Epimerization effects on coordination behaviours of phenanthroline-based phosphine-oxide ligands with uranyl ions.

Epimers of the (1,10-phenanthroline-2,9-diyl)bis(ethyl(phenyl)phosphine oxide) (Et-Ph-BPPhen) ligand with two chiral centers (R,R/S,S and R,S) were synthesized. The configurational effects on the coordination ability and mechanism between these epimeric ligands and uranyl ions were thoroughly investigated. This work is helpful to reveal the effects of different conformations of epimeric ligands on their coordination properties.

Preorganization Effects on Eu(III) Ion Coordination by Dipyridyl-Phenanthroline Ligands: A Combined Experimental and Theoretical Analysis.

Although 1,10-phenanthroline has been proven to hold a strong complexing capacity for f-block elements and their derivatives have been applied in many fields, research on more highly or completely rigid phenanthroline ligands is still rare due to the challenging syntheses. Here, we reported three tetradentate ligands 2,9-di(pyridin-2-yl)-1,10-phenanthroline (L1), 12-(pyridin-2-yl)-5,6-dihydroquinolino[8,7b][1,10]phenanthroline (L2), and 5,6,11,12-tetrahydrobenzo[2,1-b:3,4-b']bis([1,10]phenanthroline) (L3) with increasing preorganization on the side chain; among which, L3 is fully preorganized. Their complexation reactions with Eu(III) were systematically investigated by electrospray ionization mass spectrometry (ESI-MS), UV-vis titrations, and single-crystal structures. It is found that all three ligands form only 1:1 M/L complexes with Eu(III). The single-crystal structures revealed that the three ligands hold similar coordination modes, while their stability constants determined by UV-vis titrations were L3 (4.80 ± 0.01) > L2 (4.38 ± 0.01) > L1 (3.88 ± 0.01). This trend is supported not only by the thermodynamic stability of rigid ligands compared to free ligands but also by the conclusion that rigid ligands exhibit faster reaction rates (lower energy barrier) than free ligands kinetically. This work is helpful in providing theoretical guidance for the subsequent development of highly preorganized chelating ligands with strong coordination ability and high selectivity for f-block elements.

Incorporating Two Crown Ether Struts into the Backbone of Robust Zirconium-Based Metal-Organic Frameworks as Custom-Designed Efficient Collectors for Radioactive Metal Ions.

The incorporation of crown ether into metal-organic frameworks (MOFs) is garnered significant attention because these macrocyclic units can fine-tune the inherent properties of the frameworks. However, the synthesis of flexible crown ethers with precise structures as the fundamental building blocks of crystalline MOFs remains a challenging endeavor, with only a limited number of transition metal examples existing to date. Herein, 18-crown-6 and 24-crown-8 struts are successfully incorporated into the skeleton of zirconium-based MOFs to obtain two new and stable crown ether-based MOFs, denoted as ZJU-X100 and ZJU-X102. These newly developed MOFs displayed high porosity and remarkable stability when exposed to various solvents, boiling water, pH values, and even concentrated HCl conditions. Thanks to their highly ordered porous structure and high-density embedding of specific binding sites within tubular channels, these two MOFs exhibited extremely fast sorption kinetics and demonstrated outstanding performance in the uptake of strontium and cesium ions, respectively. Furthermore, the structures of Sr-adsorbed ZJU-X100 and Cs-adsorbed ZJU-X102 are solved and confirmed the precise location of Sr2+/Cs+ in the cavity of 18-crown-6/24-crown-8. This makes modular mosaic of different crown ethers into the skeleton of stable zirconium-based MOFs possible and promote such materials have broad applications in sorption, sensing, and catalysis.

Interplay between the ß-lactam side chain and an active-site mobile loop of NDM-1 in penicillin hydrolysis as a potential target for mechanism-based inhibitor design.

