Table 6.
The bond dissociation enthalpies (BDE) (kJ/mol), ionisation potentials (IP) (kJ/mol), proton dissociation enthalpies (PDE) (kJ/mol), proton affinities (PA) (kJ/mol), electron transfer enthalpies (ETE) (kJ/mol) calculated at in B3LYP/6-31G(d) level; Two means of –OH group deprotonation in the direct reaction with free radical are taken into account: * –OH of the catechol group engaged in the Zn2+ coordination, or ** –OH from the free catechol group.
| Parameter * | 5-CQA | Zn(II) 5-CQA (Structure I *) | Zn(II) 5-CQA (Structure I **) | Zn(II) 5-CQA (Structure II) |
|---|---|---|---|---|
| BDE | 307.70 | 224.49 | 319.72 | 308.58 |
| IP | 707.46 | 617.62 | 617.62 | 651.71 |
| PDE | 909.93 | 916.58 | 1011.80 | 972.76 |
| PA | 1433.96 | 1266.58 | 1385.32 | 1375.23 |
| ETE | 189.63 | 273.81 | 250.30 | 249.24 |