study of Green and Conventional Synthesis of Schiff Base And its Metal Complexes from 3, 5-Dichloro Aniline And 3-Chloro-4 Fluroaniline

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications.

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Terpyridine-Decorated Polymer Nanosphere Latex: Template Nanocarriers for the Synthesis of Cu-CeO2 Hollow Spheres.

Water-soluble polymers with the ability to complex metal ions through complexing ligands have attracted significant interest in diverse domains, such as optical or catalyst applications. In this paper, we successfully synthesized, through a one-pot process combining polymerization-induced self-assembly and reversible addition-fragmentation chain transfer polymerization, aqueous dispersions of terpyridine-decorated poly[poly(ethylene glycol)methyl ether methacrylate]-b-poly(methyl methacrylate) (tpy-PPEGMA-b-PMMA) amphiphilic block copolymers. The in-situ formation of well-defined amphiphilic block copolymers and their self-assembly led to nanosphere latex with the hydrodynamic diameters increasing from 17 to 52 nm and the length of the copolymers increasing from 21,000 to 51,000 g·mol-1. These aqueous dispersed tpy-PPEGMA-b-PMMA nanospheres effectively complex metal ions, such as Cu2+, in a stoichiometric ratio of 2:1. Subsequently, these metal-complexed nanospheres were employed as soft template nanocarriers to control, on the nanometer scale, the dispersion of metal on a nanostructured support. This is exemplified by the synthesis of copper supported on cerium oxide hollow spheres (Cu-CeO2) using Cu2+-tpy-PPEGMA-b-PMMA as template nanocarriers and CeO2 nanoparticles. This novel assembly engineering strategy for the preparation of atomically dispersed metal on a nanostructured support was highlighted through the utilization of Cu-CeO2 hollow spheres as an electrocatalyst for the nitrate reduction reaction (NO3RR) to NH3. These encouraging outcomes emphasize the potential of metal-metal oxide-nanostructured materials to treat contaminated water sources with nitrate while allowing the green production of ammonia.

Mechanistic Insights into Micelle-Enhanced Nanofiltration for Heavy Metal Removal: Transformation of Ion Transport and Fouling Phenomena.

Toxic heavy metals are widely present in typical scenarios, such as mines and electroplating wastewater, presenting significant risks to biological and environmental safety. Membrane processes encounter a challenge in effectively intercepting heavy metals due to their small hydration radius. This research showcases the high efficiency of micelle-enhanced nanofiltration (MENF) in removing heavy metals. At the critical micelle concentration, sodium dodecyl sulfate demonstrated a high removal of Cu2+, Ni2+, Zn2+, and Cd2+ while maintaining substantial potential for complexation of heavy metals. The formation of micelles and the bonding of heavy metals with surfactants bolstered the resistance of heavy metal ions to transmembrane transport. The presence of heavy metals in ionic form in wastewater facilitated their complexation with surfactants or micelles. Notably, the valence state and concentration of interfering ions in the environment could slightly influence the removal of heavy metals by MENF. Additionally, MENF displayed remarkable antifouling properties. The loose gel layer created by surfactant molecules and the micelle enhanced the membrane permeability and reduced the scaling tendency of heavy metals. This study contributes to an improved understanding of the mechanisms involved in heavy metal rejection by using MENF.

Direct synthesis of partially ethoxylated branched polyethylenimine from ethanolamine

We report here a method to make a branched and partially ethoxylated polyethyleneimine derivative directly from ethanolamine. The polymerization reaction is catalysed by a pincer complex of Earth-abundant metal, manganese, and produces water as the only byproduct. Industrial processes to produce polyethyleneimines involve the transformation of ethanolamine to a highly toxic chemical, aziridine, by an energy-intensive/waste-generating process followed by the ring-opening polymerization of aziridine. The reported method bypasses the need to produce a highly toxic intermediate and presents advantages over the current state-of-the-art. We propose that the polymerization process follows a hydrogen borrowing pathway that involves (a) dehydrogenation of ethanolamine to form 2-aminoacetaldehyde, (b) dehydrative coupling of 2-aminoacetaldehyde with ethanolamine to form an imine derivative, and (c) subsequent hydrogenation of imine derivative to form alkylated amines.