Metallo-ß-lactamases (MßLs) stand as significant resistant mechanism against ß-lactam antibiotics in Gram-negative bacteria. The worldwide dissemination of New Delhi metallo-ß-lactamases (NDMs) intensifies antimicrobial resistance, posing severe threats to human health due to the absence of inhibitors available in clinical therapy. L3, a flexible ß-hairpin loop flanking the active site in MßLs, has been proven to wield influence over the reaction process by assuming a crucial role in substrate recognition and intermediate stabilization. In principle, it potentially retards product release from the enzyme, consequently reducing the overall turnover rate although the details regarding this aspect remain inadequately elucidated. In this study, we crystallized NDM-1 in complex with three penicillin substrates, conducted molecular dynamics simulations, and measured the steady-state kinetic parameters. These analyses consistently unveiled substantial disparities in their interactions with loop L3. We further synthesized a penicillin V derivative with increased hydrophobicity in the R1 side chain and co-crystallized it with NDM-1. Remarkably, this compound exhibited much stronger dynamic interplay with L3 during molecular dynamics simulation, showed much lower Km and kcat values, and demonstrated moderate inhibitory capacity to NDM-1 catalyzed meropenem hydrolysis. The data presented here may provide a strategic approach for designing mechanism-based MßL inhibitors focusing on structural elements external to the enzyme's active center.

Enhancing the Selectivity of Trivalent Actinide over Lanthanide Using Asymmetrical Phenanthroline Diamide Ligands.

Phenanthroline diamide ligands have been widely used in the separation of trivalent actinides and lanthanides, but little research has focused on extractants with asymmetrical substitutes. Two novel asymmetrical phenanthroline-based ligands N2,N2,N9-triethyl-N9-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DE-ET-DAPhen) and N2-ethyl-N9,N9-dioctyl-N2-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DO-ET-DAPhen) were first synthesized in this work, whose extraction ability and complexation mechanism to trivalent actinides [An(III)] and lanthanides [Ln(III)] were systematically investigated. The ligands dissolved in n-octanol exhibit good extraction ability and high selectivity toward Am(III) in acidic solutions. The complexation mechanism of the ligands with Ln(III) in solution and solid state was analyzed using slope analysis, 1H NMR spectrometric titration, ESI-MS, and calorimetric titration. It is revealed that the ligands complex with Am(III)/Eu(III) with 1:1 stoichiometry. The stability constant (log ß) of the complexation reaction of Eu(III) with DE-ET-DAPhen determined by UV-vis spectrophotometric and calorimetric titration is higher than that of DO-ET-DAPhen, indicating the stronger complexation ability of DE-ET-DAPhen. Meanwhile, the calorimetric titration results show that the complexation process is exothermic with a decreased entropy. The structures of 1:1 complexes of Eu(III) and Nd(III) with DE-ET-DAPhen were analyzed through single-crystal X-ray diffraction. This work proves that ligands containing asymmetrical functional groups are promising for An(III)/Ln(III) separation, which shows great significance in efficient extractants designed for the spent nuclear fuel reprocessing process.

Hollow Core-Shell Bismuth Based Al-Doped Silica Materials for Powerful Co-Sequestration of Radioactive I2 and CH3 I.

Developing pure inorganic materials capable of efficiently co-removing radioactive I2 and CH3 I has always been a major challenge. Bismuth-based materials (BBMs) have garnered considerable attention due to their impressive I2 sorption capacity at high-temperature and cost-effectiveness. However, solely relying on bismuth components falls short in effectively removing CH3 I and has not been systematically studied. Herein, a series of hollow mesoporous core-shell bifunctional materials with adjustable shell thickness and Si/Al ratio by using silica-coated Bi2 O3 as a hard template and through simple alkaline-etching and CTAB-assisted surface coassembly methods (Bi@Al/SiO2 ) is successfully synthesized. By meticulously controlling the thickness of the shell layer and precisely tuning of the Si/Al ratio composition, the synthesis of BBMs capable of co-removing radioactive I2 and CH3 I for the first time, demonstrating remarkable sorption capacities of 533.1 and 421.5 mg g-1 , respectively is achieved. Both experimental and theoretical calculations indicate that the incorporation of acid sites within the shell layer is a key factor in achieving effective CH3 I sorption. This innovative structural design of sorbent enables exceptional co-removal capabilities for both I2 and CH3 I. Furthermore, the core-shell structure enhances the retention of captured iodine within the sorbents, which may further prevent potential leakage.

Optoelectronic Evolution in Halogen-Doped Organic-Inorganic Halide Perovskites: A First-Principles Analysis.

