Free Energy Of Activation Research Articles

Computational study on the mechanisms of inhibition of SARS-CoV-2 Mpro by aldehyde warheads based on DFT.

SARS-CoV-2 main protease, Mpro, plays a crucial role in the virus replication cycle, making it an important target for antiviral research. In this study, a simplified model obtained through truncation is used to explore the reaction mechanism of aldehyde warhead compounds inhibiting Mpro at the level of density functional theory. According to the calculation results, proton transfer (P_T)-nucleophilic attack (N_A) is the rate-determining step in the entire reaction pathway. The water molecule that plays a catalytic role occupies the oxyanion hole, which is unfavorable for the aldehyde warhead to approach the Cys145 SH. Through a hypothetical study of substituting the main chain NH with methylene, it is further confirmed that the P_T-N_A is a proton transfer-dominated process accompanied by a nucleophilic attack reaction. In this process, the oxyanion hole serves only to stabilize the aldehyde oxygen anion and therefore does not have a significant impact on the activation free energy barrier of the step. Our research results provide a unique perspective for understanding the covalent inhibition reaction of the Mpro active site. This study also offers theoretical guidance for the design of new Mpro covalent inhibitors.

Incinerability of PFOA and HFPO-DA: Mechanisms, kinetics, and thermal stability ranking

Thermal treatment is currently the only full-scale technology for the destruction of per- and polyfluoroalkyl substances (PFAS) in wastes. However, concerns exist about the emission of incomplete combustion products from incinerators. To address critical knowledge gaps around the incinerability of PFAS, highest-level coupled cluster theory was applied to elucidate the primary thermal destruction pathways, mechanisms, and kinetics for perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide dimer acid (HFPO-DA, sometimes referred to as “GenX”). These PFAS were then ranked based on U.S. EPA's Thermal Stability Index, which ranges from Class 1 for the most thermally stable chemicals to Class 7 for the most thermally labile chemicals. Initial decomposition of both carboxylic acids proceeds through HF elimination at the α-carbon, but for PFOA surprisingly shifts towards C-COOH bond dissociation in the presence of ammonia due to ammonium stabilization of the variational transition state. Branching substantially reduces the required incineration temperatures, while chain length has no impact on perfluoroalkyl carboxylic acid (PFCA) decomposition rates. Bimolecular reactions with secondary species such as counterions and radicals have lower activation barriers than unimolecular decomposition, but their second-order kinetics depend on concentration and thus waste stream composition, which varies in practice. Simulating radical concentrations under typical incineration conditions, the determined free energies of activation suggest an incinerability ranking for linear PFOA in Class 3, for branched PFOA in Class 4, and for HFPO-DA as well as both PFOA and HFPO-DA ammonium salts in Class 5. Collectively, the temperatures needed to destroy 99.99% of PFOA, HFPO-DA, and other PFCAs in 2 seconds gas residence time are well below those of other commonly incinerated organic compounds such as chlorobenzene (Class 1). Ultimately, sufficient supply of radical donors is critical to ensure safe, efficient, and complete destruction of PFAS during thermal treatment.

Kinetics, Thermodynamics and Mechanism of Enzymatic Degradation of Zearalenone in Degummed Corn Oil.

The kinetics and thermodynamics of the enzymatic degradation of zearalenone (ZEN) in degummed corn oil were investigated by analyzing the impacts of temperature, pH, ZEN hydrolase dosage and ZEN concentration on the initial reaction rate. The kinetic study found that the maximum reaction rate was 0.97 μmol × kg−1 min−1, the Michaelis constant (Km) was 11,476 μmol × kg−1 and the Michaelis equation was V = 0.97[S]/(11,476 + [S]). The thermodynamic study showed that the activation energy (Ea) was 70.37 kJ·mol−1, the activation enthalpy change of the reaction (ΔH) > 0, the free energy of activation (ΔG) > 0 and the activation entropy change (ΔS) < 0, indicating the reaction could not be spontaneous. The reaction mechanism of ZEN was studied by a hybrid quadrupole orbitrap mass spectrometer. It was found that ZEN first generated the intermediate G/L/D/W-ZEN+H2O, followed by generating the intermediate W-ZEN-H2O under the action of a degrading enzyme. Then, the lactone bond was opened to produce C18H24O6, and finally the decarboxylation product C17H24O4 formed automatically.

