Temperature-sensitive Reaction Research Articles

Au@AgPt core/cage nanoframes as photothermal catalyst for enhanced NIR-induced 4-nitrophenol reduction

The selection and optimization of catalysts have been a subject of considerable research interest in recent decades. Bimetallic and multimetallic nanocatalysts, comprised of plasmonic and catalytic components, have recently emerged as a promising approach to achieving high catalytic performance due to synergistic effects. In this study, an Au@AgPt core/cage nanoframe has been successfully fabricated. It features a controllable hollow silver-platinum alloy nanoframe with an in-built plasmonic gold nanorod, serving as a plasmon-enhanced photothermal catalyst for the reduction of 4-nitrophenol (4-NP). This well-designed trimetallic nanostructure exhibits a unique core-cage nanoframes structure and surface roughness, offering advantages in both composition and structure. The LSPR-excited local heating effect and hot-electron generation, as well as the intrinsic catalytic active sites, work synergistically and are highly beneficial for temperature-sensitive reaction of 4-NP reduction. Experimental results have shown that the optimized nanocatalysts of Au@AgPt-4, featuring an optimal Pt content and robust photothermal performance, display stable photothermal catalytic properties and the best photothermal catalytic performance compared with other nanostructures, completing the reduction reaction within approximately one minute. This study provides a rational design of nanoscale materials with plasma-enhanced properties, which can help to inspire further catalyst design and optimization.

Isoindolium-Based Allenes: Reactivity Studies and Applications in Fluorescence Temperature Sensing and Cysteine Bioconjugation.

The reaction of a series of electron-deficient isoindolium-based allenes with sulfhydryl compounds has been studied, leading to the formation of isoindolium-based vinyl sulfides. The vinyl sulfides generated could be readily converted into the corresponding indanones and amines upon heating at 30-70 °C with good yields up to 61 %. The thermal cleavage reaction of vinyl sulfides was further studied for developing temperature-sensitive systems. Notably, a novel FRET-based fluorescent temperature sensor was designed and synthesized for temperature sensing at 50 °C, giving a 6.5-fold blue fluorescence enhancement. Moreover, chemoselective bioconjugation of cysteine-containing peptides with the isoindolium-based allenes for the construction of multifunctional peptide bioconjugates was investigated. Thermal cleavage of isoindoliums on the modified peptides at 35-70 °C gave indanone bioconjugates with up to >99 % conversion. These results indicated the biocompatibility of this novel temperature-sensitive reaction.

The time-varying radiation applied in the temperature-sensitive reaction system stabilized with heat storage technology

Solar thermal plants could boost the application of methane production from microalgae. In this paper, a unique combination of solar thermal plants and microalgae bioreactor is studied. Because the microalgae pyrolysis is temperature-sensitive, and the solar radiation is time-varying, a thermocline heat storage tank is applied to stabilize the system. The impact of unsteady solar environments is important, because it is related to the versatility and flexibility of the small-scale solar systems. A theoretical model of the system, which consists of six sub-models: solar radiation, solar collector, heat storage tank, heat exchanger, pyrolysis reactor, and fermentation reactor, is developed to assess the yearly performance. In particular, the solar radiation conditions in Nanjing, China are considered. The research results show that the solar thermal bioreactor with a heat storage tank work with a steady temperature of 517 K under time-varying solar radiation. With a heat storage discharge power at 225 kW, the bioreactor produces methane at a rate around 1.4 L/s, consuming about 370 kg/day of dry microalgae. With heat storage and proper control, the variation of pyrolysis temperature is limited to 50 k, which ensures steady bioreaction. Interrupted by a short pause of solar radiation, the system has good robustness. Overall, the research results presented in this work prove the feasibility of the proposed novel system and provide a reference for the design of a solar thermal plant for clean methane production in the future.

