Cyclodextrin complexes irradiation

Literature data on cytotoxic effects of photoexcited fullerene C60 are controversial. In the studies on transformed B-lymphocytes of Raji fine, phototoxic action of water-soluble carboxy-C60 was not revealed even upon its concentration of 5 x 10 5 M (Irie et al., 1996). In the study (Kamat et al., 2000) damaging effect of fullerenes C60 in dependence on intensity of irradiation toward CHO cells has been demonstrated. Using microsomal fraction of rat liver that was treated with C -cyclodextrin complex, it was shown that already in 5-30 min after UV-irradiation the accumulation of LPO products occurs that is suppressed by antioxidants like ascorbic acid and a-tocopherol. Similar effect of fullerenes C60 has been revealed in microsomal fraction of the cells of ascitic sarcoma 180 (Kamat et al., 2000). 

Irradiation of the a-cyclodextrin complexes of m-alkoxyphenyl allyl ethers (35) gave only a single ortho isomer in each case, although in solution each ether gave two ortho and one para isomers via photo-Claisen rearrangements (Schemes 17 and 18) [156,157], This can be attributed to the difference in free volume available within the cavity near the two ortho centers and to the difference in accessibility of the radical fragments to them. In support of this conclusion, irradiation of the /1-cyclodextrin complexes of 35 results in no... 

Photolyses of the solid cyclodextrin complexes 1 were carried out with a Hano-via 450-W medium-pressure Hg lamp for 3 h at room temperature in a quartz vessel under vacuum. The photolysis vessel was tumbled continuously during the irradiation to ensure homogeneous photolysis of the sample. Conversions were limited to less than 20%. After photolysis, the solid complexes were dissolved in excess water and extracted with diethyl ether and chromatographed with hexane-ethyl acetate (5 1) to isolate the products in pure form. Irradiation of solid / -cy-clodextrin complexes of benzaldehyde resulted in an intramolecular reaction to give benzoin (/ )-(-)-2 and 4-benzoylbenzaldehyde 3 (7 3, 80%). 

The solid 1 1 complex of 1 with /5-cyclodextrin was irradiated for 100 h. Photoproducts were identified using GC by coinjection of authentic samples synthesized separately and also by their XH NMR spectra. 

Very recently, Ramamurthy and coworkers reported contrasting photobehavior of 3-cyclodextrin complexes of N-alkylpyridones (39) in aqueous solution and in the solid state [103]. Upon irradiation, the achiral V-alkylpyridone was transformed to chiral 2-azabicyclo[2.2.0]hex-5-en-3-one (40) (Scheme 15) [104-106]. Thus the solid-state irradiation of 39 afforded bicyclic (3-lactam 40 in 59% ee, whereas the solution-phase irradiation of 39 in the presence of an excess amount... 

Diclofenac sodium is an example where cyclodextrin inclusion has a positive effect on the photostability of the gel formulation. Spray dried diclofenac-cyclodextrin complexes in hydroxyethylcellulose gels showed, after three hours of irradiation. 

ABSTRACT 3-Cyclodextrin was found to form a crystalline inclusion complex with coumarin. The solid-state photoreaction of the inclusion compound was studied at 25-27 C, and compared with those of coumarin and of a mixture of coumarin with the cyclodextrin. Under irradiation at a wavelength longer than 300 nm, coumarin with or without 3-cyclodextrin and in the inclusion complex converted to a photodimer, cis-head-to-head dimer in the solid state. The conversion rate of coumarin was higher than that in the mixture, and the latter was higher than that in the complex. These indicate that 3-cyclodextrin retards the photodimerization of coumarin, but does not affect the course of the reaction in the solid state. 

The case of benzoin alkyl ethers illustrated in Figure 8.15 is a remarkable example of the effect of complexation with cyclodextrins. Such molecules normally undergo homolytic dissociation in solution (the Norrish type 1 process described in section 4.4) and there is practically no intramolecular hydrogen atom abstraction (Figure 8.15). When the benzoin alkyl ethers are complexed with a cyclodextrin to form a 1 1 association, it can be shown that one of the phenyl rings fits inside the cyclodextrin cavity in aqueous solution. When the solid complex is irradiated only the photoproducts resulting from hydrogen atom transfer are detected the opposite behaviour from irradiation of the crystal of benzoin alkyl ether as well as of solutions in benzene. 

J and Yabe et al. [155J have formed LB films of amphiphilic derivatives of jS-cyclodextrin and have incorporated azobenzene derivatives into them in such a way as to form a host-guest complex. Many workers have used the cis to trans change of structure referred to above and brought about by ultraviolet irradiation to change some measurable physical parameter of LB films formed from azobenzene derivatives [156-62J. 

Rao et al. observed that photoirradiation of tran.v-stilbene in crystalline y-cyclodextrin inclusion complexes yields a single isomer of. svn-tctraphenylcy-clobutane (119) [109] stereoselectively in high yield (70%). In contrast, the photodimerization of stilbene in solution is very inefficient, and no photodimer was observed even after prolonged irradiation of pure stilbene crystals. 

Recently, an attempt was made to induce chirality in a meta cycloaddition via complexation with cyclodextrins (Sch. 13) [48]. 1/1 inclusion complexes of 72 and P-cyclodextrin can be synthesized and irradiated at 2 = 300nm. Two regioisomers 73a and 73b are isolated with different enantiomeric excesses. The results can be explained by interactions of different intensity with the chiral environment at the transition state U. In the case of pathway (a) leading to 73a the interaction with the cyclodextrin is more expressed then for pathway (b) leading to 73b. Thus, the formation of 73a occurs with higher enantioselectivity. 

