氧化铁磁性纳米粒子的制备、表面修饰及在分离和分析中的应用

氧化铁磁性纳米粒子通过表面化学修饰得到无机、有机或聚合物壳包覆在其表面。其中的壳结构既具有生物适应性,又具有可键合生物分子如细胞、蛋白质、酶、抗体和核酸的活性基团,而核具有磁性特性。本文总结了氧化铁磁性纳米粒子的制备方法,介绍了其表面化学修饰及在分离和分析应用的最新进展。     

非表面活性剂模板溶胶-凝胶法制备磁性介孔二氧化硅实现纤维二糖酶的原位固定

以非表面活性剂为模板,通过引入磁性纳米颗粒,制备了磁性介孔硅材料,实现了纤维二糖酶的原位固定,得到了磁性固定化酶.制备流程操作简单、原料易得、使用方便.溶胶-凝胶反应在水相、常温、中性条件下进行,适用于工业化生产.对磁性固定化酶进行了气体吸附分析、热重分析、表面形貌分析和磁性表征.结果表明,磁性固定化酶具有较大的比表面积、较窄的介孔分布和软铁磁性.与非介孔固定化酶相比,磁性固定化酶表观酶活明显提高.磁性颗粒的引入对酶活性没有显著的影响,并且可以非常方便和快速地从反应系统中回收再利用,结合磁场的可控性,非表面活性剂模板溶胶-凝胶法有望实现固定化酶的大规模可控释放与回收.     

氧化铁磁性纳米粒子的表面配体交换及相转移

以苯甲醇为单一溶剂, 通过常压、高温热解乙酰丙酮铁, 制备了尺寸单分散的四氧化三铁磁性纳米粒子. 采用透射电镜(TEM), X射线衍射(XRD), 动态光散射(DLS)等方法对粒子形貌和结构进行了表征. 利用傅里叶变换红外(FT-IR)光谱和热重分析(TGA)研究了所制备纳米粒子的表面化学, 结果表明稳定四氧化三铁粒子的是苯甲酸分子, 且表面覆盖度小于20%. 所制备的磁性纳米粒子可以在室温下方便地进行表面配体交换, 从而为氧化铁磁性纳米粒子的功能化提供新的途径.     

单分散磁性纳米粒子固定化猪胰脂肪酶的研究

借助溶热法制备了一种亲水及生物相容良好的Fe3O4磁性纳米粒子,用γ-氨丙基三乙氧基硅烷直接对所得磁性粒子表面改性,然后用戊二醛偶联法制得了固定化猪胰脂肪酶.表征研究显示,所得磁性粒子粒径约200 nm,具有良好的单分散性和磁响应性.考察了戊二醛浓度、给酶量和反应时间对脂肪酶固定化过程的影响,并通过游离酶与固定化酶的比...     

α，ω─二羧基聚乙二醇磁性毫微粒固定化碱性蛋白酶的研究

本文用共沉淀法制备了平均直径为３８４纳米的α，ω─二羧基聚乙二醇磁性毫微粒．碱性蛋白酶通过吸附交联法被固定于磁性毫微粒．研究了制备过程中的吸附时间、给酶量、戊二醛浓度、ｐＨ和离子强度对磁性固定化酶活力及酶固定化率的影响．比较了磁性蛋白酶磁性固定化酶与自由酶的酶学性质，磁性固定化酶的最适温度有改变，但热稳定性显著提高；磁性固定化酶的最适ｐＨ向酸性方向移动了１．０个ＰＨ单位。     

α,ω—二羧基聚乙二醇磁性毫微粒固定化碱性蛋白酶的研究

本文用共沉淀法制备了平均直径为３８４纳米的α，ω－二羧基聚乙二醇磁性毫微粒，碱性蛋白酶通过吸附交联法被固定于磁性毫微粒，研究了制备研究中的吸附时间，给酶量，戊二醛浓度，ｐＨ和离子强度对磁性固定化酶活力及酶固定化率的影响。比较了碱性蛋白酶磁性固定化酶与自由酶的酶学性质，磁性固定化酶的最适温度没有改变，但热稳定性显著使高；磁性固定化酶的最适ｐＨ向酸性方向移动了１．０个ｐＨ单位。     

