Weak Binding Interactions Research Articles

Synergistic Linker and Linkage of Covalent Organic Frameworks for Enhancing Gold Capture.

The tunable pore walls and skeletons render covalent organic frameworks (COFs) as promising absorbents for gold (Au) ion. However, most of these COFs suffered from low surface areas hindering binding sites exposed and weak binding interaction resulting in sluggish kinetic performance. In this study, COFs have been constructed with synergistic linker and linkage for high-efficiency Au capture. The designed COFs (PYTA-PZDH-COF and PYTA-BPDH-COF) with pyrazine or bipyridine as linkers showed high surface areas of 1692 and 2076 m2 g‒1, providing high exposed surface areas for Au capture. In addition, the Lewis basic nitrogen atoms from the linkers and linkages are easily hydronium, which enabled to fast trap Au via coulomb force. The PYTA-PZDH-COF and PYTA-BPDH-COF showed maximum Au capture capacities of 2314 and 1810mg g-1, higher than other reported COFs. More importantly, PYTA-PZDH-COF are capable of rapid adsorption kinetics with achieving 95% of maximum binding capacity in 10min. The theoretical calculation revealed that the nitrogen atoms in linkers and linkages from both COFs are simultaneously hydronium, and then the protonated PYTA-PZDH-COF are more easily binding the AuCl4 ‒, further accelerating the binding process. This study gives the a new insight to design COFs for ion capture.

14-Electron Redox Chemistry Enabled by Salen-Based π-Conjugated Framework Polymer Boosting High-Performance Lithium-Ion Storage.

A paucity of redox centers, poor charge transport properties, and low structural stability of organic materials obstruct their use in practical applications. Herein, these issues have been addressed through the use of a redox-active salen-based framework polymer (RSFP) containing multiple redox-active centers in π-conjugated configuration for applications in lithium-ion batteries (LIBs). Based on its unique architecture, RSFP exhibits a superior reversible capacity of 671.8 mAh g-1 at 0.05 A g-1 after 168 charge-discharge cycles. Importantly, the lithiation/de-lithiation performance is enhanced during operation, leading to an unprecedented reversible capacity of 946.2 mAh g-1 after 3500 cycles at 2 A g-1. The structural evolution of RSFP is studied ex situ using X-ray photoelectron spectroscopy, revealing multiple active C═N, C─O, and C═O sites and aromatic sites such as benzene rings. Remarkably, the emergence of C═O originated from C─O is triggered by an electrochemical process, which is beneficial for improving reversible lithiation/delithiation behavior. Furthermore, the respective strong and weak binding interactions between redox centers and lithium ions, corresponding to theoretical capacities of 670.1 and 938.2 mAh g-1, have been identified by density functional theory calculations manifesting 14-electron redox reactions. This work sheds new light on routes for the development of redox-active organic materials for energy storage applications.

Hydrogen Sulfate-Templated Synthesis of a Bis-Ferrocene Macrocycle

AbstractA bis-ferrocene macrocycle was synthesized by reversible acylhydrazone formation under thermodynamic control, starting from a ferrocene functionalized with hydrazide and protected aldehyde moieties. A hydrogen sulfate anion acts as a template to direct the synthesis specifically toward the macrocyclic dimer, due to a weak but selective binding interaction. This work highlights the utility of dynamic combinatorial chemistry as an approach to macrocycle synthesis.

Evaluation of restricted access media for the purification of cell culture-derived Orf viruses.

Recently, multimodal chromatography using restricted access media (RAM) for the purification of nanoparticles, such as viruses has regained increasing attention. These chromatography resins combine size exclusion on the particle shell and adsorptive interaction within the core. Accordingly, smaller process-related impurities, for example, DNA and proteins, can be retained, while larger product viruses can pass unhindered. We evaluated a range of currently available RAM, differing in the shells' pore cut-off and the core chemistry, for the purification of a cell culture-derived clarified model virus, namely the Orf virus (ORFV). We examined impurity depletion and product recovery as relevant criteria for the evaluation of column performance, as well as scale-up robustness and regeneration potential for evaluating a multiple use application. The results indicate that some columns, for example, the Capto Core, enable both a high DNA and protein removal, while others, for example, the Monomix Core 60 (MC60), are more suitable for DNA depletion. Furthermore, column regeneration is facilitated by using columns with larger shell pores (5000vs. 700kDa) and weaker binding interactions (anion exchange vs. multimodal). According to these findings, the choice of RAM resins should be selected according to the respective feed sample composition and the planned number of application cycles.

