有“生命”的电线:浅析微生物纳米导线电子传递机制及其应用

微生物纳米导线是指在缺少可溶性电子受体的条件下由微生物形成类似菌毛的导电附属物,通过它传递电子是微生物为提高胞外电子传递效率而进化形成的一种有效的电子传递方式。微生物可利用具有高效导电特性的纳米导线将电子传递到远离细胞表面的地方,从而使微生物摆脱了需要直接接触胞外电子受体(Fe(Ⅲ)氧化物或电极)才能传递电子的限制。微生物纳米导线的发现丰富了人们对胞外呼吸多样性的认识,同时其在提高微生物燃料电池产电效率、促进环境中有机污染物的快速降解和生物能源等方面具有重要的应用前景,成为了当前研究的前沿和热点。本文简单介绍了微生物纳米导线的基本特性和产生纳米导线的微生物种类,重点阐述了由Geobacter和Shewanella微生物生成的纳米导线电子传递机制以及其在生物能源和生物修复等方面的应用,并展望了今后的研究重点。     

微生物电化学系统电子中介体

电化学活性微生物与电极之间的胞外电子传递在微生物电化学系统(microbial electrochemical systems,MESs)产能、生物修复等功能的实现中起着关键作用.目前,研究者对微生物胞外电子传递机理了解有限,限制了MESs的应用.相比于需要微生物功能蛋白与电极接触才能发生的直接电子传递,间接电子传递可通过具有可逆氧化还原活性的电子中介体(electron transfer mediators,ETMs)实现电子的传递,从而有效提高微生物胞外电子传递效率.在间接电子转移过程中,ETMs起着中间电子受体和中间电子供体的作用,即被还原后可将电子传递给最终电子受体并被重新还原;理论上每个ETMs分子可以循环数千次,因此ETMs对特定环境下终端氧化物(如铁离子)的循环有着极其显著的作用.本文系统总结了MESs中ETMs及间接电子传递机制近年来的研究进展,并且在此基础上探讨了ETMs在MESs中的研究趋势,以期推动MESs在生物修复、能源生产方面的实际应用.     

电子穿梭体介导的微生物胞外电子传递:机制及应用

厌氧条件下微生物将电子传递给胞外电子受体的现象非常普遍,电子穿梭体(electron shuttle,ES)是介导胞外电子传递过程的重要途径之一,但其具体的机制尚未明晰。一部分微生物自身能分泌一些物质作为内生ES,另一部分微生物能利用天然存在或人工合成的某些物质作为外生ES,并将其携带的电子传递至微生物胞外电子受体。ES介导微生物胞外电子传递的基本过程为:氧化态电子穿梭体(ES_ox)接受电子变成还原态(ES_red),ES_red传递电子给胞外电子受体,自身再次氧化成ES_ox,从而循环往复。本文重点介绍不同种类ES及其电子穿梭机制,以及ES的分子扩散、氧化还原电势及电子转移能力对胞外电子传递过程的影响。ES介导的胞外电子传递过程直接影响污染物转化和微生物产电,因此在污染修复及生物能源等方面具有重要的应用前景。     

电化学联用技术研究微生物的胞外电子传递机制

胞外电子传递（EET）是指氧化还原反应所产生的电子在微生物细胞内和细胞外的电子受体/电子供体之间互相转移的过程,这一过程伴随着能量和物质的转化。阐明EET机制是提高微生物能量和物质转化效率的基础,为元素的生物地球化学循环、金属防腐以及生物电化学系统的应用等提供理论支撑。电化学技术作为研究电极/溶液界面电子转移的简便、有效方法,在研究微生物的直接电子传递和间接电子传递机制中发挥了重要的作用,也促进了EET机制的研究从宏观层面到微观层面不断深入。本文综述了研究微生物EET机制所涉及的电化学联用技术（包括微电极、扫描电化学显微镜、电化学联用光学显微镜和光谱电化学等）;详细介绍了这些电化学联用技术的功能和优势;重点阐述了这些电化学联用技术如何推动着EET机制的研究,从宏观的生物膜层面到微观的单个微生物细胞、蛋白和分子层面不断深入;展望了新的电化学联用技术在EET研究领域的应用前景。     

革兰氏阳性电活性菌的电子传递及其应用

电活性菌将电子从胞内转移至胞外电子受体或者将胞外电子转移至胞内的过程为胞外电子传递,其在微生物群落间的电子传递及元素的地球化学循环过程中发挥重要作用。电活性菌的胞外电子传递研究前期主要集中于革兰氏阴性菌,由于革兰氏阳性菌与革兰氏阴性菌的膜结构/厚度明显不同,因此二者的电子跨膜传递途径差异明显。革兰氏阳性菌因分布广泛且可在高温、低pH、高pH和高盐等环境中生存,其电活性和电子传递机制也逐渐引起关注。本文归纳总结了革兰氏阳性电活性菌的电子传递类型,基于厚壁菌门、放线菌门和绿弯菌门的分类阐述胞外电子传递的研究进展,分析了革兰氏阳性电活性菌在污染物降解、生物能源和工业制品合成等方面的应用,并展望了未来的发展方向。     

