Chemical Activation Mechanism Research Articles

Chemical Activation and Mechanical Sensitization of Piezo1 Enhance TRAIL-Mediated Apoptosis in Glioblastoma Cells.

Glioblastoma multiforme (GBM), the most common and aggressive type of primary brain tumor, has a mean survival of less than 15 months after standard treatment. Treatment with the current standard of care, temozolomide (TMZ), may be ineffective if damaged tumor cells undergo DNA repair or acquire mutations that inactivate transcription factor p53. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in multiple tumor types, while evading healthy cells, through a transcription-independent mechanism. GBM is particularly resistant to TRAIL, but studies have found that the mechanoreceptor Piezo1 can be activated under static conditions via Yoda1 agonist to induce TRAIL sensitization in other cancer cell lines. This study examines the effects and the mechanism of chemical and mechanical activation of Piezo1, via Yoda1 and fluid shear stress (FSS) stimulation, on TRAIL-mediated apoptosis in GBM cells. Here, we demonstrate that Yoda1 + TRAIL and FSS + TRAIL combination therapies significantly increase apoptosis in two GBM cell lines relative to controls. Further, cells known to be resistant to TMZ were found to have higher levels of Piezo1 expression and were more susceptible to TRAIL sensitization by Piezo1 activation. The combinatory Yoda1 + TRAIL treatment significantly decreased cell viability in TMZ-resistant GBM cells when compared to treatment with both low and high doses of TMZ. The results of this study suggest the potential of a highly specific and minimally invasive approach to overcome TMZ resistance in GBM by sensitizing cancer cells to TRAIL treatment via chemical or mechanical activation of Piezo1.

Activation Mechanism of Coal Gangue and Its Impact on the Properties of Geopolymers: A Review.

Coal gangue is one of the industrial solid wastes that may harm the human body through the ecosystem for a long time. Using coal gangue in geopolymer preparation can effectively reduce cement output and meet the sustainability requirements. In this paper, the physical and chemical characteristics, including the heavy metal content, of coal gangue from different producing areas are described. Then, the mechanism of physical activation (mechanical and thermal activation), chemical activation, and compound activation of coal gangue are illustrated. The machinability, as well as the mechanical, microscopic, and toxicity consolidation properties of geopolymers prepared from coal gangue, are summarized and analyzed. The results indicate that the coal gangue geopolymers can have higher mobility and mechanical strength than cement-based composites by adjusting high calcium element material, alkali activator content, Na2SiO3 modulus, and curing condition. After physical activation, coal gangue is used in geopolymer preparation with a chemical activator (alkali excitation agent), which effectively forms a three-dimensional silicon aluminate polymer network. The pore structure is dense, the physical fixation and chemical bonding are strengthened, and the solidification and adsorption of heavy metal ions are improved. Further, it can also be applied to solidifying radioactive waste, which is following the future development direction.

Characteristics of activated carbon prepared from flax shive by NH4NO3 and NH4Cl activation

The thermogravimetric method was used to study one-stage pyrolysis of finely ground flax shive chemically activated by NH4NO3 (AN) and NH4Cl (NAC). Activated carbons (AC) were obtained and the chemical activation mechanism was determined. The morphology, surface area and pore size distribution of the AC samples were studied by the methods of scanning electron microscopy, low-temperature nitrogen adsorption, energy-dispersive X-ray spectroscopy and X-ray diffraction. The maximum methylene blue adsorption capacity of the obtained AC samples was determined. The optimal parameters of activated flax shive pyrolysis (temperature, time) required for obtaining AC with the maximum specific surface area and adsorption capacity were identified.

Insight into KOH activation mechanism during biomass pyrolysis: Chemical reactions between O-containing groups and KOH

