Rate acceleration of organic reaction by immediate solvent evaporation

Several types of organic reactions were accelerated by immediate evaporation of solvents because of remarkable enhancement of molecule-to-molecule contacts between reactants.     

Fluorophilicity switch by solvation

A new type of fluorous distannoxanes, [XRf2SnOSnRf2Y]2 (Rf = C6F13C2H4; X, Y = C6F13SO3 (2) and (C6F13SO2)2N, Cl (3)) was prepared successfully as hydrates from the reaction of [ClRf2SnOSnRf2Cl]2 with C6F13SO3Ag and (C6F13SO2)2NAg, respectively. Despite their high fluorine content (59.85 and 59.27% F), these distannoxanes were completely insoluble in fluorocarbons as well as hydrocarbons and halo alkanes. In contrast to this, fluorous distannoxanes 2 and 3 were soluble in polar organic solvents, such as EtOAc, acetone, and THF. When 2 and 3 were added to a two-phase mixture of fluorocarbon and EtOAc, the mixture turned miscible in proportion to the amount of 2 and 3 added, and finally, the mixture turned to a homogeneous solution.     

Synthesis and spectroscopic study of phenylene-(poly)ethynylenes substituted by amino or amino/cyano groups at terminal(s): electronic effect of cyano group on charge-transfer excitation of acetylenic π-systems

To gain insight into substituent electronic effect on charge-transfer excitation of acetylenic π-systems, phenylene-(poly)ethynylenes substituted by Ph₂N or Ph₂N/cyano groups were synthesized by combination of Sonogashira coupling and double elimination protocol of β-substituted sulfones. These substituted phenyleneethynylenes showed large molar absorption coefficients ?, and emitted strong fluorescence upon UV light irradiation. Phenylene-(poly)ethynylenes, which involve butadiyne or hexatriyne motifs, emitted fluorescence in remarkably lower fluorescence quantum yields Φ_F as their polyethynylene motifs -(CC)_n- expanded. The drastic decrease of fluorescence quantum yields Φ_F were explained in terms of increasing nonradiative reaction rate constants k_nr, which had been determined by the corresponding fluorescence quantum yields Φ_F and lifetime values τ. The emission underwent a large bathochromic shift in polar solvents because the charge-separated excited state is more stabilized than the ground state. Comparison of slope values ρ in Lippert/Mataga plot for the Ph₂N and Ph₂N/cyano-substituted phenylene-(poly)ethynylenes revealed that the latter underwent large change of dipole moments upon photo-excitation although highly expanded acetylenic π-systems with cyano group did little.     

Hydration states and metallic intercalation effects in dry DNA

Temperature dependence of the complex dielectric constant at 16.3 GHz has been measured on dry poly(dA)-poly(dT) DNA with Na⁺ counterions under different relative humidity (RH). The rotational motion of sole water dipoles hydrated in PO₂⁻ is detected at low RH, and the collective motion due to water network in major groove is successfully observed at high RH. From the infrared (IR) spectroscopy in dry DNA introducing metallic ions (M-DNA), the symmetric and antisymmetric stretching bands of PO₂⁻ distinctly depend on RH and type of metallic ions. The IR spectral change indicates that the monovalent ions (Li and Na) are arranged in PO₂⁻ though the divalent and trivalent ions connect to the base molecules.     

A note on complete intersections of height three

Let be a field of characteristic 0. If is a complete intersection generated by three homogeneous elements of degrees with , then the reduction of by a general linear form is minimally generated by three elements if and only if .

     

Highly regioselective ring opening of epoxides with alcohols catalyzed by organotin phosphate condensates

Organotin phosphate condensates proved to catalyze the ring opening reaction of epoxides with alcohols in a highly regioselective manner.     

Chemical Modification of Chitosan, 17

The Michael reaction of chitosan with acrylic acid was carried out successfully, even in water alone as the reaction medium. As a consequence of its good solubility in water, the reaction product, N‐carboxyethylchitosan, showed excellent biodegradable properties with standard activated sludge.

     

Preparation and characterization of two crystalline forms of 4-amino-5-chloro-2-methoxy-N-[(2S,4S)-1-ethyl-2-hydroxymethyl-4-pyrroli dinyl]benzamide (TKS159)

For 4-amino-5-chloro-2-methoxy-N-[(2S,4S)-1-ethyl-2-hydroxymethyl-4-pyrrolid inyl]benzamide (TKS159), two polymorphs, forms alpha and beta, were prepared and characterized by means of X-ray powder diffractometry, thermal analysis, infrared spectroscopy and 13C-NMR spectroscopy, both in the solution and solid phases. The X-ray powder diffraction analysis gave different patterns for forms alpha and beta. In the thermogravimetry and differential thermal analysis profiles, form beta exhibited characteristic endo- and exothermic peaks at 112.7 degrees C and 116.2 degrees C, respectively, due to the partial melting-induced phase transition to form alpha without accompanying weight loss, and these were followed by an additional endothermic peak at 138.2 degrees C due to fusion. For form alpha, only an endothermic peak at 137.8 degrees C due to fusion was observed. The IR spectroscopic analyses of forms alpha and beta gave different absorption bands assigned to N-H and O-H stretching, N-H bending, and C=O stretching vibrations. From the data obtained by thermal analysis, form alpha was shown to be thermodynamically more stable than form beta.     

Determination of stereochemistry of bacteriochlorophyll gF and 8(1)-hydroxy-chlorophyll aF from Heliobacterium modesticaldum

The reaction center complex of heliobacteria contains three kinds of chlorophyll pigments, bacteriochlorophyll gF (BChl gF), its 13(2)-epimer BChl gF' and 8(1)-hydroxy-chlorophyll aF (8(1)-OH-Chl aF). Because the full stereochemistry of these naturally occurring chlorophyllous pigments has remained unknown, we determined the stereochemistry of both BChl gF and 8(1)-OH-Chl aF extracted from Heliobacterium modesticaldum. The configurations of the specific functional groups at ring-B as well as those at ring-D and -E were investigated by use of nuclear Overhauser effect correlations in their 1H-NMR spectra and circular dichroism spectra, as well as by modified Mosher's method in their chemical modification: (1) E-configuration was confirmed for the 8-ethylidene group at ring-B in BChl gF, (2) R-configuration was identified for the 1-hydroxyethyl group at ring-B in 8(1)-OH-Chl aF and (3) 13(2)-(R)-, 17-(S)- and 18-(S)-configurations at ring-D and -E in both BChl gF and 8(1)-OH-Chl aF were confirmed. These stereochemistries enabled us to discuss their biosynthesis and to propose possible routes for preparation of ethylidene and 1-hydroxyethyl groups at the 8-position.     

Synthesis of 1-triazolyl-4-trimethylsilyl-2-butanol and 1-triazolyl-5-trimethylsilyl-2-pentanol derivatives and an investigation of their fungicidal activities

A new series of azole derivatives of 1-triazolyl-4-trimethylsilyl-2-butanol and 1-triazolyl-5-trimethylsilyl-2-pentanol were synthesized and evaluated for fungicidal activities against rice blast, sheath blight, and powdery mildew on barley. The derivatives of 2,4-difluorobenzene exhibited high antifungal activities when applied by spray, but exhibited no fungicidal activity by submerged application.