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Context: The performance of pristine and Pd-doped WO3 acetone gas sensors is calculated theoretically and compared with available experimental results. Temperature, humidity, and acetone concentration variation are considered in the present work. Transition state theory calculates Gibbs free energy of transition, including its components enthalpy and entropy of transition or activation. The variation of Pd doping concentration is used to obtain the maximum response and lowest response time for the optimum performance of the gas sensor. The present theory considers the reduction of acetone gas concentration as acetone reaches its autoignition temperature. Acceptable agreement between theory and experiment is obtained. The acceptance includes the decrease of Gibbs free energy with doping percentage, variation of temperature exponent to the power twelve in the considered reactions, and reduction of response time with the increase of temperature. Methods: Density functional theory at the B3LYP level is used. 6-311G** basis set (for O atoms) and SDD (for heavy Pd and W atoms) are used to optimize the structures examined in the present work. The Gaussian 09 program and accompanying software were used to perform the current tasks. [ABSTRACT FROM AUTHOR]

A variation of the topological constraint theory is proposed where an atomic network is modeled as a collection of rigid polytopes, and which explicitly distinguishes the bond angle constraints as well as rigid bond angles from flexible ones. The proposed theory allows for direct quantitative estimation of the fraction f of zero-frequency or floppy modes of the network. A preliminary model is proposed to connect the theory to the two key experimental observables that characterize glass-forming liquids, i.e., the glass transition temperature Tg and fragility m. The predicted values are tested against the literature data available for binary and ternary chalcogenides in the Ge-As-Se system. The Tg is related to f in this model by the activation entropy associated with the bond scission-renewal dynamics that is at the heart of transport and relaxation in glass-forming liquids. On the other hand, the large and temperature-dependent conformational entropy contribution of the 1-polytopes, i.e., the selenium chain elements in these chalcogenide glass-forming liquids, plays a key role in controlling the variation of m with f.

A variation of the topological constraint theory is proposed where an atomic network is modeled as a collection of rigid polytopes, and which explicitly distinguishes the bond angle constraints as well as rigid bond angles from flexible ones. The proposed theory allows for direct quantitative estimation of the fraction f of zero-frequency or floppy modes of the network. A preliminary model is proposed to connect the theory to the two key experimental observables that characterize glass-forming liquids, i.e., the glass transition temperature Tg and fragility m. The predicted values are tested against the literature data available for binary and ternary chalcogenides in the Ge-As-Se system. The Tg is related to f in this model by the activation entropy associated with the bond scission-renewal dynamics that is at the heart of transport and relaxation in glass-forming liquids. On the other hand, the large and temperature-dependent conformational entropy contribution of the 1-polytopes, i.e., the selenium chain elements in these chalcogenide glass-forming liquids, plays a key role in controlling the variation of m with f.

Elongation factor P (EF-P) and its eukaryotic homolog eIF5A are auxiliary translation factors that facilitate peptide bond formation when several sequential proline (Pro) residues are incorporated into the nascent chain. EF-P and eIF5A bind to the exit (E) site of the ribosome and contribute to favorable entropy of the reaction by stabilizing tRNA binding in the peptidyl transferase center of the ribosome. In most organisms, EF-P and eIF5A carry a posttranslational modification that is crucial for catalysis. The chemical nature of the modification varies between different groups of bacteria and between pro- and eukaryotes, making the EF-P-modification enzymes promising targets for antibiotic development. In this review, we summarize our knowledge of the structure and function of EF-P and eIF5A, describe their modification enzymes, and present an approach for potential drug screening aimed at EarP, an enzyme that is essential for EF-P modification in several pathogenic bacteria.