Understanding the specific chemical activation mechanism during biomass pyrolysis is critical for the more efficient use of biomass and biochar. In this study, the effects of KOH/biomass ratios (1:8 to 1:1) and temperatures (400–800 °C) on biomass pyrolysis were investigated. The KOH chemical activation mechanism was explored by revealing the evolution mechanisms of the gaseous product, bio-oil, biochar, and KOH, based on experiments and quantum calculations. Results showed that KOH can react with active O-containing species in biomass, which was the main reaction at lower ratios (1:8–1:2) or lower temperatures (400–600 °C). Here, KOH was completely transformed to K2CO3, leading to the formation of large amounts of gaseous products and phenols (reaching 75%). The reaction between KOH and more stable carbon fragments, however, was enhanced at higher ratios (>1:2) or higher temperatures (700–800 °C), such that it became the main reaction. With a significant decrease in the phenols and O-species, the hydrocarbons became the dominant species (reaching a content of 57.43%). For biochar, the reactions among KOH, O-containing species, and carbon fragments generated an abundance of vacancies in the biochar. The OH– from KOH rapidly entered these vacancies, forming a large amount of new O-containing groups (i.e., CO, OH, CO, OCO, and COOH groups). This also caused an increase in oxygen content (reaching 23.68 wt%) in biochar. At higher temperatures, the reactions between KOH and biomass were significantly enhanced, along with a sharp increase in the specific surface area (reaching 1351.13 m2/g). O-containing groups further transformed to more stable OH, CO, and COOH groups. Based on the evolution mechanism of pyrolytic products and KOH, the KOH chemical activation mechanism during biomass pyrolysis was revealed, allowing us, for the first time, to propose a possible chemical reaction pathway between KOH and O-containing groups.

Study on Preparation of Activated Carbon from Sludge

Sludge, a carbon-rich material and favourable precursor of activated carbon, has stimulated new methods for the production of activated carbons for water gas treatment. Herein, various influence factors, concluding sludge resource, pyrolysis process and the type of activators, of the preparation of sludge-based activated carbon have been compiled. Moreover, the mechanism of chemical and physical activation was analyzed. Finally, Then the main research directions of preparation of activated carbons from pyrolytic sludge also were proposed.

Design and Preparation of Biomass-Derived Carbon Materials for Supercapacitors: A Review

The synthesis and application of biomass-derived carbon in energy storage have drawn increasing research attention due to the ease of fabrication, cost-effectiveness, and sustainability of the meso/microporous carbon produced from various biological precursors, including plants, fruits, microorganisms, and animals. Compared to the artificial nanostructured carbons, such as fullerene, carbon nanotube and graphene, the biomass-derived carbons may obtain superior capacitance, rate performance and stability in supercapacitor applications ascribing to their intrinsic nanoporous and hierarchical structures. However, challenges remain in processing techniques to obtain biomass-derived carbons with high carbon yield, high energy density, and controllable graphitic microstructures, which may require a clear understanding over the chemical and elemental compositions, and the intrinsic microstructural characteristics of the biological precursors. Herein we present comprehensive analyses over the impacts of the chemical and elemental compositions of the precursors on the carbon yield of the biomass, as well as the mechanism of chemical activation on the nanoporous structure development of the biomass-derived carbons. The structure–property relationship and functional performance of various biomass-derived carbons for supercapacitor applications are also discussed in detail and compared. Finally, useful insights are also provided for the improvements of biomass-derived carbons in supercapacitor applications.

Quaternary Ammonium Groups Modified Starch Microspheres for Instant Hemorrhage Control

Instant rapid hemostasis is crucial not only for decreasing mortality in these conditions, but also for optimal recovery. The hemostatic agents on the market suffer from inefficiency hemostasis, nondegradability, high cost and potential safety issues. It is necessary to develop a hemostatic agent with rapid hemostatic performance, potent biodegradation and improved biocompatibility. The aim of this work was to develop a novel type of cationic modified starch microspheres (CS) and investigate its hemostatic performance. CS was firstly developed via enzymatic hydrolysis and then assembled with quaternary ammonium groups by etherification reaction with microsporous starch. The result showed that CH3-N+groups were successfully grafted on the backbone of CS. The zeta potential of CS was increased by 19 mv and the viscosity was improved with a tenfold. Rapid water absorption ratio (304.2%, only 81.8% of pure Starch) and high swelling capacity of CS (1008%, nearly quadruple higher than pure Starch), together with its porous structure, enhanced the physical hemostatic efficacy. In addition, in vitro coagulation studies showed that CS induced the adhesion of red blood cell and platelet, and thus activated the blood chemical coagulation system due to the positive charge. In vivo studies in rabbit liver injuries model further confirmed the dramatic improvement in the hemostatic capacity of CS because the synergistic effects of the chemical activation mechanism and physical absorption mechanism. Furthermore, the degradation of CS was greatly improved by the modification. This study suggested the quaternary ammonium groups modified starch microspheres could serve as an effective and promising hemostatic agent for instant rapid hemostasis.

