Kinetic Selectivity Research Articles

Investigating the Reactivity and Selectivity of [3]Cumulenes via Double-Hybrid DFT.

We present an initial foundational theoretical investigation into the reactivity of [3]cumulenes, identifying key factors influencing the reaction selectivity using DLPNO-ωB97X-2/Def2-QZVPP. Our study demonstrates moderate to high selectivity among the three double bonds in substituted [3]cumulenes. Specifically, the [4 + 2] cycloaddition reaction is kinetically favored at the terminal π-bonds and thermodynamically favored at the central π-bond. In certain tetrasubstituted [3]cumulenes, enhanced and reversed kinetic selectivity is predicted. Our findings elucidate the reversed selectivity in tetrafluoro[3]cumulene, attributed to the reduced cumulene distortion energy, and predict similar selectivity in tetramethoxy[3]cumulene due to thermodynamic influences. Future research will focus on additional kinetic factors to enhance the stability and practical application of [3]cumulenes in chemical synthesis.

A novel strategy for sequential separation of Th(IV) from highly acidic wastewater based on solid phase extraction

The potential applications and advantages of thorium(Th) in the development of the nuclear industry make the effective separation of Th(IV) crucial for depleted fuel management and environmental safety. However, selectively capturing of Th(IV) from high-concentration nitric acid remains a challenging task. In this work, a novel solid-phase extraction resin (TOPO/XAD-7) was successfully synthesized by vacuum impregnation of trioctylphosphine oxide (TOPO) into an acrylic-based polymer (XAD-7 resin). It exhibited excellent adsorption abilities for Th(IV), including wide highly concentration acid tolerance (0.01–6 mol L−1 HNO3), high adsorption capacity of 59.79 mg g−1, fast adsorption kinetic (< 60 min) and super elevated selectivity. The adsorption mechanism of the resin involves neutral chelation extraction, with the PO group being the main adsorption binding site. Additionally, the resin was demonstrated good reusability and stability under extreme conditions (high acidity, high temperature and high radiation). Furthermore, dynamic column experiments conducted using an automated separation system validated the practical application of TOPO/XAD-7 resin for the separation of Th(IV) and U(VI)/Th(IV) in wastewater, achieving high element recovery (> 99.5%) and a high U(VI) decontamination factor (3.5 × 105). This work confirms the excellent potential of TOPO/XAD-7 resin for the separation and enrichment of Th(IV) in nuclear wastewater.

The Role of Water Networks in Phosphodiesterase Inhibitor Dissociation and Kinetic Selectivity.

In search of new opportunities to develop Trypanosoma brucei phosphodiesterase B1 (TbrPDEB1) inhibitors that have selectivity over the off-target human PDE4 (hPDE4), different stages of a fragment-growing campaign were studied using a variety of biochemical, structural, thermodynamic, and kinetic binding assays. Remarkable differences in binding kinetics were identified and this kinetic selectivity was explored with computational methods, including molecular dynamics and interaction fingerprint analyses. These studies indicate that a key hydrogen bond between GlnQ.50 and the inhibitors is exposed to a water channel in TbrPDEB1, leading to fast unbinding. This water channel is not present in hPDE4, leading to inhibitors with a longer residence time. The computer-aided drug design protocols were applied to a recently disclosed TbrPDEB1 inhibitor with a different scaffold and our results confirm that shielding this key hydrogen bond through disruption of the water channel represents a viable design strategy to develop more selective inhibitors of TbrPDEB1. Our work shows how computational protocols can be used to understand the contribution of solvent dynamics to inhibitor binding, and our results can be applied in the design of selective inhibitors for homologous PDEs found in related parasites.

