Two-component generalized Ragnisco–Tu equation and the Riemann–Hilbert problem

Theoretical and Mathematical Physics - Using the Riemann–Hilbert approach, we investigate the two-component generalized Ragnisco–Tu equation. The modified equation is integrable in the...     

Description of stability for linear time-invariant systems based on the first curvature

This paper focuses on using the first curvature κ(t) of trajectory to describe the stability of linear time-invariant system. We extend the results for two and three-dimensional systems (Wang, Sun, Song et al, arXiv:1808.00290) to n-dimensional systems. We prove that for a system $\text{◂=▸}\dot{r}(t)=\text{◂⋅▸}Ar(t)$, (a) if there exists a measurable set whose Lebesgue measure is greater than zero, such that $\text{◂≠▸}\underset{t\to +\infty }{\lim }\kappa (t)\ne 0$ or $\underset{t\to +\infty }{\lim }\kappa (t)$ does not exist for any initial value in this set, then the zero solution of the system is stable; (b) if the matrix A is invertible, and there exists a measurable set whose Lebesgue measure is greater than zero, such that $\text{◂=▸}\underset{t\to +\infty }{\lim }\kappa (t)=+\infty$ for any initial value in this set, then the zero solution of the system is asymptotically stable.     

Enzymatic Extraction of Bioactive and Self‐Assembling Wool Keratin for Biomedical Applications

Keratin is widely recognized as a high‐quality renewable protein resource for biomedical applications. Despite their extensive existence, keratin resources such as feathers, wool, and hair exhibit high stability and mechanical properties because of their high disulfide bond content. Consequently, keratin extraction is challenging and its application is greatly hindered. In this work, a biological extraction strategy is proposed for the preparation of bioactive keratin and the fabrication of self‐assembled keratin hydrogels (KHs). Based on moderate and controlled hydrolysis by keratinase, keratin with a high molecular weight of approximately 45 and 28 kDa that retain its intrinsic bioactivities is obtained. The keratin products show excellent ability to promote cell growth and migration and are conferred with significant antioxidant ability because of their intrinsically high cysteine content. In addition, without the presence of any cross‐linking agent, the extracted keratin can self‐assemble into injectable hydrogels. The KHs exhibit a porous network structure and 3D culture ability, showing potential in promoting wound healing. This enzyme‐driven keratin extraction strategy opens up a new approach for the preparation of keratin that can self‐assemble into injectable hydrogels for biomedical engineering.     

Multifaceted Influences of Melanin‐Like Particles on Amyloid‐beta Aggregation

The properties of eumelanin‐like particles (EMPs) and pheomelanin‐like particles (PMPs) in regulating the process of amyloid formation of amyloid‐beta 42 (Aβ42) were examined. EMPs and PMPs are effective both in interfering with amyloid aggregation of Aβ42 and in remodeling matured Αβ42 fibers. The results suggest that some (but not all) molecular species consisting of melanin‐like particles (MPs) are responsible for their inhibiting property toward amyloid formation, and the influence is likely manifested by long‐range interactions. Incubating preformed Aβ42 fibers with catechols or MPs leads to the formation of mesh‐like, interconnected Aβ42 fibers encapsulated with melanin‐like material. MPs are kinetically more effective than catechol monomers in this process, and a detailed investigation reveals that 4,5‐dihydroxyindole, a major intermediate in the formation of melanin‐like species, and its derivatives are mainly responsible for remodeling amyloid fibers.     

3-O-Sulfation of Heparan Sulfate Enhances Tau Interaction and Cellular Uptake

Prion-like transcellular spreading of tau in Alzheimer's Disease (AD) is mediated by tau binding to cell surface heparan sulfate (HS). However, the structural determinants for tau–HS interaction are not well understood. Microarray and SPR assays of structurally defined HS oligosaccharides show that a rare 3-O-sulfation (3-O-S) of HS significantly enhances tau binding. In Hs3st1^−/− (HS 3-O-sulfotransferase-1 knockout) cells, reduced 3-O-S levels of HS diminished both cell surface binding and internalization of tau. In a cell culture, the addition of a 3-O-S HS 12-mer reduced both tau cell surface binding and cellular uptake. NMR titrations mapped 3-O-S binding sites to the microtubule binding repeat 2 (R2) and proline-rich region 2 (PRR2) of tau. Tau is only the seventh protein currently known to recognize HS 3-O-sulfation. Our work demonstrates that this rare 3-O-sulfation enhances tau–HS binding and likely the transcellular spread of tau, providing a novel target for disease-modifying treatment of AD and other tauopathies.     

