cationic the charged material may generally be any partially or fully positively charged material suitable for interaction with the phosphate groups of nucleic acids examples of suitable charged materials include xanthines hexoses purines arginine lysine polyarginine polylysine and quaternary ammonium salts the xanthine may generally be any xanthine and preferably is xanthine 1 3 7 trimethylxanthine caffeine 1 3 9 trimethylxanthine 1 3 diethyl 7 methylxanthine 1 3 diethyl 8 phenylxanthine 1 3 dimethyl 7 2 hydroxyethyl xanthine 1 3 dimethylxanthine 7 acetic acid 1 3 dipropyl7 methylxanthine 1 3 dipropyl 8 p sulfophenylxanthine 1 7 dimethylxanthine 1 7 dimethylxanthine paraxanthine 1 9 dimethylxanthine 1 allyl 3 7 dimethyl 8 phenylxanthine 1 allyl 3 7 dimethyl 8 p sulfophenylxanthine 1 butyl 4 5 dihydro 3 ethyl 8 hydroxyxanthine 1 ethyl 3 isobutylxanthine 1 methylxanthine 2 6 dithiopurine 2 u2032 deoxyinosine 3 7 dimethyl 1 propargylxanthine 3 7 dimethylxanthine 3 8 dimethyl 2 thioxanthine 3 9 dimethylxanthine 3 allyl 1 ethyl 8 hydroxyxanthine 3 cyclopropyl 1 ethyl 8 hydroxyxanthine 3 ethyl 1 propylxanthine 3 ethyl 8 hydroxy 1 methylxanthine 3 isobutyl 1 methylxanthine 3 isobutyl 1 methylxanthine 3 isobutyl 1 methylxanthine 3 isobutyl 1 methylxanthine 3 methyl 1 5 oxohexyl 7 propylxanthine 3 methyl 8 phenyl 2 thiohypoxanthine 3 methylxanthine 3 propylxanthine 6 thiohypoxanthine 6 thioxanthine 7 methylxanthine 8 3 carboxypropyl 1 3 dimethylxanthine 8 azaxanthine monohydrate 8 bromo 1 3 diethylxanthine 8 cyclopentyl 1 3 dimethylxanthine 8 cyclopentyl 1 3 dipropylxanthine 8 methoxymethyl 3 isobutyl 1 methylxanthine 8 methylxanthine 9 methylxanthine azaserine hypoxanthine hypoxanthine hypoxanthine 9 beta d arabinofuranoside hypoxanthine 9 d ribofuranoside inosine nicotinamide hypoxanthine dinucleotide phosphate nicotinamide hypoxanthine dinucleotide phosphate disodium salt nicotinamide hypoxanthine dinucleotide sodium salt selenohypoxanthine.