Kinetic Selectivity of an Electric Field-Induced Nonradical Pathway for Catalytic Oxidation of Phenolic Pollutants by Molecular Oxygen

Kinetic Selectivity of an Electric Field-Induced Nonradical Pathway for Catalytic Oxidation of Phenolic Pollutants by Molecular Oxygen

Impact of the material hydroxylation on the possibility of pentane isomers separation by UiO-66 (Zr) MOF: A combined 2H NMR and MD study

The mobility of the pentane isomers in the hydroxylated UiO-66 metal-organic framework has been characterized. 2H NMR spectroscopy was applied to measure the jump rate of alkanes guest molecules between adjacent cages and estimate the diffusivity. It is inferred that the difference in diffusion coefficients defines the kinetic separation selectivity, which is higher for the linear alkanes. The adsorption of pentane isomers in UiO-66 has been modeled with molecular dynamics (MD) simulation. The adsorbed quantity of isopentane is higher than that for n-pentane, providing the possibility of separation with selectivity α ≈ 8 in stationary conditions. The impact of the UiO-66 MOF hydroxylation state on the mobility of pentane isomers has been characterized by comparison with results obtained for the dehydroxylated UiO-66 material. The hydroxylated state of UiO-66 MOF has 6-time higher separation selectivity for pentane isomers compared to its dehydroxylated state (αhyd ≈ 76). MD calculations show that hydroxylated UiO-66 MOF is more efficient, as the separation selectivity is 4 times lower in the dehydroxylated material. The UiO-66 hydroxylation effect is compared for the mobility of C4 and C5 alkanes. The optimal conditions for C4/C5 alkanes kinetic separation by UiO-66 MOF are established.

Evolutionary Abilities of Minimalistic Physicochemical Models of Life Processes.

The ability of living organisms to persist, grow, evolve and invade environments seemingly challenges physical laws. Emerging Autonomous Systems representing autocatalytic cycles constituted of energized components in a state of Dynamic Kinetic Stability feature some of these properties. These simple theoretical models can grow, can be transferred but need an initiation to emerge and can collapse. Moreover, they can undergo kinetic selection in a way consistent with Darwinian behaviour, though they lack the ability to undergo change. The mere existence of these systems and their open-ended growth potential are proposed to constitute a transmissible factor of a non-coded kind. The onset and selection of epigenetic factors may therefore have preceded that of genetic polymers. Here is addressed the question of how these systems may arise from the diversity exhibited by abiotic organic matter, sometimes associated with intractable mixtures, which may actually be useful in providing initiators. The Darwinian description of evolution may therefore be merged without critical discontinuity within an origin scenario. Accordingly, such a theory would rests solely on physicochemical laws beginning with the potential of emerging autonomous systems to compete and invade the space dimension, and to further develop along other available dimensions including variability and, possibly, cognition.

Energetic portrait of the amyloid beta nucleation transition state.

Amyloid protein aggregates are pathological hallmarks of more than fifty human diseases including the most common neurodegenerative disorders. The atomic structures of amyloid fibrils have now been determined, but the process by which soluble proteins nucleate to form amyloids remains poorly characterised and difficult to study, even though this is the key step to understand to prevent the formation and spread of aggregates. Here we use massively parallel combinatorial mutagenesis, a kinetic selection assay, and machine learning to reveal the transition state of the nucleation reaction of amyloid beta, the protein that aggregates in Alzheimer's disease. By quantifying the nucleation of >140,000 proteins we infer the changes in activation energy for all 798 amino acid substitutions in amyloid beta and the energetic couplings between >600 pairs of mutations. This unprecedented dataset provides the first comprehensive view of the energy landscape and the first large-scale measurement of energetic couplings for a protein transition state. The energy landscape reveals that the amyloid beta nucleation transition state contains a short structured C-terminal hydrophobic core with a subset of interactions similar to mature fibrils. This study demonstrates the feasibility of using mutation-selection-sequencing experiments to study transition states and identifies the key molecular species that initiates amyloid beta aggregation and, potentially, Alzheimer's disease.