Acidic zeolites are effective catalysts for the cracking of large hydrocarbon molecules into lower molecular weight products required for transportation fuels. However, the ways in which the zeolite structure affects the catalytic activity at Brønsted protons are not fully understood. One way to characterize the influence of the zeolite structure on the catalysis is to study alkane cracking and dehydrogenation at very low conversion, conditions for which the kinetics are well defined. To understand the effects of zeolite structure on the measured rate coefficient (kapp ), it is necessary to identify the equilibrium constant for adsorption into the reactant state (Kads-H+ ) and the intrinsic rate coefficient of the reaction (kint ) at reaction temperatures, since kapp is proportional to the product of Kads-H+ and kint . We show that Kads-H+ cannot be calculated from experimental adsorption data collected near ambient temperature, but can, however, be estimated accurately from configurational-bias Monte Carlo (CBMC) simulations. Using monomolecular cracking and dehydrogenation of C3 -C6 alkanes as an example, we review recent efforts aimed at elucidating the influence of the acid site location and the zeolite framework structure on the observed values of kapp and its components, Kads-H+ and kint .

The Gibbs energy Î" G kp(Ď„, T) of kink pair formation on screw dislocations in bcc Nb has been determined as a function of shear stress Ď„ at different temperatures T â©˝ 100 K using an accelerated molecular dynamics method and a bond-boost potential. From Î" G kp(Ď„, T), the stress dependence of the entropy and the enthalpy of kink pair formation could be obtained using standard thermodynamic relations. The entropy of formation increases with increasing shear stress, following a phenomenologically predicted Ď„ 1/2 dependence. [ABSTRACT FROM AUTHOR]

We analyzed the kinetics and thermodynamics of amyloid fibril formation by the amyloidogenic variant of apolipoprotein A-I and αsynuclein based on the Finke-Watzky two-step model of a homogeneous nucleation followed by autocatalytic fibril growth. The results demonstrated that in apoA-I, the nucleation process is enthalpically unfavorable but entropically favorable likely because of the desolvation of hydrophobic regions in the molecule, whereas the nucleation of α-synuclein is enthalpically and entropically unfavorable. Interestingly, Parkinson’s disease-related mutation and C-terminal truncation in α-synuclein were found to decrease the enthalpic barrier for nucleation, thereby promoting autocatalytic nucleation in fibril formation. [ABSTRACT FROM AUTHOR]

Recent experimental work has shown that variations in the confinement of n-butane at Brønsted acid sites due to changes in zeolite framework structure strongly affect the apparent and intrinsic enthalpy and entropy of activation for cracking and dehydrogenation. Quantum chemical calculations have provided good estimates of the intrinsic enthalpies and entropies of activation extracted from experimental rate data for MFI, but extending these calculations to less confining zeolites has proven challenging, particularly for activation entropies. Herein, we report our efforts to develop a theoretical model for the cracking and dehydrogenation of n-butane occurring in a series of zeolites containing 10-ring channels and differing in cavity size (TON, FER, -SVR, MFI, MEL, STF, and MWW). We combine a QM/MM approach to calculate intrinsic and apparent activation parameters, with thermal corrections to the apparent barriers obtained from configurational-bias Monte Carlo simulations, to account for configurational contributions due to global motions of the transition state. We obtain good agreement between theory and experiment for all activation parameters for central cracking in all zeolites. For terminal cracking and dehydrogenation, good agreement between theory and experiment is found only at the highest confinements. Experimental activation parameters, especially those for dehydrogenation, tend to increase with decreasing confinement. This trend is not captured by the theoretical calculations, such that deviations between theory and experiment increase as confinement decreases. We propose that, because transition states for dehydrogenation are later than those for cracking, relative movements between the fragments produced in the reaction become increasingly important in the less confining zeolites. (Chemical Equation Presented).

The ability of deep neural networks to form powerful emergent representations of complex statistical patterns in data is as remarkable as imperfectly understood. For deep ReLU networks, these are encoded in the mixed discrete–continuous structure of linear weight matrices and non-linear binary activations. Our article develops a new technique for instrumenting such networks to efficiently record activation statistics, such as information content (entropy) and similarity of patterns, in real-world training runs. We then study the evolution of activation patterns during training for networks of different architecture using different training and initialization strategies. As a result, we see characteristic- and general-related as well as architecture-related behavioral patterns: in particular, most architectures form bottom-up structure, with the exception of highly tuned state-of-the-art architectures and methods (PyramidNet and FixUp), where layers appear to converge more simultaneously. We also observe intermediate dips in entropy in conventional CNNs that are not visible in residual networks. A reference implementation is provided under a free license1.