Biophysical study on DNA and BSA binding activity of Cu(II) complex: Synthesis, molecular docking, cytotoxic activity, and theoretical approach

The bidentate (N, O) donor Schiff base, methyl‐4‐(2‐hydroxybenzylidene‐amino) benzoate (HL), was synthesized for the synthesis of CuL2 complex. Their structures were characterized by single crystal X‐ray diffraction and spectroscopic methods. The important structural features of ligand HL are (space group: Pca21; a = 6.1434(7) Å; b = 7.1021(7) Å; c = 28.963(3) Å; α = 90.00°; β = 90.00°, and γ = 90.00°) and of CuL2 are (space group: P21/n; a = 15.763(7) Å; b = 8.1921(5) Å, and c = 20.1955(8) Å; α = 90.00°; β = 96.547(4)°, and γ = 90.00°). The DFT/TD‐DFT studies were performed to evaluate the structure optimization, MEP plot, and electronic spectroscopy data as well as the HOMO‐LUMO energy and also other electronic descriptor properties. The DNA and BSA binding property of both the ligand and complex were studied employing a variety of spectroscopic methods, viscosity experiments, and gel electrophoresis technique. Their biophysical study including 3D fluorescence, FRET calculation, and anisotropy measurements with BSA were studied by spectrofluorometric methods. The molecular docking simulation of the ligand HL and CuL2 was executed with DNA and BSA to observe their different weak and strong binding interactions and to compare their binding aptitude with biomolecules and experimental results. The software “PASS” for drug likeness prediction and “ADMET” for bioactivity were implemented to get an idea about the antineoplastic and bioactivity aspects of HL and CuL2 complex. The anticancer property of the Cu(II) complex was measured by MTT assay against human breast carcinomas (MCF‐7) cancer cell line and as well as normal human embryonic kidney cells (HEK293) and is less toxic and comparable anticancer activity compared to cisplatin and oxaliplatin. The annexin V‐FITC, propidium iodide assay by flow cytometric method, and reactive oxygen species (ROS) production assay by DCFDA were assessed in presence of the HL and CuL2 for their cell death mechanism proceed via either apoptosis or necrosis.

Developments in rapid hydrogen-deuterium exchange methods.

Biological macromolecules, such as proteins, nucleic acids, and carbohydrates, contain heteroatom-bonded hydrogens that undergo exchange with solvent hydrogens on timescales ranging from microseconds to hours. In hydrogen-deuterium exchange mass spectrometry (HDX-MS), this exchange process is used to extract information about biomolecular structure and dynamics. This minireview focuses on millisecond timescale HDX-MS measurements, which, while less common than 'conventional' timescale (seconds to hours) HDX-MS, provide a unique window into weakly structured species, weak (or fast cycling) binding interactions, and subtle shifts in conformational dynamics. This includes intrinsically disordered proteins and regions (IDPs/IDRs) that are associated with cancer and amyloidotic neurodegenerative disease. For nucleic acids and carbohydrates, structures such as isomers, stems, and loops, can be elucidated and overall structural rigidity can be assessed. We will provide a brief overview of technical developments in rapid HDX followed by highlights of various applications, emphasising the importance of broadening the HDX timescale to improve throughput and to capture a wider range of function-relevant dynamic and structural shifts.

