Temperature-responsive Pickering high internal phase emulsions for recyclable efficient interfacial biocatalysis

The field of biocatalysis is expanding owing to the increasing demand for efficient low-cost green chemical processes. However, a feasible strategy for achieving product separation, enzyme recovery, and high catalytic efficiency in biocatalysis remains elusive. Herein, we present thermoresponsive Pickering high internal phase emulsions (HIPEs) as controllable scaffolds for efficient biocatalysis; these HIPEs demonstrate a transition between emulsification and demulsification depending on temperature. Ultra-high-surface-area Pickering HIPEs were stabilized by Candida antarctica lipase B immobilized on starch particles modified with butyl glycidyl ether and glycidyl trimethyl ammonium chloride, thus simplifying the separation and reuse processes and significantly improving the catalytic efficiency. In addition, the switching temperature can be precisely tuned by adjusting the degree of substitution of the modified starches to meet the temperature demands of various enzymes. We believe that this system provides a green platform for various interfacial biocatalytic processes of industrial interest.

The thermoresponsive Pickering high internal phase emulsions stabilized by starch particles as controllable scaffolds for efficient biocatalysis, which simplified the separation and reuse processes and significantly improved the catalytic efficiency.     

CO2-responsive Pickering emulsions stabilized by soft protein particles for interfacial biocatalysis

Pickering emulsions are emulsions stabilized by colloidal particles and serve as an excellent platform for biphasic enzymatic catalysis. However, developing simple and green strategies to avoid enzyme denaturation, facilitate product separation, and achieve the recovery of enzyme and colloidal particle stabilizers is still a challenge. This study aimed to report an efficient and sustainable biocatalysis system via a robust CO₂/N₂-responsive Pickering oil-in-water (o/w) emulsion stabilized solely by pure sodium caseinate (NaCas), which was made naturally in a scalable manner. The NaCas-stabilized emulsion displayed a much higher reaction efficiency compared with conventional CO₂/N₂-responsive Pickering emulsions stabilized by solid particles with functional groups from polymers or surfactants introduced to tailor responsiveness, reflected by the fact that most enzymes were transferred and enriched at the oil–water interface. More importantly, the demulsification, product separation, and recycling of the NaCas emulsifier as well as the enzyme could be facilely achieved by alternatively bubbling CO₂/N₂ more than 30 times. Moreover, the recycled enzyme still maintained its catalytic activity, with a conversion yield of more than 90% after each cycle, which was not found in any of the previously reported CO₂-responsive systems. This responsive system worked well for many different types of oils and was the first to report on a protein-based CO₂/N₂-responsive emulsion, holding great promise for the development of more sustainable, green chemical conversion processes for the food, pharmaceutical, and biomedical industries.

An unprecedented strategy was proposed for recycled interfacial biocatalysis in a CO₂-responsive emulsion stabilized by soft protein particles. The recycled enzyme maintained its catalytic activity, with a conversion yield over 90% after 30 cycles.     

