Charged Template Research Articles

Tuning the atomic ordering of AFI framework with templates charge

In this work, AlPO4-5 (AFI) zeotype materials were synthesized using the microwave approach in the presence of two organic templates i.e. tripropylamine (R) and tetrapropylammonium (R+). The long- and short-range crystalline order of the samples were investigated by considering the effect of the template's charge on the atomic-level ordering of the AFI framework. Using advanced NMR spectroscopy, we shed the light on the importance of templates' role on the organization of the inorganic framework of aluminophosphates. The spectroscopic data clearly show a wider distribution of Al and P environments in the materials synthesized with the charged template (R+) due to the need of hydroxyl groups charge compensators that induce some bridges distortions. When a charged molecule (R+) was used, aluminum appears to be responsible for the charge compensation mechanism via the association of OH groups, impacting the environment of phosphorus as well. The hydroxyl groups needed for charge compensation in samples synthesized with R+ persist after calcination. Consequently, the hydrophilicity of the sample synthesized with R+ features approximatively two times higher values compared to the one synthesized with R.

Chemical Feedback in Templated Reaction-Assembly of Polyelectrolyte Complex Micelles: A Molecular Simulation Study of the Kinetics and Clustering.

The chemical feedback between building blocks in templated polymerization of diblock copolymers and their consecutive micellization was studied for the first time by means of coarse-grained molecular dynamics simulations. Using a stochastic polymerization model, we were able to reproduce the experimental findings on the effect of chemical feedback on the polymerization rates at low and high solution concentrations. The size and shape of micelles were computed using a newly developed software in Python conjugated with graph theory. In full agreement with the experiments, our simulations revealed that micelles formed by the templated micellization are more spherical and have a lower radius of gyration than those formed by the traditional two-step micellization method. The advantage of molecular simulation over the traditional kinetic models is that with the simulation, one studies in detail the heterogeneous polymerization in the presence of the oppositely charged template while also accounting for the incompatibility between reacted species, which significantly influences the reaction process.

Hierarchical Porous Carbon Nanofibers with Tunable Geometries and Porous Structures Fabricated by a Scalable Electrospinning Technique.

Porous carbon nanofibers (PCNFs) have rich channels for transporting ions, molecules, and nanoparticles, but the control over their porous structures is a challenge. Here, we report a scalable electrospinning technique by using poly(tetrafluoroethylene) as a pore template, boric acid as a cross-linking agent, and polyvinyl alcohol and polyurethane as dual carbon precursors to fabricate flexible PCNFs with tunable geometries and macro/meso/microporous structures. In the water solvent, the negatively charged template cross-links with the positively charged carbon precursors to form a stable sol for electrospinning. By varying the mass ratios of these precursors, the electrospun hybrid nanofibers are directly transformed into B-F-N-O doped PCNFs with tunable macro-, meso-, and micropores after carbonization. The porosity of an individual PCNF is as high as ∼85%, and the pore volume can be tuned from 0.23 to 0.58 cm3·g-1. When constructing high-sulfur-content (86 wt %) electrodes with the freestanding PCNF films, the porous structures with rich electroactive sites provide rapid pathways for poly-anions and have strong chemisorption of poly-sulfides, leading to a great electrochemical performance. The reported strategy offers a new perspective for synthesizing hierarchical PCNFs with appealing applications.

Rapid Formation of Self‐Supporting Polydimethylsiloxane Sheets with Periodic Clusters of Embedded Nickel Nanoparticles

AbstractThe direct and rapid formation of a precise pattern of metallic nanoparticles (NPs) supported and/or embedded in a flexible polymeric substrate is not easy to achive. However, the development of simpler and more reliable procedures is still highly desirable. This paper presents an innovative technique, simple, cheap, and robust, for producing a self‐supported sheet of polydimethylsiloxane (PDMS) embedding periodic arrays of clusters of nickel nanoparticles (NiNPs). The method uses the pyroelectric effect in a periodically poled lithium niobate (PPLN) crystal for producing a surface charge template able to address the patterning of the NPs by applying a simple thermal stimulation. The key advantages are rapidity, single‐step, and electrode‐free operation. The reliability of the technique is demonstrated for different geometries that are called here “dots” and “grid” and for three different periods 50, 200, and 400 µm. The resulting sheets are attractive for both their flexibility and magnetic properties that can be used for detection, entrapment, and/or patterning of micro‐ and nanoparticles in various fields such as microfluidics and biomedicine.

Self-Assembly of Viral Capsid Proteins Driven by Compressible Nanobubbles.

