A compact cesium ion source with a Wien filter is described. This source has been developed in order to produce a pure beam of cesium ions for positive SIMS analysis. The ions are produced by a surface ionization ion emitter. The initial beam is about 99% pure and the remaining 1% is removed via the Wien filter. An asymmetric einzel lens at the end provides the focusing of the beam on the target. A short description of the source is presented as well as the measured final beam characteristics.

A review with 59 refs. describing the synthesis, structure, and reactivity of monocyclopentadienyl compds. of vanadium. [on SciFinder(R)]

A study using a primary Cs’ beam to carry out positive SIMS on conductive samples is presented. The energy distribution of positive secondary ions was measured and the sputter yield, S’ was calculated for several elements, The significantly different energetic behavior found between the secondary cesium ions and those ejected from the target will be discussed. Finally, the best conditions to perform positive SIMS with such a primary beam will be described.

n/a

n/a

n/a

n/a

A new type of non-heme iron protein was purified to homogeneity from extracts of Desulfovibrio desulfuricans (ATCC 27774) and Desulfovibrio vulgaris (strain Hildenborough). This protein is a monomer of 16-kDa containing two iron atoms per molecule. The visible spectrum has maxima at 495, 368, and 279 nm and the EPR spectrum of the native form shows resonances at g = 7.7, 5.7, 4.1 and 1.8 characteristic of a high-spin ferric ion (S = 5/2) with E/D = 0.08. Mossbauer data indicates the presence of two types of iron: an FeS4 site very similar to that found in desulforedoxin from Desulfovibrio gigas and an octahedral coordinated high-spin ferrous site most probably with nitrogen/oxygen-containing ligands. Due to this rather unusual combination of active centers, this novel protein is named desulfoferrodoxin. Based on NH2-terminal amino acid sequence determined so far, the desulfoferrodoxin isolated from D. desulfuricans (ATCC 27774) appears to be a close analogue to a recently discovered gene product from D. vulgaris (Brumlik, M.J., and Voordouw, G. (1989) J. Bacteriol. 171, 49996-50004), which was suggested to be a rubredoxin oxidoreductase. However, reduced pyridine nucleotides failed to reduce the desulforedoxin-like center of this new protein.

n/a

n/a

n/a

n/a

n/a

n/a