Mechanical Bond Approach to Introducing Self-Adaptive Active Sites in Covalent Organic Frameworks for Zinc-Catalyzed Organophosphorus Degradation
Ontology highlight
ABSTRACT:
SUBMITTER: Ruan X
PROVIDER: S-EPMC8554822 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Covalent organic frameworks (COFs) are ideal platforms to spatially control the integration of multiple molecular motifs throughout a single nanoporous framework. Despite this design flexibility, COFs are typically synthesized using only two monomers. One bears the functional motif for the envisioned application, while the other is used as an inert connecting building block. Integrating more than one functional motif extends the functionality of COFs immensely, which is particularly useful for multistep reactions such as electrochemical reduction of CO2. In this systematic study, we synthesized five Ni(II)- and Zn(II)-porphyrin-based COFs, including two pure component COFs (Ni100 and Zn100) and three mixed Ni/Zn-COFs (Ni75/Zn25, Ni50/Zn50, and Ni25/Zn75). Among these, the Ni50/Zn50-COF exhibited the highest catalytic performance for the electroreduction of CO2 to CO and formate at -0.6 V vs RHE, as was observed in an H-cell. The catalytic performance of the COF catalysts was further extended to a zero-gap membrane electrode assembly (MEA) operation where, utilizing Ni50/Zn50, CH4 was detected along with CO and formate at a high current density of 150 mA cm-2. In contrast, under these conditions predominantly H2 and CO were detected at Ni100 and Zn100 respectively, indicating a clear synergistic effect between the Ni- and Zn-porphyrin units.
| S-EPMC11231983 | biostudies-literature
Project description:Two 2D covalent organic frameworks (COFs) linked by vinylene (-CH=CH-) groups (V-COF-1 and V-COF-2) are synthesized by exploiting the electron deficient nature of the aromatic s-triazine unit of C3 -symmetric 2,4,6-trimethyl-s-triazine (TMT). The acidic terminal methyl hydrogens of TMT can easily be abstracted by a base, resulting in a stabilized carbanion, which further undergoes aldol condensation with multitopic aryl aldehydes to be reticulated into extended crystalline frameworks (V-COFs). Both V-COF-1 (with terepthalaldehyde (TA)) and V-COF-2 (with 1,3,5-tris(p-formylphenyl)benzene (TFPB)) are polycrystalline and exhibit permanent porosity and BET surface areas of 1341?m2 ?g-1 and 627?m2 ?g-1 , respectively. Owing to the close proximity (3.52?Å) of the pre-organized vinylene linkages within adjacent 2D layers stacked in eclipsed fashion, [2+2] photo-cycloadditon in V-COF-1 formed covalent crosslinks between the COF layers.
| S-EPMC6851556 | biostudies-literature
Project description:Lowering of the electron kinetic energy (KE) upon initial encounter of radical fragments has long been cited as the primary origin of the covalent chemical bond based on Ruedenberg's pioneering analysis of H[Formula: see text] and H2 and presumed generalization to other bonds. This work reports KE changes during the initial encounter corresponding to bond formation for a range of different bonds; the results demand a re-evaluation of the role of the KE. Bonds between heavier elements, such as H3C-CH3, F-F, H3C-OH, H3C-SiH3, and F-SiF3 behave in the opposite way to H[Formula: see text] and H2, with KE often increasing on bringing radical fragments together (though the total energy change is substantially stabilizing). The origin of this difference is Pauli repulsion between the electrons forming the bond and core electrons. These results highlight the fundamental role of constructive quantum interference (or resonance) as the origin of chemical bonding. Differences between the interfering states distinguish one type of bond from another.
| S-EPMC7524788 | biostudies-literature
Project description:Two covalent organic frameworks comprising Lewis basic PIII centers and Lewis acidic boron atoms were prepared by poly-condensation reactions of newly obtained tris(4-diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11-hexahydroxytriphenylene and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm3 g-1 at 1 bar at 77 K), methane (20 cm3 g-1 at 1 bar at 273 K) and carbon dioxide (50 cm3 g-1 at 1 bar at 273 K). They were exploited as solid-state ligands for coordination of Pd0 centers. Alternatively, in a bottom-up approach, boronated phosphine was treated with Pd2 dba3 and poly-condensated, yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P-Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework-guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.