基于扩散强化的Pickering界面生物催化系统构建及CO2矿化过程研究

CO₂的有效利用有助于解决环境和生态问题.碳酸酐酶(CA)等酶分子可精准活化CO₂分子以降低反应能垒,为CO₂的高效和高选择性转化提供了一种有前景的途径.然而,酶离开生物体后易失活,且难以重复利用.目前,包埋型固定化酶是常用且有效的提高酶稳定性与回用率的方法之一,但载体的存在会造成反应物CO₂内扩散阻力增加,降低反应活性.此外,CO₂酶促转化是一个气-液-固三相反应过程,反应体系中CO₂的外扩散性能也需要加强.金属有机骨架(MOFs),特别是咪唑酯骨架(ZIFs),常被用作酶固定化的载体.ZIFs的拓扑结构可被设计成不同形貌,进而通过ZIFs的结构工程来加强分子向其中的内扩散.Pickering乳液是指以固体颗粒代替常规表面活性剂而稳定的乳液.当固体颗粒具有催化活性时,催化剂颗粒会扩大液-液-固或气-液-固三相接触面积,从而有效协调反应物在不同相中的扩散时间.如果酶被用作这些颗粒的活性中心,所制备的Pickering乳液也可能具备类似的特性,可加强底物分子向酶的外扩散.本文选择两种具有不同结构的ZIFs(ZIF-L和ZIF-8),原位包埋CA后形成CA@ZIFs颗粒以稳定Pickeirng乳液.ZIF-L和CA@ZIF-L颗粒显示出独特的二维层状堆叠结构.ZIF-8和CA@ZIF-8颗粒呈棱角清晰的十二面体结构.与CA@ZIF-8颗粒相比,CA@ZIF-L颗粒显示出更大的孔径和更宽的孔径分布,这有助于CO₂从CA@ZIF-L颗粒表面扩散至酶活性中心.利用酶活测试来研究内扩散是否通过结构工程得到了加强,发现CA@ZIF-L颗粒的活性比CA@ZIF-8颗粒高22.3%,推测这是由于CA@ZIF-L颗粒特殊的十字花状结构会缩短CO₂从颗粒表面扩散至酶活性中心的距离.同时,十字花状结构可暴露更多的酶活性位点(CA@ZIF-L颗粒的暴露面积是CA@ZIF-8颗粒的~8倍),从而提升了反应物浓度并显示出更高的催化活性.本文还设计了吸附实验来进一步验证上述假设,发现BSA@ZIF-L颗粒对香豆素的吸附率远高于BSA@ZIF-8颗粒,说明与ZIF-8相比,酶包埋于ZIF-L具有更强的捕获小分子的能力,表明CO₂分子向CA@ZIF-L的扩散速度更快,即CA@ZIF-L的十字花状结构可强化系统的内扩散过程.进一步比较了PIBS和游离多酶体系的催化活性,将CO₂通入每个系统,在反应前20 min,PIBS的pH值下降速度比游离体系快得多,说明PIBS通过在气相和液相间构建更大的界面,缩短了CO₂向CA的扩散距离,从而提高了催化效率,促进了CO₂转化.上述假设也通过扩散动力学的计算得到了验证.为进一步研究PIBS的CO₂矿化能力,本文开展了CaCO₃矿化反应,发现PIBS的CaCO₃产量远高于游离多酶体系,表明构建的PIBS在强化内外扩散方面具有显著优势.最后,评估了PIBS在工业应用中的性能,由CA@ZIF-L和CA@ZIF-8颗粒构建的PIBS显示出较好的可回收性,在第8个循环后,PIBS仍可保持8.9 mg/5 min的CaCO₃产量.综上,PIBS可为CO₂的酶促转化和框架提供一个新方法和新平台.     

基于扩散强化的Pickering界面生物催化系统构建及CO2矿化过程研究

CO₂的有效利用有助于解决环境和生态问题.碳酸酐酶(CA)等酶分子可精准活化CO₂分子以降低反应能垒,为CO₂的高效和高选择性转化提供了一种有前景的途径.然而,酶离开生物体后易失活,且难以重复利用.目前,包埋型固定化酶是常用且有效的提高酶稳定性与回用率的方法之一,但载体的存在会造成反应物CO₂内扩散阻力增加,降低反应活性.此外,CO₂酶促转化是一个气-液-固三相反应过程,反应体系中CO₂的外扩散性能也需要加强.金属有机骨架(MOFs),特别是咪唑酯骨架(ZIFs),常被用作酶固定化的载体.ZIFs的拓扑结构可被设计成不同形貌,进而通过ZIFs的结构工程来加强分子向其中的内扩散.Pickering乳液是指以固体颗粒代替常规表面活性剂而稳定的乳液.当固体颗粒具有催化活性时,催化剂颗粒会扩大液-液-固或气-液-固三相接触面积,从而有效协调反应物在不同相中的扩散时间.如果酶被用作这些颗粒的活性中心,所制备的Pickering乳液也可能具备类似的特性,可加强底物分子向酶的外扩散.本文选择两种具有不同结构的ZIFs(ZIF-L和ZIF-8),原位包埋CA后形成CA@ZIFs颗粒以稳定Pickeirng乳液.ZIF-L和CA@ZIF-L颗粒显示出独特的二维层状堆叠结构.ZIF-8和CA@ZIF-8颗粒呈棱角清晰的十二面体结构.与CA@ZIF-8颗粒相比,CA@ZIF-L颗粒显示出更大的孔径和更宽的孔径分布,这有助于CO₂从CA@ZIF-L颗粒表面扩散至酶活性中心.利用酶活测试来研究内扩散是否通过结构工程得到了加强,发现CA@ZIF-L颗粒的活性比CA@ZIF-8颗粒高22.3%,推测这是由于CA@ZIF-L颗粒特殊的十字花状结构会缩短CO₂从颗粒表面扩散至酶活性中心的距离.同时,十字花状结构可暴露更多的酶活性位点(CA@ZIF-L颗粒的暴露面积是CA@ZIF-8颗粒的~8倍),从而提升了反应物浓度并显示出更高的催化活性.本文还设计了吸附实验来进一步验证上述假设,发现BSA@ZIF-L颗粒对香豆素的吸附率远高于BSA@ZIF-8颗粒,说明与ZIF-8相比,酶包埋于ZIF-L具有更强的捕获小分子的能力,表明CO₂分子向CA@ZIF-L的扩散速度更快,即CA@ZIF-L的十字花状结构可强化系统的内扩散过程.进一步比较了PIBS和游离多酶体系的催化活性,将CO₂通入每个系统,在反应前20 min,PIBS的pH值下降速度比游离体系快得多,说明PIBS通过在气相和液相间构建更大的界面,缩短了CO₂向CA的扩散距离,从而提高了催化效率,促进了CO₂转化.上述假设也通过扩散动力学的计算得到了验证.为进一步研究PIBS的CO₂矿化能力,本文开展了CaCO₃矿化反应,发现PIBS的CaCO₃产量远高于游离多酶体系,表明构建的PIBS在强化内外扩散方面具有显著优势.最后,评估了PIBS在工业应用中的性能,由CA@ZIF-L和CA@ZIF-8颗粒构建的PIBS显示出较好的可回收性,在第8个循环后,PIBS仍可保持8.9 mg/5 min的CaCO₃产量.综上,PIBS可为CO₂的酶促转化和框架提供一个新方法和新平台.     

