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质子交换膜燃料电池铁基氧还原催化剂的理性设计与控制合成
No full text质子交换膜燃料电池作为一种高效清洁的能量转化技术，必定会在在未来的非化石能源体系中发挥不可替代的作用。如果将燃料电池和电解池技术结合起来，更能满足多种形式的能量储存及再转化的应用需求。廉价的高性能氧还原催化剂无疑是燃料电池技术大规模应用的关键因素。目前应用于质子交换膜燃料电池阴极的催化剂主要为Pt基的催化剂。虽然它具有很高的氧还原活性和化学稳定性，但是贵金属天然的稀缺性、催化剂的高成本和有待提高的电化学稳定性等问题限制了燃料电池技术的商业化应用。针对这个问题，本论文进行了质子交换膜燃料电池Fe基氧还原催化剂的相关工作，研究了热处理Fe/N/C类氧还原催化剂和新型的石墨化碳层包覆结构Fe基氧还原催化剂。研究主要集中在两个方面：一是探索催化剂结构、组分等性质与催化性能之间的关系，从而设计出性能更理想的催化剂；二是探索实验方法和条件合成出所期望得到的催化剂。主要研究内容如下： 1.热处理Fe/N/C类氧还原催化剂 （1）通过使用聚苯胺纳米线作为C和N共同的前驱体合成了一种自支撑的Fe/N/C类氧还原催化剂。我们发现聚苯胺纳米线形貌结构在热处理过程中能够保存下来，使所合成的催化剂具有均一的纳米棒结构。这个方法为合成形貌可控的自支撑型Fe/N/C催化剂提供了一种新的思路。此外，我们发现所合成催化剂氧还原起始电位为0.905 V (vs. RHE)，氧还原过程为四电子过程。随着前驱体中Fe含量的增加（从0到3 wt%），催化剂的性能逐步提高。前驱体中Fe含量会的进一步增加会引起催化剂活性的降低。 （2）通过比较常规Fe/N/C催化剂和P掺杂的Fe/N/C催化剂的形貌结构与性能，我们发现了P掺杂对于热处理Fe/N/C催化剂氧还原性能的促进作用。P的掺杂是通过在催化剂制备过程中加入磷酸酯作为前驱体来实现的，并且对催化剂的形貌结构没有明显影响。相比没有掺入P的催化剂, 掺杂P后的催化剂表现出了相似的氧还原起始电位但是更高的氧还原电流密度。所制得催化剂的活性和稳定性在直接甲醇燃料电池中也得到了验证。 2. 碳层包覆结构Fe基氧还原催化剂 （1）通过高压热处理的合成方法我们制得了一种新型的石墨化碳层包覆结构Fe基催化剂。这种催化剂具有均一的空心碳球结构，碳球中包覆着均一的Fe3C颗粒，催化剂表面只含有极少量的N和Fe。在酸性溶液中，碳层保护着Fe3C颗粒使其不与溶液进行反应，而Fe3C颗粒与碳层间的电子作用使表面碳层具有了一定的氧还原活性。催化剂无论是在酸性还是碱性溶液中都具有优良的氧还原活性和稳定性。这种新型的催化剂以及这对这种催化剂所提出的活性位点机理对于合成高活性高稳定性的非贵金属催化剂提供了一种新的思路。我们还在低温氢氧质子交换膜燃料电池和高温磷酸掺杂的聚苯并咪唑质子交换膜燃料电池中验证了该催化剂的活性和稳定性。 （2）我们探索了碳层包覆结构Fe基催化剂的结构形成过程和氧还原活性位点。在500oC时，前驱体中的氰胺聚合成球状的三聚氰胺，这决定了催化剂最终的球状结构。在600oC-660 oC时三聚氰胺球开始逐步分解，开始出现一定量Fe3C相以及可能的Fe-Nx/C活性位点。此时催化剂的活性很低，较低的电子导电性可能是原因之一。当热处理温度为700-800oC时，催化剂结构为空心碳球中包裹着Fe3C纳米颗粒。这种催化剂的表面含N和Fe的含量很低，而且氧还原反应是2电子和4电子混合过程。这些结果都支持我们对于催化剂活性位点的观点，即Fe3C颗粒与包裹碳层间的电子作用使外部碳层具有了氧还原活性。 （3）我们发现了一种直接简便的制备石墨烯复合材料的方法，即通过高压热处理非石墨前驱体的方法合成多层石墨烯/Fe3C颗粒复合材料。整个合成过程直接、简便，易进行放大合成。当把所得到的石墨烯/Fe3C颗粒复合材料作为氧还原催化剂进行测试，我们发现它在0.1 M KOH中具有很好的氧还原性能和稳定性。相比Pt/C 催化剂，它们具有基本一样的氧还原起始电位和半波电位。Proton exchange membrane fuel cells (PEMFCs), as a clean and efficient energy conversion device, should play key roles in the further fossil fuel-free energy scenarios. If combined with a electrolyzer, it will give solutions to different energy appliacations. Highly active and durable catalysts for the oxygen reduction reaction (ORR) are undoubtedly essential for the large-scale application of fuel cells. Pt-based materials have been so far the most active ORR catalysts. However, the prohibitive cost, limited availability and insufficient durability of Pt-based materials hinder the rapid and widespread adoption of PEMFCs. Therefore, we focus our interests in the study of iron-based oxygen reducion catalysts, including heat-treated Fe/N/C type oxygen reduction catalysts, the most active non-precious metal ORR catalyst thus far, and a new iron-based oxygen reduction catalyst with the encapsulation structure. The detailed research results are as follows: 1. Heat-treated Fe/N/C type oxygen reduction catalyst (1) We report a new approach to preparation of self-supported and nano-structured NPMCs using pre-prepared polyaniline (PANI) nanofibers as both nitrogen and carbon precursors. The synthesized NPMCs possess nanoworm structures preserved from the PANI precursor and exhibit a high onset potential of 0.905V vs. RHE and selective activity of nearly four-electron ORR pathways. A significant enhancement in the intrinsic activity and onset potential for the ORR is observed when the Fe content in the precursor is increased from 0 to 3.0 wt.%, while further addition to 10.0 wt.