Carbon-supported MoS2 is a promising electrocatalyst for hydrogen evolution reaction (HER), however, it is not well understood how carbon substrate effects might modulate MoS2 activity. Herein, we ...report on development and characterization of heterostructured thin-film electrodes consisting of MoS2 supported on nitrogenated graphitic carbons, that display well defined geometry, morphology and concentration of N-functionalities. Carbon supports were synthesized via magnetron sputtering and thermal modifications, yielding graphitized smooth thin-films rich in either pyridinic-N or graphitic-N functionalities. CVD deposition of MoS2 using close proximity precursor methods yielded MoS2/carbon electrodes with high contact area between the two phases, thus enabling investigation of substrate effects on MoS2 activity. Voltammetry in acid and alkaline electrolytes indicates that N-functionalities affect HER performance with effects being pH-dependent. At low pH, similar overpotentials and Tafel slopes are observed independently of whether graphitic-N or pyridinic-N groups are present at the carbon support. However, at high pH, pyridinic-N groups lead to suppression of HER activity. We propose that deprotonation and lone-pair availability at pyridinic-N modulate activity with electrostatic interactions leading to weaker MoS2-carbon coupling for the deprotonated form. This has important implications for smart design of heterostructured electrocatalysts where synergistic/inhibitory behaviors might be exploited/avoided to control performance in HER electrocatalysis.
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We present a collection of 52 nonlinear eigenvalue problems in the form of a MATLAB toolbox. The collection contains problems from models of real-life applications as well as ones constructed ...specifically to have particular properties. A classification is given of polynomial eigenvalue problems according to their structural properties. Identifiers based on these and other properties can be used to extract particular types of problems from the collection. A brief description of each problem is given. NLEVP serves both to illustrate the tremendous variety of applications of nonlinear eigenvalue problems and to provide representative problems for testing, tuning, and benchmarking of algorithms and codes.
One of the most commonly used bonds between two biomolecules is the bond between biotin and streptavidin (SA) or streptavidin homologues (SAHs). A high dissociation constant and the consequent ...high-temperature stability even allows for its use in nucleic acid detection under polymerase chain reaction (PCR) conditions. There are a number of SAHs available, and for assay design, it is of great interest to determine as to which SAH will perform the best under assay conditions. Although there are numerous single studies on the characterization of SAHs in solution or selected solid phases, there is no systematic study comparing different SAHs for biomolecule-binding, hybridization, and PCR assays on solid phases. We compared streptavidin, core streptavidin, traptavidin, core traptavidin, neutravidin, and monomeric streptavidin on the surface of microbeads (10–15 μm in diameter) and designed multiplex microbead-based experiments and analyzed simultaneously the binding of biotinylated oligonucleotides and the hybridization of oligonucleotides to complementary capture probes. We also bound comparably large DNA origamis to capture probes on the microbead surface. We used a real-time fluorescence microscopy imaging platform, with which it is possible to subject samples to a programmable time and temperature profile and to record binding processes on the microbead surface depending on the time and temperature. With the exception of core traptavidin and monomeric streptavidin, all other SA/SAHs were suitable for our investigations. We found hybridization efficiencies close to 100% for streptavidin, core streptavidin, traptavidin, and neutravidin. These could all be considered equally suitable for hybridization, PCR applications, and melting point analysis. The SA/SAH–biotin bond was temperature-sensitive when the oligonucleotide was mono-biotinylated, with traptavidin being the most stable followed by streptavidin and neutravidin. Mono-biotinylated oligonucleotides can be used in experiments with temperatures up to 70 °C. When oligonucleotides were bis-biotinylated, all SA/SAH–biotin bonds had similar temperature stability under PCR conditions, even if they comprised a streptavidin variant with slower biotin dissociation and increased mechanostability.
In the last two decades, while searching for interesting applications of ionic liquids as potent solvents, their solvation properties and their general impact on biomolecules, and in particular on ...proteins, gained interest. It turned out that ionic liquids are excellent solvents for protein refolding and crystallization. Biomolecules showed increased solubilities and stabilities, both operational and thermal, in ionic liquids, which also seem to prevent self-aggregation during solubilization. Biomolecules can be immobilized, e.g. in highly viscous ionic liquids, for particular biochemical processes and can be designed to some extent by the proper choice of the ionic liquid cations and anions, which can be characterized by the Hofmeister series.
Protex is an open-source program that enables proton exchanges of solvent molecules during molecular dynamics simulations. While conventional molecular dynamics simulations do not allow for bond ...breaking or formation, protex offers an easy-to-use interface to augment these simulations and define multiple proton sites for (de-)protonation using a single topology approach with two different
-states. Protex was successfully applied to a protic ionic liquid system, where each molecule is prone to (de-)protonation. Transport properties were calculated and compared to experimental values and simulations without proton exchange.