[Display omitted] • The transition rate shows an Arrhenius – antiArrhenius crossover. • The activation entropy depends on both temperature and stress. • The activation volume mainly depends on stress and much less on temperature. • The theoretical approaches do not match molecular dynamics results. • The minimum energy path is crucial to obtain an accurate activation free energy. Dislocations are the primary carriers of plasticity in metallic materials. Understanding the basic mechanisms for dislocation movement is paramount to predicting the material mechanical response. Relying on atomistic simulations, we observe a transition from non-Arrhenius to Arrhenius behavior in the rate of an edge dislocation overcoming the long-range elastic interaction with a prismatic loop in tungsten. Close to the critical resolved shear stress, the process shows a non-Arrhenius behavior at low temperatures. However, as the temperature increases, the activation entropy starts to dominate, leading to a traditional Arrhenius-like behavior. We have computed the activation entropy analytically along the minimum energy path following Schoeck's method [1] , which captures the cross-over between anti-Arrhenius and Arrhenius domains. Also, the Projected Average Force Integrator (PAFI) [2] , another simulation method to compute free energies along an initial transition path, exhibits considerable concurrence with Schoeck's formalism. We conclude that entropic effects need to be considered to understand processes involving dislocations bypassing elastic barriers close to the critical resolved shear stress. More work needs to be performed to fully understand the discrepancies between Schoeck's and PAFI compared to molecular dynamics. [ABSTRACT FROM AUTHOR]

• Shear strain rate should be the independent variable in creep. • Dislocation creep is due to a single deformation mechanism not two. • Activation entropy is a component of the flow activation energy. • Results lie on similar activation energy – temperature curves. Previously published results on the power law creep of a selection of fcc, bcc and hcp pure metals are discussed using a modified Stokes – Einstein equation originally describing Newtonian viscosity of spherical particles in a fluid. Activation energy is modified to include terms representing activation enthalpy, activation entropy and the effect of strain rate. It is similar to the Dorn equation for power law creep but with strain rate rather than stress as the independent variable. Curves of activation energy vs shear rate are linear rather than having a discontinuity as have those with stress as independent variable. All metals have linear curves of activation energy at zero rate vs temperature, the slope of which reflects the activation entropy and is similar for all metals. Intercepts which represent activation enthalpy are dependent on lattice structure. [ABSTRACT FROM AUTHOR]

Cis‐N‐phenyl‐hexahydro‐2H‐benzo[d][1,3]oxazin‐2‐imines and cis‐N‐phenyl‐hexahydro‐2H‐benzo[d][1,3]thiazin‐2‐imines were prepared and subjected to Flash Vacuum Pyrolysis (FVP). NH− and NCH3− oxazines reacted at lower temperatures than the thio‐ analogs, showing lower thermal stability, while NCH2Ph− compounds presented the opposite behavior. Oxazines and thiazines yielded different products through homolytic fragmentations of the heterocycle moiety, the stability of which increased with the N− substitution. Based on the analysis of the reaction temperatures and the unraveling of the obtained products, it is proposed that any heterocyclic ring‐opening reactions (initiated by X3−C4, C8a−N1, or C2−X3 bond rupture) require less energy than the retro‐Diels–Alder process (RDA) that yields butadiene. This concerted reaction path is only achieved at temperatures higher than 470 °C. Kinetic measurements reveal negative entropies of activation, which suggest a partially concerted way of reaction or slightly asynchronous fragmentation processes, with higher energy of activation (Ea) values for the N‐substituted derivatives compared to the unsubstituted ones. Experimental results agree with calculations at the DFT level (B3LYP/6‐311+G(d,p)) and M06‐2X (6‐311+G(d,p)) from Gaussian09 software. [ABSTRACT FROM AUTHOR]

