Articoli di riviste: "Spectroscopic. kinetic and mechanistic study"

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Orzeł, Łukasz, Maria Oszajca, Justyna Polaczek, Dominika Porębska, Rudi van Eldik e Grażyna Stochel. "High-Pressure Mechanistic Insight into Bioinorganic NO Chemistry". Molecules 26, n. 16 (16 agosto 2021): 4947. http://dx.doi.org/10.3390/molecules26164947.

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Pressure is one of the most important parameters controlling the kinetics of chemical reactions. The ability to combine high-pressure techniques with time-resolved spectroscopy has provided a powerful tool in the study of reaction mechanisms. This review is focused on the supporting role of high-pressure kinetic and spectroscopic methods in the exploration of nitric oxide bioinorganic chemistry. Nitric oxide and other reactive nitrogen species (RNS) are important biological mediators involved in both physiological and pathological processes. Understanding molecular mechanisms of their interactions with redox-active metal/non-metal centers in biological targets, such as cofactors, prosthetic groups, and proteins, is crucial for the improved therapy of various diseases. The present review is an attempt to demonstrate how the application of high-pressure kinetic and spectroscopic methods can add additional information, thus enabling the mechanistic interpretation of various NO bioinorganic reactions.

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Kallesha, Nichhapurada, Ningegowda Prasad, N. Shivakumara e Kereyagalahally H. Narasimhamurthy. "Oxidation of Cinacalcet Hydrochloride by Chloramine-B in Acid Medium: A Kinetic and Mechanistic Study". Asian Journal of Chemistry 33, n. 9 (2021): 2065–68. http://dx.doi.org/10.14233/ajchem.2021.23292.

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Kinetic and mechanistic study of cinacalcet hydrochloride by chloramine-B (CAB) in HCl medium at 308 K was the aim of this work. Analyzed the reaction at five different temperatures and determined the thermodynamic parameters using Arrhenius plots. The reaction had a stoichiometry of 1:2 and characterized the oxidation product using chromatographic and spectroscopic methods. The rate law is deduced from the marked effects, which were accompanied by plausible mechanisms.

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Wallington, Timothy J., James C. Ball, Ole J. Nielsen e Elzbieta Bartkiewicz. "Spectroscopic, kinetic and mechanistic study of fluoromethylperoxo radicals in the gas phase at 298 K". Journal of Physical Chemistry 96, n. 3 (febbraio 1992): 1241–46. http://dx.doi.org/10.1021/j100182a041.

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Delbaere, S., J. C. Micheau, J. Berthet e G. Vermeersch. "Contribution of NMR spectroscopy to the mechanistic understanding of photochromism". International Journal of Photoenergy 6, n. 4 (2004): 151–58. http://dx.doi.org/10.1155/s1110662x04000194.

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Along with classical UV-Visible spectroscopy allowing for the determination of intrinsic properties(λmax,ε), multinuclear NMR spectroscopy is a promising and useful tool for studying photochromic reactions. UV irradiation of the initial structure leads to the formation of photoproducts, which can be structurally identified by 1D and 2D NMR experiments. The kinetics of thermal back reaction are monitored by directly and separately measuring the concentrations of each long-living species at regular time intervals in NMR spectra. A plausible reaction mechanism can therefore be proposed. Based on this mechanism, the kinetic analysis and the study of the effects of temperature lead to the determination of the kinetic and thermodynamic parameters (rate coefficients, enthalpy and entropy of activation) of the photochromic system under investigation. This process has been applied to several photochromic families, spirooxazines and benzo- and naphtho-pyrans.

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Sultan, Salah M., e Edmund Bishop. "Mechanistic study and kinetic determination of vitamin C". Journal of Pharmaceutical and Biomedical Analysis 8, n. 4 (gennaio 1990): 345–51. http://dx.doi.org/10.1016/0731-7085(90)80048-t.

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Kallesha N, Prasad N, Mahadeva Swamy M e Gnanendra C.R. "The kinetic and mechanistic study of levetiracetam oxidation with chloramine-B in acid medium". World Journal of Biology Pharmacy and Health Sciences 13, n. 1 (30 gennaio 2023): 331–38. http://dx.doi.org/10.30574/wjbphs.2023.13.1.0041.

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The medicine levetiracetam, marketed under the brand name Keppra, is approved by the Food and Drug Administration, used to treat seizures. It belongs to a class of drug known as anticonvulsants. The current work uses sodium-N-chloro-benzene sulfonamide or chloramine-B to evaluate the kinetics and mechanistic of levetiracetam at 308 K in HCl medium. (CAB). The reaction has a first-order dependence on [CAB]0 and [substrate]0, as well as a fractional-order dependence on the concentration of [HCl]. Changes in ionic strength or the adding of benzene sulfonamide have no effect on the rate. We looked at the effect at five temperatures. The Arrhenius plots were used to evaluate the thermodynamic parameters. The reaction stoichiometry was found 1:2, and chromatographic and spectroscopic studies anticipated the oxidation product imine. The probable mechanism back up the above-mentioned findings. The relevant rate law has been determined because of all these discoveries.

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Saifuddin, Md, Suho Kim, Abdul Aziz e Kwang Soo Kim. "Mechanistic Study of Phosphorus Adsorption onto Iron Z-A: Spectroscopic and Experimental Approach". Applied Sciences 9, n. 22 (15 novembre 2019): 4897. http://dx.doi.org/10.3390/app9224897.

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Iron was incorporated into an LTA type zeolite using the sol-gel hydrothermal method to form Iron-zeolite-A (Iron-Z-A), and its phosphate adsorption-desorption efficiency were analyzed. Samples were characterized by EDS, SEM, XRD, EPR, FT-IR XPS, and Raman to ensure the apt synthesis of Iron-Z-A and to interpret the mechanism of adsorption-desorption of PO43− in an aqueous solution. EPR and XPS analysis confirmed that the iron was doped as Fe3+ in the LTA structure. The XPS peak shift (Fe-2p), FT-IR band shift, and intensity change (–OH) confirmed the existence of the ligand exchange mechanism. In the adsorption phase at pH 5, the derivative of phosphate (H2PO4−) acts as a ligand and interacts with OH of Fe on the zeolite surface to form “Iron-zeolite (oxy) hydroxide bound phosphate”. In the desorption phase at pH 10, phosphate ligand is detached and get mixed in the aqueous phase as HPO42−. The EDS data, Si–O–Al band shift and intensity change in FT-IR and XPS peak intensity change proved the contribution of Al in the process of adsorption. The data of adsorption fitted well with the Langmuir’s isotherm and pseudo-second-order kinetic model. The amount of PO43− adsorbed was a function of adsorbent’s surface area regardless of concentration. The amount of PO43− being adsorbed by the metal ions was found to be 382.296 mg PO43−/g Fe and 56.296 mg PO43−/g Al.

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Tellers, David M., e Robert G. Bergman. "Mechanistic study of ligand substitution processes in TpIr(III) complexes". Canadian Journal of Chemistry 79, n. 5-6 (1 maggio 2001): 525–28. http://dx.doi.org/10.1139/v00-162.

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The synthesis of the cationic hydridotris(pyrazolyl)borate iridium(III) complex [Tp(PMe3)IrMe(ClCH2Cl)][BArf] (2-CH2Cl2) is reported. Spectroscopic characterization of 2-CH2Cl2 in CH2Cl2 solution indicates that exchange of bound CH2Cl2 with free CH2Cl2 is slow on the NMR time scale. Under 50 atm (1 atm = 101.325 kPa) of N2, the CH2Cl2 in 2-CH2Cl2 is displaced by N2 to yield [Tp(PMe3)IrMe(N2)][BArf] (2-N2). The stronger nucleophile CH3CN reacts rapidly with 2-CH2Cl2 to produce [Tp(PMe3)IrMe(NCCH3)][BArf] (4). A kinetic study was performed on CH2Cl2 substitution in 2-CH2Cl2 by CD3CN. The data are most consistent with dissociative loss of CH2Cl2 to generate the unsaturated species ([Tp(PMe3)IrMe][BArf]) which then reacts with CD3CN to generate [Tp(PMe3)IrMe(NCCD3)][BArf]. Further evidence for a dissociative mechanism was obtained by comparison of ligand substitution rates for the Tp complexes with the analogous TpMe2 complexes (TpMe2 = hydridotris(3,5-dimethylpyrazolyl)borate). The relevance of these substitution experiments to CH activation by cationic iridium(III) complexes is discussed.Key words: iridium, hydridotris(pyrazolyl)borate, methylene chloride and dinitrogen complexes, dissociative substitution.

