Gibbs Free Energy Of Activation Research Articles

The effect of metal silver(I) salt on CO2 conversion to α-alkylidene cyclic carbonates: A DFT study

The cycloaddition of CO2 with propargylic alcohol (PA) catalyzed by ILs has evoked great interest in the past few decades. Recent research found that metal-assisted catalytic system can achieve higher CO2 conversion and product yield than pure IL. However, the microscopic mechanisms of different catalytic systems have not been investigated in detail. In this study, considering activation sequences of the reactants, various reaction routes of PA-activated mechanism and CO2-activated mechanism in the catalytic system with or without metal participation were simulated respectively. The PA-activated mechanism was found to be the optimal path for the carboxylative cyclization of PA with CO2, and intramolecular cyclization was the rate-determining step. Due to the synergistic catalytic effect of [Ch][Triz] and AgNO3 in the reaction, the activation Gibbs free energy of 14.2 kcal/mol in metal-assisted system is lower than that in pure IL (24.9 kcal/mol). [Ch][Triz] promotes deprotonation of the hydroxyl and elimination of metal electrophile by providing hydrogen protons, while Ag salts facilitate the intramolecular cyclization step by activating CC triple bond of the substrate. Simultaneously, the influence of cations in ionic liquids is analyzed, and it is found that the weak interaction between CO2 and cations can indirectly affect the active center through electronic effects.

The antioxidative potential of procyanidin B1: DFT (density functional theory) and docking approaches.

Procyanidin B1 is one of the natural dimeric flavonoids. It has established a great role in antioxidative activity. In the current study, we wish to provide crucial information on its antioxidative action by the DFT computational and docking approaches. From point of thermodynamic view, at the M062X/6-311G(d,p) level, the HAT (hydrogen atom transfer) and SPL-ET (sequential proton loss-electron transfer) are principal antioxidative routes of this compound in gas and methanol, respectively. OH groups of two phenyl rings of this molecule are likely to be the best antiradical sites. In the kinetics of the interactions with HOO• radicals, OH groups of phenyl rings have also generated the best ΔG# (Gibbs free energy of activation) and rate constant K. The antioxidative action of procyanidin B1 is further confirmed by its chelation to metal ions, in which complex formation with Cu2+ having lower binding energy is more stable than complex formation with Zn2+. Docking study revealed that the antioxidative activity of procyanidin B1 involved human tyrosinase enzyme inhibition through interaction with essential residues, focusing on the OH groups of two phenyl rings.

Experimental and theoretical study of the catalytic effects of potassium and calcium additives on the pyrolysis of β-O-4 type lignin model compounds

In this work, to investigate the catalytic effects of potassium and calcium additives on lignin pyrolysis, two β-O-4 type model compounds for lignin containing different oxygen-containing functional groups (a carbonyl group or a hydroxyl group) on Cα were prepared, and their catalytic fast pyrolysis experiments were carried out on Py-GC/MS. Furthermore, the possible catalytic mechanism of potassium and calcium additives is further investigated using density functional theory (DFT) calculations. The experimental results show that the addition of potassium acetate and calcium acetate is beneficial to the formation of phenol, while the promotion effect of potassium addition is stronger than that of calcium addition. Moreover, considering the contributions of temperature and activation entropy ΔS‡, the activation Gibbs free energy ΔG‡ is required as the basis to explain the pyrolysis mechanism of lignin. It is determined that the Cβ-O homolytic reaction performs the most favorable in the initial depolymerization of both dimers. By comparing the ΔG‡, it is confirmed that the addition of K+ and Ca2+ are beneficial to the Cβ-O homolytic reaction and further promote the conversion of the intermediate to phenol. Furthermore, the different effects of K+ and Ca2+ additives are compared on the side chains cleavage through homolytic reaction and concerted decomposition. The calculation results show that K+ is more conducive to the simple homolytic reaction, while Ca2+ is more conducive to the concerted decomposition.