Purpose
Although continuous improvements have been made, there is still a considerable amount of unsatisfied patients after total knee arthroplasty (TKA). A main reason for this high percentage is ...anterior knee pain, which is supposed to be provoked by post-operative increased retropatellar peak pressure. Since rotational malalignment of the implant is believed to contribute to post-operative pain, the aim of this study was to examine the influence of tibial component rotation on knee kinematics and retropatellar pressure.
Methods
Eight fresh-frozen knee specimens were tested in a weight-bearing knee rig after fixed-bearing TKA under a loaded squat from 20° to 120° of flexion. To examine tibial components with different rotations, special inlays with 3° internal rotation and 3° external rotation were produced and retropatellar pressure distribution was measured with a pressure-sensitive film. The kinematics of the patella and the femorotibial joint were recorded with an ultrasonic-based motion analysis system.
Results
Retropatellar peak pressure decreased significantly from 3° internal rotation to neutral position and 3° external rotation of the tibial component (8.5 ± 2.3 vs. 8.2 ± 2.4 vs. 7.8 ± 2.5 MPa). Regarding knee kinematics femorotibial rotation and anterior–posterior translation, patella rotation and tilt were altered significantly, but relative changes remained minimal.
Conclusion
Changing tibial rotation revealed a high in vitro influence on retropatellar peak pressure. We recommend the rotational alignment of the tibial component to the medial third of the tibial tuberosity or even more externally beyond that point to avoid anterior knee pain after TKA.
The solvation dynamics of coumarin C153 dissolved in three selected molecular ionic liquids - EMIM(+)BF4(-), EMIM(+)TfO(-), and BMIM(+)BF4(-) - was studied by molecular dynamics simulations including ...polarization forces. The solvation response function was decomposed with respect to permanent and induced charge distributions, cationic and anionic contributions, and translational and non-translational motions. The latter decomposition was accomplished by an appropriate multipole expansion. Furthermore, the difference in solvation energy was resolved radially. The dynamics in the sub-picosecond regime was elucidated as the mutual translational motion of the solute and the cage formed by the first solvation shell. For a qualitative interpretation, solvent molecules can be reduced to "quasi-atomic" ions carrying a net charge at their molecular center of mass. Towards a quantitative description, the dipole moment serves as a measure of charge anisotropy.
Classical Molecular Dynamics simulations describing electrostatic interactions only by point charges can be augmented by the inclusion of atomic polarisabilities modelling charge flexibility. Two ...widely used models, Drude oscillators and induced point-dipoles, are compared in a systematic study using their respective implementations in CHARMM and AMBER. The question of necessity and importance of polarisable hydrogen atoms is raised and two implementations, in an implicit or explicit manner, are compared to the case of non-polarisable hydrogen atoms. For all these polarisability models, the strength of the respective atomic polarisabilities was incremented in steps of ten percent up to their full values. The influence of polarisability on the structure and dynamics of the ionic liquid EMIM(⊕)CF3SO, which is chosen as a test case, is studied thoroughly. Using appropriate model functions, the respective dynamical and structural data are fitted. Thus, a small set of parameters is deduced, which highlights the effect of polarisability. Generally, flexibility of the charge distribution leads to enhanced fluidity and less pronounced structure. As this usually occurs when adding a co-solvent to an ionic liquid, the inclusion of polarisability can be seen in much the same way in that it acts like an inner solvent.
This work reports for the first time the computational, frequency-dependent dielectric spectrum of the polarizable molecular ionic liquid 1-ethyl-3-methylimidazolium triflate as well as its ...experimental analogue. In the frequency range from 500 MHz up to 20 GHz the agreement between the computational and the experimental spectrum is quantitative. For higher frequencies up to 10 THz the agreement is still remarkably good. The experimental asymptotic limit ε(∞) is 2.3. The difference in the computational value of 1.9 comes solely from the neglect of polarizability of the hydrogen atoms. For reasons of efficiency the simulations are based on the Lagrangian algorithm for the Drude oscillator model which cannot handle polarizable hydrogens. In the computational analysis the complete spectrum of the generalized dielectric constant ∑(0)*(ν) is splitted into its translational and non-translational components, called dielectric conductivity ϑ(0)(ν) and dielectric permittivity ε(ν). For 1-ethyl-3-methylimidazolium triflate both components contribute with equal weight and overlap in the complete frequency range. The inclusion of polarization forces, however, is quite different for the two components: the collective non-translational dynamics is accelerated and hence the dielectric permittivity is shifted to higher frequencies. The low frequency region of the dielectric conductivity is also affected while its high frequency part remains almost unchanged. Inductive effects are not only visible at high frequencies but also contribute in the sub-GHz region. The computational peak found in this region correlates with the experimental OKE-spectrum. It may be interpreted as the correlation between the induced dipole moment of the cations and the local electric field exerted by the anionic cage.
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