Fig. 5

Transition state of the second step (W_a attack onto γ-metaphosphate) in sequential reactions. a Methyl triphosphate fully de-protonated (number of protons n_P = 0), b α-protonated (n_P = 1), c β-protonated (n_P = 1), d αβ-protonated (n_P = 2), e αγ-protonated (n_P = 2), f βγ-protonated (n_P = 2) and g αβγ-protonated (n_P = 3). The distance between the oxygen atom of water W_a and the γ-phosphorus (solid line) is given in Å. The coordination bonds to the Mg²⁺ are shown as dotted line. The four water molecules coordinating the Mg²⁺ are not shown, but are present in the calculations