Fast Reactivity Research Articles

Metal-Dependent Asynchronicity of Concerted Proton-Electron Transfer to a High-Valent Copper(III) Complex and Its Nickel(III) Analogue.

A high-valent formally copper(III) complex, [Cu(pyalk)2]+(2) (pyalk = 2-(2'-pyridyl)-2-propanolate), is isolated and characterized by a variety of physical methods, including X-ray crystallography and DFT computational modeling. Complex 2 is found to undergo fast proton-coupled electron transfer with phenol and hydrocarbon substrates, resulting in the reduction of the metal center and protonation of the pyalk ligand. Analysis of kinetic data for the reaction of 2 with both types of substrates suggests that 2 reacts through a concerted proton-electron transfer (CPET) pathway. Thermodynamic analysis indicates that the O-H bond formed during CPET by 2 has a high bond dissociation enthalpy of 103 kcal/mol, consistent with the fast reactivity of 2 as compared to its isostructural nickel(III) analogue, [Ni(pyalk)2]+ (4). Compared to 4, 2 reacts 5-10 times faster with phenol and hydrocarbon substrates and has an O-H BDE ∼6 kcal/mol higher than 4. Further analysis suggests that 4 may undergo CPET through a more basic asynchronous pathway than 2, which may cause the CPET rate with 4 to be much faster than expected from the Bell-Evans-Polanyi principle.

Probing the Redox Reactivity of a Reduced Nontronite: A Quick XAS Operando Study.

Fe-bearing clay minerals contain structural iron that can be redox-active and can participate in electron transfer reactions with aqueous species. Although these redox properties have been studied extensively in the past decade, questions remain about the respective roles of kinetic and thermodynamic constraints in establishing steady-state redox conditions. In this study, the reduction kinetics of aqueous Cr(VI) to Cr(III) by Fe(II) contained in the structure of reduced ferruginous clay samples (reference Nontronite NAu-1) was monitored with quick-XAS (X-ray absorption spectroscopy). These measurements revealed the occurrence of at least two reaction processes with contrasting fast and slow kinetic rates. According to mass and electron balance calculations, Fe(II) located at the edge of the clay mineral particles alone cannot account for the fast reactivity of the samples, pointing out the presence of electron transfer from the inner part of the clay mineral layer structure to the reactive sites. The Fe(II)/Fe(III) ratio in the clay structure quickly reached a steady state after each Cr(VI) addition to the solution. These steady-state conditions were consistent with either a complete depletion of the Cr(VI) reactant for the first spikes of Cr(VI) or a thermodynamic equilibrium between the redox couples, i.e., between structural Fe(III)/Fe(II) and aqueous Cr(VI)/Cr(III), after the pool of fast-reacting Fe(II) was depleted. These results highlight the need to consider kinetic and thermodynamic controls of clay structural iron redox reactivity to predict the fate of redox-sensitive contaminants in the environment.

Selective peptide bond formation via side chain reactivity and self-assembly of abiotic phosphates

In the realm of biology, peptide bonds are formed via reactive phosphate-containing intermediates, facilitated by compartmentalized environments that ensure precise coupling and folding. Herein, we use aminoacyl phosphate esters, synthetic counterparts of biological aminoacyl adenylates, that drive selective peptide bond formation through side chain-controlled reactivity and self-assembly. This strategy results in the preferential incorporation of positively charged amino acids from mixtures containing natural and non-natural amino acids during the spontaneous formation of amide bonds in water. Conversely, aminoacyl phosphate esters that lack assembly and exhibit fast reactivity result in random peptide coupling. By introducing structural modifications to the phosphate esters (ethyl vs. phenyl) while retaining aggregation, we are able to tune the selectivity by incorporating aromatic amino acid residues. This approach enables the synthesis of sequences tailored to the specific phosphate esters, overcoming limitations posed by certain amino acid combinations. Furthermore, we demonstrate that a balance between electrostatic and aromatic stacking interactions facilitates covalent self-sorting or co-assembly during oligomerization reactions using unprotected N-terminus aminoacyl phosphate esters. These findings suggest that self-assembly of abiotic aminoacyl phosphate esters can activate a selection mechanism enabling the departure from randomness during the autonomous formation of amide bonds in water.

