Template-directed Self-assembly Research Articles

Segmented Template-Directed Self-Assembly of Giant Truncated Triangular Supramolecules.

The template-directed strategy has been extensively employed for the construction of supramolecular architectures. However, with the increase in the size and complexity of these structures, the synthesis difficulty of the templates escalates exponentially, thereby impeding the widespread application of this strategy. In this study, two truncated triangles T1 and T2 were successfully self-assembled through a novel segmented template strategy by segmenting the core triangular template into portions. Two metallo-organic ligands L2 and L3 were designed and synthesized by dividing the central stable triangle into three separate parts and incorporating them into the precursor ligands, which served as templates to guide the self-assembly process with ligands L1 and L4, respectively. The assembled structures were unambiguously characterized by multidimensional and multinuclear NMR (1H, COSY, NOESY), multidimensional mass spectrometry analysis (ESI-MS and TWIM-MS), and transmission electron microscopy (TEM). Moreover, we observed the formation of fiberlike nanotubes from single-molecule triangles by hierarchical self-assembly.

Highly Ordered Eutectic Mesostructures via Template-Directed Solidification within Thermally Engineered Templates.

Template-directed self-assembly of solidifying eutectics results in emergence of unique microstructures due to diffusion constraints and thermal gradients imposed by the template. Here, the importance of selecting the template material based on its conductivity to control heat transfer between the template and the solidifying eutectic, and thus the thermal gradients near the solidification front, is demonstrated. Simulations elucidate the relationship between the thermal properties of the eutectic and template and the resultant microstructure. The overarching finding is that templates with low thermal conductivities are generally advantageous for forming highly organized microstructures. When electrochemically porosified silicon pillars (thermal conductivity < 0.3 Wm-1K-1) are used as the template into which an AgCl-KCl eutectic is solidified, 99% of the unit cells in the solidified structure exhibit the same pattern. In contrast, when higher thermal conductivity crystalline silicon pillars (≈100 Wm-1K-1) are utilized, the expected pattern is only present in 50% of the unit cells. The thermally engineered template results in mesostructures with tunable optical properties and reflectances nearly identical to the simulated reflectances of perfect structures, indicating highly ordered patterns are formed over large areas. This work highlights the importance of controlling heat flows in template-directed self-assembly of eutectics.

Understanding Interactions Driving the Template-Directed Self-Assembly of Colloidal Nanoparticles at Surfaces.

Controlled deposition of colloidal nanoparticles using self-assembly is a promising technique for, for example, manufacturing of miniaturized electronics, and it bridges the gap between top-down and bottom-up methods. However, selecting materials and geometry of the target surface for optimal deposition results presents a significant challenge. Here, we describe a predictive framework based on the Derjaguin–Landau–Verwey–Overbeek theory that allows rational design of colloidal nanoparticle deposition setups. The framework is demonstrated for a model system consisting of gold nanoparticles stabilized by trisodium citrate that are directed toward prefabricated sub-100 nm features on a silicon substrate. Experimental results for the model system are presented in conjunction with theoretical analysis to assess its reliability. It is shown that three-dimensional, nickel-coated structures are well suited for attracting gold nanoparticles and that optimization of the feature geometry based on the proposed framework leads to a systematic improvement in the number of successfully deposited particles.

Classical and non-classical melatonin receptor agonist-directed micellization of bipyridinium-based supramolecular amphiphiles in water.

The addition of molecular recognition units into structures of amphiphiles is a means by which soft matter capable of undergoing template-directed micellization can be obtained. These supramolecular amphiphiles can bind with molecular templates using non-covalent bonding interactions, forming host-guest complexes that hold the amphiphiles together as they undergo micellization. In most cases, such templates are synthesized and designed for a specific molecular recognition motif. It is not clear, however, to what extent these types of amphiphile systems are responsive to members of a biologically derived class of molecular targets, for example, melatonin receptor agonists and their numerous isosteres. Herein, we describe the template-directed micellization and arrangement at the air-water interface of a bipyridinium-based gemini surfactant, driven by the influence of donor-acceptor CT interactions with a series of bioactive classical and non-classical melatonin isosteres. Under the conditions of templation by either 5-methoxytryptophol, N-acetylserotonin, N-acetyltryptamine, or the pharmaceutical agent agomelatine, favorable Gibbs free energies of micellization were observed with decreases in CMC by up to 70%, and concomitant increases of 28% in surface pressure, and decreases of 20% in contact angle versus untemplated solutions. Solid state thermochromic transition temperatures for inkjet-printed patterns of the templated amphiphile solutions were inversely correlated with trends observed for their respective CMCs, and exhibited no correlation to their binding constants. These findings contend for the generalizable use of melatonin receptor agonists as targets and/or templates for chemical systems, which rely on π-stacking donor-acceptor CT interactions in water to facilitate the actions of binding, sequestration, or template-directed self-assembly.

