pH and Salt-Assisted Macroscopic Chirality Inversion of Gadolinium Coordination Polymer

The precise adjustment of handedness of helical architectures is important to regulate their functions. Macroscopic chirality inversion has been achieved in organic supramolecular systems by pH, metal ions, solvents, chiral and non-chiral additives, temperature, and light, but rarely in coordination polymers (CPs). In particular, salt-assisted macroscopic chirality inversion has not been reported. In this work, we carried out a systematic investigation on the role of pH and salt in regulating the morphology of CPs based on Gd(NO₃)₃ and R-(1-phenylethylamino)methylphosphonic acid (R-pempH₂). Without extra NO₃⁻, the chirality inversion from the left-handed superhelix R-M to the right-handed superhelix R-P can be achieved by pH modulation from 3.2 to 3.8. The addition of NaNO₃ (2.0 eq) at pH 3.8 results in an inversion of chiral sense from R-P to R-M as a pure phase. To our knowledge, this is the first example of salt-assisted macroscopic helical inversion in artificial systems.     

Natural Antioxidants,Tyrosinase and Acetylcholinesterase Inhibitors from Cercis glabra Leaves

Cercis glabra is a plant belonging to the legume family, whose flowers and barks are commonly used as food and traditional Chinese medicines. However, its leaves are usually disposed of as wastes. This research comprehensively investigated the bioactive constituents of C. glabra leaves, and two new phenolic, ceroffesters A-B (1–2) and thirteen known compounds (3–15) were isolated. Their structures were elucidated by spectroscopic methods such as nuclear magnetic resonance (1D NMR and 2D NMR), high-resolution electrospray ionization mass spectra (HR-ESI-MS), optical rotatory dispersion (ORD) and electronic circular dichroism (ECD). All of them were assessed for their antioxidant activities through ABTS, DPPH and PTIO methodologies, and evaluated for inhibitory activities against two enzymes (mushroom tyrosinase and acetylcholinesterase). As a result, compounds 3–6, 10 and 13 exhibited evident antioxidant activities. Meanwhile, compounds 5, 10 and 13 showed the most potent tyrosinase inhibitory activities, with IC₅₀ of 0.64, 0.65 and 0.59 mM, and compared with the positive control of 0.63 mM (kojic acid). In the initial concentration of 1 mg/mL, compounds 3, 5 and 6 demonstrated moderate inhibitory activities against acetylcholinesterase with 85.27 ± 0.06%, 83.65 ± 0.48% and 82.21 ± 0.09%, respectively, compared with the positive control of 91.17 ± 0.23% (donepezil). These bioactive components could be promising antioxidants, tyrosinase and acetylcholinesterase inhibitors.     

野渡无人舟自横现象的数值研究

为了研究``野渡无人舟自横'这一自然现象,本文采用数值仿真技术模拟研究了小船在水流作用下的运动特性,得出：顺于水流以及横于水流都属于小船平衡位置。但顺于水流属于非稳定平衡位置,受扰动后将失去平衡,并再也恢复不到原平衡位置;而横于水流属于稳定平衡位置,此时即使小船受到扰动失去平衡,最终也能在自身力矩作用下重新恢复到原平衡位置。     

The Antibacterial Activity Mode of Action of Plantaricin YKX against Staphylococcus aureus

We aimed to evaluate the inhibitory effect and mechanism of plantaricin YKX on S. aureus. The mode of action of plantaricin YKX against the cells of S. aureus indicated that plantaricin YKX was able to cause the leakage of cellular content and damage the structure of the cell membranes. Additionally, plantaricin YKX was also able to inhibit the formation of S. aureus biofilms. As the concentration of plantaricin YKX reached 3/4 MIC, the percentage of biofilm formation inhibition was over 50%. Fluorescent dye labeling combined with fluorescence microscopy confirmed the results. Finally, the effect of plantaricin YKX on the AI-2/LuxS QS system was investigated. Molecular docking predicted that the binding energy of AI-2 and plantaricin YKX was −4.7 kcal/mol and the binding energy of bacteriocin and luxS protein was −183.701 kcal/mol. The expression of the luxS gene increased significantly after being cocultured with plantaricin YKX, suggesting that plantaricin YKX can affect the QS system of S. aureus.     

溴甲酚绿-Triton X-100与扑草净作用的共振光散射光谱研究

研究了扑草净-溴甲酚绿-Triton X-100体系的共振光散射光谱。加入经HCl酸化的扑草净后溴甲酚绿的共振光散射光谱有明显增强,表面活性剂TritonX-100的加入使光谱强度显著增加,产生最大散射波长为562 nm的共振散射光信号,且散射光强度与扑草净的质量浓度呈线性关系,线性范围为0.01~0.35μg/mL,检出限为7.8 ng/mL。该方法已用于实际样品中扑草净的测定。     

液相微萃取-反萃取在磺胺药物残留测定中的应用

利用液相微萃取-反萃取技术,建立测定动物组织中磺胺药物残留量的新方法.将动物组织中磺胺药物经液相微萃取-反萃取后进行高效液相色谱紫外检测.磺胺、磺胺嘧啶、磺胺二甲嘧啶、磺胺喹口恶啉4种磺胺类药物的线性范围均在0.05～10.0 μg/mL,磺胺甲口恶唑的线性范围在0.5～10.0 μg/mL之间,方法的平均回收率不低于80.2%,RSD＜6.8%,检出限为0.1 mg/kg.     

管内变密度流体流动与换热的充分发展及解析解

本文提出了圆管内变密度流体流动与换热充分发展的概念和相关假设及其推论.在所提出的概念和假设基础上对理想气体在圆管内的流动与换热进行了解析求解,得到了充分发展时的无量纲速度抛物分布及无量纲温度分布.对圆管内密度随温度变化的氩气的流动与换热数值模拟所获得的无量纲速度分布及无量纲温度分布在入口段后与上述解析解非常吻合,从而验证了在本文的计算条件范围内,圆管内变密度流体充分发展流动与换热的概念及其解析解是合理的.     

高效液相色谱法测定水产品中四环素类抗生素残留

建立了一种高效液相色谱法测定水产品中土霉素、四环素、去甲基金霉素、金霉素、脱氧土霉素的分析方法。样品用5.0%高氯酸溶液提取,上清液用OasisHLB固相萃取柱净化,用紫外检测器于355nm测定。土霉素、四环素、去甲基金霉素检测限为0.01mg/kg,金霉素、脱氧土霉素检出限为0.02mg/kg。5种药物的回收率在74.8%~89.3%之间,相对标准偏差为3.95%~9.95%。方法适用于水产品中四环素类抗生素残留的检测。     

二维材料改性水性聚氨酯防腐涂料的研究进展

水性聚氨酯涂料作为一种新兴的环保涂料,在防腐领域得到了广泛应用。然而,水性聚氨酯涂料交联密度低,耐水性稍差,不利于其长效防腐性能。利用具有独特物理化学特性的二维材料作为水性聚氨酯的填料,可以有效改善其性能。本文主要介绍了三种二维材料(石墨烯、MXene和六方氮化硼)作为填料与水性聚氨酯进行复合,并重点介绍了石墨烯、MXene和六方氮化硼的改性方法,并对水性聚氨酯复合涂层的性能进行了阐述和比较,最后对未来二维材料/水性聚氨酯的复合材料的发展和应用进行了展望。