关键词： Surface plasmon resonance spectroscopy   Kinetic parameters   Dissociation   Fluorescence   Kinetics  

摘要： Gold nanoparticles (NPs) in the ultrasmall size regime provide a new paradigm in the way that nanomaterials can be used to regulate protein structure and function. However, the rational design of ultrasmall NPs as viable synthetic effectors of protein function requires detailed quantitative understanding of their biomolecular interactions. Herein, we focused on the kinetics of NP-protein complexation-an often neglected factor in studies at the bio-nanointerface-to gain molecular-level insights into mechanisms of interactions. The protein alpha-thrombin and ultrasmall gold NPs coated with p-mercaptobenzoic acid (AuMBA) and glutathione (AuGSH) were used as model systems in our studies. Binding kinetics was quantified by surface plasmon resonance (SPR) biosensing and stopped-flow spectroscopy. The results revealed strong and weak interactions of AuMBA and AuGSH toward thrombin (K-D similar to 30 nM and 20 mu M, respectively), as well as "fast" and "slow" association kinetics (k(on) similar to 10(6)-10(7) and 10(4) M-1 s(-1) respectively). The significantly smaller k(on) for AuGSH implied the presence of a larger energy barrier along the association pathway, presumably related to the penalty required to remove interfacial ions. Analysis of dissociation reactions revealed that thrombin interactions with both NPs formed transient, weakly adhesive complexes characterized by short residence times (t(r) = 1/k(off) similar to 0.1-16 s). Interestingly, the reverse reactions were best described by multiple dissociation processes suggesting a heterogeneous population of complexes stabilized to different extent.

关键词： Hydrocarbons   Organic compounds   Transition states   Ethyl groups   Molecules  

摘要： Rate coefficients for the reactions of Cl atoms with isopropyl formate (IPF) and isobutyl formate (IBF) were measured experimentally over the temperature range of 268-363 K and at 760 Torr of nitrogen using relative rate method. Ethyl acetate and ethyl formate were used as reference compounds for the measurement of rate coefficients for the reaction of IPF with Cl atoms. Ethane and ethylene were used as reference compounds for the measurement of rate coefficients for the reaction of IBF with Cl atoms. The obtained rate coefficients for the reactions of IPF and IBF with Cl atoms at 298 K are (1.56 +/- 0.47) X 10(-11) and (7.60 +/- 1.10) X 10(-11) cm(3) molecule(-1) s(-1)respectively. The derived temperature dependent Arrhenius expression for the reactions of IPF and IBF with Cl atoms are k(R1)((268-363K))(Experimental)= (3.87 +/- 0.88) x 10(-12) exp [(418 +/- 70)/T] and k(R2(268-363K))(Experimental) = (1.83 +/- 0.45) X 10(-11) exp [(421 +/- 70)/T] cm(3) molecule(-1) s(-1) respectively. A qualitative analysis of the products formed during the reactions of Cl atoms with IPF and IBF were carried out using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared spectroscopy (GC-IR) as analytical tools, and the degradation mechanisms were proposed on the basis of end products. To rationalize our experimentally obtained results, computational calculations were performed to calculate the temperature dependent rate coefficients for these reactions over the temperature range of 200-400 K at CCSD(T)/cc-pVDZ//MP2/6-31+G(d, p) level of theory using canonical variational transition state theory (CVT) with small curvature tunneling (SCT). Detailed discussions on the thermochemistry of the reactions, branching ratios, and atmospheric implications are discussed in the manuscript.

关键词： Solvates   Hydrate formation   Cavities   Cluster chemistry   Molecules  

摘要： The formation of CH4 hydrate in a mesoporous metal-organic framework MIL-101 is investigated by microsecond molecular dynamics simulations. CH4 hydrate is observed to form preferentially in the outer space of MIL-101 cavities rather than inside the cavities;only when the hydrate formation is nearly complete in the outer space can stable hydrate form in MIL-101 cavities. The underlying reason is revealed to be the easy dissociation of small hydrate clusters formed in the nanospace of the cavities, because of the diffusion of CH4 molecules out of the cavities into the outer space. Compared with dry MIL-101, the CH4 storage capacity of H2O-saturated MIL-101 is drastically reduced as the cavities are occupied by H2O. When oversaturated with H2O, however, extra H2O molecules in the outer space of the cavities can form considerable CH4 hydrate, significantly promoting CH4 storage capacity. This study provides important mechanistic insights into the formation mechanism and process of CH4 hydrate in MIL-101 and will facilitate the design of emerging materials for energy storage.

关键词： Non-rubber components   Mechanical properties   Vulcanization kinetics  

摘要： Natural rubber (NR) with complex components has superior mechanical properties to synthetic high cis-1, 4-polyisoprene. It is still a challenge to explore the reason why NR owns superior mechanical properties. In previous studies, the excellent properties of NR have been ascribed to strain-induced crystallization phenomenon. However, in this study we find non-rubber components (NRC) in NR affecting vulcanization process, which finally contributes to excellent properties of NR. Through the changes of NRC content, the mechanical properties of NR can be tuned. The differential scanning calorimeter is used to investigate vulcanization kinetics. The results show that NRC decrease the activation energy of vulcanization process, which causes higher crosslinking density and curing rate. Through additional protein verifying and mimicking the acceleration effect of NRC, mechanical properties of NR can be tuned from soft state to tough state. Therefore, NRC affecting vulcanization kinetics is another essential reason why NR owns superior mechanical properties. This work also provides more insightful understanding toward the structure-property relationship of NR.

