Multi-bond network hydrogels with robust mechanical and self-healable properties

Multi-bond network(MBN) which contains a single network with hierarchical cross-links is a suggested way to fabricate robust hydrogels. In order to reveal the roles of different cross-links with hierarchical bond energy in the MBN, here we fabricate poly(acrylic acid) physical hydrogels with dual bond network composed of ionic cross-links between carboxylFe3+ interactions and hydrogen bonds, and compare these dually cross-linked hydrogels with singly and ternarily cross-linked hydrogels. Simple models are employed to predict the tensile property, and the results confirm that the multi-bond network with hierarchical distribution in the bond energy of cross-links endows hydrogel with effective energy-dissipating mechanism. Moreover, the dually cross-linked MBN gels exhibit excellent mechanical properties(tensile strength up to 500 k Pa, elongation at break ~ 2400%) and complete self-healing after being kept at 50 °C for 48 h. The factors on promoting self-healing are deeply explored and the dynamic multi-bonds are regarded to trigger the self-healing along with the mutual diffusion of long polymer chains and ferric ions.     

Nickel‐Catalyzed Barton Decarboxylation and Giese Reactions: A Practical Take on Classic Transforms

Two named reactions of fundamental importance and paramount utility in organic synthesis have been reinvestigated, the Barton decarboxylation and Giese radical conjugate addition. N ‐hydroxyphthalimide (NHPI) based redox‐active esters were found to be convenient starting materials for simple, thermal, Ni‐catalyzed radical formation and subsequent trapping with either a hydrogen atom source (PhSiH₃) or an electron‐deficient olefin. These reactions feature operational simplicity, inexpensive reagents, and enhanced scope as evidenced by examples in the realm of peptide chemistry.     

氧还原碳基非贵金属电催化剂研究进展

质子交换膜燃料电池是一种直接将化学能转化为电能的能量转换装置,具有环境友好、能量密度高、转化效率高等优点,能够应用于便携能源及燃料电池电动车领域.但燃料电池阴极氧还原需要大量的铂基催化剂,铂价格昂贵、储量有限、易中毒的缺点限制了它的实际应用.因此,开发低成本、高活性、高稳定性的阴极非贵金属催化剂将能够显著推动质子交换膜燃料电池的大规模商业化应用.其中碳基非贵金属催化剂作为最有可能替代铂的氧还原催化剂,引起了广泛的研究.基于此,本文首先简单介绍了氧还原的机理;其次将碳基非贵金属催化剂分为过渡金属氮碳催化剂和非金属掺杂碳催化剂,对它们在材料制备和活性中心的研究进行了总结和讨论;最后,报道了碳基非贵金属催化剂在质子交换膜燃料电池单电池中的应用进展.     

Catalytic Asymmetric Mannich‐Type Reaction Enabled by Efficient Dienolization of α,β‐Unsaturated Pyrazoleamides†

(E)‐α,β‐Unsaturated pyrazoleamides undergo facile dienolization to furnish copper(I)‐(1Z,3Z)‐dienolates as the major in the presence of a copper(I)‐(R)‐DTBM‐SEGPHOS catalyst and Et₃N, which react with aldimines to afford syn‐vinylogous products as the major diastereoisomers in high regio‐ and enantioselectivities. In some cases, the diastereoselectivity is low, possibly due to the low ratio of copper(I)‐(1Z,3Z)‐dienolates to copper(I)‐(1Z,3E)‐dienolates. (Z)‐Allylcopper(I) species is proposed as effective intermediates, which may form an equilibrium with copper(I)‐(1Z,3Z)‐dienolates. Interestingly, the present methodology is a nice complement to our previous report, in which (E)‐β,γ‐unsaturated pyrazoleamides were employed as the prenucleophiles in the copper(I)‐catalyzed asymmetric vinylogous Mannich‐Type reaction and anti‐vinylogous products were obtained. In the previous reaction, copper(I)‐ (1Z,3E)‐dienolates were generated through α‐deprotonation, which might form an equilibrium with (E)‐allylcopper(I) species. Therefore, it is realized in the presence of a copper(I) catalyst that (E)‐α,β‐unsaturated pyrazoleamides lead to syn‐products and (E)‐β,γ‐unsaturated pyrazoleamides lead to anti‐products. Finally, by use of (E)‐β,γ‐unsaturated pyrazoleamide, (E)‐α,β‐unsaturated pyrazoleamide, (R)‐DTBM‐SEGPHOS, and (S)‐DTBM‐SEGPHOS, the stereodivergent synthesis of all four stereoisomers is successfully carried out. Then by following a three‐step reaction sequence, all four stereoisomers of N‐Boc‐2‐Ph‐3‐Me‐piperidine are synthesized in good yields, which potentially serve as common structure units in pharmaceutically active compounds.     

一种检测CO32-比率荧光探针的合成及其在细胞成像中的应用

本文设计开发了一种以2,6-二甲酰基对甲苯酚为母体的新型荧光探针HMI,可用于高效识别EtOH-H₂O (8/2, v/v, HEPES 10 mM, pH =7.4)体系中的CO_3^2-。HMI在660 nm处显示发射带,加入CO_3^2-后,在600 nm的等吸收点激发时,原来在660 nm处的荧光淬灭,而以540 nm为中心的新发射带荧光显着增加,为比率型荧光探针。HMI对CO_3^2-表现出高选择性且具有较强的抗干扰能力。此外,荧光探针HMI对CO_3^2-荧光响应的检测限较低,可达到3.938×10^_-6 M。更具有意义的是,HMI探针对CO_3^2-的检测能够在实际水样中起到很好的应用,而且细胞成像研究表明,HMI可用于活体MCF-7细胞中CO_3^2-的成像。     

西南山地煤矿区耕地土壤-农作物重金属富集及健康风险评价

为了解西南某典型山地煤矿区周边农田土壤、农作物重金属的富集情况及对当地人群健康的影响程度,采集矿区周边农田土壤样品和对应的农作物样品,测定重金属Cr、Mn、Zn、As、Pb的含量。运用Nemero指数法、潜在风险指数法对土壤重金属的污染程度进行评价;采用靶标危害系数法(THQ)评价农作物重金属对人体的健康风险。结果显示,Cr、Mn、Zn、As、Pb分别是背景值的1.81、1.90、2.89、1.30、0.86倍,处于轻度污染级别,轻微危害程度。农作物重金属Cr、Pb和As含量的超标情况较严重,Zn的含量超标相对较小。各农作物富集的重金属对人体的健康风险大小为：高粱>玉米>白菜>葱>辣椒。农作物重金属对儿童健康的危害均达到了慢性中毒;对成人健康的影响,高粱处于慢性中毒,其它农作物重金属处于产生较大影响的危害程度。农作物重金属与土壤重金属的相关性分析表明,农作物重金属的含量与土壤重金属全量并无线性关系;各重金属在农作物中的转移能力不同;Pb,As在农作物中的转移能力较大,而Cr相对较小。鉴于矿区重金属的富集情况,应尽快采取修复治理措施,为保证当地人群健康,建议当地居民不再食用和种植富集重金属严重的高粱、玉米农作物。     

A Facile Strategy to Enhance the Formation of Stereocomplex Crystallites in Poly(L-lactic acid)/Poly(D-lactic acid) Blend with High Molecular Weights

Chinese Journal of Polymer Science - Blending of poly(levorotatory-lactic acid) (PLLA) and poly(dextrorotatory-lactic acid) (PDLA) produces the stereocomplex crystallites (PLA SC), which present...