Cl, Br, and I are elements in the halogen family, and are often used as dopants in semiconductors. When employed as dopants, these halogens can significantly modify the optoelectronic properties of materials. From the perspective of halogen doping, we have successfully achieved the stabilization of crystal structures in CH3NH3PbX3, CH3NH3PbI3-xClx, CH3NH3PbI3-xBrx, and CH3NH3PbBr3-xClx, which are organic-inorganic hybrid perovskites. Utilizing first-principles density functional theory calculations with the CASTEP module, we investigated the optoelectronic properties of these structures by simulations. According to the calculations, a smaller difference in electronegativity between different halogens in doped structures can result in smoother energy bands, especially in CH3NH3PbI3-xBrx and CH3NH3PbBr3-xClx. The PDOS of the Cl-3p orbitals undergoes a shift along the energy axis as a result of variances in electronegativity levels. The optoelectronic performance, carrier mobility, and structural stability of the CH3NH3PbBr3-xClx system are superior to other systems like CH3NH3PbX3. Among many materials considered, CH3NH3PbBr2Cl exhibits higher carrier mobility and a relatively narrower bandgap, making it a more suitable material for the absorption layer in solar cells. This study provides valuable insights into the methodology employed for the selection of specific types, quantities, and positions of halogens for further research on halogen doping.

Organophosphorus Extractants: A Critical Choice for Actinides/Lanthanides Separation in Nuclear Fuel Cycle.

The separation of actinides from lanthanides in spent nuclear fuel reprocessing is a vital step of nuclear fuel cycle process. As one class of mature industrial extractants, the organophosphorus extractants have been widely used for the extraction and separation of actinides and lanthanides in spent fuel reprocessing due to their strong extraction ability and low-cost acquisition. In this concept, the application scope of tributyl phosphate (TBP), bis(2-ethylhexyl) phosphate (HDEHP), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), trialkyl phosphine oxide (TRPO), and purified Cyanex 301 (bis(2,4,4-trimethylpentyl) dithiophosphinic acid, HA301) are introduced, and their extraction mechanism, as well as structure-function relationships for separation of actinides over lanthanides are also discussed. Furthermore, the design criteria, extraction properties and mechanism of several typical newly developed organophosphorus extractants (CMPO-modified calixarene/pillarene, phenanthroline-derived organophosphorus extractants, and phosphate-modified carborane) based on pre-organized skeletons are briefly reviewed. Finally, the important role played by those organophosphorus extractants is emphasized and potential applications in separation of actinides over lanthanides in future advanced nuclear fuel cycle are identified.

Recent advances in the removal of radioactive iodine by bismuth-based materials.

Nowadays, the demand for nuclear power is continue increasing due to its safety, cleanliness, and high economic benefits. Radioactive iodine from nuclear accidents and nuclear waste treatment processes poses a threat to humans and the environment. Therefore, the capture and storage of radioactive iodine are vital. Bismuth-based (Bi-based) materials have drawn much attention as low-toxicity and economical materials for removing and immobilizing iodine. Recent advances in adsorption and immobilization of vapor iodine by the Bi-based materials are discussed in this review, in addition with the removal of iodine from solution. It points out the neglected areas in this research topic and provides suggestions for further development and application of Bi-based materials in the removal of radioactive iodine.

Twofold Interpenetrated Cationic Metal-Organic Framework with Hydrophobic Channels for Effectively Trapping Toxic Oxo-Anions.

Sequestration of toxic oxo-anions (such as 99TcO4- and ClO4-) from wastewater has received constant attention due to the existing serious threat to public health and the sustainability of the environment. In view of the low energy of hydration of TcO4- and ClO4-, cationic metal-organic framework (MOF) materials with the hydrophobic microenvironment are preferred in the selection of sorbents. Herein, a twofold interpenetrated cationic MOF (ZJU-X15) with double-helical chains was constructed by tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPPE) and Cd2+ for the elimination of 99TcO4- and ClO4-. Profiting from hydrophobic channels, ZJU-X15 could remove most of ReO4- (a surrogate for 99TcO4-) and ClO4- in less than 10 and 20 min, respectively. As the result of batch experiments, ZJU-X15 could capture 356 mg of ReO4- and 221 mg of ClO4- per 1 g of sorbent, showcase decent selectivity, and still maintain high removal efficiency for anions after four recycles. Furthermore, the process of anion-exchange was confirmed by ion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy, indicating that target anions successfully entered into the body of ZJU-X15 through anion exchange.

Effectively Decontaminating Protein-Bound Uremic Toxins in Human Serum Albumin Using Cationic Metal-Organic Frameworks.

