Table 1.

Calculated thermodynamics of molecular oxygen “pre-binding” as a function of His157 conformation and protonation.

His157	χ2 (°)[a]	protonation	ΔE (kcal mol−1)	ΔH (kcal mol−1)	ΔS (cal mol−1)	ΔG (kcal mol−1)
neutral	−70.2	Nε	0.7	0.7	5.6	−1.1
positive	−70.2	Nε, Nδ	−22.8	−22.8	−18.5	−17.2
neutral, flipped	106.2	Nδ	8.2	8.2	−19.6	14.1

^[a]Reported torsion angles are those of the starting coordinates prior to geometry optimization.