Template Mechanism Research Articles

Enhancement of selective separation on molecularly imprinted monolith by molecular crowding agent.

In this study, a new molecularly imprinted polymer chiral stationary phase (MIP-CSP) was prepared utilizing molecular crowding agent for improvement the selective separation ability. S-amlodipine (S-AML), methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA), and polymethyl methacrylate (PMMA) were selected as template, functional monomer, cross-linker, and molecular crowding agent, respectively. The composition of formulas for MIP-CSP was optimized, and the permeability and structural feature of resultant MIP-CSP were characterized. The effect of mobile-phase composition, including ionic strength, pH, and organic modifier content, was investigated for achieving the selective separation of rac-amlodipine (rac-AML) on MIP-CSP. The baseline separation of rac-AML was achieved with resolution of 1.58, whereas no selective separation was observed on the imprinted monolith without molecular crowding agent. The perturbation chromatography method was successfully applied to evaluate the recognition mechanism of templates on MIP-CSP. The retention time of S-AML detected in typical analytical conditions was obviously greater than the time of negative peak derived from perturbation, which indicated the retention of template may be due to the imprinted cavities on MIP-CSP. Additionally, the result of Van't Hoff analysis indicated that the chiral separation of rac-AML on MIP-CSP was an entropy-driven process, which supported the molecular imprinting theory. These results reveal that molecular crowding is a potential strategy for preparation of MIP-CSP with excellent selective separation ability. Graphical Abstract Improvement of chiral separation on molecularly imprinted monolith by molecular crowding condition.

Tailoring Pore Structure of Ultralight Electrospun Sponges by Solid Templating

AbstractFreeze‐casted nanofiber based sponges or aerogels exhibit a hierarchical porous structure. Pore formation is only partially understood. Therefore, we studied the underlying solid templating mechanism. We were able to tailor the secondary pore size between 9.5 and 123 μm while retaining the smaller primary pores known from electrospun nanofiber membranes. To understand the effect of microstructure on the sponges’ bulk properties, mass flow through the pores and interaction with the sponges’ internal surface were investigated. By solely altering the sponges’ microstructure we indeed found tunability in permeability by a factor 7 and in filtration efficiency by a factor of 220. Hence, pore architecture of nanofiber based sponges is a key element for their performance. The selected pullulan/PVA polymer blends and aqueous electrospinning conditions are benign and allow the facile adaptation of these ultralight highly porous sponges for a large number of applications.

Controlled-release drug carriers based mesoporous silica spheres with hierarchical hollow/nano structure

Mesoporous silica spheres with hierarchical hollow/nano structure (MSSH-H/N) have been successfully prepared by a template-guided approach, in which cetyltrimethyl ammonium bromide (CTAB) and polystyrene (PS) emulsion was used as the template of mesopores and hollow core, respectively. A consecutive template mechanism and the formation of the hierarchical hollow/nano structure were proposed on basis of the combined characterizations including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction patterns (XRD) and nitrogen sorption analysis, which showed that the hierarchical structure is composed of mesoporous hollow SiO2 spheres and discrete mesoporous SiO2 nanoparticles coating on the shell. Ibuprofen (IBU) was chosen as a drug model in delivery and release experiments, and these MSSH-H/N samples exhibited higher drug loading capacity, desired low initial IBU release rate and typical two-phase drug release behavior compared with conventional single-structure (single-shelled) hollow mesoporous silica spheres due to their unique hierarchical hollow/nano structure.

Effect of in situ generated nascent magnesia and alumina from nitrate precursor on reaction sintered magnesium aluminate spinel

Synthesis of dense magnesium aluminate spinel using a single stage solid oxide reaction is difficult owing to volume expansion associated with spinel formation. In the present work, reaction sintered magnesium aluminate spinel was prepared using commercial grade oxide in a single stage solid oxide reaction reactants. The effect of incorporation of nascent MgO and Al2O3 from nitrate precursor additives was studied. Aluminium nitrate nonahydrate and magnesium hexahydrate were used up to 2wt.% as a source of nascent Al2O3 and MgO respectively. Sintering of the mixed oxide compositions was done in the temperature range 1200–1600°C after compaction under a uniaxial pressure of 150MPa. The dilatometry study was used as a tool to observe the spinel formation reaction. Sintered products were characterised by densification study, flexural strength, thermal shock resistance measurement, phase analysis and microstructural development. The presence of excess MgO and Al2O3 enhanced the spinel formation reaction and densification of spinel at a higher temperature. The template mechanism of spinel formation was observed in the microstructures. The addition of excess alumina and magnesia was found to increase strength values. Also, much higher strength retainment even after 6–8cycles of thermal shock was observed in additive contained batches.