Electrostatically driven kinetic inverse CO2/C2H2 separation in LTA-type zeolites

The identical molecular size and similar physical properties of carbon dioxide (CO2) and acetylene (C2H2) make their adsorptive separation extremely challenging to achieve with most adsorbents. Reports on the separation of CO2 and C2H2 mixtures by zeolites are even rarer with the mechanism of adsorptive separation requiring further exploration. In this paper, we report that ion modulation of zeolite 5A promotes the difference in kinetic diffusion of CO2 and C2H2, realizing the inverse separation of zeolite from selective adsorption of C2H2 to selective adsorption of CO2. Creating a compact pore space restricting the orientation of gas molecules enables charge recognition. The positive electrostatic potential at the pore openings was utilized to hinder the diffusion of C2H2 between the cages while ensuring the transfer of CO2, increasing their diffusion differences in pore channels and leading to the CO2/C2H2 kinetic selectivity of 31.97. Grand canonical Monte Carlo (GCMC) simulation demonstrates that the CO2 distribution in K-5A-β is significantly higher than that of C2H2. Dynamic breakthrough experiments verify the excellent performance of material in practical CO2/C2H2 separation, for CO2/C2H2 (50/50 and 1/99, V/V) mixtures can be separated in one step, thus directly generating high purity C2H2 (> 99.95%), which provides a promising thought for the zeolite-based separation of CO2 and C2H2.

Nuclease-assisted selection of slow-off rate aptamers.

Conventional directed evolution methods offer the ability to select bioreceptors with high binding affinity for a specific target in terms of thermodynamic properties. However, there is a lack of analogous approaches for kinetic selection, which could yield affinity reagents that exhibit slow off-rates and thus remain tightly bound to targets for extended periods. Here, we describe an in vitro directed evolution methodology that uses the nuclease flap endonuclease 1 to achieve the efficient discovery of aptamers that have slow dissociation rates. Our nuclease-assisted selection strategy can yield specific aptamers for both small molecules and proteins with off-rates that are an order of magnitude slower relative to those obtained with conventional selection methods while still retaining excellent overall target affinity in terms of thermodynamics. This new methodology provides a generalizable approach for generating slow off-rate aptamers for diverse targets, which could, in turn, prove valuable for applications including molecular devices, bioimaging, and therapy.

Selectively enriching accessible quantum sieving sites in two‐dimensional carbons for D2/H2 kinetic separation

AbstractSeparation of hydrogen isotopes (D2/H2) attracts wide interest due to its important applications, such as nuclear fusion. Kinetic quantum sieving‐induced separation over tailored nanoporous solids is a promising method; however, the dynamic separation often shows a transient feature, thus a low D2/H2 selectivity even at temperature below 50 K. Herein, we selectively enriched the accessible quantum sieving (AQS) sites in two‐dimensional carbons by chemically growing a pore‐narrowing layer. The spatial density of such AQS sites is 8.5 times higher than that of commercial carbon molecular sieves. The kinetic selectivity of D2/H2 reached 4.6 at 77 K. Column breakthrough experiments revealed that the dynamic D2/H2 separation was enhanced by such a nanopore design. Aspen simulation indicated that D2 was enriched to 93.1% within 11 pressure swing adsorption cycles with a 1% D2/99% H2 mixture as feed.

Highly porous metal-organic framework liquids and glasses via a solvent-assisted linker exchange strategy of ZIF-8

By combining the porosity of crystalline metal-organic frameworks (MOFs) with the unique processability of the liquid state, melt-quenched MOF glasses offer exciting opportunities for molecular separation. However, progress in this field is limited by two factors. Firstly, only very few MOFs melt at elevated temperatures and transform into stable glasses upon cooling the corresponding MOF liquid. Secondly, the MOF glasses obtained thus far feature only very small porosities and very small pore sizes. Here, we demonstrate solvent-assisted linker exchange (SALE) as a versatile method to prepare highly porous melt-quenched MOF glasses from the canonical ZIF-8. Two additional organic linkers are incorporated into the non-meltable ZIF-8, yielding high-entropy, linker-exchanged ZIF-8 derivatives undergoing crystal-to-liquid-to-glass phase transitions by thermal treatment. The ZIF-8 glasses demonstrate specific pore volumes of about 0.2 cm3g–1, adsorb large amounts of technologically relevant C3 and C4 hydrocarbons, and feature high kinetic sorption selectivities for the separation of propylene from propane.

