Keita Sakakibara

Natural Tubule Clay Template Synthesis of Silver Nanorods for Antibacterial Composite Coating

Halloysite is naturally available clay mineral with hollow cylindrical geometry and it is available in thousands of tons. Silver nanorods were synthesized inside the lumen of the halloysite by thermal decomposition of the silver acetate, which was loaded into halloysite from an aqueous solution by vacuum cycling. Images of individual ca. 15 nm diameter silver nanorods and nanoparticles were observed with TEM. The presence of silver inside the tubes was also verified with STEM-EDX elemental mapping. Nanorods had crystalline nature with [111] axis oriented ~68° from the halloysite tubule main axis. The composite of silver nanorods encased in clay tubes with the polymer paint was prepared, and the coating antimicrobial activity combined with tensile strength increase was demonstrated. Coating containing up 5% silver loaded halloysite did not change color after light exposure contrary to the sample prepared with loading with unshelled silver nanoparticles. Halloysite tube templates have a potential for scalable manufacturing of ceramic encapsulated metal nanorods for composite materials.

Thin-film-based nanoarchitectures for soft matter: controlled assemblies into two-dimensional worlds.

Controlling the organization of molecular building blocks at the nanometer level is of utmost importance, not only from the viewpoint of scientific curiosity, but also for the development of next-generation organic devices with electrical, optical, chemical, or biological functions. Self-assembly offers great potential for the manufacture of nanoarchitectures (nanostructures and nanopatterns) over large areas by using low-energy and inexpensive spontaneous processes. However, self-assembled structures in 3D media, such as solutions or solids, are not easily incorporated into current device-oriented nanotechnology. The scope of this review is therefore to introduce the expanding methodology for the construction of thin-film-based nanoarchitectures on solid surfaces and to try to address a general concept with emphasis on the availability of dynamic interfaces for the creation and manipulation of nanoarchitectures. In this review, the strategies for the construction of nanostructures, the control and manipulation of nanopatterns, and the application of nanoarchitectures are described; the construction strategies are categorized into three classes: i) π-conjugated molecular assembly in two dimensions, ii) bio-directed molecular assembly on surfaces, and iii) recent thin-film preparation technologies.

Aligned 1-D nanorods of a π-gelator exhibit molecular orientation and excitation energy transport different from entangled fiber networks.

Linear π-gelators self-assemble into entangled fibers in which the molecules are arranged perpendicular to the fiber long axis. However, orientation of gelator molecules in a direction parallel to the long axes of the one-dimensional (1-D) structures remains challenging. Herein we demonstrate that, at the air-water interface, an oligo(p-phenylenevinylene)-derived π-gelator forms aligned nanorods of 340 ± 120 nm length and 34 ± 5 nm width, in which the gelator molecules are reoriented parallel to the long axis of the rods. The orientation change of the molecules results in distinct excited-state properties upon local photoexcitation, as evidenced by near-field scanning optical microscopy. A detailed understanding of the mechanism by which excitation energy migrates through these 1-D molecular assemblies might help in the design of supramolecular structures with improved charge-transport properties.

