Temperature Dependence Of Kinetics Research Articles

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Field-domain rapid-scan EPR at 240 GHz for studies of protein functional dynamics at room temperature

We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ′ and χ′′, from their combined magnitude (I2+Q2). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×106 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state.

Development and validation of an oil palm model for a wide range of planting densities and soil textures in Malaysian growing conditions

A semi-mechanistic oil palm growth and yield model called Sawit.jl was developed to account for a wide range of planting densities and soil textures under Malaysia's climate conditions. The model comprises components related to meteorology, photosynthesis, energy balance, soil water content, and crop growth. The model simulates instantaneous meteorological properties using daily weather data, calculates simultaneous evaporation from crop and soil with the Shuttleworth-Wallace model, determines soil water content through Darcy's law, and adapts a biochemical C3 model for photosynthesis. The model is also parameterized using updated measurements from the newer tenera oil palm, including temperature-dependent Rubisco kinetics, specific leaf area, and the partitioning of nutrients and dry matter between various tree parts. Sawit.jl was validated using historical field measurement data from seven Malaysian oil palm sites, encompassing palm ages spanning 1–23 years. These seven sites differed in soil type (Inceptisols and Ultisols), planting density (82–299 palms ha−1), soil texture (27–59 % clay and 7–67 % sand), and rainfall (1800–2800 mm yr−1). The model showed overall good accuracy in simulating oil palm parameters (except for trunk weight) across diverse conditions, with model agreement metrics ranging from 6 to 27 % for model absolute errors, −22 to +17 % for model bias, and 0.38 to 0.98 for the Kling-Gupta Efficiency index. The model also predicted the response of oil palm yield to abrupt rainfall changes, such as those during El Niño and La Niña events, while accounting for how soil texture, rainfall, and other meteorological factors influence water deficits and crop photosynthesis. However, model accuracy varied by site, planting density, and oil palm parameter. Model accuracy can be increased by more accurately representing the oil palm microclimate, incorporating fruiting activity, and refining the dry matter partitioning mechanism for the trunk.

A combined experimental and computational investigation on the OH radical and Cl atom-initiated reaction of 2,3-dichloropropene in troposphere

Temperature-dependent kinetics of OH radical and Cl atom-initiated reaction of an important halogenated alkene, 2,3-Dichloropropene (23DCP), were investigated using absolute and relative methods over 278–363 K. Pulsed laser photolysis – laser induced fluorescence technique and relative rate method using gas chromatography with flame ionization detector were employed for studying the kinetics of 23DCP with OH radical and Cl atom, respectively. The obtained Arrhenius expressions were kOH(expt)=(4.08 ± 1.63) × 10−13exp{(1043 ± 124)/T} cm3 molecule−1 s−1 and kCl(expt)=(1.54 ± 0.24) × 10−11exp{(705 ± 48)/T} cm3 molecule−1 s−1. Computational calculations were conducted to validate our experimental kinetic results and provide new insights into the importance of a particular pathway among all based on thermodynamic parameters. The addition of OH/Cl to the terminal carbon of the double bond present in 23DCP proved to be the predominant pathway across the selected temperature range for the present study (200–400 K). The degradation mechanism of these reactions was proposed by analyzing the products with the aid of gas chromatography with mass spectrometry. Calculating various atmospheric implication parameters can help to understand how the release of 23DCP may affect the troposphere.