One-step synthesis of hollow UO2 nanospheres via radiolytic reduction of ammonium uranyl tricarbonate

Black precipitates were successfully obtained by radiolytic reduction of ammonium uranyl tricarbonate in the aqueous solution of HCOONH4 by one step. TEM, SAED, EDS, and XRD analysis indicated that the precipitates consist of hollow UO2 nanospheres (ϕ: 30–50nm, wall thickness: 8–15nm, and cavity diameter: 10–20nm). The effect of HCOONH4 concentration, irradiation time and dose rate on the morphology, and size of nanospheres was investigated. Then, a gas-bubble template mechanism was proposed.

Quaternized Chitosan-Capped Mesoporous Silica Nanoparticles as Nanocarriers for Controlled Pesticide Release.

Nanotechnology-based pesticide formulations would ensure effective utilization of agricultural inputs. In the present work, mesoporous silica nanoparticles (MSNs) with particle diameters of ~110 nm and pore sizes of ~3.7 nm were synthesized via a liquid crystal templating mechanism. A water-soluble chitosan (CS) derivative (N-(2-hydroxyl)propyl-3-trimethyl ammonium CS chloride, HTCC) was successfully capped on the surface of pyraclostrobin-loaded MSNs. The physicochemical and structural analyses showed that the electrostatic interactions and hydrogen bonding were the major forces responsible for the formation of HTCC-capped MSNs. HTCC coating greatly improved the loading efficiency (LC) (to 40.3%) compared to using bare MSNs as a single encapsulant (26.7%). The microstructure of the nanoparticles was revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The pyraclostrobin-loaded nanoparticles showed an initial burst and subsequent sustained release behavior. HTCC-capped MSNs released faster than bare MSNs in the initial stage. Pyraclostrobin-loaded HTCC-capped MSNs with half doses of pyraclostrobin technical demonstrated almost the same fungicidal activity against Phomopsis asparagi (Sacc.), which obviously reduced the applied pesticide and enhanced the utilization efficiency. Therefore, HTCC-decorated MSNs demonstrated great potential as nanocarriers in agrochemical applications.

Shape-controlled synthesis of star-shaped Cu2-xSySe1-y materials with highly enhanced chemiluminescence

In this work, six-pointed star-shaped Cu2-xSySe1-y materials were synthesized in a facile one-pot template method at relatively low temperature (85 °C). The edges, corners, length and surfaces of the star-shaped Cu2-xSySe1-y alloyed materials can be effectively tuned by adjusting the reaction temperature, and the concentrations of NaOH and hydrazine hydrate. The growth and formation mechanisms of six-pointed star-shaped Cu2O templates were investigated in detail by analysing time-dependent SEM images, and a possible growth model was proposed to explain the formation mechanism of the star-shaped Cu2O templates. Moreover, the star-shaped Cu2-xSySe1-y materials exhibited highly catalytic activity, which enhanced the chemiluminescence (CL) in a luminol–H2O2 system by approximately 100-fold. This study may provide an avenue into a new field of application for innovative Cu2-xSySe1-y materials in catalysis and environmental monitoring.

Fabrication and characterisation of GaAs nanopillars using nanosphere lithography and metal assisted chemical etching

We present a low-cost fabrication procedure for the production of nanoscale periodic GaAs nanopillar arrays, using the nanosphere lithography technique as a templating mechanism and the electrochemical metal assisted etch process (MacEtch).

Using Service Clustering and Self-Adaptive MOPSO-CD for QoS-Aware Cloud Service Selection

A promising way to effectively manage the composition of services in a heterogeneous and dynamic environment is to make workflow management able to self-adapt at runtime to react to changes in its environment by autonomously reconfiguring itself. Most of the proposed methodologies address this issue as a QoS-aware service selection problem in which a web service broker can dynamically select the “right” service that takes part in the composition, and adaptively change the bound service when the delivered QoS has changed.In this paper, we propose a self-organizing framework that uses a service clustering based discovery approach to effectively and efficiently support the selection of services in which runtime changes in the QoS of the services are taken into account. Two bio-inspired algorithms are designed to support a QoS-aware dynamic service selection mechanism. An ant-based clustering algorithm enhanced with a template mechanism that guides the artificial ants to move data items to construct and maintain a specific topology is adopted as a method for efficient service discovery. As a consequence, services can dynamically be discovered in a shorter time and with lower network traffic. To select the actual concrete services that best meet the user QoS requirements a Self-Adaptive Multi-Objective Particle Swarm Optimization Algorithm using crowding distance technique (MOPSO-CD) is executed using the topological map generated by the ant algorithm. In the end, simulation results show the effectiveness of the method proposed.

