Photodimers, reversible photodimerization

Reversible Photodimerization Annealing of the Thin Film Powder X-ray Diffraction Thermal Analysis of the Thin Films Isomers of the Photodimers Reverse Reaction in Spin-Coated Film Crystal Structure and Photodimerisation... 

Reversible photodimerizations of l- -alkylthymine in single crystals depend on the crystal structures. However, the orientation of the thymine bases in the single crystal does not correspond to the isomer of the photodimer formed because thymines undergo disrotatory motion during the photodimerization process in the single crystals. The most important factor of the crystal structure for the photodimerization is the distance between the thymine base and the terminal methyl group of alkyl chain because this can influence the rotation of the thymine bases. 

It is well known that pyrimidine bases convert to photodimers upon irradiation to UV light near the X max( > 270 nm). This photochemical reaction has a lethal effect in biological systems due to the photochemical transformation of pyrimidine bases of nucleic acids. However the photodimerization is a reversible reaction and the photodimers split to afford the original monomers very efficiently upon irradiation at a shorter wavelengths as shown in Scheme 1(1). 

In its deprotonated form, cinnamic acid already presents some prerequisites of surfactants and is easily incorporated in reversed micelles, as demonstrated bySawaki and co-workers " " and others.Then-results support the view that increased local concentration and alignment can be achieved at micellar interfaces. Substantially higher conversion of cinnamate to its photodimers is observed upon irradiation of reversed micelles formed by laurylammonium or hexadecyltrimethylammonium cinnamate in carbon tetrachloride. The photoproducts are mainly the P- and 5-truxinates, consistent with the requirements imposed by the assembly for the formation of contact ion pairs. Unfortunately, these are also the main products observed by Reiser upon irradiation of ethyl cinnamate (albeit in different proportions). Interestingly, however, the observed dimer distribution varies as a function of added water that is proposed to He near the ion pair interface. Similar results were also obtained for indene-2-carboxylate and using sodium dodecyl sulfate microemulsions in water. " The photodimerization of coumarin in micelles has been investigated by Ramamurthy and co-workers. ... 

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