Some Thermodynmic Properties of binary Mixtures of Alcohol isomers and Sulfolane at 298.15K

The refractive indices, nD densities , and viscosities h of binary mixtures of sulfolane + n -butanol + sec- butanol + iso- butanol + tert – butanol + n-propanol and iso- propanol were measured at 298.15K. Form experimental data, excess molar volum VE , excess molar refractivity nD, excess molar viscosityhE and excess molar Gibbs free energy of activation of viscous flow DG*E were calculated. From n-propanol – sulfolane and iso- propanol sulfolane mixtures showed negative nD, n-butanol – sulfolane, sec-butanal – sulfolane, iso-butanol – sulfolane and tert- butanol sulfolane , DnD was positive over the whole mole fraction rang , while VE, hE and DG*E show a negative deviation. The results obtained for binary mixtures suggest two types of molecular interaction. One is the formation of new stable complexes between the sulfone group of sulfolane and the hydroxyl group of alcohols and the second is related to the participation in destroying the mixture structure and forming a new structure. Excess molar quantities of these binary mixtures were found to be affected directly by the position of hydroxyl group and the steric associated with the methyl group.

The thermodynamic and kinetic aspects of midazolam ring closure from benzophenone to benzodiazepine form, its acid–base equilibria and aromaticity: a quantum-chemical study

The process of midazolam ring closure was studied from the thermodynamic and kinetic points of view by means of quantum-chemical methods. B3LYP/6–311 + + G(d,p) model was employed for gas phase and water environment (polarizable continuum model) calculations. It was concluded that the reaction rate determining step is the first step—carbinolamine formation from amine and carbonyl ends of the opened benzodiazepine ring. The Gibbs free energy of activation was calculated as 35.1 kcal/mol for gas- phase and 33.9 kcal/mol for water environment. Intrinsic reaction coordinate calculations were performed to verify that the transition state really connects the substrate and product. Thermodynamically, this reaction is endoergic with ΔG = 9.6 kcal/mol for gas phase and 10.0 kcal/mol for water environment. However, the next step—carbinolamine protonation with immediate water molecule loss is expected to be fast and activation barrierless, which enables further progress of the ring closure, despite the positive ΔG of the fist step. Next, the protonated imine undergoes deprotonation to final closed ring, pharmacologically active molecule of midazolam. The whole chain of reaction is exoergic with ΔG equal to − 5.6 kcal/mol for gas phase and − 7.7 kcal/mol for water environment. In order to understand the role of other than benzodiazepine/imidazole molecular fragments on the ring closure process, a model was build which contains only benzodiazepine and imidazole rings. The activation barrier for the carbinolamine formation of the model is similar to midazolam in the gas phase but higher by about 10 kcal/mol for water environment. The most interesting difference is however that for the model, the carbinolamine formation step is exoergic with ΔG equal to − 2.2 kcal/mol for gas phase and − 1.8 kcal/mol for water environment. This difference can be connected to complicated conformational shape of the midazolam molecule, which during the ring closure undergoes unfavorable deformations with accompanying rise of the energy of the molecule. The protonation sites for both midazolam and the model were also studied. In the case of midazolam, the preferred protonation site is the imidazole ring nitrogen atom, but in the case of the model it is the benzodiazepine ring nitrogen atom. The aromaticity of the 5- and 7-membered rings were analyzed using two aromaticity—HOMA and pEDA. It follows that larger stability of the cation protonated at the benzodiazepine ring is accompanied with substantial increase of the 7-ring aromaticity in the model of midazolam. The complexes of midazolam and its model with a water molecule were analyzed because they are needed for evaluation of the energy of the whole process of ring closure. In the case of midazolam, the water molecule preferentially connects to imidazole ring, but in the case of the model, complexes with both imidazole and benzodiazepine rings have similar stability.