Summary: In this research, the influence of temperature on the degradation of carotenoids, vitamin C and provitamin A in tree tomato juice was studied at 70, 80 and 90 °C. The thermal processing significantly reduced (P < 0.001) the concentration of the bioactive compounds, and the thermal degradation in the evaluated phytochemicals fit a kinetic first order, with the following activation energies (Ea, kJ mol−1): α‐carotene (69.75), β‐carotene (59.50), provitamin A (51.67), zeaxanthin (43.66), vitamin C (41.27), lycopene (18.84) and β‐cryptoxanthin (18.23). The kinetic study and thermodynamic analysis of the tree tomato juice showed that the degree of thermoresistance in the phytonutrients responded in the following order: β‐cryptoxanthin > lycopene > vitamin C > zeaxanthin > provitamin A > β‐carotene > α‐carotene. This study benefits engineering processes interested in the design and optimisation of thermal processes aimed at preserving the nutritional quality of tree tomato juice. [ABSTRACT FROM AUTHOR]

A variation of the topological constraint theory is proposed where an atomic network is modeled as a collection of rigid polytopes, and which explicitly distinguishes the bond angle constraints as well as rigid bond angles from flexible ones. The proposed theory allows for direct quantitative estimation of the fraction f of zero-frequency or floppy modes of the network. A preliminary model is proposed to connect the theory to the two key experimental observables that characterize glass-forming liquids, i.e., the glass transition temperature Tg and fragility m. The predicted values are tested against the literature data available for binary and ternary chalcogenides in the Ge-As-Se system. The Tg is related to f in this model by the activation entropy associated with the bond scission-renewal dynamics that is at the heart of transport and relaxation in glass-forming liquids. On the other hand, the large and temperature-dependent conformational entropy contribution of the 1-polytopes, i.e., the selenium chain elements in these chalcogenide glass-forming liquids, plays a key role in controlling the variation of m with f.

Many non-Newtonian materials have viscosities proportional to a power of shear rate. Although, generally, such relationships are regarded as being empirical, it is shown that power-law behavior arises when structure change with shear rate tends to saturation and results in flow activation energy being inversely proportional to shear rate. A temperature-dependent power-law index is predicted as is observed. Viscosity measurements are presented for a 10% sodium carboxymethylcellulose solution. It was found that both activation entropy and enthalpy decreased with shear rate, the former producing a small shear thickening and the latter a dominant shear thinning contribution to flow. [ABSTRACT FROM AUTHOR]

Pyrolysis processes of typical biomass, such as corn stalk and birch chips, were investigated by thermogravimetric analysis (TGA). The apparent activation energy and pre-exponential factor were calculated with the adoption of the improved Coats-Redfern integral method, 46 types of common mechanism functions, and the least square and iterative methods. By applying basic parameters of biomass pyrolysis, a reaction rate constant, activation entropy and activation enthalpy, activation Gibbs free energy, and the steric-hindrance factor were all calculated. Results showed that biomass pyrolysis can be divided into two primary reaction zones (Event 3 and Event 4). Event 3 is focused by cellulose and hemicellulose. Event 4 is oriented by lignin and cellulose. The thermogravimetric curves of the two biomass types under carbon dioxide and nitrogen atmospheres were roughly similar. The reaction mechanism function is 1 - alpha. It is possible to use activation entropy to represent the pre-exponential factor and to use the steric hindrance factor to predict the reaction rate.

Abstract: The monomolecular cracking rates of propane and n‐butane over MFI, CHA, FER and TON zeolites were determined simultaneously with the coverage of active sites at reaction condition using IR operando spectroscopy. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. The results show that the zeolite confinement mediates enthalpy–entropy trade‐offs only at the adsorbed state, leaving the true activation energy insensitive to the zeolite or alkane structure while the activation entropy was found to increase with the confinement. Hence, relative cracking rates of alkanes within zeolite pores are mostly governed by activation entropy. [ABSTRACT FROM AUTHOR]

