Organorhodium‐Functionalized Periodic Mesoporous Organosilica: High Hydrophobicity Promotes Asymmetric Transfer Hydrogenation in Aqueous Medium

Three organosilica‐bridged periodic mesoporous organosilicas were prepared by the immobilization of a chiral N‐sulfonylated diamine‐based organorhodium complex within their silicate network. Structural analysis and characterization confirmed their well‐defined single‐site active rhodium centers, whilst electron microscopy revealed their highly ordered hexagonal mesostructures. Among these three different organosilica‐bridged periodic mesoporous organosilicas, the ethylene‐bridged periodic mesoporous organosilica catalyst exhibited excellent heterogeneous catalytic activity and high enantioselectivity in the aqueous asymmetric transfer hydrogenation of aromatic ketones. This superior catalytic performance was attributed to its salient hydrophobicity, whilst its comparable enantioselectivity relative to the homogeneous catalyst was derived from the confined nature of the chiral organorhodium catalytic sites. Furthermore, this ethylene‐bridged periodic mesoporous organosilica could be conveniently recovered and reused at least 12 times without the loss of its catalytic activity. This feature makes this catalyst attractive for practical organic synthesis in an environmentally friendly manner. This study offers a general way of optimizing the bridged organosilica moiety in periodic mesoporous organosilicas, thereby enhancing its catalytic activity in heterogeneous catalysis.     

Preparation of a Novel Polymer‐Modified Si Surface for DNA Immobilization

The design of a novel polymer‐modified overlayer composed of PPAPE and GPMS on a silicon wafer for immobilization of DNA molecules is described. After hydroxylation of Si(100) surfaces, GPMS molecules were self‐assembled onto these surfaces. PPAPE molecules were then covalently attached to the epoxy‐terminated surfaces. The incubation time and concentration of PPAPE was found to effect both layer thickness and water CA. The type of organic solvent and the pH were found to change the nature of the PPAPE‐modified surface for DNA immobilization. It is concluded that PPAPE‐modified surfaces show advantages for DNA immobilization by electrostatic interactions between DNA molecules and positively charged free amino groups of the PPAPE‐modified surfaces at the appropriate pH values.

     

Differential Effects of Polymer‐Surface Decoration on Drug Delivery,Cellular Retention,and Action Mechanisms of Functionalized Mesoporous Silica Nanoparticles

Polymer‐surface decoration has been found to be an effective strategy to enhance the biological activities of nanomedicine. Herein, three different types of polymers with a cancer‐targeting ligand Arg‐Gly‐Asp peptide (RGD) have been used to decorate mesoporous silica nanoparticles (MSNs) and the functionalized nanosystems were used as drug carriers of oxaliplatin (OXA). The results showed that polymer‐surface decoration of the MSNs nanosystem by poly(ethylene glycol) (PEG) and polyethyleneimine (PEI) significantly enhanced the anticancer efficacy of OXA, which was much higher than that of chitosan (CTS). This effect was closely related to the enhancement of the cellular uptake and cellular drug retention. Moreover, PEI@MSNs‐OXA possessed excellent advantages in penetrating ability and inhibitory effects on SW480 spheroids that were used to simulate the in vivo tumor environments. Therefore, this study provides useful information for the rational design of a cancer‐targeted MSNs nanosystem with polymer‐surface decoration.     

A General Strategy for Site‐Directed Enzyme Immobilization by Using NiO Nanoparticle Decorated Mesoporous Silica

Mesoporous materials have recently gained much attention owing to their large surface area, narrow pore size distribution, and superior pore structure. These materials have been demonstrated as excellent solid supports for immobilization of a variety of proteins and enzymes for their potential applications as biocatalysts in the chemical and pharmaceutical industries. However, the lack of efficient and reproducible methods for immobilization has limited the activity and recyclability of these biocatalysts. Furthermore, the biocatalysts are usually not robust owing to their rapid denaturation in bulk solvents. To solve these problems, we designed a novel hybrid material system, mesoporous silica immobilized with NiO nanoparticles (SBA‐NiO), wherein enzyme immobilization is directed to specific sites on the pore surface of the material. This yielded the biocatalytic species with higher activity than free enzyme in solution. These biocatalytic species are recyclable with minimal loss of activity after several cycles, demonstrating an advantage over free enzymes.     