Enhanced reactivity of cationic Au(μ-H)2MCp2 complexes (M = Mo and W) enabled by bulky tris-biaryl phosphines.

[(L1)Au(μ-H)2MCp2][BF4] complexes (M = Mo and W) featuring cavity-shaped tris-2-(4,4'-di-tert-butylbi-phenylyl)phosphine (L1) have been isolated. The tungsten derivative showed a remarkably fast reactivity in photolytic hydride transfer to generate the mononuclear gold hydride (L1)AuH. Both bimetallic adducts trap Ag+ cations, forming unprecedented {Au(μ-H)M(μ-H)Ag} trimetallic assemblies with destabilized Au-M interactions.

Are enhanced rock weathering rates overestimated? A few geochemical and mineralogical pitfalls

There is considerable uncertainty when quantifying carbon dioxide removal (CDR) from enhanced rock weathering (ERW). Faster CDR rates mean ERW may significantly impact climate change mitigation, and more carbon credits will financially benefit private companies. However, overestimating CDR risks undermining ERW if meaningless carbon credits are counted. Here, we aim to contribute to the discussion of CDR quantification by describing three potential pitfalls relating to the geochemical and mineralogical compositions of rock powders. First, rock powders used for ERW are often mineralogically complex and may initially exhibit fast dissolution rates due to reactive surfaces and phases, leading to overestimating long-term CDR rates. Second, the dissolution of accessory carbonates within ERW rock powders will tend to dominate cation and dissolved inorganic carbon fluxes, which, if not identified, can be misconstrued as silicate weathering and overestimate CDR. Third, methods that rely on measuring cations may be prone to misinterpretation as cations will often not be balanced with dissolved inorganic carbon, e.g., during strong acid weathering. As another example, mineral dissolution during solid-phase testing (e.g., cation exchange) is also unrelated to carbonic acid weathering and, thus, may overestimate CDR rates. To avoid these pitfalls, we recommend (1) incorporating high-dosage test plots into ERW trials that avoid reapplication of rock powders that replenish initially fast reactivity, (2) screening rock powders for carbonate minerals using sensitive techniques and distinguishing carbonate and silicate weathering, and (3) measuring carbon to verify carbon dioxide removal. High-quality carbon credits must be durable, additional, and not overestimated.

Glasses for bone regeneration: structural features controlling physical properties and ion release of bioactive glasses 45S5, S53P4 and 13-93.

The structure, i.e. atomic arrangement, of glasses is known to determine many of their properties. This study investigates the structure of three well-known bioactive glass compositions, 45S5 (known as Bioglass), S53P4 (commercialised as BonAlive) and 13-93 (developed for improved high-temperature processing) by Si-29 and P-31 solid-state nuclear magnetic resonance and Raman spectroscopy. Results show that 45S5 has a more depolymerised silicate structure than the other two glasses, in agreement with its lowest silica content. These structural differences explain the well known high solubility and fast reactivity in vivo of 45S5 compared to the other two compositions. Differences between S53P4 and 13-93, by contrast, originate more from differences in their average modifier field strength, as their network connectivity, i.e. average silicate network polymerisation, is similar. As a result, 13-93 shows the lowest crystallisation tendency of the three glasses but also reacts relatively slowly during contact with aqueous solutions. The structural differences are also reflected in glass viscosity, where at a given temperature 45S5 has the lowest viscosity, 13-93 the highest and S53P4's viscosity is lying in between.

Indole Nucleophile Triggers Mechanistic Divergence in Ni-Photoredox N-Arylation.

