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101.
金属有机骨架(MOFs)材料因其可设计的结构以及灵活可控的配位模式,在三阶非线性光学(NLO)领域引起了广泛的关注。与液体分散状态相比,MOFs在固体状态下的三阶NLO性能更为重要,这不仅可以深入了解MOFs本身所固有的光学性能,还有助于实现MOFs在光学器件中的实际应用。然而,由于散射的存在和透光率的限制,单独的MOFs材料难以直接实现固体状态下的三阶NLO性能研究,将MOFs制备成具有较好光学透过性的薄膜是研究其NLO性能最为可行的一种策略。MOFs薄膜不仅很好地继承了MOFs所固有的三阶NLO性能,而且还结合了薄膜的高透光率以及灵活的机械性能。基于此,本文分析总结了MOFs薄膜的制备方法及其NLO性能研究方面的相关工作,并根据目前MOFs薄膜在三阶NLO性能方面的研究现状对其未来发展予以了展望。 相似文献
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αB‐crystalin, a small heat shock protein and a component of α‐crystalin, is a molecular chaperone playing an important role in preventing the formation of cataracts. It has been reported that His18 is an important site for Cu2+ to bind with to form a stable metal complex and thus to enhance this chaperone‐like activity of human αB‐crystalin. In this work, we used site‐directed mutagenesis to clone and express H18G rat lens αB‐crystalin in order to investigate the role of His18 in chaperoning activity. We found that 1 mM of Cu2+, or Zn2+, rather than Mg2+, significantly enhanced the chaperone‐like activity of wild type αB‐crystalin. Whereas, it is Zn2+ and Mg2+, not Cu2+, that significantly reduced this activity of H18G αB‐crystalin. In the absence of cation, H18G showed better activity compared to the wild type αB‐crystalin. ANS fluorescence measurement showed there was no linear relationship between chaperone‐like activity and surface hydrophobicity, indicating that surface hydrophobicity is not a prerequisite for chaperone‐like activity. An HPLC size‐exclusion chromatography study showed that in the presence of metal ions, wild type αB‐crystalin tended to aggregate via dissociation and re‐association into a high molecular aggregate with a molecular weight higher than 1400 kDa and then precipitated, suggesting that the presence of metal ions is a factor leading to the formation of cataracts. Both the near and far UV‐CD spectra suggested that the wild type αB‐crystalin reflected more β‐sheet structural characteristics; whereas the H18G reflected more random coil characteristics. The H18G induced structural alterations as to develop more random coil characteristics and more micro‐environmental changes around the tryptophan residues. This work suggested that His18 may not be a crucial binding site for Cu2+, but rather that it may be an important binding site for Zn2+ in terms of chaperone‐like activity and the process of metal induced self‐aggregation is prerequisite for chaperone‐like activity to occur. 相似文献
105.
Hongwei Shi Xiangui Huang Guixia Liu Kunqian Yu Congying Xu Weihua Li Bubing Zeng Yun Tang 《International journal of quantum chemistry》2013,113(9):1339-1348
In asymmetric Michael addition between ketones and nitroolefins catalyzed by L ‐proline, we observed that it was benzoic acid or its derivatives rather than other proton acid that could accelerate the reaction greatly, and different benzoic acid derivatives brought different yields. To explain the experimental phenomena, a density functional theory study was performed to elucidate the mechanism of proline‐catalyzed asymmetric Michael addition with benzoic acid. The results of the theoretical calculation at the level of B3LYP/6‐311+G(2df,p)//B3LYP/6‐31G(d) demonstrated that benzoic acid played two major roles in the formation of nitroalkane: assisting proton transfer and activating the nitro group. In the stage of enamine formation from imine, the energy profiles of benzoic acid derivatives were also calculated to investigate the reasons why different benzoic acid derivatives caused different yields. The results demonstrated that the pKa value was the major factor for p‐substituted benzoic acid derivatives to improve the yields, whereas for m/o‐substituted benzoic acid derivatives, both pKa value and electronic and steric effects could significantly increase the yields. The calculated results would be very helpful for understanding the reaction mechanism of Michael addition and provide some insights into the selection of efficient additives for similar experiments. © 2012 Wiley Periodicals, Inc. 相似文献
106.
A novel, convenient, efficient, three‐step, one‐pot synthesis of 2‐oxazolidinones from phenyl 2‐hydroxyalkyl selenides was developed. Using this methodology, 2‐oxazolidinones are obtained in good yields (76–85%) by reaction of phenyl 2‐hydroxyalkyl selenides with benzoyl isocyanate and subsequent oxidation/cyclization, followed by hydrolysis with hydrochloric acid solution. 相似文献
107.
A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent. 相似文献
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109.
A two-step sintering method was used to prepare Al8.31Si1.91Mg3.78O20 (corundum solid solution)/Al4.8Si1.2O9.6 (mullite solid solution)/Mg2.0Al4.02Si4.98O18 (cordierite solid solution) multiphase material, for the purposes of making these three crystal structures have point defects which could help the particles diffuse and transfer at high temperature, accelerate the sintering efficiently and enhance the material strength as well as the bulk density. The impacts of different formulas on the structure and properties of the multiphase material were investigated. With XRD and SEM analyses, for each sample, the crystal structure and microstructure were characterized, the crystalline phase content and cell parameters were determined with Rietveld Quantification software, and the properties were tested. The comparative optimal formula determined was calcinated chamotte of 80wt% and calcinated sludge of 20wt%; and its corresponding bending strength and retention rate of bending strength after a thermal shock were 29.74 MPa and 80.15%, respectively. 相似文献
110.
We report on fast-switching and high-efficient optical beam steering based on a polymerisable liquid crystal polarisation grating (PG) in combination with ferroelectric liquid crystal (FLC) phase shutter. The PG was fabricated in a convenient single-step holographic exposure process using photo-sensitive azo-dye material as alignment layer for liquid crystal (LC) director. A binary electro-optical FLC was employed for circular polarisation selection, which enables the electro-tunable steering of the combined system. The efficiency of 95.7% with 82 μs switching time is obtained for 1064 nm laser. This work provides a versatile candidate for non-mechanical beam steering devices. 相似文献