Hiroto Murakami

Noncovalent porphyrin-functionalized single-walled carbon nanotubes in solution and the formation of porphyrin–nanotube nanocomposites

Abstract Porphyrins are functional dyes with a variety of unique physical (photophysical), chemical and biological properties. We report on the first finding that porphyrin molecules dissolve single-walled carbon nanotubes (SWNTs) in organic solutions and that the SWNTs–porphyrin hybrid nanomaterials can be separated from the solutions. Atomic force microscope investigation revealed that both individually dissolved nanotubes and bundled nanotubes coexisted in the solution. The solid purified SWNTs (p-SWNTs)–porphyrin nanomaterials were readily separated from the p-SWNTs–porphyrin solution, and this nanomaterial was re-dissolvable in DMF. Measurements of its fluorescence spectrum gave evidence for the interaction between the nanotube sidewall and porphyrin molecules in solution.

Molecular bilayer-based superstructures of a fullerene-carrying ammonium amphiphile: structure and electrochemistry.

The synthesis of a water-soluble C60-carrying single-chain ammonium amphiphile, 10- (N-methyl-2-fulleropyrrolidyl)decyltrimethylammonium bromide (1) as well as the characterization of aqueous solutions and cast films of 1 are described. X-ray diffraction study suggests that cast films of 1 form a multilayer structure based on biomembrane-like molecular bilayers. Electron microscopy has revealed that 1 produces both fibrous and disk-like aggregates with 10-12 nm of thickness through self-organization of 1 in aqueous solution. Differential scanning calorimetry, dynamic light scattering, FTIR, and UV-visible absorption studies were also carried out to characterize aqueous solutions and cast films of 1. Electrochemistry for an aqueous solution and for cast films of just 1 and 1 incorporated in lipid films on electrodes was conducted. It was found that films of just 1 and of 1/lipid cast on electrodes showed electron transfer reactions leading to the generation of the fullerene dianion or trianion. In contrast, electrochemistry of aqueous solution of 1 at a bare electrode gives a cathodic current near -0.5 to -0.6 V against SCE; however, an anodic current for the solution did not appear.

A Fullerene/Lipid Electrode Device: Reversible Electron Transfer Reaction of C60 Embedded in a Cast Film of an Artificial Ammonium Lipid on an Electrode in Aqueous Solution

Two reversible one-electron transfers are observed for an electrode device made from C60 and an artificial lipid (see schematic drawing). Cyclic voltammetric studies reveal that the redox couples are unchanged even after 50 cycles, thus indicating that the C60 radical monoanion and the C60 dianion generated in aqueous solution are very stable.

Noncovalent porphyrin-functionalized single-walled carbon nanotubes: solubilization and spectral behaviors

We describe the solubilization/dispersion of as-produced and purified single-walled carbon nanotubes (raw-SWNTs and p-SWNTs) with protoporphyrin IX derivatives and tetraphenylporphyrin iron(III) chloride, the spectral behavior of the octaalkylporphyrins-solubilized shortened-SWNTs (s-SWNTs), and the electrochemistry of a p-SWNTs/FePP cast film on a glassy carbon electrode. Transmission electron and atomic force microscopies, as well as UV-visible-near IR spectroscopy, revealed that the protoporphyrin IX derivatives individually dissolved the p-SWNTs in polar solvents under mild conditions of sonication using a bath-type sonicator, followed by centrifugation at 1000 g. The raw-SWNTs were more easily dissolved than the p-SWNTs with protoporphyrin IX zinc(II) (ZnPP), whereas the amount of the solubilized/dispersed p-SWNTs did not depend on the concentration of the solubilizer and sonication time. The absorption and fluorescence spectral measurements of the octaalkylporphyrins in dimethylformamide containing 1 vol% tetrahydrofuran with various amounts of the s-SWNTs showed that the absorption maxima of the octaalkylporphyrins decreased with an increase in the concentration of the s-SWNTs without wavelength shift and the fluorescence of the porphyrins was quenched by the addition of the s-SWNTs. These spectral behaviors are direct evidence for the interaction between the nanotube sidewall and the porphyrins in the solutions. The cyclic voltammograms of the p-SWNTs/hemin (FePP) and free hemin (FePP) suggest that the nanotubes act as a conduction passage for electrons between hemin (FePP) and the glassy carbon electrode.