ABSTRACT The specific role of acetonitrile and methoxypropionitrile, as accelerators of the relaxation dynamics of polyvinyl butyral (PVB), was investigated in polymer/additive mixtures with a saturation liquid content. The aim was to improve the ionic mobility of PVB-based solid electrolytes to be used in solid dye-sensitized solar cells. Mechanical and dielectric relaxation measurements between 120 K and 380 K revealed that the α-relaxation observed above 330 K in dry-PVB is shifted quite below room temperature in PVB/additives. Both the additives cause a growing intermolecular cooperativity, the sub-glass β-relaxation exhibiting a strength enhanced by a factor 3 and a frequency factor which increases from 1015 s−1 to 1021 s−1. This discloses an activation entropy as high as 165.7 J/K mol in comparison to 40.8 J/K mol in dry-PVB. It is suggested the existence of cooperative transitions, mainly driven by bridges formed through additive molecules, which influence both short- and long-scale segmental motions and also favor the ion dynamics in PVB/additive/electrolyte systems. The room temperature ionic conductivity σrt exhibits large changes from 6.4*10−14 S/m in dry PVB, through 1.5*10−8 S/m in PVB/LiI, to 2.45*10−5 S/m in PVB/MPN/LiI. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 340-346 [ABSTRACT FROM AUTHOR]

Measurements of thermogravimetry, dynamic mechanical and dielectric analysis, and infrared absorption have been performed in polyvinyl butyral (PVB) to investigate the effect of absorbed water on relaxation dynamics. Increasing water content plasticizes PVB, also causing a growing intermolecular cooperativity mainly for the secondary relaxation motions. Mechanical and dielectric β-relaxations for dry- and wet-PVB fit onto the same Arrhenius plots showing the very close nature of underlying mechanisms. In particular, the sub-glass mechanical β-relaxation in wet-PVB exhibits a frequency factor which increases up to 10 16 s −1 , disclosing an activation entropy as high as about 59 J/Kmol. It is suggested the existence of cooperative transitions of relaxing side units in adjacent chains, mainly driven by bridges formed through water molecules between the hydroxyl groups of vinyl alcohol segments. Below the glass transition temperature T g , the bridges are mechanically stable and give rise to an increase of the elastic modulus by more than a factor 2 when compared to that of a fully dry-PVB. [ABSTRACT FROM AUTHOR]

Reaction rates of toluene disproportionation (A) and cumene cracking (B) normalized by the number of Brønsted acid sites were analyzed on aluminosilicates. The activation entropy showed linear and compensatory relationship against the activation enthalpy. The slope of entropy-enthalpy plot was in the order of (B) > (A) > small alkane cracking, whereas the intercept on the horizontal axis was in the order of propane and isobutane cracking > linear C4–8 alkanes and iso-pentane cracking > (A) > (B). The former is consistent with the bulkiness of reactant, while the latter is consistent with intrinsic difficulty of formation of intermediate cations. [ABSTRACT FROM AUTHOR]

Experiments on aqueous suspensions of Fe 2 O 3 particles indicated that the viscosity increased with temperature rather than decreased as is usual and, in terms of the Arrhenius law, the activation energy appeared to be negative. Results were interpreted in terms of an activation energy in which the activation entropy becomes important. The energy required for flow is partially used to break up the colloidal structure of the suspensions and as the structure becomes more stable at higher temperatures, the viscosity increases. Results can be interpreted in terms of a kinetic equation having positive valued activation enthalpies together with negative valued activation entropies. [ABSTRACT FROM AUTHOR]

Cross-slip of screw dislocations in crystalline solids is a stress-driven thermally activated process essential to many phenomena during plastic deformation, including dislocation pattern formation, strain hardening, and dynamic recovery. Molecular dynamics (MD) simulation has played an important role in determining the microscopic mechanisms of cross-slip. However, due to its limited timescale, MD can only predict cross-slip rates in high-stress or high-temperature conditions. The transition state theory can predict the cross-slip rate over a broad range of stress and temperature conditions, but its predictions have been found to be several orders of magnitude too low in comparison to MD results. This discrepancy can be expressed as an anomalously large activation entropy whose physical origin remains unclear. Here, we resolve this discrepancy by showing that the large activation entropy results from anharmonic effects, including thermal softening, thermal expansion, and soft vibrational modes of the dislocation. We expect these anharmonic effects to be significant in a wide range of stress-driven thermally activated processes in solids.

