Fast Kinetic Research Articles

Multiphysics factor facilitating fast reaction kinetics for high-power-density Li–Se batteries

An intriguing multiphysics factor for facilitating fast reaction kinetics is proposed herein to achieve high-power-density cathodes for lithium-selenium batteries (LSeBs) based on Se and Te-doped cathode models from the perspective of thermodynamic, chemical, and Li kinetics. Compared with the bare electrode, the optimized Te–Se electrode showed a much greater rate capability under harsh conditions in balancing the theoretical capacity and improving the redox kinetics. This fast kinetic property is understood in detail by cyclic voltammetry analysis, and a reduction in the electrochemical polarization, depending on the increase in the scan rate, is observed for the Te–Se electrode. In addition, the voltage hysteresis of the Se cathode increased rapidly in the C-rate mode, whereas that of the Te–Se electrode increased at a much slower rate. Therefore, a comparison of intrinsic thermodynamic hysteresis is performed to highlight the difference between the Se-based electrodes, and the reaction resistance and Li diffusion coefficient for the Te–Se cathode from the kinetic point of view are found to exhibit a superior feature during (dis)charging. The theoretical results are broken down into three perspectives: i) thermodynamics, ii) electronic structure, and iii) Li kinetics, systematically elucidating the fast kinetics of the Te-doped Se cathode compared to the pristine material. Lowering the formation energy, increasing the electronic population, and loosening the cation–anion bond are simultaneously triggered by Te doping, and their combined effects are deemed to be a multiphysics factor. The concrete experiment and computational understanding confirm the high power density of the Te–Se electrode relative to the reference model upon long-term cycling, and validate that the multiphysics factors pose a potentially global design strategy to enable fast kinetics for achieving high-performance LSeBs, even lithium-sulfur batteries.

High content anion (S/Se/P) doping assisted by defect engineering with fast charge transfer kinetics for high-performance sodium ion capacitors

The rate-determining process for sodium storage in TiO2 is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity. Apart from reducing the diffusion distance of ion/electron, the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed. Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO2 phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites, which can largely reduce the migration barrier of Na+. To realize the speculation, high-content anion doped anatase TiO2/C composites (9.82 at% for S in A-TiO2–x-S/C) are elaborately designed. The optimized A-TiO2–x-S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g−1 at 5000 mA g−1. The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg−1 at a power density of 150 W kg−1 when applied as anode materials. This work provides a new strategy to realize high content anion doping concentration, and enhances the charge transfer kinetics for TiO2, which delivers an efficient approach for the design of electrode materials with fast kinetic.

In vivo evidence for the unique kinetics of evoked dopamine release in the patch and matrix compartments of the striatum

The neurochemical transmitter dopamine (DA) is implicated in a number of diseases states, including Parkinson’s disease, schizophrenia, and drug abuse. DA terminal fields in the dorsal striatum and core region of the nucleus accumbens in the rat brain are organized as heterogeneous domains exhibiting fast and slow kinetic of DA release. The rates of dopamine release are significantly and substantially faster in the fast domains relative to the slow domains. The striatum is composed of a mosaic of spatial compartments known as the striosomes (patches) and the matrix. Extensive literature exists on the spatial organization of the patch and matrix compartments and their functions. However, little is known about these compartments as they relate to fast and slow kinetic DA domains observed by fast scan cyclic voltammetry (FSCV). Thus, we combined high spatial resolution of FSCV with detailed immunohistochemical analysis of these architectural compartments (patch and matrix) using fluorescence microscopy. Our findings demonstrated a direct correlation between patch compartments with fast domain DA kinetics and matrix compartments to slow domain DA kinetics. We also investigated the kinetic domains in two very distinct sub-regions in the striatum, the lateral dorsal striatum (LDS) and the medial dorsal striatum (MDS). The lateral dorsal striatum as opposed to the medial dorsal striatum is mainly governed by fast kinetic DA domains. These finding are highly relevant as they may hold key promise in unraveling the fast and slow kinetic DA domains and their physiological significance.Graphical abstract

Molecular Insight into Cu2+-Induced Conformational Transitions of Amyloid β-Protein from Fast Kinetic Analysis and Molecular Dynamics Simulations.