Influence of ozone addition on the low-temperature oxidation of dimethyl ether in a jet-stirred reactor

The influence of ozone addition on the low-temperature oxidation of dimethyl ether (DME) was investigated experimentally in an atmospheric-pressure jet-stirred reactor, over the temperature range of 400–800 K. Detailed speciation information was obtained by employing synchrotron vacuum ultraviolet photoionization mass spectrometry. Experimental results revealed that the ozone addition had a positive influence on the production of the highly reactive intermediates. Moreover, the low-temperature reactivity of DME was significantly enhanced, which resulted in the broadening of the temperature window of fuel consumption and intermediates formation at lower temperatures. Therefore, novel experimental data of the low temperature regime (400–500 K) could be obtained. The data set of this special temperature regime yielded insights into the DME low-temperature kinetics, which were further supported with modeling analysis based on two existing DME models (Metcalfe et al., 2013; Wang et al., 2015) combined with an ozone sub-mechanism (Zhao et al., 2016). The analysis showed that temperature-sensitive reactions such as the second oxygen channel could be nearly “frozen” at this low temperature (T < 440 K). Furthermore, the production of some intermediates was found to be strongly governed by reaction pairs, such as CH3OCH2 + O2 = CH3OCH2O2 and CH3OCH2 + O2 = 2CH2O + OH for the CH2O formation. This finding could be useful for examining branching ratios in both models, and the analysis suggested the further modification of the branching ratios for the oxygen addition to CH3OCH2O2 pathways and the CH3OCH2O2 self-reactions were required. Finally, the influences of the O3 addition in the sensitive reactions of the fuel initial low-temperature oxidation were investigated in this work. It was interesting to note that O3 addition could change the dominating reactions in the initial low-temperature oxidation, by the addition of some O3-related pathways with relatively high sensitivity.

Telescoped Sequence of Exothermic and Endothermic Reactions in Multistep Flow Synthesis

A multistep sequential flow synthesis of isopropyl phenol is demonstrated, involving 4-step exothermic, endothermic, and temperature sensitive reactions such as nitration, reduction, diazotization, and high temperature hydrolysis. Nitration of cumene with fuming nitric acid produces 2- and 4-nitrocumene which are converted into respective cumidines by the hydrogenation using Pd/Ni catalyst in H-cube with gravity separation. Hydrolysis of in situ generated diazonium salts in the boiling acidic conditions is carried out using integration of flow and microwave-assisted synthesis. 58% of 4-isopropyl phenol was obtained. The sequential flow synthesis can be applied to synthesize other organic compounds involving this specific sequence of reactions.

Digital microfluidic immobilized cytochrome P450 reactors with integrated inkjet-printed microheaters for droplet-based drug metabolism research

We report the development and characterization of digital microfluidic (DMF) immobilized enzyme reactors (IMERs) for studying cytochrome P450 (CYP)-mediated drug metabolism on droplet scale. The on-chip IMERs consist of porous polymer (thiol-ene) monolith plugs prepared in situ by photopolymerization and functionalized with recombinant CYP1A1 isoforms (an important detoxification route for many drugs and other xenobiotics). The DMF devices also incorporate inexpensive, inkjet-printed microheaters for on-demand regio-specific heating of the IMERs to physiological temperature, which is crucial for maintaining the activity of the temperature-sensitive CYP reaction. For on-chip monitoring of the CYP activity, the DMF devices were combined with a commercial well-plate reader, and a custom fluorescence quantification method was developed for detection of the chosen CYP1A1 model activity (ethoxyresorufin-O-deethylation). The reproducibility of the developed assay was examined with the help of ten parallel CYP-IMERs. All CYP-IMERs provided statistically significant difference (in fluorescence response) compared to any of the negative controls (including room-temperature reactions). The average (n = 10) turnover rate was 20.3 ± 9.0 fmol resorufin per minute. Via parallelization, the concept of the droplet-based CYP-IMER developed in this study provides a viable approach to rapid and low-cost prediction of the metabolic clearance of new chemical entities in vitro.

Thermodynamic analysis of F1-ATPase rotary catalysis using high-speed imaging.

