The effect of temperature on the preservation of purine and pyrimidine bases

The aerobic solid phase decomposition of the five major naturally-occurring purine and pyrimidine bases of the nucleic acids was studied spectrophotometrically. Throughout the temperature range 115-264°C, the decompositions follow first-order kinetics and obey the Arrhenius relationship except in the case of guanine where a distinct change in slope was noted at about 200°C. The energies of activation and temperature ranges studied are as follows: cytosine, 36.2 kcal/mole (121-246°C); thymine, 23.4 kcal/mole (115-221°C); uracil, 32.3 kcal/mole (115-196°C); adenine, 36·4 kcal/mole (115-221°C); guanine, 23·4 kcal/mole (115-196°C); 11.6 kcal/mole (196-264°C). Extrapolations suggest that under the conditions studied adenine and cytosine would have half-lives of approximately 10⁶ years at 25°, guanine and uracil would have half-lives of between 10⁴ and 10⁵ years, while thymine would have a half-life of less than 10³ years.