Formation Of Self-assembled Nanostructures Research Articles

Effect of isothermal annealing on formation of self-assembled nanostructures in manganese spinel ZnMnGaO4

The effects of isothermal annealing on the self-assembled nanostructures of spinel manganese oxide ZnMnGaO4 were investigated using transmission electron microscopy and x-ray diffraction. The checkerboard nanostructures and zigzag nanostructures (named “Sierra” nanostructures) coexisted owing to the chemical phase separation of Mn3+ and Ga3+ ions by isothermal annealing at 575 °C. It was observed that the checkerboard nanostructures were dominant in short-time annealing and that the volume fraction of the Sierra nanostructures became more prominent as the annealing period increase. The interdiffusion of Mn3+ and Ga3+ is indicated to play an important role in gaining the total energy of the system by the reduction in the local strain caused by the formation of nanostructures. These results provide further insights into the fabrication of distinct types of nanostructures in complex transition-metal compounds.

Insights into diphenylalanine peptide self-assembled nanostructures for integration as nanoplatforms in analytical and medical devices

New insights on the self-assembling process of diphenylalanine (FF) into nanostructures in view of its application as an alternative nanomaterial for bioanalytical and biomedical systems are presented in the frame of the present work. Experimental conditions, such as peptide concentration and solubilization medium pH, were explored to understand the hierarchical process involved in the formation of self-assembled nanostructures arising from the simple and short diphenylalanine peptide. Optical microscopy and TEM images supported by DLS data authenticated the hierarchical self-assembly outcoming from the original nature of the first nanostructures, showing individual nanotubes and vesicles stacking to grow well-defined microtubes. Moreover, the influence of metal cations on peptide self-assembly was evaluated for the first time in the presence of Mg2+ and compared with other ions, such as Na+, K+, and Ca2+. The results evidenced a tendency of Mg2+ to interact with diphenylalanine peptides to form self-assembled nanostructures showing vesicle- and ellipse-like morphologies. FF solubilization in water prepared under sonication in a bath at 65–68 °C followed by dilution into chloride metal cation solutions at 50 mmol·L−1 proved to be optimal conditions to obtain metal-coordinated self-assembled FF structures. Besides, the latter revealed fluorescence features and electron-transfer properties on carbon-based electrode surfaces, that can be further explored in analytical and bioanalytical devices for fully integrated platforms. In this context, self-assembled nanostructures achieved in the presence of Mg2+ and Ca2+ were implemented for the surface modification of carbon screen-printed electrodes and proved to increase the electrochemical response toward a redox probe. This proof of concept is particularly interesting for further use of these peptide-based nanoarchitectures as nanoplatforms for clinical imaging, therapeutic and diagnosis purposes.

Self-Assembled Nanostructures of Homo-Oligopeptide as a Potent Ice Growth Inhibitor.

This study reports the formation of self-assembled nanostructures with homo-oligopeptides consisting of amino acids (i.e., alanine, threonine, valine, and tyrosine), the resulting morphologies (i.e., spherical shape, layered structure, and wire structure) in aqueous solution, and their potential as ice growth inhibitors. Among the homo-oligopeptides investigated, an alanine homo-oligopeptide (n = 5) with a spherical nanostructure showed the highest ice recrystallization inhibition (IRI) activity without showing a burst ice growth property and with low ice nucleation activity. The presence of nanoscale self-assembled structures in the solution showed superior IRI activity compared to an amino acid monomer because of the higher binding affinity of structures on the growing ice crystal plane. Simulation results revealed that the presence of nanostructures induced a significant inhibition of ice growth and increased lifetime of hydrogen bonding compared with unassembled homo-oligopeptide. These results envision extraordinary performance for self-assembled nanostructures as a desirable and potent ice growth inhibitor.

Dispersion-Corrected DFT-D4 Study of the Adsorption of Halobenzenes and 1,3,5-Trihalobenzenes on the Cu(111) Surface─Effect of Sigma Hole Properties.