Synthesis of isoniazid analogs with promising antituberculosis activity and bioavailability: Biological evaluation and computational studies

A series of aliphatic isoniazid carbo(x/thio)amides has been synthesized by a facile one-pot green method in aqueous media by harnessing microwave irradiations. In vitro antitubercular screening of the synthesized compounds against Mycobacterium tuberculosis H37Rv (MTB strain) reveals promising antimycobacterial potential with MIC in the range of 1 to 4 µg/ml. A computational approach comprising DFT modeling, molecular docking and ADMET analysis was executed to elucidate the chemical nature, binding affinity and ADMET efficacy of the lead compounds. The docking of synthesized analogs with InhA displays weak binding interactions with the receptor and the absence of important interactions specific to direct inhibitors. However, the docking results illustrate notable binding affinity of the synthesized molecules with the KatG receptor 1SJ2 and compounds 3h and 3e showed the best docking scores (-7.2 and -6.8 kcal/mol, respectively) indicating the KatG mediated mechanism of InhA inhibition similar to isoniazid. In silico ADMET analysis of the title compounds indicate their outstanding pharmacokinetic proficiency and lower toxicity than isoniazid. The bioavailability radar further illustrates their exemplary oral availability and drug-likeliness.

Structural and Functional Characterization of Mycobacterium tuberculosis Homoserine Transacetylase.

Mycobacterium tuberculosis (Mtb) lacking functional homoserine transacetylase (HTA) is compromised in methionine biosynthesis, protein synthesis, and in the activity of multiple essential S-adenosyl-l-methionine-dependent enzymes. Additionally, deficient mutants are further disarmed by the toxic accumulation of lysine due to a redirection of the metabolic flux toward the lysine biosynthetic pathway. Studies with deletion mutants and crystallographic studies of the apoenzyme have, respectively, validated Mtb HTA as an essential enzyme and revealed a ligandable binding site. Seeking a mechanistic characterization of this enzyme, we report crucial structural details and comprehensive functional characterization of Mtb HTA. Crystallographic and mass spectral observation of the acetylated HTA intermediate and initial velocity studies were consistent with a ping-pong kinetic mechanism. Wild-type HTA and its site-directed mutants were kinetically characterized with a panel of natural and alternative substrates to understand substrate specificity and identify critical residues for catalysis. Titration experiments using fluorescence quenching showed that both substrates─acetyl-CoA and l-homoserine─engage in a strong and weak binding interaction with HTA. Additionally, substrate inhibition by acetyl-CoA and product inhibition by CoA and O-acetyl-l-homoserine were proposed to form the basis of a feedback regulation mechanism. By furnishing key mechanistic and structural information, these studies provide a foundation for structure-based design efforts around this attractive Mtb target.

Nuclear localisation sequences of chloride intracellular channels 1 and 4 facilitate nuclear import via interactions with import mediator importin-α: An empirical and theoretical perspective.

Chloride intracellular channel proteins (CLICs) display ubiquitous expression, with each member exhibiting specific subcellular localisation. While all CLICs, except CLIC3, exhibit a highly conserved putative nuclear localisation sequence (NLS), only CLIC1, CLIC3 and CLIC4 exist within the nucleus. The CLIC4 NLS, 199-KVVAKKYR-206, appears crucial for nuclear entry and interacts with mouse nuclear import mediator Impα isoform 1, omitting the IBB domain (mImpα1ΔIBB). The essential nature of the basic residues in the CLIC4 NLS has been established by the fact that mutating out these residues inhibits nuclear import, which in turn is linked to cutaneous squamous cell cancer. Given the conservation of the CLIC NLS, CLIC1 likely follows a similar import pathway to CLIC4. Peptides of the CLIC1 (Pep1; Pep1_S C/S mutant) and CLIC4 (Pep4) NLSs were designed to examine binding to human Impα isoform 1, omitting the IBB domain (hImpα1ΔIBB). Molecular docking indicated that the core CLIC NLS region (KKYR) forms a similar binding pattern to both mImpα1ΔIBB and hImpα1ΔIBB. Fluorescence quenching demonstrated that Pep1_S (Kd ≈ 237 μM) and Pep4 (Kd ≈ 317 μM) bind hImpα1ΔIBB weakly. Isothermal titration calorimetry confirmed the weak binding interaction between Pep4 and hImpα1ΔIBB (Kd ≈ 130 μM) and the presence of a proton-linked effect. This weak interaction may be due to regions distal from the CLIC NLS needed to stabilise and strengthen hImpα1ΔIBB binding. Additionally, this NLS may preferentially bind another hImpα isoform with different flexibility properties.

