Photochemistry of Nucleic Acids

The sugar and phosphate groups are essentially saturated molecules which would absorb only in the far UV. The bases are the chromophores of the DNA molecule, with an absorption maximum around 260 nm. 

The free base molecules can undergo various photochemical reactions, in 

The most important photochemical reaction of the bases of DNA is the dimerization of thymine, because this can take place not only between free molecules but also within the DNA chain when two such bases happen to be close together. Since the bases in a DNA strand form a continuous array of relatively close-packed molecules, energy transfer is efficient throughout the chain and any excitation energy will eventually find a trap such as a thymine dimer (or excimer) where the dimerization reaction can take place. 

Chemical structure of the thymine dimer (left) and absorption spectra (right) of thymine (T) and its dimer (D). Wavelength A in nm/100 

The reactive excited state in the photodimerization of thymine is probably the triplet state Tt the dimerization process can be quenched by triplet acceptor molecules such as ketones and quinones. 

---

Although a signal was detected also in irradiated pyrimidine solutions under similar conditions, it was attributed to dissociation products of the pyrimidine molecule and not to photoionization. If the purine solutions contained ethanol, then the signal of the CH3CHOH radical could also be detected this did not happen in ethanolic pyrimidine solutions. The possible importance of photoionization as the primary process in the photochemistry of nucleic acid derivatives has been supported by Kearns, from a study of photoionization in anthracene single crystals.115 He concluded that anthracene photoionization occurred via the interaction of two singlet excitons. 

Shugar, D., Photochemistry of Nucleic Acids and Their Constituent8, State Institute Hyg. Warsaw (1961) Chem. Abstr., 55, 1722 (1961). 

Cadet J, Anselmino C, Douki T, Voituriez L (1992) Photochemistry of nucleic acids in cells. J Photo-chem Photobiol B Biol 15 277-298... 

A. McLaren and D. Shugar, Photochemistry of Nucleic. Acid and Proteins. Oxford Pergamon Press, 1964. 

J.C. Burr, Advances in photochemistry of nucleic acid derivatives , Reference W, 6. 1968, 193. 

J. Cadet, P. Vigny, Photochemistry of Nucleic Acids, in H. Morrisson (Ed.), Bioorganic Photochemistry, Wiley, New York, 1990. 

Wacker, A., H. Dellweg, L. Trdger, A. Kornkauser, E. Lodemann, G. Twrck, R. Selzer, P. Chandra, and M. Ishimoto Organic photochemistry of nucleic acids. Photochem. and Photobiol. 3, 369 (1964). 

J. G. Burr, Photochemistry of Nucleic Acid Derivatives, in Advances in Photochemistry, 6, 193, Inter-science Publ. Div. John Wiley Sons, N. Y. 1968. 

Cadet J, Vigny P The photochemistry of nucleic acids. In Bioorganic Photochemistry Photochemistry and the Nucleic Acids. Edited by Morrison H. New York John Wiley Sons 1990 1—273. 

Cadet, J., Anselmino, C., Douki, X> 8c Voituriez, L. (1992). New trends in photobiology Photochemistry of nucleic acids in cells. Journal of Photochemistry and Photobiology B Biology, 15, 277-298. 

Varghese, A. J., 1972, Photochemistry of nucleic acids and their constituents. Photophysiology 7 207. 

Cadet, J. and Vigny, P., The photochemistry of nucleic acids, in Bioorganic Photochemistry, Vol. 1 Photochemistry and the Nucleic Acids, Morrison, H., Ed., John Wiley Sons, New York, 1990, p. 1. 

---