Ligand Bond Research Articles

Insights Into the Uranium Phosphine Bonds in [UCp3(PR3)]: A Combined Molecular Orbital, QTAIM and EDA‐NOCV Study

A series of ten uranium(III) complexes with cyclopentadienyl and monodentate phosphine ligands [UCp3(PR3)] with R = Me, Et, nPr, iPr, tBu, Ph, Cy, F and CF3 was investigated using density functional theory calculations. The ligand dissociation energies were calculated, as well as bonding analysis of the uranium‐phosphorus bond performed, using molecular orbitals, bond orders, quantum theory of atom in molecules (QTAIM) analysis and energy decomposition analysis with natural orbitals for chemical valence (EDA‐NOCV). It was found that the bond orders correlate well with the U‐P bond lengths and phosphine cone angles, indicating a large influence of phosphine sterics on the bond properties. All bonding analyses show partial covalent character of the U‐P bond, which is most pronounced for PF3 and least for PtBu3. π‐Backbonding was found for the most π‐acidic phosphine ligands. No good correlation was found between the ligand dissociation energies and bond metrics.

Two-Dimensional π-d Conjugated Conductive Metal-Organic Framework with Triple Active Centers as High-Performance Cathodes for Flexible Zinc Batteries.

Conductive metal-organic frameworks (C-MOFs) have received extensive interest in high-performance zinc-ion batteries (ZIBs) owing to multi-redox sites and high electrical conductivity. Here, we present a π-d C-MOF by coordinating 2,3,5,6-tetraaminobenzoquinone (TABQ) ligands with Cu2+ ions (2D Cu-TABQ) acting as cathodes for ZIBs. Benefiting from a triple active center (Cu2+, C=O, and C=N), 2D Cu-TABQ shows an ultra-high reversible capacity of 297.7 mAh g-1at 0.2 A g-1. Meanwhile, 2D Cu-TABQ also has superior cycle stability with a capacity of up to 98.2 mAh g-1 after 1000 times at 2.0 A g-1. Considering the instability of the ligand bonds of C-MOFs in aqueous electrolytes,this work uses gel electrolytes to reduce the dissolution of organic ligands into the electrolyte, thus suppressing the shuttle effect, significantly improving the cycling stability of 2D Cu-TABQ. The flexible battery assembled by 2D Cu-TABQ shows excellent capacity retention (64.4%) after 50 times at 0.2 A g-1, which is significantly better than 36.4% in the common electrolyte, as well as outstanding bending resistance and electrochemical properties at different folding angles. This investigation will highlight the electrochemical application of C-MOFs in flexible zinc ion batteries and offer novel ideas for the structural design of cathodes with multiple active centers.

Biosensor for integrin inhibition of mammalian cell adhesion and migration using micropatterned cell culture substrate and retroreflective optical signaling

Integrins are a family of transmembrane receptors that play a crucial role in cell adhesion and migration. Integrins can uniquely transduce biochemical signals bidirectionally across the membrane and physically link the cell-cell and cell-extracellular matrix (ECM) with ligand bonds. The arginyl-glycyl-aspartic acid (RGD) peptide motif is present in the ECM as a minimal recognition sequence for integrins. To leverage this property in cell-based therapy, RGD variants, such as cyclic-type RGDfK (c(RGDfK)), which share a similar structure with RGD but exhibit a higher affinity for integrins, have been developed. However, because most evaluation methods for newly developed RGD variants focus on affinity strength, tools for cellular effects are required. In this study, we developed a new platform that integrates micropatterned three-dimensional cell culture substrates with a non-spectroscopic optical analysis system to quantitatively analyze the effects of RGD variants on cell adhesion and migration. The specially micropatterned substrate provides a cell adhesive and migration area to provide a restricted analysis area. Owing to the characteristics of retroreflective Janus particles (RJPs), a non-spectroscopic optical analysis system provides long-term stable optical verification properties and a simple optical setup. These techniques were integrated to quantitatively determine the integrin inhibitory effect of various concentrations of RGD variant. To demonstrate the efficacy of the developed cellular level RGD variant testing platform, the model cell line L929 fibroblast and model RGD variant c(RGDfK) were analyzed ranging from 0 to 10 μM. The results showed that the developed system could effectively and quantitatively analyze the effects of RGD variants on cells across various concentrations.