Hierarchical Meso‐Mesoporous and Macro‐Mesoporous Silica Templated by Mixtures of Polyoxyethylene ­Fluoroalkyl Ether and Triblock Copolymer

AbstractWe report here the synthesis of different kinds of hierarchical porous silica materials by using mixtures of an amphiphilic block copolymer (Pluronic P123) and a nonionic fluorinated surfactant. In particular, we have taken advantage of the difference in polarities between the two compounds to design dual‐mesoporous materials through the cooperative templating mechanism (CTM). We have undertaken a complete study of this system by varying the composition of the mixed micelles and the synthesis conditions. We have shown that both the dual‐mesoporosity and the mesopore ordering are favored when materials are prepared with fluorine‐rich and P123‐rich micelles. However, when the P123‐rich micelles predominate, the mesostructure is less organized and the dual‐porosity depends on the P123 content. In addition, concentrated emulsions were formed by incorporating perfluorodecalin (PFD) in the surfactant mixture, and hierarchical macro‐mesoporous materials were prepared by combining the CTM and the emulsion templating mechanism.

One-step hydrothermal synthesis of (CuIn)0.2Zn1.6S2 hollow sub-microspheres for efficient visible-light-driven photocatalytic hydrogen generation

(CuIn)0.2Zn1.6S2 (CIZS) hollow sub-microspheres were prepared by a simple one-step hydrothermal method using thioacetamide (TAA) as a sulfur source. It was demonstrated that the amount of TAA played a key role on the morphology of CIZS samples. Low amount of TAA led to the formation of solid sub-microspheres. Nevertheless, high amount of TAA gave rise to the growth of hollow sub-microspheres, which could be elucidated by a bubble template mechanism. The morphology transition, as well as the reduced crystallite size, led to the increased specific surface area with the increased amount of TAA. Meanwhile, the defect states in CIZS samples were gradually decreased, when the amount of TAA was increased. The improved specific surface area and decreased defects of CIZS products contributed to higher efficiencies of charge separation and surface chemical reaction. The photocatalytic performance of CIZS photocatalysts was closely influenced by the amount of TAA. CIZS samples prepared with 5 g of TAA showed the highest hydrogen production rate, with the apparent quantum yield of 11.5% at 420 nm. It was summarized that the superior photocatalytic activity should be attributed to the larger specific surface area, decreased defects and relatively clean surface. This work not only provided a simple route to prepare hollow-structured photocatalysts, but also demonstrated the importance of sulfur source on photocatalytic properties of metal sulfide photocatalysts.

Formation of CdS in Supramolecular Dendrimer–Dye Assemblies: Electrostatic and Electrostatic-Coordination Templating

A novel concept for the formation of organic–inorganic hybrid nanostructures based on a tunable supramolecular templating mechanism involving several types of noncovalent interactions is presented. Different organic–inorganic hybrid structures with narrow size distributions composed of a cationic dendrimer, an oppositely charged divalent diazo dye, and CdS can be created: First, larger supramolecular structures consisting of several 100 to 1000 dendrimers is built based on ionic and π–π interaction. Second, with this self-assembled template, the hybrid nanostructure forms based on electrostatics and coordination interaction. The influence on shape and internal structure of the supramolecular hybrid architectures was investigated. A size control of the assemblies is possible in a range of 60–420 nm. The prospect to direct self-assembly and templating through the controlled combination of different noncovalent interactions potentially allows to create tailor-made systems for various applications.