Cu2+-mediated amyloid β-protein (Aβ) aggregation is implicated in the pathogenesis of Alzheimer's disease, so it is of significance to understand Cu2+-mediated conformational transitions of Aβ. Herein, four Aβ mutants were created by using the environment-sensitive cyanophenylalanine to respectively substitute F4, Y10, F19, and F20 residues of Aβ40. By using stopped-flow fluorescence spectroscopy and molecular dynamics (MD) simulations, the early stage conformational transitions of the mutants mediated by Cu2+ binding were investigated. The fast kinetics unveils that Cu2+ has more significant influence on the conformational changes of N-terminal (F4 and Y10) than on the central hydrophobic core (CHC, F19, and F20) under different pH conditions (pH 6.6-8.0), especially Y10. Interestingly, lag periods of the conformational transitions are observed for the F19 and F20 mutants at pH 8.0, indicating the slow response of the two mutation sites on the conformational transitions. More importantly, significantly longer lag periods for F20 than for F19 indicate the conduction of the transition from F19 to F20. The conduction time (difference in lag period) decreases from 4.5 s at Cu2+ = 0 to undetectable (<1 ms) at Cu2+ = 10 μM. The significant difference in the response time of F19 and F20 and the fast local conformational changes of Y10 imply that the conformational transitions of Aβ start around Y10. MD simulations support the observation of hydrophobicity increase at N-terminal during the conformational transitions of Aβ-Cu2+. It also reveals that Y10 is immediately approached by Cu2+, supporting the speculation that the starting point of conformational transitions of Aβ is near Y10. The work has provided molecular insight into the early stage conformational transitions of Aβ40 mediated by Cu2+.

Titanium-based ion sieve with enhanced post-separation ability for high performance lithium recovery from geothermal water

The improvement of post-separation performance of powdery lithium ion sieve with the guarantee of high adsorption capacity and fast kinetics remains to be a huge challenge. Herein, a novel granular and porous titanium-based lithium ion sieve (PIS) was developed using agar-assisted strategy and used for lithium recovery from geothermal water. The agar acted as both spherality-shaping and sacrificial porogenic agent. As a result, PIS had a 64-fold larger diameter (2.8 mm) than powdery ion sieve (IS), which could be easily separated by filtration and then reused with a steady performance. Due to its loose microstructures and rich porosity, PIS showed high adsorption capacity (25.8 mg/g) and rapid kinetic (equilibrium time 6 h) in geothermal water. In addition, the separation factors of competitive ions related to Li+ were 1162.3, 273.7 and 328.5 for Na+, K+ and Ca2+, respectively, exhibiting benign selectivity in natural geothermal water. Thus, this granular PIS with enhanced post-separation ability, high capacity and fast kinetic could be considered as a promising candidate for lithium recovery from geothermal water. Moreover, this simple and green method could be easily popularized to prepare other porous adsorbents.

Modulation of Transient Receptor Potential C Channel Activity by Cholesterol.

Changes of cholesterol level in the plasma membrane of cells have been shown to modulate ion channel function. The proposed mechanisms underlying these modulations include association of cholesterol to a single binding site at a single channel conformation, association to a highly flexible cholesterol binding site adopting multiple poses, and perturbation of lipid rafts. These perturbations have been shown to induce reversible targeting of mammalian transient receptor potential C (TRPC) channels to the cholesterol-rich membrane environment of lipid rafts. Thus, the observed inhibition of TRPC channels by methyl-β-cyclodextrin (MβCD), which induces cholesterol efflux from the plasma membrane, may result from disruption of lipid rafts. This perturbation was also shown to disrupt multimolecular signaling complexes containing TRPC channels. The Drosophila TRP and TRP-like (TRPL) channels belong to the TRPC channel subfamily. When the Drosophila TRPL channel was expressed in S2 or HEK293 cells and perfused with MβCD, the TRPL current was abolished in less than 100 s, fitting well the fast kinetic phase of cholesterol sequestration experiments in cells. It was thus suggested that the fast kinetics of TRPL channel suppression by MβCD arise from disruption of lipid rafts. Accordingly, lipid raft perturbation by cholesterol sequestration could give clues to the function of lipid environment in TRPC channel activity and its mechanism.