Antibonding p-d and s-p Hybridization Induce the Optimization of Thermal and Thermoelectric Performance of MGeTe3 (M = In and Sb)

Manipulation of phonon transport is the key to optimizing the overall energy conversion efficiency of thermoelectric materials. In this work, we demonstrate that the antibonding hybridization resulting from elemental substitution can weaken the interatomic interactions, which in turn enhances the structural anharmonicity and hinders the heat conduction of layered ABTe3 (ABSe3) (A = Al, Ga, In, As, and Sb; B = Si and Ge) compounds. It is revealed that the filled antibonded p-d state of GaSiTe3 (GaSiSe3) originates from the mixture of Ga-3d and Te-5p (Se-4p) orbitals, whereas the outer As-s electrons hybridize with the Te (Se)-p electrons to form antibonding states in AsSiTe3 (AsSiSe3). Consequently, the room temperature lattice thermal conductivity (κL) of AlGeTe3 (AlGeSe3) is reduced from 3.27 (3.86) W/mK to 0.62 (1.47) W/mK for GaSiTe3 (GaSiSe3) and 1.91 (1.74) W/mK for AsSiTe3 (AsSiSe3) in spite of their similar atomic masses and crystal structures. Based on these findings, we propose candidates of InGeTe3 and SbGeTe3 to realize potentially high thermoelectric performance by rationally incorporating heavy weight elements but still maintaining weak atomic binding interactions. Due to the low κL of 0.26 (0.6) W/mK, a high n-type (p-type) ZT value of 2.18 (1.08) at 750 (650) K is finally captured in InGeTe3 (SbGeTe3). Our results not only provide insights to understand the relationship between chemical bonding and lattice thermal conductivity but also offer an approach to design and discover materials with expected thermal transport and thermoelectric properties.

Sorption of benzo(a)pyrene and of a complex mixture of petrogenic polycyclic aromatic hydrocarbons onto polystyrene microplastics

Microplastics (MPs) largely occur in aquatic ecosystems due to degradation of larger plastics or release from MP-containing products. Due to the hydrophobic nature and large specific surface of MPs, other contaminants, such as polycyclic aromatic hydrocarbons (PAHs), can potentially sorb onto MPs. Several studies have addressed the potential impact of MPs as vectors of PAHs for aquatic organisms. Therefore the role of MPs as sorbents of these compounds should be carefully investigated. The present study aimed to determine the sorption capacity of benzo(a)pyrene (B(a)P), as a model pyrolytic PAH, to polystyrene (PS) MPs of different sizes (4.5 and 0.5 μm). In addition, the sorption of PAHs present in the water accommodated fraction (WAF) of a naphthenic North Sea crude oil to 4.5 μm MPs was also studied as a model of a complex mixture of petrogenic PAHs that could appear in oil-polluted environments. The results indicated that 0.5 μm MPs showed higher maximum sorption capacity (Qmax) for B(a)P (145–242.89 μg/g) than 4.5 μm MPs (30.50–67.65 μg/g). From the WAF mixture, naphthalene was sorbed at a higher extent than the other PAHs to 4.5 μm MPs but with weak binding interactions (Kf = 69.25 L/g; 1/n = 0.46) according to the analysis of the aqueous phase, whereas phenanthrene showed stronger binding interactions (Kf = 0.24 L/g; 1/n = 0.98) based on the analysis of the solid phase. Sorption of PAHs of the complex WAF mixture to 4.5 μm MPs was relatively limited and driven by the hydrophobicity and initial concentration of each PAH. Overall, the results indicate that sorption estimations based solely on the analysis of the aqueous phase could overestimate the capacity of MPs to carry PAHs. Therefore, controlled laboratory assays assessing the “Trojan Horse effect” of MPs for aquatic organisms should consider these findings in order to design accurate and relevant experimental procedures.

