Raman spectroscopic analysis of the effect of ultraviolet irradiation on calf thymus DNA

Raman spectroscopy was used for the first time to detect the effect of independent UVA (ultraviolet-A:320-400 nm)and UVB(ultraviolet-B:280-320 nm)irradiation on the calf thymus DNA in aqueous solution.After both UVA and UVB irradiation for 1 h or 3 h,the damage to the conformation of DNA was rnoderate,but the reduction of the B-form DNA component was obvious.Both UVA and UVB caused significant damage to the deoxyribose moiety and bases,among which the pyrimidine base pairs were more seriously affected.There appeared to be preferential damaging sites on DNA molecules caused by UVA and UVB irradiation,UVA irradiation caused more damage to the deoxyribose than UVB irradiation,while UVB irradiation caused more significant damage to the pyrimidine moiety than UVA irradiation.After UVB irradia- tion for 3 h,unstacking of the AT base pairs and the cytosine ring took place,severe damage to the thymine moiety occurred,and some base pairs were modified.Moreover,with either UVA or UVB irradiation for 3 h, the photoreactivation of DNA occurred.The damage to the DNA caused by UVB was immediate,while the damage caused by UVA was proportional to the irradiation duration.The experimental results partly indicate the formation of some cyclobutane pyrimidine dimers and(6-4)pbotoproducts.