The Hydrogen Evolution Reaction: Using Molecular Design in Transition Metal Complexes to Control Catalytic Microenvironments on Electrode Surfaces

AbstractHydrogen gas and its production from renewable power sources will be an important part of decreasing global reliance on fossil fuels and developing a sustainable energy economy. Efficient electrocatalysis, however, relies on the delivery of both protons and electrons; ideally in a concerted fashion to avoid high energy intermediates, prevent charge build‐up, and circumvent large kinetic barriers. While this can be achieved using ligand design in homogenous molecular transition metal catalysts (specifically incorporating proton shuttles in the secondary coordination sphere), heterogeneous systems are more desirable from an industrial perspective due to their ease of use and enhanced durability. Supporting transition metal catalysts on electrode surfaces is therefore a promising approach for developing next generation electrocatalysts that retain molecular level control in interfacial environments. This review will first cover key design principles from natural systems, such as hydrogenase enzymes, and then survey some representative examples of synthetic homogeneous hydrogen evolution electrocatalysts that incorporate these important features. We will then discuss transition metal species that have been supported on electrode materials, with a focus on recent advances in the field, and the major challenges that remain.

Computational Screening of Putative Catalyst Transition Metal Complexes as Guests in a Ga4L612- Nanocage.

Metal-organic cages form well-defined microenvironments that can enhance the catalytic proficiency of encapsulated transition metal complexes (TMCs). We introduce a screening protocol to efficiently identify TMCs that are promising candidates for encapsulation in the Ga4L612- nanocage. We obtain TMCs from the Cambridge Structural Database with geometric and electronic characteristics amenable to encapsulation and mine the text of associated manuscripts to curate TMCs with documented catalytic functionality. By docking candidate TMCs inside the nanocage cavity and carrying out electronic structure calculations, we identify a subset of successfully optimized candidates (TMC-34) and observe that encapsulated guests occupy an average of 60% of the cavity volume, in line with previous observations. Notably, some guests occupy as much as 72% of the cavity as a result of linker rotation. Encapsulation has a universal effect on the electrostatic potential (ESP), systematically decreasing the ESP at the metal center of each TMC in the TMC-34 data set, while minimally altering TMC metal partial charges. Collectively these observations support geometry-based screening of potential guests and suggest that encapsulation in Ga4L612- cages could electrostatically stabilize diverse cationic or electropositive intermediates. We highlight candidate guests with associated known reactivity and solubility most amenable for encapsulation in experimental follow-up studies.

The nature of metallophilic interactions in closed-shell d8-d8 metal complexes.

We have quantum chemically analyzed the closed-shell d8-d8 metallophilic interaction in dimers of square planar [M(CO)2X2] complexes (M = Ni, Pd, Pt; X = Cl, Br, I) using dispersion-corrected density functional theory at ZORA-BLYP-D3(BJ)/TZ2P level of theory. Our purpose is to reveal the nature of the [X2(CO)2M]⋯[M(CO)2X2] bonding mechanism by analyzing trends upon variations in M and X. Our analyses reveal that the formation of the [M(CO)2X2]2 dimers is favored by an increasingly stabilizing electrostatic interaction when the M increases in size and by more stabilizing dispersion interactions promoted by the larger X. In addition, there is an overlooked covalent component stemming from metal-metal and ligand-ligand donor-acceptor interactions. Thus, at variance with the currently accepted picture, the d8-d8 metallophilicity is attractive, and the formation of [M(CO)2X2]2 dimers is not a purely dispersion-driven phenomenon.