层层自组装修饰磁性纳米粒子及蛋白质吸附研究

采用层层自组装技术将聚天冬胺酸和聚乙二胺修饰到磁性纳米粒子表面上, 并研究了修饰后的磁性纳米粒子的zeta电势变化和对蛋白质的吸附. 先通过化学共沉淀的方法获得了四氧化三铁磁性纳米粒子, 然后利用层层自组装的方法对纳米粒子进行了修饰. 用TEM表征了纳米粒子的尺寸. 用红外光谱表征了修饰过程中磁性纳米粒子表面组成的变化情况. 研究了修饰过程对磁性纳米粒子的zeta电势的影响. zeta电势的正负和大小与表面连接的分子的带电性质有关. 磁性纳米粒子的等电点接近中性. 聚天冬胺酸修饰的磁性纳米粒子的Zeta电势为负值. 在聚乙二胺溶液的pH＝11时获得的双层修饰的磁性粒子的等电点接近9, 并且等电点随聚乙二胺溶液的pH的减小而减小. 结果也表明在pH＝7.4时具有不同表面电荷的磁性纳米粒子通过静电作用选择性地吸附蛋白质.     

磁性氧化石墨烯固定化氯过氧化物酶及其在奥酸性蓝45脱色中的应用

以氧化石墨烯和Fe_3O_4为原料制备磁性氧化石墨烯,采用吸附法将氯过氧化物酶固定在磁性氧化石墨烯上,考察了固定化体系缓冲溶液p H值、固定化时间及反应温度对固定效果的影响.以氯过氧化物酶催化氧化奥酸性蓝45染料脱色反应为模型反应,探讨了固定化氯过氧化物酶的操作稳定性.实验结果表明,p H=3.5,反应15 min、反应温度15℃为固定化氯过氧化物酶的最佳催化条件;采用共沉淀法制备载体,加入的NH_4Fe(SO_4)_2·12H_2O与氧化石墨烯(GO)质量比为10.7∶1时,得到的磁性氧化石墨烯(TMGO)的酶固载量大于二者质量比为5.35∶1时得到的磁性氧化石墨烯(FMGO),这可能与FMGO氧化石墨烯表面的Fe_3O_4含量不足有关;与游离酶相比,固定化氯过氧化物酶表现出更好的酸碱稳定性、H_2O_2稳定性、热稳定性和储存稳定性,在35~50℃,聚集或堆积的磁性氧化石墨烯(TMGO)片层打开,导致固定化酶活损失率明显小于游离酶.重复使用5次后,TMGO-氯过氧化物酶(CPO)的相对活性仍然保持在60%以上.     

基于DNA链置换反应的新型固定化酶反应器制备及应用

建立了一种新型的酶固定化方法,采用DNA链置换反应成功地在单链DNA标记的磁性纳米粒子上实现了酶的链置换无损更替。该技术可实现目标酶的再利用,节约了生产成本。制备的固定化胰蛋白酶微反应器具有较好的重复利用性和高酶切效率,重复使用10次后仍可保持原酶活性的86%;利用链置换反应制备的MNPs@DNATrypsin酶切马心肌红蛋白5 min后,即可获得95%±0%(n=3)的氨基酸序列覆盖率,远超过相同条件下自由酶酶切12 h的结果。实验表明,发展的固定化酶技术具有高磁响应性,便于从反应体系中回收固定化酶和重复使用,同时此技术可显著提高酶活性,因此可用于固定各种重要的酶,同时可将其广泛应用于各种酶促反应中。     

羧甲基壳聚糖磁性纳米粒子的合成及应用

通过合成油酸修饰的Fe3O4纳米粒子和羧甲基壳聚糖直接包埋油酸修饰的Fe3O4纳米粒子的两步合成法制备了羧甲基壳聚糖磁性纳米粒子。采用透射电子显微镜、傅里叶变换红外光谱、振动样品磁强计和同步热分析测试技术对制备的羧甲基壳聚糖磁性纳米粒子进行了表征。所得磁性纳米粒子呈规则球形,粒径约为10 nm;表面含羧基,且具有很好的顺磁性和稳定性。考察了羧甲基壳聚糖磁性纳米粒子对阿霉素的载药量和对阿霉素在磷酸盐缓冲溶液中的缓释性能。结果表明,磁性纳米粒子对阿霉素展示了较高的载药量(91.8 mg/g),结合了阿霉素的磁性复合物对阿霉素的缓释作用明显,说明制备的羧甲基壳聚糖磁性纳米粒子有望作为治疗肿瘤的纳米磁靶向药物输送载体。     

