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. 2013 Sep 6;78(17):8537-44.
doi: 10.1021/jo401266r. Epub 2013 Aug 13.

Autocatalytic-assisted photorelease of a sensitizer drug bound to a silica support

Dorota Bartusik  1 , Mihaela Minnis, Goutam Ghosh, Alexander Greer
Affiliations

Autocatalytic-assisted photorelease of a sensitizer drug bound to a silica support

Dorota Bartusik et al. J Org Chem. .

Abstract

The photorelease of a sensitizer from a fluorinated silica surface occurs by a reaction of singlet oxygen with the vinyl ether bond linker with scission of a dioxetane intermediate. Irradiation of the released sensitizer generates singlet oxygen, which accelerates the release of more sensitizer via an autocatalytic reaction. Sigmoidal behavior of sensitizer release in n-butanol and n-octanol occurs at an optimal temperature of 20 °C. The photorelease efficiency was reduced at low temperatures, where the sensitizer was retained on the surface due to a long-lived dioxetane with inefficient scission, and also reduced at high temperatures, due to a slower reaction of (1)O2 with the vinyl ether bond. Immediate acceleration is a result of released sensitizer being used as a dopant to eliminate the induction step, further implicating an autocatalytic mechanism. However, the sigmoidal sensitizer release was not correlated to solvent viscosity, heat, or light from the dioxetane decomposition or to minor O2 solubility enhancements caused by the fluorinated silica. The mechanistic information collected here can be used to help control the pace of drug release; however, it remains to be seen whether an autocatalytic-based drug delivery system has an advantage to those with non-sigmoidal kinetics.

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Figures

Figure 1
Figure 1
The concentration of sensU photoreleased free from the fluorinated silica sensitizer as a function of time in n-butanol at 20 °C. The fluorinated silica was removed and the concentration of sensU by UV-VIS was measured at the indicated times.
Figure 2
Figure 2
The percent yield of sensU photoreleased from the fluorinated silica sensitizer after irradiation for 40 min in n-butanol at various temperatures.
Figure 3
Figure 3
A plot of half-lives for sensitizer photorelease vs temperature. These points were taken from the halfway point between the bottom and top of the sigmoids.
Figure 4
Figure 4
Modes of photorelease of the pheophorbide sensitizer bound to the fluorinated silica surface. (a) The induction period is absent in the sample spiked with sensU at t = 0 min. (b) The sigmoidal behavior of sensitizer release from the fluorinated silica sensitizer with cooperative production of sensU. (c) The linear behavior of sensitizer release from the native silica sensitizer with non-cooperative production of sensU.
Scheme 1
Scheme 1
Proposed Autocatalytic Mechanism
Scheme 2
Scheme 2
Scheme 3
Scheme 3
See this image and copyright information in PMC

References

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