Hierarchically ordered carbon tube-sheet superstructure via template-directed self-assembly of polyimide

In this work, we report a template-directed self-assembly strategy towards the gram-level synthesis of hierarchically ordered carbon tube-sheet superstructure (CTSS) by using MoO3 nanorod as the template and polyimide (PI) as the carbon source. Even in large quantities, MoO3 nanorods can guide the assembly of PI in solution into vertically oriented nanosheet arrays with periodic patterns, which can be converted to nitrogen-doped porous CTSS after the removal of template and thermal carbonization. Possessing hierarchically ordered architecture, rich porosity and high nitrogen content, CTSS is an appealing material for energy storage and conversion devices such as high-performance lithium ion battery anode and water splitting catalyst support. More importantly, the results in this work highlight an avenue for the controllable synthesis of hierarchically ordered carbon superstructures with diversified functions and applications.

Smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing phase change material for in-situ thermal management of supercapacitors

Phase change materials (PCMs) have been widely applied for thermal energy storage and thermoregulation. This paper reported a smart design and construction of nanoflake-like MnO2/SiO2 hierarchical microcapsules containing n-docosane PCM for in-situ thermal management of supercapacitors. The microcapsules based on an n-docosane core and SiO2 shell were first synthesized through interfacial polycondensation, and then a mesoporous nanoflake-like MnO2 layer was fabricated onto the surface of SiO2 shell through template-directed self-assembly. The chemical compositions of the resultant microcapsules were confirmed by energy dispersive X-ray, X-ray photoelectron and Fourier-transform infrared spectroscopy, and their nanoflake-like hierarchical morphology and well-defined core–shell structure were identified by scanning and transmission electron microscopy. The mesoporous architecture of nanoflake-like MnO2 outer layer was determined by nitrogen adsorption–desorption isotherm. The obtained microcapsules exhibited high phase-change enthalpies, high encapsulation efficiency, good phase-change and anti-osmosis performance and an effective thermoregulation capability. Most of all, these microcapsules demonstrated a higher specific capacitance than traditional MnO2/SiO2 solid particles at operation temperatures higher than 45 °C due to in-situ thermal management by the n-docosane core. They not only achieved a high specific capacitance of 312.2F/g at 45 °C with a current density of 1.0 A/g due to the mesoporous architecture of MnO2 layer, but also presented a superior long-term cycling stability with high capacitance retention of 94.7% after 1000 charging/discharging cycles. With the above-mentioned superiorities, the microcapsules developed by this work will be a good candidate as an electrode material for supercapacitors. This study opens a new pathway for the development and applications of microencapsulated PCMs in the thermoregulatory electrode system of supercapacitors and Li-ions battery cells.

Planar-orientation polycrystalline thin film of liquid-crystalline organic semiconductor by template-directed self-assembly

We fabricated planar-orientation crystalline thin films of organic semiconductors, in which molecules sit parallel, i.e., “face-on”, on the substrate and favor vertical charge transport. Thanks to molecular orientation that is sensitive to surface properties and the self-organization of liquid crystals, planar-orientation crystalline thin films can be prepared by simply cooling a smectic liquid-crystalline organic semiconductor from isotropic temperature with the aid of a poly(vinyl alcohol) (PVA) microtemplate. The molecular orientation of crystalline thin films was investigated by polarized optical microscopy (POM) and X-ray diffraction (XRD) analysis, and the current–voltage characteristics of the films were studied in a diode configuration. The results showed high potential for device applications.

Template-directed self-assembly of dynamic covalent capsules with polar interiors.

Chiral polyimine molecular capsules with polar interiors have been prepared through template covalent dynamic self-assembly. An aryl-extended tetraaldehyde calix[4]pyrrole scaffold was condensed with suitable diamines as linkers using templates for efficient self-assembly. The capsular complexes were characterized in solution, gas phase and the solid-state. Unprecedented transfer of asymmetry was observed from a chiral diamine linker to the resulting supramolecular capsular assembly.

