An atropisomeric M2L4 cage mixture displaying guest-induced convergence and strong guest emission in water.
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ABSTRACT:
SUBMITTER: Tsutsui T
PROVIDER: S-EPMC8163439 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Subcomponent exchange transformed new high-spin FeII4L4 cage 1 into previously-reported low-spin FeII4L4 cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage's FeII centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin FeII4L6 cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system's behavior, fundamentally altering its response to the subsequent signal p-anisidine.
| S-EPMC5537689 | biostudies-literature
Project description:The encapsulation of molecular guests into supramolecular hosts is a complex molecular recognition process in which the guest displaces the solvent from the host cavity, while the host deforms to let the guest in. An atomistic description of the association would provide valuable insights on the physicochemical properties that guide it. This understanding may be used to design novel host assemblies with improved properties (i.e., affinities) toward a given class of guests. Molecular simulations may be conveniently used to model the association processes. It is thus of interest to establish efficient protocols to trace the encapsulation process and to predict the associated magnitudes ΔGbind and ΔGbind⧧. Here, we report the calculation of the Gibbs energy barrier and Gibbs binding energy by means of explicit solvent molecular simulations for the [Ga4L6]12- metallocage encapsulating a series of cationic molecules. The ΔGbind⧧ for encapsulation was estimated by means of umbrella sampling simulations. The steps involved were identified, including ion-pair formation and naphthalene rotation (from L ligands of the metallocage) during the guest's entrance. The ΔGbind values were computed using the attach-pull-release method. The results reveal the sensitivity of the estimates on the force field parameters, in particular on atomic charges, showing that higher accuracy is obtained when charges are derived from implicit solvent quantum chemical calculations. Correlation analysis identified some indicators for the binding affinity trends. All computed magnitudes are in very good agreement with experimental observations. This work provides, on one side, a benchmarked way to computationally model a highly charged metallocage encapsulation process. This includes a nonstandard parameterization and charge derivation procedure. On the other hand, it gives specific mechanistic information on the binding processes of [Ga4L6]12- at the molecular level where key motions are depicted. Taken together, the study provides an interesting option for the future design of metal-organic cages.
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Project description:Aims:Extragalactic observations of water emission can provide valuable insights into the excitation of the interstellar medium. In particular they allow us to investigate the excitation mechanisms in obscured nuclei, i.e. whether an active galactic nucleus or a starburst dominate. Methods:We use sub-arcsecond resolution observations to tackle the nature of the water emission in Arp 220. ALMA Band 5 science verification observations of the 183 GHz H2O 313-220 line, in conjunction with new ALMA Band 7 H2O 515-422 data at 325 GHz, and supplementary 22 GHz H2O 616 - 523 VLA observations, are used to better constrain the parameter space in the excitation modelling of the water lines. Results:We detect 183 GHz H2O and 325 GHz water emission towards the two compact nuclei at the center of Arp 220, being brighter in Arp 220 West. The emission at these two frequencies is compared to previous single-dish data and does not show evidence of variability. The 183 and 325 GHz lines show similar spectra and kinematics, but the 22 GHz profile is significantly different in both nuclei due to a blend with an NH3 absorption line. Conclusions:Our findings suggest that the most likely scenario to cause the observed water emission in Arp 220 is a large number of independent masers originating from numerous star-forming regions.
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Project description:A crystallographic investigation of a series of host-guest complexes in which small-molecule organic guests occupy the central cavity of an approximately cubic M8 L12 coordination cage has revealed some unexpected behaviour. Whilst some guests form 1:1 H?G complexes as we have seen before, an extensive family of bicyclic guests-including some substituted coumarins and various saturated analogues-form 1:2 H?G2 complexes in the solid state, despite the fact that solution titrations are consistent with 1:1 complex formation, and the combined volume of the pair of guests significantly exceeds the Rebek 55±9?% packing for optimal guest binding, with packing coefficients of up to 87?%. Re-examination of solution titration data for guest binding in two cases showed that, although conventional fluorescence titrations are consistent with 1:1 binding model, alternative forms of analysis-Job plot and an NMR titration-at higher concentrations do provide evidence for 1:2 H?G2 complex formation. The observation of guests binding in pairs in some cases opens new possibilities for altered reactivity of bound guests, and also highlights the recently articulated difficulties associated with determining stoichiometry of supramolecular complexes in solution.
