Encapsulation photosensitizers

Based on host-guest interaction, microporous zeolites have been used as heterogeneous host for encapsulation of metal complexes and organometallic fragments. For zeolite-encapsulated photosensitizer, the steric and electrostatic constraint imposed on the complexes within the channels or cages of zeolites can alter the photochemical and photophysical properties of the guest complexes and diminish the photodegradation and undesirable electron transfer reactions [6]. But, the pore sizes (-13 A) of microporous zeolites are too small for... 

Kim S, Ohulchanskyy TY, Pudavar HE, Pandey RK, Prasad PN (2007) Organically modified silica nanoparticles co-encapsulating photosensitizing drug and aggregation-enhanced two-photon absorbing fluorescent dyes aggregates for two-photon photodynamic therapy. 

Kojima C, et al. Preparation of polyethylene glycol-attached dendrimers encapsulating photosensitizers for application to photodynamic therapy. Bioconjugate Chem 2007 18 663-70. 

Light-responsive nanoreactors, based on PMOXA-( -PDMS-fc-PMOXA or PNVP-fc-PDMS-ft-PNVP polymer vesicles with the encapsulated photosensitizer Rose Bengal-bovine serum albumin conjugate, have been shown to serve as an efficient source of ROS on demand [47,48]. This system was uptaken by HeLa cells, and induced apoptosis only when irradiated with light of the appropriate wavelength (Fig. 11.11). These Trojan horses have been proposed as useful for photodynamic therapy. 

Nishiyama N, Jang WD, Kataoka K (2007) Supramolecular nanocarriers integrated with dendrimers encapsulating photosensitizers for effective photodynamic therapy and photochemical gene delivery. New J Chem 31 1074—1082. doi 10.1039/b616050f... 

Cobalt(III) cage complexes can also perform as electron transfer agents in the photoreduction of water.180181 Because of the kinetic inertness of the encapsulated cobalt(II) ion, the cobalt(II)/co-balt(III) redox couple can be repeatedly cycled without decomposition. Thus these complexes are potentially, useful electron transfer agents, e.g, in the photochemical reduction of water, in energy transfer and as relays in photosensitized electron transfer reactions.180,181 The problem of the short excited-state lifetimes of these complexes can be circumvented by the formation of Co(sep)3+ ion pairs, so that the complexes can be used as photosensitizers for cyclic redox processes.182 183... 

Adsorption of 2,4,6-triphenylpenten-l,5-dione onto thermally dehydrated zeolites presaturated with H2S enables the thermal ring closure to a thiopyrylium salt to be achieved within the cavities. The result is encapsulated thiopyrylium salts in which the counter ion is derived from a hydroxyl group of the zeolite cage and which are suitable for use as photosensitizers <2004NJC631>. 

Figure 19.2 Schematic view of drug delivery with photosensitive liposomes and cyclodextrin cages (a) photoinduced lamellar-to-micellar phase transition in the liposome bilayer, (b) encapsulation of the drug (triangles) inside the liposome-containing photosensitizer (circles), (c) irradiation of the liposome, (d) drug release from the opened liposome, (e) hydrophobic photosensitizer encapsulated in a water-soluble cyclodextrin cage, and (f) liberation of the photosensitizer due to cleavage of the linker...

The stability of [Co(am)6]3+ complexes allows the template construction of tricyclic ligands around the metal ion. An example is the sarcophagine complex (17-F-I) in which the metal center is irreversibly encapsulated but retains its redox activity. With suitable substituents, such complexes can act as intercalators in DNA or as photosensitizers.14... 

By the second approach, the enzyme is immobilized in a redox polymer assembly (Figure 39B). Electron-transfer quenching of the photosensitizer by the polymer matrix generates an electron pool for the activation of the enzyme. Photoreduction of nitrate to nitrite was accomplished by the physical encapsulation of NitraR in a redox-functionalized 4,4 -bipyridinium acrylamide copolymer [234]. In this photosystem, Ru(bpy)3 + was used as a photosensitizer and EDTA as a sacrificial electron donor. Oxidation of the excited photosensitizer results in electron transfer to the redox polymer, and the redox sites on the polymer mediate further electron transfer to the enzyme redox center, where the biocatalyzed transformation occurs. The rate constant for the MET from the redox polymer functionalities to the enzyme active site is — (9 + 3) x 10 s. Similarly, the enzyme glutathione reductase was electrically wired by interacting the enzyme with a redox polymer composed of polylysine modified with A-methyl-A -carboxyalkyl-4,4 -bipyridinium. The photosensitized reduction of oxidized glutathione (GSSG) (Eq. 21) ... 

The ionic pair of [Co(AMMEsar)] + cation with an anthracene carboxylate anion (A-Co(III)) was used as both a photosensitizer and an ETA in the photodecomposition of water to produce hydrogen [387]. The photoreduction of encapsulated cobalt(III) ion to cobalt(II) ion occurs on excitation of anthracene chromophore (v< 25 000 cm-i). The A-Co(III) complex shows almost no fluorescence (0<2x 10 ), whereas the A-Co(II) complex produces specific violet fluorescence (Fig. 66). The cobalt(II) complex is formed in the presence of EDTA on light irradiation of the A-Co(III) solution (v> 25 641 cm i). The visible band at 21 276 cm- disappeared, and violet fluorescence was observed. The quantum yield of cobalt(II) complex formation was... 

Typical physical properties obtainable with UV cured silicones are provided In Table I. Incorporation of reactive unsaturation into the silicone polymer backbone In combination with a photosensitization system provided the photocure capability. Properties of a standard heat-cured encapsulant developed for use on semiconductor devices, Dow Corning HIPEC R-6103, are provided for comparative purposes. Clearly, introduction of a photocrosslinking mechanism into a siloxane type composition has afforded the desired result. The one-part, solventless, UV curable silicone composition cured rapidly upon exposure to UV radiation, providing a cured composition which has retained the typical properties that make silicones so attractive for protection of semiconductor devices. 

M. Ann English, B. Shen, J.C. Scaiano, Zeolite encapsulation decreases Ti02-photosensitized ROS generation in cultured human skin fibroblasts . Photochemistry and photobiology, 82, 5-12, (2006). 

---