F1-ATPase (F1) is a rotary motor protein fueled by ATP hydrolysis. Although the mechanism for coupling rotation and catalysis has been well studied, the molecular details of individual reaction steps remain elusive. In this study, we performed high-speed imaging of F1 rotation at various temperatures using the total internal reflection dark-field (TIRDF) illumination system, which allows resolution of the F1 catalytic reaction into elementary reaction steps with a high temporal resolution of 72 µs. At a high concentration of ATP, F1 rotation comprised distinct 80° and 40° substeps. The 80° substep, which exhibited significant temperature dependence, is triggered by the temperature-sensitive reaction, whereas the 40° substep is triggered by ATP hydrolysis and the release of inorganic phosphate (Pi). Then, we conducted Arrhenius analysis of the reaction rates to obtain the thermodynamic parameters for individual reaction steps, that is, ATP binding, ATP hydrolysis, Pi release, and TS reaction. Although all reaction steps exhibited similar activation free energy values, ΔG(‡) = 53-56 kJ mol(-1), the contributions of the enthalpy (ΔH(‡)), and entropy (ΔS(‡)) terms were significantly different; the reaction steps that induce tight subunit packing, for example, ATP binding and TS reaction, showed high positive values of both ΔH(‡) and ΔS(‡). The results may reflect modulation of the excluded volume as a function of subunit packing tightness at individual reaction steps, leading to a gain or loss in water entropy.

Characterization of the temperature-sensitive reaction of F1-ATPase by using single-molecule manipulation.

F1-ATPase (F1) is a rotary motor protein that couples ATP hydrolysis to mechanical rotation with high efficiency. In our recent study, we observed a highly temperature-sensitive (TS) step in the reaction catalyzed by a thermophilic F1 that was characterized by a rate constant remarkably sensitive to temperature and had a Q10 factor of 6–19. Since reactions with high Q10 values are considered to involve large conformational changes, we speculated that the TS reaction plays a key role in the rotation of F1. To clarify the role of the TS reaction, in this study, we conducted a stall and release experiment using magnetic tweezers, and assessed the torque generated during the TS reaction. The results indicate that the TS reaction generates the same amount of rotational torque as does ATP binding, but more than that generated during ATP hydrolysis. Thus, we confirmed that the TS reaction contributes significantly to the rotation of F1.

Temperature-Sensitive Reaction of a Photosensor Protein YcgF: Possibility of a Role of Temperature Sensor

The spectrally silent photoreaction of a blue light sensor protein YcgF, composed of the N-terminal BLUF domain and the C-terminal EAL domain, was investigated by the time-resolved transient grating method. Comparing photoinduced reactions of full-length YcgF with that of the BLUF-linker construct, it was found that a major conformation change after photoinduced dimerization is predominantly localized on the EAL domain. Furthermore, the photoinduced conformational change displayed significant temperature dependence. This result is explained by an equilibrium of reactive and nonreactive YcgF species, with the population of photoreactive species decreasing as the temperature is lowered in the dark state. We consider that the dimer form is the nonreactive species and it is the dominant species at lower temperatures. The temperature sensitivity of the photoreaction of YcgF suggests that this protein could have a biological function as a temperature sensor as well as behaving as a light sensor.

Experimental and numerical study on laminar burning velocities and flame instabilities of hydrogen–air mixtures at elevated pressures and temperatures