Formation of micro/mesopores during chemical activation in tailor-made nongraphitic carbons

The mechanism of chemical activation by potassium hydroxide (KOH) was studied in highly controlled non-graphitic carbon structures to explore the constituent reactions and the related pore formation processes involved in producing highly microporous activated materials. For this purpose, nongraphitic carbon was activated independently with intermediate species of either metallic potassium (K) or potassium carbonate (K2CO3) reduced from KOH (activating agent). Structural and morphological changes during activation were probed ex situ using X-ray diffractometry and Brunauer–Emmett–Teller (BET) nitrogen gas adsorption. Reduced K and K2CO3 disordered the stacking graphene layers to different extents. While micropore features were induced upon K evaporation following infiltration, the existing micropores were expanded into mesopores by K2CO3 gasification. Exclusive activation with K or K2CO3 induced ultra-small micropores, as measured using cyclic voltammetry. This work explains why activation using a KOH solution develops the preferable porous texture for use in many devices by creating open microporous structures as a result of the synergistic activation of both K and K2CO3.

Kinetics of Hydrogen Radical Reactions with Toluene Including Chemical Activation Theory Employing System-Specific Quantum RRK Theory Calibrated by Variational Transition State Theory.

Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure.

CH3CO + O2 + M (M = He, N2) Reaction Rate Coefficient Measurements and Implications for the OH Radical Product Yield.

The gas-phase CH3CO + O2 reaction is known to proceed via a chemical activation mechanism leading to the formation of OH and CH3C(O)OO radicals via bimolecular and termolecular reactive channels, respectively. In this work, rate coefficients, k, for the CH3CO + O2 reaction were measured over a range of temperature (241-373 K) and pressure (0.009-600 Torr) with He and N2 as the bath gas and used to characterize the bi- and ter-molecular reaction channels. Three independent experimental methods (pulsed laser photolysis-laser-induced fluorescence (PLP-LIF), pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS), and a very low-pressure reactor (VLPR)) were used to characterize k(T,M). PLP-LIF was the primary method used to measure k(T,M) in the high-pressure regime under pseudo-first-order conditions. CH3CO was produced by PLP, and LIF was used to monitor the OH radical bimolecular channel reaction product. CRDS, a complementary high-pressure method, measured k(295 K,M) over the pressure range 25-600 Torr (He) by monitoring the temporal CH3CO radical absorption following its production via PLP in the presence of excess O2. The VLPR technique was used in a relative rate mode to measure k(296 K,M) in the low-pressure regime (9-32 mTorr) with CH3CO + Cl2 used as the reference reaction. A kinetic mechanism analysis of the combined kinetic data set yielded a zero pressure limit rate coefficient, kint(T), of (6.4 ± 4) × 10(-14) exp((820 ± 150)/T) cm(3) molecule(-1) s(-1) (with kint(296 K) measured to be (9.94 ± 1.3) × 10(-13) cm(3) molecule(-1) s(-1)), k0(T) = (7.39 ± 0.3) × 10(-30) (T/300)(-2.2±0.3) cm(6) molecule(-2) s(-1), and k∞(T) = (4.88 ± 0.05) × 10(-12) (T/300)(-0.85±0.07) cm(3) molecule(-1) s(-1) with Fc = 0.8 and M = N2. A He/N2 collision efficiency ratio of 0.60 ± 0.05 was determined. The phenomenological kinetic results were used to define the pressure and temperature dependence of the OH radical yield in the CH3CO + O2 reaction. The present results are compared with results from previous studies and the discrepancies are discussed.

Activating of Nickel Slag and Preparing of Cementitious Materials for Backfilling

The back-filling method is distinguished from other mining methods by its higher cost. In order to solve this problem and utilize water-granulated nickel slag as much as possible, nickel slag from flash smelting operation was used to prepare cementitious materials for backfilling. Approaches including mechanical activation and chemical activation were adopted to improve the cementitious activity of the slag. By taking the strength of the backfill materials as the evaluation standards, the hydration activity and cementitious performance of the slag were investigated under different activation conditions, and the mechanism of chemical activation was analyzed. The results shows that cementing agent prepared by using mainly the slag (occupying 85% of the total raw materials) can be used to replace cement and meet the production requirements for backfilling materials.

Mechanism of chemical activation of sodium chloride in the presence of amino acids

Sodium chloride has been shown to promote chlorination of glycerol during thermal processing. However, the detailed mechanism of this reaction is not well understood. Preliminary experiments have indicated that the reaction mixture should contain an amino acid and it should be dissolved thoroughly in water in order to induce chlorination. These observations are consistent with the process of dissociation of sodium chloride and its re-association with amino acid and eventual formation of the chlorinating agent in the form of the hydrochloride salt. Release of HCl from this salt can be manifested in chlorination and hydrolytic reactions occurring during thermal processing. The generation of HCl at room temperature from a mixture of sodium chloride and glycine was confirmed through spectrophotometric monitoring of the pH. Hydrolytic and chlorination reactions were demonstrated through monitoring of formation of HMF and chlorinated products under pyrolytic conditions using glucose or sucrose and amino acid mixtures.

