Photoreaction of poly(amino acid)s containing thymine moieties as side groups

The photodimerization reaction of thymine bases in poly-D,-L,and -DL-lysine and isopoly-L-lysine derivatives containing thymine bases was studied over a wide range of pH in aqueous buffered solution. It was found that the quantum yield of the intramolecular photodimerization of grafted thymine bases was affected by the conformation of the polymer in solution: alpha-helix or random coil. And the helical conformation was found to be favorable to cause the photodimerization of thymine bases. The photodimerization of the grafted thymine bases in poly-D, and -L-lysine derivatives caused to increase of the helix content of the poly-lysines, because the photodimer of thymine bases fixed alpha-helix of the polymer main chain.