Features of electronic structure of (<i>η</i>⁵-C₅H₅)LuCl₂(THF)₃

For the first time, a topological analysis of the electron density distribution function in a crystal for an organolanthanide compound was carried out using the CpLuCl₂(THF)₃ complex as an example. The charges on atoms were determined. A predominantly ionic nature of the Lu–ligand bond was confirmed, but the essentially covalent nature of the Lu–Cp bond was discovered. The energies of the Lu–ligand bonds were determined.

Full Picture of Energy Transfer in a Trivalent Europium Complex with Bidentate β-Diketonate Ligand.

Trivalent europium (Eu(III)) complexes emit narrow-band luminescence as a result of energy transfer following the photoexcitation of antenna ligands. Bidentate β-diketonates are typically used as antenna ligands; however, their entire energy transfer mechanism to Eu(III) remains unknown. We used time-resolved photoluminescence spectroscopy and femtosecond transient absorption spectroscopy to map the complete intramolecular energy transfer process in the [Eu(hfa)3(TPPO)2] (hfa = hexafluoroacetylacetonate, TPPO = triphenylphosphine oxide) complex; hfa is a β-diketonate antenna ligand. Our analysis provides a "full picture" of energy transfer, tracing each step from initial photoexcitation to final relaxation: intersystem crossing in the ligands, energy transfer from the ligands to the metal center, and multiple internal conversion of Eu(III). We demonstrated that the direct bonds of the bidentate ligands enabled a quick and near-unity-efficiency energy transfer from the triplet state of the ligand to the 5D2 state of Eu(III). We also revealed that the loss of the ligand-centered intersystem crossing process reduces the overall sensitization efficiency. Our findings provide a foundation for the rational design of advanced luminescent materials, paving the way for advances in lanthanide-based luminescence research.

Substrate topography regulating membrane adhesion mediated by receptor–ligand bonds

Cell adhesion can be significantly influenced by the topography of the substrate surface. However, how the adhesion molecules essentially respond to this topographical stimulus is not fully understood yet. Here, we employ an effective Monte Carlo simulation to systematically investigate a fluctuating membrane interacting with a curved substrate via adhesive proteins. Interestingly, results show that, compared with the flat substrate, curved substrates regulate the membrane adhesion in a bond length dependent manner. The effects of the substrate surface amplitude and wavelength on the number of molecular bonds and adhesion pattern are also extracted from the scaling relationship between the characteristic lateral length of the membrane and the local substrate curvature radius. Furthermore, the local substrate curvature is found to select the bond distribution in terms of the bond length and stiffness. The results suggest that the bond stiffness enhances the clustering of molecular bonds, mainly due to synergistic interactions among these molecular bonds.

In Silico Studies: Stigmastan-3,6-dione in the Ethyl Acetate Fraction of Momordica charantia L Fruit has immunostimulant and anti-inflammatory activity

Momordica charantia L fruit provides an immunomodulatory effect by stimulating certain components of the body's immune system. Bioactive phytochemicals from M. charantia L function as anti-inflammatory agents by reducing levels of pro-inflammatory cytokine secretion including IL-1, IL-6, IL-8, TNF-α, NF-kB. This research looks at the insilico mechanism of action of the active ingredient of the EtOAc fraction of M. charantia L fruit as an immunostimulant and anti-inflammatory. The materials and methods used were an Intel Core i7 10 Th Gen laptop, Chem Office Professional 17.1, Chem 2D, Chem 3D software, PDB code (6W9K) and ligand (TUA), Stigmastan-3,6 dione (C29H48O2) from the EtOAc fraction of fruit M. charantia L was docked using MVD software, RMSD and RMSF values ​​were viewed using Yasara Software, pkCSM online tool to predict compound toxicity, toxicity prediction (LD50) was used by Protox online tool. The results of molecular docking of standard compounds, namely Methylprednisolone and Prednisolone and Stigmastan-3,6-dione, have Rerank Score values of -120.62, -121.47, -79.50, respectively. The lower the Rerank score value, the lower the binding energy between the protein and the ligand, causing the protein and ligand bonds to be more stable and it is predicted that the activity of the compound will be greater. The movement of RMSD values ​​between 0.6-1.9 Å for the 3 (three) compounds, is still within stable limits and does not undergo conformation. The RMSF value of the 3 (three) compounds has the same amino acid residue pattern. The insilico toxicity prediction for the 3 (three) compounds is still within safe limits. The EtOAc fraction of M. charantia L fruit with the active compound Stigmastan-3,6-Dione in its mechanism of action in silico shows activity as an anti-inflammatory and immunostimulant that works on the NF-kB pathway.