Thermophysical modelling of transport and optical properties of 1-propanol+1,3-diaminopropane or 1,2-diaminopropane or 1-amino-2-propanol binary liquid mixture at T=298.15-318.15 K: Molecular interaction analysis by density functional theory (DFT) and graph theoretical approach (GTA)

BackgroundPure liquid properties cannot always satisfy the need of chemical processes. Therefore, liquid mixtures are preferred in different compositions, and the thermo-physical properties of liquid mixtures are highly significant for different processes. The present report involves thermo-physical of amines and 1-propanol. Amines are utilized for CO2 absorption processes. MethodsThe viscosity (η) and refractive index (nD) of 1P (1-propanol) (1) + Amines (1,3-DAP(1,3-diaminopropane), 1,2-DAP(1,2-diaminopropane) and 1A2P(1-amino-2-propanol)) (2) binary mixture were measured at T = 298.15-318.15 K under the atmospheric pressure 0.1 MPa. Experimental data of η and nD were further used to determine deviation in viscosity (Δη), excess Gibbs free energy of activation (G*E) and deviation in refractive index (ΔnD). Δη were analyzed by Bloomfield and Dewan model (BFD) and also examined in term of Graph theoretical approach (GTA). The η and nD data were further correlated by various relevant correlations Significant findingsThe derived thermo-physical properties were well correlated with Redlich-Kister polynomial equation. DFT studies indicated the strength of molecular interactions and supported the graph theory in predicting probable associative molecular species in the liquid mixtures. Further, in 1P + amines binary liquid mixtures, the dominant interaction is OH—–NH.

Effect of poly-aniline coated iron ore mining waste (PANI@IOMW) as efficient adsorbent on mitigation of Cr (VI) from aqueous solution: Experimental and statistical investigation

Present investigation is focused on the synthesis of poly-aniline coated iron ore mining waste (PANI@IOMW) adsorbent and its utilization for remediation of Cr (VI) from water using batch process. The studied adsorbent shows excellent Cr (VI) mitigation properties with highest efficiency of 99% at significantly low dosage of 0.15 g, pH 2.0, 90 min contact time and 50 mgL−1initial concentrations. Non-linear regression analysis shows that Freundlich isotherm is considers as a suitable model for mitigation of Cr (VI) with Qmax of 73.29 mg/g for 50 mgL−1 Cr (VI) concentration. Pseudo second order kinetics model is considered as a best fitted model for the present investigation. Thermodynamic study shows that adsorption is spontaneous and endothermic in nature. The value of mean free energy (0.983 J/mol at 303 K) and activation energy (7.96 kJmol−1 at 303 K) shows that adsorption of Cr (VI) on PANI@IOMW occurs through physisorption. Surface study of PANI@IOMW was done using FESEM, EDX, FTIR, XRD, XRF, XPS, HR-TEM and AFM analysis. The comparison of % efficiency of Cr (VI) removal obtained by response surface methodology (RSM) (99.06%) and experimental studies under the optimum conditions (99%) suggested that quadratic model is suitable model for Cr (VI) adsorption. The adsorbent PANI@IOMW shows regeneration ability up to two cycles without losing its properties. Thus PANI@IOMW adsorbent can be used for treatment of water containing Cr (VI) as good alternative as compared to chemical adsorbents used by the industries.

Solvent effects on direct and indirect tautomerism of pyrimidin‐2(1H)‐one/pyrimidin‐2‐ol

AbstractA theoretical study at the B3LYP/6‐311++G(d,p) level on tautomeric conversion of pyrimidin‐2(1H)‐one (PYH) to pyrimidin‐2‐ol (PY) was performed. Two mechanisms have been considered for this processes: (i) one in which the hydrogen is directly transferred, mechanisms A, through TS12 and (ii) another one in which a double hydrogen transfer takes place via TS1122, by formation of the corresponding dimer, mechanisms B. The results associated with the gas phase reveal that overcame to TS12 needs high activation free energies of 34.47 kcal/mol, as a consequence of the strain associated with the formation of the four‐membered transition state, while overcame to TS1122 requires much lower activation free energies, 4.97 kcal/mol. The effect of solvent on the studied tautomerization in implicit, explicit, and a combination of both implicit and explicit solvation models in various media (protic and aprotic polar solvents) has been considered. The results show that the use of a protic polar solvent reduces the energy barrier of the corresponding transition states in a very significant amount.

