For further insight into the role of solvent in protein conformer stabilization, the structural and dynamic properties of protein ions in vacuo have been probed by hydrogen-deuterium exchange in a Fourier-transform mass spectrometer. Multiply charged ions generated by electrospray ionization of five proteins show exchange reactions with 2H20 at 10-7 torr (1 torr = 133.3 Pa) exhibiting pseudo-first-order kinetics. Gas-phase compactness of the S-S cross-linked RNase A relative to denatured S-derivatized RNase A is indicated by exchange of 35 and 135 hydrogen atoms, respectively. For pure cytochrome c ions, the existence of at least three distinct gaseous conformers is indicated by the substantially different values-52, 113, and 74 -ofreactive H atoms; the observation of these same values for ions of a number-2, 7, and 5, respectively-of different charge states indicates conformational insensitivity to coulombic forces. For each of these conformers, the compactness in vacuo indicated by these values corresponds directly to that of a known conformer structure in the solution from which the conformer ions are produced by electrospray. S-derivatized RNase A ions also exist as at least two gaseous conformers exchanging 50-140 H atoms. Gaseous conformer ions are isomerically stable for hours; removal of solvent greatly increases conformational rigidity. More specific ion-molecule reactions could provide further details of conformer structures.The relationship between the dynamic structure ofproteins in solution and their biological activity has been of longstanding research interest. Protein folding is probably the least well understood step in the sequence of transformations relating genetic information with its expression by protein function (1). Dramatic new ionization methods for mass spectrometry (MS) have made possible the formation of protein ions in the gas phase to measure molecular weight and primary sequence information (2-4), even on fmol samples (5, 6). Recent studies indicate that protein conformations in solution can affect the resulting charge distribution of the gaseous multiply charged ions formed by electrospray ionization (ESI) (7-9) and that even noncovalent complexes can survive ESI to form gaseous multiply charged ions (10)(11)(12)(13)(14)(15).Critical information concerning solvent effects on the conformation and dynamic properties of proteins has come from NMR (16) and from isotope-exchange experiments with 2H20 (17), including those before and during ESI/MS (18,19). With an activation energy of 17-20 kcal/mol (1 cal = 4.184 J) (17), the H/2H exchange rate depends on the pH (17), electrostatic effects (20), proximity of the solvent-accessible surface (21), and conformational flexibility with hydrogen bond cleavage and formation during local unfolding and folding (22). Studies ofgaseous proteins should help delineate the role of solvent in stabilizing protein conformations, but such previous studies have been mainly theoretical (23) because of the lack of experimental approaches. We repor...

A high-resolution imaging x-ray crystal spectrometer is described for implementation on the EAST tokamak to provide spatially and temporally resolved data on the ion temperature, electron temperature and poloidal plasma rotation. These data are derived from observations of the satellite spectra of helium-like argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to EAST. Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The experimental setup and initial experimental results are presented.

Electron-impact single ionization cross sections for W q+ (q = 4-5) were calculated using the flexible atomic code (FAC) in the level-to-level distorted-wave method, considering the explicit branching ratio. The calculated cross sections are compared with the available theoretical and experiment results in detail. In the case of the contribution from the same channles as the available theoretical results, all of the calculated ionization cross sections agree with the experimental measured cross sections. But the present calculated results are larger than the experimental measurement when all channels contributions are included. Some important channels excitation autoionization (EA) contributions, such as the excitation to higher higher nl subshell from 4f and 5[s,p], were not included into the available theoretical calculation. In general, the distorted-wave (DW) results are overestimated.

No abstract