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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.

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A range of CaO-Al2O3-SiO2 glasses have been prepared by fusion of pure starting materials in platinum crucibles. Compositions containing large amounts on network formers, Al2O3 and SiO2, are difficult to crystallize. If the amount of network former is reduced, glasses will self-nucleate and crystallize more readily, but the products of crystallization tend to react with water. This conflict has been partly resolved by adding MgO and ZnO and tailoring compositions so as to produce a phase, variously designated "Q" or "pleochroite", ideally Ca20Al32-2 vMg vSivO68, with v close to 4. Pleochroite crystallizes with a typically fibrous morphology. Preliminary experiments on fragments and melt-cast glass rods indicate that these compositions can be heat treated without deformation to yield highly crystalline, transparent ceramics. © 1989 Chapman and Hall Ltd.

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Experimental results on structure defects in microcrystalline (μc) n- and p-doped μc-S1-x:Cx:H films deposited on alkali-free glass substrates by spatial plasma separation1 and obtained by electron paramagnetic resonance (EPR) are presented. The technique used for subtracting the substrate effect on recorded spectra is also discussed as well as its quantification. The microscopic structure of intrinsic defects and impurity states and their role in transport mechanisms are studied and correlated with the composition of their films. These results are also related to transport properties of deposited films in order to observe the role of dopant centres, located at conduction band tails, in controlling the electrical properties. © 1989.