Asymmetric Dehydrative Cyclization of Allyl Alcohol to Cyclic Ether Using Chiral Brønsted Acid/CpRu(II) Hybrid Catalysts: A DFT Study of the Origin of Enantioselectivity

To elucidate the reaction mechanism and the origin of the enantioselectivity of the asymmetric dehydrative cyclization of allyl alcohol to cyclic ether catalyzed by a Cp-ruthenium complex and a chiral pyridinecarboxylic acid, (R)-X-Naph-PyCOOH, density functional theory (DFT) calculations were performed. According to the DFT calculations, the rate-determining step is the dehydrative σ-allyl formation step with ΔG‡ = 18.1 kcal mol-1 at 80 °C. This agrees well with the experimental data (ΔG‡ = 19.01 kcal mol-1 at 80 °C). The DFT result showed that both hydrogen and halogen bonds play a key role in the high enantioselectivity by facilitating the major R,SRu-catalyzed reaction pathway via a σ-allyl Ru intermediate to generate the major (S)-product. In contrast, the reaction is sluggish in the presence of the diastereomeric R,RRu catalyst with an apparent activation energy of 33.1 kcal mol-1; the minor (R)-product is formed via a typical π-allyl Ru intermediate and via a minor pathway for the cyclization step. In addition, the calculated activation Gibbs free energies, 14.4 kcal mol-1 for I < 16.8 kcal mol-1 for Br < 18.1 kcal mol-1 for Cl, reproduced the observed halogen-dependent reactivity with the (R)-X-Naph-PyCOOH ligands. The origin of the halogen trend was clarified by a structural decomposition analysis.

Structural and optical properties of salicyl-N-methyl-4-stilbazolium tosylate: Thermal, DFT, MEP and Hirshfeld surface analysis

The structural characteristics and optimized geometry of salicyl-N-methyl-4-stilbazolium tosylate (SMST), a derivative of the prominent electro-nonlinear optic crystal 4-(N,N-dimethylamino)-N-methyl-4-toluene sulfonate (DAST) is investigated. Its morphology, spectral, vibrational, thermal, and electronic features have been examined in studies like FT-IR, UV-Transmittance spectroscopy, single crystal XRD and TG-DTA analysis. Thermal parameters like activation energy, entropy, enthalpy, and Gibbs free energy suggest that the reaction is slower and non-spontaneous. The optical constants like energy band gap, absorption coefficient, extinction coefficient, refractive index, and skin depth of SMST have been calculated. The energy band gap value is found to be 2.69 eV, which makes SMST a potential and promising material for non-linear optical applications. The dielectric behavior of SMST is in agreement with the property needed for NLO materials. Theoretical calculations like density functional theory and frontier molecular orbitals- HOMO and LUMO are investigated to analyze the structural properties, atomic arrangement, oriented geometry, and dipole moment. Molecular electrostatic potential (MEP), Hirshfeld surface, and 2D fingerprint plot analysis are examined to provide information about the molecular interaction, crystal packing, electron density, and intermolecular properties of atomic contacts. Second Harmonic Generation of SMST shows greater efficiency than urea, which confirms that SMST crystal can leads to many applications in the optical field.

Thermodynamic properties (excess and partial molar volume, Gibbs free energy of activation for viscous flow, enthalpy, and entropy) of propylammonium nitrate/water mixtures