关键词： Lithium-ion cells   Cell kinetics   Cell emulation   Mechanistic modeling   Alawa  

摘要： The ongoing extension of usage for lithium-ion cells and packs in both stationary and mobile applications necessitates a steeply increasing need for comprehensive tools and models to diagnose and prognose cell performance. Among those, a simple mechanistic framework using electrode half-cell data has gained a lot of attention due to its ability to synthesize the terminal voltage of battery cells based on the individual electrode potentials. Although proven valid in the quantification of cell degradation, path dependence of aging and cell-to-cell variations, the application of the model framework has been restricted so far mostly to voltage profiles recorded at low C-rates. For use in battery management systems, this limitation should preferably be overcome to enable on-board diagnostics from medium to high rates and at any temperature. For this reason, this study aims at an advanced exploration of the cell's kinetics and how it can be compensated within the mechanistic framework. This was done by investigating two previously proposed parameters, the ohmic resistance increase and the rate degradation factor. This study indicates that both parameters follow a well-defined Arrhenius dependency allowing to map the voltage behaviour of the underlying half-cell to the measured full cell data at different rates and temperatures.

关键词： COAPT   high surgical risk   left ventricular dysfunction   mechanical circulatory support   MitraClip (R) device   mitral regurgitation   transcatheter mitral valve therapies  

摘要： Patients presenting with hemodynamic instability attributable to left ventricular systolic dysfunction and concomitant severe mitral regurgitation (MR) are increasingly recognized and pose complex management challenges. Surgical therapy is typically precluded owing to prohibitive mortality. The role of percutaneous mechanical circulatory support in such cases is well established;however, such interventions may be neither sufficient to achieve optimal stability nor prove definitive. The advent of novel catheter-based mitral repair modalities now offers primary decisive therapeutic intervention. Three cases of cardiogenic shock with severe MR illustrate the salutary hemodynamic and clinical responses to percutaneous mechanical support and valve repair by mitral clip.

关键词： Computational modeling   Bifurcation analysis   Computational modeling   Rule-based modelling   Glioblastoma   TNFRSF12A   Cell signaling   Systems biology  

摘要： Fn14 is a transmembrane receptor protein belonging to the tumor necrosis factor receptor (TNFR) superfamily. Many experimental reports have shown that crosslinking of the receptor by its extracellular ligand TWEAK induces prolonged activation of transcription factor NF-kappa B. This behavior is distinct from TNF-alpha receptor, which is a more well-characterized member of the TNFR family. TNF-alpha receptor, despite sharing many similar molecular interactions with Fn14, only transiently activates NF-kappa B in response to TNF-a stimulation. Here, we investigate molecular mechanisms that enable Fn14 to display such distinctive behavior. In particular, we focus on two specific features of the Fn14 pathway that potentially give rise to a positive feedback regulation and differentiate it from the TNF-alpha receptor signaling. By developing a mechanistic model, we analyze how these features may determine the dynamics of an Fn14-NF-kappa B response. Our analysis reveals that stimulation of Fn14 by TWEAK may generate highly non-linear dynamics, including stable limit cycles and bistable responses. The type of response depends both on the strength and duration of a TWEAK signal. Our predictions and analyses also show that the molecular interactions underlying the positive feedback explain the prolonged activation of NF-kappa B under certain parameter regimes. In light of the model predictions, we propose possible deregulations of Fn14 leading to its overexpression in solid tumors and tissue injuries. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： cyclic voltammetry   electrochemistry   electrokinetics   Pt single crystal   simulation  

摘要： A detailed understanding of the electrochemistry of platinum electrodes is of great importance for the electrochemical oxidation of fuels and electrochemical reduction of dioxygen in fuel cells. The Pt(111) facet is the most representative model mimicking Pt nanoparticles and polycrystals for fundamental studies. Herein, we propose a site-specific model accompanied with the typical elementary steps of the electrochemistry of Pt(111) in non-adsorbing electrolyte within the potential range between 0.05 and 1.15 V versus reversible hydrogen electrode. Simulations were conducted at different scanning rates based on the kinetics models. We reproduce all the anodic and cathodic peaks observed in the reported experimental curves. These results demonstrate the underlying mechanisms of the peak formation in different potential regions.

关键词： molecular dynamics simulation   molecular chain deformation behavior   poly-L-lactic acid   affine deformation   potential energy  

摘要： Generally, poly-L-lactic acid (PLLA) is being developed in various medical devices;it is still urgent to elucidate the correlation between molecular chain deformation behavior and mechanical properties such as stress. In addition, there are few cases where molecular dynamics simulation is used to compare the molecular chain deformation behavior which is difficult to evaluate in the micro region and the potential energy and evaluate mechanical properties like stress. Therefore, in this study, in order to compare molecular chain deformation behavior of PLLA using molecular dynamics method, analysis models of initial orientation 0 degrees, 45 degrees, 90 degrees and four random oriented models were prepared. In addition, tensile simulation was carried out using affine deformation, and the influence on the mechanical properties exerted by molecular chain deformation behavior was evaluated. As molecular chain deformation behavior, molecular chain length, molecular chain angle, distance between centers of gravity between molecular chains were determined, and in comparison with potential energy and stress generated in tensile simulation for evaluating mechanical behavior. As a result, it was shown that the model showing the curing behavior increased the stress after reaching the lower yield point, and the model not showing a remarkable increase after the stress reached the lower yield point. In addition, it was suggested that the elongation and angle change of the molecular chain had a large influence on the stress, and among them, the influence on the stress exerted by the angle change was the largest.