CHIRAL SWITCHING CONTROL OF PHARMACEUTICAL SUBSTANCES

Objective: The aim of this study was to demonstrate that chiral switching should be recognized as a widespread phenomenon that extends beyond the production of pure enantiomeric drugs. Methods: To investigate the optical activity of substances from various chemical classes, enantiomers of chiral compounds (Sigma-Aldrich, USA) were chosen: valine and its racemic form (D-valine, L-valine, and racemic valine with optical purity ≥ 99%), L-ascorbic acid (content ≥ 99%), carbohydrates (D-glucose, D-galactose, L-galactose, contents ≥ 99.5%). Solutions were prepared using deuterium-depleted water (DDW–"light" water, D/H=4 ppm), natural deionized high-ohmic water (BD, D/H=140 ppm), and heavy water (99.9% D2O; Sigma-Aldrich). Optical activity was measured using the Atago POL-1/2 polarimeter. Results: One of the components in the racemic medication mixture can act as an inert agent, exhibit toxicity, or undergo undesirable biotransformation mechanisms, resulting in the formation of products with unknown properties. It has been established that a change in the deuterium/protium (D/H) ratio in water leads to a change in the equilibrium and kinetic characteristics of optically active compounds across various chemical classes, such as amino acids, carboxylic acids, and carbohydrates. An inequality was observed in the absolute values of the optical rotation of the L-and D-isomers of valine and galactose, depending on the D/H isotope ratio. The impact of chiral water clusters on optical rotation accounts for the sudden shift in the specific rotation of dilute solutions (less than 0.5%) of L-ascorbic acid in water, based on the D/H ratio. The influence of the isotopic composition of water was confirmed by studying the temperature-dependent mutarotation kinetics of D-glucose and L-and D-galactose in Arrhenius coordinates. The mutarotation process in natural high-resistivity water is characterized by an activation energy (Ea) of 40.8±1.4 kJ mol-1, while in deuterium-depleted water, Ea = 63.6±3.5 kJ mol-1. This results in a kinetic isotope effect for deuterium (KIED) of 1.6. Conclusion: Methodological approaches have been developed to control chiral switching based on the isotopic composition of water in vivo and in vitro. The study of changes in the optical activity of hierarchical structures in the human body, the influence of solvent properties on the mechanisms of optical rotation, as well as the use of KIED values, can be utilized to monitor various chiral transitions in vitro and living organisms.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics for High-Throughput Flow Battery Characterization

The library of redox-active organics that are potential candidates for electrochemical energy storage in flow batteries is exceedingly vast, necessitating high-throughput characterization of molecular lifetimes. Demonstrated extremely stable chemistries require accurate yet rapid cell cycling tests, a demand often frustrated by time-denominated capacity fade mechanisms. We have developed a high-throughput setup for elevated temperature cycling of redox flow batteries, providing a new dimension in characterization parameter space to explore. We utilize it to evaluate capacity fade rates of aqueous redox-active organic molecules, as functions of temperature. We demonstrate Arrhenius-like behavior in the temporal capacity fade rates of multiple flow battery electrolytes, permitting extrapolation to lower operating temperatures. Collectively, these results highlight the importance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime flow batteries.

Temperature-Dependent Kinetics of the Reactions of the Criegee Intermediate CH2OO with Hydroxyketones.

Though there is a growing body of literature on the kinetics of CIs with simple carbonyls, CI reactions with functionalized carbonyls such as hydroxyketones remain unexplored. In this work, the temperature-dependent kinetics of the reactions of CH2OO with two hydroxyketones, hydroxyacetone (AcOH) and 4-hydroxy-2-butanone (4H2B), have been studied using a laser flash photolysis transient absorption spectroscopy technique and complementary quantum chemistry calculations. Bimolecular rate constants were determined from CH2OO loss rates observed under pseudo-first-order conditions across the temperature range 275-335 K. Arrhenius plots were linear and yielded T-dependent bimolecular rate constants: kAcOH(T) = (4.3 ± 1.7) × 10-15 exp[(1630 ± 120)/T] and k4H2B(T) = (3.5 ± 2.6) × 10-15 exp[(1700 ± 200)/T]. Both reactions show negative temperature dependences and overall very similar rate constants. Stationary points on the reaction energy surfaces were characterized using the composite CBS-QB3 method. Transition states were identified for both 1,3-dipolar cycloaddition reactions across the carbonyl and 1,2-insertion/addition at the hydroxyl group. The free-energy barriers for the latter reaction pathways are higher by ∼4-5 kcal mol-1, and their contributions are presumed to be negligible for both AcOH and 4H2B. The cycloaddition reactions are highly exothermic and form cyclic secondary ozonides that are the typical primary products of Criegee intermediate reactions with carbonyl compounds. The reactivity of the hydroxyketones toward CH2OO appears to be similar to that of acetaldehyde, which can be rationalized by consideration of the energies of the frontier molecular orbitals involved in the cycloaddition. The CH2OO + hydroxyketone reactions are likely too slow to be of significance in the atmosphere, except at very low temperatures.

