Supramolecular Templating Research Articles

Recent Trends in Morphology-Controlled Synthesis and Application of Mesoporous Silica Nanoparticles.

The outstanding journey towards the investigation of mesoporous materials commences with the discovery of high surface area porous silica materials, named MCM-41 (Mobil Composition of Matter-41) according to the inventors’ name Mobile scientists in the United States. Based on a self-assembled supramolecular templating mechanism, the synthesis of mesoporous silica has extended to wide varieties of silica categories along with versatile applications of all these types in many fields. These silica families have some extraordinary structural features, like highly tunable nanoscale sized pore diameter, good Brunauer–Emmett–Teller (BET) surface areas, good flexibility to accommodate different organic and inorganic functional groups, metals etc., onto their surface. As a consequence, thousands of scientists and researchers throughout the world have reported numerous silica materials in the form of published articles, communication, reviews, etc. Beside this, attention is also given to the morphology-oriented synthesis of silica nanoparticles and their significant effects on the emerging fields of study like catalysis, energy applications, sensing, environmental, and biomedical research. This review highlights a consolidated overview of those morphology-based mesoporous silica particles, emphasizing their syntheses and potential role in many promising fields of research.

Electrostatic Self-Assembly of Protein Cage Arrays.

Protein and peptide cages are nanoscale containers, which are of particular interest in nanoscience due to their well-defined dimensions and enclosed central cavities that can be filled with material that is protected from the outside environment. Ferritin is a typical example of protein cage, formed by 24 polypeptide chains that self-assemble into a hollow, roughly spherical protein cage with external and internal diameters of approximately 12nm and 8nm, respectively. The interior cavity of ferritin provides a unique reaction vessel to carry out reactions separated from the exterior environment. In nature, the cavity is utilized for sequestration and biomineralization to render iron inert and safe by shielding from the external environment. Materials scientists have been inspired by this system and exploited a range of ferritin superfamily proteins as supramolecular templates to encapsulate cargoes ranging from cancer drugs to therapeutic proteins. Interesting possibilities arise if such containers can themselves be arranged into even higher-order structures such as crystalline arrays. Here, we describe how crystalline arrays of negatively charged ferritin protein cages can be built by taking advantage of electrostatic interactions with cationic gold nanoparticles.

Adamantane-Terminated Polypeptides: Synthesis by N-Carboxyanhydride Polymerization and Template-Based Self-Assembly of Responsive Nanocontainers via Host-Guest Complexation with β-Cyclodextrin.

The synthesis of adamantane-terminated polypeptides by N-carboxyanhydride (NCA) polymerization and their use in the template-based self-assembly of redox-responsive nanocontainers is described. Cyclodextrin vesicles (CDV) serve as a supramolecular template to anchor adamantane terminated polypeptides on to the surface of CDV and to form polypeptide shelled vesicles (PPSVss) which are stabilized by crosslinking with cystamin. Polypeptides are characterized by nuclear magnetic resonance, matrix-assisted laser desorption/ionization (MALDI), and gel permeation chromatography, and nanocontainer formation at each step is confirmed by dynamic light scattering (DLS) and zeta potential measurements. MALDI confirms the presence of the adamantane at the end of the polymers, and isothermal titration calomatry (ITC) of the adamantane-terminated polypeptides with β-cyclodextrin proves the capability of adamantane on the polypeptides to form host-guest inclusion complexes even with the longest polypeptides. Encapsulation of a model dye carboxyfluorescein in PPSVss and its redox-responsive release demonstrates the potential use of this novel type of completely biodegradable and biocompatible nanocontainer for the purpose of intracellullar delivery.

Dynamic Supramolecular Template: Multiple Stimuli-Controlled Size Adjustment of Porous Networks.