The observed photobehavior of the benzaldehyde-CDx complexes in the solid state is unique and completely different from that of these complexes in aqueous solution and also from that of benzaldehyde 36 in organic solvents. The substantial formation of 4-benzoylbenzaldehyde 38 upon irradiation in (3- and y-CDx cavities indicates that these medium-sized CDx s provide the radical pair within a fairly spacious supercage environment, thus allowing the para-rearrangement (Scheme 13). The formation of practically racemic 37 upon irradiation of the y-CDx complex may also be attributed to the looser orientation of benzaldehyde 36 in the y-CDx cavity than in the (3-CDx cavity. It was thus demonstrated that the chiral hydrophobic cavity of native cyclodextrins not only modifies the photoreactivity of the included guest but also functions as a chiral supramolecular environment for photochirogenesis, albeit resulting in only modest ee%. 

Irradiation of solid 1 1 complexes of benzaldehyde 89 and P-cyclodextrin 2 resulted in enantioselective intermolecular hydrogen abstraction and radical coupling to afford (/ )-( — )-benzoin 90 as a major product in up to 15% ee and 56% chemical yield. 4-Benzoylbenzaldehyde was obtained as a minor product (Scheme 20) [22]. This reactivity can be understood from the presence of guest-to-host (2 2) complexes generated by the head-to-head association of two 1 1 inclusion complexes. 

Photolysis of chlorpromazine (1). The photolysis of 1 results mainly in oxidation to the corresponding sulfoxide. Irradiation in the presence of a cyclodextrin (CD), however, results mainly in dechlorination to promazine (2), which is also converted into a sulfoxide, (3), on photolysis. The rate of conversion of 1 to 2 depends on the cyclodextrin used, the rates following the order /3-cyclodextrin >y-cyck)dextrin> a-cyclodextrin. Since these cyclodextrins differ in the size of the cavity, it appears that the conversion of 1 to 2 takes place within the inclusion complex. ... 

A direct solution to the problem of enantioselective furan-carbonyl photoproduct synthesis would require a photoaddition that proceeded with enantiofacial selectivity in the aldehyde or furan component and maintained the relative face selectivity that is intrinsic to the reaction. Preliminary work used host-guest chemistry to achieve this objective.In aqueous dioxane, a 1 1 1 inclusion complex of unmodified 3-cyclodextrin, furan and benzaldehyde is formed. Upon irradiation (Hanovia 450 W lamp, Vycor filter), a rapid photoaddition occurs to afford a photoproduct of 10-20% ee. 

Me R = Br, R = H) by various donors in viscous soJventa are decreased by a factor of <2 in a 0.34 T magnetic field and pressure is reported to accelerate the photoreduction of p-benzoquinone in SOS and CTAB micelles in Aerosol OT reversed micelles, the reaction is retarded.The yield of anthraquinone-2-sulphonate radical anion (AQS) generated by irradiation of AQS in aqueous acetonitrile containing propan-2-oJ has been found to depend on the water concentration and to follow Perrin s equation.Complexation of aryl alkyl ketones with /3-cyclodextrin leads to changes in the ratio of the products of elimination and cyclisation which result from reaction of the... 

Rearrangements.- E-Photoisomerization occurs readily in imines and in azo compounds. The syn-isomer (1), for example, is the major product of irradiation of nitrofurazone (2) in solution and is formed together with the corresponding azine on exposure to laboratory illumination. The photoisomerization of azobenzene derivatives in solution, in membranes, in host-guest complexes of cyclodextrins, and in polymers continues to attract attention. The reversibility of E-photoisomerization of azobenzene in cyclo-hexane solution has been established, and the E/ -ratios generated by irradiation of various azobenzene derivatives adsorbed on... 

There continues to be a high level of interest shown in photochromic systems. The optically active l,T-bi-2-naphthol gives an optically active intramolecular addition product (37) on irradiation, and on prolonged exposure, cycloreversion occurs which gives evidence for a photoequilibrium between the asymmetric molecules (Cavazza et al). A number of reports within the year describe a variety of aspects of the well-known thermally-reversible spiroindoline-oxazine to photo-merocyanine conversion. For example, the process is sensitised by triplet cam-phorquinone (Favaro et al.), the influence of complexation on indoline and phenanthroline spiropyrans with transition and rare earth metal ions has been described (Atabekyan et al.), and the photochromism of other derivatives in water using vesicles and y-cyclodextrin is reported to be faster than in methanol with the process most favoured in the vesicles (Ishiwatari et al.). 

Wenz et al. have demonstrated that photoreactions are effective for the construction of polyrotaxanes (Scheme 18) [114]. In the knowledge that stil-benes undergo [2+2]photocycloaddition to yield cyclobutane derivatives by UV irradiation, they prepared a quaternary polymeric inclusion complex from /1-cyclodextrin, y-cyclodextrin, (E)-4,4-bis(dimethylaminomethyl)stil-bene (B), and (li)-stilbene polymer (A). Upon irradiation at 312 nm, the (E)-stilbene units of A underwent [2+2]photocycloaddition with B by catalysis of y-cyclodextrin to form the tetraphenylcyclobutane group, which acted as blocking group for /1-cyclodextrin. Wenz et al. claimed that this was the... 

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