Development of a series of cross-linking agents that effectively stabilize alpha-helical structures in various short peptides

A series of cross-linking agents of varying rigidity and length were designed to stabilize helical structures in short peptides and were then synthesized. The sequences of the short peptides employed in this study each include two X residues (X=Dap, Dab, Orn, and Lys) at the i/i+4, i/i+7, or i/i+11 positions to provide the sites for cross-linking. These peptides were subjected to reaction with the synthesized cross-linking agents, and the helical content of the resulting cross-linked peptides were analyzed in detail by circular dichroism. For each of the peptide classes we found combinations with the cross-linking agents suitable for the construction of stable helical structures up to >95 % helicity at 5 degrees C. Our method could also be applied to biologically related sequences seen in native proteins such as Rev.     

A novel tripodal ligand, tris[(4'-methyl-2,2'-bipyridyl-4-yl)methyl]carbinol and its trinuclear Ru(II)/Re(I) mixed-metal complexes: synthesis, emission properties, and photocatalytic CO2 reduction

A novel tripodal ligand, tris[(4'-methyl-2,2'-bipyridyl-4-yl)methyl]carbinol (L), has been synthesized. The spectroscopic, electrochemical, and photocatalytic properties of the new trinuclear complexes (Ru(2)Re and RuRe(2)) linked by the tripodal bridging ligand L are then investigated. In addition, 2-fold-improved photocatalytic activities were obtained in the case of these trinuclear complexes compared to the mixtures of the appropriate monometallic model complexes in the reduction of CO(2) under visible irradiation.     

Carbon doping into GaAs using combined ion beam and molecular beam epitaxy method

Carbon (C) doping by combined ion beam and molecular beam epitaxy (CIBMBE) was investigated. In this technique, mass-analyzed C ions (¹²C⁺) are accelerated at low energies of 30 to 1000 eV and are irradiated onto growing GaAs substrate. Doping concentration control in CIBMBE can be very stably accomplished by simply adjusting the ion beam current density, which is independent of growth conditions of host materials. Experiments on systematic variation of C⁺ ion acceleration energy (E_C+) indicated that, in the energy range of E_C+<170 eV, net hole concentration (|N_A-N_D|) increases slightly as E_C+ increases. The highest |N_A-N_D| is obtained at E_C+ = 170 eV under the constant C⁺ ion beam current density. For E_C+>170 eV, |N_A-N_D| decreases dramatically with increasing E_C+, which can be explained in terms of enhanced sputtering effect. Although no evidence of damages induced by ion irradiation is shown for low E_C+ range of ≤170 eV, trace of damages is apparently observed for E_C+>170 eV.     

Molecular Recognition Directed Self-Assembly of Supramolecular Architectures

This paper reviews some of our research on three classes of supra-molecular architectures which are generated via various combinations of molecular, macromolecular, and supramolecular chemistry. The ability of these supramolecular architectures to form liquid crystalline phases is determined by the shape of the self-assembled architecture and will be used to visualize it via various characterization techniques. The molecular design of selected examples of structural units containing taper-shaped exo-receptors and crown ether, oligooxyethylenic, and H-bonding based endo-receptors which self-assemble into cylindrical channel-like architectures via principles resembling those of tobacco mosaic virus (TMV), of macrocyclics which self-assemble into supramolecular rigid “rodlike” architectures and of hyperbranched polymers which self-assemble.into a willowlike architecture will be discussed. In the case of TMV-like supramolecular architectures, a comparison between various supramolecular(generated via H-bonding, ionic, and electrostatic interactions) and molecular “polymer backbones” will be made. The present state of the art of the engineering of these supramolecular architectures and some possible novel material functions derived from them will be briefly mentioned.     

X-ray photoelectron spectroscopic studies on oxidation behavior of nickel and iron aluminides under oxygen atmosphere at low pressures

Oxidation behaviors of NiAl, Ni₃Al, and FeAl under oxygen atmosphere at low pressures were studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these aluminides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa without exposing to air. The oxides formed on NiAl and FeAl surfaces were Al₂O₃, whereas the oxide on Ni₃Al was NiAl₂O₄. Aluminum, nickel, and iron on clean surfaces were oxidized even at a pressure of 1.3 × 10⁻⁶ Pa. The oxidation evolves with an increase in the pressure of oxygen, and further oxidation of aluminum occurs prior to that of nickel or iron. The oxidation behaviors under such oxygen atmosphere were similar to those of the aluminides oxidized in air, and these behaviors could be predicted from thermodynamic consideration.     