Regulating solvation environment of Li ions via high donor number anions for high-performance Li-metal batteries

The evolution of solid electrolyte interphases (SEI) on Li metal anodes strongly depends on the solvation environment of Li ions in the electrolyte. Using solvent molecules with high Gutmann donor number (DN) is a commonly accepted strategy to modulate the solvation environment of Li ions. However, high DN solvent molecules react strongly with Li metal anodes. Herein, a novel strategy is developed to regulate the solvation environment via introducing salt anion with high DN as electrolyte additives, with lithium triflate (LiTf) as a case study. Tf− with high DN can effectively form an anion-dominated solvation sheath, which is confirmed by molecular dynamics (MD) simulations and Raman spectroscopy. Density functional theory (DFT) calculations show that Tf− demonstrates a strong reduction tendency during SEI formation due to its relatively low lowest unoccupied molecular orbital (LUMO) energy. Moreover, Tf− shows weak binding interaction with Li ions in the solvated structure, which is conducive to the desolvation process and preferential decomposition of the anion to form SEI. Consequently, a stable and LiF-enriched SEI is successfully constructed, leading to the effective inhibition of side reactions and achieving dendrite-free Li metal anodes. Cu@Li||Li cells based on LiTf-contained electrolytes exhibit low overpotential and long-term cycle life over 1400 h, and the Cu@Li||LiFePO4 full cells still have higher capacity retention (70 %) after 500 cycles with an overall Coulombic efficiency (99.6 %).

Anthocyanin, tartaric acid, ascorbic acid of roselle flower (Hibiscus sabdariffa L.) for immunomodulatory adjuvant therapy in oral manifestation coronavirus disease-19: An immunoinformatic approach

Context: Oral manifestations that arose from COVID-19 infection often causes morbidity and systemic drug administration is less effective. Roselle flower (Hibiscus sabdariffa) is one of the plants that is often used in infusion as it gives health benefits. Hence, H. sabdariffa may benefit from adjuvant therapy to treat oral manifestation due to COVID-19. Aims: To investigate the potential of H. sabdariffa anthocyanins, tartaric acid, and ascorbic acid chemical compounds as antiviral, anti-inflammatory, antioxidant, and increasing tissue regeneration in oral manifestation due to COVID-19 infection in silico. Methods: Chemical compounds consisted of anthocyanins, (+)-tartaric acid, and ascorbic acid beside target proteins consisted of ACE2-spike, Foxp3, IL-10, IL6, IL1β, VEGF, FGF-2, HSP70, TNFR and MDA-ovalbumin were obtained from the database, ligand samples were selected through absorption, distribution, metabolism, excretion and toxicology analysis, then molecular docking simulations, identification of protein-ligand interactions, and 3D visualization were performed. Results: Anthocyanins, tartaric acid, and ascorbic acid are the active compounds in H. sabdariffa, which act as antioxidants. The activity of anthocyanin compounds is higher than other compounds through value binding affinity, which is more negative and binds to specific domains of target proteins by forming weak binding interactions that play a role in biological responses. Anthocyanins have the most negative binding energy compared to tartaric-acid and ascorbic acid. Conclusions: Anthocyanins act as antioxidants; this mechanism increases heat shock protein-70 (HSP70), which may play an important role in increasing wound regeneration of oral manifestation in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as documented in silico.

Self-Adjusting Metal-Organic Framework for Efficient Capture of Trace Xenon and Krypton.

The capture of the xenon and krypton from nuclear reprocessing off-gas is essential to the treatment of radioactive waste. Although various porous materials have been employed to capture Xe and Kr, the development of high-performance adsorbents capable of trapping Xe/Kr at very low partial pressure as in the nuclear reprocessing off-gas conditions remains challenging. Herein, we report a self-adjusting metal-organic framework based on multiple weak binding interactions to capture trace Xe and Kr from the nuclear reprocessing off-gas. The self-adjusting behavior of ATC-Cu and its mechanism have been visualized by the in-situ single-crystal X-ray diffraction studies and theoretical calculations. The self-adjusting behavior endows ATC-Cu unprecedented uptake capacities of 2.65 and 0.52 mmol g-1 for Xe and Kr respectively at 0.1 bar and 298 K, as well as the record Xe capture capability from the nuclear reprocessing off-gas. Our work not only provides a benchmark Xe adsorbent but proposes a new route to construct smart materials for efficient separations.