The purpose of this study is to use thermodynamic functions to clarify the change in the solution structure and interaction of the propylammonium nitrate (PAN)/water system in response to changes in the temperature and water concentration. Specifically, the viscosity and density of the PAN/water system were measured over the entire water concentration range and over the temperature range from 278.15 to 323.15 K. The molar free Gibbs energy of activation for viscous flow (ΔGm‡,E), entropy (ΔSm‡,E), and entropy (ΔHm‡,E) and their PAN (ΔGm,PAN‡,E, TΔSm,PAN‡,E, ΔHm,PAN‡,E) and water (ΔGm,H2O‡,E, ΔHm,H2O‡,E and TΔSm,H2O‡,E) partial quantities were calculated, and we investigated the validity of the unique interpretation that water might be accommodated in the cavities of the liquid structure of PAN. In the water concentration dependence, TΔSm‡,E and ΔHm‡,E were consistently negative andTΔSm‡,E < ΔHm‡,E. Therefore, the results suggest that PAN forms a more ordered structure when mixed with water even though the attractive intermolecular interaction decreases. However, the increase of ΔHm‡,E and TΔSm‡,E in the temperature range 278–323 K was 2.35 kJ mol−1 and 1.60 kJ mol−1, respectively, indicating that ΔHm‡,E > TΔSm‡,E. That is, the attractive intermolecular interaction increases with increasing temperature, suggesting that the ordered structure changes toward disorder. In addition, at a water mole fraction of 0.1, which was the lowest concentration of water investigated in this study, the partial molar volume of water is 16% lower than that of pure water and both ΔHm,H2O‡,E and TΔSm,H2O‡,E are reduced, suggesting that the attractive interaction of water is weaker in PAN than in bulk water and that the structure of PAN is closer to that of a pure liquid in this concentration range. Water is speculated to be accommodated into the cavities of the PAN structure.

Thermodynamic and electrochemical investigation of inhibition efficiency of green corrosion inhibitor and its comparison with synthetic dyes on MS in acidic medium

The expedition of Green corrosion inhibitors has been initiated by the organic corrosion inhibitor as green corrosion inhibitors are bio-degradable, eco-friendly and environmental acceptable bereft of heavy metals and other toxic products. Moreover, the products obtained from the plant are cost-effective, readily available and can be renewed. In the following study, the inhibition performance of natural inhibitor i.e., black pepper extract and synthetic inhibitors i.e., thoron Dye and Phenosafranin dye on mild steel surfaces in hydrochloric acid (HCl) were inspected and for this purpose, weight loss measurements, Electrochemical Impedance Measurements (EIS) and Potentiodynamic Polarization study at different concentrations and at different temperatures were recruited. Among these inhibitors, the best inhibition efficiency was shown by black pepper extract i.e., 97% in 1 M HCl. In the prolongation of our work, entropy (ΔS), enthalpy (ΔH), gibbs free energy (ΔG), activation energy (Ea) and pre-exponential factor (A) of the reaction were calculated and it is concluded that the inhibition process follows physical adsorption on the surface and the adsorption process follows Langmuir and Tempkin isotherms also. For surface analysis, Atomic Force Microscopy (AFM) was done. The present study concludes that natural inhibitor i.e., Black pepper extract which contains alkaloid piperine becomes quite impressive in decelerating the effect of corrosion on mild steel surfaces in acidic environments as compared to synthetic inhibitors.

A promising new class of high-entropy ceramics: High-entropy oxycarbides with good oxidation resistance

(Hf0.25Zr0.25Nb0.25Ti0.25)(C0.5O0.5) high-entropy oxycarbides (HECO-1) with good oxidation resistance, as a promising new class of high-entropy ceramics, were synthesized by a facile carbothermic reduction method for the first time. The results showed that the as-synthesized HECO-1 samples had the single-phase rock-salt structure and high compositional uniformity. Compared to the as-synthesized (Hf0.25Zr0.25Nb0.25Ti0.25)C high-entropy carbides, the as-synthesized HECO-1 samples possessed the higher initial oxidation temperature and slower oxidation rate to show the better oxidation resistance, making them the promising applications in extreme environments, which was attributed to their higher oxidation activation energy and Gibbs free energy of oxidation reaction.

