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The interaction of hydrogen with a cobalt(101¯0) surface (1994)

Ernst, K.-H. ; Schwarz, E. ; Christmann, K.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 101 (1994), S. 5388-5401

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: The adsorption of hydrogen on a cobalt(101¯0) surface was investigated in ultrahigh vacuum (UHV) between 85 and 500 K using Video-LEED, temperature-programmed thermal desorption (TPD), work function (ΔΦ) measurements, and high-resolution electron energy loss spectroscopy (HREELS). Between 90 and 200 K, hydrogen adsorbs dissociatively with high sticking coefficient (s0≥0.8) via precursor kinetics and forms, with increasing exposure, a c(2×4), a p2mg (2×1) and a (1×2) LEED structure (hydrogen coverages aitch-thetaH=0.5, 1.0, and 1.5, respectively). While the first two structures represent true ordered hydrogen phases there is strong evidence that the (1×2) phase is reconstructed, likely in a paired-row configuration. The formation of the (1×2) phase is slightly thermally activated; its decomposition produces a sharp thermal desorption maximum (α state) appearing on the low-energy side of a β-TPD signal which reflects the hydrogen desorbing from the unreconstructed surface. The activation energies for desorption from the α and β states are 62 and 80 kJ/mol, respectively. Chemisorption in the β state [(2×1) phase up to aitch-thetaH=1.0] is associated with a ΔΦ of +207 meV, while the fully developed (1×2) reconstructed phase (α state) causes a ΔΦ of approximately −122 meV resulting in an overall work function change of +85 meV at saturation. From HREELS, we determine the H adsorption site in all superstructures to be threefold with a local CS symmetry. Our results are discussed and compared with previous findings for similar metal–hydrogen interaction systems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.467392

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The glucose kinase gene of Streptomyces coelicolor A3(2): its nucleotide sequence, transcriptional analysis and role in glucose repression (1992)

Angell, S. ; Schwarz, E. ; Bibb, M. J.

Oxford, UK : Blackwell Publishing Ltd

Molecular microbiology 6 (1992), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: Mutants (glk) of Streptomyces coelicolor A3(2) that are resistant to the non-utilizable glucose analogue 2-deoxyglucose are deficient in glucose kinase activity, defective in glucose repression, and usually unable to utilize glucose. A 2.9 kb Bcll fragment, previously shown to restore a wild-type phenotype to a glk deletion mutant that lacks the entire segment, contains two complete open reading frames that would encode proteins of 20.1 kDa (ORF2) and 33.1 kDa (ORF3). ORF3 is transcribed from its own promoter, and also from a promoter that initiates transcription upstream of ORF2. A derivative of the temperate phage πC31 containing ORF3 alone restored a wild-type phenotype when used to lysogenize the deletion mutant. The product of ORF3 is homologous to members of a family of repressor proteins encoded by xylR In Bacillus subtilis and Lactobacilius pentosus, and by nagC in Escherichia coli. Although this might suggest that ORF3 encodes a positive activator for glucose kinase, rather than the enzyme itself, ORF3 restored the ability to metabolize glucose to an E. coli glk mutant, and activity gels of cell extracts of E. coli containing ORF3 cloned in the pT7-7 expression vector demonstrated that the ORF3 product has glucose kinase activity.