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R Eichler

Publications and source records attributed to R Eichler.

15 recordsLinked to original sources
PubMed2002

Chemical investigation of hassium (element 108).

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

Journal Article↗
PubMed2001

The tetraheme cytochrome c NrfH is required to anchor the cytochrome c nitrite reductase (NrfA) in the membrane of Wolinella succinogenes.

The electron-transport chain that catalyzes nitrite respiration with formate in Wolinella succinogenes consists of formate dehydrogenase, menaquinone and the nitrite reductase complex. The latter catalyzes nitrite reduction by menaquinol and is made up of NrfA and NrfH, two c-type cytochromes. NrfA is the catalytic subunit; its crystal structure is known. NrfH belongs to the NapC/NirT family of membrane-bound c-type cytochromes and mediates electron transport between menaquinol and NrfA. It is demonstrated here by MALDI MS that four heme groups are attached to NrfH. A Delta nrfH deletion mutant of W. succinogenes was constructed by replacing the nrfH gene with a kanamycin-resistance gene cartridge. This mutant did not form the NrfA protein, probably because of a polar effect of the mutation on nrfA expression. The nrfHAIJ gene cluster was restored by integration of an nrfH-containing plasmid into the genome of the Delta nrfH mutant. The resulting strain had wild-type properties with respect to growth by nitrite respiration and nitrite reductase activity. A mutant (stopH) that contained the nrfHAIJ locus with nrfH modified by two artificial stop codons near its 5' end produced wild-type amounts of NrfA in the absence of the NrfH protein. NrfA was located exclusively in the soluble cell fraction of the stopH mutant, indicating that NrfH acts as the membrane anchor of the NrfHA complex in wild-type bacteria. The stopH mutant did not grow by nitrite respiration and did not catalyze nitrite reduction by formate, indicating that the electron transport is strictly dependent on NrfH. The NrfH protein seems to be an unusual member of the NapC/NirT family as it forms a stable complex with its redox partner protein NrfA.

Base Sequence↗
PubMed2000

Evidence for new isotopes of element 107: 266Bh and 267Bh

New neutron rich isotopes 267107Bh and 266107Bh were produced in bombardments of a 249Bk target with 117-MeV and 123-MeV 22Ne ions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Identification was made by observation of correlated alpha-particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. 267Bh was produced with a cross section of approximately 70 pb and decays with a 17(+14)(-6) s half life by emission of alpha particles with an average energy of 8.83+/-0.03 MeV. One atom of 266Bh was observed, decaying within 1 s by emission of a 9.29-MeV alpha particle.

Journal Article↗
PubMed2000

Chemical characterization of bohrium (element 107)

The arrangement of the chemical elements in the periodic table highlights resemblances in chemical properties, which reflect the elements' electronic structure. For the heaviest elements, however, deviations in the periodicity of chemical properties are expected: electrons in orbitals with a high probability density near the nucleus are accelerated by the large nuclear charges to relativistic velocities, which increase their binding energies and cause orbital contraction. This leads to more efficient screening of the nuclear charge and corresponding destabilization of the outer d and f orbitals: it is these changes that can give rise to unexpected chemical properties. The synthesis of increasingly heavy elements, now including that of elements 114, 116 and 118, allows the investigation of this effect, provided sufficiently long-lived isotopes for chemical characterization are available. In the case of elements 104 and 105, for example, relativistic effects interrupt characteristic trends in the chemical properties of the elements constituting the corresponding columns of the periodic table, whereas element 106 behaves in accordance with the expected periodicity. Here we report the chemical separation and characterization of six atoms of element 107 (bohrium, Bh), in the form of its oxychloride. We find that this compound is less volatile than the oxychlorides of the lighter elements of group VII, thus confirming relativistic calculations that predict the behaviour of bohrium, like that of element 106, to coincide with that expected on the basis of its position in the periodic table.

Journal Article↗
PubMed1999

First Measurement of a Thermochemical Property of a Seaborgium Compound.

With only a few atoms of seaborgium (Sg, element 106), in the form of volatile SgO(2)Cl(2), it was possible to determine the sublimation enthalpy of this compound using gas chromatography. Furthermore, it was demonstrated that in Group 6 Sg is chemically more similar to W than to Mo.

Journal Article↗
PubMed1997

[Technical adaptation of impulse oscillometry to special research conditions].

The technical adaptation of the Impulse-Oscillometry (IOS) to different conditions of measurement allows a wide range of applications so that even questions of peripheral user groups using lung function tests can be answered. Thus, the variable connection of the IOS head via fold hose opens the field of bedside measurements and additional applications in pediatrics, intensive care and veterinary medicine. Rhinomanometric examinations are possible with little expenditure and high practicability using nasal tips.

Adult↗
PubMed1992

Relative strength of central and peripheral fusion as a function of stimulus parameters.

We investigated the role of various stimulus parameters that influence motor fusion responses for peripheral as compared to central fusional stimuli. Results from the initial experiment indicated that a central stimulus equal in size to a peripheral fusion stimulus dominated the response independent of the amount of retinal eccentricity of the peripheral target. A second experiment indicated that the central stimulus dominated even when the peripheral stimulus was larger. However, when the peripheral stimulus was changed in shape so that it became an annulus surrounding the central stimulus, the peripheral stimulus was always stronger. In another phase of the experiment, we found that the extent to which a peripheral stimulus surrounded the central one determined which controlled the response. We concluded that the surrounding perceptual gestalt produced by the peripheral stimulus was the most significant variable determining the relative strengths of central and peripheral fusion stimuli. Clinical implications are discussed.

Adult↗
PubMed1992

[Osteoma of the mid-face area--a rare site].

Osteomas are benign, symptomless, slowly growing tumors that are usually found incidentally. The most frequent site of origin is a paranasal sinus. We report a 17 year old man with an osteoma of the middle face. The history, clinical findings and surgical procedure are described. Aetiological factors and possible complications of paranasal osteomas are discussed.

Adolescent↗
PubMed1980

[Leukocyte migration inhibition test in multiple sclerosis - results of a migration technic according to Clausen using brain specific antigens].

The leukocyte migration inhibitory factor (LIF) was examined in 57 test persons--27 patients with multiple sclerosis (MS) and 30 normals--with the indirect and the direct leucocyte migration inhibition test in agarose (LMIAT). The stimulation of lymphocytes was carried out by the application of myelin basic protein (BP) and a membrane-associated antigen of normal brain (NTA). The mean value of controls +/- 2 s and the migration index less than or equal to 0,80 were used for limiting. In the indirect technique could be established significant group effects (NTA- and BP-values of MS cases compared to the controls) after 10 hours of incubation. The direct method showed in MS patients a significant lowered migration-index on an average after stimulation with the NTA; controls gave negative findings (except two cases). The valence of the test system and prospective modifications for further results were indicated.

Adult↗