Thermodynamic and kinetic studies on antioxidant capacity of amentoflavone: a DFT (density functional theory) computational approach

Density functional theory (DFT) at the theoretical M06-2X/6-311G(d,p) level was used to assess thermodynamics and kinetics in the antioxidative action of amentoflavone (AF). The antioxidative HAT pathway (H-atom transfer) is assigned to this compound in gas, but the SPL-ET (sequential proton loss-electron transfer) is the main route in polar solvents methanol and water. In all four mediums gas, benzene, methanol, and water, 4‴-OH is the most active site in free radical quenching with the lowest BDE (bond dissociation enthalpy) values of 81.8–84.8 kcal/mol, as well as it exerted the PA (proton affinity) values of 29.8–33.0 kcal/mol in methanol and water. Regarding kinetics, when interacted with •OOH and •NO2 in gas and methanol, 4‴-OH group is also responsible for the lowest ΔG # values (Gibbs free energy of activation), and the highest rate constant K values. Acidic assessment also indicated that 4‴-OH is associated with the strongest acidity (the lowest pKa). Two favorable oriented 4‴-OH and 7-OH groups further exhibited antioxidative activity since they prevented metal ions Zn2+ and Fe2+ from participating in free radical producing processes, in which the most stable complex [FeAF(H2O)4] generated the lowest IE value of −206.2 kcal/mol, and E gap value of 3.491 kcal/mol, but the highest MIA values of 184.6 kcal/mol in methanol.

New insights and updated correlations for density, viscosity, refractive index, and associated properties of aqueous 4-diethyl-amino-2-butanol solution

In this study, volumetric, viscometric, and refraction properties of binary 4-diethylamino-2-butanol (DEAB) and water mixture were comprehensively investigated over an entire range of amine concentration and a temperature range of 298.15-343.15 K. In addition to typical density, viscosity, refractive index, and their excess properties, the associated properties (including partial molar volume, apparent partial molar volume, partial molar volume and apparent partial molar volume at infinite dilution, thermal expansion coefficient, excess thermal expansion coefficient, Gibbs free energy, enthalpy, entropy, excess Gibbs free energy, and excess entropy for activation of viscous flow, molar polarizability, and molar free volume) were comprehensively considered. The obtained excess properties revealed that there was a strong contraction of liquid mixture through intermolecular interaction and/or preference molecular packing. Also, Gibbs free energy for activation of viscous flow was a key parameter affecting liquid viscosity. It was suggested that refractive index should be considered with density for a molar polarizability and a free molar volume for CO2 physical solubility. Additionally, the Redlich-Kister equation was very effective for correlating the studied excess physical properties.

Preparation, Spectroscopy, Biological Activities and Thermodynamic Studies of New Complexes of Some Metal Ions with 2-[5-(2-Hydroxy-Phenyl)- 1,3,4-Thiadiazol-2-Ylimino]-Methyl-Naphthalen-1-Ol

This study describes the preparation of new series of tetra-dentate N2O2 dinuclear complexes (Cr3+, Co2+, Cu2+) of the Schiff base derived from condensation of 1-Hydroxy-naphthalene-2-carbaldehyde with 2-amino-5-(2-hydroxy-phenyl)-1,3,4-thiadiazole. The structures of the ligands were identified using IR, UV-Vis , mass, elemental analysis and 1H-NMR techniques. All prepared complexes have been characterized by conductance measurement, magnetic susceptibility, electronic spectra, infrared spectrum, theromgravimatric analysis (TGA) and metal analysis by atomic absorption. From stoichiometry of metal to ligand and all measurements show a octahedral geometry proposed for all complexes of the (Cr3+, Co2+, Cu2+). conductivity measurement shows that of the prepared (Co2+, Cu2+) complexes were non electrolyte but (Cr3+) complexes were electrolyte. The parameters of thermodynamic, activation energy Ea , enthalpy ΔH, entropy ΔS and Gibbs free energy ΔG were calculated using Coats-Redfern method by the TGA curve. The bioactivity of the prepared (LH2) and its complexes have been examined with antibacterial activity which shows significant activity against some fungi and bacteria.