Dynamically switchable porous networks offer exciting potential in functionalizing surfaces. The structure and morphology of the networks can be controlled by applying external stimuli. Here, a dynamic supramolecular template assembled by 1,3,5-tris(4-carboxyphenyl)benzene (BTB) is successfully achieved at the liquid-solid interface by applying two external stimuli simultaneously. Upon varying the concentration of BTB solution together with switching the polarity of the sample bias, self-assembled monolayers (SAMs) undergo phase transitions twice: an immediate transition from a compact structure to a macroporous (honeycomb) structure as a response to the change in the electric field and a fast-changing transition from the macroporous to a microporous (oblique) structure. With saturated BTB solution, however, the initial compact structure can only transform into the oblique structure after switching the polarity of the sample bias without the appearance of a honeycomb structure. The different phase transitions suggest that the dynamic supramolecular template can only survive at a specific concentration range and is obtainable by performing multiple stimuli simultaneously. Interestingly, introducing a guest molecule to the system can adjust the phase transition process and effectively stabilize the honeycomb structure of BTB. The flexibility associated with the porous networks renders it a dynamic supramolecular template for guest binding.

Mesoporous Strontium-Doped Phosphate-Based Sol-Gel Glasses for Biomedical Applications.

Mesoporous phosphate-based glasses have great potential as biomedical materials being able to simultaneously induce tissue regeneration and controlled release of therapeutic molecules. In the present study, a series of mesoporous phosphate-based glasses in the P2O5-CaO-Na2O system, doped with 1, 3, and 5 mol% of Sr2+, were prepared using the sol-gel method combined with supramolecular templating. A sample without strontium addition was prepared for comparison. The non-ionic triblock copolymer EO20PO70EO20 (P123) was used as a templating agent. Scanning electron microscopy (SEM) images revealed that all synthesized glasses have an extended porous structure. This was confirmed by N2 adsorption-desorption analysis at 77 K that shows a porosity typical of mesoporous materials. 31P magic angle spinning nuclear magnetic resonance (31P MAS-NMR) and Fourier transform infrared (FTIR) spectroscopies have shown that the glasses are mainly formed by Q1 and Q2 phosphate groups. Degradation of the glasses in deionized water assessed over a 7-day period shows that phosphate, Ca2+, Na+, and Sr2+ ions can be released in a controlled manner over time. In particular, a direct correlation between strontium content and degradation rate was observed. This study shows that Sr-doped mesoporous phosphate-based glasses have great potential in bone tissue regeneration as materials for controlled delivery of therapeutic ions.

Assessing mesoscopic organization in copolymer-templated silica hybrid films via solid-state nuclear magnetic resonance

In the context of increasing use of nanostructured materials, finding innovative characterization methods able to assess precisely the level of ordering is essential. To this end, a range of model organic-inorganic copolymer-silica films is synthesized using poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) amphiphilic triblock copolymer as supramolecular template. Upon increasing copolymer concentration (10–100 wt%), the order can be gradually enhanced from short-range to long-range as proved by conventional techniques such as X-ray diffraction and electron microscopy. To evaluate the level of mesoscopic organization, the same series of samples is also analyzed by solid-state nuclear magnetic resonance (NMR) spectroscopy. The disorder-to-order transition is probed by 1H and 13C magic angle spinning NMR spectra through the increase in chemical environment uniformity and chain mobility respectively, which both result from the self-assembly mechanism. 1H NMR relaxation measurements (T2) using low-field NMR spectroscopy are instrumental to identify the threshold template concentration where ordering takes place.

A facile route to synthesize mesoporous ZSM-5 with hexagonal arrays using P123 triblock copolymer

Mesoporous ZSM-5 samples were synthesized using Pluronic P123 triblock copolymer (EO20PO70EO20) as a supramolecular template through a pH adjusting method. The resulting materials were characterized using X-ray diffraction, transmission electron microscopy (TEM), nitrogen adsorption/desorption, scanning electron microscopy (SEM), solid-state nuclear magnetic resonance (MAS-NMR) and ammonia temperature programmed desorption (TPD) analyses. Adjusting the synthesis pH allowed obtaining a well-crystallized ZSM-5 material with meso-channels of size of 8–10 nm as calculated from non-local density functional theory (NLDFT) and also supported by TEM images. This strategy performs the growth of zeolite crystals with a mesostructured pore lattice in a cooperative manner, avoiding both a phase separation between the surfactant and zeolite units during crystallization and the formation of a separate amorphous mesoporous material. In addition, ammonia TPD studies revealed that the acidity of the mesoporous ZSM-5 material is comparable with the microporous conventional one. It was found from NH3-TPD profiles that in the case of the mesoporous ZSM-5 samples some of the strong acid sites have been transformed into weak acid sites which might be attributed to the acid sites present on the crystal external surface in mesopores.

