Figure 8.

Relationship between the experimental pK_a of the leaving group (PP_i or its bisphosphonate analogues) and the selected NBO charges of the [Mg·3H₂O·methyl triphosphate]^2– complex and its analogues. The purple diamonds (slope = −0.0028, R = 0.78), red circles (slope = −0.007, R = 0.89), and green triangles (slope =0.049, R = 0.90) represent the O_lg charge, average of the charges of the two nonbridging O atoms on β-phosphate, and the sum of charges on the X group (Figure 1), P_β and Pγ, respectively. Values of the X_tot + P_β + P_γ charge are depicted along the y-axis on the right.