Hypoxic condition-selective upconversion via triplet-triplet annihilation based on POSS-core dendrimer complexes.

The influence on the efficiencies of the triplet-triplet annihilation (TTA)-supported upconversion by oxygen under biomimetic conditions was investigated. From the solution containing the dendrimer complexes based on polyhedral oligomeric silsesquioxane (POSS)-core dendrimer with the Pt complex of octaethylporphyrin (PtOEP) and anthracene in PBS, the fluorescence emission of anthracene depending on the dissolved oxygen (DO) concentrations via the TTA-supported upconversion was obtained with the excitation light at 540 nm. In particular, we observed strong emission only under hypoxic conditions. In addition, it was found that the emission intensity via TTA-supported upconversion can be reversibly regulated by the DO concentrations in the solution.

Enhancement of optical properties of dyes for bioprobes by freezing effect of molecular motion using POSS-core dendrimers.

We demonstrate that the POSS-core dendrimer induced various kinds of favourable properties of trisvinyl-pyridinium triphenylamine (TP3PY) as a bioprobe. By using the amphiphilicity of the POSS core, the complexes of TP3PY with G2 POSS-core dendrimer were prepared, and the series of properties were investigated for the application as a bioprobe. Initially, it was shown that the adsorption of TP3PY onto the vessels was highly prohibited by the complex formation with the dendrimers. The solution states of the dendrimer complexes were maintained at least for 7 days. Moreover, it was found that the improvement of quantum yields and the elongation of fluorescent lifetimes were observed by the complexation with the dendrimers. Similar photochemical properties were obtained in a glassy state of 2-methyltetrahydrofuranat -196°C. The molecular rotations occurring at the excited state could be restricted by the complex formation with dendrimers. These characteristics induced by the complexation with the POSS-core dendrimer are of significance to improve the signal to noise ratio and the accuracy on the detection as a bioprobe.

Environment-responsive upconversion based on dendrimer-supported efficient triplet-triplet annihilation in aqueous media.

We report dendrimer complexes which can show triplet-triplet annihilation-supported upconversion from visible light to UV light in aqueous solutions. The Pt complex of octaethylporphyrin as a sensitizer and anthracene as an emitter were accumulated into the water-soluble dendrimers.

Monitoring of biological one-electron reduction by (19)F NMR using hypoxia selective activation of an (19)F-labeled indolequinone derivative.

Biological reduction of fluorine-labeled indolequinone derivative (IQ-F) was characterized by (19)F NMR for quantitative molecular understanding. The chemical shift change in (19)F NMR allowed monitoring of the enzymatic reduction of IQ-F. Upon hypoxic treatment of IQ-F with NADPH:cytochrome P450 reductase, IQ-F was activated via catalytic one-electron reduction to release nonafluoro-tert-butyl alcohol (F-OH), while the formation of F-OH was significantly suppressed under aerobic conditions. Similar hypoxia-selective reduction of IQ-F occurred within A549 cells, which expresses NADPH:cytochrome P450 reductase. The kinetic analysis was also performed to propose a reaction mechanism. The molecular oxygen slightly prevents the binding of IQ-F to reductase, while the rate of net reaction was decreased due to oxidation of a semiquinone anion radical intermediate generated by one-electron reduction of IQ-F. The disappearance of IQ-F and appearance of F-OH were imaged by (19)F fast spin echo, thus visualizing the hypoxia-selective reduction of IQ-F by means of MR imaging.

Acceleration of guanine oxidation under visible light irradiation by photon upconversion based on triplet-triplet annihilation.

We report the fluorescent polymer complex which can show fluorescence emission at 380 nm with the excitation of 520 nm in aqueous media. This photon upconversion based on triplet-triplet annihilation can efficiently take place via inter-molecular energy transfers between the Ru complex as a sensitizer and anthracene molecules as an emitter captured into the water-soluble network polymers. We performed the oxidation reaction of 2'-deoxyguanosine by riboflavin in the presence of the polymer complex with the visible light irradiation. It was clearly indicated that oxidative decomposition can be accelerated by UV light generation via upconversion based on triplet-triplet annihilation.

Enhancement of entrapping ability of dendrimers by a cubic silsesquioxane core.

We report that a polyhedral oligomeric silsesquioxane (POSS) core can enhance the entrapping ability of dendrimers. Compared to the G2 PAMAM dendrimer, the G2 POSS-core dendrimer can entrap a larger amount of guest molecules without loss of affinity, and consequently, the water solubility of the entrapped guest molecules can be increased. In addition, we demonstrated that a fluorophore entrapped in the G2 POSS-core dendrimer was prevented from undergoing fluorescence photobleaching.

Ratiometric multimodal chemosensors based on cubic silsesquioxanes for monitoring solvent polarity.

We report the multi-functionalized cubic silsesquioxane (POSS) as the ratiometric multimodal chemosensors for monitoring solvent polarity with fluorescence and (19)F NMR. The alteration of the dispersion state of the modified POSS by changing solvent polarity can be reflected into the orthogonal signal responses for the fluorescence and (19)F NMR. In addition, the ratiometric dual monitoring for the enzymatic reaction was performed using the POSS-based chemosensor.