Augmented polyhydrazone formation in water by template-assisted polymerization using dual-purpose supramolecular templates

Template-assisted polymerization using donor–acceptor supramolecular templates results in higher Mw and Mn values, decreased critical hydrogelation concentrations, and increased gel recovery velocity following shear-induced breakdown.

A covalent organic cage compound acting as a supramolecular shadow mask for the regioselective functionalization of C60

A trigonal-bipyramidal covalent organic cage compound serves as an efficient host to form stable 1 : 1-complexes with C60 and C70. Fullerene encapsulation has been comprehensively studied by NMR and UV/Vis spectroscopy, mass spectrometry as well as single-crystal X-ray diffraction. Exohedral functionalization of encapsulated C60via threefold Prato reaction revealed high selectivity for the symmetry-matched all-trans-3 addition pattern.

Chirality induction on non-chiral dye-linked polysilsesquioxane in nanohelical structures.

We demonstrate the direct induction of chirally arranged organic dye-linked polysilsesquioxane through a sol-gel transcription using a chiral supramolecular template. The chiral arrangement was confirmed by using electronic and vibrational circular dichroism and circularly polarized luminescence spectroscopies.

Hierarchical pore structure of zeolite/MCM obtained by supramolecular templating using ionic liquid (C16MI·Cl) as the structure-directing agent

Zeolites are microporous materials with tetrahedral three-dimensional structure; such structure allows the transfer of material through its pores, but small pores prejudice such transfer. One way to overcome these problems is the development of materials combining microporous and mesoporous structures. This study reports the synthesis at room temperature of hierarchical materials, ZSM-5/MCM-48, ZSM-35/MCM-48, ZSM-5/MCM-41 and ZSM-35/MCM-41, from ZSM-5 and ZSM-35 seeds, using ionic liquid (1-hexadecyl-3-methylimidazolium) as supramolecular template. Infrared spectroscopy and attenuated total reflectance analyses confirmed the formation of the materials through the presence of bands at 1220 and 1070 cm−1. SAXS analyses showed that most of the materials have surface fracture dimensions (3 ≤ α < 4), except the sample MCM 41/ZSM 5, having a mass fractal structure. Signals in the high-angle region correlated with XRD analysis, confirming the formation of the materials. TGA analysis shows that ionic liquid decomposition occurs at higher temperatures when the ionic liquid is within the material. Finally, the results obtained by textural analysis via N2 adsorption agreed with data reported in the literature.

Designed synthesis of an extra-large pore zeolite with a 14-membered ring channel via supramolecular assembly templating approach

Abstract Extra-large-pore zeolites are a class of important porous materials that have great potential in industrial applications as catalysts, adsorbents, etc. Organic structure directing agents (OSDAs) play a key role in the synthesis of extra-large pore zeolites. In this paper, we designed a cheap, easily available, aromatic OSDA to prepare an extra-large-pore zeolite (named as NUD-5) by using a supramolecular assembly templating (SAT) approach. NUD-5 has a zeolite framework with one-dimensional 14-member-ring pore channels, which is identical to UTD-1. The OSDA in NUD-5 can be completely removed by calcination and Al can also be directly incorporated into the NUD-5 framework during the synthesis, showing advantages over UTD-1. Al-NUD-5 possesses strong acidity and displayed good catalytic performance in the alkylation of benzene with methanol. Structural analysis of NUD-5 revealed that one-dimensional supramolecular assembles of OSDAs acted as a template for the formation of NUD-5, implying the SAT approach is a powerful preparative method to extra-large-pore zeolites.

