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.

Enzymatic RNA Production from NTPs Synthesized from Nucleosides and Trimetaphosphate

<p>A mechanism of nucleoside triphosphorylation would have been critical in an evolving “RNA world” to provide high-energy substrates for reactions such as RNA polymerization. However, synthetic approaches to produce ribonucleoside triphosphoates (rNTPs) have suffered from conditions such as high temperatures or high pH that lead to increased RNA degradation, as well as substrate production that cannot sustain replication. We demonstrate that cyclic trimetaphosphate (cTmp) can react with nucleosides to form rNTPs under mild, prebiotically-relevant conditions, with second-order rate constants ranging from 1.7 x 10^–6 to 6.5 x 10^–6 M^–1 s^–1. The ATP reaction shows a linear dependence on pH and Mg²⁺, and an enthalpy of activation of 88 ± 4 kJ/mol. At millimolar nucleoside and cTmp concentrations, the rNTP production rate is sufficient to facilitate RNA synthesis by both T7 RNA polymerase and a polymerase ribozyme. We suggest that the optimized reaction of cTmp with nucleosides may provide a viable connection between prebiotic nucleotide synthesis and RNA replication.</p>

Enzymatic RNA Production from NTPs Synthesized from Nucleosides and Trimetaphosphate

<p>A mechanism of nucleoside triphosphorylation would have been critical in an evolving “RNA world” to provide high-energy substrates for reactions such as RNA polymerization. However, synthetic approaches to produce ribonucleoside triphosphoates (rNTPs) have suffered from conditions such as high temperatures or high pH that lead to increased RNA degradation, as well as substrate production that cannot sustain replication. We demonstrate that cyclic trimetaphosphate (cTmp) can react with nucleosides to form rNTPs under mild, prebiotically-relevant conditions, with second-order rate constants ranging from 1.7 x 10^–6 to 6.5 x 10^–6 M^–1 s^–1. The ATP reaction shows a linear dependence on pH and Mg²⁺, and an enthalpy of activation of 88 ± 4 kJ/mol. At millimolar nucleoside and cTmp concentrations, the rNTP production rate is sufficient to facilitate RNA synthesis by both T7 RNA polymerase and a polymerase ribozyme. We suggest that the optimized reaction of cTmp with nucleosides may provide a viable connection between prebiotic nucleotide synthesis and RNA replication.</p>

Enzymatic RNA Production from NTPs Synthesized from Nucleosides and Trimetaphosphate

<p>A mechanism of nucleoside triphosphorylation would have been critical in an evolving “RNA world” to provide high-energy substrates for reactions such as RNA polymerization. However, synthetic approaches to produce ribonucleoside triphosphoates (rNTPs) have suffered from conditions such as high temperatures or high pH that lead to increased RNA degradation, as well as substrate production that cannot sustain replication. We demonstrate that cyclic trimetaphosphate (cTmp) can react with nucleosides to form rNTPs under mild, prebiotically-relevant conditions, with second-order rate constants ranging from 1.7 to 6.5 µM^–1 s^–1. The ATP reaction shows a linear dependence on pH and Mg²⁺, and an enthalpy of activation of 88 ± 4 kJ/mol. At millimolar nucleoside and cTmp concentrations, the rNTP production rate is sufficient to facilitate RNA synthesis by both T7 RNA polymerase and a polymerase ribozyme. We suggest that the optimized reaction of cTmp with nucleosides may provide a viable connection between prebiotic nucleotide synthesis and RNA replication.<br></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.

A DFT Study of the Hexene Hydrogenation Catalysed by the Complex RuH(CO)(Cl)(PCy3): Monophosphine vs Diphosphine Paths

A DFT study of hexene hydrogenation catalysed by the RuH(CO)(Cl)(PCy3)2 complex is presented. The investigation explores the feasibility of two different mechanisms: the first exploits a single phosphine complex and the second uses a two phosphines complex. The energy barriers involving a hydrogen transfer have a ten kcal.mol-1 higher than the one obtained through the single-phosphine mechanism. These results confirm the experimental hypothesis claiming that the departure of a phosphine is favourable at the beginning of the reaction which is the substitution of the catalyst model RuHCl(CO)(PMe3)2 by the real catalyst RuHCl(CO)(PCy3)2 shows no significant influence on the energetic barriers of hexene hydrogenation mechanism. The most important step of the mechanism is the kinetically determining step. The heterolytic cleavage of ruthenium-complexed H2 molecule leads to the generation of two Ru-H bonds and the oxidation of the ruthenium from Ru(II) to Ru(IV). The energy profile of this step is not relative to an elementary reaction because a shouldering is observed after the transition state. This results in an unusual gradient norm profile with five extrema. This is a direct consequence of the asynchronous nature of the different processes taking place during this step. In the case of the model complex RuHCl(CO)(IMes)(PMe3) with IMes = ( N , N '-bis( mesityl)imidazol-2-ylidene), an increase of the free enthalpy of activation is observed during the kinetically determining step, which is in agreement with the experimental work.