% results in a decrease in the catalytic activity. (2) By comparing the ORR activities of standard Fe/N/C catalysts synthesized with or without the doped phosphorus species, the promotional effect of phosphorus doping is discerned. Such phosphorus doping is achieved by using an acidic phosphate ester as a dopant in the synthesis, which introduces no change in catalyst morphologies and structures. The linked structure of phosphate ester cations with the nitrogen precursor, i.e., polyaniline chain, is favored for the evenly P doping of the catalyst, showing to a superior ORR activity to that for the undoped Fe/N/C catalyst. The activity and durability of the catalysts are demonstrated in direct methanol fuel cells. 2. Iron-based oxygen reduction catalyst with an encapsulation structure (1) We presents a novel type of catalysts prepared by high pressure pyrolysis. The catalyst is featured of hollow spherical morphologies consisting of uniform Fe3C nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles, which in turn synergistically activate the graphitic layers for the ORR. As a result the catalyst exhibits super activity and stability in both acid and alkaline electrolytes. The finding of the synthetic approach, carbide-based catalyst and its structure, as well as the proposed mechanism opens new avenues for catalyst development in the field. The activity and durability of the catalysts are demonstrated in both Nafion-based low temperature and acid doped polybenzimidazole-based high temperature proton exchange membrane fuel cells. (2) We present a detailed study of a novel Fe3C-based spherical catalyst with respect to synthetic parameters, nanostructure formation, ORR active sites and fuel cell demonstration. The catalyst is synthesized by high-temperature autoclave pyrolysis using decomposing precursors. Below 500oC, melamine-rich microspheres are first developed with uniformly dispersed amorphous Fe species. During the following pyrolysis at temperatures from 600 to 660 oC, a small amount of Fe3C phase with possible Fe-Nx/C active sites are formed, however, with moderate catalytic activity, likely limited by the low conductivity of the catalyst. At high pyrolytic temperatures of 700-800 oC, simultaneous formation of Fe3C nanopart
基于ROMP的新型高分子材料：设计、合成及性能研究
No full text以Grubbs催化剂为代表的钌系催化剂的出现，使得开环易位聚合（ROMP）成为高分子材料合成领域一种重要的聚合方法。Grubbs催化剂具有高活性，高官能团耐受性和可实现活性聚合等优点，使得ROMP可用于合成许多其他聚合方法难以得到的聚合物材料，如共轭导电高分子、生物活性高分子、梳形高分子、嵌段共聚物、遥爪聚合物、环状高分子等。高性能高分子材料一直以来都是高分子合成化学领域重要的研究方向。本论文利用Grubbs催化剂催化的ROMP，通过设计合成新型单体和对聚合物链结构的调控，合成并研究了一系列高性能的高分子材料。主要的研究结果如下： (1)新型高耐热型环烯烃聚合物Ⅰ(COPs)：利用一种大位阻的环烯烃单体，在Grubbs第一代催化剂(G1)的催化下，高效率的得到了主链含双键的聚合物。化学氢化后，得到的环烯烃聚合物(COP)玻璃化转变温度（Tg）达223.6 °C，这比商品化最高Tg高了近40 °C。通过溶液成膜，得到了一种高耐热型透明COP，其透光率可达90 %；拉伸测试表明，该材料也具有优良的力学性能。通过与其它两种小位阻的单体共聚，并且控制两种单体的投料比，可以精确地调节环烯烃聚合物的Tg，从而得到不同耐热品级的材料。 (2)新型高耐热型环烯烃聚合物Ⅱ(COPs)：通过控制聚合反应时间和投料比，我们首次利用大位阻降冰片烯类单体和环辛烯在G1催化下的梯度共聚得到了高Tg，高透明性的COP。COPs的Tg最高可达207 °C，溶液成膜得到透光率高达88 %的新型耐热高透COPs。虽然是利用ROMP的方法，但是所得聚合物链结构更加类似于乙烯与环烯烃共聚而得到的环烯烃共聚物(COCs)。研究表明，这种方法尤其适合于制备高Tg (> 150 °C)的COPs。 (3)新型三嵌段热塑性弹性体(TPEs)：利用活性ROMP的方法，通过次序加料得到了一系列不同类型的三嵌段(ABA or ABC)热塑弹性体。研究表明：在软段末端同时引入结晶性硬段不但可以提高材料的力学强度，而且可以提高材料的弹性恢复性。ABC结构(结晶态-高弹态-低Tg玻璃态)的三嵌段共聚物具有更长的断裂伸长率，但是拉伸强度有所下降。当在软段的两端同时引入刚性(更高Tg)和结晶性的硬段可得到同时具有高力学强度和优良弹性恢复性的高性能TPE。在此优化条件下，弹性恢复率可达93 %。该部分工作具有十分重要的科学意义，为更 优良性能的热塑弹性体的设计合成提供了一定的理论指导作用。 (4)自修复热塑弹性体(Self-healing TPEs)：利用活性ROMP方法合成了一系列软硬两嵌或硬软硬三嵌段的热塑弹性体。通过将氢键引入到软硬两嵌或硬软硬三嵌段的软段中，不仅可以提高弹性体的力学性能，并且可以赋予材料良好的自修复性能。该热塑弹性体的自修复行为是在没有任何外部刺激的条件下进行的(主动型自修复)。