Chrysin Embedded Metal Organic Framework for Anticancer Drug Delivery.

Metal-organic frameworks (MOFs) have garnered significant attention in the field of cancer drug delivery owing to their porosity, high drug-loading capacity, and large surface area. In our recent research, we synthesized a redox-responsive MOF using zirconium (Zr) as the metal ion and 4,4-dithiobisbenzoic acid (DTBA) as the organic linker. The synthesis method employed was the hydrothermal method, and it was observed that the MOF synthesized at 400°C had a particle size of less than 200 nm and a zeta potential of +35 mV, indicating its suitability as a carrier for drug delivery. Chrysin, a natural anticancer drug, was used in this study. Glutathione, which is abundantly present in tumor cells, cleaves the disulfide bond in the organic ligand (DTBA), leading to faster drug release. By incorporating chrysin into the synthesized MOF, we observed faster in vitro drug release, with 88 and 89% at pH 7.4 and 5.5, respectively. The synthesis of ZrDTBA MOF opens up new opportunities for its application in drug delivery.

Density functional theory study of substituent effects on gas-phase heterolytic Fe-N bond energies of m-G-C6H4NHFe(CO)2(η5-C5H5) and m-G-C6H4N(COMe)Fe(CO)2(η5-C5H5)

The nature and strength of metal–ligand bonds in organotransition-metal complexes are crucial to the understanding of organometallic reactions and catalysis. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe-N bond energies of meta-substituted anilinyldicarbonyl(η5-cyclopentadienyl)iron [m-G-C6H4NH(η5-C5H5)Fe(CO)2, abbreviated as m-G-C6H4NHFp (1), where G=NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO and NMe2] and meta-substituted α-acetylanilinyldicarbonyl(η5-cyclopentadienyl)iron [m-G-C6H4N(COMe)(η5-C5H5)Fe(CO)2, abbreviated as m-G-C6H4N(COMe)Fp (2)] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔHhet(Fe-N)′s. ΔΔHhet(Fe-N)′s (1 and 2) conform to the captodative principle. There are excellent linear free energy relations among ΔΔHhet(Fe-N)′s and the experimental and computational substituent effects on acidities of m-G-C6H4NH2, the differences of acidic dissociation constants (ΔpKas) of NH bonds for m-G-C6H4NH2 for series 1 or the substituent σm constants. The former correlations imply that the govering factors for these bond scissions are similar; the latter ones suggest that polar effects of meta-substituents show the dominant role to the magnitudes of ΔHhet(Fe-N)′s. And these correlations are in accordance with Hammett linear free energy relationships. The Fe-N bonds in series 1 are stronger than those in series 2. Therefore m-G-C6H4N(COMe)- are more stable than m-G-C6H4NH-. The absolute magnitudes of AEs, AEα-COMes and AEα-COMe,para-Gs are far larger than MEs, MEα-COMes and MEα-COMe,para-Gs. The influences of MEs, MEα-COMes and MEα-COMe,para-Gs are subtle. A better understanding of organometallic bond energies can suggest whether proposed new catalytic systems may work well.

Construction of a Boron Chain on a Single Metal by Dehydrocoupling of Borane Ligands.