Engineering hybrid microgels as particulate emulsifiers for reversible Pickering emulsions

Thermo-responsive microgels are unique stabilizers for stimuli-sensitive Pickering emulsions that can be switched between the state of emulsification and demulsification by changing the temperature. However, directly temperature-triggering the phase inversion of microgel-stabilized emulsions remains a great challenge. Here, a hybrid poly(N-isopropylacrylamide)-based microgel has now been successfully fabricated with tunable wettability from hydrophilicity to hydrophobicity in a controlled manner. Engineered microgels are synthesized from an inverse emulsion stabilized with hydrophobic silica nanoparticles, and the swelling-induced feature can make the resultant microgel behave like either hydrophilic or hydrophobic colloids. Remarkably, the phase inversion of such microgel-stabilized Pickering emulsions can be in situ regulated by temperature change. Moreover, the engineered microgels were capable of stabilizing water-in-oil Pickering emulsions and encapsulation of enzymes for interfacial bio-catalysis, as well as rapid cargo release triggered by phase inversion.

Hybrid poly(N-isopropylacrylamide)-based microgels are templated from inverse Pickering emulsions, and the tunable wettability renders as-prepared emulsions with reversible feature.     

Scandium trifluoromethanesulfonate as a recyclable catalyst for efficient methoxymethylation of alcohols

Scandium triflate [Sc(OTf)₃] has been found to be a recyclable catalyst for mild highly efficient methoxymethylation of a variety of alcohols using formaldehyde dimethyl acetal (FDMA).     

Molecular sieves as an efficient and recyclable catalyst for bromolactonization and bromoacetoxylation reactions

Bromolactonization of unsaturated acids and bromoacetoxylation of olefins proceeded smoothly in the presence of molecular sieves and N-bromosuccinimide. The molecular sieves can be recycled and reused, and the halogen carrier can be recovered effectively.     

Cationic nucleolipids as efficient siRNA carriers

We synthesized five novel uridine-based cationic nucleolipids, introducing basic amino acid residues at the 5' position of uridine, through 1,3-dipolar cycloaddition, and hydrophobic alkyl moieties at the 2' and 3' positions, through carbamate linkages. Their lipoplexes delivered siRNAs efficiently to cells, in vitro, without any severe toxicity.     

Clay entrapped nickel nanoparticles as efficient and recyclable catalysts for hydrogenation of olefins

Nickel nanoparticles are prepared in the interlamellar spaces of K10-Montmorillonite clay by chemical reduction at moderate temperatures. These clay entrapped nickel nanoparticles are characterized by UV-vis, powder XRD, EDX and HRTEM studies. The resultant ecofriendly supramolecular assembly with nickel content (2.84 wt %) has good catalytic efficiency in hydrogenation of alkenes and alkynes with hydrazine as a reducing agent in ethanol medium. Advantages of the present study include absence of an external hydrogen source, catalyst reusability and a green medium.     

