Thermodynamic Activation Parameters Research Articles

Pyrolysis of Energy Cane Bagasse: Investigating Kinetics, Thermodynamics, and Effect of Temperature on Volatile Products

Energy cane is a genotype derived from species of sugarcane (Saccharum officinarum and Saccharum spontaneum) with a lower sucrose content and higher fiber content for bioenergy purposes. It is a rustic plant that demands less fertile soils that do not compete with food crops. In this work, an analysis of energy cane bagasse pyrolysis products was performed, assessing the effect of reaction temperature and kinetic and thermodynamic parameters. Anhydrosugars, such as D-allose, were the primary compounds derived from the decomposition of energy cane at 500 °C. Methyl vinyl ketone and acetic acid were favored at 550 and 600 °C. At 650 °C, methyl glyoxal, acetaldehyde and hydrocarbons were favored. Among the hydrocarbons observed, butane, toluene and olefins such as 1-decene, 1-undecene, 1-tridecene and 1-tetradecene were the most produced. The Friedman isoconversional method was able to determine the average activation energies in the ranges 113.7−149.4, 119.9−168.0, 149.3−196.4 and 170.1−2913.9 kJ mol−1 for the decomposition of, respectively, pseudo-extractives, pseudo-hemicellulose, pseudo-cellulose and pseudo-lignin. The thermodynamic parameters of activation were determined within the ranges of 131.0 to 507.6 kJ mol−1 for ΔH, 153.7 to 215.2 kJ mol−1 for ΔG and −35.5 to 508.8 J mol−1 K−1 for ΔS. This study is very encouraging for the cultivation and use of high-fiber-content energy cane bagasse, after sucrose extraction, to produce biofuels as an alternative to the current method of conversion into electricity by low-efficiency burning.

Production rate of heterocyclic compounds iodinated N-(p-chlorophenyl)-3,5- dimethyl-1,1-dioxo-1,2-thiazine

ABSTRACT. Iodinated heterocyclic molecules are crucial structural components of many natural products, including hormones, vitamins, and medicines. The pharmaceutical survey is very interested in the investigation of the kinetics of the iodination of N-(p-chlorophenyl)-3,5-dimethyl-1,1-dioxo-1,2-thiazine. The rate of iodination is directly dependent on the concentration of both 1,2-thiazine and iodine under different molar ratios (1:10), (10:1) adopted on the isolation method, the observed rate of iodination, the pseudo-first-order and the second order using (1:1) molar ratio in the overall reaction using spectrophotometric techniques. Thermodynamic activation parameters activation energy Ea, enthalpy change ΔH#, entropy change ΔS#, and Gibbs free energy ΔG# of activation were calculated from the rate constant at temperatures 273, 283, 293, 303, and 318 K.
 
 KEY WORDS: Production rate, 1,2-Thiazine, Iodine (I2), Kinetic
 Bull. Chem. Soc. Ethiop. 2023, 37(5), 1253-1262. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i5.16

High Rates of Quinone-Alkyne Cycloaddition Reactions are Dictated by Entropic Factors.

Reaction rates of strained cycloalkynes and cycloalkenes with 1,2-quinone were quantified by stopped flow UV-Vis spectroscopy and computational analysis. We found that the strained alkyne BCN-OH 3 (k2 1824 M-1s-1) reacts >150 times faster than the strained alkene TCO-OH 5 (k2 11.56 M-1s-1). Also, the 8-membered strained alkyne BCN-OH 3 reacts 16 times faster than the more strained 7-membered THS 2 (k2 110.6 M-1s-1). Using the linearized Eyring equation we determined the thermodynamic activation parameters of these two strained alkynes, revealing that the SPOCQ reaction of quinone 1 with THS 2 is associated with ΔH‡ of 0.80 kcal/mol, ΔS‡ = -46.8 cal/K·mol, and ΔG‡ = 14.8 kcal/mol (at 25 °C), whereas the same reaction with BCN-OH 3 is associated with, ΔH‡ = 2.25 kcal/mol, ΔS‡ = -36.3 cal/K·mol, and ΔG‡ = 13.1 kcal/mol (at 25 °C). Computational analysis supported the values obtained by the stopped-flow measurements, with calculated ΔG‡ of 15.6 kcal/mol (in H2O) for the SPOCQ reaction with THS 2, and with ΔG‡ of 14.7 kcal/mol (in H2O) for the SPOCQ reaction with BCN-OH 3. With these empirically determined thermodynamic parameters, we set an important step towards a more fundamental understanding of this set of rapid biogenic click reactions.

