Anisotropic gold nanoparticles: Preparation and applications in catalysis

Despite the high amount of scientific work dedicated to the gold nanoparticles in catalysis, most of the research has been performed utilising supported nanoparticles obtained by traditional impreg‐nation of gold salts onto a support, co‐precipitation or deposition‐precipitation methods which do not benefit from the recent advances in nanotechnologies. Only more recently, gold catalyst scien‐tists have been exploiting the potential of preforming the metal nanoparticles in a colloidal suspen‐sion before immobilisation with great results in terms of catalytic activity and the morphology con‐trol of mono‐and bimetallic catalysts. On the other hand, the last decade has seen the emergence of more advanced control in gold metal nanoparticle synthesis, resulting in a variety of anisotropic gold nanoparticles with easily accessible new morphologies that offer control over the coordination of surface atoms and the optical properties of the nanoparticles （tunable plasmon band） with im‐mense relevance for catalysis. Such morphologies include nanorods, nanostars, nanoflowers, den‐dritic nanostructures or polyhedral nanoparticles to mention a few. In addition to highlighting newly developed methods and properties of anisotropic gold nanoparticles, in this review we ex‐amine the emerging literature that clearly indicates the often superior catalytic performance and amazing potential of these nanoparticles to transform the field of heterogeneous catalysis by gold by offering potentially higher catalytic performance, control over exposed active sites, robustness and tunability for thermal‐, electro‐and photocatalysis.

重组枯草芽孢杆菌全细胞催化生成L-酪氨酸

目的:本研究构建一株重组枯草芽孢杆菌工程菌,实现以苯酚、丙酮酸和氨为底物全细胞生成L-酪氨酸(L-tyrosine,L-Tyr),并优化其细胞培养条件和催化反应条件,以期提高L-Tyr的产量。方法:将来源于Pantoea agglomerans的酪氨酸酚裂解酶(Tyrosine Phenol-Lyase,TPL)经密码子优化后在枯草芽孢杆菌中异源表达,通过单因素实验优化了重组菌诱导表达条件和全细胞转化条件,旨在提高L-Tyr产量。结果:重组枯草芽孢杆菌在20℃,2.0 g/L木糖诱导培养36 h时TPL活性最高达到4.65±0.15 U·g^(−1),在75 mmol/L苯酚、75 mmol/L丙酮酸钠、487 mmol/L氯化铵、2.0 g/L亚硫酸钠、2.0 g/L EDTA、0.08 g/L磷酸吡哆醛(Pyridoxal Phosphat,PLP)、湿菌体50 g/L、pH=8.0、35℃的全细胞转化条件下,L-Tyr达到9.38 g/L,转化率为73.24%。为了进一步改善高浓度苯酚导致TPL酶活力下降问题,在全细胞转化环节采用分批补料方式,20 h后得到15.12 g/L L-Tyr,转化率为75.51%。结论:研究结果表明重组枯草芽孢杆菌可以成功转化苯酚、丙酮酸钠合成L-酪氨酸,为全细胞生物制备食品级L-酪氨酸提供了理论和技术基础,具有良好的应用前景。

石墨烯-金纳米材料修饰电极用于L-酪氨酸的检测

采用一种绿色简单的电化学方法将还原氧化石墨烯-金纳米复合薄膜共沉积到玻碳电极(GCE)上,作为传感器用于L-酪氨酸(L-Tyr)的检测.采用扫描电子显微镜(SEM)、循环伏安法(CV)和电化学阻抗谱(EIS)对修饰电极进行了表征.采用差分脉冲伏安法(DPV)研究了0.1 mol/L磷酸盐缓冲溶液中L-Tyr在修饰电极上的电化学行为,发现L-Tyr在修饰电极上的伏安响应比裸GCE明显提高.对复合薄膜的厚度、支撑电解质的p H值、沉积电位和积累时间进行了优化;在最佳实验条件下, L-Tyr的氧化峰电流在0.1~50μmol/L及50~1000μmol/L浓度范围内呈现良好的线性关系.该传感器的检出限为50 nmol/L,灵敏度为0.553μA·μmol·L^(-1),具有良好的重复性、稳定性和抗干扰性.