Ultrafine CuO/graphene oxide cellulose nanocomposites with complementary framework for polycyclic aromatic hydrocarbon pollutants removal

Efficient and sustainable methods for eliminating polycyclic aromatic hydrocarbon pollutants (PAHPs) are in highly desired. Proven technologies involve physical and chemical reactions that absorb PAHPs, however they encounter formidable challenges. Here, a bottom-up refining-grain strategy is proposed to rationally design ultrafine CuO/graphene oxide-cellulose nanocomposites (LCelCCu) with a mirror-like for tetracycline (TC) to substantially improve the efficient of the purification process by active integrated-sorption. The LCelCCu captures TC with a higher affinity and lower energy demand, as determined by sorption kinetic, isotherms, thermodynamics, and infrared and X-ray Photoelectron Spectroscopy. The resulting material could achieve ultra-high sorption capacity (2775.23 mg/g), kinetic (1.2499 L g−1 h−1) and high selectivity (up to 99.9 %) for TC, nearly surpassing all recent adsorbents. This study simultaneously unveils the pioneering role of simultaneous multi-site match sorption and subsequent advanced oxidation synergistically, fundamentally enhancing understanding of the structure-activity-selectivity relationship and inspires more sustainable water purification applications and broader material design considerations.

Balancing the Kinetic and Thermodynamic Synergetic Effect of Doped Carbon Molecular Sieves for Selective Separation of C2H4/C2H6.

Selective separation of ethylene and ethane (C2H4/C2H6) is a formidable challenge due to their close molecular size and boiling point. Compared to industry-used cryogenic distillation, adsorption separation would offer a more energy-efficient solution when an efficient adsorbent is available. Herein, a class of C2H4/C2H6 separation adsorbents, doped carbon molecular sieves (d-CMSs) is reported which are prepared from the polymerization and subsequent carbonization of resorcinol, m-phenylenediamine, and formaldehyde in ethanol solution. The study demonstrated that the polymer precursor themselves can be a versatile platform for modifying the pore structure and surface functional groups of their derived d-CMSs. The high proportion of pores centered at 3.5Å in d-CMSs contributes significantly to achieving a superior kinetic selectivity of 205 for C2H4/C2H6 separation. The generated pyrrolic-N and pyridinic-N functional sites in d-CMSs contribute to a remarkable elevation of Henry selectivity to 135 due to the enhancement of the surface polarity in d-CMSs. By balancing the synergistic effects of kinetics and thermodynamics, d-CMSs achieve efficient separation of C2H4/C2H6. Polymer-grade C2H4 of 99.71% purity can be achieved with 75% recovery using the devised d-CMSs as reflected in a two-bed vacuum swing adsorption simulation.

Ultrafine nickel-rhodium nanoparticles anchored on two-dimensional vanadium carbide for high performance hydrous hydrazine decomposition at mild conditions

The development of heterogeneous supported nanocatalysts with a high kinetics combined with low cost is off importance but remains still challenged for hydrazine hydrate served as a promising hydrogen storage material. Herein, by virtue of surficial functional groups, ultrafine NiRh NPs were monodispersed on the two-dimensional V2C surface via a conventional wet chemical co-reduction. The optimized NiRh/V2C system demonstrates an excellent catalytic performance toward selectively catalyzing dehydrogenation of hydrazine hydrate, affording 100% H2 selectivity with the turnover frequency (TOF) value of 987.5 h−1 at 323 K. Such an enhancement is mainly attributed to synergistic effect of nanosystem, which will optimize local surface energy and promote electron transfer in NiRh/V2C system, thereby improving the kinetic selectivity of catalytic hydrazine hydrate decomposition. This work has provided a facile strategy for developing nanocatalysts with high kinetics that could enable huge industrial applications in the future.

Bispericyclic Ambimodal Dimerization of Pentafulvene: The Origin of Asynchronicity and Kinetic Selectivity of the Endo Transition State.