Study on mechanism of chemical activation for minerals of high belite-calcium sulfoaluminate clinker

High belite-calcium sulfoaluminate (HBCSA) cement has been developed as an eco-friendly building material, as it emits up to 35% less CO2 into the atmosphere and consume around 25% less energy in production compared with ordinary Portland cements. However, the hydraulic reactivity of C2S is low. Hence, the clinker of HBCSA activated by P2O5, B2O3, BaO, and ZnO, respectively, was studied in this paper to establish a methodology to clarify the activation mechanism. X-ray powder diffraction, scanning electron microscope, and infrared spectroscopy were used to identify the mineralogical changes in the microstructure. The results showed that the stabilizers varied a lot in the effect on microstructures of minerals. Its sequence of the effect on lattice stress of HBCSA clinker as a whole is Ba2+ > P5+ > Zn2+ > reference > B3+, the same to β-C2S mineral and cement strength at 28 days. But, there is a little difference for the sequence of their effect on , P5+ > Ba2+ > Zn2+ > Reference > B3+. The minor ionic doping activates the two minerals of β-C2S and , which are caused by disorder and defects in mineral lattice at high temperature.

Thermal decomposition of alkaline-earth metal hydride and ammonia borane composites

We demonstrate a method to improve the promising hydrogen storage capabilities of ammonia borane by making composites with alkaline-earth metal hydrides using ball-milling technique. The ball-milling for the mixtures of alkaline-earth metal hydride (MgH 2 or CaH 2) and ammonia borane (AB) yields a destabilization compared with the ingredient of the mixture, showing the hydrogen capacity of 8.7 and 5.8 mass% at easily accessible dehydrogenation peak temperatures of 78 and 72 °C, respectively, without the unwanted by-product borazine. Through detailed analyses on the dehydrogenation performance of the composite at various ratios in the hydride and AB, we proposed a different chemical activation mechanism from that in the LiH/AB and NaH/AB systems reported in a previous literature.

Allosteric Activation of HtrA Protease DegP by Stress Signals during Bacterial Protein Quality Control

Unleashing the proteolytic activity of DegP: A study with synthetic mimics of cellular stress signals reveals an allosteric (chemical) activation mechanism of the bacterial HtrA protease DegP, leading to a fine-tuned amplification of protein degradation during bacterial protein quality control (see scheme: binding of a peptide sequence (circles) increases activation. The nature of the penultimate residue (red) is shown to be decisive).

Insight into hydroxides-activated coals: Chemical or physical activation?

The objective of this paper is to get an insight into the chemical activation mechanism using KOH and NaOH as activated agents. Three coals have been selected as carbon precursors. It was found that KOH and NaOH develop a similar narrow microporosity, independently of the coal rank, whereas only KOH generates supermicroporosity. Temperature-programmed desorption experiments, carried out with impregnated anthracite, show differences on the gas evolved during the activated carbon preparation using the two activating agents. Thus, whereas hydrogen profiles are quite similar for both activated agents, the CO and H 2O profiles are different. It is remarkable the high amount of H 2O evolved at the maximum treatment temperature for both activating agents. The results obtained allow concluding that the chemical activation is due to a combination of different process driving the development of material porosity.

Ab initio study of the reaction of propionyl (C2H5CO) radical with oxygen (O2)

The reaction of propionyl radical with oxygen has been studied using the full coupled cluster theory with the complete basis set. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for this important reaction in detail. The reaction takes place via a chemical activation mechanism. The barrierless association of propionyl with oxygen produces the propionylperoxy radical, which decomposes to form the hydroxyl radical and the three-center alpha-lactone predominantly or the four-center beta-propiolactone. The oxidation of propionyl radical to carbon monoxide or carbon dioxide is not straightforward rather via the secondary decomposition of alpha-lactone and beta-propiolactone. Kinetically, the overall rate constant is almost pressure independent and it approaches the high-pressure limit around tens of torr of helium. At temperatures below 600 K, the rate constant shows negative temperature dependence. The experimental yields of the hydroxyl radical can be well reproduced, with the average energy transferred per collision -DeltaE=20-25 cm(-1) at 213 and 295 K (helium bath gas). At low pressures, together with the hydroxy radical, alpha-lactone is the major product, while beta-propiolactone only accounts for about one-fifth of alpha-lactone. At the high-pressure limit, the production of the propionylperoxy radical is dominant together with a fraction of the isomers. The infrared spectroscopy or the mass spectroscopy techniques are suggested to be employed in the future experimental study of the C2H5CO+O2 reaction.