Colloidal nanobubbles occur in gas-saturated aqueous solutions following high power water electrolysis. Here the influence of nanobubble solutions on the self-assembly properties of viral capsid proteins (CP) was investigated. Interestingly, we found that gas solutions were able to trigger the self-assembly of CP of cowpea chlorotic mottle virus (CCMV) in the absence of the viral genome, most likely by acting as a negatively charged template. The process was demonstrated by three distinct techniques, namely, dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Furthermore, nanobubble-induced self-assembly of viral CP was found to depend on protein concentration. Low CP concentrations led to assembly of 18 nm virus-like particles (VLPs), comparable to T = 1 (Casper and Klug triangulation number) virus capsids, whereas high CP concentrations led to 28 nm VLPs (similar to T = 3 capsids). This paves a new route for self-assembly of VLPs.

Expanding the Synthesis Field of High-Silica Zeolites.

Aluminosilicate zeolites are synthesized under hydrothermal conditions in a basic/alkaline medium in the pH range between 9 and 14. The synthesis of MFI-type zeolite in an acidic medium is presented. The critical parameter determining the zeolite formation in an acidic medium was found to be the isoelectric point (IEP) of gel particles. MFI-type zeolite was synthesized above the isoelectric point of the employed silica source, where the silica species exhibit a negative charge and the paradigm of zeolite formation based on the electrostatic interaction with the positively charged template is retained. No zeolite formation is observed below the isoelectric point of silica. The impact of aluminum on the zeolite formation is also studied. The results of this study will serve to extend the synthesis field of high silica zeolites to the acidic medium and thus open new opportunities to control the zeolite properties.

Expanding the Synthesis Field of High‐Silica Zeolites

AbstractAluminosilicate zeolites are synthesized under hydrothermal conditions in a basic/alkaline medium in the pH range between 9 and 14. The synthesis of MFI‐type zeolite in an acidic medium is presented. The critical parameter determining the zeolite formation in an acidic medium was found to be the isoelectric point (IEP) of gel particles. MFI‐type zeolite was synthesized above the isoelectric point of the employed silica source, where the silica species exhibit a negative charge and the paradigm of zeolite formation based on the electrostatic interaction with the positively charged template is retained. No zeolite formation is observed below the isoelectric point of silica. The impact of aluminum on the zeolite formation is also studied. The results of this study will serve to extend the synthesis field of high silica zeolites to the acidic medium and thus open new opportunities to control the zeolite properties.

Giant “molecular capacitor” arrays - portable sensors to determine ionizable compounds

Portable sensors have been developed for the determination of ionizable compounds based on molecularly imprinted polymers (MIPs). These polymers are charged due to the utilization of ionizable monomers such as diallylamine and sodium vinyl sulfonate (SVS). Mediated by the charged templates, imprinted sites with specific shapes and charge distributions were build in the MIPs. At the time of molecular recognition, the imprinted sites were reoccupied by the templates, making the polymer charges neutralized. This procedure led to significant permittivity changing and contributed much to device sensitivity. The capacitive signal drop of 1 million molecules (~1.66 × 10−18 mol) adds up to >10−12 f, which is detectable to a current portable multimeter. At the same time interferent components were expediently washed off because of poor affinities to an MIP. Consequently a handheld LCR (Inductance Capacitance Resistance) meter was used to successfully monitor the molecular recognition signals. High sensitive and selective analysis has been achieved for three exemplified compounds, i.e. aspirin, propranolol hydrochloride, and glyphosate, with linear ranges as 5.50 × 10−13–10−9 mol·L−1, 3.39 × 10−13–10−6 mol·L−1 and 5.89 × 10−16–10−6 mol·L−1. Meanwhile the related detection limits are 1.68 × 10−13 mol·L−1, 3.02 × 10−13 mol·L−1 and 1.94 × 10−16 mol·L−1. The more charges the template possesses, the more sensitive the sensor is.

Mechanistic insights into a non-heme 2-oxoglutarate-dependent ethylene-forming enzyme: selectivity of ethylene-formation versusl-Arg hydroxylation.

