. 2016 Dec 20;4:e2805. doi: 10.7717/peerj.2805

Table 2. Characterization of the minimum-energy crossing points between the singlet and triplet surfaces of oxygen:(1H)-3-hydroxy-4-oxoquinoline systems in the presence of the His₂₅₁/Asp₁₂₆ catalytic dyad, at the B3LYP/BS1 level in a water continuum.

The C_β atoms of His251 and Asp126 were kept frozen to limit system flexibility to that possible in the enzyme active site. n.a: not applicable, as the ³I₁ species for these substituents are not local minima in the potential energy surface and collapse into separated substrate and triplet O₂. For the -NO₂ substituted quinoline, the substrate–oxygen distance in ¹I₁ is quite long (2.07 Å), and this intermediate is more properly described as a superoxide:substrate radical pair.

Quinoline substituent	-(CH₂)₄CH₃	-CH₃	-F	-NO₂
C–O distance (Å) at the MECP	2.308	2.23	1.568	1.968
O–O distance (Å) at the MECP	1.303	1.307	1.326	1.304
MECP energy (kcal mol⁻¹) vs. reactants	16.8	15.2	9.2	24.2
¹I₁ energy (kcal mol⁻¹) vs. reactants	11.1	9.0	−3.4	23.6
³I₁ energy (kcal mol⁻¹) vs. reactants	n.a	n.a	6.9	25.4

Table 2. Characterization of the minimum-energy crossing points between the singlet and triplet surfaces of oxygen:(1H)-3-hydroxy-4-oxoquinoline systems in the presence of the His251/Asp126 catalytic dyad, at the B3LYP/BS1 level in a water continuum.

Table 2. Characterization of the minimum-energy crossing points between the singlet and triplet surfaces of oxygen:(1H)-3-hydroxy-4-oxoquinoline systems in the presence of the His₂₅₁/Asp₁₂₆ catalytic dyad, at the B3LYP/BS1 level in a water continuum.