Halogen bonds, characterized by directionality, tunability, hydrophobicity, and variable sizes, are ideal noncovalent interactions to design and control the formation of self-assembled nanostructures. The specific self-assembly cases formed by the halogen-bonding interaction have been well studied by scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. However, there is a lack of systematic theoretical adsorption studies on halogenated molecules. In this work, the adsorption of halobenzenes and 1,3,5-trihalobenzenes on the Cu(111) surface was examined by dispersion-corrected DFT methods. The adsorption geometries, noncovalent molecule-surface interactions, electronic densities, and electrostatic potential maps were examined for their most stable adsorption sites using the DFT-D4 method. Our calculations revealed that the iodo compounds favor a different adsorption geometry from aryl chlorides and bromides. Down the halogen group (Cl to I), the adsorption energy increases and the distance between the halogen atom and Cu surface decreases, which indicates stronger molecule-surface interactions. This is supported by the changes in the density of states upon adsorption. Noncovalent interaction analysis was also employed to further understand the nature and relative strength of the molecule-surface interactions. Electrostatic potential maps revealed that the positive character of the halogen sigma hole becomes stronger upon adsorption. Thus, surface adsorption of the halogenated molecule will enhance the formation of intermolecular halogen bonds. The present theoretical findings are expected to contribute toward a more comprehensive understanding of halogen bonding on the Cu(111) surface.

Ultra-stable all-solid-state sodium metal batteries enabled by perfluoropolyether-based electrolytes.

Rechargeable batteries paired with sodium metal anodes are considered to be one of the most promising high-energy and low-cost energy-storage systems. However, the use of highly reactive sodium metal and the formation of sodium dendrites during battery operation have caused safety concerns, especially when highly flammable liquid electrolytes are used. Here we design and develop solvent-free solid polymer electrolytes (SPEs) based on a perfluoropolyether-terminated polyethylene oxide (PEO)-based block copolymer for safe and stable all-solid-state sodium metal batteries. Compared with traditional PEO SPEs, our results suggest that block copolymer design allows for the formation of self-assembled nanostructures leading to high storage modulus at elevated temperatures with the PEO domains providing transport channels even at high salt concentration (ethylene oxide/sodium = 8/2). Moreover, it is demonstrated that the incorporation of perfluoropolyether segments enhances the Na+ transference number of the electrolyte to 0.46 at 80 °C and enables a stable solid electrolyte interface. The new SPE exhibits highly stable symmetric cell-cycling performance at high current density (0.5 mA cm-2 and 1.0 mAh cm-2, up to 1,000 h). Finally, the assembled all-solid-state sodium metal batteries demonstrate outstanding capacity retention, long-term charge/discharge stability (Coulombic efficiency, 99.91%; >900 cycles with Na3V2(PO4)3 cathode) and good capability with high loading NaFePO4 cathode (>1 mAh cm-2).

Solution-Based One-Step Preparation of Three-Dimensional Self-Assembled Octadecyl Silica Nanosquare Plate and Microlamella Structures for Superhydrophobic and Icephobic Surfaces.

Icephobic surfaces have gained immense attention owing to their significant roles in decreasing the energy consumption of refrigerators and in improving safety issues by preventing the formation of ice on them. Superhydrophobic surfaces incorporating micro- or nanoscale roughness and hydrophobic functional groups have been shown to prevent ice accumulation. Herein, we report a simple, low-cost, and solution-based one-step process for the production of superhydrophobic surfaces with three-dimensional (3D) self-assembled structures. The controlled hydrolysis and polycondensation of n-octadecyltrichlorosilane (OTS-Cl) in an acetone solution produced a highly uniform superhydrophobic surface on various substrates such as glass, metals, and polymers without the limitation of the surface curvature structure. The as-prepared 3D self-assembled surface exhibited a very high contact angle of 161.7° and a low contact hysteresis of 1.47°. The solvent type, H2O content in acetone, and carbon chain length of the silane compound were critical in the formation of self-assembled nanostructures. The thickness of the superhydrophobic 3D self-assembled structure could be varied by controlling the surface properties of the glass substrate. In addition, a novel octadecyl silica nanosquare plate structure was formed as an intermediate for the microlamella structure. The water drop impact experiments on the 3D self-assembled superhydrophobic glass substrates at low temperatures (T < -25 °C) showed that the as-prepared superhydrophobic glass possessed a high impalement threshold for water contact, resulting in excellent and stable icephobic properties. The preparation method proposed in this study is scalable and can be used on a flat glass surface or in a glass vial inside a glass tube. Moreover, it can be applied to various substrates such as metals and polyurethane surfaces with curvature. Therefore, the solution-based self-assembly method proposed in this study is a promising approach to produce superhydrophobic and icephobic surfaces on a wide range of substrates regardless of their structure and properties.

