Yoshiro Tatsu

Novel molecular optical memory of luminescent Langmuir-Blodgett films

Abstract The photochemical oxidation of pure and mixed Langmuir-Blodgett (LB) films of 6-(1-(6(8)-decyl)pyrene)hexanoic acid (DPHA) and 10-(1-(6(8)-hexyl)-pyrene)decanoic acid (HPDA) in the presence of molecular oxygen was studied. The much higher rate of decrease in the fluorescence intensity than that in the UV-visible absorbance due to pyrene moieties can be ascribed to the energy transfer quenching of the photoexcited pyrene moieties by the photo-oxidative products. Energy transfer quenching of the Forster type was confirmed by examining the dependence of the fluorescence quenching on the spacer thickness between the monolayers of the pyrene moieties and the photoproducts in the heterogeneous LB films. Application of the amplified decrease in the excimer emission in terms of the quenching by photoproducts to a very sensitive photoresponsive memory was also suggested.

Photoregulation of cytochrome P450 activity by using caged compound.

Cytochrome P450 (P450) species play an important role in the metabolism of xenobiotics, and assaying the activities of P450 is important for evaluating the toxicity of chemicals in drugs and food. However, the lag time caused by the introduction and mixing of sample solutions can become sources of error as the throughput is heightened by increasing the sample number and decreasing the sample volume. To amend this technological obstacle, we developed a methodology to photoregulate the activity of P450 by using photoprotected (caged) compounds. We synthesized caged molecules of nicotinamide adenine dinucleotide phosphate (NADP(+)) and glucose 6-phosphate (G6P), which are involved in the generation of NADPH (cofactor of P450). The use of caged-G6P completely blocked the P450 catalysis before the UV illumination, whereas caged-NADP(+) resulted in a little background reaction. Upon UV illumination, more than 90% of the enzymatic activity could be restored. The use of caged-G6P enabled assays in isolated microchambers (width, 50 μm; height, 50 μm) by encapsulating necessary ingredients in advance and initiating the reaction by UV illumination. The initiation of enzymatic reaction could be observed in a single microchamber. Minimizing uncertainties caused by the introduction and mixing of solutions led to significantly reduced errors of obtained kinetic constants.