The ethylene-forming enzyme (EFE) is a unique member of the Fe(ii)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenases. It converts 2OG into ethylene plus three CO2 molecules (ethylene-forming reaction) and also catalyzes the C5 hydroxylation of l-arginine coupled to the oxidative decarboxylation of 2OG (l-Arg hydroxylation reaction). To uncover the mechanisms of the dual transformations by EFE, quantum mechanical/molecular mechanical (QM/MM) calculations were carried out. Based on the results, a branched mechanism was proposed. An FeII-peroxysuccinate complex with a dissociated CO2 generated through the nucleophilic attack of the superoxo moiety of the Fe-O2 species on the keto carbon of 2OG is the key common intermediate in both reactions. A competition between the subsequent CO2 insertion (a key step in the ethylene-forming pathway) and the O-O bond cleavage (leading to the formation of succinate) governs the product selectivity. The calculated reaction barriers suggested that the CO2 insertion is favored over the O-O bond cleavage. This is consistent with the product preference observed in experiments. By comparison with the results of AsqJ (an Fe/2OG oxygenase that leads to substrate oxidation exclusively), the protein environment was found to be crucial for the selectivity. Further calculations demonstrated that the local electric field of the protein environment in EFE promotes ethylene formation by acting as a charge template, exemplifying the importance of the electrostatic interaction in enzyme catalysis. These findings offer mechanistic insights into the EFE catalysis and provide important clues for better understanding the unique ethylene-forming capability of EFE compared with other Fe/2OG oxygenases.

Reversal of metachromasy revisited; displacement of Toluidine-blue from alginate by surfactants

The color stability of dyes is crucial in commercial dyeing, whereas their use in scientific research often depends on color changes due to metachromasy. This is the result self-organization of dye molecules into a stacked organization onto a charged template, such as an oppositely charged polyelectrolyte. Literature shows that ‘reversal of metachromasy’, caused by the dye’s displacement from its stacked state, can be induced by a.o. surfactants. This is suggested to be a generic effect. We investigated the reversal of metachromasy using the alginate-ortho toluidine blue (TBO) metachromatic complex in a low ionic strength buffered system (phosphate 1mM, pH=7). Under these conditions alginate has an ‘apparent’ pKa of 4.6 and the alginate-TBO complex shows to be 1:1 charge stoichiometric. Displacement by the cationic surfactant TEGO®trant A100 (1,3-Didecyl-2-methylimidazolium chloride, TEGO) is found to be charge stoichiometric, its pathway depending on initial complex composition. TEGO initially binds to free binding sites on alginate prior to its competition with TBO for which it arranges into similar stacks allowing cooperative binding.Further, the effect of offering TBO alternative binding sites is studied by adding negatively charged surfactants. Binding of TBO to anionic surfactants, was found to depend on the ease of these to form premicellar structures which offer an alternative binding motive for TBO. Premicellar aggregation depends on the surfactant’s structure; i.e. size of the ethylene oxide (EO) block, within a homologous series of sodium lauryl ether sulfates (SLES) and from our experiments can be ranked as (EO)2>(EO)4>(EO)0>(EO)12>(EO)30. Reversal of metachromasy by surfactants, although proceeding via a similar mechanism, is not generic but depends on surfactant structure and its chemical composition.

Layer-by-Layer Growth of Charged Polymers and Silicon Nanoparticles

We investigate the use of semiconductor nanoparticles in a polymer-semiconductor layer-by-layer growth procedure. We use polyelectrolytes for charged polymers and H-terminated Si nanoparticles for the semiconductor. Microclusters of calcium carbonates are used as charged templates. Our results show that the nanoparticles adsorb on positively as well as on negatively charged polymer layers. But, particle’s adsorption is more efficient on negatively charged polymers. The results are analyzed in terms of electrostatic polarization forces. Dissolution of the calcium carbonate template into calcium ions and carbon dioxide while retaining the silicon nanoparticles creates luminescent polymer-silicon capsules. The permeability versus robustness of polymer multilayers is investigated. Optically functionalized capsules may find applications in optical marking/tracking for biomedical applications as well as for underground water and oil exploration.

Effects of Lithium Niobate Polarization on Cell Adhesion and Morphology.

Understanding how the interfacial effects influence cell adhesion and morphology is of fundamental interest for controlling function, growth, and movement of cells in vitro and in vivo. In particular, the influence of surface charges is well-known but still controversial, especially when new functional materials and methods are introduced. Here, the influence of the spontaneous polarization of ferroelectric lithium niobate (LN) on the adhesion properties of fibroblast cells is investigated. The spontaneous polarization of LN has one of the largest known magnitudes at room temperature (∼78 μC/cm(2)), and its orientation can be patterned easily by an external voltage, this motivating highly the investigation of its interaction with cells. Immunofluorescence and migration assays show strong evidence that the surface polarity regulates the adhesion functions, with enhanced spreading of the cytoskeleton on the negative face. The results suggest the potential of LN as a platform for investigating the role of charges on cellular processes, thus favoring new strategies in fabricating those biocompatible constructs used for tissue engineering. In fact, the orientation of the high-magnitude polarization can be patterned easily and, in combination with piezoelectric, pyroelectric, and photorefractive properties, may open the route to more sophisticated charge templates for modulating the cell response.

