Adenine and thymine grafts on polyethyleneimine

Graft polymers of three different molecular weights of polyethyleneimine (PEI) with 9‐(vinylsulfonylethyl) (9‐VSE)‐adenine and 1‐(vinylsulfonylethyl) (1‐VSE)‐thymine were prepared. PEI's having molecular weights of 600, 1200, and 1800 were used and various ratios of VSE‐nucleobases to ethyleneimine were employed in the grafting process. As expected, a decrease in the nucleobase substitution in the resulting graft polymer resulted in an increase in its water solubility. The degree of substitution in the graft polymers was calculated from sulfur determinations: in most cases this degree of substitution indicated that not all of the VSE derivative has reacted with the PEI due to the highly branched nature of the latter. The presence of nucleobase stacking in the polymers was studied by UV spectroscopy. Stacking was observed for the adenine polymers in both DMSO and 0.1N HCl while stacking in the thymine polymers was observed in 0.1N HCl but not in DMSO. The absence of stackingwithin the thymine polymers in DMSO was attributed to complexation of primary amino groups of the PEI backbone with the pyrimidine ring.