In this research, Daturametel Linn seed oil was investigated for the first time as a promising non-conventional feedstock for preparation of biodiesel fuel. The maximum extraction of oil was observed to be 38.57 (wt) % and the activation energy Ea (25.8 kJ mol −1 ) was calculated. Further the thermodynamic properties for oil extraction were determined as activation enthalpy = 25.051 kJ mol −1 , activation entropy = −241.25 J mol −1 , and the Gibb's energy = 105.39 kJ mol −1 . This present study also reports the new single-step ultrasound production of biodiesel from high fatty acid D.metel Linn oil using sulfuryl chloride as catalysts in which 95.50% yield was achieved with 2 h. Different reaction parameters for oil extraction and biodiesel production were optimized. This analysis confirms that Daturametel Linn biodiesel is appropriate alternative to petroleum diesel with recommended fuel properties as per specified standards. [ABSTRACT FROM AUTHOR]

Tricyclo-DNA (tcDNA) is a sugar-modified analogue of DNA currently tested for the treatment of Duchenne muscular dystrophy in an antisense approach. Tandem mass spectrometry plays a key role in modern medical diagnostics and has become a widespread technique for the structure elucidation and quantification of antisense oligonucleotides. Herein, mechanistic aspects of the fragmentation of tcDNA are discussed, which lay the basis for reliable sequencing and quantification of the antisense oligonucleotide. Excellent selectivity of tcDNA for complementary RNA is demonstrated in direct competition experiments. Moreover, the kinetic stability and fragmentation pattern of matched and mismatched tcDNA heteroduplexes were investigated and compared with non-modified DNA and RNA duplexes. Although the separation of the constituting strands is the entropy-favored fragmentation pathway of all nucleic acid duplexes, it was found to be only a minor pathway of tcDNA duplexes. The modified hybrid duplexes preferentially undergo neutral base loss and backbone cleavage. This difference is due to the low activation entropy for the strand dissociation of modified duplexes that arises from the conformational constraint of the tc-sugar-moiety. The low activation entropy results in a relatively high free activation enthalpy for the dissociation comparable to the free activation enthalpy of the alternative reaction pathway, the release of a nucleobase. The gas-phase behavior of tcDNA duplexes illustrates the impact of the activation entropy on the fragmentation kinetics and suggests that tandem mass spectrometric experiments are not suited to determine the relative stability of different types of nucleic acid duplexes. [ABSTRACT FROM AUTHOR]

This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel's Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms. [ABSTRACT FROM AUTHOR]

[Display omitted] • A linear relationship for the activation energies and activation entropies existed over these catalysts. • Promoters altered the CO conversion rate by changing the surface CH x concentration. • The essence of change in product distribution is the alteration of carbon chain growth rate constant. The fundamentals of promoter effects in the Fischer − Tropsch synthesis over Co-based catalysts were systematically investigated by employing the Rh, Ir, Sb and Ga as promoters of Co/Al 2 O 3. Various characterizations showed the higher dispersion and reducibility over Rh- and Ir- promoted catalysts would cause a promoted adsorption property, while the Sb- and Ga- promoted catalysts showed a contrary result because the formation of alloy suppressed the accessibility of Co species. Based on the experimental results and kinetic calculations, a linear relationship for the activation energies of these catalysts as a function of activation entropies was proposed. Besides, steady state isotopic transient kinetic analysis (SSITKA) revealed that promoters mainly affected the surface CH x concentration to alter the CO reaction rate, and the chain growth rate constants would affect the product distribution. Since CoRhA and CoIrA greatly enhanced the CH x concentration and inhibited the chain growth ability, they owned a higher CO reaction rate and CH 4 selectivity. While the CoSbA and CoGaA suppressed the CH x concentration and intrinsic activity, but enhanced the chain growth ability, thereby revealing a lower CO reaction rate and CH 4 selectivity. Furthermore, the reactivity and selectivity difference were attributed to the modification of adsorption strength dictated by the enthalpy of activation on cobalt catalysts with different promoters. These findings provide kinetic insights into the promoter effects and pave the way for optimizing catalysts. [ABSTRACT FROM AUTHOR]