Borane coordination, B-H borane bond activation, and borane catenation via metal-mediated dehydrocoupling to form electron-precise B-B bonds are reported. The reaction of trans-[M(IMes)2Cl4] (M = W, Mo) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) with borates Li[BH3R] (R = Mes, Dur; Mes = 2,4,6-Me3C6H2 and Dur = 2,3,5,6-Me4C6H) afforded the complexes [M(IMes)(η2-H2BR)2(η1-H2BR)] (M = W: R = Mes 1, R = Dur 3; M = Mo: R = Mes 2, R = Dur 4). Three borane ligands are coordinated in 1-4 to the group 6 metal atom via five (σ-B-H) bonds. Reaction of 1 with the phosphines PMe3 and PEt3, respectively, led to the elimination of one of the borane ligands and afforded the hydrido (σ-B-H)-boryl bis(σ-B-H)-borane complexes trans-[W(IMes)(PR3)(η1-HBMes)(η2-H2BMes)(H)] (R = Me 5, R = Et 6), in which the metal atom inserted into one of the remaining σ-B-H bonds of the borane ligands. Reaction of 1 with an additional equivalent borane BH2Mes resulted in borane dehydrocoupling and formation of complex [W(IMes)(η4-BH2Mes-BMes-BMes-BH2Mes)] 7, featuring a unique B4 chain as a ligand. Reaction of trans-[W(IMes)2Cl4] with NaBH4 also led to B-B coupling, and the metallaborane cluster [{W(IMes)(BH4)}2(B5H9)] 9 was formed, in which two tungsten atoms bridge a B5 chain.

Withdrawal: Conductive Hydrogel Dressing With High Mechanical Strength for Joint Wound Healing.

Hydrogel wound dressing can accelerate angiogenesis to achieve rapid wound healing, but traditional hydrogel dressings are difficult to meet the repair of joint sites due to their low mechanical strength. Therefore, we constructed the gel system by designing the chemical-physical interpenetrating network structure to achieve high strength and high toughness of the hydrogel. The high-strength double-network hydrogels were synthesized by simple free radical polymerization and low-temperature physicochemical cross-linking in our experiments. The suspension was obtained by green reduction of graphene oxide with carboxymethyl chitosan, followed by the introduction of acrylamide (AM) to form a covalent cross-linked network, which was immersed in ferric chloride solution to form metal ligand bonds, and finally the chemical-physical dual cross-linked network hydrogel wound dressing was prepared. Here, reduced graphene oxide can enhance electrical conductivity and excellent near-infrared photothermal effect to the hydrogel. The cell viability of this novel wound dressing was above 90.0%, its hemolysis rate was below 2.0%, and the electrical conductivity could reach (6.89 ± 0.07 (mS/cm)). In addition, the stress-strain curve demonstrated that the double cross-linked network hydrogel could reach a stress of more than 0.8MPa at 82.0% strain, and the cyclic compression experiment shows that it can still recover its original shape after five times of repeated compression. This work can provide a reference for the exploitation of high mechanical strength hydrogel wound dressings with good electrical conductivity and near-infrared photothermal effect. This article is protected by copyright. All rights reserved.

Non-rigid metal–oxygen bonding empowered nitrate reduction on ruthenium catalysts

Electrocatalytic nitrate reduction (NitRR) offers exciting potential for mass production of ammonia (NH3) from renewables. However, the rigidity of metal−ligand bonds in most electrocatalysts renders them unable to survive the structural transformations required for NitRR. Herein, we establish a type of non-rigid metal−oxygen bonds by employing graphene oxide (GO) sheets as a 'micron-scale' ligand for transition metals (TM). Because of being confined to the interfaces between GO and TM, the oxygenated groups in GO can associate with and dissociate from the TM in response to reaction dynamics. As a proof-of-concept demonstration, an electrocatalyst was developed by dispersing nanoscale ruthenium (Ru) on graphene oxide (GO) and utilizing two-dimensional MXene to compensate for the low electrical conductivity of GO. This electrocatalyst exhibits a maximum NH3 yield of over 5 mg cm−2 h−1, with almost 100 % current-to-NH3 efficiency, far outperforming the performance of most reported Ru-based materials. What's even more remarkable is the achievement of a record-breaking performance: a 200-hour stable electrolysis with a NH3 yield of 40.2 mg cm−2 h−1, using a membrane electrode reactor. Our experimental and theoretical investigations further reveal the non-rigidity of the Ru–O bonds and how they self-regulate to adapt to diverse intermediates involved in NitRR. This work provides an approach to fabricate a high-performance electrocatalyst featuring reversible and non-rigid metal−oxygen bonds, opening new possibilities for practical nitrate electrolysis.