Self-assembled nanostructures of phosphomolybdate, nucleobase and metal ions synthesis and their in vitro cytotoxicity studies on cancer cell lines.

The ability of the multidentate nucleobases, adenine and thymine, to coordinate polyoxometalate and metal ions leading to the formation of self-assembled nanostructures and their strong cytotoxicity toward cancer cell lines have been demonstrated. A unique synthetic approach is developed to make a series of functional nanoscale hybrid materials consisting of nucleobases (adenine and thymine) and phosphomolybdic acid (PMA) through solid state chemical reaction and self-assembly process. Adenine was protonated through its ring nitrogen, while the ketone group in thymine was protonated during the addition of PMA to these nucleobases. The self-assembled nanostructures formed as a result of the electrostatic interaction between the protonated nucleobases and polyanionic PMA. To promote the base pairing between the nucleobases, chloroaurate ions and silver ions were added to each PMA/adenine and PMA/thymine nanostructures. The complexation between the nucleobases and the added metal ions was found to drive the formation of subsequent self-assembled nanostructures. All the materials were screened for their anticancer activity against breast (MDAMB-231) and prostate (PC-3) cancer cells, and non-cancerous keratinocyte cells HaCaT. PMA/adenine/[AuCl4]- and PMA/thymine/Ag+ nanostructures were found to have strong anti-cancer activity, while PMA/adenine/Ag+, PMA/thymine/[AuCl4]-, and PMA/pdenine, PMA/thymine nanostructures did not exhibit such activity. The unique redox properties of these materials and the self-assembly of the PMA and metal ions were the major factors responsible for the cytotoxicity. This unique approach of making functional nanomaterials incorporate the nucleobase, PMA and metal ions using solid state self-assembly and their anti-cancer applications are considered to be an effective approach for the development of inorganic nucleoside analogue bio-pharmaceutical agents.

Design and application of gas cluster accelerator for surface smoothing and nanostructures formation

A custom-built gas cluster ion source with energy up to 50 keV is constructed, and Ar, CO&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;, and O&lt;sub&gt;2&lt;/sub&gt; are used as the working gases. The clusters are formed by a metal supersonic conical nozzle with critical diameter in a range of 65–135 μm and a cone angle of 14°. The nozzle is powered in the pulsed mode, which improves the pumping conditions, and also makes it possible to increase the gas pressure in the stagnation zone to 15 atm and thereby obtain larger clusters. Based on the principle of ultrasonic expansion, gas cluster ions with an average size of 3000 atoms are obtained. The cluster beam current of 50 μA is obtained. The Ar cluster beam, which is less reactive, is used for treating surface, namely, surface smoothing and formation of self-assembled nanostructures. The Ar cluster bombardment perpendicular to the surface of the substrate is used to demonstrate the smoothing of the surface of Si wafers, Ti coating, and Au film. For the initial Si wafer, its root-mean-square (RMS) roughness of 1.92 nm decreases down to 0.5 nm after cluster beam treatment. The cleaning effect of the cluster beam is also observed very well. The one-dimensional (1D) isotropic power spectral density of the Si surface topography before and after smoothing are also discussed. The off-normal irradiation Ar cluster beam is also used to form self-assembled surface nanoripple arrays on the surface of flat ZnO single crystal substrates. The ripple formation is observed when the incident angle of the cluster beam is in a range of 30°–60°. The process of nanoripple fabrication is significantly governed by the cluster beam incident angle, energy and dose. The nano-ripples formed on the flat substrates remain eolian sand ripples and their formation starts at the incident angle of 30°. The most developed nanoripples are observed at the incident angle within a range of 45°–60°. The surface morphology and characteristic distribution of the nano-structures on the flat ZnO substrate are also analyzed by the two-dimensional (2D) power spectral density function. Next, Ar cluster beam is used for irradiating the ZnO nanorod arrays grown on the Si substrate. Due to various angles between the nanorod’s axis and the substrate normal, the conditions of the ripple formation on the nanorod facets are also realized. The dependence of wavelength on the accelerating voltage of the cluster ions and the dose are studied. Similar dependence of wavelength on accelerating voltage and dose are found for nanorods. Comparing with the flat ZnO surface, nanoripples on the ZnO nanorod faces at high irradiation doses demonstrate an ordering effect, and morphology of the ripples resembles that of more parallel steps rather than eolian ripples.