This study presents a Ni-photoredox method for indole N-arylation, broadening the range of substrates to include indoles with unprotected C3-positions and base-sensitive groups. Through detailed mechanistic inquiries, a Ni(I/III) mechanism was uncovered, distinct from those commonly proposed for Ni-catalyzed amine, thiol, and alcohol arylation, as well as from the Ni(0/II/III) cycle identified for amide arylation under almost identical conditions. The key finding is the formation of a Ni(I) intermediate bearing the indole nucleophile as a ligand prior to oxidative addition, which is rare for Ni-photoredox carbon-heteroatom coupling and has a profound impact on the reaction kinetics and scope. The pre-coordination of indole renders a more electron-rich Ni(I) intermediate, which broadens the scope by enabling fast reactivity even with challenging electron-rich aryl bromide substrates. Thus, this work highlights the often-overlooked influence of X-type ligands on Ni oxidative addition rates and illustrates yet another mechanistic divergence in Ni-photoredox C-heteroatom couplings.

Visualizing lysosomes hypochlorous acid in Parkinson's disease models by a novel fluorescent probe

Visualizing lysosomes hypochlorous acid in Parkinson's disease models by a novel fluorescent probe

Mechanochemical Cascade Cyclization of Cyclopropyl Ketones with 1,2-Diamino Arenes for the Direct Synthesis of 1,2-Disubstituted Benzimidazoles†.

A mechanochemical synthesis of 1,2-disubstituted benzimidazoles from donor-acceptor cyclopropyl ketones and 1,2-diaminoarenes under metal-free and solventless conditions is reported. The reaction does not require inert conditions and is promoted by a stoichiometric amount of 1,1,1,3,3,3-hexafluoroisopropanol. This cascade reaction involves ring-opening, cyclization, and retro-Mannich reaction of cyclopropyl ketones with aryl 1,2-diamines. Compared to its solution-phase counterpart, this mechanochemical approach shows fast reactivity (24 vs 1.5 h). Mechanistic investigations by electrospray ionization mass spectrometry helped us to propose the reaction mechanism.

Online headspace monitoring of volatile organic compounds using proton transfer reaction-mass spectrometry: Application to the multiphase atmospheric fate of 2,4-hexadienedial

Online headspace monitoring of volatile organic compounds using proton transfer reaction-mass spectrometry: Application to the multiphase atmospheric fate of 2,4-hexadienedial

Alkali-activated slag & fly ash as sustainable alternatives to OPC: Sorptivity and strength development characteristics of mortar

Alkali-activated slag & fly ash as sustainable alternatives to OPC: Sorptivity and strength development characteristics of mortar

Supercapacitors Based on Resveratrol/Reduced Graphene Oxide Composites

Resveratrol (Res), which is a redox activation reagent, is a remarkably cheap and high-energy pseudocapacitive material because of possessing fast and reversible redox reactivity. Herein, we investigated Res as an organic compound with oxidation–reduction activity. One of the effective strategies to address these drawbacks, which are high costs, unfriendly environment, and short redox reactivity, is to composite Res with three-dimensional graphene structures. The obtained composites of Res/reduced graphene oxide (rGO) showed an abundance of active sites and a high specific capacitance. Res/rGO composites with different amounts of Res and GO were prepared using a one-step hydrothermal method. Electrochemical performance test results showed that the addition of Res resulted in a higher specific capacitance of the composite compared with that of rGO, reaching 588 F g–1 in 6 mol L–1 potassium hydroxide when the mass ratio of GO-to-Res was 3:1. In the specific capacitance at a current density of 2 A g–1, cycling stability was good, and the initial capacitance was 88.8% after 10,000 cycles. Adsorption energies and density of states of Res on graphene surfaces are calculated to further understand the charge storage mechanism by density functional theory. The calculation results show that Res plays a crucial role in excellent electrochemical performance.