Control of colloidal CaCO3 suspension by using biodegradable polymers during fabrication

Fabrication of homogenous CaCO3 particles is a significant step in assembling polyelectrolyte capsules. It is crucial to control the dimensions, the shape and the charge of the calcium carbonate particles in order to have homogenously separated and charged templates as final result. For this reason, previously. hey have been deeply investigated.Recently, crystallization of CaCO3 was done by adding poly (sodium 4-styrenesulfonate) (PSS) as negatively charged polymer and poly (allylamine hydrochloride) (PAH) as positively charged polymer and the results were surprising. The homogenous particles were separated and they carried the same charge of the used polymer.The aim of this work was to investigate the synthesis process of CaCO3 particles in different experimental conditions: calcium carbonate was produced in presence and in absence of water and with addition of appropriate polymers. In particular, chitosan (CHI) and poly acrylic acid (PAA) were chosen as biodegradable polymers whereas PSS and PAH were chosen as non-biodegradable polymers. Shape and diameter of particles were investigated by using transmission and scanning electron microscopy, elemental composition was inferred by energy dispersive X-ray analyses whereas their charges were explored by using zeta potential.

One-step fabrication of free-standing flexible membranes reinforced with self-assembled arrays of carbon nanotubes

Here, we report on a single step approach for fabricating free-standing polymer membranes reinforced with arrayed self-assembled carbon nanotubes (CNTs). The CNTs are self-assembled spontaneously by electrode-free DC dielectrophoresis based on surface charge templates. The electrical charge template is generated through the pyroelectric effect onto periodically poled lithium niobate ferroelectric crystals. A thermal stimulus enables simultaneously the self-assembly of the CNTs and the cross-linking of the host polymer. Examples of thin polydimethylsiloxane membranes reinforced with CNT patterns are shown.

Charge templates in aromatic plus ionic liquid systems revisited: NMR experiments and molecular dynamics simulations.

The mutual solubilities of [C2C1im][Ntf2] ionic liquid and aromatic molecules (benzene and its fluorinated derivatives) can be correlated to the dipolar and quadrupolar moments of the latter molecules. This fact can be interpreted as a consequence of the charge-induced structuration of the IL ions around the aromatic molecules. In this paper we demonstrate that we can follow the above-mentioned structural changes in the mixtures using different NMR-based techniques, namely 1D (1)H and (13)C NMR and 2D (1)H-(1)H NOESY NMR spectroscopy. These have been complemented by more detailed structural analyses of the different (IL plus aromatic solute) mixtures using MD simulations. Such systematic studies included eight systems, namely mixtures of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid with benzene, fluorobenzene, 1,2-difluorobenzene, 1,4-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,4,5-tetrafluorobenzene, penta-fluorobenzene, and hexafluorobenzene.

ABAB Homoleptic Bis(phthalocyaninato)lanthanide(III) Complexes: Original Octupolar Design Leading to Giant Quadratic Hyperpolarizability

The octupolar cube, a Td symmetry cube presenting alternating charges at its corners, is the generic point charge template of any octupolar molecule. So far, transposition into real molecular structures has yet to be achieved. We report here a first step toward the elaboration of fully cubic octupolar architectures. A series of octupolar bis(2,3,16,17-tetra(hexylthio)phthalocyaninato)lanthanide double-decker complexes [Pc2Ln], Ln = Nd (1), Eu (2), Dy (3), Y (4), and Lu (5), are described, whose original three-dimensional structures display the required alternation of ABAB type for one face of the cube and the delocalization between the two rings approximating to the electronic interaction along the edges of the cube. Synthesis, X-ray crystal structure, and study of the optical properties and of the first molecular hyperpolarizability β are reported. The size of the lanthanide (III) central ion modulates the ring-to-ring distance and the degree of coupling between the two phthalocyanine rings. As a consequence, the optical properties of these octupolar chromophores and in particular the strong near-infrared absorption due to the intervalence transition between the two rings also depend on the central lanthanide (III) ion. The first oxidized and reduced states of the complexes, while keeping a similar octupolar structure, display considerably changed optical properties compared to the neutral states. Second-order nonlinear properties were determined by nonpolarized harmonic light scattering in solution at 1907 nm. Exceptionally large dynamic molecular first hyperpolarizabilities √(<βHLS(2)>1907), among the highest ever reported, were found that showed a strong dependence on the number of 4f electrons.