Relaxation kinetics of interface states and bulk traps in atomic layer deposited ZrO2/β-Ga2O3 metal-oxide-semiconductor capacitors

The study of interface states and bulk traps and their connection to device instability is highly demanded to achieve reliable β-Ga2O3 metal-oxide-semiconductor (MOS) devices. However, a comprehensive analysis of the capture/emission behavior of interface states and bulk traps can be challenging due to widespread time constant distribution. In this study, using capacitance transient measurement tools, trap states of the ZrO2/β-Ga2O3 MOS gate stack were explicitly investigated, particularly its bias- and temperature-dependent relaxation kinetics. As forward bias is enlarged, it is observed that the interface state density (Dit) increases by 12.6%. Two bulk traps with discrete levels identified as 0.43 eV (E1) and 0.74 eV (E2) below the conduction band minimum were extracted by deep-level transient spectroscopy. It is further revealed that the emission processes of E1 and E2 are thermally enhanced, while the capture processes remain insensitive to temperature. The electric-field dependence of E1 indicates that the dominant mechanism follows the rule of Poole–Frenkel emission. The capacitance–voltage (C–V) hysteresis deteriorated at a higher forward bias due to the higher trap density and increased population of trapped charges. These findings provide an important framework for future device optimization to improve the reliability and performance of β-Ga2O3 MOS devices.

Temperature-dependent aqueous OH kinetics of C2–C10 linear and terpenoid alcohols and diols: new rate coefficients, structure–activity relationship, and atmospheric lifetimes

Abstract. Aliphatic alcohols (AAs), including terpenoic alcohols (TAs), are ubiquitous in the atmosphere due to their widespread emissions from natural and anthropogenic sources. Hydroxyl radical (OH) is the most important atmospheric oxidant in both aqueous and gas phases. Consequently, the aqueous oxidation of the TAs by the OH inside clouds and fogs is a potential source of aqueous secondary organic aerosols (aqSOAs). However, the kinetic data, necessary for estimating the timescales of such reactions, remain limited. Here, bimolecular rate coefficients (kOHaq) for the aqueous oxidation of 29 C2–C10 AAs by hydroxyl radicals (OH) were measured with the relative rate technique in the temperature range 278–328 K. The values of kOHaq for the 15 AAs studied in this work were measured for the first time after validating the experimental approach. The kOHaq values measured for the C2–C10 AAs at 298 K ranged from 1.80 × 109 to 6.5 × 109 M−1 s−1. The values of activation parameters, activation energy (7–17 kJ mol−1), and average Gibbs free energy of activation (18 ± 2 kJ mol−1) strongly indicated the predominance of the H-atom abstraction mechanism. The estimated rates of the complete diffusion-limited reactions revealed up to 44 % diffusion contribution for the C8–C10 AAs. The data acquired in this work and the values of kOHaq for AAs, carboxylic acids, and carboxylate ions available in the literature were used to develop a modified structure–activity relationship (SAR). The SAR optimized in this work estimated the temperature-dependent kOHaq for all compounds under investigation with much higher accuracy compared to the previous models. In the new model, an additional neighboring parameter was introduced (F≥ (CH2)6), using the kOHaq values for the homolog (C2–C10) linear alcohols and diols. A good overall accuracy of the new SAR at 298 K (slope = 1.022, R2=0.855) was obtained for the AAs and carboxylic acids under investigation. The kinetic database (kOHaq values in this work and compiled literature data) was also used to further enhance the ability of SAR to predict temperature-dependent values of kOHaq in the temperature range 278–328 K. The calculated atmospheric lifetimes indicate that terpenoic alcohols and diols can react with the OH in aerosol, cloud, and fog water with liquid water content (LWC) ≥0.1 g m−3 and LWC ≥ 10−4 g m−3, respectively. The preference of terpenoic diols to undergo aqueous oxidation by the OH under realistic atmospheric conditions is comparable with terpenoic acids, making them potentially effective precursors of aqSOAs. In clouds, a decrease in the temperature will strongly promote the aqueous reaction with the OH, primarily due to the increased partitioning of WSOCs into the aqueous phase.

