Entropy Of Activation Research Articles

Effect of the dried limes (Citrus aurantifolia) on the caffeine kinetic extraction in black tea leaves (kinetic and thermodynamic study)

ABSTRACT. The kinetic and thermodynamic parameters were studied for the extraction of caffeine in black tea leaves and tea leaves containing antioxidant dried limes (Citrus aurantifolia). Caffeine is widely used in human consumption and is present in any liquid suitable for drinking except water. However, the health and environmental demerits make it significant to reduce caffeine to much less concentration or decaffeination. Therefore, the effect of the dried antioxidant Citrus aurantifolia on caffeine concentration followed by pseudo-first-order reaction, kinetic parameters (pseudo-first-order rate constant (k), equilibrium absorbance (A∞)), and thermodynamic activation parameters, the activation energy (Ea), change in enthalpy of activation (ΔH#), the change in entropy of activation (ΔS#) and change in activation Gibbs free energy (ΔG#) was calculated at four different temperatures 30, 60, 80, and 100 °C. Using the spectroscopic method the activation energy of the caffeine concentration in free black tea leaves solution (Ea = 13.32 kJmol-1) was higher than the black tea leaves mixed with lime solution (Ea = 9.89 kJmol-1), the higher collision of molecules A-factor (1.96 min-1), and large correlation factor (R2 = 0.95). The thermodynamic activation parameters ΔH#, ΔS#, and ΔG# demonstrate less heat absorption, irreversible, and more spontaneous interaction of lime with caffeine.
 
 KEY WORDS: Caffeine, Tea leaves, Citrus aurantifolia, Thermodynamic parameters, Kinetic
 Bull. Chem. Soc. Ethiop. 2022, 36(3), 697-705. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i3.18

An approach to the activation energy, thermodynamics, and flow injection kinetics of degradation of 2,4-dimethylaniline

Flow injection kinetics was used to investigate the activation energy and thermodynamics parameters of periodate degradation of 2,4-dimethylaniline by catalyzing the reaction with Mn(II) in a mixed medium. The impact of pH and dielectric constant was also investigated. Flow injection kinetics, activation energy, and several thermodynamic parameters have also been recorded. The value of activation energy (ΔE#) for the degradation of 2,4-dimethylaniline is 4.5350 ± 0.1302 kJmol−1, which is consistent with the speculative first-order. The value of other thermodynamic parameters were reported as Arrhenius frequency factor (A) = 3.7660 × 106 ± 0.00372 dm3mol−1s−1; Activation Entropy (ΔS#) = −208.170 ± 0.1498 Jmol−1K−1, Activation free energy (ΔG#) = 66.59 ± 1.163 kJmol−1 and activation Enthalpy (ΔH#) = 1.954 ± 0.0465 kJmol−1.

Excess properties, spectral analysis and computational chemistry of (1,3-propanediol + ethylenediamine) ion-like liquids for CS2 capture

Density and viscosity of (1,3-propanediol (1,3-PDO) (1) and ethylenediamine (EDA) (2)) ion-like liquids were measured at T = (293.15–318.15) K with the step of 5 K under atmospheric pressure. On the basis of basic density and viscosity, the activation thermodynamics and excess properties of the ion-like liquids, including the excess molar volume (VmE), partial molar volume (V¯), apparent molar volume (Vφ), thermal expansion coefficient (αP), viscosity deviation (Δη), activation enthalpy change (ΔH*), activation entropy change (ΔS*), activation Gibbs energy (ΔG*) and excess Gibbs energy of activation of viscous flow (ΔG*E), were systemically researched. Meanwhile, the Jouyban-Acree model and the nonlinear least-squares method were used to fit the density, the McAllister three-body equation, McAllister four-body equation and the Arrhenius equation were used to fit dynamic viscosity and viscosity, and the R-K equation was used to fit the excess molar volume, viscosity deviation and excess Gibbs energy of activation of viscous flow. After that, based on Fourier Transform infrared spectroscopy (FTIR), Raman spectral (Raman), ultraviolet spectral (UV), fluorescence spectral (FLS) and nuclear magnetic resonance spectroscopy (1H NMR) spectral results and density functional theory (DFT) calculation results, it is proved that there are hydrogen bonding of 1,3-PDO with EDA as the form of ···HOCH2CH2CH2OH···NH2CH2CH2N(H2)···. In addition, the existence of ion-like interaction and van der Waals effects in ion-like liquids was novelty found. This provides preliminary work preparation for exploring the absorption and fixation of CS2 in ion-like liquids.