Chiral Resolution using Supramolecular-Templated Mesostructured Materials.

Chiral resolution using non-functionalized mesoporous particles is demonstrated for a variety of enantiomeric pairs. This is achieved through the use of supramolecular templated silica materials prepared with guanosine monophosphate (NGM-1) and folic acid (NFM-1) which enable direct chiral transcription onto the surface of the mesopores after solvent extraction and post calcination of the template. The chiral selectivity and kinetics of the mesoporous materials are measured by circular dichroism (CD) spectroscopy on adsorbed molecules with different affinities for the pore surface. NGM-1 and NFM-1 have opposite enantiomeric selectivity for enantiomeric pairs. These results significantly increase the potential of mesoporous materials for chiral separation and enantiomeric catalysis.

Ammonium Complexes of Orthoester Cryptands Are Inherently Dynamic and Adaptive.

Fluxional chemical species such as bullvalene have been a valuable source of inspiration and fundamental insight into the nature of chemical bonds. A supramolecular analogue of bullvalene, i.e., a "fluxional host-guest system", in which the ensemble of a well-defined host and guest is engaged in continuous, degenerate constitutional rearrangements, is still elusive, however. Here, we report experimental and computational evidence for guest-induced dynamic covalent rearrangements in the ammonium complexes of self-assembled orthoester cryptands. This unique behavior is made possible by the ammonium guest playing a dual role: it is sufficiently acidic to initiate dynamic covalent exchange reactions at the orthoester bridgeheads, and as a hydrogen bond donor it acts as a supramolecular template, governing the outcome of a multitude of possible intra- and intermolecular rearrangement reactions. One particularly striking example of inherent dynamic behavior was observed in host-guest complex [NH4+⊂ o-Me2-2.1.1], which spontaneously rearranged into the larger and thermodynamically more stable complex [NH4+⊂ o-Me2-2.2.1], even though this process led to the formation of poor host o-Me2-1.1.1 as a consequence of the excess of one subcomponent (diethylene glycol; "1" in our nomenclature). These inherently adaptive host-guest networks represent a unique platform for exploring the interrelationship between kinetic and thermodynamic stability. For instance, as a result of optimal NH4+ binding, complex [NH4+⊂ o-Me2-2.2.1] was found to be thermodynamically stable (negligible intermolecular rearrangements over weeks), whereas computational studies indicate that the compound is far from kinetically stable ( intramolecular rearrangements).

Surface-functionalization of mesoporous silica films for effective osteoblast-like cell culture

Abstract The transparent mesoporous silica (MPS) films prepared by a supramolecular templating method was immersed in simulated body fluid (SBF), and subsequently was sterilized to evaluate the film structural stability. With immersing in SBF, the calcium and phosphate ion adsorption on the film surfaces was promoted and the mesopore structures underwent the expansion, collapse and reconstruction processes for the SBF immersion time of 6 h. The MPS films immersed in SBF for 3 h exhibited the mesostructural stability with the sterilization processes. We also investigated the Fgn adsorption states on the sterilized MPS films, which were clearly changed with the immersion time in SBF because of the different adsorption states of calcium and phosphate ions at the mesopores. Furthermore, the proliferation and differentiation behaviors of the osteoblast-like cells on the sterilized MPS films were investigated to evaluate the cell culture ability. The osteoblast–like cells cultured on the sterilized MPS films had the fibrous morphologies while maintaining the high adhesion density and were promoted to be the bone tissue formation for 14 days, indicating the preferential film environment for the cells. Therefore, it was suggested that the MPS films of this study were useful for the cell culture substrate based on their high transparency, stability against sterilization treatment, and preferential cytocompatibility.

Precise Generation of Selective Surface-Confined Glycoprotein Recognition Sites.