Gold nanoparticles as carriers for efficient transmucosal insulin delivery

Nanomaterials have gained tremendous importance in biology and medicine because they can be used as carriers for delivering small molecules such as drugs, proteins, and genes. We report herein the binding of the hormone insulin to gold nanoparticles and its application in transmucosal delivery for the therapeutic treatment of diabetes mellitus. Insulin was loaded onto bare gold nanoparticles and aspartic acid-capped gold nanoparticles and delivered in diabetic Wistar rats by both oral and intranasal (transmucosal) routes. Our principle observations are that there is a significant reduction of blood glucose levels (postprandial hyperglycemia) when insulin is delivered using gold nanoparticles as carriers by the transmucosal route in diabetic rats. Furthermore, control of postprandial hyperglycemia by the intranasal delivery protocol is comparable to that achieved using the standard subcutaneous administration used for type I diabetes mellitus, thus showing considerable promise for further development.     

Ionic liquid-coated enzyme for biocatalysis in organic solvent

Ionic liquid-coated enzyme (ILCE) is described as a useful catalyst for biocatalysis in organic solvent. An ionic liquid, [PPMIM]-[PF(6)] (1, [PPMIM] = 1-(3'-phenylpropyl)-3-methylimidazolium), which is solid at room temperature and becomes liquid above 53 degrees C, was synthesized in two steps from N-methylimidazole. The coating of enzyme was done by simply mixing commercially available enzyme with 1 in the liquid phase above 53 degrees C and then allowing the mixture to cool. A representative ILCE, prepared with a lipase from Pseudomonas cepacia, showed markedly enhanced enantioselectivity without losing any significant activity.     

Preparation of enzyme multilayers on colloids for biocatalysis

The construction of enzyme multilayer films on colloidal particles for biocatalysis is described. The enzyme multilayers were assembled on submicrometer‐sized polystyrene spheres via the alternate adsorption of poly(ethyleneimine) and glucose oxidase using a layer‐by‐layer approach. Microelectrophoresis and single particle light scattering measurements revealed regular and step‐wise assembly of the multilayers on the colloids. The high surface area bio‐multilayer coated particles formed were subsequently utilized in enzymatic catalysis.     

高效可循环离子型钯配合物催化羰化Sonogashira反应

炔酮类化合物作为一类具有生物活性的分子,是天然产物全合成中构建杂环类化合物的重要中间体.炔酮类化合物的传统合成方法是通过过渡金属催化金属有机炔烃和酰氯的交叉偶联,但存在酰氯本身稳定性和底物官能团耐受力较差的缺点.近年来,钯催化的羰化Sonogashira反应(末端炔烃和芳基卤化物与CO的偶联反应)成为合成炔酮类化合物更为直接和有效的方法,其中与钯中心原子配位的配体的电子效应和空间效应可显著调控钯配合物的催化性能.但均相钯催化的羰化Sonogashira反应体系存在催化剂流失、分离困难和难以循环使用的问题.我们以2-(1-咪唑基)噻唑为母体分子,合成了具有P,S,N杂合配体特征的配体L1,同时将配体L1通过与MeOTf的季铵化反应得到相应的离子型膦配体L2.在此基础上,利用L1和L2与过渡金属中心的配位作用合成相应的钯配合物1A和2A.由于L1和L2中含有多种不同配位能力的配体(P-配体,S-配体和/或N-配体),故通过N/S杂原子对Pd-中心原子的协同弱配位作用,可以调变相应钯配合物对羰化Sonogashira反应的催化性能.另外,2A中具有强吸电子效应的正电荷的存在,使其结构和催化性能也必然不同于中性配合物1A.实验结果表明,在温和的反应条件(90℃,lh,CO压强1.0 MPa)下,对于碘苯和苯乙炔的羰化Sonogashira偶联反应,1A体现出优于2A的催化性能,TOF值达到840 h-1;但反应温度提高到120℃时,1A的TOF高达3560 h-1,2A的TOF为2960 h-1.与L1的2JP-Se=744 Hz相比,L2的2JP-Se=768 Hz,说明L2中具有吸电子效应的正电荷的存在降低了相应P原子的σ给电子能力(2JP-Se数值越大,相应膦配体的6给电子能力越弱);同时,1A中具有弱配位能力的N配体的缺失削弱了配体对Pd活性中心的稳定作用.在底物普适性研究中发现,4-硝基溴苯在相同反应条件下几乎得不到羰化Sonogashira偶联产物.而将反应体系中的CO换为同样压强下的N2,却可以顺利实现Sonogashira偶联反应.我们推测,在CO氛围下形成的pd0-CO活性物种(与N2氛围下形成的Pd0活性物种相比)具有相对较低的对底物的氧化加成能力.离子型钯配合物2A的优势在于,当将其与室温离子液体[Bmim]PF6(溶剂)结合使用,在2A催化碘苯与苯乙炔的羰化Sonogashira偶联反应过程中,循环使用8次催化性能没有明显下降.     