Entropy Generation and Statistical Analysis of MHD Hybrid Nanofluid Unsteady Squeezing Flow between Two Parallel Rotating Plates with Activation Energy

Squeezing flow is a flow where the material is squeezed out or disfigured within two parallel plates. Such flow is beneficial in various fields, for instance, in welding engineering and rheometry. The current study investigates the squeezing flow of a hybrid nanofluid (propylene glycol–water mixture combined with paraffin wax–sand) between two parallel plates with activation energy and entropy generation. The governing equations are converted into ordinary differential equations using appropriate similarity transformations. The shooting strategy (combined with Runge–Kutta fourth order method) is applied to solve these transformed equations. The results of the conducted parametric study are explained and revealed in graphs. This study uses a statistical tool (correlation coefficient) to illustrate the impact of the relevant parameters on the engineering parameters of interest, such as the surface friction factor at both plates. This study concludes that the squeezing number intensifies the velocity profiles, and the rotating parameter decreases the fluid velocity. In addition, the magnetic field, rotation parameter, and nanoparticle volumetric parameter have a strong negative relationship with the friction factor at the lower plate. Furthermore, heat source has a strong negative relationship with heat transfer rate near the lower plate, and a strong positive correlation with the same phenomena near the upper plate. In conclusion, the current study reveals that the entropy generation is increased with the Brinkman number and reduced with the squeezing parameter. Moreover, the results of the current study verify and show a decent agreement with the data from earlier published research outcomes.

GAS PHASE DECOMPOSITION OF T-BUTYL METHYL ETHER CATALYZED BY DIFFERENT HYDROGEN HALIDES: A DFT STUDY

The gas phase decomposition of t-butyl methyl ether catalyzed by hydrogen halides is studied. Four different hydrogen halides (fluorine, chlorine, bromine, and iodine) were evaluated to determine the electronic influence of the halogen in the reaction mechanism. To describe the mechanism, the ωB97XD/LANL2DZ level of theory was used. The reactivity order found was F<Cl<Br<I. Interestingly, the activation free energy estimated for the HCl model was 133.9 kJ/mol, which is in good agreement with the experimental one (134.3 kJ/mol). Furthermore, a correlation above 0.804 was noticed when the electronegativity, the hydrogen-halide distance, and the pKa of the hydrogen halides were compared to the thermodynamic parameters (activation free energy, enthalpy, and entropy). Analyzing the mechanism in depth through the intrinsic reaction coordinate, reaction force, and reaction electronic flux plots, it was observed that though the reaction occurs in a one-step concerted way. The mechanism could be divided into two events; the first one composed by a proton transfer from the halide to the oxygen and the carbon-oxygen bond cleavage, and the second one being the rate-limiting event which includes the proton transfer from the t-butyl to the halide and the double bond formation.

Aluminum corrosion prevention in 1.0 M HCl solution by cystosiera myrica extract: An experimental and biological study

Potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS), tests, mass loss (ML) and Hydrogen evolutions (HE) methods were used to examine the effects of the newly plant extracted compound (Cystosiera myrica). All these quantities exhibited that the effectiveness of inhibition increase with a rise in inhibitor concentration and with a rise in temperature. Polarization curves displayed that the inhibitor studied was an inhibitor of a mixed kind. Langmuir isotherm was attained for the adsorption of the inhibitor on the Aluminum surface. Thermodynamic parameters were determine and deduced such as activation enthalpy (ΔH*), activation entropy (ΔS*), adsorption equilibrium constant (Kads) and free adsorption energy (Goads) have been measured. UV/visible spectral, Attenuated Total Reflection Infra-Red (ATR-IR) and Atomic Force Microscopy (AFM) tested have observed the effect of this inhibitor on Al surface morphology. All other data approaches were compatible and in line with each other.