In situ X-ray absorption spectroscopy using the FAME autoclave: a window into fluid-mineral-melt interactions in the Earth’s crust

ABSTRACT We discuss the X-ray absorption spectroscopy (XAS) methods elaborated using the high pressure and high-temperature autoclaves installed at FAME and FAME-UHD beamlines. These methods are based on the in situ acquisition of X-ray transmission and fluorescence spectra of hydrothermal fluids and silicate melts and enable the derivation of both solubility and speciation information about metal complexes. The technological assets of our autoclaves are described across a wide range of experimental conditions spanning from different types of hydrothermal fluids, from liquid-like to vapor-like densities having metal concentrations of <1–10,000 ppm, to magmatic fluid-melt systems at 1000°C. Scientific examples are presented to illustrate the use and the advantages of our spectroscopic ‘micro-batch’ reactors. Finally, the integration of our autoclave setups on the FAME-UHD crystal analyzer spectrometer and the benefits of this technique are demonstrated.

Complexation with Metal Ions Affects Chlorination Reactivity of Dissolved Organic Matter: Structural Reactomics of Emerging Disinfection Byproducts.

Metal ions are liable to form metal-dissolved organic matter [dissolved organic matter (DOM)] complexes, changing the chemistry and chlorine reactivity of DOM. Herein, the impacts of iron and zinc ions (Fe3+ and Zn2+) on the formation of unknown chlorinated disinfection byproducts (Cl-DBPs) were investigated in a chlorination system. Fe3+ preferentially complexed with hydroxyl and carboxyl functional groups, while Zn2+ favored the amine functional groups in DOM. As a consequence, electron-rich reaction centers were created by the C-O-metal bonding bridge, which facilitated the electrophilic attack of α-C in metal-DOM complexes. Size-reactivity continuum networks were constructed in the chlorination system, revealing that highly aromatic small molecules were generated during the oxidation and decarbonization of metal-DOM complexes. Molecular transformation related to C-R (R represents complex sites) loss was promoted via metal complexation, including decarboxylation and deamination. Consequently, complexation with Fe3+ and Zn2+ promoted hydroxylation by the C-O-metal bonding bridge, thereby increasing the abundances of unknown polychlorinated Cl-DBPs by 9.6 and 14.2%, respectively. The study provides new insights into the regulation of DOM chemistry and chlorine reactivity by metal ions in chlorination systems, emphasizing that metals increase the potential health risks of drinking water and more scientific control standards for metals are needed.

Biological and Computational Studies of Hydrazone based Transition Metal(II) Complexes.

In the chronicles of human history, infectious diseases played a pivotal role, influencing societies, steering advancements in medicine, and significantly impacting the well-being of people worldwide. Consequently, in the pursuit of identifying effective combating agents for infectious ailments, the Co(II), Ni(II), Cu(II), Zn(II) complexes of N'-(4-nitrobenzylidene)benzohydrazide were synthesized in the current investigation. Numerous spectral and physical analysis were conducted to characterize the compounds which revealed octahedral stereochemistry of complexes. The anti-tuberculosis, anti-inflammatory, antibacterial and antifungal investigations demonstrated that the compounds (1-5) have significant efficacy for these infectious ailments. The [Zn(L)2(H2O)2] complex (5) has comparable TB inhibition potency to streptomycin as shown by MIC value of 0.0196 ± 0.0003 µmol/mL. Additionally, the anti-inflammatory, antibacterial and antifungal studies also revealed the comparable inhibiting property of (5) to standard drugs with significant IC50 (07.49 ± 0.08 µM) and MIC (0.0098 µmol/mL) values. Furthermore, pharmacophore modeling with addition of molecular docking, DFT, MESP, ADMET were employed against (1-5) to give a new insight in biological evaluations. The pharmacophore modeling suggested that (5) has a distinctive pharmacophoric features including cationic sites, hydrogen-bond donors and acceptors which provide valuable insights into drug design for pharmacological applications. Moreover, another in silico investigations authenticate the bioactivity of (5).

Unveiling Anti-malarial, Antimicrobial, Antioxidant Efficiency and Molecular Docking Study of Synthesized Transition Metal Complexes Derived From Heterocyclic Schiff Base Ligands.