单分散磁性纳米粒子靶向药物载体

本文综述了单分散磁性氧化铁纳米粒子的主要制备方法、表面修饰以及在生物医学靶向药物方面的应用研究进展。金属有机前驱体高温热分解法、溶剂热合成法和LSS（liquid-solid-solution）法是目前制备高质量单分散磁性纳米粒子比较有效的手段。通过表面修饰制备出的具有良好水溶性、生物相容性和活性功能基团的磁靶向药物载体将可能实现定位蓄积、高效载药、控制释药和可生物降解等靶向治疗癌症的目的。开发出具有荧光检测、主动靶向识别、高效载药、智能控药释放、无毒副作用和生物相容性于一体的多功能靶向药物载体将是其发展趋势。     

Protease Immobilization on γ‐Fe2O3/Fe3O4 Magnetic Nanoparticles for the Synthesis of Oligopeptides in Organic Solvents

The use of nanobiocatalysts, with the combination of nanotechnology and biotechnology, is considered as an exciting and rapidly emerging area. The use of iron oxide magnetic nanoparticles, as enzyme immobilization carriers, has drawn great attention because of their unique properties, such as controllable particle size, large surface area, modifiable surface, and easy recovery. In this study, various γ‐Fe₂O₃/Fe₃O₄ magnetic nanoparticles with immobilized proteases were successfully prepared by three different immobilization strategies including A) direct binding, B) with thiophene as a linker, and C) with triazole as a linker. The oligopeptides syntheses catalyzed by these magnetic nanoparticles (MNPs) with immobilized proteases were systematically studied. Our results show that i) for magnetic nanoparticles immobilized α‐chymotrypsin, both immobilization strategies A and B furnished good reusability for the Z‐Tyr‐Gly‐Gly‐OEt synthesis, the MNPs enzymes can be readily used at least five times without significant loss of its catalytic performance: ii) In the case of Z‐Asp‐Phe‐OMe synthesis catalyzed by magnetic nanoparticles immobilized thermolysin, immobilization Strategy B provided the best recyclability: iii) For the immobilized papain, although Strategy A or B afforded an immobilized enzyme for the first cycle of Z‐Ala‐Leu‐NHNHPh synthesis in good yield, their subsequent catalytic activity decreased rapidly. In general, the γ‐Fe₂O₃ MNPs were better for use as an immobilization matrix, rather than the Fe₃O₄ MNPs, owing to their smaller particle size and higher surface area.     

Synthesis, assembly and reaction of a nanocatalyst in microfluidic systems: a general platform

We present a successive microfluidic approach to create and characterize hierarchical catalyst structures consisting of metal-decorated nanoparticles that are assembled into porous microparticles ("supraball" catalysts). First, using a silicon microreactor, platinum nanoparticles with a very narrow size distribution are grown and immobilized uniformly onto iron oxide/silica core-shell nanospheres. The Pt-decorated silica nanospheres are then assembled into uniform, spherical, micron-sized particles by using emulsion templates generated with a microfluidic drop generator. Finally, the assembled supraballs are loaded into a packed-bed microreactor for characterization of the catalytic reactivity. The prepared material showed excellent catalytic activity for the oxidation of aldehyde with only ～1 mg of material (containing ～50 μg of platinum nanoparticles). After the reactions, all the supraball catalysts are recovered by using the magnetic property of the underlying iron oxide/silica core-shell nanospheres.     

Palladium magnetic nanoparticle‐polyethersulfone composite membrane as an efficient and versatile catalytic membrane reactor

Developing polymer catalytic membrane reactors is an aim due to its outstanding advantages. In this paper, a novel catalytic membrane containing palladium‐supported magnetic nanoparticles is introduced. Silica‐iron oxide core shell nanoparticles were first prepared and functionalized by phosphine ionic liquid functionalized poly(ethylene glycol). The modified magnetic nanoparticles were used as support for immobilization of palladium. The final palladium‐immobilized nanoparticles were used as active filler for the preparation of membrane reactor. The prepared membranes were characterized, and their activities were tested in carbon‐carbon bond formation and catalytic reduction. The catalytic membrane showed good performance in the mentioned reactions.     