Structural and Antimicrobial Investigation of Some New Nanoparticles Mixed Ligands Metal Complexes of Ethyl 6-Amino-4-(4-chlorophenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate in Presence of 1,10-Phenanthroline

A new series of some biologically active Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) complexes was synthesized from the reaction of Ethyl 6-amino-4-(4-chlorophenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate (L) with the previous biological metals in the presence of 1,10-phenanthroline monohydrate (Phen). The structures of the obtained L along with their complexes were authenticated by different analytical and spectral techniques. The data prove that L chelates with all metal ions as bidentate through the nitrogen of the amino group and the nitrogen of the cyano group. Furthermore, Phen chelated with metal ions via two nitrogen atoms. The molar conductance values reflect that all complexes are electrolyte, confirming the 1:3 electrolytic natures for trivalent metal ions and 1:2 electrolytic for bivalent metal ions. The thermal stability and the general thermal decomposition pathways of metal complexes, L, and Phen were evaluating according to the thermogravimetric technique. The activation thermodynamic parameters were estimated from TG curves by utilizing Horowitz–Metzger (HM) and Coats–Redfern (CR) techniques. Powder X-ray diffraction (XRD) analysis proved that L, Cu(II), and Zn(II) compounds have a crystalline nature, whereas, Cr(III), Fe(III), Co(II), and Ni(II) complexes are semicrystalline. The investigated compounds were examined in vitro for their antimicrobial activity towards G(+ve) Staphylococcus aureus and Bacillus subtilis and G(−ve) Escherichia coli and Pseudomonas aeruginosa bacteria, and two fungi: Candida albicans and Aspergillus flavus. According to the findings, the Co(II) complex has a significant efficiency toward bacteria, additionally, Cr(III) complex is highly significant towards fungal strains.

Conformational transformation of N-[arylsulfonylimino(phenyl)methyl]-1,4-benzoquinonemonoimines

It was established that in the solutions of N-[arylsulfonylimino(phenyl)methyl]-1,4-benzoquinonemonoimines there are both Z,E-isomerization relative to C=N bonds and atropoisomerism (inhibited rotation around the =N1–C= bond). The latter can be detected when there are the diastereotopic isopropyl groups in the quinoid ring. The rate constants of this process were calculated by the method of analysis of the full line in the 1H NMR spectra. Activation thermodynamic parameters were determined on their basis. With the help of quantum-chemical calculations, we proved that the determined experimental barriers corresponded exactly to the inhibited rotation around the bond =N1–C=.

Physicochemical properties, pyrolysis kinetics, thermodynamic parameters of activation, and evolved volatiles of mango seed waste as a bioenergy feedstock: A potential exploration

An investigation was conducted to elucidate the bioenergy potential of mango seed waste through pyrolysis kinetics, thermodynamics parameters of activation, and analysis of evolved volatiles. Experiments were performed in a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared (FTIR) spectrometer. The pyrolysis behavior was assumed to be the sum of four independent parallel reactions corresponding to the devolatilization of extractives, hemicellulose, cellulose, and lignin. The four applied isoconversional methods could determine the average activation energies in the ranges of 113.7 − 120.3, 150.0 − 159.9, 190.0 − 201.1, and 172.6 − 184.8 kJ mol−1 for the decomposition of these components, respectively. The pre-exponential factors obtained by Kissinger's method fell between 3.7 × 1011 and 2.6 × 1015 min−1, with A > 109 min−1, indicating that only simple chemistry reactions occurred. The master plot method assigned F-type reaction models to the devolatilization of pseudo-extractives, pseudo-hemicellulose, and pseudo-lignin. Yet, an A-type model matched well with the devolatilization of pseudo-cellulose. From the verification step of the overall kinetic expression, it was found that the simulated pyrolysis progress profiles match with an excellent agreement with the experimental data with a minimum quality of fit of 92.9%. Thermodynamic parameters of activation were determined within the range of 109.3 − 183.3 kJ mol−1 for ΔH≠, 141.7 − 191.2 kJ mol−1 for ΔG≠, and (−71.3)−3.1 J mol−1K − 1 for ΔS≠. TGA–FTIR analysis indicated that most volatile species, comprising propanoic acid, methanol, acetaldehyde, dimethyl ether, and ethanol, are released below 650 K. The results of this study are important for using mango seed waste as a low-priced material for pyrolysis, with the potential of producing bioenergy and bio-based chemicals. This approach aligns with the valorization principle of utilizing lignocellulosic residues.

