Perchlorate salts confer psychrophilic characteristics in α-chymotrypsin

Studies of salt effects on enzyme activity have typically been conducted at standard temperatures and pressures, thus missing effects which only become apparent under non-standard conditions. Here we show that perchlorate salts, which are found pervasively on Mars, increase the activity of α-chymotrypsin at low temperatures. The low temperature activation is facilitated by a reduced enthalpy of activation owing to the destabilising effects of perchlorate salts. By destabilising α-chymotrypsin, the perchlorate salts also cause an increasingly negative entropy of activation, which drives the reduction of enzyme activity at higher temperatures. We have also shown that α-chymotrypsin activity appears to exhibit an altered pressure response at low temperatures while also maintaining stability at high pressures and sub-zero temperatures. As the effects of perchlorate salts on the thermodynamics of α-chymotrypsin’s activity closely resemble those of psychrophilic adaptations, it suggests that the presence of chaotropic molecules may be beneficial to life operating in low temperature environments.

Dielectric Relaxation and Thermodynamic Study of Caffeine-Chloroform Solution using TDR

The Complex permittivity of caffeine – Chloroform solution for different temperature and various concentrations have been measured in the range of 10MHZ to 30 GHz using Time Domain Reflectometry. From complex permittivity spectra, Static dielectric constant (εo) and relaxation time (τ) were determined using nonlinear least square fit method. Using Erying rate equation, for different molar concentration of caffeine Enthalpy of Activation ∆H and Entropy of Activation ∆S were determined.

CORROSION INHIBITION EFFICIENCY, ADSORPTION BEHAVIOR, KINETICS AND THERMODYNAMIC STUDIES OF LANNEA ACIDA ETHANOL LEAVES EXTRACT ON MILD STEEL IN HYDROCHLORIC ACID

The corrosion inhibition potential of lannea acida (LA) ethanol leaves extract was investigated using mild steel in 1.0 M HCl solution. The leaves extract was characterized using FT- IR Spectroscopy. The surface analysis of the mild steel was also studied using scanning electron microscopy. The study was carried out at an ambient temperature and selected high temperatures. The LA leaves extract concentration ranges from 0.1- 0.9g/L. The data obtained from weight loss measurements show that the leaves extract repressed the corrosion rate of mild steel. The increase in temperature with a corresponding increase or decrease in the inhibitor efficiency of LA leaves extract shows that the adsorption mechanism obeyed comprehensive adsorption. The value of activation energies (Ea) obtained which ranged from 15.32 to 17.63 kJ mol-1 agrees with the physical adsorption mechanism. The values of enthalpy of activation (ΔH*) obtained were positive and ranged from 38.29 to 59.00 KJ mol-1 is an indication that the dissolution of the mild steel is an endothermic reaction and requires less energy in the presence of LA leaves extract. The values of entropy of activation (ΔS*) obtained which were negative indicate that the activated complex in the rate-determining step is associative rather than dissociative. The kinetics study shows the adsorption process follows first-order kinetics. The adsorption isotherm data fitted best into Freundlich adsorption isotherm

pH Dependent Mechanisms of Hydrolysis of 4-Nitrophenyl β-D-Glucoside

<p>1,2-<i>trans</i>-Glycosides hydrolyze through a range of mechanisms under conditions of different pH, but systematic studies are lacking. Here we report the pH-rate constant profile for the hydrolysis of<i> </i>4-nitrophenyl β-D-glucoside. An inverse kinetic isotope effect (<i>k</i>(H₃O⁺)/<i>k</i>(D₃O⁺) = 0.63) in the acidic region indicates that the mechanism requires the formation of the conjugate acid of the substrate for the reaction to proceed, with heterolytic cleavage of the glycosidic C-O bond. Reactions in the pH-independent region extrapolated to zero buffer concentration show a small inverse solvent isotope effect <i>k</i>(H₂O)/<i>k</i>(D₂O) = 1.1 and a positive entropy of activation (D<i>S</i>^‡ = 3.07 cal mol^–1 K^–1), which is consistent with water attack through a dissociative mechanism. In the basic region, solvolysis in ¹⁸O-labelled water and H₂O/MeOH mixtures allowed detection of bimolecular hydrolysis and neighboring group participation, and to a minor degree, nucleophilic aromatic substitution. Under mildly basic conditions, a bimolecular dissociative mechanism is implicated through a solvent isotope effect of <i>k</i>(HO^-)/<i>k</i>(DO^-) = 0.5 and a strongly negative entropy of activation (D<i>S</i>^‡ = –13.6 cal mol^–1 K^–1). Finally, at high pH, an inverse solvent isotope effect of <i>k</i>(HO^-)/<i>k</i>(DO^-) = 0.6 and a weakly negative entropy of activation (D<i>S</i>^‡ = –5.5 cal mol^–1 K^–1) indicates that the formation of 1,2-anhydrosugar is the rate determining step. <b></b></p>

Kinetic Oxidation Studies of Pentoxifylline by N-Chlorosuccinimide in Acidic Medium Using Iridium(III) Chloride as Inhibitor