Structural Study of Model Rhodium(I) Carbonylation Catalysts Activated by Indole-2-/Indoline-2-Carboxylate Bidentate Ligands and Kinetics of Iodomethane Oxidative Addition

The rigid-backbone bidentate ligands Indoline-2-carboxylic acid (IndoliH) and Indole-2-carboxylic acid (IndolH) were evaluated for rhodium(I). IndoliH formed [Rh(Indoli)(CO)(PPh3)] (A2), while IndolH yielded the novel dinuclear [Rh1(Indol’)(CO)(PPh3)Rh2(CO)(PPh3)2] (B2) complex (Indol’ = Indol2−), which were characterized by SCXRD. In B2, the Rh1(I) fragment [Rh1(Indol’)(CO)(PPh3)] (bidentate N,O-Indol) exhibits a square-planar geometry, while Rh2(I) shows a ‘Vaska’-type trans-[O-Rh2(PPh3)2(CO)] configuration (bridging the carboxylate ‘oxo’ O atom of Indol2−). The oxidative addition of MeI to A2 and B2 via time-resolved FT-IR, NMR, and UV/Vis analyses indicated only Rh(III)-alkyl species (A3/B3) as products (no migratory insertion). Variable temperature kinetics confirmed an associative mechanism for A2 via an equilibrium-based pathway (ΔH≠ = (21 ± 1) kJ mol−1; ΔS≠ = (−209 ± 4) J K−1mol−1), with a smaller contribution from a reverse reductive elimination/solvent pathway. The dinuclear complex B2 showed the oxidative addition of MeI only at Rh1(I), which formed a Rh(III)-alkyl, but cleaved the bridged Rh2(I) site, yielding trans-[RhI(PPh3)2(I)(CO)] (5B) as a secondary product. A significantly smaller negative activation entropy [ΔH≠ = (73.0 ± 1.2) kJ mol−1; ΔS≠ = (−21 ± 4) J K−1mol−1] via a more complex/potential interchange mechanism (the contribution of ΔS≠ to the Gibbs free energy of activation, ΔG≠, only ±10%) was inferred, contrary to the entropy-driven oxidative addition of MeI to A2 (the contribution of ΔS≠ to ΔG≠ ± 75%).

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane.

Building up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine-coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.

Triflylpyridinium Enables Rapid and Scalable Controlled Reduction of Carboxylic Acids to Aldehydes using Pinacolborane

AbstractBuilding up new and efficient methods for the controlled conversion of carboxylic acids to aldehydes is important. Herein, we report a rapid, modular and scalable method for the conversion of carboxylic acids to aldehydes using pinacolborane at ambient temperature, in which a triflylpyridinium reagent is used. The conversion of carboxylic acid to intermediate acylpyridinium by triflylpyridinium is new. A binary pyridine‐coordinated boronium complex is generated after reduction. The unprecedented reduction of the acylpyridinium by HBpin opens up a practically direct synthesis of aldehydes from carboxylic acids. Theoretical studies indicate that the reduction of acylpyridinium requires a lower activation free energy than that of the product aldehyde. The synthetic advantage of this protocol is further highlighted by the scalable synthesis of aldehyde via continuous flow process. Configuration retention for chiral acids are presented in those syntheses.

Chemical fixation of CO2 with epoxides catalyzed by DBO as activator for the LiI promoted system: A theoretical study

Chemical fixation of carbon dioxide into value-added products is a promising idea. However, its conversion to valuable organic compounds requires highly efficient and safe catalytic system. In this work, the catalytic efficiency of the nontoxic organic base 1, 4‑Diazabicyclo Oct-4-ene (DBO) and its improved result after it has been cooperated with LiI salt have been studied. We gained more insight into the catalytic effects of DBO/LiI on the fixation of CO2 by means of density functional theory calculations using exchange–correlation functional B3LYP through basis sets of LANL2DZ for iodine and 6–31 + G(d,p) for non-iodine atoms. The calculations were carried out in both gas phase and in the presence of water as a solvent. Two reaction mechanisms were proposed and their respective energy was investigated to identify the favorable path for DBO/LiI system catalyzed reaction. Mechanism I is more favorable, in which the ring-opening of epoxide is the rate-limiting step which demands 32.20 kcal mol−1 Gibbs free energy of activation in the gas phase and 20.60 kcal mol-1in water. Lastly, this work validates that DBO in the presence of LiI displayed better catalytic activity for the title reaction and water is a good solvent for DBO/LiI catalyzed cycloaddition of CO2 with an epoxide.