Silica sulfate as a recyclable and efficient catalyst for Beckmann rearrangement under microwave irradiation

Silica sulfate has been proved to be an efficient and recyclable catalyst for Beckmann rearrangement of a variety of oximes in acetone under microwave irradiation. This protocol has advantages of high conversion, high selectivity, short reaction time, no environmental pollution, and simple work-up procedure.     

Pickering emulsion templated interfacial atom transfer radical polymerization for microencapsulation

This Article describes a new microencapsulation method based on a Pickering emulsion templated interfacial atom transfer radical polymerization (PETI-ATRP). Cationic LUDOX CL nanoparticles were coated electrostatically with an anionic polymeric ATRP initiator, poly(sodium styrene sulfonate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate) (PSB), prepared by radical copolymerization of sodium styrene sulfonate and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). The resulting PSB-modified CL particles were surface active and could be used to stabilize oil-in-water Pickering emulsions. ATRP of water-soluble cross-linking monomers, confined to the oil-water interface by the surface-bound PSB, then led to nanoparticle/polymer composite shells. This method allowed encapsulation of core solvents (xylene, hexadecane, perfluoroheptane) with different solubility parameters. The microcapsule (MC) wall chemistry could accommodate different monomers, demonstrating the versatility of this method. Double-walled MCs were formed by sequentially carrying out PETI-ATRP and in situ polymerization of encapsulated monomers. The double-walled structure was verified by both transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).     

Cellulose-based functional polycarbonates as degradable enzyme carriers

Cellulose-based matrices are expected to be ideal enzyme carriers due to their sustainability and biocompatibility. However, the linkages between immobilized enzymes and celluloses often suffer from low-density and non-biodegradability, leading to inefficient loading of enzymes as well as persistent generation of solid wastes after reuse. In the present study, cellulose-based functional materials with degradable polycarbonates brushes have been successfully synthesized as enzyme carriers via ring-opening polymerization of 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one (MAC) following with ally epoxidation of MAC units. After covalent bonding with laccase, the resulting HPC-PMAC-Laccase could assemble in aqueous solution to form spherical nanoparticles with an enzyme immobilization efficiency of 88%. The immobilized laccase showed more tolerance towards pH and high temperature compared with free laccase. Moreover, the immobilized laccase demonstrated effective removal efficiency of bisphenol A and reached 83% in 3 h. After repeated usage for 8 times, the HPC-PMAC-Laccase still maintained relatively high enzyme activity. Especially, the polycarbonates brushes in the enzyme carriers could be totally hydrolyzed in 12 h to achieve its degradable property.

Graphical abstract

Cellulose-based functional polycarbonates as degradable enzyme carriers.

     

MOF-253 immobilized Pd and Cu as recyclable and efficient green catalysts for Sonogashira reaction

MOF-253·Pd(OAc)₂ and MOF-253·CuI were prepared, characterized, and evaluated firstly as heterogeneous co-catalysts, which showed high catalytic activity in Sonogashira coupling reaction of various substituted (hetero)aryl halides with terminal alkynes at 70–120 °C, and afforded the corresponding products in 45–99% yields with high TON (～2722 for Pd). The best result was achieved with an extremely low Pd (0.036 mol%) and Cu (0.397 mol%) loading. Moreover, the catalysts can be reused at least five times without significantly reducing the activity. Besides, Hg(0) and PVP-poisoning experiments confirmed that the present catalysts were efficient and heterogeneous catalysts in this coupling reaction.     

Titanium aminophosphates as efficient,economical, and recyclable catalysts for the synthesis of xanthenediones

Titanium aminophospates have been used as catalysts in the synthesis of xanthenediones at room temperature. Among the three catalysts tested, titanium n-propyl aminophosphate (TNPAP) was found to be more efficient catalyst for the synthesis of xanthenediones. The solvent-screening studies for this catalytic reaction reveals that MeOH: H₂O was the most suitable solvent system, yielding higher amounts (89%) of products. The TNPAP catalyst was found to be reusable for five successive cycles. The optimized reaction conditions are 1.0?mmol of benzaldehyde, 2.0?mmol of dimedone, methanol/water (5.0?mL) as solvent, rt, and 100?mg of TNPAP. A plausible mechanism for the catalytic reactions has been proposed.