Other Photosensitizers

Lutetium texaphyrin (Lu-tex) is a water-soluble, porphyrin-related molecule which has been studied as a photosensitizer in experimental models of atherosclerosis and various tumors (29). In vitro work in our laboratory revealed preferential uptake of Lu-Tex by bovine capillary endothelial cells when compared with retinal pigment epithelial cells, suggesting the possibility of increased selectivity (R. Z. Renno and J. W. Miller, unpublished data). When Lu-Tex PDT was applied to the monkey model of experimental CNV, closure of the neovascular membranes was achieved at doses of l-2mg/kg with irradiation 10-40 minutes after injection using 732nm light at 50-100 J/cm2 (30). Limited toxicity to retinal and choroidal structures, similar to that seen with verteporfin was observed. 

Preclinical studies using another chlorin, mono-L-aspartyl chlorin e6 (NPe6) have been conducted in rabbits and monkeys (34). PDT using Npe6 was performed 

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Mathews-Roth, M.M., Carotenoids in erythropoietic protoporphyria and other photosensitivity disease. Carotenoids Hum. Health, 691, 127, 1993. 

In should be noted that the same problem exists for both other photosensitizers and other methods for decontamination of the blood and its components (e.g. absorption) (Mohr, 2000). The use of fullerenes is to be preferred to the use of photoactive dyes because the former are water-soluble components. Due to its insolubility in water, fullerene may be easily removed from the liquid phase after the procedure of decontamination. 

Other photosensitive polybenzoxazole resins, (II), were prepared by the authors... 

Addition polymers consisting of pentaerythritol triallyl ether, (I), and pentaer-ythritolntetrakis(3-mercaptopropionate), (H), were previously prepared by the authors (2) and used in dental restorative materials. Other photosensitive addition polymer mixtures using triallyl l,3,5-triazine-2,4,6-trione, ( ), are also described by the authors (3). 

If an appropriate electron acceptor is available, the photoexcited porphyrin may transfer an electron to it. The acceptors may be organic molecules such as JV-alkylnicotinamide, metal complexes such as [Fe(CN)6]3- or another porphyrin molecule.131 The second order reaction rate for the Zn(uroporphyrin)-acceptor system at infinite ionic strength is estimated to be 108M 1s l. The electron travels from Zn(Por) to V-benzylnicotiamide or to [Fe(CN)6]3 over a distance of 15 A or 30 A respectively. Since the reaction creates charged species, polar media accelerate the process. The back reaction or other photosensitization processes such as 02 generation become favourable in nonpolar solvents. 

Besides DNA strand breaks, DNA-protein cross-links are also formed upon photodynamic action of chloroalbumine phthalocyanine (Ramakrishnan et al. 1988) and by a large variety of other photosensitizers (Villanueva et al. 1993). 

Experimentally, electron transfer across vesicle membranes with an asymmetrically embedded photosensitizers was first observed in System 17 of Table 1. Katagi et al. [64, 65] succeeded in embedding a photosensitizer (ZnC18TMPyP3+) into the bilayer membrane both uniformly and selectively in its outer monolayer, i.e. asymmetrically. In the latter case no electron transfer across the membrane took place until the other photosensitizer (ZnTPP) was introduced into the membrane uniformly. The proposed mechanism of electron transfer involved two photochemical steps ... 

Ashwood-Smith, M. J., Poulton, G. A., Ceska O., Liu, M. and Furniss, E. 1983. An ultra-sensitive bioassay for the detection of furocoumarins and other photosensitizing molecules. Photochem. Photobiol. 38, 113-118... 

There are several excellent photosensitizers one of them is [Ru(bpy)3]2+ [6]. There are two optical isomers in this complex one is A [Ru(bpy)3]2+ and the other is A-[Ru(bpy)3]2 +, as shown in Scheme 1. Thus one can expect to perform the stereoselective electron transfer reaction with A- and A-[Ru(bpy)3]2 +. Unfortunately, however, the racemization of [Ru(bpy)3]2+ is induced photochemically [7]. The reasonable way to suppress the photoracemiza-tion of this complex is to introduce the optically active organic functional group into the transition metal complexes, as will be discussed in Sec. II.B. The other photosensitizer that is useful for the photoinduced electron transfer reaction is the copper(I) complexes with 1,10-phenanthroline and their derivatives [8,9]. Zinc(II) porphyrin is also an excellent photosensitizer for photoinduced electron transfer reaction [10]. In these complexes, molecular chirality does not exist, unlike in [Ru(bpy)3]2 +. Thus one must introduce some chiral functional group into these compounds, to use these complexes as chiral photosensitizers. 