Biosynthesis of NiFe2O4 nanoparticles using Murayya koenigii for photocatalytic dye degradation and antibacterial application

Biosynthesis of nickel ferrite (NiFe2O4) nanoparticles (NPs) using an aqueous extract of Murraya koenigii (M. koenigii) leaves is a novel, environmentally benign and cost effective method. NiFe2O4 NPs were characterized by different spectroscopic and microscopic techniques, including Ultraviolet–Visible (UV–Vis) spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, Thermogravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), High-Resolution Scanning Electron Microscopy (HRSEM), Energy-dispersive X-ray spectrometry (EDX) and Vibrating-Sample Magnetometer (VSM). The observed results revealed that prepared NiFe2O4 NPs are highly pure, crystalline, partially spherical with an average size of 2–6 nm and attribute magnetic properties. The magnetization of the obtained biosynthesized nanoparticles is noticed ∼5.2 emu/g at 10 K Oe. The NiFe2O4 NPs exhibited a heterogeneous photo Fenton's catalytic feature in the presence of oxalic acid at ambient conditions. The effects of pH, dosage of NiFe2O4 catalyst and doses of oxalic acid on the degradation efficiency of 10 mg/L MB dye were assessed. The optimal degradation efficiency of ⁓ 98.5% was achieved within 70 min, and the observed results elucidated that the photocatalytic reactions follow first-order chemical kinetics. Thermodynamic parameters such as activation energy (Ea), enthalpy of activation (ΔH‡), entropy of activation (ΔS‡), and free energy of activation (ΔG‡) were evaluated, applying Arrhenius and activated complex theory ascertained the endothermic, less random and nonspontaneous features of photocatalytic process. NiFe2O4 NPs were also tested against different bacteria and found to have antibacterial properties. Hence, magnetic NiFe2O4 NPs can be exploited for its multifunctional applications, and specifically for the remediation of dye-contaminated wastewater.

Electrochemical Reduction of Halogenated Alkanes and Alkenes Using Activated Carbon-Based Cathodes.

Granular activated carbon (GAC) is used to sorb a broad range of halogenated contaminant classes, but spent GAC disposal is costly. Taking advantage of GAC's conductivity, this study evaluated the conversion of the GAC to cathodes for electrochemical reductive dehalogenation of 15 halogenated alkanes and alkenes exhibiting a diversity of structures (type of halogen, number of halogens, functional groups) and including contaminants of practical importance (e.g., trichloroethylene). Alkane degradation rates increased with the number of halogens and in the order: chlorine < bromine < iodine. Quantitative structure-activity relationships (QSARs) correlating experimental first-order degradation rate constants for alkanes with molecular descriptors associated with an outer-sphere one-electron transfer calculated using density functional theory indicated that correlations with molecular descriptors improved in the order: aqueous phase reduction potentials (E0,aq) < energy of the substrate's lowest unoccupied molecular orbital (ELUMO) < Marcus theory activation free energies (ΔG‡) ∼ gas-phase standard reduction free energies (ΔG0,gas). Chlorinated alkene degradation rates increased with decreasing number of chlorines, and QSAR correlations were opposite those of alkanes, indicating a different reaction mechanism. Degradation timescales ranged from 1 min to 3 h with halides as predominant products. These results suggest that the electrochemical reduction of halogenated alkanes and alkenes can be used to regenerate spent GAC.

Enthalpic and entropic contributions to the activation free energy of single noncovalent bonds in molecular systems: A computational methodology

Insight into enthalpic and entropic contributions to the activation free energy of noncovalent bonds is crucial for understanding various phenomena in molecular systems, from formation of different molecular conformers to complex biophysical and biochemical processes. Standard experimental and computational methods provide only the average strength of noncovalent bonds. In this paper, we present a simple, formal, computational framework to determine both energy contributions for a single bond. Our approach is based on steered molecular dynamics simulations, the dynamic force spectroscopy method, and a modified theoretical model of force-induced bond rupture. To demonstrate the methodology, the enthalpic and entropic components for a single intramolecular hydrogen bond of a peptide helix were determined. The sum of the contributions is in agreement with the previously reported Gibbs energy for intramolecular hydrogen bonds. The proposed methodological framework is universal and can be applied to other noncovalent interactions in various molecular systems.

