Dynamics of water in real space and time

Owing to marked advances in instrumentation in X-ray and neutron scattering the time-dependent pair correlation function, the Van Hove function, can now be determined by inelastic X-ray and neutron scattering measurements. The local dynamics of water in real space and time is visualised by this approach. We discuss how the dynamic properties, such as viscosity and diffusion, can be elucidated through the Van Hove function of water.     

Ultrafast Single-Scan 2D NMR Spectroscopic Detection of a PHIP-Hyperpolarized Protease Inhibitor

Two-dimensional NMR spectroscopy is one of the most important spectroscopic tools for the investigation of biological macromolecules. However, due to the low sensitivity of NMR spectroscopy, it takes usually from several minutes to many hours to record such spectra. Here, the possibility of detecting a bioactive derivative of the sunflower trypsin inhibitor-1 (SFTI-1), a tetradecapeptide, by combining parahydrogen-induced polarization (PHIP) and ultrafast 2D NMR spectroscopy is shown. The PHIP activity of the inhibitor was achieved by labeling with O-propargyl-l -tyrosine. In 1D PHIP experiments a signal enhancement of a factor of approximately 1200 compared to standard NMR was found. This enhancement permits measurement of 2D NMR correlation spectra of low-concentrated SFTI-1 in less than 10 seconds, employing ultrafast single-scan 2D NMR detection. As experimental examples PHIP-assisted ultrafast single-scan TOCSY spectra of SFTI-1 are shown.     

Size‐Dependence of the Melting Temperature of Individual Au Nanoparticles

Nanoparticles have an immense importance in various fields, such as medicine, catalysis, and various technological applications. Nanoparticles exhibit a significant depression in melting point as their size goes below ≈10 nm. However, nanoparticles are frequently used in high temperature applications such as catalysis where temperatures often exceed several 100 degrees which makes it interesting to study not only the melting temperature depression, but also how the melting progresses through the particle. Using high‐resolution transmission electron microscopy, the melting process of gold nanoparticles in the size range of 2–20 nm Au nanoparticles combined with molecular dynamics studies is investigated. A linear dependence of the melting temperature on the inverse particle size is confirmed; electron microscopy imaging reveals that the particles start melting at the surface and the liquid shell formed then rapidly expands to the particle core.     

Hydrogen-induced dynamic slowdown of metallic glass-forming liquids

Dynamics of hydrogen doped Cu_(50) Zr_(50) glass-forming liquids are investigated by using the newly developed modified embedded atomic method(MEAM) potential based on molecular dynamics simulations. We find that the doping of hydrogen atoms slows down the relaxation dynamics, reduces the fragility of supercooled melts, and promotes the occurrence of glass transitions. The dynamic slowdown is suggested to be closely related to the effect of hydrogen atoms on locally ordered structure of melts. With increasing concentration of hydrogen, the five-fold symmetry associated with Cu-and Zr-centered polyhedrons is lowered, on the other hand, the local order featuring metal hydrides is enhanced. The latter dominates the dynamic behaviors of glass-forming liquids, especially for Zr atoms, and results in the dynamic slowdown.     

The Fundamental Equations of Change in Statistical Ensembles and Biological Populations

A recent article in Nature Physics unified key results from thermodynamics, statistics, and information theory. The unification arose from a general equation for the rate of change in the information content of a system. The general equation describes the change in the moments of an observable quantity over a probability distribution. One term in the equation describes the change in the probability distribution. The other term describes the change in the observable values for a given state. We show the equivalence of this general equation for moment dynamics with the widely known Price equation from evolutionary theory, named after George Price. We introduce the Price equation from its biological roots, review a mathematically abstract form of the equation, and discuss the potential for this equation to unify diverse mathematical theories from different disciplines. The new work in Nature Physics and many applications in biology show that this equation also provides the basis for deriving many novel theoretical results within each discipline.     

