Amplified Rate Acceleration by Simultaneous Up-Regulation of Multiple Active Sites in an Endo-Functionalized Porous Capsule

Using the hydrolysis of epoxides in water as a model reaction, the effect of multiple active sites on Michaelis-Menten compliant rate accelerations in a porous capsule is demonstrated. The capsule is a water-soluble 4-symmetry Keplerate-type complex of the form, [{(Mo6O21)-O-VI(H2O)(612){(Mo2O4)-O-V(L)}(30)](42-), in which 12 pentagonal "ligands," {(Mo-VI)(Mo5O2)-O-VI, (H2O)(6)}(6-), are coordinated to 30 dimolybdenum sites, {(Mo2O4L)-O-V}(1+) (L = an endohedrally coordinated 772-bound carboxylate anion), resulting in 20 MO9O9 pores. When "up-regulated" by removal of ca. one-third of the blocking ligands, L, an equal number of dimolybdenum sites are activated, and the newly freed-up space allows for encapsulation of nearly twice as many substrate guests, leading to a larger effective molarity (amplification), and an increase in the rate acceleration (k(cat)/L-uncat) from 16,000 to an enzyme-like value of 182,800.