Phytochemical Constituent and Anti-corrosion Properties of the Root Extract of Phyllanthus mellerianus (Nvo-nkwu) Plant on Mild Steel in 1.5M HCl Medium

The research reports on the phytochemical constituents and anti-corrosion properties of the root extract of Phyllanthus mellerianus on mild steel in 1.5M HCl. The powdered root was extracted with ethanol and concentrated with a rotary evaporator. The phytochemical constituents’ were achieved through GC-MS, FTIR and wet analysis. The anticorrosion properties were investigated via weight loss, hydrogen evolution techniques, and SEM analysis. The phytochemical investigation reveals the presence of tannins, flavonoids, phenols, and terpenoids at reasonable percentages. At different temperatures of 303K, 313K, and 323K, the inhibition efficiency, enthalpy, entropy, activation energy, Gibbs free energy, and adsorption isotherms were extrapolated with some models. The inhibition efficiency increased with an increase in the concentration of the extract, an indication of the inhibitive property of the root extract. This was supported through the extrapolation of Gibbs free energy, activation energy, enthalpy, and entropy change. The thermodynamic variable shows that the mechanism of inhibition was physisorption, whereas the kinetics study confirmed a first-order kinetic on the corrosion of mild steel in hydrochloric acid. The values of the linear regression R2 confirm the inhibitive impact of the root extract on mild steel in an acid medium. The presence of the heteroatoms N, O, and S in the root extracts of Phyllanthus mellerianus has been attributed to their inhibitory effectiveness.

A comparative optimization and modeling of ammonia–nitrogen adsorption from abattoir wastewater using a novel iron-functionalized crab shell

High-grade adsorbent (Fe–CS) was successfully synthesized from waste crab shells (CS) for the adsorptive removal of ammonia–nitrogen (A–N) from abattoir wastewater. Fe–CS was analyzed using Fourier transform infrared spectroscopy, x-ray diffraction, Scanning electron microscopy, and Thermogravimetric analysis. The characterization results indicated that Fe–CS possessed important qualities required for surface-driven chelation. The analysis of variance result showed that Fe–CS dosage (with f–value of 284.5) was the most effective process parameter of influence during A-N adsorption. The regression coefficients obtained from the process modeling illustrated the applicability of RSM (R2 = 0.9799), ANN (R2 = 0.9025), and ANFIS (R2 = 0.9998) in predicting the A–N adsorptive removal, while the comparative statistical analysis established the superiority of ANFIS model over ANN and RSMs’ data prediction accuracy. The optimization result further demonstrated that ANFIS–GA predicted an optimum removal efficiency of 92.60% at pH of 6.5, a dosage of 2.2 g, A–N conc. of 18.8 mg/L, Temp. of 317 K, and adsorption time of 156 min. The mechanistic plot obtained from Weber–Morris model depicted that three regions were involved in the adsorption process. Boyd model parameters revealed that intraparticle diffusion controlled the process at low A–N concentration (A–N concentration ≤ 15 mg/L), while film diffusion dominated the adsorption process at concentrations higher than 15 mg/L. The average Gibbs free energy value (- Delta G^{0} = 3.08212 kJ/mol), enthalpy (Delta H^{0} = 4.1150 kJ/mol), activation energy (E_{A} = 3.7454 kJ/mol) and entropy (Delta S^{0} = 22.9710 J/mol K) obtained from thermodynamic studies confirmed the spontaneous, endothermic, favorable and physical nature of the process.