通过优化条件，所得的自修复弹性体断裂伸长率修复率最高可达85 %。我们的工作为设计合成具有良好自修复性能的热塑弹性体提供了一种新的设计理念。 (5)新型两亲性嵌段共聚物的合成：含羧基的两亲性嵌段共聚物具有很大的应用潜力。利用酸酐的水解的方法得到两亲性嵌段共聚物是一种简便的合成方法。然而对于含酸酐的单体，很难实现活性ROMP。通过设计合成一系列含不同取代基的酸酐单体，优化条件下，首次实现了酸酐单体的活性ROMP。我们的工作表明，对于强极性的基团，通过合理的设计单体结构，Grubbs催化剂仍然能够实现活性聚合。这丰富Grubbs催化剂催化活性聚合的理论内容，也为合成含羧基的两亲性嵌段共聚物提供了新的合成方法和路径。With the advent of Grubbs catalysts, Ring-opening metathesis polymerization (ROMP) has become one of the most powerful methods in polymer synthesis. Based on ruthenium, those Grubbs catalysts have many advantages, such as high reactivity, high functional group tolerance and living polymerization character, which make ROMP capable of synthesizing kinds of polymer that could not be able to synthesize by other methods, such as conjugated polymers, bioactive polymers, bottlebrush polymers, telechelic polymers, cyclic polymers, and so on. High-performance polymeric materials have always been the main topic of polymer synthesis chemistry. In this doctoral dissertation, we designed and synthesized several novel high-performance polymeric materials by ROMP utilizing Grubbs catalysts. The performances of these synthesized polymeric materials were systemic investigated. The main results are listed as follows: (1) Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefin, exo-1,4,4a,9,9a,10-hexahydro-9,10(1’,2’)-benzeno-l,4-methanoanthracene (HBM), with high glass-transition temperature (Tg), excellent thermal stability, high transparency and improved mechanical performance, have been achieved by ROMP and subsequent hydrogenation. The “first generation Grubbs” catalyst, RuCl2(PCy3)2(CHPh) (Cy = cyclohexyl) (G1), displays very high activity for homo/co-polymerization with complete conversion. Homopolymer of the HBM after complete hydrogenation showed a highest Tg = 223.6 °C. Copolymerization of HBM with tricyclo[4.3.0.12,5]deca-3-ene or 5-n-hexylnorbornene were also carried out. These two series COPs were characterized by GPC, NMR, DSC, and TGA. The Tg of the resulted COPs linear increased with HBM content, which is easily controlled by changing feed ratios. The tensile test indicates that these copolymers have good mechanical performance, as all this copolymers show a higher strain at break compared with commercial products (TOPAS?). (2) Novel COPs with excellent transparency and high Tg synthesized from bulky norbornene derivative, HBM, and cis-cyclooctene (COE) by ring-opening metathesis copolymerization utilizing G1, and subsequent hydrogenation was reported herein. To get amorphous copolymers, it was of great importance to control the feed ratios and the polymerization time for gradient copolymerization. All of these copolymers showed very high Tgs (141.1-201.2 °C), which varied with the content of HBM. The films of the gradient copolymers with only one Tg were highly transparent. On the contrary, all the block copolymers synthesized through sequential addition showed two thermal transition temperatures, Tg and melt temperature (Tm), and the films of these block copolymers were opaque. The mechanical performances of the COPs were also investigated. It is the first report that transparent COP could be prepared from bulky norbornene derivative and monocyclic olefin. (3) A series of ABA or ABC triblock copolymers based thermoplastic elastomers (TPEs) were synthesized by living ROMP utilizing the Grubbs third generation catalyst RuCl2(3-bromopyridine)2(H2IMes)(CHPh) (G3, H2IMes = N,N-dimesityl-4,5-dihydroimidazol-2-ylidene) and subsequent hydrogenation. By introducing crystalline block into both end of soft block, improved tensile strength and elastic recovery were observed. Furthermore, TPE with both the crystalline and high Tg hard blocks showed the best tensile strength and the best elastic recovery (up to 93.5 %). (4) A simple design of hard-soft diblock and hard-soft-hard triblock copolymers based TPEs that combine good mechanical performances with autonomic healing capability is achieved. Those block copolymers were synthesized by living ROMP through one-pot sequential addition of bulky monomer and a “soft” monomer with secondary amide group for weak hydrogen bonding utilizing G3. The mechanical properties were mainly studied by monotonic and step cyclic tensile tests. As assumed, the mechanical properties were great
原位电化学方法研究炭电极材料在电化学电容器中的储能机理
No full text电化学电容器作为一种清洁高效的储能器件，因具有功率密度高、循环寿命长等诸多突出的优点而受到广泛关注。炭材料是电化学电容器最经典的电极材料，主要通过离子在表面的吸附或层间的插嵌来存储电量。在之前的工作中，我们发现溶剂对离子的吸/脱附、插/脱嵌过程有很大的影响。为了揭示其中的微观机理，我们开展了以下几部分工作： 1、以电化学石英晶体微天平（EQCM）为主要工具，研究了不同浓度NaClO4水溶液中活性炭电极/电解质溶液界面上离子的水合状态。结果表明，随着NaClO4浓度的增加，活性炭电极孔隙中吸附的离子的水合数不断减小。本体溶液中Na+水合数大于电极/溶液界面上的Na+水合数，即Na+在从本体溶液被吸附到活性炭孔隙的过程中发生了去溶剂化。另外，活性炭电极孔隙中Na+的水合数与活性炭负极的比电容有明显的线性关系。 2、利用EQCM研究了5 M NaClO4水溶液中的防冻添加剂（甲醇、乙醇）对Na+在活性炭表面吸附过程的影响。结果表明，甲醇、乙醇分子与Na+形成了溶剂化离子，随Na+一起吸附到了活性炭孔隙中；随着本体溶液中甲醇、乙醇浓度的增加，与吸附到活性炭孔隙中的每个Na+络合的甲醇、乙醇分子越来越多；随Na+吸附到活性炭孔隙中的甲醇、乙醇分子挤占了一定的孔隙，同时降低了双电层的介电常数，从而降低了Maxsorb电极在负电势区的比电容。 3、采用原位X射线衍射（XRD）和EQCM研究了BF4?在EC、GBL、PC中插嵌石墨电极的过程。结果表明，EC抑制了BF4?在石墨层间的插嵌。EC、GBL、PC分子都随BF4?一起嵌入了石墨电极，但嵌入的方式各不相同。同时，BF4?在石墨层间的溶剂化状态与对应的活性炭/石墨电容器的循环性能密切相关。 4、采用非原位XRD和原位Raman研究了ClO4?在EC、GBL、PC中插嵌石墨的过程。非原位XRD的测试结果表明，在PC和GBL中，ClO4?嵌入了石墨中并形成了长程有序的ClO4?-GICs，而且GBL分子极有可能也随ClO4?一起嵌入了石墨层间。而在EC中，ClO4?也嵌入了石墨中但没能形成长程有序的ClO4?-GICs，即EC抑制了ClO4?在石墨层间的插嵌。当提高测试温度时，EC对ClO4?的抑制作用会大大减弱。原位Raman结果还表明ClO4?在EC中插嵌石墨的速度要比在GBL和PC中慢很多，可逆性也差很多。 5、采用原位XRD、原位Raman和EQCM研究了PF6?在GBL中插嵌石墨的过程，并与在PC和EC中的插嵌行为进行了比较。结果表明，GBL对PF6?的插嵌也有抑制作用，尽管要比EC的抑制作用弱。同时，我们还发现PF6?在GBL中与BF4?在EC中的插嵌行为十分相似，这进一步说明GBL与EC的抑制作用在本质上是一样的。与此同时，实验结果再次表明，溶剂对活性炭/石墨电容器的性能具有决定性的影响。As a clean and highly efficient electric storage device，electrochemical capacitors have drawn widespread attention due to their numerous merits, such as high power density, long cycle life etc. Carbon materials are the most classical electrode materials for electrochemical capacitors. The charge storage of carbon materials is mainly by ions’ adsorption on the interfaces or intercalation into graphene layers. In our previous work, solvents were found to have great influence on the adsorption/desorption and intercalation/de-intercalation of ions. In order to throw light on its mechanism, following work has been done by us: (1) Electrochemical Quartz Crystal Microbalance (EQCM) was used to study the mass changes on activated carbon electrodes in various NaClO4 aqueous solutions during the course of ions adsorption into the pores of the electrode. Results indicated the hydration number of ions absorbed into the pores decreased with the concentration increase of NaClO4. The hydration number of Na+ in the bulk solutions is much larger than that in the pores of activated carbon electrodes, which demonstrated desolvation occurred during the migration of Na+ from the bulk solutions into the pores. Moreover, the specific capacitance of activated carbon negative electrodes is linearly dependent on the hydration number of Na+ in