Biomedical subjects
Publications and source records attributed to Tsuyoshi Michinobu.
Monolayers of the cholesterol-armed cyclen Na+ complex at the air-water interface display a remarkable, surface pressure dependent enantioselectivity of amino acid recognition. Upon compression of the monolayer, the binding constants of amino acids increase accompanying an inversion of chiral selectivity from the d- to l-form in the case of valine.
Room temperature liquid C60 derivatives bearing a 2,4,6-trialkyloxyphenyl branch show a dramatic decrease in viscosity with an increase in the length of the alkyl chains. This feature, when combined with electrochemical activities similar to those of pristine C60 and relatively high charge carrier mobility, makes them an extremely attractive novel carbon material for future applications in materials science.
Fullerene derivatives bearing long alkyl chains epitaxially adsorb on the basal plane of graphite forming well-ordered one-dimensional lamellae. Within the lamellae, the C60 moieties are organized in a zigzag-type fashion. The ordering is mainly governed by the substitution pattern and chain length of the alkyl chains. The electrochemical activity of the C60 groups is fully maintained in the surface-confined assemblies.
A wide variety of monomeric and oligomeric, donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2+2] cycloaddition between tetracyanoethylene (TNCE) and donor-substituted alkynes, followed by electrocyclic ring opening of the initially formed cyclobutenes. Reaction yields are often nearly quantitative but can be affected by the electron-donating power and steric demands of the alkyne substituents. The intramolecular charge-transfer (CT) interactions between the donor and TCBD acceptor moieties were comprehensively investigated by X-ray crystallography, electrochemistry, UV-visible spectroscopy, and theoretical calculations. Despite the nonplanarity of the new chromophores, which have a substantial twist between the two dicyanovinyl planes, efficient intramolecular CT interactions are observed, and the crystal structures demonstrate a high quinoid character in strong donor substituents, such as N,N-dimethylanilino (DMA) rings. The maxima of the CT bands shift bathochromically upon reduction of the amount of conjugative coupling between strong donor and acceptor moieties. Each TCBD moiety undergoes two reversible, one-electron reduction steps. Thus, a tri-TCBD derivative with a 1,3,5-trisubstituted benzene core shows six reversible reduction steps within an exceptionally narrow potential range of 1.0 V. The first reduction potential E(red,1) is strongly influenced by the donor substitution: introduction of more donor moieties causes an increasingly twisted TCBD structure, a fact that results in the elevation of the LUMO level and, consequently, a more difficult first reduction. The potentials are also strongly influenced by the nature of the donor residues and the extent of donor-acceptor coupling. A careful comparison of electrochemical data and the correlation with UV-visible spectra made it possible to estimate unknown physical parameters such as the E(red,1) of unsubstituted TCBD (-0.31 V vs Fc+/Fc) as well as the maxima of highly broadened CT bands. Donor-substituted TCBDs are stable molecules and can be sublimed without decomposition. With their high third-order optical nonlinearities, as revealed in preliminary measurements, they should become interesting chromophores for ultra-thin film formation by vapor deposition techniques and have applications in opto-electronic devices.
For utilization of highly sophisticated functions of biomaterials in nano-scale functional systems, immobilization of biomaterials on artificial devices such as electrodes via thin film technology is one of the most powerful strategies. In this review, we focus on three major organic ultrathin films, self-assembled monolayers (SAM), Langmuir-Blodgett (LB) films, and layer-by-layer (LBL) assemblies, and from the viewpoints of biomaterial immobilization, typical examples and recent progresses in these film technologies are described. The SAM method allows facile contact between biomaterials and man-made devices, and well used for bio-related sensors. In addition, recent micro-fabrication techniques such as micro-contact printing and dip-pen nanolithography were successfully applied to preparation of biomaterial patterning. A monolayer at the air-water interface, which is a unit structure of LB films, provides a unique environment for recognition of aqueous biomaterials. Recognition and immobilization of various biomaterials including nucleotides, nucleic acid bases, amino acids, sugars, and peptides were widely investigated. The LB film can be also used for immobilization of enzymes in an ultrathin film on an electrode, resulting in sensor application. The LBL assembling method is available for wide range of biomaterials and provides great freedom in designs of layered structures. These advantages are reflected in preparation of thin-film bio-reactors where multiple kinds of enzymes sequentially operate. LBL assemblies were also utilized for sensors and drug delivery systems. This kind of assembling structures can be prepared on micro-size particle and very useful for preparation of hollow capsules with biological functions.
We investigated the third-order nonlinear optical properties of several donor-substituted cyanoethynylethene molecules in the zero-frequency limit. We observed nonlinearities that are extraordinarily large relative to the small molecular mass of these molecules and that are within a factor of 50 from the fundamental limit. At a wavelength of 1.5 microm, the rotational average of the third-order molecular polarizability is 53 +/- 13 x 10(-48) m5 V(-2) (3.8 x 10(-33) esu) for the best molecule, which corresponds to 1.7 x 10(-48) m5 V(-2) per delocalized electron. The high nonlinear efficiency of these molecules is due to the compact two-dimensional conjugated system and the effective donor-acceptor substitution patterns.
Self-assembly of a fullerene derivative with long alkyl chains in different solvents results in the formation of hierarchically-ordered supramolecular assemblies with well-defined 1, 2 and 3D architectures such as vesicles, fibers, discs and cones, whose fundamental structural sub-unit consists of bilayers.
Donor-acceptor molecules with 4-(dimethylamino)phenyl donor and 1,1,4,4-tetracyanobuta-1,3-diene acceptor moieties are readily prepared by short, high-yielding routes. The quite small chromophores are characterised by X-ray crystallography and feature intense intramolecular charge-transfer bands, substantial quinoid character in the donor rings, reversible electrochemical reductions and oxidations and powerful third-order optical nonlinearities.
[structure: see text] High molecular weight and networked aromatic polyamines prepared by palladium-catalyzed polycondensation were oxidized to yield the corresponding poly(aminium cationic radical)s, which displayed a substantial stability and an intramolecular ferromagnetic interaction of eight or nine spins.