Fabrication of Nonperiodic Metasurfaces by Microlens Projection Lithography.

This paper describes a strategy that uses template-directed self-assembly of micrometer-scale microspheres to fabricate arrays of microlenses for projection photolithography of periodic, quasiperiodic, and aperiodic infrared metasurfaces. This method of "template-encoded microlens projection lithography" (TEMPL) enables rapid prototyping of planar, multiscale patterns of similarly shaped structures with critical dimensions down to ∼400 nm. Each of these structures is defined by local projection lithography with a single microsphere acting as a lens. This paper explores the use of TEMPL for the fabrication of a broad range of two-dimensional lattices with varying types of nonperiodic spatial distribution. The matching optical spectra of the fabricated and simulated metasurfaces confirm that TEMPL can produce structures that conform to expected optical behavior.

Stacked Pairing of Anionic Porphyrins on a Tetracationic Macrocyclic Template

Dimers of dianionic porphyrins were formed via template-directed self-assembly on a tetracationic macrocycle. Single-crystal X-ray structural analyses revealed that [5,10-bis(4-sulfonatophenyl)-15,20-diphenylporphyrinato]nickel(II) (Ni(II)TPPS2A2−) or [5,15-bis(4-sulfonatophenyl)-15,20-diphenylporphyrinato]nickel(II) (Ni(II)TPPS2O2−) formed discrete J-type slipped cofacial dimers, which are structural analogues of a typical natural cofacial porphyrin dimer, on the tetracationic template in the crystals.

High-sensitive electrochemical sensor of Sudan I based on template-directed self-assembly of graphene-ZnSe quantum dots hybrid structure

In this work, a very sensitive electrochemical sensor for Sudan I was established based on nanohybrids of graphene-ZnSe quantum dots. Positively charged cetyltrimethyl-ammonium bromide (CTAB) functionalized graphene was used as a template-directed building block to self-assemble negatively charged ZnSe quantum dots (QDs). The hybrids of ZnSe-CTAB-graphene exhibited strong enrichment effect on Sudan I and gave superior electrocatalytic activity towards the oxidation of Sudan I. Applying differential pulse voltammetry (DPV), the peak current of Sudan I is proportional to its concentration in the range from 0.004 to 2.0μM and 2.0 to 15.0μM. This report is the first on applying graphene-ZnSe hybrids for electrochemical sensing.

C-doped hollow TiO2 spheres: in situ synthesis, controlled shell thickness, and superior visible-light photocatalytic activity

The persistent efforts have been paid to shift the ultraviolet of titania to visible-light-driven photocatalysis. In this work, we explored a facile, cost-effective method to in situ create C-doped hollow TiO2 spheres. This method involved the preparation of monodisperse cationic polystyrene spheres (CPS), sequential deposition of TiO2 precursor via template-directed self-assembly, and the removal of CPS template by calcination at 450°C. The structure and properties of hollow TiO2 catalysts were characterized by N2 desorption–adsorption, X-ray diffraction (XRD), UV–vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results confirmed the carbon doping in the as-prepared hollow TiO2 lattice. When C-doped hollow TiO2 spheres were used as photocatalysts for the degradation of Rhodamine B under visible-light irradiation, the as-synthesized hollow anatase exhibited a superior photocatalytic activity than the commercial P25 and many TiO2-based photocatalysts reported in literature, significantly broadening its potential for many practical applications.

Template-directed self-assembly of a designed amphiphilic hexapeptide on mica surface

Self-assembly of small molecules into highly ordered nanostructures offers many important potential applications in science research and industry. Precise self-assembling with the assistance of inorganic substrate is considered as an ideal strategy. In this experiment, the highly ordered mica surface was used to template the assembling of a novel designed amphiphilic hexapeptide to form orderly parallel fibers. The nanostructure and the self-assembly mechanism were investigated by atomic force microscopy (AFM), transmission electron microscopy, Fourier transform infrared spectroscopy, and circular dichroism techniques. By the experimental results, a dramatic conformation transition from random coil and/or α-helix into β-sheet was found after the peptide assembled on the mica surface under certain conditions, which was considered as a key factor for the ordered nanostructure. Finally, according to the AFM images and the simulated length of peptide molecules, a trilaminar β-sheet structure model was proposed to explain the hierarchical self-assembly mechanism.

