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- Abu-Youssef, Morsy A. M., et al.
(författare)
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New homogeneous and alternating Mn(II)-azido 1D systems
- 2005
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Ingår i: Polyhedron. - : Elsevier BV. - 0277-5387. ; 24:4, s. 557-562
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of sodium azide with manganese(II) and 4-amino-1,2,4-triazol or 3-chloropyridine leads to the 1D systems [Mn(N-3)(2) (4-amtr)(2)](,) (1) or {[Mn(N-3)(2)(3-Clpy)(2)]center dot 1/2(3-Clpy)}(n) (2), respectively. Compound 1 crystallises in the C2/m (monoclinic) group and consists of chains of Mn(II) cations bridged by double mu(1,3)-azido bridges in trans arrangement. Compound 2 crystallises in the I2/a (monoclinic) group and in this case the 1D system shows alternating double mu(1,1) and mu(1,3) bridges. Magnetic properties follow the expected antiferromagnetic (compound 1) and alternating ferro-antiferromagnetic (compound 2) behaviour. (c) 2005 Published by Elsevier Ltd.
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| 4. |
- Calcatelli, A., et al.
(författare)
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Results of the regional key comparison EUROMET.M.P-K1.a in the pressure range from 0.1 Pa to 1000 Pa
- 2005
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Ingår i: Metrologia. - 0026-1394 .- 1681-7575. ; 42:SUPPL.
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Tidskriftsartikel (refereegranskat)abstract
- Within EUROMET a regional key comparison (EUROMET.M.P-K1.a) was performed in order to compare national vacuum standards in the pressure range from 0.1 Pa to 1000 Pa. The participants were BNM-LNE (France), CEM (Spain), OMH (Hungary), IMGC-CNR (Italy), NPL (United Kingdom), MIKES (Finland), PTB (Germany), NMi (The Netherlands), SP (Sweden) and UME (Turkey). IMGC-CNR acted as pilot laboratory. The measurements were carried out from November 1998 to April 2002. The chosen pressure values (from 0.1 Pa to 1000 Pa) cover the most commonly required range for calibration in low-pressure applications. The transfer standards were commercially available capacitance diaphragm gauges (CDGs): one of them was prepared for the comparison by BNM-LNE (Fr) and two were prepared by IMGC-CNR (It). Two sensors had 133 Pa full scale (one absolute and one relative used as absolute) and one 1333 Pa full scale (absolute). For the two 133 Pa full scale sensors seven pressure steps were generated between 0.1 Pa and 100 Pa; for the 1333 Pa full scale sensor nine pressure steps were generated generally between 0.1 Pa and 1000 Pa. The uncertainty of the generated pressure was reported by each participant in the tables of the results that consisted in the generated pressure value, the uncertainty of the generated pressure, the reading of the gauge and the temperature of the standard at each target pressure. The pilot laboratory has analysed the results, after application of the correction for thermal transpiration, in terms of gauge factors for each gauge, and the combined uncertainty was evaluated by considering, besides the component due to the standards, taking into account the components due to the transfer standards to guarantee a uniform uncertainty analysis for all the participants. At each target pressure a EUROMET reference pressure was calculated; finally the difference between the pressures generated by each laboratory from the reference values was calculated and compared with its expanded uncertainty. The results of most of the laboratories showed a good agreement with the reference values. Only a few values of two laboratories were significantly off the reference values. From the available data a linkage to the CCM.P-K4 key comparison results from 1 Pa to 1000 Pa was possible by means of the results of three laboratories in the (1-30) Pa range and two for the (100-1000) Pa range who took part in both the comparisons. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the Mutual Recognition Arrangement (MRA).
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| 5. |
- Martínez-Vicente, Marta, et al.
(författare)
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Effects of mutagenesis in the switch I region and conserved arginines of Escherichia coli MnmE protein, a GTPase involved in tRNA modification
- 2005
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 280:35, s. 30660-30670
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Tidskriftsartikel (refereegranskat)abstract
- MnmE is an evolutionarily conserved, three domain GTPase involved in tRNA modification. In contrast to Ras proteins, MnmE exhibits a high intrinsic GTPase activity and requires GTP hydrolysis to be functionally active. Its G domain conserves the GTPase activity of the full protein, and thus, it should contain the catalytic residues responsible for this activity. In this work, mutational analysis of all conserved arginine residues of the MnmE G-domain indicates that MnmE, unlike other GTPases, does not use an arginine finger to drive catalysis. In addition, we show that residues in the G2 motif (249GTTRD253), which resides in the switch I region, are not important for GTP binding but play some role in stabilizing the transition state, specially Gly249 and Thr251. On the other hand, G2 mutations leading to a minor loss of the GTPase activity result in a non-functional MnmE protein. This indicates that GTP hydrolysis is a required but non-sufficient condition so that MnmE can mediate modification of tRNA. The conformational change of the switch I region associated with GTP hydrolysis seems to be crucial for the function of MnmE, and the invariant threonine (Thr251) of the G2 motif would be essential for such a change, because it cannot be substituted by serine. MnmE defects result in impaired growth, a condition that is exacerbated when defects in other genes involved in the decoding process are simultaneously present. This behavior is reminiscent to that found in yeast and stresses the importance of tRNA modification for gene expression.
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| 6. |
- Mautner, F. A., et al.
(författare)
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New Topology in Azide-Bridged Cobalt(II) Complexes: the Weak Ferromagnet Co-2(N-3)(4)(Hexamethylenetetramine)(H2O) (n)
- 2009
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 48:13, s. 6280-6286
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Tidskriftsartikel (refereegranskat)abstract
- The new polynuclear azido-bridged Co(II) compound with formula [Co-2(N-3)(4)(HMTA)(H2O)](n). (1)(HMTA = hexamethylenetetramine) shows a complex 3D structure. To best understand the structure, a network analysis for 1 as bulk compound and also an analysis of the magnetic network has been made, emerging with a new network topology.
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