Comparison of Penta and Tetra-pyridyl Cobalt-based Catalysts for Water Reduction: H2 Production Cycle,Solvent Response and Reduction Free Energy

Understanding water reduction towards H₂ generation is crucial to overcome today's renewable energy obstacles. Previous studies have shown the superior H₂ production performances of Cobalt based penta-pyridyl (CoaPPy) and tetra-pyridyl (CoaTPy) complexes in solution. We investigate H₂ production cycles of CoaPPy and CoaTPy complexes immersed in water solution by means of Ab-initio Molecular Dynamics and Density Functional Theory. We monitor dynamic properties of the systems, solvent response and structural changes occurring in the catalysts, by simulating all intermediate steps of the H₂ production cycle. Reduction free energies and reorganization energies are calculated. Our results show that, following the first electron injection, H₂ production proceeds with the singlet spin state. Following the first electron insertion, we observe a significant rearrangement of the hydrogen bonding network in the first solvation shell. The cobalt center turns out to be more accessible for the surrounding water molecules in the case of CoaTPy at all the intermediate steps, which explains its higher catalytic performance over CoaPPy. Following the first reduction reaction, a larger gain in reduction free energy is estimated for CoaTPy with respect to CoaPPy, with a difference of 0.14 eV, in line with the experiments. For the second reduction, instead, CoaPPy shows more negative reduction potential, by 0.41 eV.     

利用可见-近红外-中红外超快光谱揭示离子交换法制备的少层MoS2中缺陷介导的载流子动力学

本文结合可见-近红外-中红外瞬态吸收光谱技术对离子交换法制备的少层MoS₂中缺陷介导的载流子动力学进行了详细的解析. 在近红外瞬态吸收光谱中观察到的宽带漂白信号表明少层MoS₂纳米片带隙中分布着大量的缺陷态. 实验结果明确揭示了载流子被缺陷态的快速捕获以及进一步的复合过程，证明带隙中的缺陷态对MoS₂光生载流子动力学过程起着至关重要的作用. 在中红外瞬态吸收光谱中观察到的正信号到负信号的转变进一步证实了在导带下小于0.24 eV处存在被载流子占据的缺陷态. 这些在少层MoS₂纳米片中存在的缺陷态可以作为有效的载流子捕获中心来辅助光生载流子在皮秒时间尺度内完成非辐射复合过程.     

Evaluating the potential of vaccine-induced type replacement for high-risk human papillomaviruses

Persistent infection with human papillomavirus (HPV) is the main cause of cervical cancer. Current HPV vaccines protect against both HPV-16 and -18, which are known to cause approximately 70% of cervical cancer cases worldwide. These vaccines have shown to be highly effective in preventing infection by their targeted types. However, there is a broad diversity of HPV types not targeted by the vaccines, and there is controversy about a possible increase in the prevalence of these non-targeted types after a vaccination program. Here, we propose a within-host metapopulation model to study the possibility of vaccine-induced type replacement for oncogenic types. It is generally believed that the theoretical possibility of type replacement strongly depends on the existence of natural type competition mechanisms. Nevertheless, our results suggest that type replacement is viable at the within-host level if the degree of cross-protection induced by the vaccine is low, even if there is no underlying competition among HPV types. Consequently, the impact of current HPV vaccines at both the immunological and epidemiological levels rely upon the level of cross-protection.     

Ultrafast Excited State Dynamics of Biliverdin Dimethyl Ester Coordinate with Zinc Ions

As one of the biological endogenous pigments, biliverdin (BV) and its dimethyl ester (BVE) have extremely weak fluorescence in solution with quantum yield less than 0.01%. However, the situation reverses with the addition of zinc ions. The strength for fluorescence of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex is greatly enhanced and fluorescence quantum yield can increase to \begin{document}$ \sim $\end{document}5%. Herein, we studied ultrafast excited state dynamics of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in ethanol, \begin{document}$ n $\end{document}-propanol, and DMSO solutions in order to reveal the mechanism of fluorescence quantum yield enhancement. The results show that BVE can form a stable coordination complex with zinc with 1:1 stoichiometry in solution. BVE is structurally and energetically more stable in the complex. Using picosecond time-resolve fluorescence and femtosecond transient absorption spectroscopy, we show that smaller non-radiative rate constant of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in DMSO is the key to increasing its fluorescence quantum yield and the excited state decay mechanism is also revealed. These results provide valuable information about the fluorescence property change after BVE binding to metal ions and may provide a guidance for the study of phytochromes or other fluorescence proteins in which BV/BVE acts as chromophores.