Drug-Lipid Conjugates for Enhanced Oral Drug Delivery.

Oral drug delivery route is one of the most convenient and extensively utilised routes for drug administration. But there exists class of drugs which exhibit poor bioavailability on oral drug administration. Designing of drug-lipid conjugates (DLCs) is one of the rationale strategy utilised in overcoming this challenge. This review extensively covers the various dimensions of drug modification using lipids to attain improved oral drug delivery. DLCs help in improving oral delivery by providing benefits like improved permeability, stability in gastric environment, higher drug loading in carriers, formation of self-assembled nanostructures, etc. The clinical effectiveness of DLCs is highlighted from available marketed drug products along with many DLCs in phase of clinical trials. Conclusively, this drug modification strategy can potentially help in augmenting oral drug delivery in future.

Cyclic peptide-based nanostructures as efficient siRNA carriers

RNA interference shows a great strategy for biological studies; however, delivering of small interfering RNA (siRNA) remains challenging. Although several delivery vehicles, including cell-penetrating peptides, have been developed, their implementation is often restricted because of their endosomal entrapment. Herein, we report the formation of self-assembled nanostructures from rationally designed cyclic peptides and explore them for efficient delivery of functional biomacromolecules such as siRNA into mammalian cells. The newly obtained soft materials make stable complexes with siRNAs, thereby increasing their stability and deliver fluorescent labelled siRNA inside the cells as evident from confocal microscopy analysis. Flow cytometry analysis reveals that significant uptake of FAM-siRNA occurs in the presence of peptide nanostructures compared with siRNA alone. Peptide nanostructure-mediated delivery of very low concentration of siRNA causes significant knockdown of the target gene as observed at protein level by Western blot analysis, which is comparable to lipofectamine, commercially available transfection agent.

Self-assembled oligosaccharide-based block copolymers as charge-storage materials for memory devices

Over the past few years, extremely high charge-storage capacities of glucose-based oligo- or polysaccharides have been discovered that enables such materials to hold a great potential in electronics applications due to their abundant and renewable materials. Typically, the introduction of an α-glucan-containing polysaccharide into the dielectric layer of a transistor-type memory device causes excellent irreversible electron-capture properties; hence, a transistor device embedded with oligosaccharide maltoheptaose domains expresses write-once-read-many (WORM)-type behavior, which confirms that green materials can be used for advanced electronics. However, their irreversible WORM-type characteristics also restrict the application α-glucan-containing polysaccharides in high-performance electronic devices. Recent advances in oligosaccharide-based block copolymers through the inherent immiscibility of different polymer segments can enhance not only the formation of self-assembled nanostructures but also the switching of memory properties. Furthermore, supramolecular structures composed of oligosaccharide-based block copolymers and conjugated moieties can be developed into high-performance nonvolatile organic field-effect transistor (OFET) memory devices. This mini review presents an overview of the recent literature in oligosaccharide maltoheptaose-based block copolymers and their promising applications in organic memory devices.

