What is the energy of activation of uncatalyzed ATP hydrolysis reaction?

If we ignore all the biological significans for a while, ATP hydrolysis, the reaction:
ATP + H2O -> ADP + Pi
is still a chemical reaction that must go through transition state to yield product. This is no doubt a nucleophillic substitution reaction that, according to all the paper I've found, occurs by SN2 mechanism. But what's totally missing is the energy of activation of the uncatalyzed reaction.
There are a lot of paper on the mechanism of ATP hydrolysis in the active site of this enzyme and that motor. There are a few paper on uncatalyzed reaction and various nucleophile. A few paper does estimate the activation energy of ATP hydrolysis by various enzyme and motor proteins. But I haven't found a single paper estimating the Eact of the uncatalyzed reaction.
My failure apart, what is the energy of activation of this reaciton without the aid of any enzyme or other catalyst? Did nobody make any estimation?