苯丙氨酸解氨酶合成L-2-氯苯丙氨酸的研究

L-2-氯苯丙氨酸要求旋光对映体过量(ee)≥98%,导致使用化学拆分法合成L-2-氯苯丙氨酸的收率不足50%。为提高收率,文章采用具有立体专一性的苯丙氨酸解氨酶(PAL),催化邻氯肉桂酸与氨合成L-2-氯苯丙氨酸,旋光对映体过量(ee)>99%。通过考察不同形态PAL酶的稳定性,研究得出全细胞冻融法制作的PAL酶稳定性较好,结合氮气保护,反应80 h依然能保留62%的酶活。同时,优化PAL酶催化反应的pH、温度、酶用量,确定最佳条件后,结合分段补料的方式进行酶催化反应,最终使L-2-氯苯丙氨酸的累积量达到了68.5 g/L,转化率达到了97.8%。该技术合成L-2-氯苯丙氨酸的产量和收率较高,有效降低了成本,提升了L-2-氯苯丙氨酸的市场价值。

Gold-containing metal nanoparticles for catalytic hydrogen generation from liquid chemical hydrides

Liquid chemical hydrides, which store hydrogen in the form of chemical bonds, are considered one of the most promising classes of hydrogen storage materials. Their application depends heavily on the development of efficient catalytic systems. Gold‐containing metal nanoparticles have exhibited excellent catalytic performance for hydrogen generation from liquid chemical hydrides. The present mini‐review focuses on recent developments in hydrogen generation from liquid chemical hydrides using gold‐nanoparticle and gold‐containing heterometallic nanoparticle catalysts.

过量表达甲酸脱氢酶提高大肠杆菌合成L-2-氨基丁酸的效率

为了实现L-2-氨基丁酸(L-ABA)的高效生物合成,借助pACYCDuet-1和pET28a共表达系统,构建了携带L-苏氨酸脱氨酶(L-TD)、L-亮氨酸脱氢酶(L-L-DH)和不同活性甲酸脱氢酶(FDH)编码基因的重组大肠杆菌,分别命名为:E.coli BL21(DE3)/pACYCDuet-1-Ec TD-Es LeuDH:pET28a-Cb FDH和E.coli BL21(DE3)/p ACYCDuet-1-Ec TD-Es Leu DH:p ET28a-Cb FDH^(M)。经诱导表达后,L-苏氨酸脱氨酶和L-亮氨酸脱氢酶在两个重组大肠杆菌中的表达水平基本一致,而后者的甲酸脱氢酶酶活表达水平为(342.00±9.40)IU/mL,显著高于前者的(196.00±6.20)IU/mL。在50 mL反应体系中,200 mmol/L L-苏氨酸经220 r/min、30℃下反应6 h时,前者L-ABA得率为71%,后者为85%。结果表明,提高甲酸脱氢酶的表达水平可以显著提高L-ABA的合成效率。此外,优化反应温度后,在35℃下反应6 h时,L-ABA的得率可达90%。

Vinyl chloride monomer production catalysed by gold: A review

In this review we discuss the history of research into the use of gold for the acetylene hydrochlorin‐ation reaction, and describe the recent developments which have led to its commercialisation. We discuss the use of different precursors and the addition to gold of a secondary metal as methods which attempt to improve these catalysts, and consider the nature of the active gold species. The vast majority of poly vinyl chloride （PVC） produced globally still uses a mercuric chloride as a cata‐lyst, despite the environmental problems associated with it. Due to the agreement by the Chinese government to remove mercury usage in the PVC industry over the course of the next few years there is an obvious need to find a replacement catalyst;the potential use of gold for this process has been well known for several decades and to date gold seems to be the best candidate for this, pri‐marily due to its superior selectivity when compared to other metals.

Redox behavior of gold supported on ceria and ceria-zirconia based catalysts

A series of gold-based catalysts were prepared by deposition precipitation or incipient wetness impregnation on CexZ1-xO2 solid solutions （0.28≤x≤1.00）. The morphological and structural characterization of these catalysts were carried out with X-ray diffraction, trans- mission electron microscopy （TEM） analysis and physical adsorption technique, and their redox properties were studied by temperature programmed reduction using both H2 and CO as probe molecules. Two cycles of oxidation/reduction were carried out in order to evaluate the effects of redox aging and gold sintering on the oxygen exchange capability. As observed with other noble metals, gold enhanced and promoted the ceria reduction at lower temperatures. Reduction by CO was shown to be dependent on the fine dispersion of gold and to be nega- tively affected by the ageing process more than reduction with hydrogen. This might have implications in reactions like water gas shift and CO-PROX which involve CO as a main reactant.