Self‐Adjusting Metal–Organic Framework for Efficient Capture of Trace Xenon and Krypton

AbstractThe capture of the xenon and krypton from nuclear reprocessing off‐gas is essential to the treatment of radioactive waste. Although various porous materials have been employed to capture Xe and Kr, the development of high‐performance adsorbents capable of trapping Xe/Kr at very low partial pressure as in the nuclear reprocessing off‐gas conditions remains challenging. Herein, we report a self‐adjusting metal‐organic framework based on multiple weak binding interactions to capture trace Xe and Kr from the nuclear reprocessing off‐gas. The self‐adjusting behavior of ATC‐Cu and its mechanism have been visualized by the in‐situ single‐crystal X‐ray diffraction studies and theoretical calculations. The self‐adjusting behavior endows ATC‐Cu unprecedented uptake capacities of 2.65 and 0.52 mmol g−1 for Xe and Kr respectively at 0.1 bar and 298 K, as well as the record Xe capture capability from the nuclear reprocessing off‐gas. Our work not only provides a benchmark Xe adsorbent but proposes a new route to construct smart materials for efficient separations.

A simple 4-amino-1,8-naphthalimide hydrazine based “turn-on” fluorescent chemosensor for selective and reversible detection of Zn(II) ion

A new 4-amino-1,8-naphthalimide hydrazine fluorophore (Nap-NH2) has been synthesized in quantitative yield via a one-pot imidation reaction between 4-amino-1,8-naphthalic anhydride and hydrazine hydrate (N2H4·H2O) and successfully employed as a fluorescent “turn-on” chemosensor for metal cations. The sensor Nap-NH2 displayed a positive solvatochromism in different solvents with varying polarities. The fluorescence titration studies of Nap-NH2 with various metal cations disclosed the high selectivity and reversible binding affinity of Nap-NH2 towards Zn(II) ions with nanomolar (10 nm) sensitivity. The fluorescence emission intensity of Nap-NH2 was drastically enhanced upon binding with Zn(II) ion and the Stern-Volmer binding constant is KSV = 1.13 × 104 M−1. Interestingly, the presence of commonly coexisting different metal cations {Fe(II), Cu(II), Mg(II), Cd(II), Ni(II), Co(II), Mn(II), Ba(II), Al(III), Ce(III), Sn(II), Pb(II), Cr(III) and Ca(II)} showed negligible changes in the emission intensity and thus weak binding interactions with Nap-NH2. These studies demonstrate that Nap-NH2 is a potential fluorescence “turn-on” chemosensor for selective, sensitive detection and quantification of biologically relevant metal cations.

The formation of phycocyanin-EGCG complex for improving the color protection stability exposing to light

Phycocyanin (PC) is a natural pigment-protein complex in food dye applications. In this study, a phycocyanin-epigallocatechin gallate (EGCG) complex (PE) was prepared and the effects of EGCG on the structure and color stability of PC were evaluated. The fluorescence results showed that the binding number n was 62.1 ± 3.41 (EGCG/PC) and the binding constant K was 4.39 (±0.2) × 105 M−1, indicating a weak-binding interaction. Fourier transform-infrared analysis showed that EGCG caused structural changes in PC by partially uncoiling α-helix and increasing β-sheet content. The EGCG induced a PC association at a reaction molar ratio above 40:1 (EGCG/PC). Moreover, EGCG protected phycocyanobilin against color fading, making PE more stable relative to PC under 8-days storage in light. This study provides a novel scheme to stabilize PC by forming a complex with polyphenols, which will facilitate the PC application as a natural blue pigment in food.

Mechanism of Inhibitor Selectivity Revealed by Mutagenesis and pre‐Steady‐State Studies