the pores of activated carbon electrodes. (2) EQCM was used to investigate the adsorption of Na+ into the micropores of activated carbons in 5 M NaClO4 aqueous solutions with different concentrations of methanol or ethanol. Molecule numbers of methanol or ethanol associated with each Na+ at the interfaces were estimated. Results showed that methanol and ethanol were adsorbed into the micropores together with Na+; the more concentrated methanol and ethanol in bulk solutions, the more molecule numbers of methanol or ethanol associated with each Na+ adsorbed into the pores; methanol and ethanol adsorbed into the pores occupied some space of the micropores and lower the dielectric constant of the double layers, which suppressed the specific capacitance of Maxsorb negative electrodes. (3) in situ XRD and EQCM techniques were adopted to probe the intercalation scenario of solvated BF4? into graphite electrodes in PC, GBL and EC. EC suppresses the insertion of BF4? into graphite. All the solvent molecules co-intercalated into graphite electrodes with BF4?，nevertheless，they are in different ways. Moreover, the solvation states of BF4? were in close relation to the cycle performance of corresponding AC/graphite capacitors. (4) ex situ XRD and in situ Raman were utilized to investigate the intercalation of ClO4? from PC-, GBL-, EC-based electrolyte solutions into graphite electrodes. ex situ XRD measurements showed ClO4? intercalated into graphite electrodes from GBL and PC, and generated ClO4?-GICs with long-range order; GBL co-intercalated with ClO4? into the space between graphene layers. In the EC-based solution, ClO4? also succeeded to insert graphite electrodes, but no ClO4?-GICs with long-range order came into being, which indicated the intercalation of ClO4? was suppressed by EC. Elevating temperature weakened the suppression effect of EC. In situ Raman demonstrated the intercalation of ClO4? from EC was slower and less reversible than that from GBL and PC. (5) in situ XRD, in situ Raman and EQCM were employed to study the intercalation of PF6? from GBL-based solution. The cases of PC- and EC-based solutions were used for comparision. Results proved the intercalation of PF6? was suppressed by GBL, even though the suppression effect of GBL was weaker than that of EC. Moreover, the intercalation behavior of PF6? in GBL was similar to that of BF4? in EC, which further demonstrated the suppression effects of GBL and EC were identical in nature. At the same time, results also proved the crucial effect of solvents on the performance of AC/graphite capacitors
手性磷酰胺催化的2,3’-二吲哚基取代的三芳基甲烷的不对称合成
No full text杂-三芳基甲烷是一类结构比较特殊的骨架，在材料科学、生物化学以及药物化学等领域都有广泛的应用，其中双吲哚取代的三芳基甲烷因其在抗肿瘤方面所表现出的广阔前景而倍受关注。由于缺乏对映选择性合成双吲哚取代的三芳基甲烷的有效方法，这就制约了其手性分子在生物活性方面的研究。目前，仅有两例关于不对称合成3,3’-二吲哚基取代的三芳基甲烷的策略，而针对2,3’或2,2’-二吲哚基取代的三芳基甲烷的不对称合成尚未见报道。本论文以2-吲哚甲基醇衍生物和吲哚作为反应底物，在手性磷酰胺的催化作用下，首次实现了2,3’-二吲哚基取代的三芳基甲烷的不对称合成，并通过NMR波谱分析方法和CD光谱确定了其绝对构型。 首先，我们综述了吲哚C-3、C-2和N-1位参与的手性碳中心构建方法的研究进展，在此基础上提出了选题依据，设计了一种通过2-吲哚甲基醇和吲哚的不对称反应来合成2,3’-二吲哚基取代的三芳基甲烷的策略。接着设计并合成了一系列2-吲哚甲基醇衍生物以及BINOL为手性基本骨架的Br?nsted酸催化剂。 其次，我们通过一种在吲哚C-2位构建手性中心的新方法实现了2,3’-二吲哚基取代的三芳基甲烷的不对称合成。该方法以低反应活性的2-吲哚甲基醇衍生物作为反应底物，在最简单BINOL衍生 的N-Tf取代磷酰胺的催化作用下，经碳正离子与吲哚的不对称亲电取代反应而得以实现，且唯一副产物是水，具有简单、清洁和原子经济性的优点。同时，该反应具有较好的普适性，对于不同结构的底物，所得产物的收率几乎都大于90%，ee值35-96%。 最后，我们借助NMR波谱分析方法和CD光谱确定了手性2,3’-二吲哚基取代的三芳基甲烷类化合物的绝对构型。我们将手性2,3’-二吲哚基取代的三芳基甲烷分别与(R)-和(S)-甲氧基苯乙酸缩合，得到了一对非对映异构体结构。