The accuracy of the resulting ACE MLP was assessed by conducting 500 fs ACE MLP-MD simulations starting from two configurations not included in the training set. The first configuration, which is similar to subset 2, consisted of the gas phase TS and three water molecules forming HBs with the carbonyl group of MVK. The resulting dynamics are stable with the energy error of 2 meV atom -1 , demonstrating the ability of the ACE MLP to represent reactions and specific HB interactions (Fig. ). The second one corresponds to a TS immersed in a box containing 55 water molecules (box size: 12.42 Å, Fig. ). The resulting accuracy confirms that ACE MLP is reliable for investigating the reaction of CP and MVK in solution. Validation of the other systems is provided in the SI § S6.