HCN channels at the cell soma ensure the rapid electrical reactivity of fast-spiking interneurons in human neocortex

Accumulating evidence indicates that there are substantial species differences in the properties of mammalian neurons, yet theories on circuit activity and information processing in the human brain are based heavily on results obtained from rodents and other experimental animals. This knowledge gap may be particularly important for understanding the neocortex, the brain area responsible for the most complex neuronal operations and showing the greatest evolutionary divergence. Here, we examined differences in the electrophysiological properties of human and mouse fast-spiking GABAergic basket cells, among the most abundant inhibitory interneurons in cortex. Analyses of membrane potential responses to current input, pharmacologically isolated somatic leak currents, isolated soma outside-out patch recordings, and immunohistochemical staining revealed that human neocortical basket cells abundantly express hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel isoforms HCN1 and HCN2 at the cell soma membrane, whereas these channels are sparse at the rodent basket cell soma membrane. Antagonist experiments showed that HCN channels in human neurons contribute to the resting membrane potential and cell excitability at the cell soma, accelerate somatic membrane potential kinetics, and shorten the lag between excitatory postsynaptic potentials and action potential generation. These effects are important because the soma of human fast-spiking neurons without HCN channels exhibit low persistent ion leak and slow membrane potential kinetics, compared with mouse fast-spiking neurons. HCN channels speed up human cell membrane potential kinetics and help attain an input-output rate close to that of rodent cells. Computational modeling demonstrated that HCN channel activity at the human fast-spiking cell soma membrane is sufficient to accelerate the input-output function as observed in cell recordings. Thus, human and mouse fast-spiking neurons exhibit functionally significant differences in ion channel composition at the cell soma membrane to set the speed and fidelity of their input-output function. These HCN channels ensure fast electrical reactivity of fast-spiking cells in human neocortex.

A photodynamic color sensor using diacetylene vesicles for the rapid visualization of singlet oxygen

A photodynamic color sensor using diacetylene vesicles for the rapid visualization of singlet oxygen

Cation-Induced Fibrillation of Microbial Glycolipid Biosurfactant Probed by Ion-Resolved In Situ SAXS.

Biological amphiphiles are molecules with a rich phase behavior. Micellar, vesicular, and even fibrillar phases can be found for the same molecule by applying a change in pH or by selecting the appropriate metal ion. The rich phase behavior paves the way toward a broad class of soft materials, from carriers to hydrogels. The present work contributes to understanding the fibrillation of a microbial glycolipid, glucolipid G-C18:1, produced by Starmerella bombicola ΔugtB1 and characterized by a micellar phase at alkaline pH and a vesicular phase at acidic pH. Fibrillation and prompt hydrogelation is triggered by adding either alkaline earth, Ca2+, or transition metal, Ag+, Fe2+, Al3+, ions to a G-C18:1 micellar solution. A specifically designed apparatus coupled to a synchrotron SAXS beamline allows the performing of simultaneous cation- and pH-resolved in situ monitoring of the morphological evolution from spheroidal micelles to crystalline fibers, when Ca2+ is employed, or to wormlike aggregates, when Fe2+ or Al3+ solutions are employed. The fast reactivity of Ag+ and the crystallinity of Ca2+-induced fibers suggest that fibrillation is driven by direct metal-ligand interactions, while the shape transition from spheroidal to elongated micelles with Fe2+ or Al3+ rather suggest charge screening between the lipid and the hydroxylated cation species.

Interactive Dashboard with Visual Sensing and Fast Reactivity

These days, technology is growing rapidly, and the market has been introduced with lots of fascinating ways to interact with computers. The advancement of deep learning models and hardware technology also enables more applications with fancy features to be built. The importance of hand gesture recognition has increased due to the prevalence of touchless applications. However, developing an efficient recognition system needs to overcome the challenges of hand segmentation, local hand shape representation, global body configuration representation, and a gesture sequence model. This paper proposed an interactive dashboard that could react to hand gestures. This is also an initiative of the Tunku Abdul Rahman University College (TAR UC) Smart Campus project. Deep learning models were investigated in this research and the optimal model was selected for the dashboard. In addition, 20BN Jester Dataset was used for the dashboard development. To set up a more user-friendly dashboard, the data communication stream between the captured input stream and commands among the devices were studied. As to achieve higher responsiveness from the dashboard, evaluation on data communication protocols which were used to pass the input data were included in the study.

Linker Engineering of 2D Imine Covalent Organic Frameworks for the Heterogeneous Palladium-Catalyzed Suzuki Coupling Reaction.

