nP
[b]
| | ΔE
1
ǂ [c]
|
E
meta [d]
|
E
2 [e]
| ΔE
2
ǂ [f]
|
|---|
0 | | 14.2 | 11.2 | 45.9 | 34.7 |
1 | α: | 1.82 | −7.07 | 30.4 | 37.5 |
1 | β: | 1.99 | −36.0 | −4.6 | 31.4 |
1 | γ: [g]
| --- | --- | --- | --- |
2 | αβ: | 0.34 | −38.2 | −9.0 | 29.2 |
2 | αγ: | 14.5 | 13.9 | 40.9 | 27.0 |
2 | βγ: | 8.02 | 3.8 | 29.1 | 25.3 |
3 | αβγ: | 4.9 | −3.27 | 18.6 | 21.9 |
-
[a] Energy barriers (AM1/d, in kcal mol−1) along the sequential reaction for different protonation states. [b] nP is the number of protons on the triphosphate (α, β and γ indicate which phosphate is protonated). [c] ΔE
1
ǂ is the barrier of the metaphosphate formation, i.e., the energy difference between the saddle point for Pγ-Oβγ bond cleavage and the reactant. Note that ΔE
1
ǂ is the same as E
1 defined in the main text. [d]
E
meta
is the energy of the geometry-optimised metaphosphate intermediate, relative to the initial reactant. [e]
E
2 is the energy of the saddle point for Wa attack onto the metaphosphate, relative to the reactant. [f] ΔE
2
ǂ = (E
2 - E
meta) is the activation barrier for water Wa attack onto the metaphosphate. [g] Various searches for a sequential reaction failed (hydrolysis always proceeded through a concurrent mechanism)