Co-pyrolysis of lychee and plastic waste as a source of bioenergy through kinetic study and thermodynamic analysis

The use of hazardous materials like plastic waste can be improved by adding value to viable biomass candidates. The current study is focused on lychee and plastic waste co-pyrolysis for the production of energy and chemicals. Based on this knowledge of the subject matter sample mixture was pyrolysed at four different heating rates: 10 °C min−1, 20 °C min−1, 30 °C min−1, and 40 °C min−1. To establish the pyrolysis reaction process, the data was subjected to kinetic modelling, which predicted thermodynamic parameters. The co-pyrolysis standard method of lychee and plastic waste demonstrated 83% of thermal degradation was achieved. This result proves that the co-pyrolysis of lychee waste and waste plastics can increase the output of bio-oil, reduce carbon coking, improve profitability and cost competitiveness, make industrial production possible and environmentally friendly. The kinetic parameters, such as average activation energy, pre-exponential factors, enthalpy and Gibbs free energy, were shown to be 64 kJ mol−1 to 71 kJ mol−1, 102 s−1 to 1011 s−1, 58 kJ mol−1 to 65 kJ mol−1 and 299 kJ mol−1 to 308 kJ mol−1. The obtained quantitative synergetic kinetic and thermodynamic attributes of lychee and plastic waste may indicate its potential for bioenergy generation.

Preparation and characterization of the dimethyl sulfide-β-cyclodextrin inclusion complex.

Dimethyl sulfide has been widely used in flavors and can also be used as a solvent and catalyst. However, dimethyl sulfide is volatile, and its lasting power is weak. Furthermore, dimethyl sulfide is insoluble in water and is unstable in some cases. This study concentrated on the encapsulation of dimethyl sulfide in β-cyclodextrin to form an inclusion complex and to improve the durability, water solubility, and stability of dimethyl sulfide. The product was successfully produced and characterized by scanning electron microscopy, diffraction of X-rays, and thermal analysis. The dimethyl sulfide loading capacity is 6.40±0.08%. Based on the thermal release characteristics of dimethyl sulfide, the kinetic and thermodynamic parameters were obtained. The apparent activation energy, pre-exponential factor, and reaction order of the dimethyl sulfide release reaction were obtained and the values were 95.0±0.1kJ/mol,1.03×1015 s-1 , and 1, respectively. The activation entropy change, activation enthalpy change, and activation Gibbs free energy change were 41.6 J/K, 95.0kJ/mol, and 81.3kJ/mol, respectively, during the process of dimethyl sulfide release at 56.7℃. To make it clear that the dimethyl sulfide molecule interacts with β-cyclodextrin molecule, molecular simulation was used to investigate the formation process of the dimethyl sulfide-β-cyclodextrin inclusion complex. The binding energy and the optimized structure were obtained. When the Z coordinate of the S atom in the dimethyl sulfide molecule is 1.1×10-10 m, the binding energy attained the minimum value, -51.3kJ/mol. These basic data are helpful for understanding the dimethyl sulfide-β-cyclodextrin inclusion complex formation mechanism and the interaction between dimethyl sulfide and β-cyclodextrin. PRACTICAL APPLICATION: By forming an inclusion complex with β-cyclodextrin, the stability, durability, and water solubility of dimethyl sulfide can be improved. Dimethyl sulfide-β-cyclodextrin inclusion complex can be widely used in the food, beverage, flavor, and fragrance industries. The kinetic and thermodynamic parameters, binding energy, and the results of molecular simulation are helpful to understand the dimethyl sulfide-β-cyclodextrin inclusion complex formation mechanism and the interaction between dimethyl sulfide and β-cyclodextrin.