Malaria, a persistent and ancient adversary, continues to impact vast regions worldwide, afflicting millions and severely affecting human health and well-being. Recently, despite significant progress in combating this parasitic disease, malaria remains a major global health concern, especially in areas with limited resources and vulnerable populations. Consequently, identifying and developing effective agents to combat malaria and its associated dysfunctions is essential therefore the two new Schiff base ligands incorporated Co(II), Ni(II), Cu(II) and Zn(II) ions were synthesized and thoroughly characterized. The synthesized compounds were assessed for in vitro anti-malarial and antimicrobial efficacy, compounds (9, 10) demonstrated highest potential with IC50=1.08±0.09 to 1.18±0.04 μM against P. falciparum and MIC=0.0058 μmol/mL against C. albicans and E. coli, respectively. The complexes (5, 6) were effectively reduce mitigate oxidative stress with lowest IC50 value of 2.69±0.12 to 2.87±0.09 μM. Moreover, the biological findings were reinforced by a molecular docking investigation involving the potential compounds (2, 7-10) against dihydroorotate dehydrogenase and sterol 14-alpha demethylase proteins which exposed complex's excellent biological response than their parent ligands. ADMET profiling was used to confirm the compounds' oral drug-like features. This research offers promising prospects for future multi-functional drug innovations targeting malaria, pathogenic infections, and oxidative stress.

Synthesis, Characterization, Antimicrobial Activity, DFT, Molecular Docking, and ADMET of 4-Chlorophenyazolquniolin-8-ol and Its Metal Complexes

In this study, we prepared 4-chlorophenylazoquinoline, a derivative of 8-hydroxyquinoline, with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) ions to create metal complexes. We used various physical and spectroscopic methods to characterize the compound and its metal complexes, including molar conductivity measurements, melting point analysis, elemental analysis, electronic absorption spectroscopy, mass spectrometry, magnetic resonance spectroscopy, infrared spectroscopy, and thermogravimetric analysis. The octahedral geometry of all prepared complexes has been confirmed. To assess the antimicrobial activity, we examined two types of bacterial strains and two types of fungal strains. The antimicrobial activity of the prepared compounds was observed, and the higher increase was observed in the copper complex. The compounds were studied computationally after optimizing the angles, lengths, and bonds using the basic set 6-31G(d,p)/LANL2DZ. The molecular docking study of the compounds with the Alzheimer's disease protein 4BDT showed significant activity in binding to the amino acids of HL, C1, C2, C3, C4, and C5 compounds, with affinity energies of -6.4, -6.9, -6.9, -6.7, and -7.2 kcal.mol-1 for the compounds, respectively. To evaluate the safety of the prepared compounds in different drug designs, we employed the ADMET study, reducing the risk of failure in advanced drug design stages. The results of the ADMET showed a relative decrease in the toxicity and carcinogenicity factor. However, there are indications of metabolic risk and cellular uptake, requiring further study.

Extraction of Cynaroside from Honeysuckle by Nonionic Surfactant-Mediated Aqueous Extraction with Cloud Point Enrichment and Purification by Metal Complexation

Extraction of Cynaroside from Honeysuckle by Nonionic Surfactant-Mediated Aqueous Extraction with Cloud Point Enrichment and Purification by Metal Complexation

Impact of ligand substituents on the spiral arrangement in glutarohydrazide-based binuclear-iron(II) helicates

Coordination-driven self-assembly, particularly, helical metal complexes are quite interesting considering their distinctive architectures. Herein, we assemble new Fe(II) compounds namely, [Fe2(L1)2](BF4)4·2H2O, 1 and [Fe2(L2)2](BF4)4, 2 from flexible glutarohydazide ligands featuring helical-like di-nuclear arrays. Structurally, in all the compounds, the two chelating ligands were arranged differently, i.e. inverted U-shaped conformation for 1 and a twisted spiral arrangement for 2 were observed respectively. Interestingly, the observed structural variations of all compounds are a result of the ligand substituents in the six positions of the pyridyl moiety in which the relatively bulky methyl group substituted ligand resists the spiral arrangement which was observed in the Br substituted analog. Magnetic investigations revealed that compounds 1 and 2 are in the high spin state at all the measured temperature ranges. Further ligand fine-tunings in the pyridyl-aldehyde moiety for the presented helical-like arrays bearing relatively strong ligand field strength are suggested for achieving the spin crossover (SCO) event.