Synthesis of biodiesel from fish processing waste by nano magnetic catalyst and its thermodynamic analysis

The current work describes the synthesis of Nano magnetic catalysts, oil extraction from fish waste and processing of biodiesel. The first-order thermodynamic equations are considered to determine its kinetic and thermodynamic parameters involved in extraction process. The study has considered the rate constant (k), activation energy (Ea), frequency factor (A), entropy (ΔS), enthalpy (ΔH), and Gibb's free energy (ΔG) as variables at different temperatures. The maximum activation energy, rate constant, enthalpy and entropy are 59.31 kJ mol −1 , 27.15 s −1 , 65.87kJmol -1 and 27.63kJmol- 1 k −1 respectively. The important parameters affecting the process of biodiesel production is reaction temperature and catalyst concentration. Here, the nano magnetic catalysts accelerate the production of biodiesel from fish waste. So, the biodiesel yield is high at 55 °C reaction temperature (95 wt%) than 32 °C reaction temperature (65 wt%). The resulting biodiesel was tested according to ASTM standards and obtained the closer values as per ASTM D6751 specification.

Corrosion inhibition of mild steel in hydrochloric acid environment using thiadiazole derivative: Weight loss, thermodynamics, adsorption and computational investigations

The corrosion inhibition potency of 1-(2-ethylamino-1,3,4-thiadiazol-5-yl)-3-phenyl-3-oxopropan (ETO) for mild steel in 1.0 M hydrochloric acid was investigated by applying weight loss techniques, and quantum chemical calculations. Conditions that determine the potential for corrosion inhibition, including; concentration, the structure of ETO, and solution temperature, were chosen for the study. The highest inhibitive efficacy of ETO was 98.4%, at the optimum concentration (500 ppm) and room temperature. ETO has superior corrosion inhibitive potency in the HCl environment, owing to the presence of the thiadiazole and benzene rings, in addition to carbonyl and amino groups. Applicable thermodynamical equations were used to calculate the activation energy, enthalpy, and entropy. The adsorption isotherms were applied to determine the Gibbs free energy difference. The experimental findings of the investigation revealed that the activation energy of an inhibited process was higher than for an uninhibited process. Furthermore, the increased inhibition efficiency with improving temperature, and the values of ΔGo, indicated that ETO molecules coated the mild steel surface in both chemical adsorption and physical interactions. The adsorption process on the mild steel surface obeys the Langmuir adsorption isotherm. Both experimental and density functional theory (DFT) findings in the current investigation are in excellent agreement.

Study of Human Perception of Time using Brain Entropy and Inverse Problem Analysis of Brain Activities

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Experimental and theoretical investigation of corrosion inhibition effect of two 8-hydroxyquinoline carbonitrile derivatives on mild steel in 1 M HCl solution

The inhibiting effect of two newly synthesized organic compounds based on 8-hydroxyquinoline, 2-amino-4-phenyl-2H-pyrano[3,2-h]quinolin-3-carbonitrile (QP-H) and 2-amino-4-(4-methoxyphenyl)-2H-pyrano[3,2-h]quinolin-3-carbonitrile (QP-OCH3), on mild steel (MS) corrosion in 1 M HCl has been assessed using various electrochemical techniques [potentiodynamic polarization curves (PP curves) and electrochemical impedance spectroscopy (EIS)], scanning electron microscopy (SEM), UV–visible spectroscopy, and theoretical calculations. The experimental results have revealed that QP-H and QP-OCH3 significantly prevent MS corrosion and that their inhibition efficacy improves upon increasing their concentration. The maximum inhibition efficiency of QP-H and QP-OCH3 was determined to be 92 and 79.1% at 10−3 M, respectively. QP-H and QP-OCH3 are mixed-type inhibitors, according to our PP study. Thermodynamic specific data such as the energy, entropy and enthalpy of activation have been determined and discussed. The adsorption of BQMT and QMHC on the MS surface has been examined using SEM, UV–visible spectroscopy, and different isotherm models, which obeys the Langmuir isotherm model. Simulations based on density functional theory (DFT) and molecular dynamics simulation (MDS) have been used to further understand the corrosion resistance mechanism.

Energetic and Structural Insights into Phospholipid Transfer from Membranes with Different Curvatures by Time-Resolved Neutron Scattering.