Promoter effect of La2O3 on gold catalyst with different textural structures

Silica supported gold nanoparticles were synthesized and promoted by lanthanum oxide as dopant. The influences of LaOand silica textural structure on the gold dispersion, formation of active species, crystalline composition and the reacting role of dopants were studied in detail. The characterization results suggested that the dispersion of gold nanoparticles depended on the textural structure of silica without lanthanum oxide doping where small mesopores are more preferable to disperse gold nanoparticles. The addition of lanthanum oxide largely increased the dispersion of gold nanoparticles and oxygen active sites independent of the textural structure of silica support. The interaction between lanthanum oxide and silica enhanced by the synergy facilitated the release of oxygen vacancies and transition of active oxygen species. In addition, the chemical properties were greatly changed after lanthanum oxide addition which was only inconspicuously impacted by the initial textural structure of silica supports, shedding light on the further design of economic gold catalyst based on simple synthesis method.

Gold Nanozymes:From Concept to Biomedical Applications

In recent years,gold nanoparticles have demonstrated excellent enzyme-mimicking activities which resemble those of peroxidase,oxidase,catalase,superoxide dismutase or reductase.This,merged with their ease of synthesis,tunability,biocompatibility and low cost,makes them excellent candidates when compared with biological enzymes for applications in biomedicine or biochemical analyses.Herein,over 200 research papers have been systematically reviewed to present the recent progress on the fundamentals of gold nanozymes and their potential applications.The review reveals that the morphology and surface chemistry of the nanoparticles play an important role in their catalytic properties,as well as external parameters such as pH or temperature.Yet,real applications often require specific biorecognition elements to be immobilized onto the nanozymes,leading to unexpected positive or negative effects on their activity.Thus,rational design of efficient nanozymes remains a challenge of paramount importance.Different implementation paths have already been explored,including the application of peroxidase-like nanozymes for the development of clinical diagnostics or the regulation of oxidative stress within cells via their catalase and superoxide dismutase activities.The review also indicates that it is essential to understand how external parameters may boost or inhibit each of these activities,as more than one of them could coexist.Likewise,further toxicity studies are required to ensure the applicability of gold nanozymes in vivo.Current challenges and future prospects of gold nanozymes are discussed in this review,whose significance can be anticipated in a diverse range of fields beyond biomedicine,such as food safety,environmental analyses or the chemical industry.

PREPARATION OF POLYMER MICROSPHERES WITH PYRIDYL GROUP AND THEIR STABILIZED GOLD METALLIC COLLOIDS

Narrow disperse poly（ethyleneglycol dimethacrylate-co-4-vinylpyridine） （poly（EGDMA-co-4-VPy）） microspheres were prepared by distillation-precipitation copolymerization of ethyleneglycol dimethacrylate （EGDMA） and 4-vinylpyridine （4-VPy） with 2,2＇-azobisisobutyronitrile （AIBN） as initiator in neat acetonitrile. The polymer microspheres containing pyridyl group were then utilized as stabilizer for gold metallic colloids with the diameter around 7 nm, which were prepared by the in situ reduction of gold chloride trihydrate with sodium borohydride through the coordination of the pyridyl group on the gel layer and surface of the microsphere with the gold metallic nano-particles. The catalytic properties of the pyridyl- functionalized microsphere-stabilized gold metallic colloids and the behavior of the stabilized-catalyst for the recycling were investigated with reduction of 4-nitrophenol to 4-aminophenol as a model reaction.