A Mechanically Controlled Indicator Displacement Assay

Detection and quantification of biologically active analytes is of paramount importance. These substances, whether therapeutic or harmful, are routinely evaluated for a range of properties, such as pharmaceutical activity and chemical toxicity. Such analyses are routinely performed in a variety of scientific disciplines, including drug discovery, environmental pollution monitoring, medical testing, and food safety evaluation. To this end, many studies aim to control the selectivity of a binding event such that the energy of binding between a receptor and an analyte is maximized. To translate binding into detection and quantification, colorimetric or fluorescent molecular sensors are regarded as a very promising approach. One sensing strategy is the indicator displacement assay (IDA). This approach uses a competitive binding event, between an indicator and a guest, to a complimentary site on a host. This method allows the determination of total guest (or analyte) concentration accurately, leading to the broad use of this approach for developing multicomponent optical sensors and enantioselective assays. To further develop the IDA strategy, we sought methods to increase the binding between host and guest molecules. The high effective concentration observed for molecular interfaces allows accentuated binding events, as compared to similar solution-based studies. The binding that occurs between a host in one layer and a guest in another layer provides a conceptual mimic to the binding that occurs in living cells. One promising interfacial sensing environment is the air– water interface. Here, the position between the host and guest in the two-phase boundary facilitates and enhances binding. Furthermore, a variety of monolayer assemblies have been prepared in an attempt to facilitate molecular recognition of biologically important substances. One of the more promising strategies is mechanically controlled molecular recognition at interfaces, which enables facile control of molecular conformation. This control has allowed for reversible capture and release of guests, enantioselective binding of amino acids, and discrimination of nucleobases differing only by a single methyl group, all by using a simple and versatile stimulus, namely mechanical force. Herein, we introduce what we call a mechanically controlled indicator displacement assay (MC-IDA). This strategy utilizes a deformable monolayer assembly of fluorescently tagged host molecules formed at the air–water interface. This monolayer acts as a mechanically controllable signal-emission unit. External compression and expansion of monolayers in lateral directions can alter molecular conformations, resulting in control of molecular recognition (Scheme 1). We demonstrate that the fluorescent signaling between a host and an indicator can be switched on by surface compression, and the displacement of this indicator in response to an analyte can be enhanced to give very sensitive molecular sensing. The goal of the present study was to demonstrate the application of mechanically controlled molecular recognition at interfaces to create novel applications of the IDA. For this task, we designed and synthesized an amphiphilic dilysine peptide host 1 (Figure 1a; see the Supporting Information for details of the synthesis). The host was designed to contain three important motifs: a phenylboronic acid, a cholesterol moiety, and a carboxyfluorescein indicator at the N-terminus of the peptide. The phenylboronic acid was chosen because it allows for reversible covalent bond formation with vicinal diols, as found in carbohydrates, glycopeptides, and ahydroxycarboxylic acids. The cholesterol group provides a hydrophobic functionality, imparting compatibility with organic media. The carboxyfluorescein was chosen as a fluo-

Langmuir Nanoarchitectonics: One-Touch Fabrication of Regularly Sized Nanodisks at the Air–Water Interface

In this article, we propose a novel methodology for the formation of monodisperse regularly sized disks of several nanometer thickness and with diameters of less than 100 nm using Langmuir monolayers as fabrication media. An amphiphilic triimide, tri-n-dodecylmellitic triimide (1), was spread as a monolayer at the air-water interface with a water-soluble macrocyclic oligoamine, 1,4,7,10-tetraazacyclododecane (cyclen), in the subphase. The imide moieties of 1 act as hydrogen bond acceptors and can interact weakly with the secondary amine moieties of cyclen as hydrogen bond donors. The monolayer behavior of 1 was investigated through π-A isotherm measurements and Brewster angle microscopy (BAM). The presence of cyclen in the subphase significantly shifted isotherms and induced the formation of starfish-like microstructures. Transferred monolayers on solid supports were analyzed by reflection absorption FT-IR (FT-IR-RAS) spectroscopy and atomic force microscopy (AFM). The Langmuir monolayer transferred onto freshly cleaved mica by a surface touching (i.e., Langmuir-Schaefer) method contained disk-shaped objects with a defined height of ca. 3 nm and tunable diameter in the tens of nanometers range. Several structural parameters such as the disk height, molecular aggregation numbers in disk units, and 2D disk density per unit surface area are further discussed on the basis of AFM observations together with aggregate structure estimation and thermodynamic calculations. It should be emphasized that these well-defined structures are produced through simple routine procedures such as solution spreading, mechanical compression, and touching a substrate at the surface. The controlled formation of defined nanostructures through easy macroscopic processes should lead to unique approaches for economical, energy-efficient nanofabrication.

Mechanical tuning of molecular machines for nucleotide recognition at the air-water interface

Molecular machines embedded in a Langmuir monolayer at the air-water interface can be operated by application of lateral pressure. As part of the challenge associated with versatile sensing of biologically important substances, we here demonstrate discrimination of nucleotides by applying a cholesterol-armed-triazacyclononane host molecule. This molecular machine can discriminate ribonucleotides based on a twofold to tenfold difference in binding constants under optimized conditions including accompanying ions in the subphase and lateral surface pressures of its Langmuir monolayer. The concept of mechanical tuning of the host structure for optimization of molecular recognition should become a novel methodology in bio-related nanotechnology as an alternative to traditional strategies based on increasingly complex and inconvenient molecular design strategies.

