Hybrid molecular orbitals for reacting systems

A method of describing the interactions between two systems in terms of coupled hybrid molecular orbitals of fragments is discussed and is applied to simple interacting systems to provide information on the processes of bond formation.     

Platinum-catalyzed intramolecular vinylchalcogenation of alkynes with beta-phenylchalcogeno conjugated amides

Platinum-catalyzed intramolecular vinylthiolation and -selenation of internal alkynes with vinylchalcogenides 1 having a carbamoyl group on cis-beta-position of vinyl moiety was developed. The conjugated six-membered lactam framework 2 was constructed in high yields. Density functional theory calculations for alkyne insertion processes suggest seven-membered platinacycle 3 is a kinetically favored intermediate of this catalytic system.     

Templating route for mesostructured calcium phosphates with carboxylic acid- and amine-type surfactants

Mesostructured calcium phosphates constructed by ionic frameworks were synthesized using carboxylic acid- and amine-type surfactants in mixed solvent systems of ethanol and water. A lamellar mesostructured calcium phosphate was prepared using palmitic acid as an anionic surfactant, as in the case using n-alkylamines. A wormhole-like mesostructured calcium phosphate can be obtained using dicarboxyl N-lauroyl- l-glutamic acid, whose headgroup is larger than that of palmitic acid. Similar mesostructured product was obtained using 4-dodecyldiethylenetriamine with a large headgroup containing two primary amine groups. Interactions of carboxyl and primary amino groups in the surfactant molecules with inorganic species are quite important for the formation of mesostructured calcium phosphates. The Ca/P molar ratio of mesostructured calcium phosphates was strongly affected by the molecular structure of surfactants containing carboxyl and primary amino groups. Ca-rich materials can be obtained using carboxylic acid-type surfactants (Ca/P approximately 1.7) rather than amine-type surfactants (Ca/P approximately 1.0).     

High-resolution NMR spectra of n-alkanes penetrating into carbon fibers and of protons in carbon fibers

We present a simple NMR method for microscopically exploring the local environment in carbon fibers. The method utilizes n-alkanes as probe molecules, where the n-alkanes penetrate carbon fibers of interest. The high-resolution (1)H NMR spectra for a mixture of a carbon fiber and n-alkanes acquired by this method show a shift of the resonance line, which is due to the local structure of the fiber. The utility of this method is discussed on the basis of the (1)H NMR spectra obtained. In addition, the (1)H distribution and the local motion in the structure of the carbon fiber are revealed in view of the (1)H NMR spectra.     

Self-assembled amphotericin B is probably surrounded by ergosterol: bimolecular interactions as evidenced by solid-state NMR and CD spectra

Amphotericin B (AmB) is thought to exert its pharmacological effects by forming a barrel-stave assembly with ergosterol in fungal membranes. To examine the interaction between AmB and ergosterol (Erg) or cholesterol (Cho), (13)C- and (19)F-labelled covalent conjugates were prepared as reported previously (N. Matsumori et al. Chem. Biol. 2004, 11, 673-679). The CD spectra of the conjugates in a membrane-bound form suggested that the distance between the heptaene moieties of the ergosterol conjugates AmB-C(2)-(6-F)Erg 2 and AmB-C(2)-Erg 3 is similar to that of AmB in ergosterol-containing membranes, but significantly larger than that of AmB in nonsterol or cholesterol-containing membranes. These observations suggest that, as is the case with ergosterol-containing membranes, the conjugated sterol moiety prevents the close contact between the heptaene moieties within the membrane that would reduce channel conductivity of the AmB assemblies. To further investigate this bimolecular interaction, we recorded the solid-state NMR spectra of conjugates 2 and AmB-C(2)-(6-F)Cho 4, which are composed of uniformly (13)C-labelled AmB and 6-fluorinated ergosterol or cholesterol; the conjugates were expected to facilitate the estimation of distances between the fluorine and carbon atoms. By using rotor-synchronous double resonance (rotational echo double resonance of X cluster; RDX) experiments, we deduced the distance between the fluorine atom and its nearest carbon atom in the heptaene moiety of 2 to be less than 8.6 A. This indicates that the B ring of ergosterol comes close to the AmB polyene moiety. A conformational search of the AmB-ergosterol conjugate by using distance constraints derived from the RDX results suggested that ergosterol molecules possibly surround the AmB assembly, which is in contrast with the conventional image in which ergosterol is inserted into AmB molecules.     

Palladium-catalyzed selenoacylation of allenes leading to the regioselective formation of functionalized allyl selenides

Palladium-catalyzed regio- and stereoselective selenoacylation of allenes with selenol esters proceeded to produce functionalized allyl selenides with the acyl moiety at the inner carbon and the SePh group at the terminal carbon in high yields. A mechanism accounting for the observed regio- and stereoselectivities is proposed based on the results of DFT calculations.     

N-carbonylation of lithium azaenolates of amides, formamides, ureas, and carbamates with carbon monoxide mediated by selenium

N-Carbonylation of less nucleophilic nitrogen compounds was achieved by the reaction of the lithium azaenolates with carbon monoxide and selenium. This reaction proceeds in the cases of amides, formamides, ureas, and carbamates, leading to the formation of the corresponding carbamoselenoates in good to high yields after trapping with BuI.     

Loss of moisture from harvested rice seeds on MRI

The drying of rough rice seeds was visualized with the single point mapping imaging (SPI) technique by magnetic resonance imaging (MRI) at various temperatures, and the results were compared with those of the oven-drying method. Most of the water was present in the embryo and endosperm. The water reduction rate was larger on the outside than in the central position of the rice seeds at 50 degrees C, although this discrepancy was not obvious at 40 degrees C. Water reduction was brought about with time according to the kinetics of the multiple components, for both MR imaging and the ventilated-oven method. Images were continuously measured (10 min per image for 100 min). The reduction rate of water from rice kernels increased rapidly with temperature (up) to near 60 degrees C then rose slowly above 60 degrees C. Latent heat was calculated as 15 kcal/mol. deg from the changes of drying rate at temperatures below 60 degrees C.