Experimental and numerical study on hydrogen–air flames at elevated pressures and temperatures was conducted. Meanwhile, the calculation is extended to initial pressure and temperature up to 8.0 MPa and 950 K, respectively. Laminar burning velocities and Markstein lengths were obtained at the elevated pressures and temperatures. Sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The study shows that laminar burning velocities are increased with the increase of initial temperature, and they decrease with the increase of initial pressure. With the increase of initial pressure, advancement of the onset of cellular instability is presented and Markstein length is decreased, indicating an increase of flame instability with the increase of initial pressure. The study shows insensitivity of flame instability to initial temperature. Laminar burning velocity is depended on the competition between the main chain branching reactions and chain termination reaction. The chain branching reactions are the temperature-sensitive reaction, while the termination reaction is the temperature-insensitive reaction. Through the extraction of the overall reaction orders, it is demonstrated that with increasing pressure, the overall reaction orders give a decreasing trend and then increasing trend. This behavior suggests an analogy to three explosion limits of hydrogen/oxygen mixtures. Numerical study also shows that the suppression (or enhancement) of overall chemical reaction with the increase of initial pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames. On the basis of the numerical data, an empirical formula for laminar burning velocity is correlated for the hydrogen–air premixed mixture at elevated pressures and temperatures. The correlated laminar burning velocities are in good agreement with the known experimental results and simulated results with CHEMKIN. The correlation can be used in the calculation of laminar burning velocities at evaluated pressures and temperatures.

Single-molecule Study on the Temperature-sensitive Reaction of F1-ATPase with a Hybrid F1 Carrying a Single β(E190D)

F1-ATPase is a rotary molecular motor in which the γ-subunit rotates against the α3β3 cylinder. The unitary γ-rotation is a 120° step comprising 80 and 40° substeps, each of these initiated by ATP binding and ADP release and by ATP hydrolysis and inorganic phosphate release, respectively. In our previous study on γ-rotation at low temperatures, a highly temperature-sensitive (TS) reaction step of F1-ATPase from thermophilic Bacillus PS3 was found below 9 °C as an intervening pause before the 80° substep at the same angle for ATP binding and ADP release. However, it remains unclear as to which reaction step the TS reaction corresponds. In this study, we found that the mutant F1(βE190D) from thermophilic Bacillus PS3 showed a clear pause of the TS reaction below 18 °C. In an attempt to identify the catalytic state of the TS reaction, the rotation of the hybrid F1, carrying a single copy of βE190D, was observed at 18 °C. The hybrid F1 showed a pause of the TS reaction at the same angle as for the ATP binding of the incorporated βE190D, although kinetic analysis revealed that the TS reaction is not the ATP binding step. These findings suggest that the TS reaction is a structural rearrangement of β before or after ATP binding.

Experimental and numerical study on lean premixed methane–hydrogen–air flames at elevated pressures and temperatures

Abstract Experimental and numerical study on the lean methane–hydrogen–air flames at elevated pressures and temperatures was conducted. The unstretched laminar burning velocities and Markstein lengths were obtained over a wide range of hydrogen fractions at elevated pressures and temperatures. The sensitivity analysis and flame structure were also analyzed. The results show good agreement between the computed results and experimental data. The unstretched laminar burning velocities are increased with the increase of initial temperature and hydrogen fraction, and they are decreased with the increase of initial pressure. With the increase of initial pressure and hydrogen fraction, Markstein lengths are decreased, indicating the increase of flame instability. Laminar burning velocity is depended on the competition between the main chain branching reaction and chain recombination reaction. The chain branching reaction is a temperature-sensitive reaction, while the recombination reaction is a temperature-insensitive reaction. Numerical study shows that the suppression (or enhancement) of overall chemical reaction with the increase of initial pressure (or temperature) is closely linking to the decrease (or increase) of H, O and OH mole fractions in the flames. Strong correlation is existed between burning velocity and maximum radical concentrations of H and OH radicals in the reaction zone of premixed flames.

How is the Temperature Sensitive (TS) Reaction of F1-ATPase Coupled with its Rotation?