In the field of replacement of conventional dialysis treatment, searching superior materials for removal of protein-bound uremic toxins is a challenge on account of strong interactions between proteins and uremic toxins. Herein, we first adopted cationic metal-organic frameworks (MOFs), ZJU-X6 and ZJU-X7, as sorbents to decontaminate uremic toxins (p-cresyl sulfate and indoxyl sulfate). ZJU-X6 and ZJU-X7 exhibited innate advantage for sequestration of uremic toxins by utilizing a positive charge framework with exchangeable anions. Especially, ZJU-X6 showed a higher sorption capacity and faster sorption kinetics than those of most reported materials. Moreover, the cationic MOF materials could selectively remove uremic toxins even if in the presence of competitive chloride ions and proteins. Meanwhile, pair distribution function (PDF) and density functional theory (DFT) were employed to elucidate the sorption mechanism between uremic toxins and sorbents. This work suggests an attractive avenue for constructing new types of sorbents to eliminate uremic toxins for uremia treatment.

Separation and Complexation of Trivalent Actinides and Lanthanides by Two Novel Asymmetric N,O-Hybrid Pyridyl Ligands: A Combination of Phosphoryl and Triazinyl Groups.

Two novel asymmetric hard-soft combined ligands, diphenyl(6-(5,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanobenzo-[1,2,4]triazin-3-yl)pyridin-2-yl)phosphine oxide (Ph2-MTP) and butylphenyl(6-(5,9,9-trimethyl-5,6,7,8-tetrahydro-5,8-methanobenzo-[1,2,4]triazin-3-yl)pyridin-2-yl)phosphine oxide (BuPh-MTP), were designed based on the combination of the nature of phosphoryl and triazinyl groups for the selective extraction of trivalent minor actinides from lanthanides. The synthesis of these two ligands and their solvent extraction and complexation behaviors with Am(III) and typical lanthanides were investigated using UV-vis and time-resolved fluorescence spectrophotometry, 1H/31P NMR spectrometry, single-crystal X-ray diffraction, and DFT calculation methods. Solvent extraction experiments showed that both the ligands had strong extraction ability and high selectivity toward Am(III) over Eu(III) from the highly acidic HNO3 solution. The separation factors (SFAm/Eu) of these two ligands ranged from 17 to 26, with the concentrations of HNO3 increasing from 1.0 to 4.0 M. Slope analysis showed that the 3:1 ligand/metal complex was the prevailing species formed during extraction. The formation of the 3:1 ratio of the species of these two ligands with lanthanides was also identified by UV-vis spectrophotometry and single crystallography methods. The stability constants for the formation of the 1:3 complexes of Ph2-MTP and BuPh-MTP with Nd(III) were determined as 7.06 ± 0.015 and 6.67 ± 0.007, respectively. The geometric structures of the 1:3 complexes were clearly illustrated using the single-crystal X-ray diffraction technique and DFT theoretical calculation. This work provides an effective strategy to design new asymmetric hard-soft mixed actinide extractants by combining two different functional groups in one ligand, and the interaction mechanism between the functional groups and metal ions needs to be further investigated.

Two-Fold Interlocking Cationic Metal-Organic Framework Material with Exchangeable Chloride for Perrhenate/Pertechnetate Sorption.

Albeit reported substantial sorbents for elimination of TcO4-, the issue of secondary contamination caused by released counterions (such as NO3-) from the cationic metal-organic framework (MOF) has not come into the sufficient limelight for researchers. Herein, our efforts are dedicated to settle the matter through synthesis of NiCl2 based on the cationic MOF (ZJU-X4). Less harmful chlorides are used as exchangeable anions for replacing hazardous anions. Notably, ZJU-X4 exhibited fast sorption kinetics, high sorption capacity of 395 mg/g, decent selectivity, and excellent reusability in four recycles. The results of ion chromatography revealed that the released chloride ion was equal to sorption of target ions, and pair distribution functions were employed to analyze the changes in ZJU-X4 after sorption of ReO4-, clearly elucidating the anion-exchange mechanism. Furthermore, in the dynamic sorption experiments, ReO4- could be facilely and effectively removed and recovered, showing the value of practical applications. This work indicated that cationic MOF-based metal chloride salts would be a better choice for anionic sorbents.

