. Author manuscript; available in PMC: 2011 Jan 14.

Published in final edited form as: J Phys Chem B. 2010 Jan 14;114(1):349–360. doi: 10.1021/jp9082085

Table 5.

Comparison of the relative solvation free energies for the tautomeric protonation of N-Me piperazine in different solvents from Monte Carlo simulations and IEF-PCM calculations^a

	ΔG(FEP)_sol	ΔG(PCM)_sol^b
Water
Infinitely dilute, CHELPG	−3.22±0.11
Infinitely dilute, RESP	−3.79±0.11	−4.52, −4.50
Ewald + counterion (fix distance), CHELPG	−3.10±0.11
Ewald + counterion (fix distance), RESP	−2.90±0.11
CH₃CN, CHELPG charges
Infinitely dilute,	−4.46±0.07	−4.25, −4.30
Ewald + counterion (fix distance)	−4.38±0.07
Ewald + counterion (freely moving)	−1.48±0.07
CH₂Cl₂, CHELPG charges
Infinitely dilute	−2.38±0.05	−3.74, −3.72
Ewald + counterion (fix distance)	−1.96±0.04
Ewald + counterion (freely moving)	−4.40±0.05

Energies in kcal/mol. Values are for the free energy difference of G_sol(H⁺N(secondary)) − G_sol(H⁺N(tertiary)). Unless indicated, atomic charges were derived upon the CHELPG fit to the in-solution IEF-PCM/B3LYP/6-31G* molecular electrostatic potential for Monte Carlo calculations. Reaction field corrections applied in simulations with infinitely dilute solutions.

Relative solvation free energy values on the basis B3LYP/6-311++G** and QCISD(T)/CBS calculations from Table S4b.