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Cho, Hyejin, e Wansik Cha. "Rapid Hydrolysis of Organophosphates Induced by U(IV) Nanoparticles: A Kinetic and Mechanistic Study using Spectroscopic Analysis". Colloids and Interfaces 3, n. 4 (26 novembre 2019): 63. http://dx.doi.org/10.3390/colloids3040063.

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The heterogeneous interactions of colloidal U particles with organophosphates, leading to the formation of U-phosphate minerals, can retard the migration of U in contaminated sites. Here, we studied the hydrolytic mechanism of p-nitrophenyl phosphate (NPP) on the surfaces of tetravalent uranium nanoparticles (U(IV)NPs), resulting in the formation of U-phosphate precipitates. Our study shows that the reaction rate of NPP hydrolysis is significantly enhanced by U(IV)NPs through a multi-step heterogeneous reaction on the particle surfaces. The end products of the reaction were identified as U(IV)NPs-aggregates with surface-bound phosphates. Colloidal properties, such as high positive values of the zeta-potential (>+30 mV) and large surface areas of U(IV)NPs due to their unique cluster structures consisting of relatively small primary UO2(cr)-particles, are correlated with their reactivity towards hydrolysis reaction. Reaction kinetic modeling studies using spectrophotometric data indicated the presence of two distinct reaction intermediates as the surface complexes of NPP on U(IV)NPs. We suggest the involvement of the NPP inner-sphere complexes in the rate-determining step based on the results obtained by analyzing the ATR-FTIR spectra and the surface-enhanced infrared absorption of NPP bound to substrate surfaces.

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Iuga, Cristina, C. Ignacio Sainz-Díaz e Annik Vivier-Bunge. "Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study". Environmental Chemistry 12, n. 2 (2015): 236. http://dx.doi.org/10.1071/en14138.

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Environmental context The presence of air-borne mineral dust containing silicates in atmospheric aerosols should be considered in any exploration of volatile organic compound chemistry. This work reports the mechanisms, relative energies and kinetics of free-radical reactions with formic acid adsorbed on silicate surface models. We find that silicate surfaces are more likely to act as a trap for organic radicals than to have a catalytic effect on their reactions. Abstract Heterogeneous reactions of atmospheric volatile organic compounds on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in air-borne mineral dust in atmospheric aerosols, and radical reactions can be different in the presence of these mineral particles. In this work, we use quantum-mechanical calculations and computational kinetics to explore the reaction of a hydroxyl free radical with a formic acid molecule previously adsorbed on several models of silicate surfaces. We find that the reaction is slower and takes place according to a mechanism that is different than the one in the gas phase. It is especially interesting to note that the reaction final products, which are the formyl radical attached to the cluster surface, and a water molecule, are much more stable than those formed in the gas phase, the overall reaction being highly exothermic in the presence of the surface model. This suggests that the silicate surface is a good trap for the formed formyl radical. In addition, we have noted that, if a second hydroxyl radical approaches the adsorbed formyl radical, the formation of carbonic acid on the silicate surface is a highly exothermic and exergonic process. The carbonic acid molecule remains strongly attached to the surface, thus blocking CO2 formation in the formic acid oxidation reaction. The spectroscopic properties of the systems involved in the reaction have been calculated, and interesting frequency shifts have been identified in the main vibration modes.

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WALLINGTON, T. J., J. C. BALL, O. J. NIELSEN e E. BARTKIEWICZ. "ChemInform Abstract: Spectroscopic, Kinetic, and Mechanistic Study of CH2FO2 Radicals in the Gas Phase at 298 K." ChemInform 23, n. 21 (22 agosto 2010): no. http://dx.doi.org/10.1002/chin.199221107.

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Fawzy, Ahmed, Saleh A. Ahmed, Ismail I. Althagafi, Moataz H. Morad e Khalid S. Khairou. "Kinetics and Mechanistic Study of Permanganate Oxidation of Fluorenone Hydrazone in Alkaline Medium". Advances in Physical Chemistry 2016 (25 luglio 2016): 1–9. http://dx.doi.org/10.1155/2016/4526578.

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The oxidation kinetics of fluorenone hydrazone (FH) using potassium permanganate in alkaline medium were measured at a constant ionic strength of 0.1 mol dm−3 and at 25°C using UV/VIS spectrophotometer. A first-order kinetics has been monitored in the reaction of FH with respect to [permanganate]. Less-than-unit order dependence of the reaction on [FH] and [OH−] was revealed. No pronounced effect on the reaction rate by increasing ionic strength was recorded. Intervention of free radicals was observed in the reaction. The reaction mechanism describing the kinetic results was illustrated which involves formation of 1 : 1 intermediate complex between fluorenone hydrazones and the active species of permanganate. 9H-Fluorenone as the corresponding ketone was found to be the final oxidation product of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy. The expression rate law for the oxidation reaction was deduced. The reaction constants and mechanism have been evaluated. The activation parameters associated with the rate-limiting step of the reaction, along with the thermodynamic quantities of the equilibrium constants, have been calculated and discussed.

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Khosla, Ekta, Satindar Kaur e Pragnesh N. Dave. "Mechanistic Study of Adsorption of Acid Orange-7 over Aluminum Oxide Nanoparticles". Journal of Engineering 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/593534.

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The adsorption behavior of acid orange-7 (AO-7) on aluminum oxide nanoparticles (ANP) generated by sol-gel method has been investigated to understand the physicochemical process involved and to explore the potential use of nano particles in textile effluent treatment and management. The results revealed that ANP can remove AO-7 dye up to 97.6 mg/g at 303 K. The adsorption process is found to be pH dependent and the optimum pH obtained is 2.0. The equilibrium was established in 1 h. Langmuir, Freundlich, and Temkin Isotherm models were applied on the system. Scanning electron microscopic analysis reveals eye-catching nanoporous morphology of the material. The results of FTIR spectroscopy reveal that the process is electrostatic complexation mechanism driven. XRD studies revealed nanocrystalline structure of ANP. BET surface area measurement suggests high pore volume and surface area of adsorbent. The kinetic measurements suggest pseudo-second-order kinetic processes. The thermodynamic measurements suggest that all processes are endothermic accompanied with negative ΔG° and positive ΔS°, ΔH°.

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Carre, C., C. Decker, J. P. Fouassier e D. J. Lougnot. "Lasers and Photopolymers". Laser Chemistry 10, n. 5-6 (1 gennaio 1990): 349–66. http://dx.doi.org/10.1155/1990/74727.

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A general outline of new applications of lasers in polymer photochemistry is given. The fields covered include the kinetic and mechanistic study of various elementary processes (in solution model compounds) by laser spectroscopies and the extension of this approach to practical systems (solids or in polymerization samples, thin films) by holographic techniques or real-time infrared spectroscopy. Stress is laid on the great importance of laser techniques in understanding the fundamental aspects of the processes involved in polymer photochemistry.

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Chen, Mei, Katie Won, Robert S. McDonald e Paul H. M. Harrison. "Regioselectivity of glycoluril-directed Claisen condensations — A kinetic and mechanistic study of substituent effects in the nucleophilic acyl group". Canadian Journal of Chemistry 84, n. 9 (1 settembre 2006): 1188–96. http://dx.doi.org/10.1139/v06-147.

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The Claisen-like condensation of a series of 1-arylacetyl-6-acetyl-3,4,7,8-tetramethylglycolurils (Ar = Ph, p-OMeC6H4, and p-ClC6H4) was studied in preparative experiments and by analysis of kinetic data. The reactions proceeded in virtually quantitative yield and were highly regioselective: the corresponding N-(2′-aryl-3′-ketobutanoyl)-3,4,7,8-tetramethylglycolurils were obtained in all cases, with none of the 4′-aryl regioisomers being detected. Clean bimolecular kinetics were observed for each conversion using UV spectroscopy. Reaction rates followed the order Ar = p-OMeC6H4 < Ph < p-ClC6H4. The results are explained by a mechanism in which the deprotonation of the substrates is rate-limiting; thus, deprotonation of the arylacetyl groups is favoured. The ensuing enolate reacts rapidly in the C–C bond-forming step.Key words: glycoluril, biomimetic, Claisen condensation, regioselectivity, kinetics, mechanism, substituent effects.