Design and Synthesis of Cyclodextrin-Based Rotaxanes and Polyrotaxanes

Rotaxanes are compounds in which a ring is threaded by a chain having bulky terminal cap groups. In this article, we review the design, synthesis and characterization of rotaxanes and polyrotaxanes of cyclodextrins threaded by an alkyl chain or a poly(ethylene glycol) as well as the synthesis of a light-driven molecular shuttle based on a cyclodextrin-rotaxane.

Electrochemical fabrication of single-walled carbon nanotubes–DNA complexes by poly(ethylenedioxythiophene) and photocurrent generation by excitation of an intercalated chromophore

It was found that single-walled carbon nanotubes (SWNTs) solubilized into water by complexation with DNA (salmon testes) can be readily deposited on the ITO electrode by electrochemical oxidative polymerization of ethylenedioxythiophene (EDOT). The driving force for this novel deposition is an electrostatic interaction between the anionic charges of wrapping DNA and the cationic charges of poly(EDOT) formed in the oxidative polymerization process. The presence of poly(EDOT), SWNTs and DNA in the composite was confirmed by measurements of UV-Vis, IR, resonance Raman spectra, cyclic voltammetry (CV) and confocal laser scanning microscopy (CLSM). The composite adsorbed a DNA intercalator (ethidium bromide: EB) very efficiently, which is regarded to be further evidence for inclusion of DNA. The surface morphology, characterized by CLSM, SEM and AFM, featured the network structure consisting of 0.5-ca. 10 microm nanorods. Very interestingly, we found that photoexcitation of EB bound to the DNA generates the photocurrent, indicating that the excited energy of EB is injected into SWNTs, which is collected by the electroconductive poly(EDOT) film on the ITO electrode. We believe, therefore, that the present system is a very convenient method to explore new materials related to redox and photochemical functions.

Metal-induced conversion of a ‘closed’ receptor to an ‘open’ receptor on a p-tert-butylcalix[4]arene diamide derivative; fluorescence detection of a molecular recognition process

Molecular receptors, which change from a ‘closed’ form with intramolecular hydrogen bonds to an ‘open’ form with intermolecular hydrogen bonds with a pteridine guest upon Na+-binding designed on a calix[4]arene platform are described; the conversion process is monitored easily by a fluorescence change in a flavin guest.

Sugar sensing utilizing aggregation properties of boronic-acid-appended porphyrins and metalloporphyrins

It has been shown that saccharides in water can be sensitively detected by a boronic-acid-appended porphyrin (1) and its metal complexes (2M2+). The idea is based on the phenomenon that absorption and fluorescence spectra of porphyrins change sensitively in response to a shift in the aggregation–deaggregation equilibrium and that the self-association of saccharides with boronic acids in water affects this equilibrium. Among four monosaccharides tested in detail, the spectral change occurs in the order D-fructose > D-arabinose > D-mannose > D-glucose. In 2M2+ the saccharide-binding process is detectable visually through the colour change. The saccharide-induced fluorescence changes are very large because 1 and 2M2+ aggregates are almost non-fluorescent whereas monomeric 1 and 2M2+ generated by saccharide-binding are strongly fluorescent. This is a novel method for sugar sensing, useful in an aqueous system.

Catalytic reduction of organohalides at hemin and hemin–imidazole polymer films on pyrolytic graphite electrodes

Abstract The electrochemical properties of cast films of hemin-dioctadecyldimethylammonium bromide and a hemin–imidazole complex polymer, HmP, on basal plane pyrolytic graphite (BPG) electrodes were investigated and compared to those previously reported at a hemin cast (or adsorbed) film on a BPG electrode and at a HmP-modified edge plane pyrolytic graphite electrode. By means of four different electrodes, modified with cast (or adsorbed) films of hemin, hemin-dioctadecyldimethylammonium bromide and HmP, as well as of adsorbed hemin film on BPG electrodes, we explored the possibility of the catalytic reduction of organohalides including trichloroacetic acid, dichloroacetic acid, dichloroacetonitrile, dichloroacetone, chloral hydride, monochloroacetic acid, trichloroethanol, tetrachloroethylene, 1,1,1-trichloroethane, chloroform and 1,1,1-trichloroethane. It was found that all of these electrodes reduce trichloroacetic acid, dichloroacetic acid, dichloroacetonitrile, dichloroacetone and chloral hydride catalytically. Among the four modified electrodes, the efficiency of the catalytic reduction is the highest at the HmP-modified electrode.

Synthesis and optical resolution of an asymmetrically substituted calix[4]arene

A cone-shaped, asymmetrically substituted calix[4]arene, 1, has been synthesized and successfully optically resolved for the first time.