Temperature-Dependent Kinetics for the Reactions of Fen- (n = 2-17) and FexNiy- (x + y = 3-9) with O2: Comparison of Pure and Mixed Metal Clusters with Relevance to Meteor Radio Afterglows and Surface Oxidation.

Rate constants and product branching fractions were measured from 300-600 K for Fen- + O2 (n = 2-17) and for 300-500 K for FexNiy- + O2 (x + y = 3-9) using a selected-ion flow tube (SIFT) apparatus. Rate constants for 46 species are reported. All rate constants increased with increasing temperature, and several were in excess of the Langevin-Gioumousis-Stevenson (LGS) capture rate at elevated temperatures. As with previously studied transition metal anion oxidation reactions, the collision limit is treated as the sum of the LGS limit along with a hard-sphere contribution, allowing for determination of activation energies. These values are compared to each other along with previous results for Nin-. Measured rate constants for all three series (Fen-, Nin-, and FexNy-) vary over a relatively narrow range (1-5 × 10-10 cm3 s-1 at 300 K) being at least 15% of the collision rate constant. All reaction rate constants increase with temperature, described by small activation energies of 0.5-4 kJ mol-1. The data are consistent with an anticorrelation between the electron binding energy and rate constant, previously noted in other systems. The Fen- reaction produces a larger population of higher energy electrons than do the Nin- reactions, with FexNiy- producing an intermediate amount. The results suggest that the overall rate constant is limited by a small energetic barrier located at a large internuclear distance where electrostatic forces dominate, causing the potentials to be similar across systems, while the product formation is determined by the shorter-range, valence portion of the potential, which varies widely between systems.

Pressure and temperature dependent kinetics and the reaction mechanism of Criegee intermediates with vinyl alcohol: a theoretical study.

Criegee intermediates (CIs), the key intermediates in the ozonolysis of olefins in atmosphere, have received much attention due to their high activity. The reaction mechanism of the most simple Criegee intermediate CH2OO with vinyl alcohol (VA) was investigated by using the HL//M06-2X/def2TZVP method. The temperature and pressure dependent rate constant and product branching ratio were calculated using the master equation method. For CH2OO + syn-VA, 1,4-insertion is the main reaction channel while for the CH2OO + anti-VA, cycloaddition and 1,2-insertion into the O-H bond are more favorable than the 1,4-insertion reaction. The 1,4-insertion or cycloaddition intermediates are stabilized collisionally at 300 K and 760 torr, and the dissociation products involving OH are formed at higher temperature and lower pressure. The rate constants of the CH2OO reaction with syn-VA and anti-VA both show negative temperature effects, and they are 2.95 × 10-11 and 2.07 × 10-13 cm3 molecule-1 s-1 at 300 K, respectively, and the former is agreement with the prediction in the literature.

Enhanced condensation kinetics in aqueous microdroplets driven by coupled surface reactions and gas-phase partitioning.

