PAIR FORMATION OF FREE NUCLEOBASES AND MONONUCLEOSIDES IN THE GAS-PHASE

The formation of neutral bimolecular clusters of unsubstituted nucleob ases and mononucleosides in the gas phase has been studied by IR laser desorption of the neutral molecules into a supersonic beam expansion. The complementary nucleobase pairs adenine-thymine and cytosine-guani ne of DNA have been found to be formed in preference to non complement ary base pairs. Association constants for the formation of the dimers of free nucleobases and nucleosides in the gas phase are calculated fr om the experimental results. A strong influence due to side groups aff ecting the dimer formation of the nucleobases is shown.