Enhanced photo-catalytic activity of gold ion and gold modified

The gold ion modified TiO2 was prepared by means of sol-gel whereas gold deposited TiO2 was prepared by means of photoreduction. The physical properties were influenced significantly by the presence of gold ion or gold. The enhanced photo-activity of gold modified TiO2 vas quantified in terms of methylene blue degradation. The presence of gold ion in TiO2 lattices or gold on TiO2 surface enhanced their-photo-activity. The optimum molar content of gold ion doping and gold deposition all was 0.5%. The first-order rates constants of gold modified TiO2 was more than that of pure TiO2, and decreased by increasing the content of gold ion and gold when their contents were more than 0.5%. Gold ion doped in TiO2 lattices was more effective to enhance the photo-activity than gold on TiO2 surface. Moreover, the relationship between physical properties, chemical properties and photo-activity has been discussed.

Extrapolation of the gold-catalyzed cycloisomerization to the palladium-catalyzed cross-coupling/cycloisomerization of acetylenic alcohols for the synthesis of polysubstituted furans:Scope and application to tandem processes

This paper describes the development of an integrated approach for the preparation of diverse furan derivatives from acetylenic alcohols by gold and palladium catalyzed π-activation chemistry.Notably,this new method was found to be amenable to cyclooctyl-containing substrates,which represents a significant extension to this methodology compared with our previous reports.Furthermore,this newly developed method allowed for the direct construction of cyclooctyl furans from their synthetic precursors under Sonogashira conditions.Experimental results revealed that palladium played two major functions in these reactions,including（1） an essential catalyst in the cross-coupling reaction of the substrates;and（2）facilitating the cyclization of the acetylenic alcohol intermediates through a typical π-activation process.The scope of this chemistry was highlighted by the one-pot synthesis of 3-iodofuran,which provided an opportunity for further functionalization（via coupling methods）.Finally,the AuBr3 protocol was also elaborated to domino cyclization/C-H activation reactions,as well as the cyclization of acyclic precursors.Taken together,the results of this study demonstrate that gold and palladium catalysts can be used to complement each other in cyclization reactions.

Highly efficient base-free aerobic oxidation of alcohols over gold nanoparticles supported on ZnO-CuO mixed oxides

The design and preparation of suitable supports are of great importance for gold catalysts to attain excellent catalytic performance for alcohol oxidation.In this work,we found that ZnO-CuO mixed oxides supported gold catalysts showed much better catalytic activity for base-free aerobic oxidation of benzyl alcohol than Au/ZnO and Au/CuO catalysts,and among them Au/Zn0.7Cu0.3O displayed the best catalytic performance.In addition,the Au/Zn0.7Cu0.3O catalyst could selectively catalyze the aerobic oxidation of a wide range of alcohols to produce the corresponding carbonyl compounds with high yields under mild conditions without base.Further characterizations indicated that the outstanding catalytic performance of Au/Zn0.7Cu0.3O was correlated with the small size of Au nanoparticles(NPs),good low-temperature reducibility,high concentration of surface oxygen species,and collaborative interaction between Au NPs and mixed oxide.

Gold-catalyzed addition reaction between creatinine and isatin:A sustainable and green chemistry approach for the diastereoselective synthesis of 3-substituted-3-hydroxyisatins

The aldolization of various isatins with creatinine under gold catalysis in water has been developed.The reaction is operationally simple as the products can be isolated by simple filtration without requiring tedious solvent extraction and column chromatographic techniques.The generality of this methodology is showcased through the reactions of a wide range of isatin derivatives with creatinine to afford the respective aldol products in excellent yields with complete syn‐selectivity.The scope of this chemistry is further extended to a tandem reaction involving isatins,creatinine and malononitrile to afford multicomponent products in excellent yields with complete anti‐selectivity.The antioxidant potency of the synthesized compound was assessed by a spectrophotometric method,which revealed that three compounds containing halogen atoms(2c,2d and2e)were the most active compared with the standard.

Richard L. Abbott,MD,to Receive Duke Elder International Gold Medal at the WOC2014

27 January 2014San Francisco,CA,USA-The International Council of Ophthalmology(ICO)Board of Trustees is pleased to announce the selection of Richard L.Abbott,MD,as the 2014 International Duke Elder medalist.The Duke Elder Medal is awarded every four years to an ophthalmologist who,by his/her distinction,leadership,and teaching,has contributed most to the development of international relations and friendship between ophthalmologists,and who has advanced the field by his/her contributions in writing and organization in ophthalmology.

