Structure and Stability of Chemically Modified DNA Bases: Quantum Chemical Calculations on 16 Isomers of Diphosphocytosine

Table 4

Thermodynamic parameters for different tautomers (kcal/mol) at B3LYP/6-31+G(d) in water.

	Δ𝐸0^a	Δ𝐸0^b	Δ𝐻298	Δ𝐺298
PC1	3.531	0.658	2.021	22.773
PC2	0.177	0.122	0.137	0.275
PC3	0.000	0.000	0.000	0.000
PC4	27.936	23.999	25.904	25.843
PC5	28.035	23.887	25.919	25.612
PC6	26.048	22.526	24.159	24.496
PC7	26.193	22.510	24.229	24.550
PC8	16.902	10.067	13.404	13.409
PC9	19.178	11.994	15.528	15.411
PC10	5.515	2.203	3.824	3.970
PC11	0.177	0.126	0.137	0.287
PC12	0.000	0.000	0.000	0.000
PC13	25.953	22.167	23.990	24.103
PC14	26.648	22.727	24.617	24.804
PC15	24.025	20.722	22.223	22.721
PC16	24.613	21.245	22.773	23.353

aUncorrected energy;  ^bcorrected for zero-point and thermal energy.