transient kinetics
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2022 ◽  
Author(s):  
Dominik Meyer ◽  
Jannik Schumacher ◽  
Jens Friedland ◽  
Robert Güttel

The utilization of renewable electricity for power-to-gas (PtG) applications induces fluctuations in the H2 availability from water electrolysis. For subsequent methanation of CO or CO2 the unsteady-state operation of the respective reactor allows to minimize H2 storage capacities. However, the impact of temporal fluctuations in feed gas composition on the methanation reaction and the respective transient kinetics has not yet been fully understood. We investigated the methanation of various CO/CO2 (COx) feed gas mixtures under periodically changing gas compositions with emphasis on the effect of the frequency on the reactor response. We show that the frequency response of CH4 exhibits a characteristic hysteresis, which depends on the switching direction between COx-lean and COx-rich feeds and their composition. From the shape of the hysteresis we are able to conclude on the preferred COx species being hydrogenated to CH4 under respective conditions, which also provides mechanistic insights. By applying high cycling frequencies, the highly reactive species present under CO methanation conditions can even selectively be activated, which explains the higher reactivity compared to steady-state conditions reported, frequently.


Author(s):  
Aseel G.S. Hussien ◽  
Constantinos M. Damaskinos ◽  
Aasif Dabbawala ◽  
Dalaver H. Anjun ◽  
Michalis A. Vasiliades ◽  
...  

2021 ◽  
Author(s):  
Akhil Gargey Iragavarapu ◽  
Yuri Nesmelov

Double mutation D208Q:K450L was introduced in the beta isoform of human cardiac myosin to remove the salt bridge D208:K450 connecting loop 1 and the seven stranded beta sheet within the myosin head. Beta isoform specific salt bridge D208:K450 was previously discovered in the molecular dynamics simulations. It was proposed that loop 1 modulates nucleotide affinity to actomyosin and we hypothesized that the electrostatic interactions between loop 1 and myosin head backbone regulates ATP binding to and ADP dissociation from actomyosin, and therefore, the time of the strong actomyosin binding. Wild type and the mutant of the myosin head construct (843 amino acid residues) were expressed in differentiated C2C12 cells, and the kinetics of ATP induced actomyosin dissociation and ADP release were characterized using transient kinetics spectrophotometry. Both constructs exhibit a fast rate of ATP binding to actomyosin and a slow rate of ADP dissociation, showing that ADP release limits the time of the strongly bound state of actomyosin. We observed a faster rate of ATP induced actomyosin dissociation with the mutant, compared to the wild type actomyosin. The rate of ADP release from actomyosin remains the same for the mutant and the wild type actomyosin. We conclude that the flexibility of loop 1 is a factor affecting the rate of ATP binding to actomyosin and actomyosin dissociation. We observed no effect of loop 1 flexibility on the rate of ADP release from actomyosin.


2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
S Pabel ◽  
M Knierim ◽  
T Stehle ◽  
F Alebrand ◽  
M Paulus ◽  
...  

Abstract   Atrial fibrillation (AF) is often found in patients with heart failure (HF). Clinical data indicated that the arrhythmic component of AF alone could contribute to left-ventricular (LV) dysfunction. However, the effects of non-tachycardic AF with arrhythmic excitation of the human LV, are unknown. We investigated human LV myocardium from patients with sinus rhythm (SR) or normofrequent AF (mean EF>50%, matched clinical data, derived from septal resections during AVR). In histological analysis we detected no difference between SR (n=17 patients) and AF patients (n=18) regarding the amount and distribution of fibrosis. We isolated human LV cardiomyocytes (CM) and studied cellular Ca-handling (Fura-2). Systolic Ca-transient amplitude of LV CM was reduced in patients suffering from AF (n=8 AF patients vs. 11 SR), while diastolic Ca-levels and Ca-transient kinetics were not significantly changed. These results were confirmed in LV CM from non-failing donors (NF) with AF (n=4 AF patients vs. 8 SR). For the standardized investigation of a normofrequent arrhythmia, we simulated AF in vitro by using arrhythmic (60 bpm, 40% beat-to-beat variability) or rhythmic (60 bpm) field stimulation. Human LV CM from NF SR patients (n=8) showed an impaired Ca-transient amplitude after 24h arrhythmic culture pacing without changes in diastolic Ca and Ca-transient kinetics. For studying a model suitable for more standardized chronic pacing, we utilized human iPSC cardiomyocytes (iPSC-CM) from healthy donors (n=6). After 7 days, arrhythmically paced iPSC-CM exhibited a reduced systolic Ca-transient amplitude, a trend towards a prolonged Ca-elimination time and a reduced sarcoplasmic reticulum Ca-load. Confocal line-scans of arrhythmically paced cells (Fluo-4 AM) showed an increased diastolic Ca-leak from the sarcoplasmic reticulum, possibly underlying the reduced Ca-load. Coupled with the Ca changes, cytosolic Na was elevated after arrhythmia. We found an increased late INa, which could explain the detrimentally altered Ca/Na-interplay. Accordingly, Patch-clamp experiments revealed a prolonged action potential duration after arrhythmia. We further elucidated the underlying mechanisms of this electrophysiological remodeling by showing that oxidative stress (H2O2, LPO) is increased in the LV of patients suffering from AF (n=6 AF patients vs. 6 SR), which was associated with an enhanced NOX2/-4 activity. Consecutively, Ca2+/calmodulin-dependent protein kinase IIδ (CaMKII) was found to be more oxidized (CaMKII-Met281/282) in the LV of AF patients (n=7 AF patients vs. 7 SR) leading to an increased CaMKII activity, which adversely regulated EC-coupling protein phosphorylation including RyR2 hyperphosphorylation. Normofrequent arrhythmia/AF impairs human ventricular EC-coupling via increased oxidative stress and enhanced CaMKII. Thus, this translational study provides the first mechanistic characterization and the potential negative impact of isolated AF on the human LV. FUNDunding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Else Kröner-Fresenius-Stiftung (EKFS) and Deutsche Gesellschaft für Innere Medizin