Photophysical properties of benzo[i]dipyrido[3,2-a:2′,3′-c] phenazine (dppn) – A prospective ligand for light-activated anticancer complexes

Benzo[i]dipyrido[3,2-a:2′,3′c]phenazine (dppn) is a prospective ligand for constructing light-activated anticancer complexes of platinum metals. In spite of practical importance, only scarce information on the dppn photophysics and photochemistry was found in the literature. In this work photophysical properties of dppn in acetonitrile solutions were studied by means of stationary and laser flash photolysis, time-resolved luminescence, time-resolved singlet oxygen detection and ultrafast TA spectroscopy. Quantitative characteristics of luminescence (quantum yield 0.26, lifetime 52 ns in deaerated solutions) were measured. Triplet state of the initial compound 3dppn* is formed with the quantum yield estimated as 0.4 from the singlet oxygen production; the main channels of 3dppn* are quenching by dissolved oxygen and self-quenching by the ground state of dppn. Combining the data of ultrafast TA absorption and time-resolved luminescence, we detected the formation of “dark” (not emissive) excited state of dppn with the decay time ca. 150 ps. Two hypotheses on the nature of the dark state were put forward.

Sorbate metal complexes as newer antibacterial, antibiofilm, and anticancer compounds

BackgroundThe ineffectiveness of treatments for infections caused by biofilm-producing pathogens and human carcinoma presents considerable challenges for global public health organizations. To tackle this issue, our study focused on exploring the potential of synthesizing new complexes of Co(II), Cu(II), Ni(II), and Zn(II) with sorbic acid to enhance its antibacterial, antibiofilm, and anticancer properties.MethodsFour novel complexes were synthesized as solid phases by reacting sorbic acid with Co(II), Cu(II), Ni(II), and Zn(II). These complexes were characterized by various technique, including infrared spectra, UV–Visible spectroscopy, proton nuclear magnetic resonance (1H NMR), and thermal analysis techniques, including thermogravimetry (TG).ResultsThe data acquired from all investigated chemical characterization methods confirmed the chemical structure of the sorbate metal complexes. These complexes exhibited antibacterial and antibiofilm properties against both Gram-positive and Gram-negative bacteria. Furthermore, these complexes enhanced the antibacterial effects of commonly used antibiotics, such as gentamicin and imipenem, with fractional inhibitory concentration (FIC) indices ≤ 0.5. Notably, the Cu(II) complex displayed the most potent antibacterial and antibiofilm activities, with minimum inhibitory concentration (MIC) values of 312.5 µg/mL and 625.0 µg/mL for Bacillus cereus and Escherichia coli, respectively. Additionally, in vitro assays using the methyl thiazolyl tetrazolium (MTT) method showed inhibitory effects on the growth of the human colon carcinoma cell line (HCT-116 cells) following treatment with the investigated metal complexes. The IC50 values for Co(II), Cu(II), Zn(II), and Ni(II) were 3230 µg/mL, 2110 µg/mL, 3730 µg/mL, and 2240 µg/mL, respectively.ConclusionOur findings offer potential for pharmaceutical companies to explore the development of novel combinations involving traditional antibiotics or anticancer drugs with sorbate copper complex.