Volumetric, viscometric and spectroscopic studies of molecular interactions of glutamic acid with potassium sorbate and sodium benzoate in aqueous medium at T = 293.15–313.15 K

The empirically procured data of physical properties like density and viscosity for the solutions of glutamic acid (Glu) with various concentrations in H2O and H2O + (1.5, 2.0 and 2.5 mol.kg-1) potassium sorbate (PS)/sodium benzoate (SB) at five different temperature (T = 293.15–313.15 K) and atmospheric pressure (101.1 kPa) has been used in order to calculate volumetric and viscometric parameters such as apparent molar volume (Vϕ), partial apparent molar volume (V∅0), limiting apparent molar expansibility (E∅0), viscosity B-coefficients (BJ), pair and triplet interaction co-efficients etc. Structure making properties of glu being present with PS/SB in the solutions are explained by the positive Hepler’s constant (∂2V∅0/∂T2)P values. This structure building tendency of Glu is further supported by the positive (BJ) and negative (∂BJ/∂T) values. For both solute and solvent Gibbs free energy of activation (Δμ10,#andΔμ20,# respectively) has been evaluated and including these parameters the thermodynamic parameters like ΔS0,#andΔH0,# profound the stability of the transition state. For a refined understanding of distinct intermolecular interactions prevailing in the designed systems the co-sphere overlap model has been employed. The procured results acknowledge that solute-solvent interactions reduce with a rise in temperature. Additionally, FTIR spectral analysis was carried out on the studied systems and relying on the shifting oh O-H stretching band the presence of hydrogen bond as well as different kinds of interactions are confirmed for the investigated system.

Xenon Derivatives as Aerogen Bond-Donating Catalysts for Organic Transformations: A Theoretical Study on the Metaphorical "Spherical Cow in a Vacuum" Provides Insights into Noncovalent Organocatalysis.

Computations indicate that cationic and noncharged xenon derivatives should exhibit higher catalytic activity than their iodine-based noncovalent organocatalytic congeners. Perfluorophenyl xenonium(II) is expected to demonstrate the best balance between catalytic activity and chemical stability for use in organocatalysis. Comparing its catalytic activity with that of isoelectronic perfluoroiodobenzene indicates that the high catalytic activity of cationic noncovalent organocatalysts is predominantly attributed to the electrostatic interactions with the reaction substrates, which cause the polarization of ligated species during the reaction progress. In contrast, the electron transfer and covalent contributions to the bonding between the catalyst and substrate have negligible effects. The dominant effect of electrostatic interactions results in a strong negative correlation between the calculated Gibbs free energies of activation for the modeled reactions and the highest potentials of the σ-holes on the central atoms of the catalysts. No such correlation is observed for noncharged catalysts.

A Molecular Electron Density Theory Study of the [3+2] Cycloaddition Reaction of Pseudo(mono)radical Azomethine Ylides with Phenyl Vinyl Sulphone

The [3+2] cycloaddition (32CA) reaction of an azomethine ylide (AY), derived from isatin and L-proline, with phenyl vinyl sulphone has been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) level. ELF topological analysis of AY classifies it as a pseudo(mono)radical species with two monosynaptic basins at the C1 carbon, integrating a total of 0.76 e. While vinyl sulphone has a strong electrophilic character, AY is a supernucleophile, suggesting a high polar character and low activation energy for the reaction. The nucleophilic Parr functions indicate that the pseudoradical C1 carbon is the most nucleophilic center. The 32CA reaction presents an activation Gibbs free energy of 13.1 kcal·mol−1 and is exergonic by −26.8 kcal·mol−1. This reaction presents high endo stereoselectivity and high meta regioselectivity. Analysis of the global electron density transfer (GEDT) at the most favorable meta/endo TS, 0.31 e, accounts for the high polar character of this 32CA reaction, classified by forward electron density flux (FEDF). A Bonding Evolution Theory (BET) study along the most favorable meta/endo reaction path characterizes this 32CA reaction, taking place through a non-concerted two-stage one-step mechanism, as a pseudo(mono)radical-type 32CA reaction, in agreement with the ELF analysis of the AY.

