Photosensitization, use

Intermolecular photocycloadditions of alkenes can be carried out by photosensitization with mercury or directly with short-wavelength light.179 Relatively little preparative use has been made of this reaction for simple alkenes. Dienes can be photosensitized using benzophenone, butane-2,3-dione, and acetophenone.180 The photodimerization of derivatives of cinnamic acid was among the earliest photochemical reactions to be studied.181 Good yields of dimers are obtained when irradiation is carried out in the crystalline state. In solution, cis-trans isomerization is the dominant reaction. 

Photosensitivity Use sunscreens (moisturizing), protective clothing, and sun avoidance... 

Fig. 5 shows the SEC/UV and SEC/IR traces of PMMA samples (78) which were photopolymerized with different concentrations of photogensitizer (0.05 x 10 M, 0.08 x 10 M, 0.25 x 10 M and 0.5 X 10 M). The photosensitizer used was 4,4 bis-(diethyl amino) benzophenone (DEABP). From the UV traces it is seen that the photosensitizers are chemically bound to the polymer chains. The results also seem to indicate that a greater number of sensitizer fragments reside in the lower molecular weight regions. A considerable amount of free sensitizer can be detected by the UV detector (retention volume 210 ml) when t e Initial concentration of the sensitizer is above 0.08 x 10 M. The other... 

FIGURE 3.8 Major classes of photosensitizers used for antimicrobial treatment. 

Stevia Stevia rebaudiana) Uses Natural sweetener, hypoglycemic and hypotensive properties Actions Multiple chemical components sweetness d/t glycoside, stevioside hypotensive effect may be d/t diuretic action or vasodilation action Available forms Liq extract, powder, caps Notes/SE HA, dizziness, bloating Interactions T Hypotensive effects W/ antihypertensives esp CCB, diuretics EMS Monitor BP does not encourage dental caries may -1-glucose St. John s Wort (Hypericum perforatum) Uses Mild-mod depression, anxiety, anti-inflammatory, immune stimulant/anti-HIV/antiviral, gastritis, insomnia, vitiligo Action MAOI in vitro, not in vivo bacteriostatic bactericidal, T capillary blood flow, uterotonic activity in animals Efficacy Variable benefit w/ mild-mod depression in several trials, but not always seen in clinical practice Available forms Teas, tabs, caps, tine, oil ext for topical use Dose 2-4 g of herb or 0.2-1 mg of total hypericin (standardized extract) daily Notes/SE Photosensitivity (use sunscreen) rash, dizziness, dry mouth, GI distress Interactions Enhance MAOI activity, EtOH, narcotics, sympathomimetics EMS T Risk of photosensitivity Rxns t effects of opioids and sympathomimetics... 

Dingle and Gunning (10) have investigated a series of alkyl chlorides and fluorine-substituted alkyl chlorides in 2ll2Hg photosensitization, using experimental techniques similar to those of the two studies just described. The results of this significant work are summarized in Table VI. 

The use of photochemical treatment to stimulate translocation of endocytosed macromolecules into the cytosol is a novel technology to improve therapeutic efficacy. The technology as described in this review is derived from photodynamic therapy (PDT) and is named PCI. In both cases a photosensitizer is used in combination with light to exert the treatment effects. The basic mechanisms of the photosensitizers and their tissue interaction in combination with light will be described with emphasis on the properties of the photosensitizers used in PCI before describing the use of PCI for cytosolic delivery of macromolecules. 

Hammond and Cole reported the first asymmetric photosensitized geometri-r cal isomerization with 1,2-diphenylcyclopropane (Scheme 2) [29]. The irradiation of racemic trans-1,2-diphenylcylcopropane 2 in the presence of the chiral sensitizer (R)-N-acetyl-1 -naphthylethylamine 4 led to the induction of optical activity in the irradiated solution, along with the simultaneous formation of the cis isomer 3. The enantiomeric excess of the trans-cyclopropane was about 1% in this reaction. Since then, several reports have appeared on this enantiodifferentiating photosensitization using several optically active aromatic ketones as shown in Scheme 2 [30-36]. The enantiomeric excesses obtained in all these reactions have been low. Another example of a photosensitized geometrical isomerization is the Z-E photoisomerization of cyclooctene 5, sensitized by optically active (poly)alkyl-benzene(poly)carboxylates (Scheme 3) [37-52]. Further examples and more detailed discussion are to be found in Chap. 4. 

There is much evidence that the photolysis of ketene, diazomethane, and diazirine produces methylene predominantly in the singlet state. It is, however, possible, by using mercury photosensitization or by photosensitization using benzophenone to produce triplet methylene. Since the triplet is the ground state for methylene, it is also possible to produce triplet methylene from singlet methylene by carrying out reactions in the presence of a large excess of inert gas. Recently, much evidence has accumulated to indicate that even in the normal photolysis of all three of the methylene precursors, some of the methylene is produced in the triplet state. ... 

In this case, the activated compound (C) cannot be produced by direct irradiation with light of frequency v. Instead, the activated photosensitizer (Z) transfers energy to tiie monomer or initiator at an appropriate frequency that can be absorbed by C. Typical photosensitizers used in photochemically-initiated polymerizations are benzophenone, fluorescein, and eosin. 

Myelosuppression highly emetogenic flu-like syndrome fever, myalgia, malaise (may last for several days after dacarbazine administration) facial flushing photosensitivity use caution with sun exposure... 

Photosensitization using a dye is convenient and we employed this method for our work in environmental purification. Quantum efficiencies of generating singlet oxygen (,o2) using Rose Bengal, Methylene Blue, and Eosin, for examples, are known to be 0.80 0.50 and 0.42, respectively. Two mechanisms have been... 

Since the ground-breaking discovery of enantiodifferentiating photosensitized geometrical isomerization by Hammond and Cole [47], extensive work has been carried out in this area. However, in spite of considerable efforts devoted to a variety of asymmetric photosensitizations using many different substrates and sensitizers, the op s reported have only recently begun to reach appreciable levels... 

Other Processes. - 1,3-Dioxolanes are formed on SET induced ring opening of a-epoxyketones in acetone using 2,4,6-triphenylpyrylium tetrafluorobor-ate as the sensitizer. The dioxolanes are formed by CO bond cleavage while reduction products are the result of CC bond fission. Photosensitized (using... 

Pharmacokinetic properties may be the least understood and controllable of all of the necessary properties for photosensitizer used in vivo. For practical reasons it would not be possible to use photosensitizers which are present in tumors only transiently, since the photodynamic effect producing damage is a product of both the drug level and the light fluence. If the former changes rapidly during treatment (i.e., over 30-60 min), it would be very difficult to provide proper dosimetry to achieve Em. If the tumor were to show little tendency to retain the photosensitizer after clearance from the serum and... 

Figure 16.2-7. Photosensitizers used for photochemical regeneration of NAD(P)+ from NAD(P)H.

C.J. Corner (1991). Preclinical examination of first and second generation photosensitizers used in photodynamic therapy. Photochem. PhotobioL, 54, 1093-1107. 

Figure 1. Absorption spectra of several photosensitizers used in PDT. Note the strong absorption peak in the far-red region (above 650 nm) for second-generation photosensitizers compared to the weak absorption at the maximum wavelength around 630 nm for the...

For most photosensitizers used clinically at present for cancer treatment, and with surface irradiation, the typical energy densities required are around 100 J cm. The energy densities for some other treatments (e.g. macular degeneration or actinic keratosis) are much less, and some photosensitizers (e.g. mTHPC) require much less... 

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