Investigation of self-aggregation properties of amino functionalized zinc chlorins

Zinc chlorin derivatives consisting of primary, secondary and tertiary amine unit were prepared and their aggregation properties have been studied both in solution and in solid state in order to investigate the influence of the amine moiety on the formation of self-assembled nanostructures. The supramolecular organization ability of these derivatives have been investigated on the solid substrate, namely, highly oriented pyrolytic graphite (HOPG) by using AFM (atomic force microscopy) and STM (scanning tunneling microscopy) spectroscopy. The supramolecular organization of zinc chlorin derivatives in solution has been further supported by UV–vis spectroscopy. Zinc chlorins bearing primary, secondary amine exhibit well-ordered J-type aggregation in solution and well-defined self-organization on HOPG. On the other hand, the self-organization of tertiary amine substituted zinc chlorin both in solution and in solid state was less pronounced.

Supramolecular assembly of a phosphole-based moiety into nanostructures dictated by alkynylplatinum(ii) terpyridine complexes through non-covalent Pt···Pt and π-π stacking interactions: synthesis, characterization, photophysics and self-assembly behaviors.

A new class of platinum(ii) terpyridine complexes with a phosphole-derived bridging alkynyl ligand have been prepared. The X-ray crystal structure of complex 2 has been determined, and reveals a polymeric zig-zag chain structure with the existence of π-π stacking interactions. The photophysical properties have also been studied, with 3MLCT/3LLCT phosphorescence exhibited in degassed CH2Cl2; the energy of which is varied by the π-conjugation of the terpyridine ligands. The solvent-induced assembly of complex 1 has been studied. The incorporation of hydrophobic hydrocarbon chains has been shown to play an important role in assisting the formation of self-assembled nanostructures via Pt···Pt, π-π stacking and hydrophobic-hydrophobic interactions. It has been established that an isodesmic growth mechanism operates in polar media to give nanospheres, while fibrous networks originate from the self-assembly of the complexes in non-polar media, predominantly driven by π-π stacking interactions.

Formation of low-dimensional GaN on trenched Si(5 5 12), probed by STM and XPS

We report the formation of self-assembled nanostructures of GaN, with controlled size and shape on the trenched planar Si (5 5 12) surface. Adsorbing low coverages of Ga on Si (5 5 12) forms 1D arrays of Ga adatoms. The Ga adsorbed Si surface is annealed to 300 °C, which results in the formation of Ga 2D nanoparticles (NPs). These Ga NPs were exposed to various fluence of energetic 2 keV ions followed by annealing which yields GaN nanostructures self-assembled along the direction. These studies were performed in ultrahigh vacuum using in situ scanning tunneling microscopy and ex situ x-ray photoelectron spectroscopy, to observe the structural and chemical evolution of the interface.

Cholesterol-tethered AIEE fluorogens: formation of self-assembled nanostructures

Design and synthesis of cholesterol conjugated chromophores exhibiting intramolecular charge transfer (ICT) and Aggregation Induced Enhanced Emission (AIEE) and their self-assembling behavior is described.

Supramolecular Chemistry in the Formation of Self-Assembled Nanostructures from a High-Molecular-Weight Rod-Coil Block Copolymer.

The self-assembled nanostructures of a high-molecular-weight rod-coil block copolymer, poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS), in p-xylene are studied. The cylindrical micelles, long segmental cylindrical micelle associates, spherical micelles, and spherical micelle associates are observed with increased copolymer concentration. The high molecular weight of PS leads to the entanglement between PS chains from different micelles, which is the force for supramolecular interactions. Short cylindrical micelles are connected end-to-end via this supramolecular chemistry to form long segmental cylindrical micelle associates, analogue to the condensation polymerization process, with direction and saturation. On the other hand, spherical micelles assemble via supramolecular chemistry to form spherical micelle associates, yet without any direction due to their isotropic properties.

