Control and optical mapping of mechanical transitions in polymer networks and DNA-based soft materials

Complex mechanical changes in response to an external trigger are pervasive in natural soft materials and often sought for applications. Be it the reversible stiffening of sea cucumber, the failure of a polymeric or colloidal gel under load, or the dissolution of a biosensing hydrogel upon target binding, mechanical transitions are typically enabled, and critically affected, by heterogeneous structures and reversible bonds. New possibilities to monitor evolving properties and to gain access to stress propagation with temporal and spatial resolution are being disclosed by mechanochromic molecules and molecular complexes, which transduce a mechanical stress into a light signal and act as built-in stress reporters. I will review recent strategies and identify future directions for the design of mechanically responsive soft networks and for their optical mapping, focusing particular attention on the emerging class of hydrogels based on DNA self-assembly.     

Green one-pot multicomponent synthesis of pyrrolidinones using planetary ball milling process under solvent-free conditions

This paper presents a novel and efficient protocol for the synthesis of pyrrolidinones using catalytic loading of 1,1'-butylenebis(3-sulfo-3H-imidazol-1-ium) hydrogen sulfate as a recyclable Brönsted acid ionic liquid through ball milling process at room temperature under solvent-free conditions. The developed method provides good to excellent yields of various pyrrolidinones in environmentally friendly conditions. Furthermore, this efficient protocol displays a combination of the synthetic advantage of one-pot multicomponent reaction with ecological benefits and convenience of a mechanochemical procedure.     

Recent applications of mechanochemistry in enantioselective synthesis

In recent years, sustainable organocatalysis has become a relevant target in asymmetric organic synthesis. Among the most successful strategies to achieve “greener” organocatalyzed processes are (1) the elimination of solvent from reaction media, and (2) the use of alternative activation energies such as solvent-free mechanochemistry in high speed ball mills. In recent years we have stepped up efforts in the pursuit of organocatalysts and biocatalysts that allow reactions to take place in the absence of solvent and under mechanochemical activation. In this article we present the application of small dipeptides as chiral organocatalysts under solvent-free and high-speed ball milling conditions, with focus on the asymmetric aldol addition reaction. Finally, we report on recent results using supported enzymes for the resolution of racemic β-amino acids and amines, under mechanochemical conditions.     

量子化学模型方法在机械力化学中的应用

机械力化学作为一种无需溶剂的绿色化学技术得到广泛关注。然而,机械力化学反应机制需要从原子和分子尺度上深入理解力诱导的化学反应。在过去的20年中,量子化学模型方法在机械力化学机理研究中得到广泛应用,高精度量化计算可得到外力下变形分子的几何结构、能量、过渡态等诸多性质。本文介绍了目前机械力化学领域的主流量子化学模型的基本原理,同时也关注了这些模型方法在软件上的具体实现,并借助典型的案例阐述了量子化学模型在解释机械力化学机理中的作用与价值。     

Catalytic activity of novel thermoplastic/cellulose-Au nanocomposites prepared by cryomilling

Due to environmental concerns, increasing attention has been focused on the application and preparation of biobased polymers and their blends. In this study, cellulose, the most spread biopolymer on Earth, was used in the preparation of novel cotton/polypropylene-Au and cotton/polyethylene-Au nanocomposites via a green mechanochemical approach. First, mechanoradicals were generated by ball milling of the cotton and thermoplastics under cryo conditions, and then, these radicals were used in the reduction of Au ions to Au nanoparticles (Au NPs). Nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The application of mechanochemistry in obtaining the cotton/thermoplastic blends allowed homogenous and fine blending of the samples and in addition, excluded the usage of toxic solvents. Since Au NPs exhibit a wide range of applications, e.g., in catalysis, cotton/thermoplastic-Au nanocomposites were used to catalyze the reduction reaction of 4-nitrophenol to
4-aminophenol, followed by UV-Vis spectroscopy. Finally, the hydrophobicity of the nanocomposites was alternated by tuning the blend composition. In the prepared nanocomposites, cotton and thermoplastics acted as very good supporting matrices for the Au NPs and provided satisfactory access to the NPs.     

