Chlorophyll (Chl)-c1 and Chl-c2 were extracted from a commercially available diatom Chaetoseros calcitrans, and the former (8-ethyl) and the latter (8-vinyl) were efficiently separated by reverse-phase HPLC using a polymeric octadecylsilyl column to afford analytically pure compounds in an amount adequate for further chemical modification. The conformation of the unique acrylate moiety at the 17-position of isolated Chls-c in THF was unambiguously determined to be "cisoid" around the C17-C17(1) bond using 1H-1H NOE correlations: C17(1)=C17(2) was on the same side as C17=C18. Interestingly, correlations originating from the "transoid" conformer could not be observed under the present NMR conditions, indicating that the rotation of the acrylate was considerably restricted. To elucidate the function of the rigid acrylate in Chls-c, we examined their electronic absorption properties using two synthetic types of esters possessing a porphyrin pi-system: acrylate-type (17-CH=CH-COOR) prepared by esterification of natural Chl-c1 and Chl-c2, and propionate-type (17-CH2-CH2-COOR) by 17,18-oxidation of natural Chl-a and its 8-vinyl analog. The Soret absorption bands at around 450 nm of the acrylate-type were red-shifted and broadened more than those of the propionate-type. Consequently, the unique acrylate in Chls-c serves as an aid for expanding the absorption region around 400-500 nm in order to capture intense irradiation from the sun for photosynthesis.
The physical and electrochemical properties of room-temperature ionic liquids based on quaternary phosphonium cations containing a benzyl group in combination with bis(fluorosulfonyl)amide anion. It was found that the benzylphosphonium RTILs showed lower melting points, lower viscosities and higher conductivities than those of the corresponding TFSA-based benzylphosphonium and ammonium RTILs. The thermal stability of the benzyl-phosphonium RTILs was significantly improved by introducing a phenyl group into the phosphonium cations. The introduction of a phenyl group tended to reduce the electrochemical stability of the benzylphosphonium RTILs.
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