Template-directed self-assembly by way of molecular recognition at the micellar–solvent interface: modulation of the critical micelle concentration

By incorporating the concepts of structural preorganisation and complementarity in concert with non-covalent donor-acceptor [ππ] and hydrophobic interactions, a duo of π-electron deficient bipyridinium-based linear and gemini amphiphiles capable of responding to molecular templation have been designed and synthesised. When combined with π-electron rich di(ethylene glycol)-disubstituted 1,5-dihydroxynaphthalene, a dramatic decrease in the critical aggregation concentration by ≈66% was observed with concomitant increases in the hydrodynamic diameter, ζ-potential, and Langmuir surface pressures of the micellar solutions-thus enhancing the detergents' efficiency and effectiveness at lowering the surface tension of water. By employing a phase separation model that takes into account the degree of counterion binding to the micellar aggregate superstructure, the effects of donor-acceptor templation on the Gibb's free energy of micellisation (ΔG) for the amphiphiles was quantified. It was found that donor-acceptor templation was capable of lowering ΔG by up to 1.75 kcal mol(-1) at which point it was observed, while under the influence of molecular templation, that linear single hydrophobic tailed detergent molecules exhibit properties characteristic of double-tailed phospholipid-like gemini surfactants.

Abstract 2842: Development of a novel TrkA HTS assay using template directed self assembly (TDA)

Abstract Tropomyosin-related kinases (Trks A, B, and C) are a family of membrane-associated receptor tyrosine kinases (RTKs) activated by neurotrophins. RTKs are shown to be implicated in Alzheimer's disease, depression, pain sensation and various cancers including tumor cell growth and survival signaling. Inhibitors of Trk receptor kinases might provide targeted treatments for neurodegenerative diseases, pain and cancer. One strategy to indentify Trk isoform-specific inhibitors is to develop an assay where compound libraries can be screened in a more-native membrane associated lipid environment. Template-Directed Self Assembly (TDA) is a biomimetic technology designed to restore membrane-associated proteins to more relevant physiological conditions. This technology utilizes recombinant histidine-tagged proteins bound to the surface of nickel-chelated liposomes. Recombinant HIS-tagged proteins are engineered on the correct terminus of the protein to reflect the polarity of the enzyme with respect to the membrane. This allows the HIS-tagged proteins to bind to the liposome creating an environment much like a cellular membrane. The lipids in TDA are fully fluid within the surface of the liposome and associated proteins can rotate freely. Furthermore it promotes the formation of high-order structures such as homo- or hetro-dimers and shown to recruit accessory factors. Coupling of membrane associsted kinases to liposomes reconstitutes an environment that confers proper polarity, stereochemistry, topology and other critical properties, thereby creating a more relevant biochemical assay. To date, we have shown that several RTKs have enhanced biochemical specific activity and substrate specificity that resembles physiological conditions when coupled to TDA. The TDA approach restores TrkA activity to a more-native environment; therefore, we hypothesize that we will be able to identify compounds that are more specific and selective. To address the need of an enzyme assay near a lipid membrane environment, we successfully developed a robust TrkA assay shown to exhibit up to 20-fold increase in specific activity and a reduction in Km for ATP relative to TrkA in a conventional assay. Furthermore, TDA-associated TrkA exhibited a rapid and robust trans-activation, obviating the need for a pre-activation step. Thus, assays of TrkA coupled to TDA have the potential to identify more chemically diverse and specific inhibitors. We are currently (1) validating the TDA assay with known inhibitors (2) screening a focus library to identify novel hits (3) testing the primary hits against a small kinase selectivity panel and (4) designing and developing a TrkA specific reporter cell line to confirm the primary hits. The advantages of the TDA technology will be also discussed against other therapeutically relevant RTKs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2842. doi:1538-7445.AM2012-2842

Periodic Mesoporous Hydridosilica − Synthesis of an “Impossible” Material and Its Thermal Transformation into Brightly Photoluminescent Periodic Mesoporous Nanocrystal Silicon-Silica Composite