Principles of Cold-Adaptation of Fish Lactate Dehydrogenases Revealed by Computer Simulations of the Catalytic Reaction.

Cold-adapted enzymes from psychrophilic and psychrotolerant species are characterized by a higher catalytic activity at low temperature than their mesophilic orthologs and are also usually found to be more thermolabile. Computer simulations of the catalytic reactions have been shown to be a very powerful tool for analyzing the structural and energetic origins of these effects. Here, we examine the cold-adaptation of lactate dehydrogenases from two Antarctic and sub-Antarctic fish species using this approach and compare our results to those obtained for the orthologous dogfish enzyme. Direct calculations of thermodynamic activation parameters show that the cold-adapted fish enzymes are characterized by a lower activation enthalpy and a more negative entropy term. This appears to be a universal feature of psychrophilic enzymes and it is found to originate from a higher flexibility of certain parts of the protein surface. We also carry out free energy simulations that address the differences in thermal stability and substrate binding affinity between the two cold-adapted enzymes, which only differ by a single mutation. These calculations capture the effects previously seen in in vitro studies and provide straightforward explanations of these experimental results.

Kinetics and structure reactivity correlation in the oxidation of some para- substituted benzhydrols by benzimidazolium dichromate

The oxidation of some para-substituted benzhydrols by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide (DMSO) medium, results in the formation of corresponding diphenyl ketone. The reaction has been investigated on the condition of pseudo-first order. In terms of both BIDC and hydrogen-ion, the reaction is first order. In the case of benzhydrols, however, Michaelis-Menten type kinetics is observed. At different temperatures, the formation constants and rates of breakdown of benzhydrol-BIDC complexes have been determined. Complex formation thermodynamic parameters and activation parameters for complex decomposition have been computed. The kinetic isotope effect found in the oxidation of benzhydrol ((kH/kD = 5.93 at 293 K) shows that the rate-determining step involved α-C-H bond fission. For the kinetic analysis of the reaction, nineteen organic solvents have been utilized. The solvent impact have been investigated, and found that cation-solvation plays a significant role. A suitable mechanism is proposed based on the kinetic data, solvent effect analysis, and results of various non-kinetic parameters.

Autothermal pyrolysis of lignocellulosic biomass: Experimental, kinetic, and thermodynamic studies

Autothermal pyrolysis that generates in situ heat is a promising way to convert lignocellulosic biomass into value-added products. Autothermal pyrolysis of pinewood under different oxygen concentrations (i.e., 3 %, 5 %, and 10 % O2) was performed in this work. The results showed oxygen addition significantly decreased the selectivity of anhydrosugars in bio-oil by 41.90% at most. Micropores formation in the char was enhanced in the autothermal pyrolysis, and the BET surface area of char obtained under 10 % O2 was 21.9045 m2·g−1. Fraser-Suzuki function was adopted to deconvolute the biomass autothermal pyrolysis process into four pseudo-reactions; namely three degradation reactions of hemicellulose, cellulose, and lignin and a combustion reaction of char residues. The activation energies of three pseudo-degradation reactions decreased after oxygen was introduced, whereas the activation energy of pseudo-combustion reaction of char increased from 69.08 to 88.34–127.47–163.13 kJ·mol−1 as oxygen content increased from 3 % to 10 %. Three major thermodynamic parameters of activation for each pseudo-reaction were also calculated. ΔS‡ results indicated that three pseudo-degradation reactions at the transition state became more ordered at higher oxygen concentration, whereas pseudo-combustion of char showed an opposite trend. The results obtained from this study provide systematic and precise fundamental information for biomass autothermal pyrolysis scale-up.