MOLECULAR DOCKING ANALYSIS AND ADMET PREDICTION Of Caesalpinia sappan COMPOUNDS AS ANTIINFLAMMATORY THROUGH CYCLOOXYGENASE-2 INHIBITION

Selective COX-2 inhibitors have been considered safer treatments than NSAIDs for inflammation from its side effect. Sappanwood was already known for its antiinflammatory activity, but its selectivity towards COX-2 has not been tested. The purpose of this study was to determine the potential activity of compounds in Caesalpinia sappan as anti-inflammatory agents by inhibiting COX-2 and determine their ADMET’s properties through in silico study. Qulified compound from Lipinski’s rule of five evaluation would be continued to the molecular docking using Autodock Tools and ADMET prediction using SwissADME and ADMETLab. Three compounds known to have the best free bond energy (ΔG) values were Caesalpiniaphenol A, Sappankalkon, and Deoxysappanone B with ΔG values respectively (-9.36 ; -9.23 ; -9.02 kcal/mol) and their inhibition constant values of (124.44 ; 172.43 ; 244.75 nM) respectively. Amino acid residues that are known to involve to the formation of hydrogen bonds in ligands are GLN 192 and PHE518. Toxicity results showed that these three compounds were predicted to be neither hepatotoxic nor hERG inhibitors, but 3-deoxysappanone B and sappankalkon was predicted to cause AMES mutagenicity and skin sensitivity. It can be concluded that these third compound has the potential as an inhibitor of the COX-2 enzyme.

Extracellular matrix hydrogels with fibroblast growth factor 2 containing exosomes for reconstructing skin microstructures

Decellularized extracellular matrix hydrogel (ECM hydrogel), a natural material derived from normal tissue with unique biocompatibility properties, is widely used for tissue repair. However, there are still problems such as poor biological activity and insufficient antimicrobial property. To overcome these drawbacks, fibroblast growth factor 2 (FGF 2) containing exosome (exoFGF 2) was prepared to increase the biological activity. Furthermore, the antimicrobial capacity of ECM hydrogel was optimised by using copper ions as a ligand-bonded cross-linking agent. The decellularized extracellular matrix hydrogel, intricately cross-linked with copper ions through ligand bonds and loaded with FGF 2 containing exosome (exoFGF 2@ECM/Cu2+ hydrogel), has demonstrated exceptional biocompatibility and antimicrobial properties. In vitro, exoFGF 2@ECM/Cu2+ hydrogel effectively promoted cell proliferation, migration, antioxidant and inhibited bacterial growth. In vivo, the wound area of rat treated with exoFGF 2@ECM/Cu2+ hydrogels were significantly smaller than that of other groups at Day 5 (45.24% ± 3.15%), Day 10 (92.20% ± 2.31%) and Day 15 (95.22% ± 1.28%). Histological examination showed that exoFGF 2@ECM/Cu2+ hydrogels promoted angiogenesis and collagen deposition. Overall, this hydrogel has the potential to inhibit bacterial growth and effectively promote wound healing in a variety of clinical applications.

Preparation of a self‐supported zeolite glass composite membrane for CO2/CH4 separation

AbstractThe low porosity of metal‐organic framework glass makes it difficult to prepare membranes with high permeability. To solve this problem, we fabricated a series of self‐supported zeolite glass composite membranes with different 4A zeolite loadings using the abundant pore structure of the zeolite. The 4A zeolite embedded in the zeolite glass composite membrane preserved the ligand bonds and chemical structure. The self‐supported zeolite glass composite membranes exhibited good interfacial compatibility. More importantly, the incorporation of the 4A zeolite significantly improved the CO2 adsorption capacity of the pure agZIF‐62 membranes. In addition, gas separation performance measurements showed that the (agZIF‐62)0.7(4A)0.3 membrane had a permeability of 13,329 Barrer for pure CO2 and an ideal selectivity of 31.7 for CO2/CH4, which exceeded Robeson's upper bound. The (agZIF‐62)0.7(4A)0.3 membrane exhibited good operational stability in the variable pressure test and 48 h long‐term continuous test. This study provides a method for preparing zeolite glass composite membranes.

