The Photobleaching of the Free and Encapsulated Metallic Phthalocyanine and Its Effect on the Photooxidation of Simple Molecules

Brenda Gomes Fanchiotti, Marcella Piffer Zamprogno Machado, Letícia Camilato de Paula, Mahmut Durmuş, Tebello Nyokong, Arlan da Silva Gonçalves, André Romero da Silva

J Photochem Photobiol B. 2016 Dec;165:10-23.

PMID: 27755995

Abstract:

The photobleaching of an unsubstituted phthalocyanine (gallium(III) phthalocyanine chloride (GaPc)) and a substituted phthalocyanine (1,4-(tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato) indium(III) chloride (InTBPPc)) was monitored for the free photosensitizers and for the phthalocyanines encapsulated into nanoparticles of PEGylated poly(D,L-lactide-co-glycolide) (PLGA-PEG). Phosphate-buffered solutions (PBS) and organic solutions of the free GaPc or the free InTBPPc, and suspensions of each encapsulated photosensitizer (2-15μmol/L) were irradiated using a laser diode of 665nm with a power of 1-104mW and a light dose of 7.5J/cm2. The relative absorbance (RA) of the free GaPc dissolved in 1-methyl-2-pyrrolidone (MP) decreased 8.4 times when the laser power increased from 1mW to 104mW. However, the free or encapsulated GaPc did not suffer the photobleaching in PBS solution. The RA values decreased 2.4 times and 22.2 times for the free InTBPPc dissolved in PBS solution and in dimethylformamide (DMF), respectively, but the encapsulated InTBPPc was only photobleached when the laser power was 104mW at 8μmol/L. The increase of the free GaPc concentration favored the photobleaching in MP until 8μmol/L while the increase from 2μmol/L to 5μmol/L reduced the photodegradation in PBS solution. However, the photobleaching of the free InTBPPc in DMF or in PBS solution, and of each encapsulated photosensitizer was not influenced by increasing the concentration. The influence of the photobleaching on the capability of the free and encapsulated GaPc and InTBPPc to photooxidate the simple molecules was investigated monitoring the fluorescence of dimethylanthracene (DMA) and the tryptophan (Trp). Free InTBPPc was 2.0 and 1.8 times faster to photooxidate the DMA and Trp than it was the free GaPc, but the encapsulated GaPc was 3.4 times more efficient to photooxidize the Trp than it was the encapsulated InTBPPc due to the photodegradation suffered by the encapsulated InTBPPc. The participation of the singlet oxygen was confirmed with the sodium azide in the photobleaching of all free and encapsulated photosensitizer, and in the photooxidation of the DMA and Trp. The asymmetry of InTBPPc increased the solubility of the free compound, decreasing the aggregation state of the photosensitizer and favoring the photobleaching process. The encapsulation shows capability in decreasing the photobleaching of both photosensitizers but the confocal micrographs showed that the increase of the solubility favored the InTBPPc photobleaching during the acquisition of optical cross section.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP19631197-A	Indium(III) phthalocyanine chloride		19631-19-7	Price
AP19717794	Gallium(III)-phthalocyanine chloride		19717-79-4	Price