The propensity of fulvenes to undergo dimerization has long been known, although the in-depth mechanism and electronic behavior during dimerization are still elusive. Herein, we made an attempt to gain insights into the reactivity of pentafulvene for Diels-Alder (DA) and [6 + 4]-cycloadditions via conventional and ambimodal routes. The result emphasizes that pentafulvene dimerization preferentially proceeds through a unique bifurcation mechanism where two DA pathways merge together to produce two degenerate [4 + 2]-cycloadducts from a single TS. Despite the [6 + 4]-cycloadduct being thermodynamically preferred, [4 + 2]-cycloaddition reactions are kinetically driven. Singlet biradicaloid is involved in through-space 6e- delocalization as a secondary orbital interaction that originates asynchronicity and stabilizes the bispericyclic transition state (TS). The transformation of various actively participating intrinsic bonding orbitals (IBOs) unambiguously forecasts the formation of multiple products from a single TS and rationalizes the mechanism of ambimodal reactions that are rather difficult to probe with other analyses. The changes in active IBOs clearly distinguish the conventional reactions from bifurcation reactions and can be employed to characterize and confirm the ambimodal mechanism. This report gains a crucial theoretical insight into the mechanism of bifurcation, the origin of asynchronicity, and electronic behavior in ambimodal TS, which will certainly be of enormous value for future studies.

Comparative analysis of kinetic model-fitting methods and selection priority for horse manure pyrolysis

The diverse origins of biomass wastes provide a constraint on the practical application of pyrolysis, as it leads to uncertain chemical reactions, feedstock conversion, and energy consumption. Various model-fit methods are available to identify the decomposition kinetics, however, limited studies have compared the reliability and accuracy of those kinetic models. This work compared five different kinetic models, two based on model-fit methods (Coats–Redfern (CR), Kennedy-Clark (KC) and three based on the application forms of Criado Master Plots (CMP I, CMP II and CMP III). The mass loss data from the pyrolysis of horse manure (HM) through a thermogravimetric analyser was used as a biomass sample for evaluation. Results demonstrated that all five model-fit methods report different kinetics data. Although the model-fit methods (CR and KC) allow a direct determination of kinetic triplets, the accuracy of data is lower. The CMP-II and CMP-III methods (incorporating model-free data in the model-fit methods) showcase multi-step chemical kinetics and better describe the decomposition behavior of HM due to its multi-compositional properties. To obtain kinetic triplets with enhanced accuracy, it is recommended to incorporate model-free data into the model-fit method. Improved precision of the kinetics data is essential for developing experimental parameters and optimizing the process. Future research should include the selection criteria of model-fit methods shown in this study to improve the accuracy of kinetic data.

Binary ion-exchanged ETS-4 (Sr/Ba-ETS-4): Synthesis, characterization, and selective nitrogen adsorption from methane for natural gas purification

Several variants of ETS-4 were synthesized through single-cation and binary-cation exchange, with a particular emphasis on Sr/Ba-ETS-4. The impact of binary-cation exchange on the structural characteristics was investigated using various analytical techniques, including XRD, FESEM, EDX, ICP-MS, TGA, and FT-IR analysis. The effect of mixed Sr and Ba exchange within ETS-4 on the adsorption, separation, and kinetic behavior of nitrogen and methane gases was explored utilizing the volumetric method at 30 °C and up to 100 kPa. Additionally, the investigation extended to examining the influence on diffusion coefficients employing the macropore-micropore kinetic model. ICP-MS results revealed a competitive advantage of barium in the exchange process among incoming cations. Notably, significant discrepancies in the adsorption capacity for nitrogen and methane gases were observed between the Sr-ETS-4 and Ba-ETS-4 samples. Experimental isotherm data suggested that the Sips model offered the most suitable fit, unlike the Langmuir or Freundlich models. Among the Sr/Ba-ETS-4 adsorbents investigated, the adsorbent with the highest barium content in the framework exhibited superior nitrogen adsorption capacity (0.33 mmol/g) and the lowest methane adsorption capacity (0.07 mmol/g), leading to high nitrogen over methane equilibrium selectivity (3.12) and kinetic selectivity (167.6).