Preparation of transparent and flexible regenerated kenaf CNF composite films with curcumin-metal complex for food packaging applications

Cellulose nanofibers (CNF) derived from kenaf plant were combined with curcumin (Cur)-metal complexes to produce regenerated composite films. Cur was used to synthesize homoleptic Cur-metal complexes with diamagnetic Zn(II) and paramagnetic Cu(II) metal ions. Cur-Zn(II) complex and Cur-Cu(II) complex were synthesized under the same reaction conditions to check the synergistic effect of engaging the diketone electrons of Cur with strong coordination bonds with two different metal ions. The synthesized Cur-metal complexes were used as fillers to produce CNF composite films for biodegradable food packaging film. Results showed that the Cur-Zn(II) complex-loaded CNF composite films exhibit higher antioxidant activity than other films whereas Cur-Cu(II) complex-loaded CNF composite films showed prominent antibacterial activity against foodborne pathogenic bacteria such as Listera monocytogenes and Escherichia coli. It is due to the coordination of the diketone electron of Cur with diamagnetic and paramagnetic metal ions that influenced the antioxidant and antibacterial properties of Cur. Overall, this study proved that it was possible to use Cur in the form of Cur-Zn(II) complex as an antioxidant filler and Cur-Cu(II) complex as an antibacterial filler for active food packaging applications.

Synthesis, characterization and antioxidant screening of a 1,10-phenanthroline-based tetraza-macrocyclic ligand and its nickel complex with therapeutic potential and catalytic significance

Abstract In this study, we present a synthetic route for the preparation of a novel 1,10- phenanthroline-based tetraza-macrocyclic ligand, 5,12,25,28-tetraazaheptacyclo [14.8.4.2⁴,⁷.210,13.0⁶,11.019,27.022,26]dotriaconta-1 (25),4,6,8,10,12,16(28),17,19(27),20,22(26),23,29, 31-tetradecaene, 3 and its corresponding nickel complex, (28Z)-1,3,6,31-tetraaza-2-nickelaoctacyclo [17.9.3.2⁷,28.0³,16.0⁴,13.0⁵, 10.022,30.025,29]tritriaconta-4(13),5(10),6,8,11,14,16,19(31),20,22(30), 23,25(29),26,28(32)-tetradecaene, 8. The ligand was synthesized via a condensation reaction involving 2,9-dimethyl-1,10-phenanthroline and 2,9-dicarbaldehyde-1,10 phenanthroline, followed by nickel metal complexation. Fourier-transformed infrared (FT-IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and thermal analyses were employed to characterize the ligand and its Ni complex. Their ADMET parameters and potential macromolecular targets calculations showed they have therapeutic potentials. The antioxidant assay shows that Ni-complex is approximately 9 times more potent than the ligand with IC50 values of 0.045 mg/ml and 0.404 mg/ml, respectively. Their microspecies distribution which was predicted using ChemAxon Predictor revealed their catalytic potentials The reaction mechanisms involved are discussed. The 1,10-phenanthroline-based macrocyclic ligand and its nickel complex significantly expand the structural diversity within the tetraza-macrocyclic ligand system and serve as base ligands for the development of possible derivatives, with concomitant applicability in drug development and catalysis.

Selective Liquid-Liquid Extraction of Thorium(IV) from Rare-Earth Element Mixtures.

One of the major challenges in processing rare-earth element (REE) materials arises from the large amounts of radioactive thorium (Th) that are often found within REE minerals, encouraging enhanced metal separation procedures. We report here a study aimed at developing improved systems for REE processing with the goal of efficient extraction of Th(IV) from acidic solution. A tripodal ligand, TRPN-CMPO-Ph, was prepared that utilizes carbamoylmethylphosphine oxide (CMPO) chelators tethered to a tris(3-aminopropyl)amine (TRPN) capping scaffold. The ligand and its metal complexes were characterized by using elemental analysis, NMR, Fourier transform infrared spectroscopy, mass spectrometry, and luminescence spectroscopy. Using a liquid-liquid metal extraction protocol, TRPN-CMPO-Ph selectively extracts Th(IV) at an efficiency of 79% from a mixture of Th(IV), UO22+, and all rare-earth metal cations (except promethium) dissolved in nitric acid into an organic solvent. Th(IV) extraction selectivity is maintained upon extraction from a mixture that approximates a typical monazite leach solution containing several relevant lanthanide ions, including two ions at higher concentration relative to Th(IV). Comparative studies with a tris(2-aminoethyl)amine (TREN)-capped derivative are presented and support the need for a larger TRPN capping scaffold in achieving Th(IV) extraction selectivity.