Developing ion mobility methods for studying structure and assembly of biomolecules

The advent of electrospray ionization (ESI) has allowed for the study of macromolecules, such as non-covalently bound clusters and proteins, in the gas phase. Thus, a number of techniques have been developed to probe the fundamental aspects of biomolecules in the gas phase. Key to this work is the coupling of ion mobility spectrometry (IMS), in which gas phase ions are separated based on charge state and collision cross section, to time-of-flight mass spectrometry (MS). This work begins with application of IMS-MS to study structural transitions and gas phase protein unfolding pathways of ubiquitin ions stored in a 3-dimensional Paul trap. Next, the sensitivity of the instrument was increased by incorporating a 2-dimensional linear octopole ion trap into the IMS-MS instrument. In addition, sonic spray and desorption electrospray ionization sources have been interfaced for specific biomolecular analysis.; The final portion of this work involves the study of non-covalently bound amino acid clusters formed by ESI. One of the most studied systems is the serine octamer, which forms a stable magic cluster and displays an unusual homochiral preference. Although, the spontaneous resolution of racemic mixtures is rarely observed in nature, results presented here suggest that chiral resolution of the serine octamer may be general to other amino acid cluster systems with different sizes and geometries. Chiral preference analysis has been extended to other amino acid clusters from which proline showed the most interesting result. IMS-MS results reveal significant structural features of enantiopure proline clusters as a function of cluster size. Analysis of large ( x = 50 to 100) proline cluster sizes show an extended rod-like geometries that are chirally resolved. However, the most dramatic structural feature of enantiopure proline clusters is the discovery of a remarkably stable icosahedron [12Pro+H]+ cluster ion that is also chirally resolved. Detailed analysis involving experiments and molecular mechanics simulations provide insights into the underlying mechanisms involved in the chiral resolution of higher ordered structures.