Effective biosorption of U(VI) from aqueous solution using calcium alginate hydrogel beads grafted with amino-carbamate moieties

Novel amino-carbamate moiety grafted calcium alginate hydrogel beads (CA-1) were synthesized by reacting sodium alginate with 4-phenylsemicarbazide followed by ionotropic crosslinking with Ca(II) ions. As compared to pure calcium alginate hydrogel beads (CA), CA-1 exhibited fast kinetics and enhanced sorption capacity towards U(VI) ions, from mild acidic conditions. The sorption kinetic could be described by pseudo-second order equation, with the chemisorption as the rate-controlling step. The sorption isotherm were fitted well by Langmuir (qm = 233.2 mg/g at 298 K). CA-1 hydrogel beads exhibited fast kinetic, high sorption capacity and excellent selectivity for U(VI) sorption, thus it could be potentially used for the removal/recovery of U(VI) ions from wastewater.

Comparison of mass transfer performance of pulsed columns with Tenova kinetics internals and standard disc and doughnut internals

One of the limitations to the application of columns to solvent extraction in the minerals industry is their relative inefficiency in slow kinetic systems such as those used for the separation of copper. In order to overcome this, this work examines the performance of a new kinetic internal and compares it to standard column internals for both a fast and slow kinetic system.The mass transfer performance of a pilot scale pulsed solvent extraction column with Tenova Kinetics Internals (TKI) and standard disc and doughnut internals (DDI) are compared, including the effect of pulsation intensity, continuous and dispersed phase velocities using the H2SO4 – Alamine® 336 system, a fast kinetic system, and CuSO4 – LIX® 84 system, a slow kinetic system. The height of mass transfer unit (Hoc) for the CuSO4 – LIX 84 system increased with continuous and dispersed phase velocity and decreased with the increase of pulsation intensity. The Hoc for TKI was lower than the DDI for the same operating conditions and the TKI reduced the impact of both phase velocities on mass transfer. TKI can maintain the mass transfer performance for the fast kinetics H2SO4-Alamine 336 system compared to standard disc and doughnut internals and improve mass transfer performance for slow kinetics CuSO4- LIX® 84 system. An empirical correlation to predict the height of mass transfer unit in both internals was developed with absolute relative errors of 28.0% and 19.2% for the H2SO4 – Alamine 336 system and CuSO4 – LIX 84 system, respectively.

Blocking Polysulfides and Facilitating Lithium-Ion Transport: Polystyrene Sulfonate@HKUST-1 Membrane for Lithium-Sulfur Batteries.

Minimizing the shuttle effect of polysulfides (PS) is crucial for practical applications of lithium-sulfur (Li-S) batteries. However, the trade-off between effective suppression of the shuttle effect and fast redox reaction kinetics is inevitable for separator-based Li-S batteries. Herein, via a self-confined solid-conversion process, we develop a polystyrene sulfonate (PSS)-threaded well-intergrown HKUST-1 (Cu3(BTC)2) (BTC: 1,3,5-benzenetricarboxylic acid)-coated Celgard separator (PSS@HKUST-1/Celgard, PHC) for high-performance Li-S batteries. The PHC membrane favors the interception and accommodation of long-chain PS. Notably, enormous sulfonate groups of the three-dimensional PSS networks in PSS@HKUST-1 membrane significantly facilitate lithium-ion transport, which guarantee fast redox kinetics. The PHC separator demonstrates efficient inhibition of PS (i.e., 4 orders of magnitude lower in PS permeation rate) with fast Li+ transportation (i.e., 71% higher in ionic conductivity) than the Celgard separator. When applying the PHC membrane in Li-S batteries with conventional sulfur/super P carbon cathode, highly reversible capacity with an average fading rate of 0.05% per cycle is maintained for 500 cycles at 0.5 C, excellent rate performance up to 5 C, and high areal capacity over 7 mA h cm-2 are also achieved. This work paves a new way for addressing the trade-off between suppressing the PS shuttle effect and fast kinetic reaction for separator-based Li-S batteries.

