[eng Long-chain N-alkyl substituted purine and pyrimidine bases are very interesting ligands for studying interaction motifs of biological relevance. The understanding of new types of recognition patterns between bases like RNA quartets combined with C<br>H/ , lone pair<br> and anion<br> interactions is necessary to study and control many biological processes. These interactions are essential for the packing of the crystals, and some studies have already proved their importance in biology. One of the major revelations is the importance of anion<br> interactions with both pyrimidine and purine rings. In many studies, anion<br> interactions with biologically relevant anions like chloride or bromide have been shown, anticipating that these interactions are likely present in biological systems.