Understanding how lipid dynamics change with membrane curvature is important given that biological membranes constantly change their curvature and morphology through membrane fusion and endo-/exocytosis. Here, we used time-resolved small-angle neutron scattering and time-resolved fluorescence to characterize the properties and dynamics of phospholipids in vesicles with different curvatures. Dissociation of phospholipids from vesicles required traversing an energy barrier comprising positive enthalpy and negative entropy. However, lipids in membranes with high positive curvature have dense acyl chain packing and loose headgroup packing, leading to hydrophobic hydration due to water penetration into the membrane. These properties were found to lower the hydrophobic hydration enhancement associated with phospholipid dissociation and mitigate the acyl chain packing of lipids adjacent to the space created by the lipid dissociation, resulting in an increase in activation entropy. The results of this study provide important insights into the functions of biomembranes in relation to their dynamic structural changes.

Biodiesel Production through Acid Catalyst In Situ Reactive Extraction of Chlorella vulgaris Foamate

A method of biodiesel production from the freshwater microalgae Chlorella vulgaris based on the conversion of the dewatered algal biomass from a foam column (“foamate”) was investigated. The foam column collected and concentrated the microalgae. The foam was generated by passing air through a pool of algae, to which a collector/surfactant cetyltrimethylammonium bromide (CTAB) had been added. To produce biodiesel, the resultant “foamate” was esterified in situ using sulfuric acid and methanol. The effect of reaction temperature (30–70 °C), reaction time (30–120 min) and methanol/oil molar ratio (100–1000), were examined in a single-stage extraction–transesterification experiment on biodiesel yield at concentration of the catalyst H2SO4/oil molar ratio of (8.5/1). The thermodynamics and kinetics of transesterification of the microalgae oil were also investigated. The maximum biodiesel yield (96 ± 0.2%) was obtained at a reaction temperature of 70 °C, a reaction time of 90 min and methanol/oil molar ratio of 1000/1. Reaction kinetic parameters were determined that fitted the experimental data at all temperatures. A reversible reaction with first order forward and second order backward kinetics were found to be a good match for the experimental results. The kinetic model fitted experiments well under various temperatures and methanol/oil mole ratios. Under the most suitable conditions of reaction temperature, reaction time and methanol/oil molar ratio, the apparent activation energy was found to be 18.7 kJ/mol and pre-exponential factor 51.4 min−1. The activation entropy (ΔS), change in Gibbs free energy (ΔG) and variation in activation enthalpy (ΔH) revealed that the transesterification reaction is endergonic and unspontaneous, while the endothermic nature of the reaction was confirmed by the positive value (16.6 kJ/mol) of the ΔH. The thermodynamic information and kinetic model reported here will provide valuable insight into the understanding of the in situ transesterification process from algae foamate to biodiesel.

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.

Controlled reversible aggregation of thermoresponsive polymeric nanoparticles by interfacial Diels-Alder reaction

HypothesisStimuli-responsive polymers, with properties changing upon different environmental factor variations such as pH, light, mechanical stress or temperature, and polymeric nanoparticles have found many important applications in fields such as drug delivery, biosensing and environmental research. ExperimentsIn this work, thermoresponsive nanoparticles that are able to react by Diels-Alder reaction (a diene-dienophile cycloaddition) were studied. Thermoresponsive polymers were synthesized from a biocompatible polymer (poly(lactic-co-glycolic) acid, PLGA) and diene (furan) or dienophile (maleimide) derivatives. Emulsification-evaporation method was then used as a fast and reproducible method to obtain highly monodispersed polymeric nanosuspensions able to react by Diels-Alder (DA) reaction. FindingsThe nanoparticles’ size decreased down to 25 nm by increasing the emulsification’s time. The possible direct and retro-Diels-Alder (rDA) reactions between furan- and maleimide-functionalized nanoparticles were studied by dynamic light scattering and electron microscopy. For the first time, the reactivity of the interfacial DA and rDA reactions between functionalized-nanoparticles was studied, leading to the determination of the activation energy, the enthalpy of activation and the entropy of activation.