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Project description:The nature of the actinide-actinide bonds is of fundamental importance to understand the electronic structure of the 5f elements. It has attracted considerable theoretical attention, but little is known experimentally as the synthesis of these chemical bonds remains extremely challenging. Herein, we report a strong covalent Th-Th bond formed between two rarely accessible Th3+ ions, stabilized inside a fullerene cage nanocontainer as Th2@Ih(7)-C80. This compound is synthesized using the arc-discharge method and fully characterized using several techniques. The single-crystal X-Ray diffraction analysis determines that the two Th atoms are separated by 3.816 Å. Both experimental and quantum-chemical results show that the two Th atoms have formal charges of +3 and confirm the presence of a strong covalent Th-Th bond inside Ih(7)-C80. Moreover, density functional theory and ab initio multireference calculations suggest that the overlap between the 7s/6d hybrid thorium orbitals is so large that the bond still exists at Th-Th separations larger than 6 Å. This work demonstrates the authenticity of covalent actinide metal-metal bonds in a stable compound and deepens our fundamental understanding of f element metal bonds.
| S-EPMC8062539 | biostudies-literature
Project description:A self-assembled M(2)L(4) palladium-pyridyl cluster with a "paddle-wheel" structure shows binding affinity in competitive organic solvents for neutral organic guests that possess both the correct size and electrostatic complementarity.
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Project description:Supramolecular self-assembly of biomolecules provides a powerful bottom-up strategy to build functional nanostructures and materials. Among the different biomacromolecules, protein cages offer various advantages including uniform size, versatility, multi-modularity, and high stability. Additionally, protein cage crystals present confined microenvironments with well-defined dimensions. On the other hand, molecular hosts, such as cyclophanes, possess a defined cavity size and selective recognition of guest molecules. However, the successful combination of macrocycles and protein cages to achieve functional co-crystals has remained limited. In this study, we demonstrate electrostatic binding between cationic pillar[5]arenes and (apo)ferritin cages that results in porous and crystalline frameworks. The electrostatically assembled crystals present a face-centered cubic (FCC) lattice and have been characterized by means of small-angle X-ray scattering and cryo-TEM. These hierarchical structures result in a multiadsorbent framework capable of hosting both organic and inorganic pollutants, such as dyes and toxic metals, with potential application in water-remediation technologies.
| S-EPMC9305414 | biostudies-literature
Project description:We examine the low-temperature states supported by the quasiperiodic host-guest structure of elemental bismuth at high pressure, Bi-III. Our electronic transport and magnetization experiments establish Bi-III as a rare example of type II superconductivity in an element, with a record upper critical field of ~ 2.5 T, unusually strong electron-phonon coupling, and an anomalously large, linear temperature dependence of the electrical resistivity in the normal state. These properties may be attributed to the peculiar phonon spectrum of incommensurate host-guest structures, which exhibit additional quasi-acoustic sliding modes, suggesting a pathway toward strong coupling superconductivity with the potential for enhanced transition temperatures and high critical fields.
| S-EPMC5898833 | biostudies-other
Project description:Concentration- and time-dependent genomic changes in the mouse urinary bladder following exposure to arsenate in drinking water for up to twelve weeks. Inorganic arsenic (Asi) is a known human bladder carcinogen. The objective of this study was to examine the concentration dependence of the genomic response to Asi in the urinary bladders of mice. C57BL/6J mice were exposed for 1 or 12 weeks to arsenate in drinking water at concentrations of 0.5, 2, 10, and 50 mg As/L. Urinary bladders were analyzed using gene expression microarrays. A consistent reversal was observed in the direction of gene expression change: from predominantly decreased expression at 1 week to predominantly increased expression at 12 weeks. These results are consistent with evidence from in vitro studies of an acute adaptive response that is suppressed on longer exposure due to down-regulation of Fos. Pathways with the highest enrichment in gene expression changes were associated with epithelial-to-mesenchymal transition, inflammation, and proliferation. Benchmark dose (BMD) analysis determined that the lowest median BMD values for pathways were above 5 mg As/L, despite the fact that pathway enrichment was observed at the 0.5 mg As/L exposure concentration. This disparity may result from the non-monotonic nature of the concentration-responses for the expression changes of a number of genes, as evidenced by the much fewer gene expression changes at 2 mg As/L compared to lower or higher concentrations. Pathway categories with concentration-related gene expression changes included cellular morphogenesis, inflammation, apoptosis/survival, cell cycle control, and DNA damage response. The results of this study provide evidence of a concentration-dependent transition in the mode of action for the subchronic effects of Asi in mouse bladder cells in the vicinity of 2 mg Asi/L.
2011-09-15 | GSE32102 | GEO
Project description:The affinity of guanidinium and Cu(II) containing hosts for polycarboxylate guests is studied in water by using UV-visible spectroscopy and isothermal titration calorimetry. By combining a Cu(II) coordination site and a diguanidinium moiety around a single scaffold it is found that the Gibbs free-energy release upon binding is greater than could be expected based on the sum of the free energy released by the binding functional groups when operating in isolation. This effect is known as positive cooperativity and has rarely been observed with synthetic hosts in water. The isothermal titration calorimetry data suggest that the source of this positive cooperativity is enthalpic in origin. We propose that covalently positioning the cationic binding moieties in close proximity destabilizes the unbound host, and thereby the stabilizing effect of binding the anionic carboxylates is exothermic and also, the source of positive cooperativity observed herein.
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