Energetic dissection of Gleevec's selectivity toward human tyrosine kinases.

Protein kinases are obvious drug targets against cancer due to their central role in cellular regulation. Since the discovery of Gleevec, a potent and specific inhibitor of Abl kinase, as a highly successful cancer therapeutic, the ability of this drug to distinguish between Abl and other tyrosine kinases like Src has been intensely investigated, but without much success. Using NMR and fast kinetics, we establish a novel model that solves this longstanding question of two tyrosine kinases adopting almost identical structures when bound to Gleevec, yet having vastly different affinities. In contrast to all other proposed models we show that the origin of Abl’s high affinity lies predominantly in a conformational change after binding. An energy landscape that provides tight affinity via an induced-fit and binding plasticity via conformational selection mechanism is likely to be general for many inhibitors.

Structural basis for a hand-like site in the calcium sensor CatchER with fast kinetics.

Calcium ions, which are important signaling molecules, can be detected in the endoplasmic reticulum by an engineered mutant of green fluorescent protein (GFP) designated CatchER with a fast off-rate. High resolution (1.78-1.20 Å) crystal structures were analyzed for CatchER in the apo form and in complexes with calcium or gadolinium to probe the binding site for metal ions. While CatchER exhibits a 1:1 binding stoichiometry in solution, two positions were observed for each of the metal ions bound within the hand-like site formed by the carboxylate side chains of the mutated residues S147E, S202D, Q204E, F223E and T225E that may be responsible for its fast kinetic properties. Comparison of the structures of CatchER, wild-type GFP and enhanced GFP confirmed that different conformations of Thr203 and Glu222 are associated with the two forms of Tyr66 of the chromophore which are responsible for the absorbance wavelengths of the different proteins. Calcium binding to CatchER may shift the equilibrium for conformational population of the Glu222 side chain and lead to further changes in its optical properties.

Design and Application of Fluorescent Calcium Binding Proteins with Fast Kinetics

Transient changes of spatio-temporal cytosolic calcium concentrations initiate calcium signaling for downstream physiological actions. The intracellular calcium stores serve as the major source for these calcium transients. To probe calcium release in such high calcium environments, there is a pressing need to develop calcium sensors with fast kinetic properties to fulfill the requirements for understanding calcium signaling during fast physiological events such as action potentials and EC-coupling. In this study, we will report the design of calcium binding proteins with unprecedented fast kinetics that is about two orders of magnitude faster than natural calcium binding proteins. using various spectroscopic methods, we have shown that the designed calcium binding proteins exhibit desired affinity, metal selectivity and optical properties attributed to the calcium binding induced local conformation and dynamic change in the chromophore environment. We then report the application of developed calcium sensors in variety of biological processes including extracellular calcium signaling, the store-operated calcium entry, and the calcium release dynamics from SR in skeletal muscle in aging mice.

Preparation and characterization of nano-magnetic cellulose with fast kinetic properties towards the adsorption of some metal ions

Nano-magnetic cellulose hybrid was obtained from precipitation of cellulose in presence of Fe(II)/Fe(III) mixture. The hybrid material obtained was then functionalized with amino group through successive treatment by glycidylmethacrylate and tetraethylenepentamine. The functionalized hybrid cellulose was investigated by means of FT-IR, TGA, TEM, XRD and nitrogen adsorption surface area measurements. The prepared material showed adsorption capacity of 2, 1.5 and 1.2mmol/g for Hg(II), Cu(II) and Ag(I), respectively. The adsorbent showed fast kinetics with exothermic nature for the adsorption of the three studied metal ions. The regeneration of the loaded adsorbent was carried out by acidified thiourea.