Although aqueous microdroplets have been shown to exhibit enhanced chemical reactivity compared to bulk solutions, mechanisms for these enhancements are not completely understood. Here we combine experimental measurements and kinetic modeling to show the strong coupling of interfacial reactions and gas/droplet partitioning in the condensation reaction of pyruvic acid (PA) to yield zymonic acid (ZA) in acidic aqueous microdroplets. Experimental analysis of single microdroplets reveals the substantial influence of evaporation of PA and partitioning of water on the size-, relative humidity (RH)- and temperature-dependent sigmoidal reaction kinetics for the condensation reaction. A newly developed diffusion-reaction-partitioning model is used to simulate the complex kinetics observed in the microdroplets. The model can quantitatively predict the size and compositional changes as the reaction proceeds under different environmental conditions, and provides insights into how microdroplet reactivity is controlled by coupled interfacial reactions and the gas-phase partitioning of PA and water. Importantly, the kinetic model best fits the data when an autocatalytic step is included in the mechanism, i.e. a reaction step where the product, ZA, catalyzes the interfacial condensation reaction. Overall, the dynamic nature of aqueous microdroplet chemistry and the coupling of interfacial chemistry with gas-phase partitioning are demonstrated. Furthermore, autocatalysis of small organic molecules at the air-water interface for aqueous microdroplets, shown here for the first time, has implications for several fields including prebiotic chemistry, atmospheric chemistry and chemical synthesis.

Thermogravimetric study of metal–organic precursors and their suitability for hybrid molecular beam epitaxy

Although metal–organic (MO) precursors are widely used in technologically relevant deposition techniques, reports on their temperature-dependent evaporation and decomposition behaviors are scarce. Here, MO precursors of the metals Ti, V, Al, Hf, Zr, Ge, Ta, and Pt were subjected to thermogravimetric analysis to experimentally determine their vapor pressure curves and to gain insight into their temperature-dependent decomposition kinetics. Benzoic acid was used as a calibration standard and vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The obtained data is used to discuss the suitability of these MO precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular. All MOs, except for Ta- and one Ti-based MOs, were deemed suitable for gas inlet systems. The Ta-based MO demonstrated suitability for an effusion cell, while all MOs showed compatibility with cracker usage.Graphical

The temperature-dependent kinetics and bacteria regrowth by performic acid and sodium hypochlorite disinfection.

Sodium hypochlorite (NaOCl) has been widely used as a disinfectant in water and wastewater treatment, because of its high efficiency and low cost, whereas the bio-toxicity of its disinfection byproducts (DBPs) raised great concern. Performic acid (PFA) produces less DBPs and shows strong oxidation abilities. In this study, the effect of temperature on NaOCl and PFA disinfection as well as bacteria regrowth were evaluated. First, the inactivation of Escherichia coli, Staphylococcus aureus, and Bacillus subtilis by NaOCl and PFA at 4 and 20 °C, detected by cell cultured-based plate counting were fitted to kinetic models, and the predicted CTs were calculated. The results showed that NaOCl was more effective than PFA for E. coli and S. aureus inactivation, and the temperature was positively correlated to disinfection. Second, bacteria regrowth was evaluated at different temperatures (4 and 20 °C) of disinfection and storage. The results showed that the bacteria inactivated by NaOCl regrew prominently, especially for those inactivated at 4 and stored at 4 °C, probably through the mechanism of reactivation of viable but non-culturable (VBNC) bacteria. PFA was superior in suppressing bacteria regrowth, and it may be used as an alternate disinfectant in water treatment in cold environment.

Kinetic study of C1 criegee intermediate with diethylamine and ethylamine and their atmospheric implications

This paper investigates the pressure and temperature-dependent kinetics of CH2OO reacting with diethylamine (DEA) and ethylamine (EA) using the OH laser-induced fluorescence method. Pressure independence was observed within the range of 5.4–75 Torr. The rate coefficients for these reactions at 298 K are (2.49 ± 0.39) × 10−11 and (8.14 ± 1.25) × 10−12 cm3 molecule−1 s−1. The activation energies, determined from experiments conducted between 283 and 328 K, are (−2.01 ± 0.08) and (−1.35 ± 0.02) kcal mol−1. These reactions may contribute to the degradation of DEA and EA under specific environmental conditions.