通过1H-NMR、1H-1H NOESY、1H-13C HSQC和1H-13C HMBC波谱分析，我们对每一个非对映异构体质子化学位移做了归属并建立了优势构象模型。最终，我们通过这对非对映异构体质子化学位移差别判定了手性2,3’-二吲哚基取代的三芳基甲烷类化合物的绝对构型。另外，CD光谱分析结果也与前面NMR判定的手性2,3’-二吲哚基取代的三芳基甲烷的绝对构型一致。这些结果为将来研究手性对2,3’-二吲哚基取代的三芳基甲烷的生物活性影响具有重要意义。Hetero-triarylmethanes are unique structural motifs and have a broad range of applications in areas such as materials science, biochemistry, and pharmaceuticals. Among which, diindolylarylmethanes represent appealing hetero-triarylmethanes due to their highly promising therapeutic utility as anticancer agents. Despite these important advances, the biological properties of the chiral derivatives remain unexplored due to the lack of effective methods for enantioselective synthesis of such compounds. So far, two protocols for the asymmetric synthesis of 3,3’-diindolylarylmethanes have been developed. However, methods for the asymmetric synthesis of 2,3’- or 2,2’-diindolylarylmethanes have not been achieved. In this dissertation, we present the first asymmetric reaction of indol-2-yl carbinol derivatives with indoles catalyzed by chiral phosphoramides for the enantioselective synthesis of 2,3’-diindolylarylmethanes and the determination of the absolute configuration of these compounds by using the combination of NMR spectroscopic and circular dichroism (CD) techniques. First, we summarised the progress of methods for the asymmetric construction of stereogenic carbon centers adjacent to the indole C-3, C-2 and N-1 positions. Based on existing works, we designed a strategy for the enantioselective synthesis of 2,3’-diindolylarylmethanes by the asymmetric reaction of indol-2-yl carbinols with indoles. Then, a series of indol-2-yl carbinol derivatives and BINOL-based chiral Br?nsted acids were designed and synthesized. Second, we have developed a novel methodology for the construction of a stereogenic carbon center adjacent to the indole C-2 position to achieve the enantioselective synthesis of 2,3’-diindolylarylmethanes successfully. The reaction of indol-2-yl carbinol derivatives was achieved in the presence of the most readily available BINOL-based N-triflylphosphoramide as catalyst through the asymmetric electrophilic substitution reaction of carboncations with indoles. The reaction can proceed in a very simple, clean, and atom-economical manner, bacause the only byproduct of the reaction was water. The method exhibited a broad generality. Excellent yields of over 90% as well as high enantioselectivity ranging from 35% to 96% ee were obtained for a rich range of both substrates. Finally, we present the determination of the absolute con?guration of chiral 2,3’-diindolylarylmethanes by using the combination of NMR spectroscopic and circular dichroism (CD) techniques. Namely, by condensation of a chiral 2,3’-diindolylarylmethane with the two enantiomers of (R)- and (S)-methoxyphenylacetic acid (MPA), respectively, we could obtain a pair of diastereoisomers. The proton chemical shifts and the favored conformers for each of the diastereoisomers were assigned by utilizing the combination of 1H-NMR, 1H-1H NOESY, 1H-13C HSQC, and 1H-13C HMBC spectroscopics. Consequently, the absolute con?guration of chiral 2,3’-diindolylarylmethanes could be determined on the basis of the observed differences in 1H NMR chemical shifts of the two diastereoisomers. Moreover, the CD analytical conclusion is entirely consistent with the previous determination of the absolute con?guration of chiral 2,3’-diindolylarylmethanes by NMR.The results would be useful for the future study of the effect of chirality on the bilogical activity of 2,3’-diindolylarylmethanes