Thin single-crystalline Bi2(Te1−xSex)3 ternary nanosheets synthesized by a solvothermal technique

Bi2(Te1−xSex)3 ternary nanosheets have been successfully synthesized through a facile solvothermal technique using diethylenetriamine as solvent, where x can vary from 0 to 1. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) indicate that the as-synthesized Bi2(Te1−xSex)3 samples are nanosheets with rhombohedral structure, and the thickness of the nanosheets can be as thin as several nanometers. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) reveal that the nanosheets are single crystalline with a rhombohedral structure. Energy disperse spectroscopy (EDS) and XRD analysis by Vegard׳s law confirm that the ternary Bi2(Te1−xSex)3 nanosheets have been obtained here. The growth of the nanosheets is discussed based on an amine-based molecular template mechanism that has been employed to synthesize some other metal chalcogenides.

Nano-emulsions as imprints for the design of hierarchical porous silica through a dual templating mechanism

Due to their properties nano-emulsions are excellent candidates to be used as imprints to create a macropore network. In this study nano-emulsions have been formulated from the Remcopal 4/decane/water system and mineralized by a dual templating mechanism in the presence of Pluronic P123 micelles. After removing the organic matter, macro-mesostructured silica materials are obtained. Small angle X-ray scattering patterns of the materials and transmission electronic microscopy experiments show that the mesoporous network (mesopore size around 9 nm) adopts a hexagonal arrangement.Macropores have been characterized by transmission electron microscopy, scanning electron microscopy and mercury porosity. As determined by mercury porosimetry, the size of the macropores imprinted by the nano-emulsions is of about 240 nm. A second macroporosity is also detected in the micrometer range and could be related to the further fusion of nano-emulsions during the hydrothermal process and to interparticular porosity. To better address the formation mechanism of the hierarchical structure of the silica material, the stability of nano-emulsions in the presence of methanol, P123 and both of them has been investigated.We have also evidenced the dual role played by the Pluronic micelles. They do not only induce the mesopore network through the cooperative templating mechanism, but their presence also avoids the total destructuration of the nano-emulsion by methanol, released during the hydrolysis of the silica precursor.

Ionic liquid assisted hydrothermal synthesis of hollow core/shell MoS2 microspheres

Hollow core/shell MoS2 microspheres were successfully hydrothermally synthesized by adding an ionic liquid 1-ethyl-3-methylimidazolium bromide ([EMIM] Br) as additive. The obtained MoS2 products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). MoS2 microspheres have uniform morphology with the mean diameter of 2.5μm and the shell thickness of about 0.8μm. The surfaces of the hollow core/shell MoS2 microspheres are constructed by MoS2 nanosheets. Ionic liquids play an important role in the formation of hollow core/shell MoS2 microspheres. MoS2 microspheres with double-shell structure can be acquired by increasing the dosage of ionic liquid. A soft template mechanism of the hollow core/shell structure is proposed.

Origin of life. Primordial genetics: Information transfer in a pre-RNA world based on self-replicating beta-sheet amyloid conformers

The question of the origin of life on Earth can largely be reduced to the question of what was the first molecular replicator system that was able to replicate and evolve under the presumably very harsh conditions on the early Earth. It is unlikely that a functional RNA could have existed under such conditions and it is generally assumed that some other kind of information system preceded the RNA world. Here, I present an informational molecular system that is stable, self-replicative, environmentally responsive, and evolvable under conditions characterized by high temperatures, ultraviolet and cosmic radiation. This postulated pregenetic system is based on the amyloid fold, a functionally unique polypeptide fold characterized by a cross beta-sheet structure in which the beta strands are arranged perpendicular to the fiber axis. Beside an extraordinary structural robustness, the amyloid fold possesses a unique ability to transmit information by a three-dimensional templating mechanism. In amyloidogenesis short peptide monomers are added one by one to the growing end of the fiber. From the same monomeric subunits several structural variants of amyloid may be formed. Then, in a self-replicative mode, a specific amyloid conformer can act as a template and confer its spatially encoded information to daughter molecular entities in a repetitive way. In this process, the specific conformational information, the spatially changed organization, is transmitted; the coding element is the steric zipper structure, and recognition occurs by amino acid side chain complementarity. The amyloid information system fulfills several basic requirements of a primordial evolvable replicator system: (i) it is stable under the presumed primitive Earth conditions, (ii) the monomeric building blocks of the informational polymer can be formed from available prebiotic compounds, (iii) the system is self-assembling and self-replicative and (iv) it is adaptive to changes in the environment and evolvable.

