The structures and energetics of neutral, ionized and protonated methyl tert-butyl ether (MTBE) clusters and (MTBE)(m)(H2O)(n) clusters are investigated by tunable vacuum-UV photoionization mass spectrometry and DFT calculations. While the mass spectra of bare MTBE clusters show unprotonated and protonated clusters ions, the mass spectra of mixed clusters show protonated ions that exhibit magic numbers that correspond to n = m - 2 combinations. Ab initio calculations show that in the larger clusters a multiple proton transfer leads to a protonated water core where all available hydrogen bonds interact with MTBE molecules. The resulting bond structure explains the cluster stability. (C) 2013 Elsevier B. V. All rights reserved.