Glass Transitions of Ordinary and Heavy Water within Silica‐Gel Nanopores

The dynamic properties of water confined within nanospaces are of interest given that such water plays important roles in geological and biological systems. The enthalpy‐relaxation properties of ordinary and heavy water confined within silica‐gel voids of 1.1, 6, 12, and 52 nm in average diameter were examined by adiabatic calorimetry. Most of the water was found to crystallize within the pores above about 2 nm in diameter but to remain in the liquid state down to 80 K within the pores less than about 1.6 nm in diameter. Only one glass transition was observed, at T_g=119, 124, and 132 K for ordinary water and T_g=125, 130, and 139 K for heavy water, in the 6‐, 12‐, and 52‐nm diameter pores, respectively. On the other hand, two glass transitions were observed at T_g=115 and 160 K for ordinary water and T_g=118 and 165 K for heavy water in the 1.1‐nm pores. Interfacial water molecules on the pore wall, which remain in the noncrystalline state in each case, were interpreted to be responsible for the glass transitions in the region 115–139 K, and internal water molecules, surrounded only by water molecules in the liquid state, are responsible for those at 160 or 165 K in the case of the 1.1‐nm pores. It is suggested that the glass transition of bulk supercooled water takes place potentially at 160 K or above due to the development of an energetically more stable hydrogen‐bonding network of water molecules at low temperatures.     

Three‐Dimensional Ultralarge‐Pore Ia3d Mesoporous Silica with Various Pore Diameters and Their Application in Biomolecule Immobilization

Highly ordered mesoporous three‐dimensional Ia3d silica (KIT‐6) with different pore diameters has been synthesized by using pluronic P123 as surfactant template and n‐butanol as cosolvent at different synthesis temperatures in a highly acidic medium. The materials were characterized by XRD and N₂ adsorption. The synthesis temperature plays a significant role in controlling the pore diameter, surface area, and pore volume of the materials. The material prepared at 150 °C, KIT‐6‐150, has a large pore diameter (11.3 nm) and a high specific pore volume (1.53 cm³ g^?1). We also demonstrate immobilization of lysozyme, which is a stable and hard protein, on KIT‐6 materials with different pore diameters. The amount of lysozyme adsorbed on large‐pore KIT‐6 is extremely large (57.2 μmol g^?1) and is much higher than that observed for mesoporous silicas MCM‐41, SBA‐15, and KIT‐5, mesoporous carbons, and carbon nanocages. The effect of various parameters such as buffer concentration, adsorption temperature, concentration of the lysozyme, and the textural parameter of the adsorbent on the lysozyme adsorption capacity of KIT‐6 was studied. The amount adsorbed mainly depends on solution pH, ionic strength, adsorption temperature, and pore volume and pore diameter of the adsorbent. The mechanism of adsorption on KIT‐6 under different adsorption conditions is discussed. In addition, the structural stability of lysozyme molecules and the KIT‐6 adsorbent before and after adsorption were investigated by XRD, nitrogen adsorption, and FTIR spectroscopy.     

Alkane Oxidation by an Immobilized Nickel Complex Catalyst: Structural and Reactivity Differences Induced by Surface‐Ligand Density on Mesoporous Silica

Immobilized nickel catalysts SBA*‐ L ‐x/Ni ( L =bis(2‐pyridylmethyl)(1H‐1,2,3‐triazol‐4‐ylmethyl)amine) with various ligand densities ( L content (x)=0.5, 1, 2, 4 mol % Si) have been prepared from azidopropyl‐functionalized mesoporous silicas SBA‐N₃‐x. Related homogeneous ligand LtBu and its Ni^II complexes, [Ni( LtBu )(OAc)₂(H₂O)] ( LtBu /Ni) and [Ni( LtBu )₂]BF₄ (2 LtBu /Ni), have been synthesized. The L /Ni ratio (0.9–1.7:1) in SBA*‐ L ‐x/Ni suggests the formation of an inert [Ni L ₂] site on the surface at higher ligand loadings. SBA*‐ L ‐x/Ni has been applied to the catalytic oxidation of cyclohexane with m‐chloroperbenzoic acid (mCPBA). The catalyst with the lowest loading shows high activity in its initial use as the homogeneous LtBu /Ni catalyst, with some metal leaching. As the ligand loading increases, the activity and Ni leaching are suppressed. The importance of site‐density control for the development of immobilized catalysts has been demonstrated.     

Step‐Up Synthesis of Periodic Mesoporous Organosilicas with a Tyrosine Framework and Performance in Horseradish Peroxidase Immobilization

New amino‐acid‐bridged periodic mesoporous organosilicas (PMOs) were constructed by hydrolysis and condensation reactions under acid conditions in the presence of a template. The tyrosine bissilylated organic precursor (TBOS) was first prepared through a multistep reaction by using tyrosine (a natural amino acid) as the starting material. PMOs with the tyrosine framework (Tyr‐PMOs) were constructed by simultaneously using TBOS and tetraethoxysilane as complex silicon sources in the condensation process. All the Tyr‐PMOs materials were characterized by XRD, FTIR spectroscopy, N₂ adsorption–desorption, TEM, SEM, and solid‐state ²⁹Si NMR spectroscopy to confirm the structure. The horseradish peroxidase (HRP) enzyme was first immobilized on these new Tyr‐PMOs materials. Optimal conditions for enzyme adsorption included a temperature of 40 °C, a time of 8 h, and a pH value of 7. Furthermore, the novel Tyr‐PMOs materials could store HRP for approximately 40 days and maintained the enzymatic activity, and the Tyr‐PMOs–10 % HRP with the best immobilization effect could be reused at least eight times.     