Since glycoproteins have become increasingly recognized as key players in a wide variety of disease processes, there is an increasing need for advanced affinity materials for highly selective glycoprotein binding. Herein, for the first time, a surface-initiated controlled radical polymerization is integrated with supramolecular templating and molecular imprinting to yield highly reproducible synthetic recognition sites on surfaces with dissociation constants (KD) in the low micromolar range for target glycoproteins and minimal binding to nontarget glycoproteins. Importantly, it is shown that the synthetic strategy has a remarkable ability to distinguish the glycosylated and nonglycosylated forms of the same glycoprotein, with a >5-fold difference in binding affinity. The precise control over the polymer film thickness and positioning of multiple carbohydrate receptors plays a crucial role in achieving an enhanced affinity and selectivity. The generated functional materials of unprecedented glycoprotein recognition performance open up a wealth of opportunities in the biotechnological and biomedical fields.

Minimal Reconstitution of Membranous Web Induced by a Vesicle-Peptide Sol-Gel Transition.

Positive strand RNA viruses replicate in specialized niches called membranous web within the cytoplasm of host cells. These virus replication organelles sequester viral proteins, RNA, and a variety of host factors within a fluid, amorphous matrix of clusters of endoplasmic reticulum (ER) derived vesicles. They are thought to form by the actions of a nonstructural viral protein NS4B, which remodels the ER and produces dense lipid-protein condensates. Here, we used in vitro reconstitution to identify the minimal components and elucidate physical mechanisms driving the web formation. We found that the N-terminal amphipathic domain of NS4B (peptide 4BAH2) and phospholipid vesicles (∼100-200 nm in diameter) were sufficient to produce a gel-like, viscoelastic condensate. This condensate coexists with the surrounding aqueous phase and affords rapid exchange of molecules. Together, it recapitulates the essential properties of the virus-induced membranous web. Our data support a novel phase separation mechanism in which phospholipid vesicles provide a supramolecular template spatially organizing multiple self-associating peptides thereby generating programmable multivalency de novo and inducing macroscopic phase separation.

Reversible modulation of plasmonic chiral signals of achiral gold nanorods using a chiral supramolecular template.

We report here the fabrication of a multiple stimuli-responsive chiral plasmonic system based on the reversible self-assembly of phenylboronic acid-capped gold nanorods (PBA-Au NRs) guided by a supramolecular glycopeptide mimetic template. The plasmonic chiral signals of PBA-Au NRs can be reversibly switched on and off by temperature, light, pH and glucose concentration variations.

Self-Assembly of Ferritin: Structure, Biological Function and Potential Applications in Nanotechnology.

Protein cages are normally formed by the self-assembly of multiple protein subunits and ferritin is a typical example of a protein cage structure. Ferritin is a ubiquitous multi-subunit iron storage protein formed by 24 polypeptide chains that self-assemble into a hollow, roughly spherical protein cage. Ferritin has external and internal diameters of approximately 12nm and 8nm, respectively. Functionally, ferritin performs iron sequestration and is highly conserved in evolution. The interior cavity of ferritin provides a unique reaction vessel to carry out reactions separated from the exterior environment. In nature, the cavity is utilized for sequestration of iron and bio-mineralization as a mechanism to render iron inert and safe from the external environment. Material scientists have been inspired by this system and exploited a range of ferritin superfamily proteins as supramolecular templates to encapsulate different carrier molecules ranging from cancer drugs to therapeutic proteins, in addition to using ferritin proteins as well-defined building blocks for fabrication. Besides the interior cavity, the exterior surface and sub-unit interface of ferritin can be modified without affecting ferritin assembly.

Circularly polarized luminescence of single-handed helical tetraphenylethylene-silica nanotubes.

Two single-handed helical tetraphenylethylene-silica nanotubes with circularly polarized luminescence (CPL) properties and enhanced fluorescence efficiency were fabricated through a supramolecular templating approach using the self-assemblies of chiral gelators as templates. This work provides a facile strategy for constructing CPL-active organic-inorganic hybrid nanomaterials with single-handed helical morphologies.