The Influence of Homogenisation Parameters on the Microstructure and Hardness of AlMnFeMgSi(Zr) Wrought Alloys

The purpose of this investigation is to improve the mechanical properties of AlMnFeMgSi wrought alloys by forming a high number density of nano-scaled strengthening dispersoids during homogenisation annealing. The process chain for AlMnFeMgSi wrought alloys includes homogenisation annealing after continuous casting. In this step, inhomogeneities and segregations are dissolved and dispersoids are precipitated. The formed dispersoids hinder grain growth, but usually cannot increase the strength due to their coarse size of some 100 nm. Lower homogenisation temperatures should result in the precipitation of smaller dispersoids during homogenisation. The addition of Zr was investigated to increase this effect. Zr should form further dispersoids from the Al3Zr phase. This requires a fundamental understanding of the temperature-dependent kinetics and the nature of precipitation formation during homogenisation. For this purpose, the as-cast state is first characterised via differential scanning calorimetry. Subsequently, a large number of homogenisation parameters are investigated and quantified via hardness testing. The micro- and nanostructure are investigated for promising parameters and a particle analysis is performed. In the present study, it was possible to precipitate fine dispersoids of few 10 nm by reducing the homogenisation temperature, which resulted in a significant increase in hardness. Alloying with Zr enabled the precipitation of further dispersoids with a size of a few nm in a high number density, which further increased the strength.

Galactose isomerization to tagatose over MgBr2 follows a temperature-dependent reaction rate kinetics as predicted by first principles-based theories

Tagatose, a classified low-calorie sugar, possesses anti-hyperglycaemic and prebiotic characteristics. Therefore, it is considered a potential food additive supplement (sweetener) for lifestyle health problems in humans. While many reports on its production via biological and chemical methods have been published, the thermodynamic behavior of its synthesis using galactose is rarely focused on. Herein, we report the MgBr2-mediated galactose interconversion to tagatose (single-step) and its kinetic mechanism. The oppositely charged counterions (Mg2+ and Br‒) can induce the reaction via different pathways in a parallel fashion, i.e., the Mg2+ behaving as a Lewis acid can enable via a 1,2-hydride shift pathway, whereas the Br‒ offering the Brønsted basic sites via a proton transfer pathway. This resulted in a tagatose production as high as 22% and 73% selectivity within 60 min at 120 °C in water. Furthermore, the reaction has yielded a single co-product formation (talose up to 7%). From the inverse-gated quantitative NMR analysis, the contribution of the counterions in the reaction is roughly 52%:48% by Mg2+:Br‒. The determination of the temperature-dependent reaction kinetics (elementary steps) was made by employing the first-principles-based theories (i.e., transition state-Eyring theory for the proton transfer pathway that involves no hydride shift and Marcus theory for the hydride shift pathway). The energy calculations of the pathways made via DFT modeling suggested the higher feasibility of a hydride shift mechanism of galactose to tagatose.

Selection of lactic acid bacteria for biopreservation of salmon products applying processing-dependent growth kinetic parameters and antimicrobial mechanisms

Biopreservation using lactic acid bacteria (LAB) is a promising technology to prevent the growth of pathogenic microorganisms in fresh and mildly processed food. The main aim of this study was to select LAB, originally isolated from ready-to-eat (RTE) seafood, for biopreservation of fresh salmon and processed salmon products. Ten LAB strains (five Carnobacterium and five Leuconostoc) were selected based on previously demonstrated bioprotective properties to investigate their antimicrobial mechanisms and temperature-dependent growth kinetics in a sterile salmon juice model system. Furthermore, five strains (three Carnobacterium and two Leuconostoc) were selected to test process-dependent growth kinetic parameters relevant to the secondary processing of salmon. Two strains (Carnobacterium maltaromaticum 35 and C. divergens 468) showed bacteriocin-like activity against Listeria innocua, while inhibitory effect of cell-free supernatants (CFS) was not observed against Escherichia coli. All selected strains were able to grow in sterile salmon juice at tested temperatures (4, 8, 12 and 16 °C), with specific growth rates (μ) ranging from 0.01 to 0.04/h at 4 °C and reaching a maximum population density of 8.4–9 log CFU/ml. All five strains tested for process-dependent growth kinetic parameters were able to grow in the range of 0.5–5% NaCl and 0.13–0.26% purified condensed smoke (VTABB and JJT01), with inter- and intraspecies variation in growth kinetics. According to the temperature-dependent growth kinetics and antimicrobial assay results, two strains, Leuconostoc mesenteroides 68 (Le.m.68) and C. divergens 468 (C d.468), were selected for in situ test to validate their ability to grow in vacuum-packed fresh salmon at 4 °C. Both strains were able to grow at maximum growth rates of 0.29 ± 0.04/d for Le. m.68 and 0.39 ± 0.06/d for C.d.468, and their final concentrations were 7.91 ± 0.31 and 8.02 ± 0.25 log CFU/g, respectively. This study shows that LAB, originally isolated from RTE seafood, have promising potential as bioprotective strains in fresh and processed salmon products.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics to Accelerate Redox Flow Battery Active Material Characterization

