Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer.

Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF3 )ppy}2 (dtbpy)]PF6 , and was successfully applied to the C-C coupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.

Specific effect of polyunsaturated fatty acids on the cholesterol-poor membrane domain in a model membrane.

To understand more fully the effect of polyunsaturated fatty acids (PUFAs) on lipid bilayers, we investigated the effects of treatment with fatty acids on the properties of a model membrane. Three kinds of liposomes comprising dipalmitoylphosphatidylcholine (DPPC), dioleylphosphatidylcholine (DOPC), and cholesterol (Ch) were used as the model membrane, and the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and detergent insolubility were determined. Characterization of the liposomes clarified that DPPC, DPPC/Ch, and DPPC/DOPC/Ch existed as solid-ordered phase (L beta), liquid-ordered phase (l o), and a mixture of l o and liquid-disordered phase (L alpha) membranes at room temperature. Treatment with unsaturated fatty acids such as oleic acid (OA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) markedly decreased the fluorescence anisotropy value and detergent insolubility. PUFAs and OA had different effects on the model membranes. In DPPC liposomes, the most prominent change was induced by PUFAs, whereas, in DPPC/Ch and DPPC/DOPC/Ch liposomes, OA had a stronger effect than PUFAs. The effect of PUFAs was strongly affected by the amount of Ch in the membrane, which confirmed a specific effect of PUFAs on the Ch-poor membrane domain. We further explored the effect of fatty acids dispersed in a water-in-oil-in-water multiple emulsion and found that unsaturated fatty acids acted on the membranes even when incorporated in emulsion form. These findings suggest that treatment with PUFAs increases the segregation of ordered and disordered phase domains in membranes.