Gold Nanoparticles of Multiple Shapes Synthesized in L-Tryptophan Aqueous Solution

In this paper, we describe a simple and efficient synthesis of gold nanoparticles(GNPs) of various shapes(spherical, rod-like, hexagonal, truncated triangular, and triangular) using Au(Ⅲ) reduction in aqueous solutions by L-tryptophan. We evaluated the influences of reaction temperature, foreign metal ions Ag(Ⅰ), and surfactants of nonionic(polyethylene glycol, PEG), anionic(sodium dodecyl sulfate, SDS), and cationic(cetyltrimethyl ammonium bromide, CTAB) on GNPs synthesis. We characterized the resultant GNPs using UV–visible adsorption spectroscopy, transmission electron microscopy/high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, selected-area electron diffraction, and Fourier-transform infrared spectroscopy. We fabricated the variously sized GNPs by controlling the rate of the reduction of gold ions in aqueous solution by varying the reaction temperature: the higher the temperature, the smaller the gold nanospheres. We found the existence of Ag(Ⅰ) to reinforce the reduction of Au(Ⅲ) and to correspond with the appearance of some amorphous bimetallic Au/Ag nanoparticles. Additionally, we found the presence of surfactants to greatly influence the shape of the formed GNPs, especially the presence of CTAB, which results in the anisotropic growth of gold nanocrystals into hexagonal, truncated triangular, and triangular nanoplates. In addition, with the increase in CTAB concentration, we found the amount of gold nanoplates to first increase and then decrease. Finally, we performed preliminary explorations of the reduction process and morphological evolution to propose possible corresponding reduction and morphological evolution pathways.

Morphological Control of Gold Nanoparticles by Green Synthesis Using L-Tryptophan and Other Additives

This study focuses on shape-controlled synthesis of gold nanoparticles, using the green reducing agent L-Tryptophan(L-Trp), which is non-toxic and eco-friendly. This specific agent was investigated to realize certain morphology controlling effects by changing the relative growth rates among various crystal planes. Experimental samples were characterized by transmission electron microscope, UV-Vis spectrophotometer and X-ray diffraction(XRD) for size and morphological information. The effects of the specific additives of PVP((C_6 H_9 NO)_n), CTAB(C_(16)H_(33)(CH_3)_3 NBr), and KBr were examined for their morphological control individually and synergistically in this system. Hexagonal gold nanoparticles were successfully obtained via the PVP/CTAB and PVP/KBr systems. Particular amounts of PVP/KBr produced various polyhedron structures, such as cubes, and others with triangular and rhombic straight-side cross sections.

多酶体系中谷胱甘肽HPLC分析方法研究

为了建立一种快速有效的方法来满足体外酶催化法生产谷胱甘肽中各复杂成分的定性及定量检测。依据反应液各组分的性质与特性,利用HPLC研究建立了一种新的分离方法。结果表明,通过此方法可实现L-半胱氨酸、L-谷氨酸钠、ATP、AMP、ADP、还原型谷胱甘肽、氧化型谷胱甘肽各组分的分离,分离度均>1.5,L-半胱氨酸与甘氨酸分离度>1.2;底物及产物曲线线性为R^(2)>0.99,回收率为94.6%~110.0%,连续检测6次RSD均<2.0%;且单个样品检测时间为15 min,与药典片剂检测方法45 min相比,缩短了检测时间,可快速出具检测结果,更有利于日常分析检测。

基于壳聚糖-纳米金/纳米普鲁士蓝/L-半胱氨酸修饰的葡萄糖传感器的研究

在金电极表面修饰带正电荷的L-半胱氨酸,再利用静电吸附作用固定纳米普鲁士蓝(nano-PB),然后利用壳聚糖-纳米金复合膜将葡萄糖氧化酶(GOD)固定于修饰电极表面,制成新型的葡萄糖传感器.通过交流阻抗技术,循环伏安法和计时电流法考察了电极的电化学特性.在优化的实验条件下,该传感器在葡萄糖浓度为3.0×10-6～1.0×10-3mol/L范围内有线性响应,检测下限为1.6×10-6mol/L.此外该传感器具有响应快、稳定性好和选择性良好的特点,能有效排除常见干扰物质如抗坏血酸、尿酸等对测定的影响.