Reaction mechanism in the mechanochemical synthesis of dibenzophenazine: application of vibronic coupling density analysis

The reaction mechanism for mechanochemical synthesis of dibenzophenazine was theoretically investigated in terms of the vibronic coupling density, which describes the interactions between electrons and nuclear motions. The concept theoretically indicates experimentally observed reactive sites that cannot be explained by the conventional frontier orbital theory. The results of vibronic coupling density analysis suggested the difference between reaction mechanisms under thermal and mechanochemical conditions.     

Oxidation of 1,3-pentadiene on vanadium containing HZSM-5

The possibility of mechanochemical promotion of skeletal nickel catalysts has been shown with the use of mechanical Ni−Al−Mo alloys as Raney nickel precursors in hydrogenation reactions. The mechanochemical promotion makes it possible to introduce molybdenum atoms into the catalyst lattice in the form of a solid solution. These catalysts are more active than pyrometallurgical ones. The increased activity of the catalysts in explained by changes in the structure and energetic state of the catalyst surface     

Comprehensive experimental investigation of mechanically induced 1,4-diazines synthesis in solid state

Compared mechanosynthesis of two condensed 1,4-diazines were investigated in ball milling conditions from o-phenylenediamine. ¹³C CP-MAS NMR revealed a hemiaminal intermediate for dibenzo[a,c]phenazine synthesis accumulated under mechanical action, as confirmed by calorimetry. Such intermediate, which is not detected in the case of 2,3-diphenylquinoxaline synthesis, provides experimental evidence of a concerted reaction between highly reactive mechanically-excited diamine and 9,10-phenanthrenequinone.     

Formation of liquid menisci in flexible nanochannels

In the present paper a novel mechanochemical process for the elimination of organic pollutants dissolved in water is proposed. In this regard, phenol aqueous solutions (100 mg L⁻¹) were ball-milled for 0, 12, 18, 24, 36, 48, and 72 h with and without a well-characterized (XRD, SEM, and N₂ Adsorption), rutile powder catalyst and the reaction products analyzed with UV and GC/MS. It was found that when the catalyst was not included in the process, phenol was not affected, but when it was included, phenol was decomposed. The catalyst itself did not change and the reaction follows a pseudo-first-order kinetics. Besides, intermediates which are characteristic of the OH radical mechanism were found in the reaction products. Then, a mechanism similar to those accepted for other advanced oxidation processes was proposed. The value measured for the pseudo-first-order reaction constant was very low, indicating that the reported process is inefficient. Nevertheless, this problem could be solved by applying catalysts consisting of particles with smaller diameters.     

Mechanochemical Synthesis of High Crystalline Cerium Hexaboride Nanoparticles from CeO2‐B2O3‐Mg Ternary System

High crystalline cerium hexaboride (CeB₆) nanoparticles (NPs) were synthesized using mixture of mag‐ nesium (Mg), cerium oxide (CeO₂) and boron oxide (B₂O₃) via the mechanochemical process at room tem‐ perature. Based on the results, magnesiothermic reduction of B₂O₃ occurred after about 2 h of milling in a mechanically induced self‐sustaining reaction (MSR). The significant amount of heat produced by the reduction reaction resulted in CeO₂ reduction to elemental Ce which finally reacted with elemental B and formed CeB₆ compound. According to XRD analyses, the degree of crystallinity and lattice parameter of the product was calculated about 93 % and 4.1458 Å, respectively. The morphology observations revealed that the synthesized CeB₆ had semi‐cubic shape with the range of size 25–60 nm. The synthesis of CeB₆ during the thermal treatment was studied by simultaneous thermal analysis (STA) technique. It was found that the reduction of B₂O₃ took place after melting of Mg meanwhile, no CeB₆ phase achieved even up to 1100 °C.