Congestion Recognition of the Air Traffic Control Sector Based on Deep Active Learning

The air traffic control sector (ATCS) is the basic unit of the airspace system. If we can identify the congestion of an ATCS, it will help provide decision support for planning and daily operations. However, current methods mainly characterize congestion from the static structure and the dynamic operational features, resulting in poor generalization and operability. To this end, we propose a deep learning method from the perspective of complex networks. It takes aircraft as nodes to construct an aircraft network and utilizes the complexity indices to characterize it. So, the problem of identifying congestion becomes the complexity of the aircraft network. Inspired by active learning methods, we construct a deep active learning (DAL) model for congestion recognition. It adopts an iterative semi-supervised approach to reduce the number of labeled samples while ensuring recognition performance. To make full use of a large number of unlabeled samples, the sparse autoencoder is employed to characterize all labeled samples and unlabeled samples. The hidden layer of the deep neural network is constructed by stacking. In the process of active learning iteration, minimum confidence, marginal sampling, and information entropy are introduced as measures to select samples from the unlabeled sample set with significantly different features from the labeled sample set. The model is applied to three representative sectors in China’s airspace as cases. Results suggest that DAL can reduce the labeled sample set’s redundancy and achieve the desired performance with the smallest number of samples. Additionally, DAL is superior to the existing mainstream methods in the four objective evaluation indices.

Metathesis between E−C(sp n ) and H−C(sp 3 ) σ‐Bonds (E=Si, Ge; n =2, 3) on an Osmium‐Polyhydride

The silylation of a phosphine of OsH6(PiPr3)2 is performed via net-metathesis between Si−C(spn) and H−C(sp3) σ-bonds (n=2, 3). Complex OsH6(PiPr3)2 activates the Si−H bond of Et3SiH and Ph3SiH to give OsH5(SiR3)(PiPr3)2, which yield OsH4{κ1-P,η2-SiH-[iPr2PCH(Me)CH2SiR2H]}(PiPr3) and R−H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first-order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si-substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH6(PiPr3)2 with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH5(SiR2R′)(PiPr3)2, which evolve into OsH4{κ1-P,η2-GeH-[iPr2PCH(Me)CH2SiR2H]}(PiPr3) (R=Me, OSiMe3) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et3GeH. The latter reacts with OsH6(PiPr3)2 to give OsH5(GeEt3)(PiPr3)2, which loses ethane to form OsH4{κ1-P,η2-GeH-[iPr2PCH(Me)CH2GeEt2H]}(PiPr3).

Metathesis between E-C(spn ) and H-C(sp3 ) σ-Bonds (E=Si, Ge; n=2, 3) on an Osmium-Polyhydride.

The silylation of a phosphine of OsH6(PiPr3)2 is performed via net‐metathesis between Si−C(sp n ) and H−C(sp3) σ‐bonds (n=2, 3). Complex OsH6(PiPr3)2 activates the Si−H bond of Et3SiH and Ph3SiH to give OsH5(SiR3)(PiPr3)2, which yield OsH4{κ1‐P,η2‐SiH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) and R−H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first‐order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si‐substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH6(PiPr3)2 with dimethylphenylsilane, and 1,1,1,3,5,5,5‐heptamethyltrisiloxane afford OsH5(SiR2R′)(PiPr3)2, which evolve into OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2SiR2H]}(PiPr3) (R=Me, OSiMe3) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et3GeH. The latter reacts with OsH6(PiPr3)2 to give OsH5(GeEt3)(PiPr3)2, which loses ethane to form OsH4{κ1‐P,η2‐GeH‐[iPr2PCH(Me)CH2GeEt2H]}(PiPr3).

Conversion of Sewage Water into H2 Gas Fuel Using Hexagonal Nanosheets of the Polyaniline-Assisted Deposition of PbI2 as a Nanocomposite Photocathode with the Theoretical Qualitative Ab-Initio Calculation of the H2O Splitting.