Fura-2荧光探针研究Ca2+对大肠杆菌细胞的跨膜作用

以Fura-2／AM作为荧光探针,研究了Ca^2 对大肠杆菌HB101细胞的跨膜作用．考察了不同浓度外源钙离子处理不同生长时期细胞的跨膜行为,并采用停流技术测定了荧光动力学．结果表明大肠杆菌在用CaCl2溶液处理后,胞外Ca^2 可大量进入胞内,且进入细胞的钙离子量与胞外钙离子浓度相关;处于对数生长前期的细胞与对数生长后期和稳定期的细胞相比,胞内自身Ca^2 浓度低,但其摄取外源Ca^2 的能力最强,这应该与其生理代谢活性是相关的,而且这一时期是大肠杆菌细胞最易建立人工诱导感受态的时期．该研究对于测定革兰氏阴性菌细胞内Ca^2 浓度及胞外离子的跨膜传导行为,以及探索钙离子诱导的大肠杆菌人工感受态建立的生理机制都具有重要意义．     

光电子协同微生物介导的重金属离子还原与电子转移机理

重金属污染是一个亟待解决的环境和社会问题。重金属元素在自然界常会形成各种价态的矿物,具有不同的理化性质,对重金属污染治理具有重要的参考意义。重金属离子价态的改变可通过微生物、电极电子及半导体矿物光电子传递与吸收实现。本文分析了微生物及其电化学系统、半导体矿物光电子与光电子协同作用对重金属离子的还原作用,从氧化还原电势角度分析了微生物及其电化学系统与光电子对重金属离子的还原机理。重点从微生物跨膜电子传递过程及分子网络角度阐述了微生物还原变价重金属离子的直接/间接电子传递途径、从微生物向电极的正/逆向电子传递与吸收利用角度揭示了微生物电化学系统与光电子协同微生物对重金属离子价态调控的机制。最后,提出了微生物、电极、半导体矿物与光在重金属价态调控中的作用网络与能量利用途径。可为进一步研究微生物胞外电子传递及微生物光电子利用与光电子协同微生物调控重金属离子价态及其环境治理提供参考。     

基于大肠杆菌的全细胞微生物传感器的构建及其在急性生物毒性检测中的应用

构建了以大肠杆菌为指示生物的全细胞微生物传感器,初步探讨了其在重金属(Cu2+,Zn2+,Pb2+)及其二元联合毒物、农药污染物(莠灭净、乙酰甲胺磷)的急性生物毒性分析中的应用性能。结果表明,基于对数生长后期和稳定期的大肠杆菌微生物传感器具有良好的毒性分析性能。最优实验条件为:E.coli培养16 h,苯醌为电子传递介体,呼吸基质pH 6～8。所测毒物对E.coli的呼吸抑制作用大小顺序为:Cu2+>Zn2+>Pb2+,乙酰甲胺磷>莠灭净,与发光细菌、鱼类、藻类等其它方法检测所得结果一致。这种电化学全细胞生物传感器毒性分析方法具有快速灵敏、成本低廉、操作简单等优点,有望用于水体急性生物毒性的在线监测。     

O2/CO2煤粉燃烧时含铁矿物质转化行为的实验研究

通过乌兰木伦煤和哈拉沟煤在沉降炉中的燃烧实验,采用57Fe M(o)ssbauer谱仪,对煤中含铁矿物质及其在O2/N2和O2/CO2燃烧条件下生成的灰中含铁成分进行分析和比较,研究了O2/CO2煤粉燃烧时含铁矿物质的转化行为.结果表明,与O2/N2燃烧相比,O2/CO2燃烧对灰中生成的主要含铁矿物相种类没有影响,但显著地改变了灰中含铁矿物相的相对含量;O2/CO2燃烧更有利于内在黄铁矿和菱铁矿生成硅酸盐玻璃体而不是氧化成铁氧化物.灰中含铁矿物相的相对含量变化表明O2/CO2燃烧影响煤的结渣趋势,对于含内在含铁矿物较多的煤,O2/CO2燃烧会增加其结渣的趋势.     

电驱动下的环境污染物厌氧生物转化—电子转移原理和应用实例

厌氧环境下一些微生物能够接受来自于电极的电子并将电子传递至环境污染物,这使得电驱动下生物还原技术在可持续性废水处理以及生物修复方面受到越来越多关注.此体系中,阴极电子传递被认为是影响环境污染物厌氧转化可行性和效率的制约因素.文中首先评述可能的电子传递原理,包括水解氢气介导的间接电子传递、人工合成电子穿梭体或者细菌分泌电子穿梭体介导的间接电子传递、以及电极与细菌之间的直接电子传递等途径.相比间接电子传递,直接电子传递避免了将电子传递给没有起作用的介体及没有和电极接触的浮游微生物,因而更加节能.另外,列举了自养反硝化、生物还原脱氯、重金属生物还原、CO2生物还原以及硫酸盐生物还原等应用实例.最后,提出了此领域研究发展亟需解决的两个重要问题,包括阴极生物膜的培养以及电子从电极转至微生物内在机理的解析.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.