Evidence for spontaneous resolution of icosahedral proline.

Here we show experimental evidence for the spontaneous chiral resolution of icosahedral [12Pro+H]+ cluster ion. Molecular simulations reveal that the icosahedron consists of 12 equally spaced prolines where the rigid pyrrolidine ring of each monomer is sticking out of the closed cage. The tightly packed chiral cage traps a single proton in the center cavity. On the other hand, racemic [12Pro+H]+ cluster size exhibits a prismatic structure that can easily incorporate and lose proline monomeric unit sequentially, thus easily forming other geometries. Mechanisms which account for these observations are discussed.