In Silico Study of the Potential of Brazilein Sappan Wood as a Beta-Lactamase Inhibitor against Extended-Spectrum Beta-Lactamase-Encoding Genes.

Infectious illnesses are a serious health concern in Indonesia. Widespread use of self-medication by the community increases the risk of developing multi-drug resistant (MDR) bacteria. This study assessed the potential of sappan wood as an inhibitor of extended-spectrum beta-lactamase (ESBL) encoded by blaSHV, blaTEM and blaCTX-M genes. In silico testing was conducted to develop an effective and economical starting strategy. Thereby, this study significantly advances the development of novel treatments to combat antibiotic resistance. Using clavulanic acid as the benchmark medicine, the potency of the beta-lactamase inhibitor brazilein was predicted. Using the Molegro Virtual Docker computer tool, docking was performed to estimate the chemical and physical properties of the compounds, as well as the biological activity of brazilein toward the required receptor. The receptors used were SHV-1 beta-lactamase, PDB code: 2H0T; TEM-1 beta-lactamase, PDB code: 4OQG and CTX-M-14 beta-lactamase, PDB code: 6VHS. Data analysis was performed by comparing the binding energies of the docking results between the ligands and the target receptor. The more stable the bond that formed between the ligand and the target receptor, the lower the bond energy. The in silico test results on the blaSHV gene were as follows: binding energy of ligand MA4_400[A] = -100.699, brazilein = -82.206, clavulanic acid = -79.3704; in the blaTEM gene: ligand bond energy 2UL_301[B] = -107.681, brazilein = -82.0296, clavulanic acid = -103.3; in the blaCTX-M gene: X57_301[A] ligand bond energy = -86.6197, and brazilein = -88.1586, clavulanic acid = -101.933. The findings of this study demonstrate the significant potential of brazilein sappan wood to block the beta-lactamase activity of blaCTX-M.

Extraction of uranyl from spent nuclear fuel wastewater via complexation—a local vibrational mode study

ContextThe efficient extraction of uranyl from spent nuclear fuel wastewater for subsequent reprocessing and reuse is an essential effort toward minimization of long-lived radioactive waste. N-substituted amides and Schiff base ligands are propitious candidates, where extraction occurs via complexation with the uranyl moiety. In this study, we extensively probed chemical bonding in various uranyl complexes, utilizing the local vibrational modes theory alongside QTAIM and NBO analyses. We focused on (i) the assessment of the equatorial O-U and N-U bonding, including the question of chelation, and (ii) how the strength of the axial U=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$=$$\\end{document}O bonds of the uranyl moiety changes upon complexation. Our results reveal that the strength of the equatorial uranium-ligand interactions correlates with their covalent character and with charge donation from O and N lone pairs into the vacant uranium orbitals. We also found an inverse relationship between the covalent character of the equatorial ligand bonds and the strength of the axial uranium-oxygen bond. In summary, our study provides valuable data for a strategic modulation of N-substituted amide and Schiff base ligands towards the maximization of uranyl extraction.MethodQuantum chemistry calculations were performed under the PBE0 level of theory, paired with the relativistic NESCau Hamiltonian, currently implemented in Cologne2020 (interfaced with Gaussian16). Wave functions were expanded in the cc-pwCVTZ-X2C basis set for uranium and Dunning’s cc-pVTZ for the remaining atoms. For the bonding properties, we utilized the package LModeA in the local modes analyses, AIMALL in the QTAIM calculations, and NBO 7.0 for the NBO analyses.Graphical abstract