Kinetic and Mechanistic Study of Oxidative Degradation and Detoxification of Fast Yellow Azo Dye Using Surfactant Assisted Ir-Ni Bimetallic Nanocatalyst

Aim: Catalytic degradation of azo dye. Background: Azo dyes are toxic agents and pollutants and the degradation of these dyes has an important application in the treatment of textile industry wastes. Catalytic decolorization of fast yellow dye by hexacyanoferrate (III), abbreviated as HCF(III) using polyvinylpyrrolidone abbreviated as PVP stabilized Ir-Ni bimetallic nanocrystals has been evaluated by kinetic spectrophotometric method at 440nm wavelength of the reaction mixture. Methods: The impact of various operational factors such as fast yellow dye abbreviated as [FY], oxidant [HCF(III)] ions, promoter iridium-nickel bimetallic nanoparticles abbreviated as [(Ir-Ni)] BMNPs, and solution pH on the rate of the reaction have been examined. Results: The results represent that the reaction follows first -order kinetics model with respect to [oxidant] at optimum pH 8 and fix temperature 40±0.1◦C. Thermodynamic parameters such as activation energy (Ea), enthalpy (ΔH#), entropy (ΔS#), frequency factor (A), and free energy of activation (ΔF#) have been evaluated by examining the reaction rate at four temperatures i.e. 40⁰C, 45⁰C, 50⁰C, and 55⁰C. On the basis of experimental outcomes, an appropriate mechanism involving complex formation has been proposed. Conclusion: Analytical techniques such as UV-Vis spectroscopy, FTIR, and LCMS of degraded products represent the formation of easier and less harmful compounds.

Assessing the Effect of Dopants on the C-H Activation Activity of γ-Al2 O3 using First-Principles Calculations.

In recent years, the high availability of methane in the shale gas reserves has raised significant interest in its conversion to high-value chemicals but this process is still not commercially viable. Metal oxides, due to their surface heterogeneity and the presence of Lewis acidic and basic site pairs are known to facilitate the activation of C-H bonds of methane. In this work, we investigate the C-H bond activation of methane on pristine and doped γ-Al2 O3 clusters using density functional theory (DFT) calculations. Our results demonstrate that the polar pathway is energetically preferred over the radical pathway on these systems. We found that the metal dopants (boron and gallium) not only alter the catalytic activity of dopant sites but this effect is more pronounced on some of the adjacent sites (non-local). Among the selected dopants, gallium greatly improves the catalytic activity on most of the site pairs (including most active and least active) of pristine γ-Al2 O3 . Additionally, we identified a correlation between H2 binding energies and the C-H activation free energies on Ga-doped γ-Al2 O3 .

Assessing Thermal Response of Redox Conduction for Anti-Arrhenius Kinetics in a Microbial Cytochrome Nanowire.

A micrometers-long helical homopolymer of the outer-membrane cytochrome type S (OmcS) from Geobacter sulfurreducens is proposed to transport electrons to extracellular acceptors in an ancient respiratory strategy of biogeochemical and technological significance. OmcS surprisingly exhibits higher conductivity upon cooling (anti-Arrhenius kinetics), an effect previously attributed to H-bond restructuring and heme redox potential shifts. Herein, the temperature sensitivity of redox conductivity is more thoroughly examined with conventional and constant-redox and -pH molecular dynamics and quantum mechanics/molecular mechanics. A 30 K drop in temperature constituted a weak perturbation to electron transfer energetics, changing electronic couplings (⟨Hmn⟩), reaction free energies (ΔGmn), reorganization energies (λmn), and activation energies (Ea) by at most |0.002|, |0.050|, |0.120|, and |0.045| eV, respectively. Changes in ΔGmn reflected -0.07 ± 0.03 V shifts in redox potentials that were caused in roughly equal measure by altered electrostatic interactions with the solvent and protein. Changes in intraprotein H-bonding reproduced the earlier observations. Single-particle diffusion and multiparticle steady-state flux models, parametrized with Marcus theory rates, showed that biologically relevant incoherent hopping cannot qualitatively or quantitatively describe electrical conductivity measured by atomic force microscopy in filamentous OmcS. The discrepancy is attributed to differences between solution-phase simulations and solid-state measurements and the need to model intra- and intermolecular vibrations explicitly.