Application of Designed Calcium Sensors with Fast Kinetic Responses

Transient change of cytosolic calcium level leads to physiological actions, which are modulated by the intracellular calcium store, as well as membrane calcium channels. To probe fast calcium responses in high calcium environments, there is a pressing need to develop calcium sensors to overcome the limitation of relatively slow kinetics of current GECIs with τ value around several hundred milliseconds. We have developed single green fluorescence protein-based calcium sensors, with tunable calcium binding affinity and fast kinetics.

Strong Cross-bridges Potentiate the Ca2+ Affinity Changes Produced by Hypertrophic Cardiomyopathy Cardiac Troponin C Mutants in Myofilaments: A FAST KINETIC APPROACH

This spectroscopic study examined the steady-state and kinetic parameters governing the cross-bridge effect on the increased Ca(2+) affinity of hypertrophic cardiomyopathy-cardiac troponin C (HCM-cTnC) mutants. Previously, we found that incorporation of the A8V and D145E HCM-cTnC mutants, but not E134D into thin filaments (TFs), increased the apparent Ca(2+) affinity relative to TFs containing the WT protein. Here, we show that the addition of myosin subfragment 1 (S1) to TFs reconstituted with these mutants in the absence of MgATP(2-), the condition conducive to rigor cross-bridge formation, further increased the apparent Ca(2+) affinity. Stopped-flow fluorescence techniques were used to determine the kinetics of Ca(2+) dissociation (k(off)) from the cTnC mutants in the presence of TFs and S1. At a high level of complexity (i.e. TF + S1), an increase in the Ca(2+) affinity and decrease in k(off) was achieved for the A8V and D145E mutants when compared with WT. Therefore, it appears that the cTnC Ca(2+) off-rate is most likely to be affected rather than the Ca(2+) on rate. At all levels of TF complexity, the results obtained with the E134D mutant reproduced those seen with the WT protein. We conclude that strong cross-bridges potentiate the Ca(2+)-sensitizing effect of HCM-cTnC mutants on the myofilament. Finally, the slower k(off) from the A8V and D145E mutants can be directly correlated with the diastolic dysfunction seen in these patients.

Antioxidant capacity of sulfated polysaccharides from seaweeds. A kinetic approach

The antioxidant capacity of sulfated galactans from Gigartina skottsbergii and Schizymenia binderi, commercial carrageenans, and fucoidan from Lessonia vadosa was evaluated by the oxygen radical absorbance capacity (ORAC) method using fluorescein and c-phycocyanin as target molecules. Even though, relative ORAC values for sulfated galactans are similar for both employed probes, they are higher for fluorescein. Results of antioxidant capability are analyzed in terms of the structural parameters of polysaccharides. Fucoidan, from the brown seaweed L. vadosa and the sulfated galactan from the red seaweed, S. binderi exhibit the highest antioxidant capacity by the ORAC method. Although, the ORAC assay is not used to evaluate the quenching of peroxyl radicals by polysaccharides, we demonstrated that this method constitutes an adequate assay for evaluating the antioxidant capacity of aqueous soluble polysaccharides. The antioxidant capacity was also evaluated by ABTS and hydroxyl radical scavenging assays. The kinetic profiles for the reaction of ABTS + with polysaccharides display a fast initial reaction kinetics followed by a slow component. Antioxidant activity, obtained from the end of the fast kinetic, was higher for fucoidan and sulfated galactan from S. binderi than for commercial carrageenans. The reaction of the polysaccharides with hydroxyl radicals is complex. Kinetics studies showed a fast reaction followed by a slower reaction that leads polysaccharide derived radicals to inhibit the antioxidant activity.