2021 ◽  
pp. 117156
Author(s):  
Matias Alvear ◽  
Michele Emanuele Fortunato ◽  
Vincenzo Russo ◽  
Tapio Salmi ◽  
Martino Di Serio

2021 ◽  
Author(s):  
Dominik Meyer ◽  
Jens Friedland ◽  
Jannik Schumacher ◽  
Robert Güttel

Due to rising interest for the integration of chemical energy storage into the electrical power grid, the unsteady-state operation of chemical reactors is gaining more and more attention with emphasis on heterogeneously catalyzed reactions. The transient response of those reactions is influenced by effects on different length scales, ranging from the active surface via the individual porous catalyst particle up to the full-scale reactor. The challenge, however, is to characterize unsteady-state effects under realistic operation conditions and to assign them to distinct transport processes. Therefore, the periodic transient kinetics (PTK) method is introduced, which allows for the separation of kinetic process dynamics at different length scales experimentally under realistic operation conditions. The methodology also provides the capability for statistical analysis of the experimental results and therefore improved reliability of the derived conclusions. Therefore, the PTK method provides the experimental basis for model-based derivation of reaction kinetics valid under dynamic conditions. The applicability of the methodology is demonstrated for the methanation reaction chosen as an example process for heterogeneously catalyzed reactions relevant for chemical energy storage purposes. <br>


2021 ◽  
Author(s):  
Dominik Meyer ◽  
Jens Friedland ◽  
Jannik Schumacher ◽  
Robert Güttel

Due to rising interest for the integration of chemical energy storage into the electrical power grid, the unsteady-state operation of chemical reactors is gaining more and more attention with emphasis on heterogeneously catalyzed reactions. The transient response of those reactions is influenced by effects on different length scales, ranging from the active surface via the individual porous catalyst particle up to the full-scale reactor. The challenge, however, is to characterize unsteady-state effects under realistic operation conditions and to assign them to distinct transport processes. Therefore, the periodic transient kinetics (PTK) method is introduced, which allows for the separation of kinetic process dynamics at different length scales experimentally under realistic operation conditions. The methodology also provides the capability for statistical analysis of the experimental results and therefore improved reliability of the derived conclusions. Therefore, the PTK method provides the experimental basis for model-based derivation of reaction kinetics valid under dynamic conditions. The applicability of the methodology is demonstrated for the methanation reaction chosen as an example process for heterogeneously catalyzed reactions relevant for chemical energy storage purposes. <br>


Author(s):  
Kyriaki Polychronopoulou ◽  
Ayesha A. AlKhoori ◽  
Angelos M. Efstathiou ◽  
Maguy Abi Jaoude ◽  
C. M. Damaskinos ◽  
...  

2021 ◽  
pp. 129610
Author(s):  
M. Ross Kunz ◽  
Adam Yonge ◽  
Zongtang Fang ◽  
Rakesh Batchu ◽  
Andrew J. Medford ◽  
...  

Chem ◽  
2021 ◽  
Author(s):  
David Hess ◽  
Veronika Dockalova ◽  
Piia Kokkonen ◽  
David Bednar ◽  
Jiri Damborsky ◽  
...  

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