No abstract

The toxic effect of six heavy metals on cyanobacteria Synechocystis aquatilis was studied by absorption, fluorescence, flow cytometry, and photothermal measurements. This study indicates that at the concentration used, the cyanobacteria are more sensitive to silver, copper, and mercury than to cadmium, lead, and zinc metals. Disregarding the decrease in the yields of the related radiative processes caused by photochemical processes and/or damage to phycobilisomes, no changes were detected in the efficiency of thermal deactivation processes within a few microseconds, which can indicate the lack of disturbances in the photosynthetic light reaction and the lack of damage to the photosystem caused by the heavy metal ions in the concentrations used. The results demonstrate that the relative values of fluorescence yield as well as promptly generated heat calculated for the metal-affected and unaffected (reference) bacteria are sensitive indicators of environmental pollution with heavy metal ions, whereas the complementary methods proposed could be used as a noninvasive and fast procedure for in vivo assessment of their toxicity.

Meso-tetrakis (4-sulphonatophenyl)porphyrin (TSPP) and its complex with TiO 2 were studied by absorption, fluorescence, and steady-state and time-resolved photothermal spectroscopy. A TiO 2 -TSPP complex was obtained by covalent bonding of anionic porphyrin with the nanostructural form of TiO 2 . The TiO 2 colloidal carriers modifying the thermal energy distribution and considerably influencing the photophysical processes were found to lead to changes in the population of the porphyrin singlet and triplet states, resulting in singlet oxygen generation and/or electron transfer.

Time-resolved photothermal responses of merocyanine dyes were used to estimate such parameters as the quenching rate constant of dye triplet states and dye capability of singlet oxygen generation, which are helpful in explanation of the dye photochemical activity. The results have shown that the high photostability of the salt form of merocyanine dyes and their resistance against reactive oxygen species as well as dye-oxygen interaction by triplet-triplet energy transfer make merocyanines efficient singlet oxygen generators in simple and complex systems.