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Marin, Mireia, Miguel A. Miranda e M. Luisa Marin. "A comprehensive mechanistic study on the visible-light photocatalytic reductive dehalogenation of haloaromatics mediated by Ru(bpy)3Cl2". Catal. Sci. Technol. 7, n. 20 (2017): 4852–58. http://dx.doi.org/10.1039/c7cy01231d.

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Warthegau, Stefan S., Magnus Karlsson, Robert Madsen, Pernille Rose Jensen e Sebastian Meier. "Kinetic and Mechanistic Study of Aldose Conversion to Functionalized Furans in Aqueous Solutions". Catalysts 14, n. 3 (18 marzo 2024): 199. http://dx.doi.org/10.3390/catal14030199.

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Reaction mixtures of naturally abundant aldoses and CH nucleophiles allow for the formation of functionalized furan precursors using low temperatures and metal-free catalysis in aqueous solutions of dilute base catalysts. We employ in situ NMR assays to clarify the mechanism and kinetics of the conversion. Catalysis serves a double role in ring-opening of stable aldoses such as glucose and xylose and facilitating the subsequent reactions with CH acids such as malononitrile or cyanoacetamide. Resultant acyclic products are shown to convert quickly to a monocyclic product prior to the slower formation of a more stable bicyclic intermediate and dehydration to tri-functionalized furan. Especially the reversible 5-exo-dig ring closure entailing oxygen attack onto a nitrile carbon is surprisingly fast with an equilibrium vastly towards the cyclic state, sequestering reactive groups and allowing the selective conversion to tri-functionalized furan. The reaction hinges on the fast formation of intermediates without CH acidity and competes with the oligomerization of CH nucleophiles. Insight derived from in situ NMR analysis shows the prowess of high-resolution in situ spectroscopy in clarifying the interplay between catalysts and reactants. Such insight will be vital for the optimization of reactions that upgrade biorenewables under benign conditions.

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Konidari, C. N., e M. I. Karayannis. "Kinetic and mechanistic study of the reduction of 2,6-dichlorophenol indophenol by dithionites". Analytica Chimica Acta 224 (1989): 199–210. http://dx.doi.org/10.1016/s0003-2670(00)86559-9.

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Jelić, Dijana, Snežana Papović, Milan Vraneš, Slobodan Gadžurić, Silvia Berto, Eugenio Alladio, Dragana Gajić e Bojan Janković. "Thermo-Analytical and Compatibility Study with Mechanistic Explanation of Degradation Kinetics of Ambroxol Hydrochloride Tablets under Non-Isothermal Conditions". Pharmaceutics 13, n. 11 (11 novembre 2021): 1910. http://dx.doi.org/10.3390/pharmaceutics13111910.

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Ambroxol hydrochloride (AMB), used as a broncho secretolytic and an expectorant drug, is a semi-synthetic derivative of vasicine obtained from the Indian shrub Adhatoda vasica. It is a metabolic product of bromhexine. The paper provides comprehensive and detailed research on ambroxol hydrochloride, gives information on thermal stability, the mechanism of AMB degradation, and data of practical interest for optimization of formulation that contains AMB as an active compound. Investigation on pure AMB and in commercial formulation Flavamed® tablet (FT), which contains AMB as an active compound, was performed systematically using thermal and spectroscopic methods, along with a sophisticated and practical statistical approach. AMB proved to be a heat-stable and humidity-sensitive drug. For its successful formulation, special attention should be addressed to excipients since it was found that polyvinyl pyrrolidone and Mg stearate affect the thermal stability of AMB. At the same time, lactose monohydrate contributes to faster degradation of AMB and change in decomposition mechanism. It was found that the n-th order kinetic model mechanistically best describes the decomposition process of pure AMB and in Flavamed® tablets.

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Steinbauer, Johannes, Christoph Kubis, Ralf Ludwig e Thomas Werner. "Mechanistic Study on the Addition of CO2 to Epoxides Catalyzed by Ammonium and Phosphonium Salts: A Combined Spectroscopic and Kinetic Approach". ACS Sustainable Chemistry & Engineering 6, n. 8 (4 giugno 2018): 10778–88. http://dx.doi.org/10.1021/acssuschemeng.8b02093.

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Sulzbach, Michael, e Thorsten Geisler. "The Replacement of Celestine (SrSO4) by Strontianite (SrCO3) in Aqueous Solution Studied In Situ and in Real Time Using Fluid-Cell Raman Spectroscopy". Minerals 14, n. 2 (2 febbraio 2024): 164. http://dx.doi.org/10.3390/min14020164.

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The replacement of celestine (SrSO4) by strontianite (SrCO3) has extensively been studied over the past few decades. It also represents an ideal reaction to in situ study the kinetic and fundamental mechanistic details of mineral replacement reactions in aqueous solutions via fluid-cell Raman spectroscopy. This technique allows us to study the reaction process in real time by continuously analysing the solution or by imaging the solid–liquid interface where the reaction takes place and while the replacement process is ongoing. Two sets of experiments were conducted, the first of which was carried out with celestine powder and an equimolar Na2CO3 solution in a heated fluid cell between 30 and 60 °C. The progress of the reaction was followed by Raman spectroscopic in situ measurements of the solution. Another experiment was performed with a polished cuboid cut from a single celestine crystal and a 1 M Na2CO3 solution in a fluid cell at room temperature (21 °C). In this experiment, the reaction was studied in situ, spatially resolved, and in real time. The results of both types of experiments revealed that the replacement occurs via a coupled dissolution–precipitation mechanism and that the evolution of the solution composition cannot fully be explained by a single rate law derived from a shrinking core model. By applying the model-independent time-to-a-given-fraction method, three kinetic regimes could be identified and the associated activation energies quantified.

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Carpentier, Philippe, Antoine Royant, Jérémy Ohana e Dominique Bourgeois. "Advances in spectroscopic methods for biological crystals. 2. Raman spectroscopy". Journal of Applied Crystallography 40, n. 6 (10 novembre 2007): 1113–22. http://dx.doi.org/10.1107/s0021889807044202.

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A Raman microspectrophotometer is described that allows the spectroscopic investigation of protein crystals under exactly the same conditions as those used for X-ray data collection. The concept is based on the integration of the Raman excitation/collection optics into a microspectrophotometer built around a single-axis diffractometer and a cooling device. It is shown that Raman spectra of outstanding quality can be recorded from crystallized macromolecules under non-resonant conditions. It is proposed that equipment developed in the context of macromolecular cryocrystallography, such as commonly used cryoloops, can be advantageously used to improve the quality of Raman spectra. In a few examples, it is shown that Raman microspectrophotometry provides crucial complementary information to X-ray crystallography,e.g.identifying the chemical nature of unknown features discovered in electron-density maps, or following ligand-binding kinetics in biological crystals. The feasibility of `online' Raman measurements performed directly on the ESRF macromolecular crystallography beamlines has been investigated and constitutes a promising perspective for the routine implementation of combined spectroscopic and crystallographic methods.In crystalloRaman spectroscopy efficiently complements absorption/fluorescence microspectrophotometry for the study of biological crystals and opens up new avenues for difficult structural projects with mechanistic perspectives in the field of protein crystallography.

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R. Osunkwo, C., I. U. Nkole, A. D. Onu e S. O. Idris. "Electron transfer reaction of Tris(1,10-phenanthroline) cobalt(III) complex [Co(phen)3]3+ and thiosulphate ion (S2O32−) in an aqueous acidic medium". International Journal of Advanced Chemistry 6, n. 1 (12 giugno 2018): 121. http://dx.doi.org/10.14419/ijac.v6i1.11326.

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The electron transfer reaction of Tris (1,10-phenanthroline)cobalt(III) complex by thiosulphate ion has been studied in an aqueous acidic medium. Stoichiometric determination shows that for one mole of the oxidant that was reduced, one mole of the reductant was consumed; the reaction conforms to an overall equation: 2[Co(phen)3]3+ + 2S2O32− → 2[Co(phen)3]2+ + S4O62− Kinetics study carried out under pseudo-first order condition shows that the reaction proceeded via a one-way acid-dependent pathway and was third order overall; zero order with respect to the oxidant concentration, second order with respect to the reductant concentration and first order with respect to the hydrogen ion concentration. The empirical rate law conforms to the equation: − {Co(phen)3}3+] = a [H+] [S2O32−]2 ‘a’ = 128.26 dm6 mol−2 s−1: at [H+] = 2.0 × 10−2 mol dm−3, µ = 0.4 mol dm−3 (NaCl), T = 28 ± 1˚C and λmax = 495 nm.The rate of reaction increased at the increase in ionic strength and at the decrease in medium dielectric constant. Added cations and anions catalyzed and inhibited the reaction rates respectively. The Michaelis-Menten plot of 1/k1 versus 1/[S2O32−]2 started from the origin. Hence based on spectroscopic investigation, thermodynamic information from temperature dependence studies and kinetic evidence from Michaelis–Menten plots and the interactions with added ions, an outer-sphere mechanism has been rationalized for this reaction. The mechanistic scheme of the reaction was proposed via the stated mechanistic route.