Recent advances in electrochemiluminescence
No full textThe great success of electrochemiluminescence (ECL) for in vitro diagnosis (IVD) and its promising potential in light-emitting devices greatly promote recent ECL studies. More than 45% of ECL articles were published after 2010, and the first international meeting on ECL was held in Italy in 2014. This critical review discusses recent vibrant developments in ECL, and highlights novel ECL phenomena, such as wireless ECL devices, bipolar electrode-based ECL, light-emitting electrochemical swimmers, upconversion ECL, ECL resonance energy transfer, thermoresponsive ECL, ECL using shape-controlled nanocrystals, and ECL as an ion-selective electrode photonic reporter, a paper-based microchip, and a self-powered microfluidic ECL platform. We also comment on the latest progress in bioassays, light-emitting devices and, the computational approach for the ECL mechanism study. Finally, perspectives and key challenges in the near future are addressed (198 references)
Structural chemistry of uranium phosphonates
No full textUranium phosphonates, an important class of actinide-organic coordination polymers, exhibit an exceptionally diverse and broad range of crystal structures. A variety of structure topologies have been identified for hexavalent uranium phosphonates, including cage clusters, chains, ribbons and tubes, sheets, and three-dimensional frameworks. In contrast, only a handful of tetravalent uranium phosphonates are known. This review presents a comprehensive account of the crystal structures of uranium phosphonates and the various building units (e.g. discrete monomers, polymeric units, infinite chains, and sheets) that result from the numerous coordination modes of phosphonate ligands with uranium. (C) 2015 Elsevier B.V. All rights reserved
Bacteriorhodopsin/Ag Nanoparticle-Based Hybrid Nano-Bio Electrocatalyst for Efficient and Robust H-2 Evolution from Water
No full textSearching for novel hybrid electrocatalysts with high activity and strong durability for a direct electrochemical hydrogen evolution reaction (HER) is extremely desirable but still remains a significant challenge. Herein, we report a novel solid carbon cloth-supported hybrid nano-bio electrocatalyst, decorated with Ag nanoparticles and proton-pumping bacteriorhodopsin (bR) (Ag/bR/CP) that were prepared by in situ electroless deposition and vesicle fusion technology, respectively. When applied as a hydrogen evolution cathode, the Ag/bR/CP shows a low onset overpotential of 63 mV, good durability (no detectable change in its catalytic activity for up to 1000 cycles in alkaline media), and enhanced HER performance under 550 nm irradiation, attributed to the activation of Ag and synergistic effects following light absorption, demonstrated by photoelectrochemical measurements
Layer-Filter Threshold Technique for Near-Infrared Laser Ablation in Organic Semiconductor Device Processing
