Melting stability of base pair stacks (B DNA)[6] Step Melting ΔG°37 (Kcal/mol) T A -0.12 T G or C A -0.78 C G -1.44 A G or C T -1.29 A A or T T -1.04 A T -1.27 G A or T C -1.66 C C or G G -1.97 A C or G T -2.04 G C -2.70