Other photosensitive systems for hologram recording in acrylamide have been described by Sugawara and co-workers (45,... 

In general, group X in the prepolymer could be a number of possible photolabile groups. Benzoin alkylethers are usually superior to other photosensitizers studied for the photopolymerization of allylamines Therefore, prepolymers are prepared in which group X is derived from an unsaturated benzoin derivative of which several suitable structures are shown ... 

Since epoxy groups can be attached on differently structured backbones R and combined with other photosensitive groups L, taylor-made photosensitive resin systems can be prepared. From a formal point of view, photocrosslinkable epoxy resins may come in three types ... 

In vinyl compound polymerization of vinyl acetate, alcohol, bromide, chloride, or carbonate, ascorbic acid can be a component of the polymerization mixture (733-749). Activators for the polymerization have been acriflavine (734), other photosensitive dye compounds (737,738), hydrogen peroxides (740,741,742), potassium peroxydisulfate (743), ferrous sulfate, and acyl sulfonyl peroxides (747). Nagabhooshanam and Santappa (748) reported on dye sensitized photopolymerization of vinyl monomers in the presence of ascorbic acid-sodium hydrogen orthophosphate complex. Another combination is vinyl chloride with cyclo-hexanesulfonyl acetyl peroxide with ascorbic acid, iron sulfate, and an alcohol (749). Use of low temperature conditions in emulsion polymerization, with ascorbic acid, is mentioned (750,751). Clarity of color is important and impact-resistant, clear, moldable polyvinyl chloride can be prepared with ascorbic acid as an acid catalyst (752) in the formulation. 

In contrast to other photosensitized systems, many of the secondary processes occurring in the Hg-photosensitized decompositions are identical to those in the direct photolyses, and the conclusions drawn from the former are often applicable to the latter. 

The relative complexity of the proton transfer mechanism in bR or other photosensitive proteins explain why the mechanism of photosynthesis in plants is much less understood than that performed by H. salinarum, a bacterium that is much less familiar than green leaves. 

For the PDT mechanism, there have been many reports about involvement of singlet oxygen produced by energy transfer from excited state of porphyrins or other photosensitizers. Our intention is not to deny such mechanism however the electron transfer mechanism which leads to production of or hydrogen peroxide by the following scheme... 

Photocells and other photosensitive devices utilizing the fact that... 

The photosensitive polyamlc acid discussed here Is made directly from the precursor polyamlc acid. Of the few other photosensitive polyamlc acids reported in the literature (2), the workers initially photo-functionallze the monomers. This latter approach requires more steps and requires more care as the photosensitive moiety is isolated and carried through the entire synthesis process. A comparison of the two processes is shown in Scheme II. 

Unlike other photosensitive polyimides (2), the use of N-phenylmaleImide (10% to polymer weight) as crosslinking agent did not improve the photopolymerization of PSiPI. 

While many other photosensitizers are being examined as potential PDT agents (see below), to date only Hpd and Photofrin have been used in man. 

Patients must not be taking other photosensitizing drugs, for example phenothiazines and benzodiazepines (Chapter 12), NSAIDs (Chapter 7) and some antibiotics (Chapter 9). 

Coating compositions for this process can contain cyclic ethers, vinyl ether monomers, organosilicone monomers, and a wide variety of mono-, di-, and polyepoxy functional materials. Further modifications to this process include the addition of free radical polymerizable monomers in combination with the cationic polymerizable monomers so that both curing processes may take place at the same time. The photoinitiator systems that generate acid catalyst intermediates also generate free radical intermediates or can be combined with other photosensitizer materials such that both... 

A third reason for the popularity of ALA-PDT has to do with its versatility in terms of delivery methods. ALA is effective when applied topically to any accessible surface (skin, oral cavity, urinary bladder, vagina, uterus), it can be injected intradermally or intralesionally in order to produce a higher local concentration of ALA than is possible by topical application, and it can be given systemically (orally, or by subcutaneous or intravenous injection). Under certain conditions it can even be given regionally, via the lymphatics. No other photosensitizer is known which can match ALA-induced PpIX for versatility. 

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