F1-ATPase (F1) is a rotary molecular motor in which γ subunit rotates against α3β3 cylinder. So far, 80° and 40° substeps in rotation of F1 have been observed, and kinetic analysis has shown that the 80° substep is initiated by concomitant ATP binding and ADP release, and the 40° substep occurs after ATP hydrolysis and inorganic phosphate release. Temperature sensitive (TS) reaction of F1 has found recently at the ATP binding angle at the temperature below 10 °C, and it has been suggested to correspond to ADP release (Watanabe et al., EMBO report 2008). In this study, TS reaction of βE190D mutant, that has much slower ATP hydrolysis rate than wild type, was found below 20 °C. Q10 factor of TS reaction of βE190D mutant was 16, that is comparable to that of wild type. Previous single-molecule rotation observations of the hybrid F1 that has only one mutant β subunit, α3β(WT)2β(E190D)γ have shown that the β subunit binds ATP at 0°, cleaves ATP at 200°, and release ADP and inorganic phosphate after cleavage of ATP (Ariga et al., NSMB 2007). In contrast to our expectation, observation of hybrid F1 α3β(WT)2β(E190D)γ rotation at 18 °C has revealed that TS reaction occurs at ATP binding angle(0°) to mutated β subunit. Furthermore, simultaneous observation at the video rate (30 frames per seconds) showed that Cy3-ATP bindings and steps in rotation occur concomitantly. We will discuss about the reaction schemes that can explain these results.

S1.29 Exploring rotary ATP synthase by electron tomography of two-dimensional crystals

ATPase is the catalytic domain of FoF1-ATP synthase. In this presentation, we will introduce three different topics; one is the temperature-sensitive reaction intermediate state of F1-ATPase. This state was found as an intervening pause in the rotation assay of F1-ATPase at low temperature. The intermediate reaction step occurs at the ATP-binding angle, and that it is not relevant to ATPbinding but to ADP-releasing step. The second topic is the correlation between the rotational substeps of F1-ATPase found in single molecule studies and the chemical state in the crystal structures of F1-ATPase. To directly clarify the question which rotational pausing states the crystal structure of F1-ATPase represent, we crosslink the β and γ subunits of F1-ATPase to fix the conformational state in the crystal structure during the single molecule rotation assay. The last topic is the development of a fluorescent ATP sensor. The recent studies show that the e subunit of F1-ATPase undergoes a large conformational change upon ATP binding. By conjugating CFP and YFP at the Nand Ctermini of the e subunit respectively, we developed the fluorescent ATP sensor which largely enhances the efficiency of FRET from CFP to YFP. We will show some movies of intracellular ATP imaging during several cellular activities such as apoptosis and cell division.

Selective leaching of antimony and arsenic from mechanically activated tetrahedrite, jamesonite and enargite

In this study, the changes in surface area, morphology and leachability of antimony and arsenic from tetrahedrite, jamesonite and enargite mechanically activated by a high-energy planetary mill were investigated. It appears that the leaching of antimony from tetrahedrite and jamesonite and arsenic from enargite in alkaline solution of sodium sulphide is temperature-sensitive reaction. The temperature dependencies of all reactions were investigated in the interval 313–363 K. Resulting experimental activation energies were E a = 111–182 kJ mol − 1 for mechanically activated minerals. The values of E a are characteristic for processes controlled by surface chemical reactions.

CEVd-Induced Symptom Modification as a Response to a Host-Specific Temperature-Sensitive Reaction

Natural selection of two new variants of citrus exocortis viroid (CEVd) was detected by observing tissues displaying both severe and mild symptoms from a single Gynura aurantiaca. The variants CEVd-S (severe) and CEVd-M (mild), differing by only five nucleotides confined to the pathogenic (P) domain, remained stable when propagated by rooted cuttings or from successive plants inoculated with tissue extracts or transcripts from cDNA clones. CEVd-S induces a very severe reaction in Gynura that is consistent throughout a range of environmental conditions. However, symptoms resulting from CEVd-M infection can vary from a nonsymptomatic condition to a severe reaction when grown at 40°C. This differential response was confined to a single host, Gynura aurantiaca, and expressed under standard growing conditions. The distinct host responses induced by these variants could not be correlated with any changes in sequence or conformation of the dominant viroid variant, as predicted by molecular modeling. Therefore, the variable symptom expression appears to be associated with a specific temperature-sensitive response of Gynura aurantiaca.