Synthesis of CoFe2O4/MCM-41/TiO2 composite microspheres and its performance in degradation of phenol

The core–shell structural magnetically separable catalyst CoFe2O4/MCM-41/TiO2 composite microspheres were synthesized, and the catalytic properties were systematically studied. Specifically, the preformed monodisperse magnetic CoFe2O4 particles were prepared by solvothermal method, the intermediate MCM-41 layer was prepared by the method of liquid crystal templating mechanism and subsequent TiO2 layer was synthesized by the method of esters precipitation. In this approach, the CoFe2O4/MCM-41/TiO2 composite microspheres synthesized under optimum condition were spherical particles, about 660nm in diameter. It consisted of mesoporous structure with a surface area of 682.83m2g−1, an average pore size of 2.93nm and excellent magnetic properties of 7.43emug−1. The photocatalytic activities were evaluated under simulated sunlight irradiation using the photocatalytic degradation of phenol as a model reaction. The prepared CoFe2O4/MCM-41/TiO2 composite microspheres showed higher photodegradation ability for phenol than Degussa P25. The degradation of phenol achieved up to 85% after 120min under simulated sunlight irradiation, and the composite microspheres could be recycled and reused. The synthesized magnetic hybrid composite microspheres displayed high photocatalytic efficiency and potential applications for cleaning polluted water with the help of magnetic separation.

Yeast prions: structure, biology, and prion-handling systems.

A prion is an infectious protein horizontally transmitting a disease or trait without a required nucleic acid. Yeast and fungal prions are nonchromosomal genes composed of protein, generally an altered form of a protein that catalyzes the same alteration of the protein. Yeast prions are thus transmitted both vertically (as genes composed of protein) and horizontally (as infectious proteins, or prions). Formation of amyloids (linear ordered β-sheet-rich protein aggregates with β-strands perpendicular to the long axis of the filament) underlies most yeast and fungal prions, and a single prion protein can have any of several distinct self-propagating amyloid forms with different biological properties (prion variants). Here we review the mechanism of faithful templating of protein conformation, the biological roles of these prions, and their interactions with cellular chaperones, the Btn2 and Cur1 aggregate-handling systems, and other cellular factors governing prion generation and propagation. Human amyloidoses include the PrP-based prion conditions and many other, more common amyloid-based diseases, several of which show prion-like features. Yeast prions increasingly are serving as models for the understanding and treatment of many mammalian amyloidoses. Patients with different clinical pictures of the same amyloidosis may be the equivalent of yeasts with different prion variants.

3-D Network Pore Structures in Copper Foams by Electrodeposition and Hydrogen Bubble Templating Mechanism

Copper foams with various pore structures have been prepared using hydrogen bubbles as templates by electrodeposition method. By adjusting deposition time and incorporating different additives, the pore structures of copper deposit layers were effectively tuned as the results of controlled nucleation, growth, coalescence and detachment of hydrogen bubbles on the deposition interfaces. According to the analysis of experimental results, a tentative templating mechanism of hydrogen bubbles has been proposed, in which the well-grown hydrogen bubbles on the deposition interface are believed to contribute mostly to the formation of pore structures in the copper deposit layers, while the bubbles enlarged through interconnection and coalescence make no templating contributions due to their easy detachment from the interface. A larger average size of templating hydrogen bubbles at the upper layer than at the lower layer should arise from the quasi close-packing of growing hydrogen bubbles with their nucleation sites confined to the areas unoccupied by the pre-existing bubbles. In terms of this templating mechanism of hydrogen bubbles, the influences of relative concentrations of Cu2+ and H+ in the electrolyte solutions, deposition current density, chemical species and concentrations of additives on the evolution of pore-structures in the electrodeposited copper foams may be well explained and understood.

Interaction between cationic monomer and sodium dodecyl sulfate in concentrated aqueous solutions: EPR spectroscopy and rotational viscometry

The interaction of a cationic monomer, trimethyl[methacryloxyethyl]ammonium methyl sulfate, with sodium dodecyl sulfate (SDS) has been studied in relatively concentrated solutions containing SDS (70–500 mM) and the monomer (from 7 mM to 2.5 M). The high concentrations of the components do not prevent the monomer from bonding to oppositely charged SDSs, which confirms the possibility in principle to polymerize ionic monomers through a template mechanism using micelles of oppositely charged surfactants as templates. The range of component ratios 0.5 ≤ [monomer]/[SDS] ≤ 2 is most promising for realization of the template mechanism of polymerization. The effect of SDS on the macroscopic and microscopic properties of the system significantly and to a maximum extent decreases upon a further rise in the relative concentration of the monomer.