ZnCl2: A Green Brønsted Acid for Selectively Recovering Rare Earth Elements from Spent NdFeB Permanent Magnets.

The spent neodymium-iron-boron (NdFeB) magnet is a highly valuable secondary resource of rare earth elements (REEs). Hydrometallurgical processes are widely used in recovering REEs from spent NdFeB magnets, but they will consume large amounts of organic chemicals, leading to severe environmental pollution. This work developed an alternative green route to selectively recover REEs from spent NdFeB permanent magnets using a purely inorganic zinc salt. The Hammett acidity measurement showed that concentrated ZnCl2 solutions could be regarded as a strong Brønsted acid. Concentrated ZnCl2 solutions achieved a high separation factor (>1 × 105) between neodymium and iron through simple dissolution of their corresponding oxide mixture. In the simulated recovery process of spent NdFeB magnets, the Nd2O3 product was successfully recovered with a purity close to 100% after selective leaching by ZnCl2 solution, sulfate double-salt precipitation, and oxalic acid precipitation. The separation performance of the ZnCl2 solution for Nd2O3 and Fe2O3 remained almost unchanged after four cycles. The energy consumption and chemical inputs of this process are about 1/10 and half of the traditional hydrometallurgy process separately. This work provides a promising approach for the green recovery of secondary REE resources.

Cobalt Metal-Organic Frameworks with Aggregation-Induced Emission Characteristics for Fluorometric/Colorimetric Dual Channel Detection of Nitrogen-Rich Heterocyclic Compounds.

Nitrogen-rich heterocyclic compounds (NRHCs) are an emerging type of explosive, and their quantification is important in national security inspection and environmental monitoring. Up until now, designing an efficient NRHCs sensing strategy was still in the early stages. Herein, a new metal-organic framework (MOF) with aggregation-induced emission (AIE) characteristics is synthesized with fluorometric/colorimetric responses for rapid and selective detection of NRHCs. The nonemissive probe is designed with tetraphenylethylene derivative as the linker and Co as the node, quencher, and color-changing agent. Cobalt AIE-MOF exhibits a turn-on emission enhancement due to the competitive coordination substitution between NRHCs and the scaffold as well as the following AIE process of the liberative linkers. Meanwhile, the color appearance of the probe changes from blue to yellow based on the dissociation of the original Co coordinating system. Using this dual-mode probe, single- and dual-ring NRHCs are successfully detected from 5 µM to 7.5 mM within 25 s. The cobalt AIE-MOF exhibits excellent selectivity of NRHCs against a variety of interferences, providing a promising tool for designing a multichannel detection strategy.

Complexation Behaviors of a Tridentate Phenanthroline Carboxamide Ligand with Trivalent f-Block Elements in Different Anion Systems: A Thermodynamic and Crystallographic Perspective.

The counteranion has a strong influence on the complexation behavior of tridentate phenanthroline carboxamide ligands with actinides and lanthanides, but the thermodynamic and underlying interaction mechanism at the molecular level is still not clear. In this work, a tridentate ligand, N-ethyl-N-tolyl-2-amide-1,10-phenanthroline (Et-Tol-PTA), was synthesized, and the effects of different anions (Cl-, NO3-, and ClO4-) on the complexation behavior of Et-Tol-PTA with typical lanthanides were thoroughly studied by using 1H nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-vis) spectrophotometry, and single-crystal X-ray diffraction. The NMR spectroscopic titration of Lu(III) showed that there were three species (1:1, 2:1, and 3:1 ligand-metal complexes) formed in Cl- solution systems while two species (2:1 and 1:1) were formed in NO3- and ClO4- solution systems. When Et-Tol-PTA was titrated with La(III), two species (2:1 and 1:1) were formed in NO3- systems and only one species (1:1) was formed in Cl- and ClO4- systems. In addition, the stability constant was determined via UV-vis spectroscopic titration, which showed that the complexation strength between Et-Tol-PTA and Eu(III) decreased in the following order: ClO4- > NO3- > Cl-. This indicated that Et-Tol-PTA had the strongest complexation ability with Eu(III) in the ClO4- system. The structures of Et-Tol-PTA complexed with EuCl3, Eu(NO3)3, and Eu(ClO4)3 were further elucidated by single-crystal X-ray diffraction and agreed well with the results of UV-vis titration experiments. The results of this work revealed that the mechanisms of complexation of lanthanides with the asymmetric ligand Et-Tol-PTA were strongly affected by different anionic environments in solution and in the solid state. These findings may lead to the improvement of the separation of trivalent actinides and lanthanides in nuclear waste.