In present study, the kinetics and mechanism of oxidation of pentoxifylline (PTX) by N-chlorosuccinimide (NCS) in acidic conditions at 40 ± 0.1 ºC is reported. The reaction depicts first-order kinetics in regard to [NCS], [PTX] and [HClO4]. The reaction rate goes on decreasing as the concentration of iridium(III) chloride is increased. This shows that iridium(III) chloride plays the role of an inhibitor in the reaction under investigation. Nil impact of [Hg(OAc)2], [NHS] and dielectric constant (D) of the medium on the rate of oxidation of pentoxifylline have been observed. This reaction has been investigated from 308-323 K and the monitored rate of reaction suggests a direct relationship between temperature and the rate of reaction. From the graph between log k and 1/T, value of activation energy (Ea) was numerated and more activation parameters like enthalpy of activation (ΔH#), entropy of activation (ΔS#) and free energy of activation (ΔG#) were calculated with the help of activation energy (Ea). On account of experimentally determined the kinetic orders and activation parameters, a most plausible reaction path has been suggested for the oxidation of pentoxifylline in presence of Ir(III) as an inhibitor.

Kinetic Study of Disulfonimide-Catalyzed Cyanosilylation of Aldehydes by Using a Method of Progress Rates

Kinetic study of organic reactions, especially multistep catalytic reactions, is crucial to in-depth understanding of reaction mechanisms. Here we report our kinetic study on the chiral disulfonimide-catalyzed cyanosilylation of an aldehyde, which revealed that two molecules of TMSCN are involved in the rate-determining C–C bond-forming step. In addition, the apparent activation energy, enthalpy of activation, and entropy of activation were deduced through a study of the temperature dependence of the reaction rates. More importantly, a novel and efficient method that makes use of the progress rates was developed to treat kinetic data obtained by continuous monitoring of the progress of a reaction by in situ FTIR.

Kinetic Study of Disulfonimide Catalyzed Cyanosilylation of Aldehyde Using a Method of Progress Rates

Kinetic study of organic reactions, especially multistep catalytic reactions, is crucial to in-depth understanding of reaction mechanisms. Here we report our kinetic study of the chiral disulfonimide catalyzed cyanosilylation of aldehyde, which reveals that two molecules of TMSCN are involved in the rate-determining C-C bond forming step. In addition, the apparent activation energy, enthalpy of activation and entropy of activation were deduced through the study of temperature dependence of the reaction rates. More importantly, a novel and efficient method which makes use of the progress rates was developed to treat the kinetic data obtained from continuous monitoring of the reaction progress with <i>in situ</i> FT-IR.

Kinetic Study of Disulfonimide Catalyzed Cyanosilylation of Aldehyde Using a Method of Progress Rates

Kinetic study of organic reactions, especially multistep catalytic reactions, is crucial to in-depth understanding of reaction mechanisms. Here we report our kinetic study of the chiral disulfonimide catalyzed cyanosilylation of aldehyde, which reveals that two molecules of TMSCN are involved in the rate-determining C-C bond forming step. In addition, the apparent activation energy, enthalpy of activation and entropy of activation were deduced through the study of temperature dependence of the reaction rates. More importantly, a novel and efficient method which makes use of the progress rates was developed to treat the kinetic data obtained from continuous monitoring of the reaction progress with <i>in situ</i> FT-IR.

Ground state chemistry under vibrational strong coupling: dependence of thermodynamic parameters on the Rabi splitting energy

Vibrational strong coupling (VSC) is currently emerging as a tool to control chemical dynamics. Here we study the impact of strong coupling strength, given by the Rabi splitting energy (ħΩR), on the thermodynamic parameters associated with the transition state of the desilylation reaction of the model molecule 1-phenyl-2-trimethylsilylacetylene. Under VSC, the enthalpy and entropy of activation determined from the temperature-dependent kinetic studies varied nonlinearly with the coupling strength. The thermodynamic parameters of the noncavity reaction did not show noticeable variation, ruling out concentration effects other than the enhanced ħΩR for the changes observed under VSC. The difference between the total free energy change under VSC and in noncavity was relatively smaller possibly because the enthalpy and entropy of activation compensate each other. This thermodynamic study gives more insight into the role of collective strong coupling on the transition state that leads to modified dynamics and branching ratios.

Density, Viscosity, and Excess Properties of Ternary Aqueous Mixtures of MDEA + MEA, DMEA + MEA, and DEEA + MEA

This study presents the measured densities and viscosities of three ternary aqueous mixtures of tertiary and primary amines. The tertiary amines of n-methyldiethanolamine (MDEA), dimethylethanolamine (DMEA), diethylethanolamine (DEEA), and the primary amine monoethanolamine (MEA) at different concentrations (mass%) were mixed to prepare the liquid mixtures. The excess molar volume VE of the mixtures was analyzed using measured densities to acquire a better understanding of the molecular packing and intermolecular interactions in the mixtures. The excess free energy of activation ∆GE* and excess entropy of activation ∆SE* for viscous flow were determined from the measured viscosities by implementing the theory of rate processes of Eyring. Correlations based on the Redlich–Kister type polynomial were adopted to correlate the excess properties VE and ∆GE* as a function of the amine mole fraction and temperature. The results showed that the correlations were able to represent the measured data with satisfactory accuracies for engineering calculations.