Kinetics and mechanism of methylene blue sorption onto palm kernel fibre

The kinetics and mechanism of the sorptive removal of methylene blue dye from aqueous solution using palm kernel fibre as adsorbent have been investigated. Batch kinetic experiments were performed and system variables investigated includes pH and initial dye concentration. The kinetic data were fitted to the pseudo-first, pseudo-second, intraparticle diffusion and mass transfer models. The pseudo-first order reaction kinetics fitted to the experimental data only in the first 5 min of sorption and then deviated, while the pseudo-second order kinetic model was found to fit the experimental data for the entire sorption period with high coefficient of determination. Equations were developed using the pseudo-second order model, which predicts the amounts of methylene blue at any contact time and initial concentration within the given range. This suggests that the sorption of methylene blue onto palm kernel fibre follows a chemical activation mechanism. A mathematical relationship was also drawn between the equilibrium sorption capacity and the change in pH (Δ H +) at the end of the kinetic experiments with varying initial dye concentration, supporting the fact that chemical reaction (ion exchange) occurred and is important in the rate determining step. Mass transfer was found to be favoured at high concentrations while intraparticle diffusion was favoured at low concentrations.

Mechanistic and Kinetic Study of the O + CH2OH Reaction

The mechanism for the O + CH2OH reaction was investigated by various ab initio quantum chemistry methods. For the chemical activation mechanism, that is, the addition/elimination path, the couple-cluster methods including CCSD and CCSD(T) were employed with the cc-pVXZ (X = D, T, Q, 5) basis sets. For the abstraction channels, multireference methods including CASSCF, CASPT2, and MRCISD were used with the cc-pVDZ and cc-pVTZ basis sets. It has been shown that the production of H + HCOOH is the major channel in the chemical activation mechanism. The minor channels include HCO + H2O and OH + CH2O. The hydrogen abstraction by an O atom from the CH2OH radical produces either OH + CH2O or OH + HCOH. Moreover, the two abstraction reactions are essentially barrierless processes. The rate constants for the association of O with CH2OH have been calculated using the flexible transition state theory. A weak negative temperature dependence of the rate constants is found in the range 250-1000 K. Furthermore, it is estimated that the abstraction processes also play an important role in the O + CH2OH reaction. Additionally, the falloff behavior for the OCH2OH --> H + HCOOH reaction has been investigated. The present theoretical results are compared to the experimental measurements to understand the mechanism and kinetic behavior of the O + CH2OH reaction and the unimolecular reaction of the OCH2OH radical.

The Four Isotopomer Reactions of NH(a) and ND(a) with NH3(X̃) and ND3(X̃)

Abstract The reactions NH(a) + NH3(X̃) → products (1) ND(a) + NH3(X̃) → products (2) NH(a) + ND3(X̃) → products (3) ND(a) + ND3(X̃) → products (4) were studied in a quasi-static reaction cell at room temperature and pressures of 10 and 20mbar with He as the main carrier gas. The electronically excited reactants NH(a) and ND(a) were generated by laser-flash photolysis of HN3 and DN3, respectively, at λ = 308nm and detected by laser-induced fluorescence (LIF). Also the ground state species NH(X) and ND(X) as products were detected by LIF. From the measured concentration-time profiles of NH(a) and ND(a) under pseudo-first order conditions, the following rate constants were obtained: NH(a) + NH3(X̃) → products (1) ND(a) + NH3(X̃) → products (2) NH(a) + ND3(X̃) → products (3) ND(a) + ND3(X̃) → products (4) k 1 = (9.1 ± 0.9) × 1013 cm3mol−1s−1 k 2 = (9.6 ± 1.0) × 1013 cm3mol−1s−1 k 3 = (8.0 ± 1.0) × 1013 cm3mol−1s−1 k 4 = (7.2 ± 0.8) × 1013 cm3mol−1s−1. The major products are the corresponding NH i D2 − i (X̃) radicals (i = 0, 1, 2), whereas quenching processes such as NH(a) + ND3 → NH(X) + ND3 are of minor importance (1%). The isotope exchange NH(a) + ND3 → ND(X) + NHD2 is negligible, and the corresponding channel on the singlet surface NH(a) + ND3(X ~) → ND(a) + NHD2(X̃) contributes with 1% to the overall NH(a) depletion in that reaction. The experimental findings are discussed in terms of a chemical activation mechanism by means of statistical rate theory.