Highly asymmetrical porphyrins with enhanced push-pull character for dye-sensitized solar cells.

A porphyrin π-system has been modulated by enhancing the push-pull character with highly asymmetrical substitution for dye-sensitized solar cells for the first time. Namely, both two diarylamino moieties as a strong electron-donating group and one carboxyphenylethynyl moiety as a strong electron-withdrawing, anchoring group were introduced into the meso-positions of the porphyrin core in a lower symmetrical manner. As a result of the improved light-harvesting property as well as high electron distribution in the anchoring group of LUMO, a push-pull-enhanced, porphyrin-sensitized solar cell exhibited more than 10% power conversion efficiency, which exceeded that of a representative highly efficient porphyrin (i.e., YD2)-sensitized solar cell under optimized conditions. The rational molecular design concept based on highly asymmetric, push-pull substitution will open the possibilities of further improving cell performance in organic solar cells.

Effects of Bulky Substituents of Push-Pull Porphyrins on Photovoltaic Properties of Dye-Sensitized Solar Cells.

To evaluate the effects of substituent bulkiness around a porphyrin core on the photovoltaic properties of porphyrin-sensitized solar cells, long alkoxy groups were introduced at the meso-phenyl group (ZnPBAT-o-C8) and the anchoring group (ZnPBAT-o-C8Cn, n = 4, 8) of an asymmetrically substituted push-pull porphyrin with double electron-donating diarylamino groups and a single electron-withdrawing carboxyphenylethynyl anchoring group. The spectroscopic and electrochemical properties of ZnPBAT-o-C8 and ZnPBAT-o-C8Cn were found to be superior to those of a push-pull porphyrin reference (YD2-o-C8), demonstrating their excellent light-harvesting and redox properties for dye-sensitized solar cells. A power conversion efficiency (η) of the ZnPBAT-o-C8-sensitized solar cell (η = 9.1%) is higher than that of the YD2-o-C8-sensitized solar cell (η = 8.6%) using iodine-based electrolyte due to the enhanced light-harvesting ability of ZnPBAT-o-C8. In contrast, the solar cells based on ZnPBAT-o-C8Cn, possessing the additional alkoxy chains in the anchoring group, revealed the lower η values of 7.3% (n = 4) and 7.0% (n = 8). Although ZnPBAT-o-C8Cn exhibited higher resistance at the TiO2-dye-electrolyte interface by virtue of the extra alkoxy chains, the reduced amount of the porphyrins on TiO2 by excessive addition of coadsorbent chenodeoxycholic acid (CDCA) for mitigating the aggregation on TiO2 resulted in the low η values. Meanwhile, the ZnPBAT-o-C8-sensitized solar cell showed the lower η value of 8.1% than the YD2-o-C8-sensitized solar cell (η = 9.8%) using cobalt-based electrolyte. The smaller η value of the ZnPBAT-o-C8-sensitized solar cell may be attributed to the insufficient blocking effect of the bulky substituents of ZnPBAT-o-C8 under the cobalt-based electrolyte conditions. Overall, the alkoxy chain length and substitution position around the porphyrin core are important factors to affect the cell performance.

Structures and absolute stereochemistry of dinapinones A1 and A2, inhibitors of triacylglycerol synthesis, produced by penicillium pinophilum FKI-3864.

During our screening program for microbial inhibitors of triacylglycerol synthesis in mammalian cells, four structurally related new compounds, dinapinones A1 (1) and A2 (2) and monapinones A (3) and B (4), were isolated from the culture broth of Penicillium pinophilum FKI-3864. Compounds 3 and 4 were produced by the fungus only when fermented in seawater-supplemented medium. The structures of 1 to 4 were elucidated by spectroscopic studies including various NMR experiments. Compounds 1 and 2 were atropisomers consisting of two monomers with the same planar structure of dihydronaphthopyranone as 3. The absolute stereochemistry of 3 was elucidated by NOE experiment and circular dichroism spectra. Furthermore, the stereochemistry of 1 and 2 was elucidated by in vitro conversion from the structure-defined 3 to its dimers 1 and 2.

Production of monapinones by fermentation of the dinapinone-producing fungus Penicillium pinophilum FKI-3864 in a seawater-containing medium.

Five new monapinones, including a dinapinone monomer, were isolated from the culture broth of the dinapinone-producing Penicillium pinophilum FKI-3864 in a medium modified to contain seawater. The structures of these monapinones were elucidated by various NMR experiments. Monapinones possessed the same dihydronaphthopyranone skeleton as the dinapinones, with different hydroxyalkyl chains: monapinone A was identified as the monomeric portion of the atropisomer dinapinones A1 and A2, and monapinones A and B showed weak inhibition of triacylglycerol (TG) synthesis in intact mammalian cells, whereas the others showed almost no effect on TG synthesis.

Expression of two human acyl-CoA:diacylglycerol acyltransferase isozymes in yeast and selectivity of microbial inhibitors toward the isozymes.

Two isozymes for human acyl-coenzyme A:diacylglycerol acyltransferase (DGAT), DGAT1 and DGAT2, were independently expressed in DGAT-deficient Saccharomyces cerevisiae to establish DGAT1- and DGAT2-S. cerevisiae. The selectivity of DGAT inhibitors of natural origin towards the isozymes was assessed in enzyme assays using the microsomal fractions prepared from DGAT1- and DGAT2-S. cerevisiae. Amidepsines and xanthohumol inhibited DGAT1 and DGAT2 with similar potency, whereas roselipins were found to inhibit DGAT2 selectively.