The complex structure of ionic liquids at an atomistic level: from “red-and-greens” to charge templates

Abstract In this article, we discuss how the relation between interactions and structure in ionic liquids (ILs) can be probed at a molecular level using ab initio and molecular dynamics (MD) methodologies. The first part of the discussion will focus on the unique and complex properties of ILs as pure substances including the existence of an extended and flexible polar network and the possibility of a second nanosegregated subphase containing the nonpolar residues of the molecular ions that constitute some ILs. The discussion will then be extended to IL plus molecular species mixtures/solutions. In this context the concept of ILs as charge templates for the electronic make-up of the molecular species will be analyzed at length. Finally, that concept will be extended to ILs adsorbed over solid substrates.

Hybrid ferroelectric–polymer microfluidic device for dielectrophoretic self-assembling of nanoparticles

Carbon nanoparticles are becoming ubiquitous in many fields of science and technology. However, a grand challenge remains in assembling, patterning, and positioning or even simple manipulation of CNTs for complex functional assemblies. CNTs have in fact enormous perspectives for application in biotechnologies as bactericide agents or as prominent tools for investigating cell mechanisms, or more in general as functionalized nanoparticle-vectors, but their exploitation requires viable technology at the lab-on-a-chip scale. Many approaches have been attempted in developing technologies for manipulating CNTs. One elective approach is based on electric fields driven mechanisms such as DEP forces. A variety of chips have been designed and realized with this aim. Here we report on a novel hybrid microfluidic chip made by assembling a polar-dielectric crystal with polymeric microfluidic channels. One challenging feature of such a hybrid device approach, based on an electrode-free dielectrophoretic (DEP) approach, is that it makes use of surface charge templates for self-assembling and manipulation of CNTs in liquid media directly into a microfluidic channel. Here various examples of self-assembly in microfluidic channels as well as separation and collection of two classes of nano/microparticles are reported. The method can open the way to novel fabrication protocols for the realisation of future flexible devices with new and more complex functionalities, highly desirable in electronics as well as in biotechnology at the lab-on-a-chip scale.

Spontaneous Assembly of Carbon-Based Chains in Polymer Matrixes through Surface Charge Templates

Stable chains of carbon-based nanoparticles were formed directly in polymer matrixes through an electrode-free approach. Spontaneous surface charges were generated pyroelectrically onto functionalized ferroelectric crystals, enabling the formation of electric field gradients that triggered the dipole-dipole interactions responsible for the alignment of the particles, while embedded in the polymer solution. The phenomenon is similar to the dielectrophoretic alignment of carbon nanotubes reported in the literature. However, here the electric fields are generated spontaneously by a simple heat treatment that, simultaneously, aligns the particles and provides the energy necessary for curing the host polymer. The result is a polymer sheet reinforced with well-aligned chains of carbon-based particles, avoiding the invasive implementation of appropriate electrodes and circuits. Because polymers with anisotropic features are of great interest for enhancing the thermal and/or the electrical conductivity, the electrode-free nature of this technique would improve the scaling down and the versatility of those interconnections that find applications in many fields, such as electronics, sensors, and biomedicine. Theoretical simulations of the interactions between the particles and the charge templates were implemented and appear in good agreement with the experimental results. The chain formation was characterized by controlling different parameters, including surface charge configuration, particle concentration, and polymer viscosity, thus demonstrating the reliability of the technique. Moreover, micro-Raman spectroscopy and scanning electron microscopy were used for a thorough inspection of the assembled chains.

Theoretical and practical considerations in electrostatic depositioning of charged polymers

ABSTRACTAn interfacial engineering technology, based on the electrostatic deposition of charged polyelectrolytes onto surfaces of oppositely charged templates is reviewed with an emphasis on practical applications in the food, pharmaceutical and personal care industries. On interfaces of disperse systems consecutively deposited polymers provide major advantages in terms of physical and chemical stability of dispersions against superimposed stresses (pH, temperature, ionic strength, freezing, chilling, dehydration, lipid oxidation). The controlled deposition of multiple layers allows for a controlled and triggered release of incorporated functional components. This review highlights the basic principles of the layer‐by‐layer (LbL) electrostatic deposition method as well as some major advantages and drawbacks of this approach. An overview of several systems that can be used as templates for the deposition including emulsion droplets, liposomal vehicles, colloidal aggregates, and planar surfaces is given. Suitable substrates for the deposition are presented with a focus on charged biopolymers such as proteins or polysaccharides since they play an essential role in the formulation and stabilization of food, pharmaceutical and personal care applications. Issues and difficulties associated with implementing the technology on a larger, industrial scale are discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40099.