The inhibitive action of 2-mercaptobenzothiazole on the porosity of corrosion film formed on aluminum and aluminum–titanium alloys in hydrochloric acid solution

2-Mercaptobenzothiazole (2-MBT) in a solution of 0.5 M HCl is an effective corrosion inhibitor for aluminum and aluminum–titanium alloys. Tafel polarization and electrochemical impedance spectroscopy (EIS) were employed to assess this heterocyclic compound’s anticorrosive potential and complementary by scanning electron microscope (SEM) and calculating porosity percentage in the absence and presence of various inhibitor concentrations. Inhibition efficiency (IE%) was strongly related to concentration (10–6–10–3 M). Temperature’s effect on corrosion behavior was investigated. The data exhibited that the IE% decreases as the temperature increases. An increase in activation energy (Ea) with increasing the inhibitor concentration and the decrease in the IE% value of the mentioned compound with raising the temperature indicates that the inhibitor molecules are adsorbed physically on the surface. Thermodynamic activation parameters for Al and Al–Ti alloy dissolution in both 0.5 M HCl and the inhibited solution were calculated and discussed. According to Langmuir’s adsorption isotherm, the inhibitor molecules were adsorbed. The evaluated standard values of the enthalpy (Delta {H}_{ads.}^{o}), entropy (Delta {S}_{ads.}^{o}) and free energy changes (Delta {G}_{ads.}^{o}) showed that Delta {H}_{ads.}^{o} and Delta {G}_{ads.}^{o} are negative, while Delta {S}_{ads.}^{o} was positive. The formation of a protective layer adsorbed on the surfaces of the substrates was confirmed with the surface analysis (SEM). The porosity percentage is significantly reduced in the inhibitor presence and gradually decreased with increasing concentration. Furthermore, the density functional theory (DFT) and Monte Carlo (MC) simulations were employed to explain the variance in protecting the Al surface from corrosion. Interestingly, the theoretical findings align with their experimental counterparts. The planarity of 2-MBT and the presence of heteroatoms are the playmakers in the adsorption process.

Synthesis and characterization of novel acrylamide derivatives and their use as corrosion inhibitors for carbon steel in hydrochloric acid solution

Two new acrylamide derivatives were prepared namely: “N-(bis(2-hydroxyethyl) carbamothioyl) acrylamide (BHCA) and N-((2-hydroxyethyl) carbamothioyl) acrylamide( HCA) and their chemical structures were analyzed and confirmed using IR and 1H NMR”. These chemicals were investigated as corrosion inhibitors for carbon steel (CS) in 1 M HCl medium using chemical method (mass loss, ML), and electrochemical techniques including potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). The results showed that the acrylamide derivatives work well as corrosion inhibitors, with inhibition efficacy (%IE) reaching 94.91–95.28% at 60 ppm for BHCA and HCA, respectively. Their inhibition depends mainly on their concentration and temperature of the solution. According to the PDP files, these derivatives function as mixed-type inhibitors that physically adsorb on the CS surface in accordance with the Langmuir adsorption isotherm, creating a thin coating that shields the CS surface from corrosive fluids. The charge transfer resistance (Rct) increased and the double layer capacitance (Cdl) decreased as a result of the adsorption of the used derivatives. Calculated and described were the thermodynamic parameters for activation and adsorption. Quantum chemistry computations and Monte Carlo simulations were examined and discussed for these derivatives under investigation. Surface analysis was checked using atomic force microscope (AFM). Validity of the obtained data was demonstrated by the confirmation of these several independent procedures.

Biopolymer sodium alginate based titania and magnetite nanocomposites as natural corrosion inhibitors for mild steel in acidic medium

Green biopolymeric materials and its hybrid nanocomposites, i.e. sodium alginate grafted polymethylmethacrylate based titanium dioxide and iron oxide (SA-g-PMMA/TiO2 and SA-g-PMMA/Fe3O4) have been explored for the prevention of mild steel's corrosion in 15% HCl. It is reflected from the electrochemical impedance data that SA-g-PMMA/TiO2 exhibits maximum inhibition efficiency of 97.28% followed by SA-g-PMMA/Fe3O4 that gives 96.82% efficiency while the unmodified sodium alginate possess merely 84.74% efficiency. The declining trend of inhibition efficiency with rising temperature has been explained through gravimetric studies conducted at 303 K- 333 K. The thermodynamic activation and adsorption parameters revealed the mixed mode of adsorption of inhibitors over mild steel surface which follow Langmuir adsorption isotherm. It has been observed from tafel polarization studies that all studied inhibitors are mixed type in nature. The surface morphological inspection of the mild steel samples was done through FE-SEM and AFM, which revealed the formation of better protective adsorption layer over the exposed metallic surface by the nanocomposites in comparison to sodium alginate alone. In addition to this, the elemental composition of adsorbed film on inhibited mild steel specimens was obtained by XPS technique. Quantum parameters obtained through Density Functional Theory (DFT) further corroborate the experimental outcomes.

Kinetic studies on the persulfate oxidation of methylene blue in the absence and presence of silver(I) as a catalyst in aqueous and micellar media

AbstractThe kinetics and mechanism of the oxidative decolorization of methylene blue (MB+) as a cationic dye by persulfate using silver(I) catalyst in aqueous acidic medium were studied. The effects of different parameters like [H+], [Ag+], reactant concentration, micelles, and temperatures were investigated. The kinetic data showed that the oxidative decolorization of [MB]+ by persulfate obeyed pseudo‐first‐order kinetics by taking a large excess of [S2O82−] over [MB+]. The observed rate constant increases with increasing of [H+]. A plausible mechanism for the silver(I) enhanced decolorization of [MB]+ by persulfate is suggested which is consistent with the experimental rate law. The effect of micelles such as SDS and Triton X‐100 on the reaction rate is investigated. The rate of reaction decreases with increasing [SDS] but is not affected by Triton X‐100. The mechanism of the electron transfer process between [MB]+ and S2O82– proceeds through an outer‐sphere mechanism. Thermodynamic activation parameters ΔH* and ΔS* were calculated. The experimental data may be useful for the layout of wastewater treatment containing various types of dyes.

The influence of torrefaction on the biochar characteristics produced from sesame stalks and bean husk

Torrefaction encourages homogeneity and enhances the energy-producing capabilities of biomass. In the current study, bean husk (BH) and sesame stalks (SS) were torrefied for 30 and 60 min at operating temperatures of 200, 225, 250 and 275, and 300 °C with nitrogen purging. Mass yield (MY), higher heating value (HHV), energy yields (EY), and torrefaction severity index (TSI) were examined. The variations of the biochar characteristics, pyrolysis kinetics by applying two models (Coats and Redfern (CR) and Direct Arrhenius (DA)), and crystallinity index (CRI) were depicted. Depending on pyrolysis kinetics, thermodynamic activation parameters were derived to elucidate biomass pyrolysis. The alterations in the torrefied materials’ composition were also analyzed using Fourier transform infrared spectroscopy (FTIR). The calculations revealed that the torrefied SS and BH decreased MY by 32.74, 29.02% and decreased EY 26, 20.97%, increased high heating values by 14.1, 13.52%, increased fixed carbon by 55.1, 39.91% respectively, and had a slight reduction in bulk density (approximately 2%). Generally, 275 °C and 30 min were the optimal conditions for a balanced torrefaction of SS and BH based on the HHV that reached to 20.5, 16.2 MJ/kg and EY that reached to 86.16 and 85.56% respectively. The FTIR, XRD, and the thermogravimetric results showed that the torrefaction treatment altered samples owing to carbohydrate breakdown, a rise in lignin, and a reduction in hemicellulose as the temperature of the torrefaction process increased. The CR methodology yielded greater frequency factor (A) and activation energy (Ea) values than the DA method. The broadest peak width, lowest average Ea, and lnA were seen in sesame stalks that had been torrefied at 300 °C and 30 min that reached to 107.85 (kJ/mol) and 13.57 (min−1). Results indicated an excellent linear relationship with the index of comprehensive pyrolysis (CPI), CRI, atomic H/C ratio, severity index, and EY.