A multiscale dynamic model of cell–substrate interfaces

Cell–extracellular matrix (ECM) interactions play a pivotal role in many functions of cells, for example, sensing, signaling, migration, and gene expression. The spatial–temporal dynamic evolution of cell–substrate adhesions involves complicated mechano-bio-chemical coupling mechanisms of integrin, adaptor and signaling proteins, as well as the interplay between the cytoskeleton and ECM. In this paper, we establish a multiscale dynamic model of cell–substrate interfaces considering intermolecular force transmission pathways, i.e., intra- and extra-cellular bond dynamics, and mechanochemical coupling regulations. To illustrate its applications, this model is used to reproduce several adhesion-related experimental phenomena of cells, including substrate rigidity sensing, actin-assisted focal adhesion formation, and biphasic interface stress–actin speed relation. The results suggest that the cluster growth patterns are mediated by the intermolecular force transmission pathway and the actin flow speed, and that the integrin–ligand (IL) bond strengthening tends to inhibit the motion of clusters. We reveal that the monotonic-to-biphasic transition of force transmission and adhesion assembly is regulated by the bond rupture mechanosensitivity of integrin adhesion complexes (IACs). It is also demonstrated that this multiscale dynamic model can well describe the spatial–temporal evolutions of collective cell–substrate adhesions with the effects of actin flow and substrate deformation, and can also capture the morphological features of adhesion clusters and related interface force transmissions. This work provides a theoretical tool for studying mechano-biochemical mechanisms of cell–substrate interactions and for understanding various subcellular and cellular dynamic processes in, for example, tumors.

Complexation of trivalent Eu and Am ions with phenanthroline-derived ligands tuned by rotating thiazole/oxazole substituents

The reprocessing of spent nuclear fuels is greatly challenging, as the current separation technique of lanthanide (Ln) and actinide (An) suffers too many difficulties. In this paper, selective ligands of phenanthroline derivatives modified by thiazole/oxazole were designed by relativistic density functional theory calculations. Their complexation of Eu3+ and Am3+ and the mechanism of selective separation were comprehensively examined. The spatial rotation against the CC bond between phenanthroline and thiazole/oxazole has access to six ligands. It is shown that Looo with oxazole substituents and their oxygens being opposite is the best electron donor for metal ions. The results of WBIs and MBO unravel that Am-L bond has more covalency than respective Eu-L bond. From topological analyses, it is found that these metal–ligand bonds are dominated by electrostatic interaction and largely of ionic bond character. Thermodynamically, all ligands prefer binding Eu3+ to Am3+.

Exploring the bonding and extraction separation effects of N donor ligands with different skeletons on Am(III) and Eu(III)

Designing ligands for effective separation of actinide(III)/lanthanide(III) is one of the key issues in the treatment of spent nuclear fuel. However, due to the chemical similarity of trivalent actinides and lanthanides, their separation faces a great challenge in the reprocessing of spent nuclear fuel. Nitrogen donor extractants are considered as promising reagents for separation of trivalent actinides and lanthanides. To the best of our knowledge, the pre-organized structure of the ligand has a strong influence on the extraction separation capacity. In this work, we designed four N-donor ligands (L1 and L2 with pyridine and bipyridine skeletons, respectively, and L3 and L4 both with phenanthroline skeletons) with different pre-organized structures and investigated their selective extraction for Am(III) and Eu(III) by using scalar relativistic density functional theory (DFT). The absolute minimum ESP values of these ligands and the higher HOMO level suggest that the ligand L2 may have a stronger affinity for Am(III)/Eu(III) ions than other ligands. The three average bond lengths of each complex indicate that the Am(III) and Eu(III) ions have larger bond lengths with N2 atoms than with N1 atoms. Various theoretical approaches have been used to evaluate the properties of the four ligands as well as the coordination structures, bonding properties and thermodynamic properties of the complexes of the four ligands with Am(III) and Eu(III). The WBIs, QTAIM, NBO, DOS and EDA analysis indicate that the metal–ligand bonds are mainly ionic in character, the Am-N bond has more covalency than the Eu-N bond because the Am 5f orbitals are more involved in bonding with ligand than Eu 4f orbitals. According to the extended transition state and natural orbital chemical valence theory (ETS-NOCV) analysis, electrons are obviously transferred from the lone pair of the ligand N atom to the hybrid s, d and f orbitals of the metal ion. The thermodynamic results show that the four ligands can coordinate well with the Am and Eu ions, and also have suitable separation capacity for Am and Eu. Among the four ligands, the L2 and L3 ligands have the strongest coordination ability for metals and the best extraction separation effect for Am and Eu. It can be seen that the bridging skeleton of the ligand and the number of N atoms on the five-membered ring and also different organic solvents have obvious effects on the extraction and separation capacity of the ligand. This study provides a theoretical basis for the efficient separation of Am(III)/Eu(III) by adjusting the preorganization level of ligands, and provides a theoretical basis for the design and screening of ligands by preorganization.