铈基介孔金属有机骨架固定化酶的构建及催化性能

金属有机骨架(MOF)材料由于其孔隙率高、比表面积大以及具有发达的内联通孔道结构等优点,可以作为优良的生物分子固定化载体。通过表面活性自组装策略制备了铈基介孔MOF(Ce-MOF-F),表征结果表明,该材料有大的比表面积和呈辐射状的介孔孔道结构。以其为载体、南极假丝酵母脂肪酶B(CALB)为模型酶,通过物理吸附法制备了生物催化剂CALB@Ce-MOF-F,对该固定化酶的酶载量和催化性能进行了研究。在优化条件下,CALB的负载量为162.0mg/g载体,水解活性为899.1U/g蛋白。与游离CALB相比,CALB@Ce-MOF-F表现出对高温、酸碱和有机溶剂等有更强的耐受性;将Ce-MOF-F用于多种酶的固定化,研究其作为载体的普适性,结果表明,介孔Ce-MOF-F对洋葱伯克氏菌脂肪酶(BCL)和漆酶有良好的固定效果,可以作为良好载体,并能对酶起到较好的保护作用。     

Generation of Nanopores Down to 10 nm for Use in Deep‐Nulling Interferometry

Scanning electron microscope images show that it is easy to generate nanopores on polycarbonate membranes with well‐defined pore diameters by ion‐track perforation and subsequent magnetron sputtering with metal. The size reduction of the nanopores during sputtering with gold is a linear function of time. Images of different angles and from the bottom side of the membrane show that the channels are the smallest very close to the surface of the metal layer, have a conelike shape, and reach about half as much into the polymer membranes as the metal‐layer thickness. This topographical pore shape is ideal for use as optically coherent near‐field sources in deep‐nulling microscopy. We present the first results of significantly improved nulling stabilization in the presence (<2 nm optical pathway difference) and the absence (<0.6 nm optical pathway difference) of the nanoapertures in the focal region of a deep‐nulling microscope.     

Cascades in Compartments: En Route to Machine‐Assisted Biotechnology

Biological compartmentalization is a fundamental principle of life that allows cells to metabolize, propagate, or communicate with their environment. Much research is devoted to understanding this basic principle and to harness biomimetic compartments and catalytic cascades as tools for technological processes. This Review summarizes the current state‐of‐the‐art of these developments, with a special emphasis on length scales, mass transport phenomena, and molecular scaffolding approaches, ranging from small cross‐linkers over proteins and nucleic acids to colloids and patterned surfaces. We conclude that the future exploration and exploitation of these complex systems will largely benefit from technical solutions for the integrated, machine‐assisted development and maintenance of a next generation of biotechnological processes. These goals should be achievable by implementing microfluidics, robotics, and added manufacturing techniques supplemented by theoretical simulations as well as computer‐aided process modeling based on big data obtained from multiscale experimental analyses.     

Theoretical trends of diffusion and reaction into tubular nano- and mesoporous structures: general physicochemical and physicomathematical modeling

A general and adaptable physicochemical model is presented to evaluate the mass transport within nanopores of mesoporous particles when the mass transport is coupled to heterogeneous kinetics occurring at active sites located onto the nanopore walls surface. The model framework encompasses almost all situations of practical interest in solutions and may be used for characterizing the kinetic rates and constants controlling the system under different sets of experimental conditions. Furthermore, it allows the delineation of simple effective parameters, which should be most useful for optimizing a given material in view of specific applications. For the sake of clarification the simplified model is presented and its results discussed by specializing it for cases where the reactions involve a simple adsorption of a target species on the nanopore immobilized sites as observed for inorganic sponges used in water decontamination. Yet it may easily be extended further to encompass a wider variety of situations where the sites immobilized onto the nanopore walls perform chemical or biochemical transformations as occur in supported catalysis in liquid solution.     