Elongation factor P (EF-P) and its eukaryotic homolog eIF5A are auxiliary translation factors that facilitate peptide bond formation when several sequential proline (Pro) residues are incorporated into the nascent chain. EF-P and eIF5A bind to the exit (E) site of the ribosome and contribute to favorable entropy of the reaction by stabilizing tRNA binding in the peptidyl transferase center of the ribosome. In most organisms, EF-P and eIF5A carry a posttranslational modification that is crucial for catalysis. The chemical nature of the modification varies between different groups of bacteria and between pro- and eukaryotes, making the EF-P-modification enzymes promising targets for antibiotic development. In this review, we summarize our knowledge of the structure and function of EF-P and eIF5A, describe their modification enzymes, and present an approach for potential drug screening aimed at EarP, an enzyme that is essential for EF-P modification in several pathogenic bacteria., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (©2023TheAuthors.PublishedbyElsevierB.V.)

In this work, resonant ejection coupled with surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer is used to examine fragmentation kinetics of two singly protonated hexapeptides, RYGGFL and KYGGFL, containing the basic arginine residue and less basic lysine residue at the N-terminus. The kinetics of individual reaction channels at different collision energies are probed by applying a short ejection pulse (1 ms) in resonance with the cyclotron frequency of a selected fragment ion and varying the delay time between ion-surface collision and resonant ejection while keeping total reaction delay time constant. Rice-Ramsperger-Kassel-Marcus (RRKM) modeling of the experimental data provides accurate threshold energies and activation entropies of individual reaction channels. Substitution of arginine with less basic lysine has a pronounced effect on the observed fragmentation kinetics of several pathways, including the b 2 ion formation, but has little or no effect on formation of the b 5 +H 2 O fragment ion. The combination of resonant ejection SID, time- and collision energy-resolved SID, and RRKM modeling of both types of experimental data provides a detailed mechanistic understanding of the primary dissociation pathways of complex gaseous ions. [ABSTRACT FROM AUTHOR]

The anomerization of monosaccharides is a very important process to understand how their stereoisomers are stabilized in aqueous solutions. For glucose and mannose, it has been known that α - and β -anomers of hexopyranose exist as the major components. In order to examine the anomerization pathway for glucose and mannose in aqueous solutions, it is indispensable to determine the thermodynamic parameters such as the activation energy, the activation Gibbs free energy (Δ G ‡ ), enthalpy (Δ H ‡ ), and entropy (Δ S ‡ ). Although several research groups reported these quantities in aqueous solution, they have still been controversial especially for Δ S ‡ . In this paper, we employ 1 H NMR spectroscopy for monitoring the population of both α - and β -anomers of glucose and mannose. The contribution of Δ S ‡ to Δ G ‡ for glucose in water is estimated to be ca. 30%, while that for mannose is 8.0%. The large difference in Δ S ‡ suggests that the anomerization pathway is not the same for glucose and mannose. [ABSTRACT FROM AUTHOR]

The kinetics of Pu(IV) reduction with zinc amalgam under different conditions [HSO concentration 0.5-4.0 M, initial Pu(IV) concentration (1.11-4.80) × 10 M, temperature 294.0-323.0 K] was studied by spectrophotometry. The kinetic scheme of the Pu(IV) transformation and the rate law were suggested, and the reduction rate constants were determined. The activation energies E and the thermodynamic functions of formation of the activated complex (activation Gibbs energy Δ G, enthalpy Δ H, entropy Δ S) were determined. [ABSTRACT FROM AUTHOR]