Semibatch Reactor Dynamics and State Estimation

The dynamic behavior of semibatch reactors is characterized by a strongly nonlinear, and especially an inherently nonstationary nature. These dynamic features give rise to difficulties in reactor operation particulary with highly exothermic and temperature-sensitive reaction . Typical operational problems are attributable to these dynamic characteristics, and to insufficient information from the commonly measured variables. This paper provides an outline of semibatch reactor dynamics, and state estimation examples in industrial practice.

Temperature-sensitive genes for resistance to Puccinia striiformis in Triticum dicoccoides

Twenty-six selections of wild emmer collected at different sites in Israel and three entries obtained from Turkey were studied for the possible presence of temperature-sensitive genes controlling reaction to Puccinia striiformis. In tests carried out in Israel with a local P. striiformis isolate at two temperature regimes, 16 selections showed a change in infection rating toward resistance at the higher temperature regime. In comparable tests performed in the United States with a Montana P. striiformis isolate of different virulence pattern-including 14 of the same selection—ten entries displayed a temperature-sensitive reaction. Although slightly different temperature regimes were used in Israel and the United States, the results obtained were in general agreement. The shift toward resistance observed in the seedling tests at the higher temperature-profile was also evident in the field in the mature plant stage with increasing spring temperatures.

The effect of temperature on the amplitude distributions of miniature endplate potentials in the mouse diaphragm

The effect of temperature (11 to 45°C) on miniature endplate potential (MEPP) distributions was examined at the mouse diaphragm. MEPP distributions were composed of two populations ('skew-MEPPS' and ‘bell-MEPPs’) and the mode of the skew-MEPP population (subminiature endplate potential, sub-MEPP) had an amplitude equal to 1/10 to 1/15 the mean of the normally distributed bell-MEPP class. The overall MEPP frequency increased with a Q 10 of 2.2 between 11 and 30°C, and an Arrhenius plot indicated two temperature-sensitive reactions between 11 and 45°C. Below 30°C, the activation energy was 10.4 kcal/mole K and between 30 and 45°C the activation energy was 38.7 kcal/ mole K. The proportion of skew-MEPPs between different fibers was independent of the overall MEPP frequency and varied between 1% and 31% at temperatures of 11–34°C. However, as the temperature was lowered below 24°C, the decrease in frequency of skew-MEPPs was more than that of bell-MEPPs. Conversely, an increase in temperature from 24 to 34°C increased the bell-MEPP frequency but either reduced or had little effect on the frequency of skew-MEPPs. Following heat challenges (T > 40°C), MEPP distributions contained a large percentage of skew-MEPPs and the profile of the MEPP distribution became uniform. Before complete cessation of spontaneous activity with multiple heat challenges, MEPP amplitude distributions were either uniform or were composed primarily of sub-MEPPs. MEPP time courses were slower after heat challenges, and in some preparations, inflections were observed on many MEPP rising phases. Amplitude histograms of these inflections yielded distributions similar to control distributions of skew-MEPPs. The presence of inflections on MEPPs following heat challenges supports the hypothesis that skew-MEPPs and bell-MEPPs are composed of subunits. These results suggest that skew- and bell-MEPPs are caused by the release of transmitter by different temperature-sensitive mechanisms.

Temperature Control of Germination of Helenium Amarum Seeds

Germination of seeds of the common bitterweed was tested under several temperature regimes. The effect of constant temperatures depended upon duration of storage. Fresh seeds germinated well without statistically significant differences at 11°, 15°, and 19°C. Extended storage at room temperature resulted in general loss of viability, increase in optimum temperature for germination, and decreased temperature sensitivity, especially decreased inhibition by higher temperatures. Alternating temperatures did not generally increase germination. The temperature—sensitive reactions are interpreted as ecologic adaptations rendering the plants highly successful in disturbed areas throughout the southeastern United States. The adaptation specially allows establishment of seedlings in the autumn and growth through the winter without competition.