Immobilization of Amino-site into a Pore-Partitioned Metal-Organic Framework for Highly Efficient Separation of Propyne/Propylene.

Adsorptive separation of propyne/propylene (C3H4/C3H6) is a crucial yet complex process, however, it remains a great difficulty in developing porous materials that can meet the requirements for practical applications, particularly with an exceptional ability to bind and store trace amounts of C3H4. Functionalization of pore-partitioned metal-organic frameworks (ppMOFs) is methodically suited for this challenge owing to the possibility of dramatically increasing binding sites on highly porous and confined domains. We here immobilized Lewis-basic (-NH2) and Lewis-acidic (-NO2) sites on this platform. Along with an integrated nature of high uptake of C3H4 at 1 kPa, high uptake difference of C3H4-C3H6, moderated binding strength, promoted kinetic selectivity, trapping effect and high stability, the NH2-decorated ppMOF (NTU-100-NH2) can efficiently produce polymer-grade C3H6 (99.95 %, 8.3 mmol ⋅ g-1) at room temperature, which is six times more than the NO2-decorated crystal (NTU-100-NO2). The in situ infrared spectroscopy, crystallographic analysis, and sequential blowing tests showed that the densely packed amino group in this highly porous system has a unique ability to recognize and stabilize C3H4 molecules. Moving forward, the strategy of organic functionalization can be extended to other porous systems, making it a powerful tool to customize advanced materials for challenging tasks.

Immobilization of Amino‐site into a Pore‐Partitioned Metal–Organic Framework for Highly Efficient Separation of Propyne/Propylene

AbstractAdsorptive separation of propyne/propylene (C3H4/C3H6) is a crucial yet complex process, however, it remains a great difficulty in developing porous materials that can meet the requirements for practical applications, particularly with an exceptional ability to bind and store trace amounts of C3H4. Functionalization of pore‐partitioned metal–organic frameworks (ppMOFs) is methodically suited for this challenge owing to the possibility of dramatically increasing binding sites on highly porous and confined domains. We here immobilized Lewis‐basic (−NH2) and Lewis‐acidic (−NO2) sites on this platform. Along with an integrated nature of high uptake of C3H4 at 1 kPa, high uptake difference of C3H4−C3H6, moderated binding strength, promoted kinetic selectivity, trapping effect and high stability, the NH2‐decorated ppMOF (NTU‐100‐NH2) can efficiently produce polymer‐grade C3H6 (99.95 %, 8.3 mmol ⋅ g−1) at room temperature, which is six times more than the NO2‐decorated crystal (NTU‐100‐NO2). The in situ infrared spectroscopy, crystallographic analysis, and sequential blowing tests showed that the densely packed amino group in this highly porous system has a unique ability to recognize and stabilize C3H4 molecules. Moving forward, the strategy of organic functionalization can be extended to other porous systems, making it a powerful tool to customize advanced materials for challenging tasks.

Aromatic-Carbonyl Interactions as an Emerging Type of Non-Covalent Interactions.

Aromatic-carbonyl (Ar···C═O) interactions, attractive interactions between the arene plane and the carbon atom of carbonyl, are in the infancy as one type of new supramolecular bonding forces. Here the study and functionalization of aromatic-carbonyl interactions in solution is reported. A combination of aromatic-carbonyl interactions and dynamic covalent chemistry provided a versatile avenue. The stabilizing role and mechanism of arene-aldehyde/imine interactions are elucidated through crystal structures, NMR studies, and computational evidence. The movement of imine exchange equilibria further allowed the quantification of the interplay between arene-aldehyde/imine interactions and dynamic imine chemistry, with solvent effects offering another handle and matching the electrostatic feature of the interactions. Moreover, arene-aldehyde/imine interactions enabled the reversal of kinetic and thermodynamic selectivity and sorting of dynamic covalent libraries. To show the functional utility diverse modulation of fluorescence signals is realized with arene-aldehyde/imine interactions. The results should find applications in many aspects, including molecular recognition, assemblies, catalysis, and intelligent materials.