Efficient Immobilization of Porcine Pancreatic α-Amylase on Amino-Functionalized Magnetite Nanoparticles: Characterization and Stability Evaluation of the Immobilized Enzyme

The potential of the modified magnetic nanoparticles for covalent immobilization of porcine pancreatic α-amylase has been investigated. The synthesis and immobilization processes were simple and fast. The co-precipitation method was used for synthesis of magnetic iron oxide (Fe₃O₄) nanoparticles (NPs) which were subsequently coated with silica through sol–gel reaction. The amino-functionalized NPs were prepared by treating silica-coated NPs with 3-aminopropyltriethoxysilane followed by covalent immobilization of α-amylase by glutaraldehyde. The optimum enzyme concentration and incubation time for immobilization reaction were 150 mg and 4 h, respectively. Upon this immobilization, the α-amylase retained more than 50 % of its initial specific activity. The optimum pH for maximal catalytic activity of the immobilized enzyme was 6.5 at 45 °C. The kinetic studies on the immobilized enzyme and its free counterpart revealed an acceptable change of K_m and V_max. The Km values were found as 4 and 2.5 mM for free and immobilized enzymes, respectively. The V_max values for the free and immobilized enzymes were calculated as 1.75 and 1.03 μmol mg^?1 min^?1, in order, when starch was used as the substrate. A quick separation of immobilized amylase from reaction mixture was achieved when a magnetically active support was applied. In comparison to the free enzyme, the immobilized enzyme was thermally stable and was reusable for 9 cycles while retaining 68 % of its initial activity.     

A comparison of lipase and trypsin encapsulated in mesoporous materials with varying pore sizes and pH conditions

Immobilized enzymes have an advantage over enzymes free in solution in that they are easily recovered after completed reaction. In addition, immobilization often gives enhanced stability. Entrapment of an enzyme in the pores of a mesoporous material is an attractive procedure since the enzyme is immobilized without any covalent bonding to a support which may be detrimental to the catalytic performance. The objective of this work is to compare the encapsulation and catalytic performance of lipase from Mucor miehei and trypsin from bovine pancreas, two hydrolases with rather dissimilar properties and structures. We also demonstrate the importance of the pore dimensions and the pH for proper function of the encapsulated enzyme. Mesoporous silica particles (SBA-15) with three different pore sizes (50 Å, 60 Å and 89 Å) were synthesized and hexagonal structures with narrow pore size distributions were confirmed with TEM, SAXS and N₂-adsorption. Lipase and trypsin were encapsulated separately in the silica particles and the results indicate distinct differences between the two enzymes, both in loading capacity and catalytic activity. For trypsin the encapsulation rate and the loading capacity were large with a maximum reached at pH 7.6. The largest product yield was obtained with the particles with 60 Å pores, however, the yield was significantly lower than with free trypsin. For lipase optimal encapsulation rate and loading capacity were reached with the particles with 89 Å pores at pH 6.0 but were low compared to trypsin. However, the catalytic activity of the encapsulated lipase was more than twice as large as for free lipase, which can be explained by an interfacial activation of lipase at the silica surface.     

Improved Thermal and Reusability Properties of Xylanase by Genipin Cross-Linking to Magnetic Chitosan Particles

Enzymes are gradually increasingly preferred over chemical processes, but commercial enzyme applications remain limited due to their low stability and low product recovery, so the application of an immobilization technique is required for repeated use. The aims of this work were to produce stable enzyme complexes of cross-linked xylanase on magnetic chitosan, to describe some characteristics of these complexes, and to evaluate the thermal stability of the immobilized enzyme and its reusability. A xylanase was cross-linked to magnetite particles prepared by in situ co-precipitation of iron salts in a chitosan template. The effect of temperature, pH, kinetic parameters, and reusability on free and immobilized xylanase was evaluated. Magnetization, morphology, size, structural change, and thermal behavior of immobilized enzyme were described. 1.0?±?0.1 μg of xylanase was immobilized per milligram of superparamagnetic chitosan nanoparticles via covalent bonds formed with genipin. Immobilized xylanase showed thermal, pH, and catalytic velocity improvement compared to the free enzyme and can be reused three times. Heterogeneous aggregates of 254 nm were obtained after enzyme immobilization. The immobilization protocol used in this work was successful in retaining enzyme thermal stability and could be important in using natural compounds such as Fe₃O₄@Chitosan@Xylanase in the harsh temperature condition of relevant industries.