Ni单原子催化剂表面CO2电还原动力学的电化学谱学解析

针对Ni单原子催化剂表面的CO₂电还原反应(CO₂RR), 提出了以Ni为活性位点的“单中心”机理以及同时借助Ni位点还原和碳氮锚定位水解的“双功能”机理. 依据稳态极化的实验结果, 开展了CO₂RR的动力学解析与模型参数的敏感性分析; 借助暂态模型方程, 分别获取可表达CO₂RR线性与非线性频响特征的电化学阻抗谱(EIS)与总谐波失真(THD)谱. 研究结果表明, CO₂的溶解分压对CO₂RR活性影响最显著. 若CO₂RR遵循“单中心”机理, Ni位点COOH_ads的形成为速率控制步骤; 但若为“双功能”机理, 碳氮锚定位的水解与Ni位点的CO_2,ads还原同为速率控制步骤. EIS理论上可用于区分CO₂RR的“单中心”机理与“双功能”机理; 与之相比, THD谱在CO₂RR的机理识别中并无优势.     

Catalytic cross-coupling of aniline by pyrite and dissolved oxygen under alkaline conditions

Pyrite catalyzes oxidation of various organic contaminants by dissolved oxygen (DO) under acidic conditions; however, the catalytic mechanism under alkaline conditions is still not clear. In this study, we observe increased oxidation rates of aniline with increasing pHs (7.0–11.0). Electron paramagnetic resonance (EPR) analysis and quenching experiments rule out contributions of •OH, O₂^•−, ¹O₂ and Fe (IV) to aniline oxidation and suggest that the Fe (III)–OOH peroxo and/or H₂O₂ are the primary oxidative species in the oxidation of aniline at pH 11.0. In addition, 200 mg L⁻¹ H₂O₂ does not apparently increase the oxidation rate of aniline, which also rules out the predominant contribution of the produced H₂O₂ to aniline oxidation. We therefore suggest that the Fe (III)–OOH peroxo is indeed the primary oxidative species in the pyrite–DO system under alkaline conditions. Analyses of solid total organic carbon (TOC), gas chromatography–mass spectrometry and Fourier-transform infrared spectroscopy further reveal that more than 83.3% aniline has been polymerized to polyaniline, instead of being mineralized into CO₂ and H₂O, indicating that H-abstraction from aniline by the Fe (III)–OOH peroxo is an important step in the oxidation of aniline under alkaline conditions. This study provides new insight into the oxidative species in the pyrite–DO system, and opens a new door for organic degradations under alkaline conditions.     

基于分子工程的方法设计首例具有Sr2Be2B2O7 (SBBO)结构的深紫外氟碳酸盐双折射晶体AMgLi2(CO3)2F (A=K,Rb)※

分子结构设计是开发新化合物和通过原子尺度操纵优化晶体结构的一种引人注目的策略. 在这个工作中, 利用分子工程的思想, 基于SBBO结构, 成功设计并合成两个新型氟碳酸盐KMgLi₂(CO₃)₂F和RbMgLi₂(CO₃)₂F. 在两个结构中, a-b平面是由CO₃和LiO₃F阴离子基团组成的无限[Li₃C₃O₆F₃]_∞层, 进一步相邻的层通过F原子连接形成一个独特的[Li₆C₆O₁₂F₃]_∞双层. 这种结构特征对改善晶体的层状生长习性和消除晶体的多晶性有很大的帮助. 光学测试表明, 该系列晶体具有大的双折射和短的紫外截止边, 是深紫外双折射晶体良好的候选材料.