Prospects for study

When the new term permease was coined to designate bacterial membrane proteins specialized in the transport of specific metabolites [1,2], it covered a concept which was not quite new. The existence of membrane transport systems had been demonstrated in animal tissues by Cori as early as 1925 (see [3]). However, the discovery and characterization of permeases in bacteria revolutionized prospects for studying the properties of transport systems, opening the way to a new field and a very fruitful methodology. 

The separation of molecular conformations using differences in their ion mobility is generally perceived to require substantial differences in their size and/or shape and thus their cross section for interaction with the buffer gas. Perhaps not as obviously, appreciable changes in cross section can also be induced by variations in the electronic state of an atomic ion, which otherwise would seem to have very similar sizes and shapes. Indeed the development of ion mobility mass spectrometry as we know it today has its roots in this particular application. Exciting prospects for studying electronic state-specific chemistry, especially that of heavier metal elements, is made possible by this interesting observation. In this chapter, the theory behind such separations and the historical development of this area along with recent advances are reviewed. Table 2.1 lists the mobilities of the various atomic cations discussed in the remainder of this chapter. 

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