Constructing Cationic Metal-Organic Framework Materials Based on Pyrimidyl as a Functional Group for Perrhenate/Pertechnetate Sorption.

Cationic metal-organic framework (MOF) materials are widely used in the anion separation field, but there are few reports of pyrimidyl ligands as building units. In this work, three new cationic MOFs based on pyrimidyl as functional group ligands were synthesized for the removal of radioactive pertechnetate from aqueous solution. The pyrimidyl ligands were designed by incorporating pyrimidyl units into the skeletons of benzene, triphenylamine, and tetraphenylethylene, respectively. Taking advantage of multiple coordination sites of pyrimidyl groups, three cationic MOFs (ZJU-X11, ZJU-X12, and ZJU-X13) with diverse structures were solvothermally synthesized using silver ion as the metal node. Scanning electron microscopy-energy-dispersive spectroscopy mapping demonstrated that these three cationic MOFs could capture ReO4- via anion exchange, but the sorption capabilities were distinctly different. With 95% removal toward ReO4-, ZJU-X11 showed the strongest anion-exchange competence among the three MOFs. According to the results of batch experiments, ZJU-X11 could achieve sorption equilibrium within 10 min, remove 518 mg of ReO4- per 1 g of ZJU-X11, remove most of ReO4- after four recycles, and maintain satisfactory selectivity in the presence of excess competing anions, which is one of the best MOF materials for removing ReO4-/TcO4- among the three cationic MOFs. This work indicates that the pyrimidyl group is a promising multiple site to build versatile cationic MOFs.

Selective Capture Mechanism of Radioactive Thorium from Highly Acidic Solution by a Layered Metal Sulfide.

Thorium as a potential nuclear fuel for the next-generation thorium-based molten salt reactors holds significant environmental and economic promise over the current uranium-based nuclear reactors. However, because thorium (Th4+) usually coexists with other rare earth elements, alkali or alkaline earth metals in minerals, or highly acidic radioactive waste, seeking acid-resistant sorbents with excellent selectivity, high capacity, and fast removal rate for Th4+ is still a challenging task. In this work, we investigated a robust layered metal sulfide (KInSn2S6, KMS-5) for Th4+ removal from strong acidic solutions. We report that KMS-5 could capture Th4+ from a 0.1 M HNO3 solution with extremely high efficiency (∼99.9%), fast sorption kinetics (equilibrium time < 10 min), and large distribution coefficient (up to 1.5 × 106 mL/g). Furthermore, KMS-5 exhibited excellent sorption selectivity towards Th4+ in the presence of large amounts of competitive metal ions like Eu3+, Na+, and Ca2+. This extraordinary capture property for Th4+ is attributed to the facile ion exchange of Th4+ with K+ in the interlayers and subsequent formation of a stable coordination complex via Th-S bonds. These results indicate that KMS-5 is a promising functional sorbent for the effective capture of Th4+ from highly acidic solutions.

Crystal and solution structures of a novel antimicrobial peptide from Chrysomya megacephala.

Antimicrobial peptides (AMPs) are small amphipathic peptides that exhibit bactericidal activity against a wide range of pathogenic microorganisms and are considered to be potential substitutes for antibiotics effective against microbial infection. PSK, an 84-amino-acid AMP recently isolated from Chrysomya megacephala larvae, probably belongs to the mitochondrial ATPase inhibitor family according to its sequence. No member of this family from an insect has been structurally characterized to date. In this study, the crystal structure of full-length PSK determined by molecular replacement using an ab initio modeled ensemble as a search model and a solution structure obtained from small-angle X-ray scattering (SAXS) measurements are reported. The crystal structure reveals a distinct fold compared with those of homologous peptides, in that PSK comprises two antiparallel α-helices rather than a single long helix, which is in good agreement with the SAXS-based ab initio model. However, the peptide exists as a monomer in solution, even though a stable dimer was observed in the crystal structure. This apparent contradiction may reflect different oligomerization states that may be implicated in its bioactivity. The data presented here have established a solid basis for further mechanistic studies of this novel insect AMP.

Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides.

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO3 solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. 1H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log ß) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.