Reactions of 2-Pyridyl Substituted Phosphine Oxides and Phosphonium Salts with Organometallic Reagents and in Aqueous Media

Phosphine oxides bearing two or three 2-pyridyl groups react with organometallic reagents affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2-pyridyl or substituted 2-pyridyl groups also give the corresponding 2,2′-bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′-bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.     

Preparation of the TiO2 Thin Film Photocatalyst by the Dip-Coating Process

Titanium dioxide (TiO2) coated glass-plate thin film photocatalysts for elimination of air pollutants, were prepared by the dip-coating process with titanium alkoxide including polyethylene glycol (PEG). The surface structure of these thin films changed drastically with the size of the PEG. They were either transparent or opaque. Nitrogen oxides (NOx), one of the most hazardous of air pollutants, were found to be efficiently eliminated by the thin film photocatalyst. The photocatalytic activities of the transparent and opaque thin films were found to be almost equal. This may be due to the two films having the same surface area. The highest activity was obtained for thin films around 1 m.     

Does B3LYP correctly describe magnetism of manganese complexes with various oxidation numbers and various structural motifs?

We assessed the applicability and basis set dependency of the B3LYP functional to investigate magnetic interactions of Mn complexes. For the purpose, we constructed a test set consisting of 16 Mn complexes with various oxidation states and structural motifs.The B3LYP results correctly reproduced magnetism and magneto–redox correlation of the standard μ-oxo motifs with superexchange paths, while it does not work for weak magnetic complexes. We also showed that a modest basis set yields results similar to those of triple-zeta plus diffuse-and-polarization functions. This basis set is expected to be a standard basis set for investigating magnetism of manganese complexes.     

Optical properties of organic-inorganic hybrid films prepared by the two-step growth process

Thin films of microcrystalline (C₈H₁₇NH₃)₂PbBr₄ have been prepared by the two-step growth process as follows: (1) precipitation of nanometer-sized PbBr₂ particles on substrates by vapor deposition and then (2) growth of (C₈H₁₇NH₃)₂PbBr₄ films by exposing PbBr₂ particles to C₈H₁₇NH₃Br vapor. Atomic force microscope observations reveal that the substrate is fully covered with nanometer-sized rodlike precipitates. X-ray diffraction studies suggest that (C₈H₁₇NH₃)₂PbBr₄ films are found to be microcrystalline form, single phase and highly oriented with the c-axis perpendicular to the substrate surface. (C₈H₁₇NH₃)₂PbBr₄ films show a clear exciton absorption and free-exciton emission even at room temperature. At low temperatures below 40 K, the emission band separates into three bands at 3.07 (A-band), 3.14 (B-band) and 3.20 (C-band) eV, respectively. Both A- and C-bands correspond to the free-exciton emission with large binding energies. On the contrary, time-resolved PL spectra indicate that the B-band is attributed to phosphorescence formed by the intersystem crossing.     

Quantifying the electronic effect of substituted phosphine ligands via molecular electrostatic potential

Values of the molecular electrostatic potential minimum (V(min)) corresponding to the lone pair region of several substituted phosphine ligands (PR(3)) have been determined at the DFT level. The V(min) value is proposed as a quantitative measure of the electronic effect of the PR(3) ligands. Good linear correlation between V(min) and Tolman electronic parameter of PR(3) has been obtained. V(min) is also proportional to the pK(a) values of the conjugate acids of PR(3), viz., [PR(3)H](+). Further, the DeltaE values of the reaction Ni(CO)(3) + PR(3) --> Ni(CO)(3)PR(3) and ScH(3) + PR(3) --> ScH(3)PR(3) are also linearly proportional to the V(min) values. However, if there is a strong metal to phosphorus pi-back-bonding, the DeltaE and V(min) do not fit to a line. It is also found that the standard reduction potential as well as the enthalpy change corresponding to the electrochemical couple eta-Cp(CO)(PR(3))(COMe)Fe(+)/eta-Cp(CO)(PR(3))(COMe)Fe(0) is linearly proportional to the V(min) values of PR(3). These correlations suggest that V(min) is a quantitative measure of the sigma-donating ability of the phosphine. It is hoped that, in phosphine-metal coordination chemistry, the V(min) based electronic parameter could be more advantageous than nu-CO and pK(a) based electronic parameters as it solely represents the inherent electronic property of the ligand.     

Accurate calculation of aromaticity of benzene and antiaromaticity of cyclobutadiene: new homodesmotic reactions

Newly designed homodesmotic reactions based on radical systems predict an absolute aromaticity of 29.13 kcal/mol for benzene and an absolute antiaromaticity of 40.28 kcal/mol for cyclobutadiene at the MP4(SDQ)/6-31G(d,p) level.     

Amphotericin B dimers with bisamide linkage bearing powerful membrane-permeabilizing activity

[structure: see text] Covalently linked dimers of amphotericin B were prepared by cross-linking its carboxylic acid. Among these, a dimer with a linkage of 1,6-hexanediamine revealed potent hemolytic activity (EC50, 0.25 microM) while its N-acetyl derivative gave rise to large K+ ion flux in phosphatidylcholine liposomes, regardless of the presence or absence of sterols, suggesting that the dimers may serve as a tool for elucidating the structure of the ion channel assemblage formed by amphotericin B.     

Picosecond study of energy transfer between rhodamine 6G and 3,3'-diethylthiacarbocyanine iodide in the premicellar region: förster mechanism with increased local concentration

The mechanism of enhancement in the energy transfer between rhodamine 6G and 3,3'-diethylthiacarbocyanine iodide by sodium lauryl sulfate in the premicellar region was studied by a picosecond laser technique. The Forster mechanism with an increased local concentration suggesting dye-rich induced micelle formation was concluded from the shape of the decay curve.