     

金属卟啉类超分子催化剂*

金属卟啉类超分子催化剂是超分子催化研究领域的重要内容之一,其关键环节是以金属卟啉为基础构建超分子微反应器,使反应活性中心处在一个特定的微环境中,从而实现高的催化效率和选择性。本文分别从超分子催化剂母体结构构筑（借助环糊精、模板等）和催化应用（模拟细胞色素P-450系列酶、光电催化等）的角度详细评述了近年来金属卟啉类超分子催化剂的设计、结构及催化作用的研究进展,并对该研究领域的前景进行了展望。     

Molecular Solar Thermal Batteries through Combination of Magnetic Nanoparticle Catalysts and Tailored Norbornadiene Photoswitches

Cobalt catalysts are immobilized on the surface of iron oxide nanoparticles for the preparation of highly active quasi-homogeneous catalysts toward an efficient release of photochemically stored energy in norbornadiene-based photoswitches. The facile separation of the iron oxide nanoparticles through exploitation of the intrinsic magnetic properties of this material enables efficient cyclization of energy storage and release. Through the transition from cobalt (II) salphen to cobalt porphyrins, a 22.6-fold increase in the catalytic efficiency of the QC-NBD back-conversion is achieved, with an initial TOF of up to 3.64 s⁻¹ and excellent TON of over 3305. In addition, a series of novel “push–pull” functionalized norbornadiene derivatives is prepared, featuring excellent absorption properties with maxima up to 366 nm, quantum yields around 70 %, high energy storage capacities of up to 98.0 kJ mol⁻¹, and outstanding thermal stability with t_1/2 (25 °C) over 100 days. Finally, the energy storage potential of these molecular solar thermal (MOST) systems is harnessed in a heat release experiment. This demonstrates the potential of norbornadiene-based photoswitches in combination with efficient magnetic catalysts for the generation of environmentally benign process heat.     

Iron Oxide Nanoparticles Embedded onto 3D Mesochannels of KIT‐6 with Different Pore Diameters and Their Excellent Magnetic Properties

Here, we report the results of our detailed study on the fabrication of iron oxide magnetic nanoparticles confined in mesoporous silica KIT‐6 with a 3D structure and large, tunable pore diameters. It was confirmed by XRD, nitrogen adsorption, high‐resolution (HR) TEM, and magnetic measurements that highly dispersed iron oxide nanoparticles are occupied inside the mesochannels of KIT‐6. We also demonstrated that the size of the iron oxide nanoparticle can be controlled by simply changing the pore diameter of the KIT‐6 and the weight percentage of the iron oxide nanoparticles. The effect of the weight percentage and size of the iron oxide nanoparticles, and the textural parameters of the support on the magnetic properties of iron oxide/KIT‐6 has been demonstrated. The magnetization increases with decreasing iron content in the pore channels of KIT‐6, whereas coercivity decreases for the same samples. Among the KIT‐6 materials studied, KIT‐6 with 7.5 wt % of iron showed the highest saturation magnetic moment and magnetic remanence. However, all the samples register a coercivity of around 2000 Oe, which is generally observed for the hard magnetic materials. In addition, we have found a paramagnetic‐to‐superparamagnetic transition at low temperature for samples with different iron content at low temperature. The cause for this exciting transition is also discussed in detail. Magnetic properties of the iron oxide loaded KIT‐6 were also compared with pure iron oxide and iron oxide loaded over SBA‐15. It was found that iron oxide loaded KIT‐6 showed the highest magnetization due to its 3D structure and large pore volume. The pore diameter of the iron oxide loaded KIT‐6 support also plays a critical role in controlling the magnetization and the blocking temperature, which has a direct relation to the particle diameter and increases from 48 to 63 K with an increase in the pore diameter of the support from 8 to 11.3 nm.