Study on a Novel Synthetic Route and Properties of 1‐trinitromethyl‐3‐nitro‐1,2,4‐triazole (TNMNT)

AbstractMaterials with low melting point and high energy density have become the focus of research on energy‐containing materials thanks to their superb detonation performance and wide applications. This paper proposed a new synthetic route for an energy‐containing compound 1‐trinitromethyl‐3‐nitro‐1,2,4‐triazole (TNMNT), using 3‐nitro‐1,2,4‐triazole as the raw material, low toxic chloroacetone as the substitute and KBr as the catalyst. These substances reacted at 70 °C for 3 h in a DMF reaction solvent system. The intermediate 1‐acetonyl‐3‐nitro‐1,2,4‐triazole (ANT) was obtained with a yield of 38 %. The nitration process increased the volume ratio of mixed nitric and sulfuric acids (1 : 3), and the reaction time was 36 h. TNMNT as a nitrogen‐rich compound having low melting point and high energy density was synthesized with a yield of 43 %. Compared with the traditional process, the experimental period was significantly shortened, and this synthetic method proved more environment‐friendly. Scanning Electron Microscopy (SEM), Differential Scanning Calorimeter (DSC) and mechanical sensitivity tests were performed on the products. It was found that the melting and decomposition points of TNMNT were 100.5 °C and 166.4 °C, respectively, the characteristic drop height H50 was 21.3 cm, and the frictional sensitivity was 56 %. Results show that the TNMNT crystals synthesized by this new route have better morphology, higher purity, and lower melting point. Compared with the raw material, the introduction of the trinitromethyl group produced higher mechanical sensitivity than other compounds having low melting point. Calculation of the thermal decomposition parameters found: activation energy of 104.4 kJ ⋅ mol−1, pre‐exponential factor of 2.27×1010 s−1, activation enthalpy of 100.9 kJ ⋅ mol−1, activation entropy of 57.98 J ⋅ mol−1 ⋅ K−1, and activation free energy of 125.72 kJ ⋅ mol−1.

WO3/rGO nanocomposite-based sensor for the detection and degradation of 4-Chlorophenol

Chlorinated organic compounds are useful chemicals or intermediates that are used extensively in both industry and agriculture. The 4-chlorophenol (4CP) in low concentration poses a serious environmental problem and causes many health issues, including cancer and liver disease. In this work, we demonstrated the detection of 4CP at carbon paste electrodes modified using tungsten oxide (WO3) nanorods and reduced graphene oxide (rGO) nanoparticles. The significance of pH on the voltammetric response of 4CP was investigated, and it was discovered that an alkaline pH is an optimal condition for detecting substituted phenols. Moreover, parameters like heterogeneous rate constant, accumulation time, temperature effect, Gibb's free energy, scan rate, enthalpy, activation energy, and entropy were studied. The excellent catalytic and bulk properties of tungsten oxide nanostructures make it an effective modifier in electrochemical sensors. The employment of nanostructured WO3 for the assay of 4CP offers excellent sensitivity, selectivity, and applicability. The WO3 nanostructures are obtained hydrothermally and characterized in detail to understand the crystalline, quantitative and chemical properties. The electrochemical behavior of 4CP was studied utilizing voltammetry techniques. The CV technique was used to optimize and affect many factors in the electrochemical behavior of 4CP. The scan rate investigation helps to examine the physicochemical characteristics of the electrode process, and the electrooxidation of 4CP included 2 electrons and 2 protons. With 4CP, the modified electrode displayed a broad range of linearity. The limit of detection was determined to be 0.102 nM, while the limit of quantification was 0.3433 nM. The concentration of 4CP ranged between 0.1 × 10−7 M and 3.5 × 10−7 M. The fabricated electrode was also used to detect 4CP in soil and water samples. Good recoveries were obtained from the soil and water samples. The proposed electrode was used for analytical applications, including 4CP detection with high selectivity, low detection limit, sensitivity, and rapid response.