Self-assembled phthalocyanine derivatives on highly ordered pyrolytic graphite

A novel unsymmetrically substituted hydroxy-functionalized Zn ( II ) phthalocyanine (Pc) 1, bearing long aliphatic chains, namely, dodecyloxy units, has been designed and synthesized to investigate the influence of the terminal hydroxyl group on the formation of self-assembled nanostructures. The symmetric derivative, octadodecyloxy- Zn ( II ) Pc (2) has been also synthesized and used as reference compound for comparison purposes. The supramolecular organization of the Pcs has been carried out by spin-coating on a highly ordered pyrolytic graphite (HOPG) surface and has been investigated by atomic force microscopy (AFM) and scanning electron microscopy (STM). AFM and STM studies showed that unsymmetrically substituted hydroxy-functionalized Zn ( II ) Pc 1 gives rise to the formation of wire-like structures in different lengths from nanometer to micrometer scales, whereas in the case of the symmetrical Zn ( II ) Pc 2 the formation of the wires on HOPG was less pronounced.

Tuning of spectroscopic properties via variation of the alkyl chain length: a systematic study of molecular structural changes on self-assembly of amphiphilic sulfonate-pendant platinum(ii) bzimpy complexes in aqueous medium

A series of amphiphilic sulfonate-pendant platinum(II) bzimpy complexes with different lengths of alkyl chains on the alkynyl ligands has been found to show unusual absorption and emission behavior with changes to the length of the alkyl chain. The spectroscopic changes are found to be associated with the formation of self-assembled nanostructures and through the studies of their spectroscopic properties and aggregate morphology, further insights into the relationship between the molecular structures and their molecular packing are obtained.

Switchable Catalytic Activity: Selenium‐Containing Peptides with Redox‐Controllable Self‐Assembly Properties

Mimicking nature: The reversible formation of self-assembled nanostructures of selenium-containing peptides can be controlled by redox triggers (see scheme, VC = vitamin C). As a consequence, the catalytic activity of these peptides is switchable. These results should lead to the development of nature-mimicking smart materials with promising properties.

Self-Assembly in Tailor-Made Polyfluorenes: Synergistic Effect of Porous Spherical Morphology and FRET for Visual Sensing of Bilirubin

Two new fluorene-based homo- (PDP–PF) and copolymers (PDPPF-co-Ph) were synthesized with a bulky 3-pentadecylphenoxy (PDP) group appended hexyl chains at the 9, 9′ position using Suzuki coupling polymerization. Investigation on the morphology of the polymers using microscopic techniques like TEM and AFM indicated formation of self-assembled nanostructures like vesicles by PDP–PF and porous spheres by PDPPF-co-Ph respectively. Dynamic as well as static light scattering studies (DLS, SLS) in THF also indicated the existence of self-assembled nanosized particles in solution with a shape factor (ρ) of 0.76 and 0.96 for PDP–PF and PDPPF-co-Ph, respectively, confirming the existence of vesicles in the case of the former and spherical particles in the case of the latter polymer. The favorable photophysical properties of the polyfluorenes were taken advantage of for the selective sensing of unbound bilirubin (BR) in THF. A high energy transfer efficiency of 86% upon addition of bilirubin with color change from blue (polyfluorene emission) to green (FRET-induced bilirubin emission) was observed with PDPPF-co-Ph. Steady state fluorescence measurements gave a minimum donor–acceptor distance of 36 A0 and time-resolved fluorescence decay measurements showed a reduction in average lifetime of PDPPF-co-Ph (from 450 to 240 ps) upon addition of bilirubin indicating efficient energy transfer. The open porous spherical assembly of PDPPF-co-Ph enabled better adsorption of the analyte, which along with the good spectral overlap resulted in greater efficiency for FRET-induced energy transfer. Sensing of unbound bilirubin was also attempted in THF/water solvent mixture in an effort to simulate the unbound (THF soluble) and bound (water-soluble) bilirubin equilibrium. Enhancement of bilirubin emission coupled with quenching of polyfluorene emission makes this approach adaptable for visual fluorimetric color change (blue to green) based sensor. Structural analogues such as biliverdin and porphyrin showed poor fluorescence quenching efficiency, thus highlighting the selectivity and sensitivity of the FRET-based sensing of bilirubin by the newly designed polyfluorene.