No full textAlthough conventional laser ablation (CLA) method has widely been used in patterning of organic semiconductor thin films, its quality control still remains unsatisfied due to the ambiguous photochemical and photothermal processes. Based on industrial available near-infrared laser source, herein, a novel layer-filter threshold (LFT) technique is proposed, which involves the decomposition of targeted layer-filter and subsequent explosive evaporation process to purge away the upper layers instead of layer-by-layer ablation. For photovoltaic device with structure of metal/blend/PEDOT:PSS/ITO/glass, the PEDOT:PSS layer as the layer-filter is first demonstrated to be effective, and then the merged P1-P2 line and metal electrode layer are readily patterned through the self-aligned effect and regulation of ablation direction, respectively. The correlation between laser fluence and explosive ablation efficacy is also investigated. Finally, photovoltaic modules based on classical P3HT:PC61BM and low-bandgap PBDT-TFQ:PC71BM systems are separately fabricated following the LFT technique. It is found that over 90% of geometric fill factor is achieved while device performances maintain in a limited change with increased number of series cells. In comparison to conventional laser ablation methods, the LFT technique does not require sophisticated instruments but reaches comparable processing accuracy, which shows promising potential in the fabrication and commercialization of organic semiconductor thin-film devices
Poly(Acrylic Acid) Modification of Nd3+-Sensitized Upconversion Nanophosphors for Highly Efficient UCL Imaging and pH-Responsive Drug Delivery
No full textIn this work, a simple method is demonstrated for the synthesis of multifunctional core-shell nanoparticles NaYF4:Yb,Er@NaYF4:Yb@NaNdF4:Yb@NaYF4:Yb@PAA (labeled as Er@Y@Nd@Y@PAA or UCNP@PAA), which contain a highly effective 808-nm-to-visible UCNP core and a thin shell of poly(acrylic acid) (PAA) to achieve upconversion bioimaging and pH-sensitive anticancer chemotherapy simultaneously. The core-shell Nd3+-sensitized UCNPs are optimized by varying the shell number, core size, and host lattices. The final optimized Er@Y@Nd@Y nanoparticle composition shows a significantly improved upconversion luminescence intensity, that is, 12.8 times higher than Er@Y@Nd nanoparticles. After coating the nanocomposites with a thin layer of PAA, the resulting UCNP@PAA nanocomposite perform well as a pH-responsive nanocarrier and show clear advantages over UCNP@mSiO(2), which are evidenced by in vitro/in vivo experiments. Histological analysis also reveals that no pathological changes or inflammatory responses occur in the heart, lungs, kidneys, liver, and spleen. In summary, this study presents a major step forward towards a new therapeutic and diagnostic treatment of tumors by using 808-nm excited UCNPs to replace the traditional 980-nm excitation
G-Quartet-Based Nanostructure for Mimicking Light-Harvesting Antenna
No full textArtificial light-harvesting systems have received great attention for use in photosynthetic and optoelectronic devices. Herein, a system involving G-quartet-based hierarchical nanofibers generated from the self-assembly of guanosine 5'-monophosphate (GMP) and a two-step Forster resonance energy transfer (FRET) is presented that mimics natural light-harvesting antenna. This solid-state property offers advantages for future device fabrication. The generation of photocurrent under visible light shows it has potential for use as a nanoscale photoelectric device. The work will be beneficial for the development of light-harvesting systems by the self-assembly of supramolecular nanostructures