Pyrobacteriopheophorbide-a derivatives possessing various hydrophilic esterifying groups at the C17-propionate residues for photodynamic therapy

Aiming at the application to photodynamic therapy, natural bacteriochlorophyll-a was converted to chemically stable free-base derivatives possessing different kinds of hydrophilic C17-propionate residues. These semi-synthetic bacteriochlorins were found to have self-assembling ability in an aqueous environment and formed stable J-type aggregates in a cell culture medium containing 0.2% DMSO. The electronic absorption spectra of all the sensitizers showed Qy absorption maxima at 754 nm in DMSO as their monomeric states, while a drastic shift of the red-most bands to ca. 880 nm was observed in the aqueous medium. The circular dichroism spectra in the medium showed much intense signals compared to those measured in DMSO, supporting the formation of well-ordered supramolecular structures. By introducing hydrophilic side chains, the bacteriochlorin sensitizers could be dispersed in the aqueous medium as their J-aggregates without the use of any surfactants. Cellular uptake efficiencies as well as photodynamic activities were evaluated using human cervical adenocarcinoma HeLa cells. Among the 11 photosensitizers investigated, the best result was obtained for a charged derivative possessing trimethylammonium terminal (17-CH2CH2COOCH2CH2N+(CH3)3I-) and photocytotoxicity of EC50 = 0.09 μM was achieved by far-red light illumination of 35 J/cm2 from an LED panel (730 nm).

C31-Selective substitution of cationic N-heteroaromatic groups into a 3-vinylated chlorophyll-a derivative

A variety of N-containing heteroarenes were site-selectively introduced at the C31-position of a chlorophyll-a derivative possessing a 3-vinyl group through a C-N+ bond via oxidative reactions using iodine in the presence of a silver(i) salt. Electron-rich N-heteroarenes were effectively substituted, while electron-withdrawing or bulky nitrogen-neighboring substituents suppressed the reactivities. The cationic products formed were characterized by 1D/2D NMR, and their optical properties were also investigated.

Visible-light driven hydrogen production using chlorophyll derivatives conjugated with a viologen moiety in the presence of platinum nanoparticles

Effective visible-light driven hydrogen production was accomplished using viologen bonded pyropheophorbide-a in the presence of platinum nanoparticles via the reduction of external methyl viologen.