This study is very promising for providing a renewable enrgy (H2 gas fuel) under the elctrochemical splitting of the wastwater (sewage water). This study has double benefits: hydrogen generation and contaminations removel. This study is carried out on sewage water, third stage treated, from Beni-Suef city, Egypt. Antimony tin oxide (ATO)/polyaniline (PANI)/PbI2 photoelectrode is prepared through the in situ oxidative polymerization of PANI on ATO, then PANI is used as an assistant for PbI2 deposition using the ionic adsorption deposition method. The chemical structural, morphological, electrical, and optical properties of the composite are confirmed using different analytical tools such as X-ray diffreaction (XRD), scanning electron microscope (SEM), transmision electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. The prepared PbI2 inside the composite has a crystal size of 33 nm (according to the peak at 12.8°) through the XRD analyses device. SEM and TEM confirm the hexagonal PbI2 sheets embedded on the PANI nanopores surface. Moreover, the bandgap values are enhanced very much after the composite formation, in which the bandgap values for PANI and PANI/PbI2 are 3 and 2.51 eV, respectively. The application of ATO/PANI/PbI2 nanocomposite electrode for sewage splitting and H2 generation is carried out through a three-electrode cell. The measurements carreid out using the electrocehical worksattion under th Xenon lamp (100 mW.cm−2). The produced current density (Jph) is 0.095 mA.cm−2 at 100 mW.cm−2 light illumination. The photoelectrode has high reproducibility and stability, in which and the number of H2 moles is 6 µmole.h−1.cm−1. The photoelectrode response to different monochromatic light, in which the produced Jph decreases from 0.077 to 0.072 mA.cm−2 with decreasing of the wavelengths from 390 to 636 nm, respectively. These values confirms the high response of the ATO/PANI/PbI2 nanocomposite electrode for the light illuminaton and hydrogen genration under broad light region. The thermodynamic parameters: activation energy (Ea), enthalpy (ΔH*), and entropy (ΔS*) values are 7.33 kJ/mol, −4.7 kJ/mol, and 203.3 J/mol.K, respectively. The small values of ΔS* relted to the high sesnivity of the prepared elctrode for the water splitting and then the hydrogen gneration. Finally, a theoretical study was mentioned for calculation geometry, electrochemical, and thermochemistry properties of the polyaniline/PbI2 nanocomposite as compared with that for the polyaniline.

M379A Mutant Tyrosine Phenol‐lyase from Citrobacter freundii Has Altered Conformational Dynamics

The M379A mutant of Citrobacter freundii tyrosine phenol-lyase (TPL) has been prepared. M379A TPL is a robust catalyst to prepare a number of tyrosines substituted at the 3-position with bulky groups that cannot be made with wild type TPL. The three dimensional structures of M379A TPL complexed with L-methionine and 3-bromo-DL-phenylalanine have been determined by X-ray crystallography. Methionine is bound as a quinonoid complex in a closed active site in 3 of 4 chains of homotetrameric M379A TPL. M379A TPL reacts with L-methionine about 8-fold slower than wild type TPL. The temperature dependence shows that the slower reaction is due to less positive activation entropy. The structure of the M379A TPL complex of 3-bromo-DL-phenylalanine has a quinonoid complex in two subunits, with an open active site conformation. The effects of the M379A mutation on TPL suggest that the mutant enzyme has altered the conformational dynamics of the active site.

Identity of the metal oxide support controls outer sphere interactions that change rates and barriers for alkene epoxidations at isolated Ti atoms

Atomically disperse Ti sites on metal oxides (MOx, including SiO2, γ-Al2O3, ZnO, GeO2) activate H2O2 to create intermediates active for alkene epoxidations. Turnover rates for 1-hexene epoxidation in acetonitrile vary 1000-fold at identical conditions due to differences in apparent activation enthalpies (ΔH‡epox) and entropies (ΔS‡epox). Ligand-to-metal charge transfer energies and vibrational frequencies of reactive species assessed by in situ UV–Vis and Raman spectroscopy, respectively, indicate supports do not detectably change electronic properties of H2O2-derived intermediates. However, isoelectric points and solution-phase water uptakes for these metal oxides correlate with ΔH‡epox and suggest that non-covalent interactions at the solid-liquid interface influence the stability of epoxidation transition states. Supports with lower pKa values concentrate water near the solid-liquid interface and enthalpically stabilize the transition state. These findings illustrate that outer sphere interactions impact epoxidation reactions upon metal oxide catalysts including titanium silicates.