A series of experiments on co-combustion of the retorting residue of Huadian oil shale and cornstalks at different blending proportions were performed on a Pyris-1 thermogravimetric analyzer (TGA) to investigate the mechanism of the reactions involved. Moreover, the abrupt curvature changes of thermogravimetric (TG) curves and the multi-peaks and -shoulders of differential thermal gravity (DTG) curves for the blends were analyzed based on a simulation model of multi-component combustion. Results showed that the processes of combustion represented a multistage procedure of a clearly segmented nature. The processes can be divided into three stages of different temperature ranges: the first stage (135-380 °C), the second stage (380-560 °C) and the third stage (560-700 °C). With increasing blending ratio of cornstalks, the free energy of activation of combustion in the first and second stages is much lower than that in the third stage. Meanwhile, the continuous reaction processes of the samples combustion were analyzed by the Kissinger-Akahira-Sunose (KAS) kinetics model. Results showed that the activation enthalpy, activation entropy and free energy of activation of the samples combustion in its different stages varied. Moreover, with the addition of cornstalks, the portion of the ordered structure of activated molecules increased and the combustion characteristics of the retorting residue improved. [ABSTRACT FROM AUTHOR]

The kinetics of reduction of U(VI) with zinc amalgam at HSO concentrations of 0.5-4.0 M, initial UO concentrations of (2.08-40.00) × 10 M, and temperatures of 295.0-325.0 K was studied by spectrophotometry. The kinetic scheme of the UO transformation, the rate law, and the reduction rate constants were determined. The activation energy E and the thermodynamic functions of formation of the activated complex (Gibbs energy Δ G, enthalpy Δ H, and entropy Δ S of activation) were calculated. [ABSTRACT FROM AUTHOR]

Many suspensions of practical importance exhibit non-Newtonian fluid behaviour. For a given particle concentration and temperature, these often have relative viscosities that vary with shear rate and this necessitates modifications to the frequently applied Krieger–Dougherty equation. A simple way to analyse viscosity data is by consideration of the activation energy. It is demonstrated as an example of the approach that the properties of a non-Newtonian suspension of starch in a carboxymethylcellulose solution may be described simply in terms of the activation entropy which can be interpreted as a semi- empirical measure of the degree to which structural re-arrangement occurs during flow. [ABSTRACT FROM AUTHOR]

• Amino acid ionic liquids [C 4 Dmim][Gly], [C 4 Dmim][Ala] and [C 4 Dmim][Thr] were prepared. • The values of ρ , γ and η for three binary mixtures of ILs with H 2 O were measured. • The surface tensions of three binary mixtures of ILs with H 2 O were predicted. • The variation trend of V E (or g s E) and x 1 for binary mixture was studied. • The calculated values of Δ η , Δ G ≠ r , Δ S ≠ r and Δ H ≠ r were obtained. Amino acid ionic liquids (ILs) 1-butyl-2,3-dimethylimidazolium glycine ([C 4 Dmim][Gly]), 1-butyl-2,3-dimethylimidazolium alanine ([C 4 Dmim][Ala]) and 1-butyl-2,3-dimethylimidazolium threonine ([C 4 Dmim][Thr]) were prepared. Over the temperature from (288.15–318.15) K, the density, surface tension and viscosity for binary system mixtures of ILs with H 2 O were measured, and excess thermodynamic properties and activation properties for viscous flow of these binary system mixtures were systematically studied. Secondly, the variation trend between excess molar volume (V E)/excess molar surface Gibbs energy (g s E) and mole fraction for ILs + H 2 O binary system mixtures was investigated. With the increase of mole fraction, the V E and g s E values of binary system mixtures increased firstly and then decreased, and they were positive value, which may be due to the weak chemical interaction between ILs and H 2 O in the mixture. Furthermore, according to the thermodynamic formula, the Gibbs energy of activation for viscous flow of the relative viscosity (Δ G ≠ r), activation entropy (Δ S ≠ r) and activation enthalpy (Δ H ≠ r) were calculated. Over the entire concentration range, the Δ G ≠ r values for binary system mixtures of ILs with H 2 O were negative value, and the result was in good agreement with relative viscosity (η r). [ABSTRACT FROM AUTHOR]

This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel’s Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms.