Peridynamic modeling and simulation of coupled thermomechanical removal of ice from frozen structures

Meccanica - In this work, a bond-based peridynamic de-icing model has been developed to simulate the thermo-mechanical ice removal process of frozen structures. In the proposed numerical method,...     

Electrophilic fluoroalkylthiolation induced diastereoselective and stereospecific 1,2-metalate migration of alkenylboronate complexes

A transition metal free process for conjunctive functionalization of alkenylboron ate-complexes with electrophilic fluoroalkylthiolating reagents is described, affording β-trifluoroalkylthiolated and difluoroalkylthiolated boronic esters in good yield and excellent diastereoselectivity. The potential applicability of the method was demonstrated by the preparation of a difluoromethylthiolated mimic 12 of a potential drug molecule PF-4191834 for the treatment of asthma.

A transition metal free process for conjunctive functionalization of alkenylboron ate-complexes with electrophilic fluoroalkylthiolating reagents affords β-tri- and difluoroalkylthiolated boronic esters in good yield and diastereoselectivity.

An electrophile-induced 1,2-metalate migration of an alkenylboron “ate” complex and subsequent base-promoted β-elimination to form a functionalized cis-alkene, now the so-called Zweifel reaction, was first reported by Zweifel and co-workers in 1967 (Fig. 1A).^1–3 The reaction was proposed to proceed via an initial attack of the π electron of the alkene moiety to iodine to generate a zwitterionic iodonium ion, which then undergoes a stereospecific 1,2-metalate to afford a β-iodoboronic ester, followed by anti-elimination upon treatment with a base to afford a cis-olefin. Thus, if the iodine is replaced by an alternative electrophilic reagent and the use of a base is omitted, an interrupted-Zweifel reaction for the preparation of a stereospecific β-functionalized boronic ester could be realized. Toward this end, Aggarwal reported the first example of such a reaction by employing PhSeCl as the electrophilic reagent.⁴ It was proposed that PhSeCl first reacts with an alkenylboronate complex to form a zwitterionic seleniranium ion. Subsequent diastereospecific 1,2-metalate migration affords the stereospecific β-seleno-alkylboronate (Fig. 1B). Likewise, shortly after, Denmark and co-workers reported an analogous Lewis-base catalysed enantioselective and diastereoselective carbosulfenylation of an alkenylboronate complex using N-arylthiosaccharin as the electrophile (Fig. 1C).⁵Open in a separate windowFig. 1The interrupted Zweifel reaction.In light of these discoveries and our recent success in the development of a toolbox of electrophilic fluoroalkylthiolating reagents including three trifluoromethylthiolating reagents α-cumyltrifluoromethane sulfenate,⁶N-trifluoromethylthio-saccharin⁷ and N-trifluoromethylthiodibenzenesulfonimide,⁸ and two difluoromethylthiolating reagents N-difluoromethylthiophthalimide⁹ and S-(difluoromethyl)benzenesulfonothioate,¹⁰ we wondered whether these electrophilic fluoroalkylthiolating reagents could also trigger the proposed stereospecific 1,2-metalatation of the alkenylboronate complex to afford β-fluoroalkylthiolated borane derivatives (Fig. 1D). The trifluoromethylthio (–SCF₃) and the difluoromethylthio (–SCF₂H) groups have gained great attention recently, partially because of their high and tuneable lipophilicity¹¹ that might improve the drug candidate''s cell membrane permeability and consequently, its overall pharmacokinetics.¹² Thus, the development of new efficient reactions for the incorporation of the trifluoromethylthio¹³ or difluoromethylthio groups¹⁴ would be of vital importance in facilitating medicinal chemists'' endeavours in new drug discovery. Herein, we report that by employing electrophilic difluoromethylthiolating reagent PhSO₂SCF₂H 2a as the electrophile, the proposed difluoromethylthiolating induced stereospecific 1,2-metalate migration of alkenyl boronate complexes occurred smoothly to afford β-difluoromethylthiolated boronic esters in good yields and excellent diastereoselectivity. Likewise, when electrophilic trifluoromethylthiolating reagent N-trifluoromethylthiosaccharin 7 was used, an analogous reaction for the diastereoselective formation of β-trifluoromethylthiolated boronic esters was successfully achieved.We began our study by examining the reaction of the electrophilic difluoromethylthiolating reagent 2a with the alkenylboronate complex which was generated in situ by mixing 1a and PhLi in diethyl ether. It was found that the reaction in CH₃CN occurred in full conversion after 12 hours at room temperature, affording the corresponding product 3a in 53% yield (Table 1, entry 1). When the amount of PhLi was increased to 1.3 equivalents, the yield was increased to 76%, while the yield decreased to 66% when 2.0 equivalents of PhLi were used, likely due to the decomposition of the product under strong basic conditions (Table 1, entries 1–5). We then further investigated the effect of the reaction temperature and the solvent. It was found that the temperature did not affect the reaction significantly since the yields of the desired products were decreased slightly to 72% and 70%, respectively, when the reactions were conducted at 0 °C or −15 °C (Table 1, entries 6 and 7). Likewise, the reaction was not sensitive to the polarity of the solvent since reactions conducted in less polar solvents such as THF or CH₂Cl₂ or nonpolar solvents like toluene occurred in slightly lower 60–73% yields (Table 1, entries 9–11). We also found that reaction using N-difluoromethylthiophthalimide as the electrophilic difluoromethylthiolating reagent gave the same product in a slightly lower yield (Table 1, entry 8).Optimization of conditions for the reaction of the alkenyl boronate complex with PhSO₂SCF₂H^a