酶的改造及其催化工程应用

酶作为生物催化剂在食品、饲料、化妆品以及医药等诸多领域逐渐发挥重要作用。但是,酶对外界环境如pH和温度等很敏感,而实际的反应条件和生物体的生理环境差异较大,因此酶在实际应用中不稳定、容易失活,催化效率下降。酶的这一特点大大限制了其工业化应用。目前,定向进化、糖基化以及化学修饰等方法被广泛用于酶分子的改造以提高其稳定性、催化效率以及扩大其底物范围。其中,定向进化通过模拟自然进化机制,在体外改造基因从而获得性能优化的酶突变体,已经成为了酶改造的重要技术。在酶的实际应用过程中,介质工程、固定化以及多酶催化体系构建等技术被广泛用于提高酶的催化效率。其中,多酶催化体系由于其底物通道效应可以显著提高级联酶反应的效率而备受关注。本文首先重点介绍了近年酶应用的现状,然后从酶定向进化、糖基化以及化学修饰的角度总结了酶改造的方法,最后从介质工程、酶固定化以及体外多酶催化体系等方面进一步总结了酶实际应用中的催化工程策略。     

Functionalized Periodic Mesoporous Organosilica: A Highly Enantioselective Catalyst for the Michael Addition of 1,3‐Dicarbonyl Compounds to Nitroalkenes

A functionalized periodic mesoporous organosilica with incorporated chiral bis(cyclohexyldiamine)‐based Ni^II complexes within the silica framework was developed by the co‐condensation of (1R,2R)‐cyclohexyldiamine‐derived silane and ethylene‐bridge silane, followed by the complexation of NiBr₂ in the presence of (1R,2R)‐N,N′‐dibenzylcyclohexyldiamine. Structural characterization by XRD, nitrogen sorption, and TEM disclosed its orderly mesostructure, and FTIR and solid‐state NMR spectroscopy demonstrated the incorporation of well‐defined single‐site bis(cyclohexyldiamine)‐based Ni^II active centers within periodic mesoporous organosilica. As a chiral heterogeneous catalyst, this functionalized periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in the asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes, comparable to those with homogeneous catalysts. In particular, this heterogeneous catalyst could be recovered easily and reused repeatedly up to nine times without obviously affecting its enantioselectivity, thus showing good potential for industrial applications.     

A Free‐Blockage Controlled Release System Based on the Hydrophobic/Hydrophilic Conversion of Mesoporous Silica Nanopores

A pH‐responsive free‐blockage release system was achieved through controlling the hydrophobic/hydrophilic conversion of mesoporous silica nanopores. This system further presented pulsatile release with changing pH values between 4.0 and 7.0 for several cycles. This free‐blockage release system could also release antitumor agents to induce cell death after infecting tumor cells and could have the ability of continuous infection to tumor cells with high drug‐delivery efficiency and few side effects.     

Oleochemical‐Tethered SBA‐15‐Type Silicates with Tunable Nanoscopic Order,Carboxylic Surface,and Hydrophobic Framework: Cellular Toxicity,Hemolysis, and Antibacterial Activity

Novel silicates were prepared by using silylated natural fatty acids (derived from triglyceride renewable oils) as co‐condensing reagents in presence of tetraethyl orthosilicate (TEOS) and the triblock copolymer, pluronic P123, as a structure directing agent. A series of carboxylic acid functionalized SBA‐15‐type mesoporous silicates were obtained with tunable nanoscopic order and reactive functional groups that allow the conjugation of amino probes by peptide coupling. Photophysical studies of the covalently linked aminopyrene substantiated that the internal framework of these materials have pronounced hydrophobicity. Moreover, phase separation that can emanate from the bulkiness of the starting fatty silanes has been ruled out owing to the absence of excimers after aminopyrene grafting. The hemotoxicity, cytotoxicity, and antimicrobial activity of these novel silicates were then evaluated. Without discrimination, the functionalized silicates show a significant decrease of red blood cell hemolysis as compared to bare SBA‐15‐silica material. Within the modified silicate series, germanium‐free mesoporous silicates induce only a slight decrease in cell viability and, more interestingly, they exhibit negligible hemolytic effect. Moreover, increasing their concentration in the medium reduces the concentration of released hemoglobin as a result of Hb adsorption. Promising antimicrobial properties were also observed for these silicates with a slight dependency on whether phenylgermanium fragments were present within the silicate framework.     

Polarity Control at Interfaces: Quantifying Pseudo‐solvent Effects in Nano‐confined Systems

Surface functionalization controls local environments and induces solvent‐like effects at liquid–solid interfaces. We explored structure–property relationships between organic groups bound to pore surfaces of mesoporous silica nanoparticles and Stokes shifts of the adsorbed solvatochromic dye Prodan. Correlating shifts of the dye on the surfaces with its shifts in solvents resulted in a local polarity scale for functionalized pores. The scale was validated by studying the effects of pore polarity on quenching of Nile Red fluorescence and on the vibronic band structure of pyrene. Measurements were done in aqueous suspensions of porous particles, proving that the dielectric properties in the pores are different from the bulk solvent. The precise control of pore polarity was used to enhance the catalytic activity of TEMPO in the aerobic oxidation of furfuryl alcohol in water. An inverse relationship was found between pore polarity and activity of TEMPO in the pores, demonstrating that controlling the local polarity around an active site allows modulating the activity of nanoconfined catalysts.