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Fazal, Aliya, e Uzaira Rafique. "Mechanistic study of Cd adsorption through esterification and acetylation of novel biosorbent Gallus Domesticus chemically modified biomaterial for heavy metal". Journal of Water Reuse and Desalination 4, n. 2 (16 dicembre 2013): 76–84. http://dx.doi.org/10.2166/wrd.2013.033.

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The inevitable expansion of industries for development is at the cost of release of industrial pollutants into the natural reservoirs of the environment. Biosorption is becoming an important component in the integrated approach to the treatment of aqueous effluents. The adsorption properties of Gallus Domesticus are determined as a function of batch operating conditions including contact time, solution initial concentration and temperature. Metal ion fixed Fourier transform infrared spectroscopy spectrum depicted amine, alcohol, carboxyl, and carbonate ion as active sites for metal sorption. Augmentation of removal capacity to 5 and 17% is tailored by esterification and acetylation of different surface functional groups of the base matrix. Kinetics is dissected through diffusion-based kinetic models, and best fit was figured out for Elovich equation. The thermodynamic relationship draws that enthalpy (ΔH° 45.48 KJ/mol) and entropy (ΔS° 153.32 J/mol K) are positive and entropy of the system is much larger than enthalpy. Results propose alteration of domestic waste into economical adsorbent for commercialization with no processing in the efficient removal of cadmium from wastewater.

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Alsaedi, Mossab K., Ghada K. Alothman, Mohammed N. Alnajrani, Omar A. Alsager, Sultan A. Alshmimri, Majed A. Alharbi, Majed O. Alawad, Shahad Alhadlaq e Seetah Alharbi. "Antibiotic Adsorption by Metal-Organic Framework (UiO-66): A Comprehensive Kinetic, Thermodynamic, and Mechanistic Study". Antibiotics 9, n. 10 (21 ottobre 2020): 722. http://dx.doi.org/10.3390/antibiotics9100722.

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Bacterial antibiotic resistance has been deemed one of the largest modern threats to human health. One of the root causes of antibiotic resistance is the inability of traditional wastewater management techniques, such as filtration and disinfection, to completely eliminate residual antibiotics from domestic and industrial effluents. In this study, we examine the ability of UiO-66; a metal-organic framework (MOF); in removing the antibiotic Doxycycline from aqueous environments. This study’s findings suggest that UiO-66 was able to remove nearly 90% of the initial Doxycycline concentration. To correlate the isothermal data, Langmuir and Freundlich models were used. It was determined that the Langmuir model was best suited. Pseudo-first and -second order models were examined for kinetic data, where the pseudo-second order model was best suited—consistent with the maximum theoretical adsorption capacity found by the Langumir model. Thermodynamic analysis was also examined by studying UiO-66 adsorption under different temperatures. Mechanisms of adsorption were also analyzed through measuring adsorption at varying pH levels, thermogravimetric analysis (TGA), Infrared spectroscopy (IR) and Brunauer–Emmet–Teller (BET). This study also explores the possibility of recycling MOFs through exposure to gamma radiation, heat, and heating under low pressure, in order for UiO-66 to be used in multiple, consecutive cycles of Doxycycline removal.

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Wan, Chin-Feng, Wei-Hong Chen, Cheng-Ta Chen, Margaret Dah-Tsyr Chang, Lee-Chiang Lo e Yaw-Kuen Li. "Mutagenesis and mechanistic study of a glycoside hydrolase family 54 α-L-arabinofuranosidase from Trichoderma koningii". Biochemical Journal 401, n. 2 (21 dicembre 2006): 551–58. http://dx.doi.org/10.1042/bj20060717.

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A GH (glycoside hydrolase) family 54 α-L-arabinofuranosidase from Trichoderma koningii G-39 (termed Abf) was successfully expressed in Pichia pastoris and purified to near homogeneity by cation-exchange chromatography. To determine the amino acid residues essential for the catalytic activity of Abf, extensive mutagenesis of 24 conserved glutamate and aspartate residues was performed. Among the mutants, D221N, E223Q and D299N were found to decrease catalytic activity significantly. The kcat values of the D221N and D299N mutants were 7000- and 1300-fold lower respectively, than that of the wild-type Abf. E223Q was nearly inactive. These results are consistent with observations obtained from the Aspergillus kawachii α-L-arabinofuranosidase three-dimensional structure. This structure indicates that Asp221 of T. koningii Abf is significant for substrate binding and that Glu223 as well as Asp299 function as a nucleophile and a general acid/base catalyst for the enzymatic reaction respectively. The catalytic mechanism of wild-type Abf was further investigated by NMR spectroscopy and kinetic analysis. The results showed that Abf is a retaining enzyme. It catalyses the hydrolysis of various substrates via the formation of a common intermediate that is probably an arabinosyl–enzyme intermediate. A two-step, double-displacement mechanism involving first the formation, and then the breakdown, of an arabinosyl–enzyme intermediate was proposed. Based on the kcat values of a series of aryl-α-L-arabinofuranosides catalytically hydrolysed by wild-type Abf, a relatively small Brønsted constant, βlg=−0.18, was obtained, suggesting that the rate-limiting step of the enzymatic reaction is the dearabinosylation step. Further kinetic studies with the D299G mutant revealed that the catalytic activity of this mutant depended largely on the pKa values (>6) of leaving phenols, with βlg=−1.3, indicating that the rate-limiting step of the reaction becomes the arabinosylation step. This kinetic outcome supports the idea that Asp299 is the general acid/base residue. The pH activity profile of D299N provided further evidence strengthening this suggestion.

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Hortelano, Carlos, Marta Ruiz-Bermejo e José L. de la de la Fuente. "Kinetic Study of the Effective Thermal Polymerization of a Prebiotic Monomer: Aminomalononitrile". Polymers 15, n. 3 (17 gennaio 2023): 486. http://dx.doi.org/10.3390/polym15030486.

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Aminomalononitrile (AMN), the HCN formal trimer, is a molecule of interest in prebiotic chemistry, in fine organic synthesis, and, currently, in materials science, mainly for bio-applications. Herein, differential scanning calorimetry (DSC) measurements by means of non-isothermal experiments of the stable AMN p-toluenesulfonate salt (AMNS) showed successful bulk AMN polymerization. The results indicated that this thermally stimulated polymerization is initiated at relatively low temperatures, and an autocatalytic kinetic model can be used to appropriately describe, determining the kinetic triplet, including the activation energy, the pre-exponential factor, and the mechanism function (Eα, A and f(α)). A preliminary structural characterization, by means of Fourier transform infrared (FTIR) spectroscopy, supported the effective generation of HCN-derived polymers prepared from AMNS. This study demonstrated the autocatalytic, highly efficient, and straightforward character of AMN polymerization, and to the best of our knowledge, it describes, for the first time, a systematic and extended kinetic analysis for gaining mechanistic insights into this process. The latter was accomplished through the help of simultaneous thermogravimetry (TG)-DSC and the in situ mass spectrometry (MS) technique for investigating the gas products generated during these polymerizations. These analyses revealed that dehydrocyanation and deamination processes must be important elimination reactions involved in the complex AMN polymerization mechanism.

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28

Nelson, Peter N., e Willem H. Mulder. "Thermodynamic and kinetic models for acid chloride formation: A computational and theoretical mechanistic study". Journal of Molecular Graphics and Modelling 112 (maggio 2022): 108139. http://dx.doi.org/10.1016/j.jmgm.2022.108139.