Inosine 5’-monophosphate dehydrogenase (IMPDH) catalyzes the oxidation of IMP to XMP, with concomitant reduction of NAD+ to NADH. This is the pivotal step for de novo guanine nucleotide biosynthesis. The structural and functional differences between mammalian and bacterial IMPDHs make this a promising antibiotic target. Selective and potent inhibitors of bacterial IMPDHs with different scaffolds, like A110 and C91, bind in the cofactor site. Despite the high conservation of this site, some inhibitors display a surprising preference for certain bacterial IMPDHs. The structural basis for this selectivity is unclear even though 16 crystal structures of IMPDH-inhibitor complexes have been solved. IMPDH contains an active site flap that is highly dynamic and disordered. Here, we hypothesize that transient interactions with the flap may account for varied inhibitor potencies. In this work, we report a mutagenesis study and pre-steady-state stopped-flow kinetic investigation of Bacillus anthracis IMPDH (BaIMPDH) aimed to determine the role of the flap in inhibitor selectivity. We introduced a L413A flap mutation in BaIMPDH and measured how inhibitor potencies changed. The results show some inhibitors (eg. A110) have the same potency towards both wild type and mutant enzymes, but other inhibitors (eg. C91) were found to have different potencies. To determine if the mutation changes the relative amount of inhibitor binding intermediates in catalytic cycle, we performed stopped-flow kinetic experiments to defined eleven microscopic rate constants and two equilibrium constants that characterize both the catalytic cycle and details of the inhibition mechanism. Together with steady-state initial rate studies, the results obtained for wild type BaIMPDH show that both A110 and C91 binds with high affinity predominantly to the covalent intermediate (E-XMP*) on the reaction pathway (Kd ≍ 50 nM for A110 and Kd ≍ 40 nM for C91). Only a weak binding interaction (Kd ≍ 1 μM) is observed between A110 and E•IMP, while C91 has a bit stronger interaction with E•IMP (Kd ≍ 0.5 μM). Further pre-steady-state stopped-flow kinetic investigation for BaIMPDH/L413A are in progress to determine the effects of this particular mutation on the microscopic rate constants that characterize the catalytic cycle and on the details of the inhibition mechanism.

A three-component copper phosphonate complex as a sensor platform for sensitive Cd2+ and Zn2+ ion detection in water via fluorescence enhancement

A three-component molecular copper phosphonate [Cu2(H4tpmm)2(Hpybim)2]·H2O (1·H2O), where H6tpmm ​= ​2,4,6-tris(phosphorylmethyl)mesitylene and Hpybim ​= ​2-(2-pyridyl)benzimidazole, showing high thermal stability up to approximately 370 ​°C has been prepared. Complex 1·H2O has a dinuclear structure symmetry-related by a crystallographic inversion center, in which the Cu(II) center suits a highly distorted square pyramidal geometry. Complex 1·H2O shows two extremely weak emission bands in both solid state and H2O suspension phase. However, as Cd2+ and Zn2+ were added into the H2O suspension of 1·H2O, the fluorescence intensity would be remarkably enhanced by 11.1 and 25.2 times, respectively, with a dramatic change in the emission band shape. The fluorescence enhancement sensing of 1·H2O toward Cd2+ and Zn2+ in H2O is highly sensitive with limit of detection (LOD) values of 1.35 and 0.89 ​μM, respectively. Such sensing performances are negligibly interfered by most perturbed metal ions but largely affected by Fe3+, Ni2+, and Co2+. EDX and XPS analyses show the occurrence of weak binding interactions between the Cd2+/Zn2+ ions and the structure of 1·H2O, resulting in fluorescence enhancement. This work demonstrates a highly water stable molecular copper phosphonate behaving as a sensor platform suitable for Cd2+ and Zn2+ ion detection in water via remarkable fluorescence enhancement, providing a new method for metal phosphonate complexes.

Integrating redox-response in crown ethers by disulfide incorporation: a computational approach

Reducing properties are investigated for the minimum energy conformers of selected thiacrown systems with redox-responsive disulfide linkage. The adiabatic electron affinity values of the investigated host systems in the gas phase lie in a range that makes them capable to undergo reversible redox reactions. In water, these show a high propensity to get reduced. Their binding energy with different alkali metal ions (Li+, Na+, and K+) is also determined under gas and aqueous phase conditions. The computational analysis reveals the weak metal binding interactions of disulfide systems than the parent thiacrown ethers. Such weak interaction energies in host-guest complexes indicate the possibility of reversible complexation-decomplexation. This assumably assists the fast release of guest molecules from the disulfide systems in response to the redox stimuli. Possibilities of incorporating such disulfide incorporated moieties in thiacalixarenes are also discussed. The results discussed in the present work are valuable for further development in the practical applications of crown ether–based host materials.