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as promising and potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources for use over long discharge durations when the sun isn’t shining and the wind isn’t blowing. AORFBs could become preferred over Li-ion batteries for grid-scale stationary storage due to their potentially low-cost active materials made of earth-abundant elements, their inherent non-flammability, and the intrinsic decoupling of energy and power capacities in the flow battery design. Our group has demonstrated that calendar life, rather than cycle life, limits molecular lifetimes in AORFBs due to various molecular instabilities that lead to side reactions, thus inhibiting performance [1]. To accurately determine molecular fade rates, we utilize potentiostatic cycling to avoid artifacts caused by drifts in internal resistance and employ volumetrically unbalanced, compositionally symmetric cell configurations to distinguish molecular fade from membrane crossover or cell unbalancing. Redox-active organic molecule stability has improved to the point that the most stable chemistries degrade at less than 1% per year [2]. With further lifetime increases, the measurement of lower capacity fade rates necessitates higher precision coulometry methods [3] and thermally accelerated degradation protocols [4] to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade.We have developed a high-throughput setup for cycling AORFBs at elevated temperatures, providing a new dimension in the flow battery characterization space to explore. Capacity fade rates of previously published redox-active organic molecules, as functions of temperature, are evaluated in the high-throughput setup providing the ability to extrapolate fade rates to lower operating temperatures. The effect of temperature on electrochemical regeneration [5,6] of decomposed organic molecules is also explored. Collectively, these results highlight the importance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime AORFBs, which may enable massive grid penetration of intermittent renewable energy.[1] M.-A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods,” Journal of The Electrochemical Society , 165, A1466 (2018).[2] M. Wu, Y. Jing, A. A. Wong, E. M. Fell, S. Jin, Z. Tang, R. G. Gordon, M. J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors,” Chem, 6, 1432 (2020).[3] T. M. Bond, J. C. Burns, D. A. Stevens, H. M. Dahn, J. R. Dahn, "Improving Precision and Accuracy in Coulombic Efficiency Measurements of Li-Ion Batteries", Journal of The Electrochemical Society, 160, A521 (2013).[4] D. A. Stevens, R. Y. Ying, R. Fathi, J. N. Reimers, J. E. Harlow, J. R. Dahn, "Using High Precision Coulometry Measurements to Compare the Degradation Mechanisms of NMC/LMO and NMC-Only Automotive Scale Pouch Cells", Journal of The Electrochemical Society, 161, A1364 (2014).[5] M. Wu, M. Bahari, E. M. Fell, R. G. Gordon, M. J. Aziz, “High-performance anthraquinone with potentially low cost for aqueous redox flow batteries”, Journal of Materials Chemistry A, 9, 26709 (2021).[6] Y. Jing, E. W. Zhao, M.-A. Goulet, M. Bahari, E. M. Fell, S. Jin, A. Davoodi, E. Jónsson, M. Wu, C. P. Grey, R. G. Gordon, M. J. Aziz, “In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries,” Nature Chemistry, 14, 1103, (2022).Figure caption: Capacity fade rates of an anthraquinone derivative, measured in symmetric cells, as a function of temperature. Figure 1