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29

Kaminskaia, Natalia V., G. Matthias Ullmann, D. Bruce Fulton e Nenad M. Kostić. "Spectroscopic, Kinetic, and Mechanistic Study of a New Mode of Coordination of Indole Derivatives to Platinum(II) and Palladium(II) Ions in Complexes". Inorganic Chemistry 39, n. 22 (ottobre 2000): 5004–13. http://dx.doi.org/10.1021/ic000254l.

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30

Kourtelesis, Marios, Kalliopi Kousi e Dimitris I. Kondarides. "CO2 Hydrogenation to Methanol over La2O3-Promoted CuO/ZnO/Al2O3 Catalysts: A Kinetic and Mechanistic Study". Catalysts 10, n. 2 (3 febbraio 2020): 183. http://dx.doi.org/10.3390/catal10020183.

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Abstract (sommario):

The hydrogenation of CO2 to methanol has been investigated over CuO/ZnO/Al2O3 (CZA) catalysts, where a part of the Al2O3 (0, 25, 50, 75, or 100%) was substituted by La2O3. Results of catalytic performance tests obtained at atmospheric pressure showed that the addition of La2O3 generally resulted in a decrease of CO2 conversion and in an increase of methanol selectivity. Optimal results were obtained for the CZA-La50 catalyst, which exhibited a 30% higher yield of methanol, compared to the un-promoted sample. This was attributed to the relatively high specific surface area and porosity of this material, the creation of basic sites of moderate strength, which enhance adsorption of CO2 and intermediates that favor hydrogenation steps, and the ability of the catalyst to maintain a large part of the copper in its metallic form under reaction conditions. The reaction mechanism was studied with the use of in situ infrared spectroscopy (DRIFTS). It was found that the reaction proceeded with the intermediate formation of surface formate and methoxy species and that both methanol and CO were mainly produced via a common formate intermediate species. The kinetic behavior of the best performing CZA-La50 catalyst was investigated in the temperature range 190–230 °C as a function of the partial pressures of H2 (0.3–0.9 atm) and CO2 (0.05–0.20 atm), and a kinetic model was developed, which described the measured reaction rates satisfactorily.

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31

LI, Yaw-Kuen, Jiunly CHIR e Fong-Yi CHEN. "Catalytic mechanism of a family 3 β-glucosidase and mutagenesis study on residue Asp-247". Biochemical Journal 355, n. 3 (24 aprile 2001): 835–40. http://dx.doi.org/10.1042/bj3550835.

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Abstract (sommario):

A family 3 β-glucosidase (EC 3.2.1.21) from Flavobacterium meningosepticum has been cloned and overexpressed. The mechanistic action of the enzyme was probed by NMR spectroscopy and kinetic investigations, including substrate reactivity, secondary kinetic isotope effects and inhibition studies. The stereochemistry of enzymic hydrolysis was identified as occurring with the retention of an anomeric configuration, indicating a double-displacement reaction. Based on the kcat values with a series of aryl glucosides, a Bronsted plot with a concave-downward shape was constructed. This biphasic behaviour is consistent with a two-step mechanism involving the formation and breakdown of a glucosyl–enzyme intermediate. The large Bronsted constant (β =-0.85) for the leaving-group-dependent portion (pKa of leaving phenols > 7) indicates substantial bond cleavage at the transition state. Secondary deuterium kinetic isotope effects with 2,4-dinitrophenyl β-D-glucopyanoside, o-nitrophenyl β-D-glucopyanoside and p-cyanophenyl β-D-glucopyanoside as substrates were 1.17±0.02, 1.19±0.02 and 1.04±0.02 respectively. These results support an SN1-like mechanism for the deglucosylation step and an SN2-like mechanism for the glucosylation step. Site-directed mutagenesis was also performed to study essential amino acid residues. The activities (kcat/Km) of the D247G and D247N mutants were 30000- and 200000-fold lower respectively than that of the wild-type enzyme, whereas the D247E mutant retained 20% of wild-type activity. These results indicate that Asp-247 is an essential amino acid. It is likely that this residue functions as a nucleophile in the reaction. This conclusion is supported by the kinetics of the irreversible inactivation of the wild-type enzyme by conduritol-B-epoxide, compared with the much slower inhibition of the D247E mutant and the lack of irreversible inhibition of the D247G mutant.

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32

Liu, Fangwei, Wenchao Lu, Xunlong Yin e Jianbo Liu. "Mechanistic and Kinetic Study of Singlet O2 Oxidation of Methionine by On-Line Electrospray Ionization Mass Spectrometry". Journal of The American Society for Mass Spectrometry 27, n. 1 (26 agosto 2015): 59–72. http://dx.doi.org/10.1007/s13361-015-1237-4.

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33

Ullah, Shaheed, Michael L. McKee e Alexander Samokhvalov. "Interaction of a Porphyrin Aluminum Metal–Organic Framework with Volatile Organic Sulfur Compound Diethyl Sulfide Studied via In Situ and Ex Situ Experiments and DFT Computations". Nanomaterials 13, n. 22 (8 novembre 2023): 2916. http://dx.doi.org/10.3390/nano13222916.

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Abstract (sommario):

The study presents complementary experiments and quantum chemical DFT computations to reveal the molecular-level interactions of an advanced nanomaterial, porphyrin aluminum metal–organic framework (compound 2), with the volatile organic sulfur compound diethyl sulfide (DES). First, the intermolecular host–guest interactions during the sorption of DES were explored under dynamic conditions, using the vapor of DES in flowing air. The in situ time-dependent ATR-FTIR spectroscopy in a controlled atmosphere was significantly improved though the use of a new facilely built spectroscopic mini-chamber. The binding site of DES in compound 2 involves the μ(O–H) and COO- groups of the linker of the sorbent. Further, the chemical kinetics of the sorption of DES was investigated, and it follows the Langmuir adsorption kinetic model. That is, depending on the time interval, the process obeys either the pseudo-first- or pseudo-second-order rate law. For the Langmuir adsorption of the pseudo-first order, the rate constant is robs = 0.165 ± 0.017 min−1. Next, the interaction of compound 2 with the saturated vapor of DES yields the adsorption complex compound 3 [Al-MOF-TCPPH2]2(DES)7. The adsorbed amount of DES is very large at 36.5 wt.% or 365 mg/g sorbent, one of the highest values reported on any sorbent. The molecular modes of bonding of DES in the complex were investigated through quantum chemical DFT computations. The adsorption complex was facilely regenerated by gentle heating. The advanced functional material in this work has significant potential in the environmental remediation of diethyl sulfide and related volatile organic sulfur compounds in air, and it is an interesting target of mechanistic studies of sorption.

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Gogoi, P., M. Das, P. Begum e T. K. Maji. "Nature of sorption of trivalent arsenic on novel iron oxyhydroxide stabilized starch/OMMT composite: A mechanistic approach". Journal of Water and Health 19, n. 2 (25 marzo 2021): 336–50. http://dx.doi.org/10.2166/wh.2021.267.

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Abstract (sommario):

Abstract Materials which are chemically, energetically and operationally acceptable for arsenic water treatment are highly required. In this study a hybrid material (SICC) of aminated starch, oxyhydroxide of iron and OMMT clay has been demonstrated for arsenic treatment. This new material was highly efficient in arsenic water treatment which could reduce arsenic concentration far below detection limits. All binding interactions during material preparation and arsenic sorption were exclusively characterized with FT-IR, XRD and other spectroscopic tools. A molecular modeling on the basis of density functional theory was carried out to verify the above findings. Influence of material dose, treatment time, initial ion concentration, varying temperatures, etc., on extent of sorption was studied in detail. The thermodynamic parameters viz. ΔG (>–11 kJ/mol), ΔH (42.48 kJ/mol), ΔS (177.6 JK−1 mol−1) and E a (59.16 kJ/mol) determined the feasibility of the process, its endothermic behavior and most importantly the chemical nature of the sorption accompanied by ion-exchange to some extent. The sorption followed a monolayer chemisorption pattern as determined by the Langmuir model (R2 = 0.973, R L = 0.081) with a qmax = 2.04 at 303 K. The binding of As(III) on the material was governed by a pseudo second order kinetic model.

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35

Cellupica, Edoardo, Aureliano Gaiassi, Ilaria Rocchio, Grazia Rovelli, Roberta Pomarico, Giovanni Sandrone, Gianluca Caprini et al. "Mechanistic and Structural Insights on Difluoromethyl-1,3,4-Oxadiazole Inhibitors of HDAC6". International Journal of Molecular Sciences 25, n. 11 (28 maggio 2024): 5885. http://dx.doi.org/10.3390/ijms25115885.

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Abstract (sommario):

Histone deacetylase 6 (HDAC6) is increasingly recognized for its potential in targeted disease therapy. This study delves into the mechanistic and structural nuances of HDAC6 inhibition by difluoromethyl-1,3,4-oxadiazole (DFMO) derivatives, a class of non-hydroxamic inhibitors with remarkable selectivity and potency. Employing a combination of nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) kinetic experiments, comprehensive enzymatic characterizations, and X-ray crystallography, we dissect the intricate details of the DFMO-HDAC6 interaction dynamics. More specifically, we find that the chemical structure of a DMFO and the binding mode of its difluoroacetylhydrazide derivative are crucial in determining the predominant hydrolysis mechanism. Our findings provide additional insights into two different mechanisms of DFMO hydrolysis, thus contributing to a better understanding of the HDAC6 inhibition by oxadiazoles in disease modulation and therapeutic intervention.

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Theologides, C. P., G. G. Olympiou, P. G. Savva, N. A. Pantelidou, B. K. Constantinou, V. K. Chatziiona, L. Y. Valanidou, C. T. Piskopianou e C. N. Costa. "Novel catalytic and mechanistic studies on wastewater denitrification with hydrogen". Water Science and Technology 69, n. 3 (4 dicembre 2013): 680–86. http://dx.doi.org/10.2166/wst.2013.781.

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Abstract (sommario):

The present work reports up-to-date information regarding the reaction mechanism of the catalytic hydrogenation of nitrates in water media. In the present mechanistic study, an attempt is made, for the first time, to elucidate the crucial role of several catalysts and reaction parameters in the mechanism of the NO3−/H2 reaction. Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed on supported Pd-Cu catalysts for the NO3−/H2 and NO3−/H2/O2 reactions. The latter experiments revealed that the formation and surface coverage of various adsorbed active intermediate N-species on the support or Pd/Cu metal surface is significantly favored in the presence of TiO2 in the support mixture and in the presence of oxygen in the reaction's gaseous feed stream. The differences in the reactivity of these adsorbed N-species, found in the present work, adequately explain the large effect of the chemical composition of the support and the gas feed composition on catalyst behaviour (activity and selectivity). The present study leads to solid mechanistic evidence concerning the presence of a hydrogen spillover process from the metal to the support. Moreover, this study shows that Cu clusters are active sites for the reduction of nitrates to nitrites.

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Zhao, Jun, Huihua Luo, Yutong Liu, Ju Liu, Liqing Peng, Mei Cen e Fengyuan Li. "Mechanistic Study and Application of Anionic/Cationic Combination Collector ST-8 for the Flotation of Spodumene". Minerals 13, n. 9 (7 settembre 2023): 1177. http://dx.doi.org/10.3390/min13091177.

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Abstract (sommario):

The mechanism of anionic/cationic combination collector ST-8 for the efficient separation of spodumene and feldspar was investigated by flotation tests, surface tension measurements, zeta potential measurements and infrared spectroscopy analysis. The flotation results indicated that when the optimum molar ratio of sodium oleate and dodecylamine was 6:1–10:1 and pH = 8.5, the recovery of spodumene reached a maximum of 80% and that of feldspar reached about 24.5%. Zeta potential measurements showed that the negative shift of the kinetic potential on the surface of spodumene was much stronger than that on the surface of feldspar, indicating that the adsorption capacity of the combined collector on spodumene surface and feldspar surface was greatly different. From the surface tension as well as the synergistic parameters, there was a strong mutual attraction between dodecylamine and sodium oleate, and there was a significant synergistic effect between them. Infrared spectroscopy indicated that the combined collector chemisorbed on the mineral surface, and the intensity of the absorption peak after the action of spodumene was much stronger than that after the action of feldspar. The solution chemistry of the combined collector revealed that at pH 8.5, the positively charged ions RNH3+ and (RNH3+)22+ in dodecylamine and the negatively charged RCOO− and (RCOO−)22− ions in oleic acid form highly reactive complexes to interact with the mineral surface by electrostatic gravitation, thus achieving efficient separation of spodumene and feldspar. Finally, from the closed-circuit test results, a flotation index of 6.34% Li2O grade and 88.51% Li2O recovery was obtained.

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Lesanavičius, Mindaugas, Alessandro Aliverti, Jonas Šarlauskas e Narimantas Čėnas. "Reactions of Plasmodium falciparum Ferredoxin:NADP+ Oxidoreductase with Redox Cycling Xenobiotics: A Mechanistic Study". International Journal of Molecular Sciences 21, n. 9 (2 maggio 2020): 3234. http://dx.doi.org/10.3390/ijms21093234.

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Abstract (sommario):

Ferredoxin:NADP+ oxidoreductase from Plasmodium falciparum (PfFNR) catalyzes the NADPH-dependent reduction of ferredoxin (PfFd), which provides redox equivalents for the biosynthesis of isoprenoids and fatty acids in the apicoplast. Like other flavin-dependent electrontransferases, PfFNR is a potential source of free radicals of quinones and other redox cycling compounds. We report here a kinetic study of the reduction of quinones, nitroaromatic compounds and aromatic N-oxides by PfFNR. We show that all these groups of compounds are reduced in a single-electron pathway, their reactivity increasing with the increase in their single-electron reduction midpoint potential (E17). The reactivity of nitroaromatics is lower than that of quinones and aromatic N-oxides, which is in line with the differences in their electron self-exchange rate constants. Quinone reduction proceeds via a ping-pong mechanism. During the reoxidation of reduced FAD by quinones, the oxidation of FADH. to FAD is the possible rate-limiting step. The calculated electron transfer distances in the reaction of PfFNR with various electron acceptors are similar to those of Anabaena FNR, thus demonstrating their similar “intrinsic” reactivity. Ferredoxin stimulated quinone- and nitro-reductase reactions of PfFNR, evidently providing an additional reduction pathway via reduced PfFd. Based on the available data, PfFNR and possibly PfFd may play a central role in the reductive activation of quinones, nitroaromatics and aromatic N-oxides in P. falciparum, contributing to their antiplasmodial action.

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van Niekerk, Daniël M. E., Theodor E. Geswindt e Wilhelmus J. Gerber. "Kinetic UV–Vis Spectroscopic and DFT Mechanistic Study of the Redox Reaction of [OsVIIIO4(OH)n]n− (n = 1, 2) and Methanol in a Basic Aqueous Matrix". Inorganic Chemistry 60, n. 2 (7 gennaio 2021): 782–97. http://dx.doi.org/10.1021/acs.inorgchem.0c02799.

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40

Mecheri, Razika, Ammar Zobeidi, Salem Atia, Salah Neghmouche Nacer, Alsamani A. M. Salih, Mhamed Benaissa, Djamel Ghernaout, Saleh Al Arni, Saad Ghareba e Noureddine Elboughdiri. "Modeling and Optimizing the Crystal Violet Dye Adsorption on Kaolinite Mixed with Cellulose Waste Red Bean Peels: Insights into the Kinetic, Isothermal, Thermodynamic, and Mechanistic Study". Materials 16, n. 11 (30 maggio 2023): 4082. http://dx.doi.org/10.3390/ma16114082.

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Abstract (sommario):

In this study, a new eco-friendly kaolinite–cellulose (Kaol/Cel) composite was prepared from waste red bean peels (Phaseolus vulgaris) as a source of cellulose to serve as a promising and effective adsorbent for the removal of crystal violet (CV) dye from aqueous solutions. Its characteristics were investigated through the use of X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and zero-point of charge (pHpzc). The Box–Behnken design was used to improve CV adsorption on the composite by testing its primary affecting factors: loading Cel into the composite matrix of Kaol (A: 0–50%), adsorbent dosage (B: 0.02–0.05 g), pH (C: 4–10), temperature (D: 30–60 °C), and duration (E: 5–60 min). The significant interactions with the greatest CV elimination efficiency (99.86%) are as follows: BC (adsorbent dose vs. pH) and BD (adsorbent dose vs. temperature) at optimum parameters (A: 25%, B: 0.05 g, C: 10, D: 45 °C, and E: 17.5 min) for which the CV’s best adsorption capacity (294.12 mg/g) was recorded. The Freundlich and pseudo-second-order kinetic models were the best isotherm and kinetic models fitting our results. Furthermore, the study investigated the mechanisms responsible for eliminating CV by utilizing Kaol/Cel–25. It detected multiple types of associations, including electrostatic, n-π, dipole–dipole, hydrogen bonding interactions, and Yoshida hydrogen bonding. These findings suggest that Kaol/Cel could be a promising starting material for developing a highly efficient adsorbent that can remove cationic dyes from aqueous environments.

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Chen, Xiaoxiao, Yanhui Sun, Youxiao Qi, Lin Liu, Fei Xu e Yan Zhao. "Mechanistic and Kinetic Investigations on the Ozonolysis of Biomass Burning Products: Guaiacol, Syringol and Creosol". International Journal of Molecular Sciences 20, n. 18 (11 settembre 2019): 4492. http://dx.doi.org/10.3390/ijms20184492.

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Abstract (sommario):

The lignin pyrolysis products generated by biomass combustion make an essential contribution to the formation of secondary organic aerosols (SOAs). The ozone-initiated oxidation of guaiacol, syringol and creosol, major constituents of biomass burning, were investigated theoretically by using the density functional theory (DFT) method at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. Six primary addition reaction pathways and further decomposition routes with corresponding thermodynamic values were proposed. The Criegee intermediates can be excited by small molecules, such as NOx, H2O in the atmosphere, and would further proceed via self-decomposition or isomerization. The most predominant product for ozonation of guaiacol is the monomethyl muconate (P1). At 295 K and atmospheric pressure, the rate constant is 1.10 × 10−19 cm3 molecule−1 s−1, which is lies a factor of 4 smaller than the previous experimental study. The branching ratios of the six channels are calculated based on corresponding rate coefficient. The present work mainly provides a more comprehensive and detailed theoretical research on the ozonation of methoxyphenol, which aspires to offer novel insights and reference for future experimental and theoretical work and control techniques of SOAs caused by lignin pyrolysis products.

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42

Kabanda, Mwadham M., e Indra Bahadur. "A DFT and MP2 mechanistic and kinetic study on hypohalogenation reaction of cysteine and N-acetylcysteine in aqueous solution". Journal of Molecular Liquids 349 (marzo 2022): 118191. http://dx.doi.org/10.1016/j.molliq.2021.118191.

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43

Moffat, Karen A., Gordon K. Hamer e Michael K. Georges. "Stable Free Radical Polymerization Process: Kinetic and Mechanistic Study of the Thermal Decomposition of MB-TMP Monitored by NMR and ESR Spectroscopy". Macromolecules 32, n. 4 (febbraio 1999): 1004–12. http://dx.doi.org/10.1021/ma981155i.

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44

Rout, Sudhanshu Sekhar, Durga Madhab Kar, Sudam Chandra Si, Ajaya Kumar Patnaik e Prakash Mohanty. "Reaction of Carbidopa with cis-[Cr(C2O4)2(H2O)2]− in Aqueous Medium: A Kinetic, Mechanistic and Antiparkinsonian Study of the Product Complex". Asian Journal of Chemistry 32, n. 7 (2020): 1653–59. http://dx.doi.org/10.14233/ajchem.2020.22633.

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Abstract (sommario):

For the treatment of Parkinson′s disease, the second most common neurodegenerative disorder, requires a combination of levodopa with a peripheral decarboxylase inhibitor, such as carbidopa which provides a symptomatic relief to patients. Reaction of carbidopa with cis-[Cr(C2O4)2(H2O)2]– has been carried out in aqueous medium over the range 35 ≤ t ≤ 50 ºC, 4.0 ≤ pH ≤ 6.0 , 3.75 × 10-3 mol dm-3 ≤ [carbidopa] ≤ 9.38 × 10-3 mol dm-3, I (KNO3) = 0.1 mol dm-3. There is outersphere association between cis-[Cr(C2O4)2(H2O)2]– and conjugate base of carbidopa followed by first chelation. The characterization of the product was performed by using NMR and infrared spectroscopies. The product showed better antiparkinsonian activity than the combination of levodopa and carbidopa

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Birben, Nazmiye Cemre, Ezgi Lale, Renato Pelosato, Nazli Turkten, Isabella Natali Sora e Miray Bekbolet. "Photocatalytic Bactericidal Performance of LaFeO3 under Solar Light in the Presence of Natural Organic Matter: Spectroscopic and Mechanistic Evaluation". Water 13, n. 19 (8 ottobre 2021): 2785. http://dx.doi.org/10.3390/w13192785.

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Abstract (sommario):

Solar photocatalytic inactivation (SPCI) of E. coli as the indicator microorganism using LaFeO3 (LF) has already been investigated under various experimental conditions, excluding any role of natural organic matter (NOM). However, comprehensive information about the behavior of E. coli and its inactivation mechanism in the presence of NOM, as well as the behavior of NOM components via solar photocatalysis using LF as a photocatalyst, has prime importance in understanding real natural water environments. Therefore, in this study, further assessment was devoted to explore the influence of various NOM representatives on the SPCI of E. coli by using LF as a novel non-TiO2 photocatalyst. The influence of NOM as well as its sub-components, such as humic acids (HA) and fulvic acids (FA), was also investigated to understand different NOM-related constituents of real natural water conditions. In addition to spectroscopic and mechanistic investigations of cell-derived organics, excitation emission matrix (EEM) fluorescence spectra with parallel factor multiway analysis (PARAFAC) modeling revealed further information about the occurrence and/or disappearance of NOM-related and bacteria-related fluorophores upon LF SPCI. Both the kinetics as well as the mechanism of the LF SPCI of E. coli in the presence of NOM compounds displayed substrate-specific variations under all conditions.

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Dai, Huidong, Seongmin Bak, Luisa Larissa Arnaldo Gomes, Kevin Yang, Derrick Maxwell, Srinidi Badhrinathan, Yonghua Du, Gaind P. Pandey e Sanjeev Mukerjee. "Mechanistic Understanding of the Role of Bis(4-nitrophenyl) Carbonate (BNC) As Additive on the Solvation Structure and Polysulfides Shuttling Effect Towards Capacity Improvement in Lithium-Sulfur Batteries". ECS Meeting Abstracts MA2024-01, n. 2 (9 agosto 2024): 196. http://dx.doi.org/10.1149/ma2024-012196mtgabs.

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Abstract (sommario):

The lithium-sulfur (Li-S) batteries are considered as one of the most promising devices for next-generation energy storage applications, owing to its exceptional theoretical capacity and energy density. However, persistent challenges have hampered its performance, notably the sluggish polysulfides conversion kinetics and the polysulfides shuttling phenomenon. These issues lead to irreversible active material loss, rapid capacity decay, low coulombic efficiency, and a limited cycle life. This study demonstrates that bis(4-nitrophenyl) carbonate (BNC) can serve as an effective agent in anchoring dissolved polysulfides, thereby preventing their migration to the anode. Furthermore, this investigation indicates that BNC has the capability to modify the solvation structure of polysulfides in the electrolyte. The presence of 0.01M BNC induces a downfield shift in the 7Li NMR spectrum, signifying a strengthened solvation structure on Li-ion. This solvation modification results in altered kinetics, specifically a reduced Li2S2/Li2S conversion without sacrificing capacity, as confirmed by operando X-ray absorption spectroscopy (XAS). Operando Raman spectroscopy reveals the suppression of long-chain polysulfides (at 400 cm-1) and intermediate polysulfides (at 453 cm-1) with 0.01M BNC, mitigating sulfur shuttling to the anode. This observation is corroborated by X-ray fluorescence (XRF) mapping. Analysis of the corresponding X-ray absorption near-edge structure (XANES) demonstrates that both anodes and cathodes with 0.01M BNC exhibit lower levels of unconverted polysulfides over extended cycles. This improvement is attributed to the kinetic consequences resulting from solvation structure alteration. However, this investigation cautions against an indiscriminate increase in BNC concentration, as higher concentrations may lead to the over-conversion of soluble polysulfides. This nuanced understanding of the solvation structure's intrinsic mechanism, coupled with chemical reactions, provides valuable insights for practical design of Li-S batteries Figure 1

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47

Wang, Hetong, Chenpeng Zuo, Siyuan Zheng, Yanhui Sun, Fei Xu e Qingzhu Zhang. "Mechanistic and Kinetic Study on Self-/Cross- Condensation of PCTA/DT Formation Mechanisms from Three Types of Radicals of 2,4-Dichlorothiophenol". International Journal of Molecular Sciences 20, n. 11 (28 maggio 2019): 2623. http://dx.doi.org/10.3390/ijms20112623.

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Chlorothiophenols (CTPs) are known to be key and direct precursors of polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs). Self/cross-coupling of the chlorothiophenoxy radicals (CTPRs), sulfydryl-substituted phenyl radicals and thiophenoxyl diradicals evolving from CTPs are initial and important steps for PCTA/DT formation. In this study, quantum chemical calculations were carried out to investigate the homogenous gas-phase formation of PCTA/DTs from self/cross-coupling of 2,4-dichlorothiophenoxy radical (R1), 2-sulfydryl-3,5-dichlorophenyl radical (R2) and 3,5-dichlorothiophenoxyl diradical (DR) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants of crucial elementary steps were deduced over 600–1200 K, using canonical variational transition state theory with a small curvature tunneling contribution. For the formation of PCTAs, the S•/σ-C• condensation with both thiophenolic sulfur in one radical and ortho carbon in the other radical bonded to single electron is the most efficient sulfur-carbon coupling mode, and the ranking of the PCTA formation potential is DR + DR > R2 + DR > R1 + DR > R1 + R2 > R1 + R1. For the formation of PCDTs, the σ-C•/σ-C• coupling with both ortho carbon in the two radicals bonded to single electron is the energetically favored carbon-carbon coupling mode, and the ranking of the PCDT formation potential is: R2 + DR > R2 + R2 > R1 + DR > R1 + R2 > R1 + R1. The PCTA/DTs could be produced from R1, R2 and DR much more readily than PCDD/DFs from corresponding oxygen substituted radicals.

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48

Morasch, Barbara, Hans H. Richnow, Bernhard Schink e Rainer U. Meckenstock. "Stable Hydrogen and Carbon Isotope Fractionation during Microbial Toluene Degradation: Mechanistic and Environmental Aspects". Applied and Environmental Microbiology 67, n. 10 (1 ottobre 2001): 4842–49. http://dx.doi.org/10.1128/aem.67.10.4842-4849.2001.

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ABSTRACT Primary features of hydrogen and carbon isotope fractionation during toluene degradation were studied to evaluate if analysis of isotope signatures can be used as a tool to monitor biodegradation in contaminated aquifers. D/H hydrogen isotope fractionation during microbial degradation of toluene was measured by gas chromatography. Per-deuterated toluene-d 8 and nonlabeled toluene were supplied in equal amounts as growth substrates, and kinetic isotope fractionation was calculated from the shift of the molar ratios of toluene-d 8 and nondeuterated toluene. The D/H isotope fractionation varied slightly for sulfate-reducing strain TRM1 (slope of curve [b] = −1.219), Desulfobacterium cetonicum(b = −1.196), Thauera aromatica(b = −0.816), and Geobacter metallireducens (b = −1.004) and was greater for the aerobic bacterium Pseudomonas putidamt-2 (b = −2.667). The D/H isotope fractionation was 3 orders of magnitude greater than the13C/12C carbon isotope fractionation reported previously. Hydrogen isotope fractionation with nonlabeled toluene was 1.7 and 6 times less than isotope fractionation with per-deuterated toluene-d 8 and nonlabeled toluene for sulfate-reducing strain TRM1 (b = −0.728) andD. cetonicum (b = −0.198), respectively. Carbon and hydrogen isotope fractionation during toluene degradation by D. cetonicum remained constant over a growth temperature range of 15 to 37°C but varied slightly during degradation by P. putida mt-2, which showed maximum hydrogen isotope fractionation at 20°C (b = −4.086) and minimum fractionation at 35°C (b = −2.138). D/H isotope fractionation was observed only if the deuterium label was located at the methyl group of the toluene molecule which is the site of the initial enzymatic attack on the substrate by the bacterial strains investigated in this study. Use of ring-labeled toluene-d 5 in combination with nondeuterated toluene did not lead to significant D/H isotope fractionation. The activity of the first enzyme in the anaerobic toluene degradation pathway, benzylsuccinate synthase, was measured in cell extracts of D. cetonicum with an initial activity of 3.63 mU (mg of protein)−1. The D/H isotope fractionation (b = −1.580) was 30% greater than that in growth experiments with D. cetonicum. Mass spectroscopic analysis of the product benzylsuccinate showed that H atoms abstracted from the toluene molecules by the enzyme were retained in the same molecules after the product was released. Our findings revealed that the use of deuterium-labeled toluene was appropriate for studying basic features of D/H isotope fractionation. Similar D/H fractionation factors for toluene degradation by anaerobic bacteria, the lack of significant temperature dependence, and the strong fractionation suggest that analysis of D/H fractionation can be used as a sensitive tool to assess degradation activities. Identification of the first enzyme reaction in the pathway as the major fractionating step provides a basis for linking observed isotope fractionation to biochemical reactions.

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49

Zhong, Lin, Qi He, Fangfang Chen, Hongtan Wu e Yu-Pei Chen. "Exploring the inhibitory effects of glutamic acid on melanin production: Mechanistic insights and molecular docking analysis". BIO Web of Conferences 111 (2024): 03018. http://dx.doi.org/10.1051/bioconf/202411103018.

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Glutamic acid is widely recognized as safe and has various applications in the medical and food industries. This study demonstrated its significant inhibition of tyrosinase, acting as a mixed-type inhibitor according to enzymatic kinetic analysis. Fluorescence spectroscopy analysis and investigation of tyrosinase activity under different pH confirmed that glutamic acid induced changes in the protein structure of tyrosinase, leading to its reduced activity through acidification and binding effects. Additionally, glutamic acid was found to inhibit L-DOPA auto-oxidation, thereby preventing further formation of dopachrome. The IC50 values for glutamic acid inhibiting tyrosinase activity and L-DOPA auto-oxidation were detected to be 4.69 mM and 0.72 mM, respectively. Glutamic acid had a better inhibitory effect on L-DOPA autooxidation than tyrosinase activity. The L-DOPA auto-oxidation process can also lead to the formation of melanin, and its inhibition by glutamic acid further supported its potential in controlling melanin synthesis. Moreover, glutamic acid demonstrated a dose-dependent decrease in melanin production in B16 cells while maintaining cell viability. Western blot analysis revealed decreased protein expression of TYR and TRP-1, both of which are involved in melanin production, with increasing concentrations of glutamic acid. Molecular docking analysis suggested a potential mechanism involving the disruption of copper binding sites on tyrosinase. These findings underscore the potential of glutamic acid as a promising agent for controlling melanin production and associated disorders.

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50

Mukhametgalieva, Aliya R., Andrey V. Nemtarev, Viktor V. Sykaev, Tatiana N. Pashirova e Patrick Masson. "Activation/Inhibition of Cholinesterases by Excess Substrate: Interpretation of the Phenomenological b Factor in Steady-State Rate Equation". International Journal of Molecular Sciences 24, n. 13 (21 giugno 2023): 10472. http://dx.doi.org/10.3390/ijms241310472.

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Cholinesterases (ChEs) display a non-michaelian behavior with positively charged substrates. In the steady-state rate equation, the b factor describes this behavior: if b > 1 there is substrate activation, if b < 1 there is substrate inhibition. The mechanistic significance of the b factor was investigated to determine whether this behavior depends on acylation, deacylation or on both steps. Kinetics of human acetyl- (AChE) and butyryl-cholinesterase (BChE) were performed under steady-state conditions and using a time-course of complete substrate hydrolysis. For the hydrolysis of short acyl(thio)esters, where acylation and deacylation are partly rate-limiting, steady-state kinetic analysis could not decide which step determines b. However, the study of the hydrolysis of an arylacylamide, 3-(acetamido)-N,N,N-trimethylanilinium (ATMA), where acetylation is rate-limiting, showed that b depends on the acylation step. The magnitude of b and opposite b values between AChE and BChE for the hydrolysis of acetyl(thio)- versus benzoyl-(thio) esters, then indicated that the productive adjustment of substrates in the active center at high concentration depends on motions of both the Ω and the acyl-binding loops. Benzoylcholine was shown to be a poor substrate of AChE, and steady-state kinetics showed a sudden inhibition at high concentration, likely due to the non-dissociation of hydrolysis products. The poor catalytic hydrolysis of this bulky ester by AChE illustrates the importance of the fine adjustment of substrate acyl moiety in the acyl-binding pocket. Molecular modeling and QM/MM simulations should definitively provide evidence for this statement.

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