| S-EPMC7589431 | biostudies-literature
Project description:The transfer of phosphate groups is an essential function of many intracellular biological enzymes. The transfer is in many cases facilitated by a protein scaffold involving two closely spaced magnesium "ions". It has long been a mystery how these "ions" can retain their closely spaced positions throughout enzymatic phosphate transfer: Coulomb's law would dictate large repulsive forces between these ions at the observed distances. Here we show, however, that the electron density can be borrowed from nearby electron-rich oxygens to populate a bonding molecular orbital that is largely localized between the magnesium "ions". The result is that the Mg-Mg core of these phosphate transfer enzymes is surprisingly similar to a metastable [Mg2]2+ ion in the gas phase, an ion that has been identified experimentally and studied with high-level quantum-mechanical calculations. This similarity is confirmed by comparative computations of the electron densities of [Mg2]2+ in the gas phase and the Mg-Mg core in the structures derived from QM/MM studies of high-resolution X-ray crystal structures. That there is a level of covalent bonding between the two Mg "ions" at the core of these enzymes is a novel concept that enables an improved vision of how these enzymes function at the molecular level. The concept is broader than magnesium-other biologically relevant metals (e.g., Mn and Zn) can also form similar stabilizing covalent Me-Me bonds in both organometallic and inorganic crystals.
| S-EPMC5573160 | biostudies-literature
Project description:Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material's morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications.
| S-EPMC5269657 | biostudies-literature
Project description:Covalent organic frameworks (COFs) are an emerging class of highly tuneable crystalline, porous materials. Here we report the first COFs that change their electronic structure reversibly depending on the surrounding atmosphere. These COFs can act as solid-state supramolecular solvatochromic sensors that show a strong colour change when exposed to humidity or solvent vapours, dependent on vapour concentration and solvent polarity. The excellent accessibility of the pores in vertically oriented films results in ultrafast response times below 200 ms, outperforming commercially available humidity sensors by more than an order of magnitude. Employing a solvatochromic COF film as a vapour-sensitive light filter, we demonstrate a fast humidity sensor with full reversibility and stability over at least 4000 cycles. Considering their immense chemical diversity and modular design, COFs with fine-tuned solvatochromic properties could broaden the range of possible applications for these materials in sensing and optoelectronics.
| S-EPMC6143592 | biostudies-literature
Project description:Two-dimensional (2D) covalent-organic frameworks (COFs) with a well-defined and tunable periodic porous skeleton are emerging candidates for lightweight and strong 2D polymeric materials. It remains challenging, however, to retain the superior mechanical properties of monolayer COFs in a multilayer stack. Here, we successfully demonstrated a precise layer control in synthesizing atomically thin COFs, enabling a systematic study of layer-dependent mechanical properties of 2D COFs with two different interlayer interactions. It was shown that the methoxy groups in COFTAPB-DMTP provided enhanced interlayer interactions, leading to layer-independent mechanical properties. In sharp contrast, mechanical properties of COFTAPB-PDA decreased significantly as the layer number increased. We attributed these results to higher energy barriers against interlayer sliding due to the presence of interlayer hydrogen bonds and possible mechanical interlocking in COFTAPB-DMTP, as revealed by density functional theory calculations.
| S-EPMC10104513 | biostudies-literature
Project description:CatalyCEST MRI can detect enzyme activity by employing contrast agents that are detected through chemical exchange saturation transfer (CEST). A CEST agent, Tm-DO3A-cadaverine, has been designed to detect the catalytic activity of transglutaminase (TGase), which creates a covalent bond between the agent and the side chain of a glutamine amino acid residue. CEST appeared at -9.2 ppm after TGase conjugated Tm-DO3A-cadaverine to albumin, which also caused a decrease in CEST from albumin at +4.6 ppm. Studies with model peptides revealed similar appearances and decreases in detectable CEST effects following TGase-catalyzed conjugation of the contrast agent and peptide. The MR frequencies and amplitudes of these CEST effects were dependent on the peptide sequence, which demonstrated the sensitivity of CEST agents to ligand conformations that may be exploited to create more responsive molecular imaging agents. The chemical exchange rates of the substrates and conjugated products were measured by fitting modified Bloch equations to CEST spectra, which demonstrated that changes in exchange rates can also be used to detect the formation of a covalent bond by catalyCEST MRI.
| S-EPMC3667154 | biostudies-literature
Project description:Synthetic control over chirality and function is the crowning achievement for metal-organic frameworks, but the same level of control has not been achieved for covalent organic frameworks (COFs). Here we demonstrate chiral COFs (CCOFs) can be crystallized from achiral organic precursors by chiral catalytic induction. A total of nine two-dimensional CCOFs are solvothermally prepared by imine condensations of the C3-symmetric 1,3,5-triformylphloroglucinol (Tp) with diamine or triamine linkers in the presence of catalytic amount of (R)- or (S)-1-phenylethylamine. Homochirality of these CCOFs results from chiral catalyst-induced immobilization of threefold-symmetric tris(N-salicylideneamine) cores with a propeller-like conformation of one single handedness during crystallization. The CCOF-TpTab showed high enantioselectivity toward chiral carbohydrates in fluorescence quenching and, after postsynthetic modification of enaminone groups located in chiral channels with Cu(II) ions, it can also be utilized as a heterogeneous catalyst for the asymmetric Henry reaction of nitroalkane with aldehydes.
| S-EPMC5882852 | biostudies-other