Versatile synthesis of fluorescent, cross-linked peptides as biological probes with the advantage of high helix content

A variety of fluorophores were introduced at the N-termini of short peptides for use as biological-probes. The fluorescent peptides were cross-linked with a diacetylenic cross-linking agent between the amino acid side chains of ornithine (Orn) residues to produce peptides with high helix content.     

Synthesis and Photochemical Properties of Covalently-Linked Dimers of Ruthenium(II) Tris (Bipyridine) Complex: Comparison with Ru(II)(bpy)2 (Poly-4-Methyl-4′-Vinylbipyridine)

Covalently linked dimers of Ru(bpy)₃ ²⁺ (3 and 4) connected by two or three carbon atoms were synthesized as models for Ru(bpy)₃ ²⁺-containing vinyl polymer (1). The luminescence properties of 3 and 4 were compared with those of its component monomer, 4,4′-dimethyl-2,2′-bipyridine-bis(2,2′-bipyridine)ruthenium(II) complex (2). In excited 3 and 4, intramolecular interaction leading to enhanced quenching was not observed. Electron-transfer quenching of the excited dimer with methylviologen (MV²⁺) and the zwitterionic viologen, 1,1′-bis(3-sulfopropyl)4,4′-bipyridinium (SPV), was studied and compared with that of 1 and 2. The low quenching efficiency in 1, 3, and 4 systems can be ascribed to the steric hindrance of unexcited ruthenium complex. Energy migration between ruthenium complexes in the excited 1, 3, and 4 can be ruled out from the kinetic evidence.     

Preparation and luminescence properties of tris(bipyridine) ruthenium(II)-containing vinyl polymers: Ru(bpy)2 (poly-6-vinyl-2,2′-bipyridine)Cl2 and Ru(bpy)2(poly-4-methyl-4′-vinyl-,2,2′-bipyridine)Cl2

Ruthenium (II) complex-containing polymers were prepared and characterized by absorption and luminescence spectra, luminescence quantum yield, and luminescence lifetime. The polymers are Ru(bpy)₂(poly-6-vinyl-2,′2-bipyridine)CI₂ ( 1 ) and Ru(bpy)₂(poly-4-methyl-4′-methyl-4′ -vinyl-2,2′-bipyridine)CI₂ ( 2 ). The absorption spectra and luminescence spectra of polymers 1 and 2 were substantially the same as that of Ru(bpy)₃CI₂. The lifetime of polymers 1 and 2 was similar to that of the respective monomer model compounds. The lifetime of polymer 1 was very short (ca. 13 ns) in comparison to Ru(bpy)₃CI₂ (660 ns), whereas the lifetime of polymer 2 (660 ns) was similar to that of Ru(bpy)₃CI₂. The temperature-dependency of the lifetime was discussed in terms of Watts' model.     

Effects of pressure on flame propagation in a premixture containing fine fuel droplets

Combustion experiments on fuel droplet–vapor–air mixtures have been performed with a rapid expansion apparatus which generates monodispersed droplet clouds with narrow diameter distribution using the condensation method. The effects of fine fuel droplets on flame propagation were investigated for ethanol droplet–vapor–air mixtures at various pressures from 0.2 to 1.0 MPa. A stagnant fuel droplet–vapor–air mixture, generated in a rapid expansion chamber, was ignited at the center of the chamber using an ignition wire. Spherical flame propagation under constant-pressure conditions was observed with a high-speed video camera and flame speed was measured. Total equivalence ratio, and the ratio of liquid fuel mass to total fuel mass, was varied from 0.6 to 1.4 and from zero to 56%, respectively. The mean droplet diameter of fuel droplet–vapor–air mixtures was set at 8.5 and 11 μm. It was found that the flame speed of droplet–vapor–air mixtures less than 0.9 in the total equivalence ratio exceeds that of premixed gases of the same total equivalence ratio at all pressures. The flame speed of fuel droplet–vapor–air mixtures decreases as the pressure increases in all total equivalence ratios. At large ratios of liquid fuel mass to total fuel mass, the normalized flame speed (the flame speed of droplet–vapor–air mixtures divided by the flame speed of the premixed gas with the same total equivalence ratio), increases with the increase in pressure for fuel-lean mixtures, and it decreases for fuel-rich mixtures. The outcome is reversed at small ratios of liquid fuel mass to total fuel mass; the normalized flame speed decreases with the increase in pressure for fuel-lean mixtures, and increases for fuel-rich mixtures. The results suggest that the increase in pressure promotes droplet evaporation in the preheat zone.