Volumetric and Spectroscopic Studies of 1-ethyl-3-methylimidazolium Ethylsulfate/Propane-1-ol Binary Mixtures at Different Temperatures

Binary mixtures of an ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate ([C2mim]C2H5SO4) with propane-1-ol were prepared over an entire composition range and density, dynamic viscosity, and refractive index at T = 293.15 to T = 333.15 K at atmospheric pressure were measured. The excess properties for the binary systems were determined and successfully fitted to a polynomial equation of the Redlich–Kister type. The variation of excess thermodynamic parameters predicted stronger intermolecular interactions and effective packing in the binary system compared to components. Thermodynamic activation parameters were also calculated from the Eyring equation, which varied with the concentration of [C2mim]C2H5SO4. The variation of these parameters also suggested the presence of strong heteromolecular interactions. The near-infrared (NIR) spectroscopic measurements were conducted in the temperature range from 293.15 K to 333.15 K and spectral variations were analyzed. The NIR data were further evaluated using principal component analysis (PCA) and two-dimensional (2D) correlation spectroscopy. The predicted molecular-level interactions mainly come from different types of HBs formed between unlike molecules in the binary system. The binary mixture may open up a plethora of possible uses due to its novel, distinctive molecular-level interactions, and favorable thermodynamic properties.

Chlorination mechanism and kinetics of cathode materials for spent LiCoO2 batteries in the presence of graphite

In the face of the rapid growth of lithium industry's demand for energy metals, recycling spent lithium-ion batteries (LIBs) has become the key to the sustainable development of related industries. The chlorination roasting process is effective at recycling spent LIBs. Factories usually recycle the black mass as raw material instead of only the cathode material in actual production. The black mass is mainly composed of cathode material and graphite. However, studies on the effect of graphite on the chlorination process of cathode materials are lacking. In this study, the effect of graphite on the chlorination process of cathode materials is investigated, focusing on the reaction mechanism and kinetics aspects. The results show that the presence of graphite can accelerate the destruction of the LiCoO2 structure, thereby reducing the pyrolysis temperature of LiCoO2. The cobalt in the roasted product exists in the form of metallic cobalt rather than cobalt oxide or cobalt chloride. The reaction model of the LiCoO2 chlorination stage conforms to the random nucleation and nuclear growth modes. The mechanism function is g(α) = [-ln(1-α)]3/4. Ea and A are 196.107 kJ/mol and 3.575 × 106, respectively. Furthermore, thermodynamic activation parameters are calculated and equations are established.

NMR Studies of Aromatic Ring Flips to Probe Conformational Fluctuations in Proteins.

Aromatic residues form a significant part of the protein core, where they make tight interactions with multiple surrounding side chains. Despite the dense packing of internal side chains, the aromatic rings of phenylalanine and tyrosine residues undergo 180° rotations, or flips, which are mediated by transient and large-scale "breathing" motions that generate sufficient void volume around the aromatic ring. Forty years after the seminal work by Wagner and Wüthrich, NMR studies of aromatic ring flips are now undergoing a renaissance as a powerful means of probing fundamental dynamic properties of proteins. Recent developments of improved NMR methods and isotope labeling schemes have enabled a number of advances in addressing the mechanisms and energetics of aromatic ring flips. The nature of the transition states associated with ring flips can be described by thermodynamic activation parameters, including the activation enthalpy, activation entropy, activation volume, and also the isothermal volume compressibility of activation. Consequently, it is of great interest to study how ring flip rate constants and activation parameters might vary with protein structure and external conditions like temperature and pressure. The field is beginning to gather such data for aromatic residues in a variety of environments, ranging from surface exposed to buried. In the future, the combination of solution and solid-state NMR spectroscopy together with molecular dynamics simulations and other computational approaches is likely to provide detailed information about the coupled dynamics of aromatic rings and neighboring residues. In this Perspective, we highlight recent developments and provide an outlook toward the future.

Intracluster ligand rearrangement: an NMR-based thermodynamic study.