Covalent organic frameworks (COFs) are an emerging class of porous organic polymers that have been utilized as scaffolds for anchoring metal active species to act as heterogeneous catalysts. Though several examples of such COFs exist, a thorough experimental and computational analysis on such catalysts is limited. In this work, a series of two-dimensional (2D) imine COFs (TTA-DFB COF (N), TTA-TBD COF (N∧O), and TTA-DFP COF(N∧N)) were synthesized by using suitable building units to obtain three different coordination sites (N, N∧O, and N∧N). These were post-modified with Pd(II) to catalyze the Suzuki-Miyaura coupling reaction. Pd@TTA-DFB COF, where Pd(II) was coordinated to N sites, showed the fastest reactivity and lower stability. Pd@TTA-DFP COF showed highest stability but slowest reactivity. Pd@TTA-TBD COF was the best among the three with both high stability and fast reactivity. By combining both experimental and computational results, we conclude that the Pd(II) to Pd(0) reduction is a key step in the difference between the catalytic reactivities of the three COFs. This study demonstrates the importance of the building block approach to design COFs for efficient heterogeneous catalysis and to understand the fate of the reaction profile.

Alcohol addition improves the liquid-phase plasma process for “Green” reduction of graphene oxide

Alcohol addition improves the liquid-phase plasma process for “Green” reduction of graphene oxide

Transient Radiation-Induced Berkelium(III) and Californium(III) Redox Chemistry in Aqueous Solution.

Despite the significant impact of radiation-induced redox reactions on the accessibility and lifetimes of actinide oxidation states, fundamental knowledge of aqueous actinide metal ion radiation chemistry is limited, especially for the late actinides. A quantitative understanding of these intrinsic radiation-induced processes is essential for investigating the fundamental properties of these actinides. We present here a picosecond electron pulse reaction kinetics study into the radiation-induced redox chemistry of trivalent berkelium (Bk(III)) and californium (Cf(III)) ions in acidic aqueous solutions at ambient temperature. New and first-of-a-kind, second-order rate coefficients are reported for the transient radical-induced reduction of Bk(III) and Cf(III) by the hydrated electron (eaq-) and hydrogen atom (H•), demonstrating a significant reactivity (up to 1011 M-1 s-1) indicative of a preference of these metals to adopt divalent states. Additionally, we report the first-ever second-order rate coefficients for the transient radical-induced oxidation of these elements by a reaction with hydroxyl (•OH) and nitrate (NO3•) radicals, which also exhibited fast reactivity (ca. 108 M-1 s-1). Transient Cf(II), Cf(IV), and Bk(IV) absorption spectra are also reported. Overall, the presented data highlight the existence of rich, complex, intrinsic late actinide radiation-induced redox chemistry that has the potential to influence the findings of other areas of actinide science.

Cation Exchange in Smectites as a New Approach to Mineral Carbonation

Mineral carbonation of alkaline mine residues is a carbon dioxide removal (CDR) strategy that can be employed by the mining industry. Here, we describe the mineralogy and reactivity of processed kimberlites and kimberlite ore from Venetia (South Africa) and Gahcho Kué (Canada) diamond mines, which are smectite-rich (2.3–44.1 wt.%). Whereas, serpentines, olivines, hydrotalcites and brucite have been traditionally used for mineral carbonation, little is known about the reactivity of smectites to CO2. The smectite from both mines is distributed as a fine-matrix and is saponite, Mx/mm+Mg3(AlxSi4−x)O10(OH)2·nH2O, where the layer charge deficiency is balanced by labile, hydrated interlayer cations (Mm+). A positive correlation between cation exchange capacity and saponite content indicates that smectite is the most reactive phase within these ultramafic rocks and that it can be used as a source of labile Mg2+ and Ca2+ for carbonation reactions. Our work shows that smectites provide the fast reactivity of kimberlite to CO2 in the absence of the highly reactive mineral brucite [Mg(OH)2]. It opens up the possibility of using other, previously inaccessible rock types for mineral carbonation including tailings from smectite-rich sediment-hosted metal deposits and oil sands tailings. We present a decision tree for accelerated mineral carbonation at mines based on this revised understanding of mineralogical controls on carbonation potential.