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(CE). The proteins within each group have the same number of modified ionizable sites, so each group constitutes one "rung" in the charge ladder. Smith, Whitesides, and colleagues created charge ladders for three proteins: bovine carbonic anhydrase II (BCAII), bovine pancreatic trypsin inhibitor (BPTI), and hen egg-white lysozyme (HEL). After creating a charge ladder using CE, the researchers used on-line electrospray ionization (ESI) to produce ions in the gas phase and MS to measure the masses and charges of the ions. Throughout the CEESIMS procedure, the researchers used "gentle" conditions to preserve the native structure of the proteins. The relationship between the number of amino groups on the proteins, the net charge of the proteins in solution and the distribution of charge states of the gas-phase ions examined The researchers confirmed that each rung of the charge ladder consisted of proteins with the same number of acetylated amino groups. They also found evidence that the compact structure of the native proteins in solution is preserved across the rungs of the charge ladder. Finally, they showed that the distribution of charge states of gas-phase ions did not necessarily correspond to the net charge of the native protein in solution or to the number of available amino groups. Instead, the researchers said, the magnitude of the charge states appeared to be related to the available surface area of the proteins (/ Phys Chem B 1998 102 11056-601)
Controlling fluid motion and position Networks of channels and liquid arrays are becoming commonplace in the separations world, as analytical instruments continue down the road to miniaturization. But the best way to pump and position liquids on submillimeter scales is not always obvious. Nicholas L. Abbott and co-workers at the University of Wisconsin-Madison and the University of California-Davis describe an electrochemical procedure for actively controlling fluid motion based on changes in surface tension. In contrast to current methods for fluid control such as those based on electrokinetic phenomena, the method imps low voltages (