Mechanistic Studies of Oxygen-Atom Transfer (OAT) in the Homogeneous Conversion of N2O by Ru Pincer Complexes

As the overall turnover-limiting step (TOLS) in the homogeneous conversion of N2O, the oxygen-atom transfer (OAT) from an N2O to an Ru-H complex to generate an N2 and Ru-OH complex has been comprehensively investigated by density functional theory (DFT) computations. Theoretical results show that the proton transfer from Ru-H to the terminal N of endo N2O is most favorable pathway, and the generation of N2 via OAT is accomplished by a three-step mechanism [N2O-insertion into the Ru-H bond (TS-1-2, 24.1 kcal mol−1), change of geometry of the formed (Z)-O-bound oxyldiazene intermediate (TS-2-3, 5.5 kcal mol−1), and generation of N2 from the proton transfer (TS-3-4, 26.6 kcal mol−1)]. The Gibbs free energy of activation (ΔG‡) of 29.0 kcal mol−1 for the overall turnover-limiting step (TOLS) is determined. With the participation of potentially existing traces of water in the THF solvent serving as a proton shuttle, the Gibbs free energy of activation in the generation of N2 (TS-3-4-OH2) decreases to 15.1 kcal mol−1 from 26.6 kcal mol−1 (TS-3-4). To explore the structure–activity relationship in the conversion of N2O to N2, the catalytic activities of a series of Ru-H complexes (C1–C10) are investigated. The excellent linear relationships (R2 &gt; 0.91) between the computed hydricities (ΔGH−) and ΔG‡ of TS-3-4, between the computed hydricities (ΔGH−) and the ΔG‡ of TOLS, were obtained. The utilization of hydricity as a potential parameter to predict the activity is consistent with other reports, and the current results suggest a more electron-donating ligand could lead to a more active Ru-H catalyst.

Adsorptive Behavior of Tartaric Acid Treated Holarrhena antidysenterica and Citrullus colocynthis Biowastes for Decolourization of Congo Red Dye from Aqueous Solutions

The aim of the present work is to eradicate Congo red (CR) dye from aqueous solutions since the dye compounds are harmful to human life and the environment leading to detrimental results. For this purpose, Holarrhena antidysenterica (HA) and Citrullus colocynthis (CC) adsorbents were used for the adsorptive removal of Congo red dye from wastewaters. The unmodified adsorbents (U-HA and U-CC) were chemically modified using tartaric acid (TA). Morphological structures were examined by FTIR and SEM. Batch adsorption studies were tested at a variety of pH, time exposure, temperatures, and adsorbent dosages. Thermodynamic parameters such as Gibbs free energy ( ∆ G ° ), enthalpy ( ∆ H ° ), entropy changes ( ∆ S ° ), and energy of activation ( E a ) were also calculated. The results revealed that tartaric acid-Citrullus colocynthis (TA-CC) gave optimum conditions of time of contact (35 min), temperature conditions (40°C), pH (3), and dosage of adsorbent (1.6 g) for maximum dye removal. Tartaric acid-Holarrhena antidysenterica (TA-HA) gave equilibrium time of contact (30 min), temperature (40°C), and pH optimum (2) along with a 1.6 g dosage of adsorbent. Mechanistic understanding of adsorption isotherm provided that the Langmuir model was followed by raw and modified adsorbents. Maximum adsorption capacities Q max attained were 60.61 (mg g-1), 128.21 (mg g-1), 87.71 (mg g-1), and 131.57 (mg g-1), respectively, for U-HA, TA-HA, U-CC, and TA-CC. The results of kinetic modeling displayed a high value of R 2 (0.99) along with minimal error (RMSE) for dye removal showing that the pseudo-second-order kinetic model has acceptable accuracy. Fourier transform infrared proposed the electrostatic, pi-pi interactions, and hydrogen bonding as dominant adsorption mechanisms at acidic pH, respectively. Rate-determining steps comprise both surface and intraparticle diffusions. Thermodynamics indicated that the dye adsorption of CR is spontaneous, exothermic, and favorable in nature. These agricultural wastes due to specific points such as low cost, availability, and high removal rates of adsorption are highly competent for the expulsion of anionic dye like CR from wastewaters.