Primary Steps of the Na+-translocating NADH:Ubiquinone Oxidoreductase Catalytic Cycle Resolved by the Ultrafast Freeze-Quench Approach

The Na(+)-translocating NADH:ubiquinone oxidoreductase (Na(+)-NQR) is a component of respiratory chain of various bacteria, and it generates a redox-driven transmembrane electrochemical Na(+) potential. Primary steps of the catalytic cycle of Na(+)-NQR from Vibrio harveyi were followed by the ultrafast freeze-quench approach in combination with conventional stopped-flow technique. The obtained sequence of events includes NADH binding ( approximately 1.5 x 10(7) m(-1) s(-1)), hydride ion transfer from NADH to FAD ( approximately 3.5 x 10(3) s(-1)), and partial electron separation and formation of equivalent fractions of reduced 2Fe-2S cluster and neutral semiquinone of FAD ( approximately 0.97 x 10(3) s(-1)). In the last step, a quasi-equilibrium is approached between the two states of FAD: two-electron reduced (50%) and one-electron reduced (the other 50%) species. The latter, neutral semiquinone of FAD, shares the second electron with the 2Fe-2S center. The transient midpoint redox potentials for the cofactors obtained during the fast kinetics measurements are very different from ones achieved during equilibrium redox titration and show that the functional states of the enzyme realized during its turning over cannot be modeled by the equilibrium approach.

Rapid fluidic exchange microsystem for recording of fast ion channel kinetics in Xenopus oocytes

We present a new lab-on-a-chip system for electrophysiological measurements on Xenopus oocytes. Xenopus oocytes are widely used host cells in the field of pharmacological studies and drug development. We developed a novel non-invasive technique using immobilized non-devitellinized cells that replaces the traditional "two-electrode voltage-clamp" (TEVC) method. In particular, rapid fluidic exchange was implemented on-chip to allow recording of fast kinetic events of exogenous ion channels expressed in the cell membrane. Reducing fluidic exchange times of extracellular reagent solutions is a great challenge with these large millimetre-sized cells. Fluidic switching is obtained by shifting the laminar flow interface in a perfusion channel under the cell by means of integrated poly-dimethylsiloxane (PDMS) microvalves. Reagent solution exchange times down to 20 ms have been achieved. An on-chip purging system allows to perform complex pharmacological protocols, making the system suitable for screening of ion channel ligand libraries. The performance of the integrated rapid fluidic exchange system was demonstrated by investigating the self-inhibition of human epithelial sodium channels (ENaC). Our results show that the response time of this ion channel to a specific reactant is about an order of magnitude faster than could be estimated with the traditional TEVC technique.

On the use of “fast kinetics” to determine the mechanism of ligand substitution at a solvated transition‐metal intermediate

AbstractSubstitution of the weakly‐coordinated solvent molecule at a solvated transition‐metal intermediate is frequently investigated by “fast kinetic” methods. In typical experiments, the kinetics of the reaction are determined by following the time dependence of the changes in the reaction mixture's UV‐visible or infrared spectrum following photolytic creation of the intermediate. We consider the two limiting mechanisms (associative and dissociative), as well as the case of competition between them, and show that under typical “fast kinetics” experimental conditions, the different mechanisms are kinetically indistinguishable. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 427–433, 2004

Autocatalytic Oscillations in the Early Phase of the Photoreduced Methyl Viologen-initiated Fast Kinetic Reaction of Hydrogenase

The kinetic characteristics of the hydrogen uptake reaction of hydrogenase, obtained by conventional activity measurements, led to the proposal of an autocatalytic reaction step in the hydrogenase cycle or during the activation process. The autocatalytic behavior of an enzyme reaction may result in oscillating concentrations of enzyme intermediates and/or products contributing to the autocatalytic step. This behavior has been investigated in the early phase of the hydrogenase-methyl viologen reaction. To measure fast hydrogenase kinetics, flash-reduced methyl viologen has been used as a light-induced trigger in transient kinetic phenomena associated with intermolecular electron transfer to hydrogenase. Here we report fast kinetic measurements of the hydrogenase-methyl viologen reaction by use of the excimer laser flash-reduced redox dye. The results are evaluated on the assumption of an autocatalytic reaction in the hydrogenase kinetic cycle. The kinetic constants of the autocatalytic reaction, i.e. the methyl viologen binding to and release from hydrogenase, were determined, and limits of the kinetic constants relating to the intramolecular (intraenzyme) reactions were set.