Ken Okamoto

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.

Micrometer-level naked-eye detection of caesium particulates in the solid state

Abstract Large amounts of radioactive material were released from the Fukushima Daiichi nuclear plant in Japan, contaminating the local environment. During the early stages of such nuclear accidents, iodine I-131 (half-life 8.02 d) is usually detectable in the surrounding atmosphere and bodies of water. On the other hand, in the long-term, soil and water contamination by Cs-137, which has a half-life of 30.17 years, is a serious problem. In Japan, the government is planning and carrying out radioactive decontamination operations not only with public agencies but also non-governmental organizations, making radiation measurements within Japan. If caesium (also radiocaesium) could be detected by the naked eye then its environmental remediation would be facilitated. Supramolecular material approaches, such as host–guest chemistry, are useful in the design of high-resolution molecular sensors and can be used to convert molecular-recognition processes into optical signals. In this work, we have developed molecular materials (here, phenols) as an optical probe for caesium cation-containing particles with implementation based on simple spray-on reagents and a commonly available fluorescent lamp for naked-eye detection in the solid state. This chemical optical probe provides a higher spatial resolution than existing radioscopes and gamma-ray cameras.

Diverse Self-Assembly in Soluble Oligoazaacenes: A Microscopy Study†

The synthesis and morphologies of self-assembled aggregates of novel oligoazapentacene 2 and oligoazaheptacene 3 derivatives are reported. Double nucleophilic substitution on 2,3-dicyano-[h,j]-dibenzo-1,4,5,10-tetrazaanthracene 4 gives the corresponding dihydro-oligoacene derivatives, which were then N-alkylated using n-dodecyl bromide to yield self-assembling acene molecules. 2 and 3 self-assemble in solution, leading to a variety of aggregated structures including rolled-up sheets, foams, and fibrous structures reminiscent of organogels. These structures are of substantial interest because of their potential electronic properties and because individual fibers can be exfoliated. Structures of the aggregates are discussed. Additionally, the crystal structure of precursor 4 is reported because it gives information regarding the intermolecular interactions (hydrogen bonding and intermolecular stacking) in similar compounds. Crystal data for 4: space group P2(1)/n, a = 9.3164(17) angstroms, b = 7.0649(13) angstroms, c = 23.684(4) angstroms, alpha = 90.00 degrees, beta = 99.945(3) degrees, gamma = 90.00 degrees, and V = 1535.4(5) angstroms3.

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.

Detection of ethanol in alcoholic beverages or vapor phase using fluorescent molecules embedded in a nanofibrous polymer.

An alcohol sensor was developed using the solid-state fluorescence emission of terphenyl-ol (TPhOH) derivatives. Admixtures of TPhOH and sodium carbonate exhibited bright sky-blue fluorescence in the solid state upon addition of small quantities of ethanol. A series of terphenol derivatives was synthesized, and the effects of solvent polarities and the structures of these π-conjugated systems on their fluorescence were systematically investigated by using fluorescence spectroscopy. In particular, π-extended TPhOHs and TPhOHs containing electron-withdrawing groups exhibited significant solvatochromism, and fluorescence colors varied from blue to red. Detection of ethanol contents in alcohol beverages (detection limit ∼ 5 v/v %) was demonstrated using different TPhOHs revealing the effect of molecular structure on sensing properties. Ethanol contents in alcoholic beverages could be estimated from the intensity of the fluorescence elicited from the TPhOHs. Moreover, when terphenol and Na2CO3 were combined with a water-absorbent polymer, ethanol could be detected at lower concentrations. Detection of ethanol vapor (8 v/v % in air) was also accomplished using a nanofibrous polymer scaffold as the immobilized sensing film.

Self-Assembly of Optical Molecules with Supramolecular Concepts

Fabrication of nano-sized objects is one of the most important issues in nanoscience and nanotechnology. Soft nanomaterials with flexible properties have been given much attention and can be obtained through bottom-up processing from functional molecules, where self-assembly based on supramolecular chemistry and designed assembly have become crucial processes and techniques. Among the various functional molecules, dyes have become important materials in certain areas of nanotechnology and their self-assembling behaviors have been actively researched. In this short review, we briefly introduce recent progress in self-assembly of optical molecules and dyes, based mainly on supramolecular concepts. The introduced examples are classified into four categories: self-assembly of (i) low-molecular-weight dyes and (ii) polymeric dyes and dye self-assembly (iii) in nanoscale architectures and (iv) at surfaces.

Studies on Langmuir monolayers of polyprenyl phosphates towards a possible scenario for origin of life.

Although some biological components such as RNA are believed to play a crucial role in the processes which led to the formation of the first living systems, we cannot ignore the importance of lipids in the genesis of cell membranes. To answer the fundamental question of what the oldest cell-forming components were the Ourisson/Nakatani group has extensively investigated the origin of lipids and they have proposed polyprenyl phosphates and related molecules as plausible candidates for precursors of modern lipids. These molecules have been demonstrated as being capable of forming vesicle structures, and this feature has been extended to preparation of Langmuir monolayers of polyprenyl phosphates in collaboration with the Ourisson/Nakatani group. In this review, after a brief outline of chemical evolution of cell components, we summarize research on Langmuir monolayers of polyprenyl phosphates and related molecules. Two topics are described: the evaluation of any reinforcing effects and the determination of interfacial acid dissociation. Rules governing reinforcing effects in molecular structures and unusual shifts of acid dissociation constants at interfaces were established. Finally, we propose a revised possible scenario of how the first cell-like membranes formed based on the former results.

Multicolour Fluorescent Memory Based on the Interaction of Hydroxy Terphenyls with Fluoride Anions

Memory operations based on variation of a molecules properties are important because they may lead to device miniaturization to the molecular scale or increasingly complex information processing protocols beyond the binary level. Molecular memory also introduces possibilities related to information-storage security where chemical information (or reagents) might be used as an encryption key, in this case, acidic/basic reagents. Chemical memory that possesses both volatile and non-volatile functionality requires reversible conversion between at least two chemically different stable or quasi-stable states. Here we have developed the phenol-phenoxide equilibrium of phenol fluorophores as a data storage element, which can be used to write or modulate data using chemical reagents. The properties of this system allow data to be stored and erased either in non-volatile or volatile modes. We also demonstrate non-binary switching of states made possible by preparation ofxa0 a composite containing the molecular memory elements.