Afterglow Implant for Arterial Embolization and Intraoperative Imaging

Transcatheter arterial embolization (TAE) is wildly used in clinical treatments. However, the online monitoring of the thrombosis formation is limited due to the challenges of the direct visualization of embolic agents and the real-time monitoring of dynamic blood flow. Thus, we developed a photochemical afterglow implant with strong afterglow intensity and a long lifetime for embolization and imaging. The liquid pre-implant injected into the abdominal aorta of mice was rapidly transformed into a hydrogel in situ to embolize the blood vessel. The vascular embolism position can be observed by the enhanced afterglow of the fixed implant, and the long lifetime of afterglow can also be used to monitor the effect of embolization. This provides an excellent candidate in bio-imaging to avoid the autofluorescence interference from continuous light excitation. The study suggests the potential usefulness of the implant as an embolic agent in TAE and artery imaging during a surgical procedure.     

Chemical Constituents of Selaginella moellendorffii

Chemistry of Natural Compounds -     

金属衬底在石墨烯化学气相沉积生长中的作用

以过渡金属为催化衬底的化学气相沉积法(Chemical Vapor Deposition，CVD)已经可以制备与机械剥离样品相媲美的石墨烯，是实现石墨烯工业应用的关键技术之一。原子尺度理论研究能够帮助我们深刻理解石墨烯生长机理，为实验现象提供合理的解释，并有可能成为将来实验设计的理论指导。本文从理论计算的角度，总结了各种金属衬底在石墨烯CVD生长过程中的各种作用与相应的机理，包括在催化碳源裂解、降低石墨烯成核密度等，催化加快石墨烯快速生长，修复石墨烯生长过程中产生的缺陷，控制外延生长石墨烯的晶格取向，以及在降温过程中石墨烯褶皱与金属表面台阶束的形成过程等。在本文最后，我们对当前石墨烯生长领域中亟需解决的理论问题进行了深入探讨与展望。     

Patterning catalyst via inkjet printing to grow single-walled carbon nanotubes

We demonstrated a method to pattern catalyst via inkjet printing to grow SWNTs, using metal salt solutions as the inks and an ordinary office-use printer. We printed water solutions of cobalt acetate on hydrophilic Si substrates and grew high quality SWNT films.     

一种基于自适应单元删除率的BESO方法

在ESO中采用动态删除率能有效地提高优化效率和稳定性，但现有的动态删除率策略都含有经验参数，确定删除率的过程较为复杂。本文提出了一种用于BESO的无经验参数自适应单元删除率确定方法。通过分析单元删除率对优化稳定性的影响，得到了结构优化过程中单元删除率的理想变化规律和单元灵敏度均匀化信息对删除率的影响情况，并据此分析了经验参数引入的原因，从而构造了评价单迭代步的单元灵敏度均匀化程度指标。然后，基于单迭代步的单元灵敏度均匀化程度指标，构造了全部迭代步信息下的单元灵敏度均匀化程度相对指标，结合单元删除率的推荐范围值，给出了一种自适应于结构优化进程的单元删除率自适应函数。最后，给出了基于自适应单元删除率的BESO方法实现流程。经典算例的结果对比说明，本文方法在保证优化质量相近的情况下，具有更好的优化效率和稳定性。     

Graph-Theoretical Method to the Existence of Stationary Distribution of Stochastic Coupled Systems

In this paper, by linking Fokker–Planck equations with stochastic coupled systems, a new method is provided to investigate the existence of a stationary distribution of stochastic coupled systems. Based on the graph theory and the Lyapunov method, an appropriate Lyapunov function associated with stationary Fokker–Planck equations is constructed. Moreover, a Lyapunov-type theorem and a coefficients-type criterion are obtained to guarantee the existence of a stationary distribution. Furthermore, theoretical results are applied to explore the existence of a stationary distribution of stochastic predator–prey models with dispersal and a sufficient criterion is presented correspondingly. Finally, a numerical example is given to illustrate the effectiveness of our results.     

Multiple positive solutions for Schrödinger‐Poisson system involving singularity and critical exponent

In this paper, the existence and multiplicity of positive solutions is established for Schrödinger‐Poisson system of the form where 0 ∈ Ω is a smooth bounded domain in , , and λ > 0 is a real parameter. Combining with the variational method and Nehari manifold method, two positive solutions of the system are obtained.