Ligand and metal exchange reactions are powerful methods to tailor the properties of atomically precise metal nanoclusters. Hence, a deep understanding of the mechanisms behind the dynamics that rule the ligand monolayer is crucial for its specific functionalization. Combining variable-temperature NMR experiments and dynamic-NMR simulations, we extract the thermodynamic activation parameters of a new exchange reaction: the intracluster ligand rearrangement between the two symmetry-unique positions in [Ag25(DMBT)18]- and [Ag24Au(DMBT)18]- clusters. We report for the first time that this peculiar intracluster modification does not seem to proceed via metal-sulphur bond breaking and follows a first-order rate law, being therefore a process independent from the well-described collisional ligand exchange.

Photochromism of tetrahydroindolizines. Part XXVI: Mechanochemical synthesis, tunable photophysical properties and combined experimental and theoretical studies of novel photochromic tetrahydroindolizines

Herein, eighteen novel photochromic tetrahydroindolizines (THIs) have been successfully prepared using a well-established mechanochemical synthetic approach. These products were obtained in good to excellent yields and the purification process was relatively straightforward devoid of any isolation challenges. The new THIs incorporate various substituents in region C (base part) which include both electron donating and withdrawing groups in the ortho, meta and para positions of the phenyl ring. The absorption maxima (λmax) of both closed form (THI) and the colored form (betaine, after UV-irradiation) were spectrophotometrically determined in dichloromethane solution. The colored betaines displayed two absorption maxima, one between 472 and 485 nm, and the second one appearing in the white region between 658 and 724 nm with tailing extending to the near infra-red (NIR) region. The impact of the nature and position of substituent in the 10′b-phenyl ring on the absorption of the betaines indicated that substitution in the ortho-position with absorption maxima between 658 and 690 nm leads to a hypsochromic shift largely caused by the steric effect of the substituents in the o-position of the THI molecule 10′b-phenyl ring compared to the meta- and para-substituted species with absorption maxima between 700 and 724 nm. The calculated ring closure thermodynamic activation parameters of colored betaines were found to be in good agreement with previous reported results. The 1,5-electrocyclization reaction kinetics of the investigated photochromic THIs were monitored and calculated. Intriguingly, substitution with electron donating and withdrawing groups in the o-, m-, and p-positions of the phenyl ring enabled distinctive tunability of the kinetic behavior. Furthermore, possible mechanism of the thermal 1,5-electrocyclization back reaction of betaines was explored based on density functional theory calculations (DFT), delivering more understanding into ring opening and ring closure processes in addition to the distinct THI-substituents effect (region C). The geometries and the relative energies of the THI, betaine isomers, and transition states along reaction coordinates were optimized and assessed by DFT. Based on the obtained synthetic methodology results, unprecedent tunability of the photochromic properties and the combined experimental and theoretical studies, the current work launches a new dimension and contributes further developments to the field of high-performance photochromic materials.

Experimental and computational chemical studies on the corrosion inhibitive properties of metamizole sodium pharmaceutical drug compound for CS in hydrochloric acid solutions

The effect of sodium metamizole as a corrosion inhibitor for carbon steel (CS) in 1 M hydrochloric acid at various concentrations was studied by using chemical (weight loss, WL) and electrochemical [electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP)] methods. The results of WL showed that the effectiveness of sodium metamizole as a CS preservative in a hydrochloric acid solution at room temperature raised by improvement of the concentration of the inhibitor and reached 82.87% at 300 ppm and 25 °C. The effect of temperature on the CS was studied and the thermodynamic parameters of activation and adsorption were computed and discussed. The results showed that the inhibition efficiency (IE) decreases with increasing temperature, suggestive of physisorption. This was collaborated by values of activation energy, which are all below 80 kJ mol−1 and free energy which are below 20 kJ mol−1. The adsorption mechanism was coherent with Langmuir adsorption model. Results of the PDP revealed that the inhibitor was adsorbed on CS surface by mixed type of behavior. Furthermore, EIS revealed the dip in the values of double-layer capacitance and improvement in the charge transfer resistance with increased dose of sodium metamizole. Surface examinations were performed using altered techniques. The theoretical studies were calculated to confirm the validity of the practical results and the results of both were compared with each other, demonstrating the validity of the results obtained.