shifts of ribose and adenine protons support a model in which triprotonated spermidine engages the phosphate anion with the c-3 diamine segment in a conformation to maximize interaction and the c-4 amino segment extended to interact with adenine n-7 ( base anti , 2 ' endo , g ' g ' and gg nucleoside conformation ) .
C0031603
phosphate
C0003075
anion