Surface Engineering of Cellulose Nanofiber by Adsorption of Diblock Copolymer Dispersant for Green Nanocomposite Materials

An effective approach for the dispersion of hydrophilic cellulose nanofiber (CNF) in hydrophobic high-density polyethylene (HDPE) is presented using adsorption of a diblock copolymer dispersant. The dispersant consists of both resin compatible poly(lauryl methacrylate) (PLMA) and cellulose interactive poly(2-hydroxyethyl methacrylate) blocks. The PLMA-adsorbed CNFs are characterized by FT-IR and contact angle measurement, revealing successful hydrophobization. X-ray CT imaging shows there are apparently less CNF aggregates in the nanocomposites if adding amount of the dispersant was enough. The good dispersion results in a high mechanical reinforcement, corresponding to 140% higher Youngs modulus and 84% higher tensile strength than the neat HDPE. This approach is broadly applicable and allows for easy manufacturing process for strong and lightweight CNF-reinforced nanocomposite materials.

Polythiophene-cellulose composites: synthesis, optical properties and homogeneous oxidative co-polymerization

Abstract Composites of cellulose and conjugated polymers based on oligo- and polythiophene are reported, inspired by the assembly of cellulose and lignin in wood as a composite that survives harsh environmental conditions and meets most complex demands. The regioselectively oligothiophene-substituted cellulose derivatives were synthesized according to a protecting group strategy and used to prepare the polythiophene-cellulose composites through a FeCl3-initiated oxidative co-polymerization with thiophene co-monomers. The optical property of the cellulose derivatives with mono-, bi- and terthiophene moieties at the C-6 position was investigated with ultraviolet-visible (UV-Vis) and circular dichroism (CD) spectroscopy. The UV-Vis absorption spectra exhibited a broad band reflecting the intense π-π* transition within the conjugated oligothiophene side chains, which were greater than those of the corresponding reference monomers owing to their intermolecular π-electron interactions, even in solution. This was also supported by the negative CD band, indicative of cellulosic supramolecular stacking structures in solution. The soluble polythiophene-cellulose composites were prepared by the oxidative co-polymerization of the oligothiophene substituted celluloses with excess 3-hexylthiophene in the presence of FeCl3 as the oxidative initiator. The supplied amount of thiophene co-monomer was crucial for producing large π-conjugated structures and a cross-linked network structure. The soluble composites, with properties, such as electric conductivity, semiconductivity, or photoelectroactivity, were applied for the preparation of thin films which will have to be optimized for the respective application.

Dynamic supramolecular systems at interfaces

Nanotechnology from a bottom-up approach relies heavily on supramolecular chemistry that can potentially provide nano- and microstructures with molecular level precision of internal configurations through low-energy spontaneous processes. Moreover, supramolecular assemblies at the two-dimensional interface have great potential to be integrated into artificial devices. Studies on supramolecular chemistry at interfaces are, therefore, highly relevant for the development of nanotechnology. Another distinct aspect of supermolecules exists in their advanced dynamic properties that are anticipated to provide various stimuli-responsive systems. Here, we summarise the recent literature describing the dynamic behaviours of supermolecules at interfaces and supramolecular chemistry at dynamic interfaces categorised into three classes: (i) dynamic behaviour at solid surfaces, (ii) supermolecules at dynamic interfaces in liquid media and (iii) supermolecules at the air–water interface.

Light-Harvesting Nanorods Based on Pheophorbide-Appending Cellulose

In contrast to the success in artificial DNA- and peptide-based nanostructures, the ability of polysaccharides to self-assemble into one-, two-, and three-dimensional nanostructures are limited. Here, we describe a strategy for designing and fabricating nanorods using a regioselectively functionalized cellulose derivative at the air-water interface in a stepwise manner. A semisynthetic chlorophyll derivative, pyro-pheophorbide a, was partially introduced into the C-6 position of the cellulose backbone for the design of materials with specific optical properties. Remarkably, controlled formation of cellulose nanorods can be achieved, producing light-harvesting nanorods that display a larger bathochromic shift than their solution counterparts. The results presented here demonstrate that the self-assembly of functionalized polysaccharides on surfaces could lead the nanostructures mimicking the naturally occurring chloroplasts.