There has always been a fascination with "impossible" compounds, ones that do not break any rules of chemical bonding or valence but whose structures are unstable and do not exist. This instability can usually be rationalized in terms of chemical or physical restrictions associated with valence electron shells, multiple bonding, oxidation states, catenation, and the inert pair effect. In the pursuit of these "impossible" materials, appropriate conditions have sometimes been found to overcome these instabilities and synthesize missing compounds, yet for others these tricks have yet to be uncovered and the materials remain elusive. In the scientifically and technologically important field of periodic mesoporous silicas (PMS), one such "impossible" material is periodic mesoporous hydridosilica (meso-HSiO(1.5)). It is the archetype of a completely interrupted silica open framework material: its pore walls are comprised of a three-connected three-dimensional network that should be so thermodynamically unstable that any mesopores present would immediately collapse upon removal of the mesopore template. In this study we show that meso-HSiO(1.5) can be synthesized by template-directed self-assembly of HSi(OEt)(3) under aqueous acid-catalyzed conditions and after template extraction remains stable to 300 °C. Above this temperature, bond redistribution reactions initiate a metamorphic transformation which eventually yields periodic mesoporous nanocrystalline silicon-silica, meso-ncSi/SiO(2), a nanocomposite material in which brightly photoluminescent silicon nanocrystallites are embedded within a silica matrix throughout the mesostructure. The integration of the properties of silicon nanocrystallinity with silica mesoporosity provides a wealth of new opportunities for emerging nanotechnologies.

Assembly of Polygonal Nanoparticle Clusters Directed by Reversible Noncovalent Bonding Interactions

The reversible molecular template-directed self-assembly of gold nanoparticles (AuNPs), a process which relies solely on noncovalent bonding interactions, has been demonstrated by high-resolution transmission electron microscopy (HR-TEM). By employing a well-known host-guest binding motif, the AuNPs have been systemized into discrete dimers, trimers, and tetramers. These nanoparticulate twins, triplets, and quadruplets, which can be disassembled and reassembled either chemically or electrochemically, can be coalesced into larger, permanent polygonal structures by thermal treatment using a focused HR-TEM electron beam.

Peptide-mediated surface-immobilized quantum dot hybrid nanoassemblies with controlled photoluminescence

Combinatorially selected peptides and peptide–organic conjugates were used as linkers with controlled structural and organizational conformations to attach quantum dots (QDs) at addressable distances from a metal surface. This study demonstrates an approach towards nanophotonics by integrating inorganic, organic, and biological constructs to form hybrid nanoassemblies through template-directed self-assembly. Peptide–organic-linked QD arrays showed stronger fluorescence than peptide-linked QD arrays. We attribute this difference primarily to the increased number density of QDs on peptide–organic-linked QD arrays.

Template‐Directed Self‐Assembly Enhances RTK Catalytic Domain Function

Receptor Tyrosine Kinases (RTKs) comprise a large family of single-pass transmembrane proteins. Test-tube phosphorylation assays routinely employ cloned RTK catalytic domain fragments, but these are removed from the membrane environment and thus cannot exhibit full function. Consequently, we developed template-directed self-assembly of RTK catalytic domains to recreate the membrane environment with the objective of restoring native activity and function. Autophosphorylation and substrate phosphorylation of template-assembled catalytic domains from the Insulin and EphB2 receptors (IR and EphB2R, resp.) were substantially larger than corresponding activities in solution. Robust IR domain autophosphorylation was found on templates, where only a background level was observed with domains in the absence of template. EphB2R domain autophosphorylation increased ~4-fold by with template. Template assembly increased the total (auto- plus substrate) phosphorylation exhibited by the IR and EphB2R domains 20-fold and 8-fold, respectively. Results with catalytic domains from other RTKs support the conclusion that the effect is general. Although we used templates to serve as platforms for assembling receptor domains, we also note that domains from co-receptors, adaptor proteins and various other signaling components may also be used to permit easy and effective reassembly of several required components. These results and the underlying similarity in organization of transmembrane signaling systems suggest that template-directed assembly of signaling pathways will provide widespread benefits to basic and applied signal transduction research.

Fabrication of super-hydrophobic film with dual-size roughness by silica sphere assembly

Two simple approaches were developed for the fabrication of super-hydrophobic film with dual-size roughness by taking advantage of assembling silica micro- and nanospheres. Electrostatic adsorbing technique and template-directed self-assembly were used here. The dual-size surface, which mimics the surface topology of lotus leaves, comprises both the micro-scale and nano-scale roughness. After the roughened surface was chemically modified with a layer of fluoroalkylsilane, super-hydrophobicity with a water contact angle higher than 160° and sliding angle as low as 0.5° can be achieved. The simplicity and cheapness of this procedure may make widespread applications of this super-hydrophobic film possible.