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. Author manuscript; available in PMC: 2010 Dec 1.

Published in final edited form as: J Phys Chem B. 2007 Feb 1;111(4):720–730. doi: 10.1021/jp066478s

TABLE 4.

Energetics for Urea Hydrolysis by the Addition/Elimination Mechanism

	PDDG	PDDG GB/SA	QM/MM MC/FEP	B3LYP/6-311++G**	MP2/6-311++G** ICPM
	First Step

ΔE^‡ (ZPE-corrected), kcal/mol	41.3^b			50.5	53.5^d
ΔE^‡₀ = ΔE^‡ + ΔE_thermal^a				48.0
ΔH^‡ = ΔE^‡ + ΔnRT, kcal/mol				48.6
ΔG^‡ = ΔE^‡ − TΔS, kcal/mol				49.0	51.2^d
ΔG^‡_solution = ΔG^‡ + ΔΔG_solvation		39.8^b,^c	39.9	45.0^c	46.8^d

	Second Step

ΔE^‡ (ZPE-corrected), kcal/mol	36.8^b			31.8	23.2
ΔE^‡₀ = ΔE^‡ + ΔE_thermal^a				27.8
ΔH^‡ = ΔE^‡ + ΔnRT, kcal/mol				27.2
ΔG^‡ = ΔE^‡ − TΔS, kcal/mol				26.9	24.1
ΔG^‡_solution = ΔG^‡ + ΔΔG_solvation		38.0^b,^c	18.6	25.6^c	23.3

^a

E_thermal = E_vibtational + E_rotational + E_{translational}.

^b

Vibrational frequencies were not calculated at the PDDG level.

^c

The values include the ΔG of hydration obtained from the GB/SA model.

^d

Results from Ref. 17.