Biomedical subjects

Michael Moseler

Publications and source records attributed to Michael Moseler.

8 recordsLinked to original sources

PubMed2007

Size-dependent structural evolution and chemical reactivity of gold clusters.

Ground-state structures and other experimentally relevant isomers of Au(15) (-) to Au(24) (-) clusters are determined through joint first-principles density functional theory and photoelectron spectroscopy measurements. Subsequent calculations of molecular O(2) adsorption to the optimal cluster structures reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis of the underlying electronic structure shows that the chemical reactivity of the gold cluster anions can be elucidated in terms of a partial-jellium picture, where delocalized electrons occupying electronic shells move over the ionic skeleton, whose geometric structure is strongly influenced by the directional bonding associated with the highly localized "d-band" electrons.

Journal Article↗

PubMed2006

Structural relaxation made simple.

We introduce a simple local atomic structure optimization algorithm which is significantly faster than standard implementations of the conjugate gradient method and often competitive with more sophisticated quasi-Newton schemes typically used in ab initio calculations. It is based on conventional molecular dynamics with additional velocity modifications and adaptive time steps. The surprising efficiency and especially the robustness and versatility of the method is illustrated using a variety of test cases from nanoscience, solid state physics, materials research, and biochemistry.

Algorithms↗

PubMed2005

Oxidation of magnesia-supported Pd-clusters leads to the ultimate limit of epitaxy with a catalytic function.

Oxide-supported transition-metal clusters and nanoparticles have attracted significant attention owing to their important role as components of model catalysts, sensors, solar cells and magnetic recording devices. For small clusters, functionality and structure are closely interrelated. However, knowledge of the structure of the bare cluster is insufficient as the interaction with the chemical environment might cause drastic structural changes. Here we show by ab initio simulations based on the density functional theory that the reaction with molecular oxygen transforms small, non-crystalline, magnesia-supported Pd-clusters to crystalline Pd(x)O(y) nano-oxide clusters that are in epitaxy with the underlying support. Restructuring of the Pd backbone is controlled by the electrostatic interaction with magnesia leading to a strong reduction of the O2 dissociation barrier. The supported Pd(x)O(y) clusters are likely to serve as Mars-van Krevelen oxygen reservoirs in catalytic oxidation reactions as observed for PdO overlayers and demonstrated here for the oxidation of CO molecules.

Catalysis↗

PubMed2005

The ultrasmoothness of diamond-like carbon surfaces.

The ultrasmoothness of diamond-like carbon coatings is explained by an atomistic/continuum multiscale model. At the atomic scale, carbon ion impacts induce downhill currents in the top layer of a growing film. At the continuum scale, these currents cause a rapid smoothing of initially rough substrates by erosion of hills into neighboring hollows. The predicted surface evolution is in excellent agreement with atomic force microscopy measurements. This mechanism is general, as shown by similar simulations for amorphous silicon. It explains the recently reported smoothing of multilayers and amorphous transition metal oxide films and underlines the general importance of impact-induced downhill currents for ion deposition, polishing, and nanopattering.

Journal Article↗

PubMed2004

Symmetry and electronic structure of noble-metal nanoparticles and the role of relativity.

We present high resolution UV-photoelectron spectra of cold mass selected Cun-, Agn-, and Aun- with n=53-58. The observed electron density of states is not the expected simple electron shell structure, but is strongly influenced by electron-lattice interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show completely different spectra with almost no degeneracy, which indicates that they have structures of much lower symmetry. This behavior is related to strong relativistic bonding effects in gold, as demonstrated by ab initio calculations for Au55-.

Journal Article↗

PubMed2003

Polymorphisms in the IL 18 gene are associated with specific sensitization to common allergens and allergic rhinitis.

BACKGROUND: Atopy has been linked to chromosome 11q22, a region that harbors the IL18 gene. IL-18 enhances IL-4/IL-13 production and induces IgE production that is directly associated with the pathogenesis of atopic disorders. OBJECTIVE: We sought to investigate whether genetic abnormalities in the regulatory regions of the IL18 gene predispose, in part, to susceptibility to atopy. METHODS: Among a white population of 105 families, the oldest child was examined with regard to atopic phenotypes and single-nucleotide polymorphisms (SNPs) within the IL18 gene. RESULTS: We have identified 5 novel SNPs in the IL18 gene (-920[t/c], -133[c/g], and -132[a/g] in promoter 2 [upstream of exon 2]; +179[c/a; Ser35Ser] in exon 4; and +486[c/t; Phe137Phe] in exon 6). Three SNPs are located in promoter 2, and one (-133[c/g]; nuclear factor 1 site) was significantly associated with high serum IgE levels (P =.001; odds ratio, 3.96) and specific sensitization to common allergens (P =.005; OR, 4.12). In addition, previously identified SNPs in exon 1 (+113[t/g] and +127[c/t]) and in promoter 1 (-137[g/c], GATA3 site) of the IL18 gene were significantly associated with high IgE levels (P < or =.005; OR, 3.27-3.90) and specific sensitization (P =.02 to.008; OR, 3.27-3.83). The SNP +127(g/t) in exon 1 was also a susceptibility locus for seasonal allergic rhinitis (P =.008; OR, 3.22). CONCLUSION: IL18 might be responsible for the linkage effects seen in the chromosomal region 11q22, which has been found previously with the phenotype "sensitization to mite allergen." Thus a suspected direct role of IL18 in the pathogenesis of atopy has been strengthened by the presence of 8 common SNPs in the promoter regions of IL18.

Alleles↗

PubMed2002

Bonding in Cu, Ag, and Au clusters: relativistic effects, trends, and surprises.

Electronic structure and bonding in anionic coinage metal clusters are investigated via density-functional calculations, focusing on an extensive set of isomers of Cu(-)(7), Ag(-)(7), and Au(-)(7). While the ground states of Cu(-)(7) and Ag(-)(7) are three dimensional (3D), that of Au(-)(7) is planar, separated from the optimal 3D isomer by 0.5 eV. The simulated thermally weighted photoabsorption spectrum of Au(-)(7) is dominated by planar structures, and it agrees well with the measured one. The propensity of Au(-)(N) clusters to favor planar structures (with N as large as 13) is correlated with strong hybridization of the atomic 5d and 6s orbitals due to relativistic effects.

Journal Article↗

PubMed2002

Circadian variation of exhaled nitric oxide and urinary eosinophil protein X in asthmatic and healthy children.

Asthmatic symptoms and the frequency of admissions to hospital because of acute asthma tend to increase in the early morning hours, and it is therefore possible that airway inflammation increases during the night. To elucidate the hypothetical circadian variation of airway inflammation, we measured concentrations of exhaled nitric oxide (FeNo), urinary eosinophil protein X excretion (EPX), and forced expiratory volume in the first second (FEV1) in 20 asthmatic and 6 nonatopic nonasthmatic children every 3 h during a 21-h period. Compared with control subjects, asthmatic subjects had higher FeNo (median, 22.7 versus 10.3 ppb, p = 0.016) and lower FEV1 % predicted (median, 91.0 versus 101.9%, p = 0.045), but did not differ significantly in EPX (median, 153.8 versus 148.7 microg/mmol creatinine, p = 0.83) at 7 AM. However, differences in gender and age do not allow direct comparisons between asthmatic and control children. FeNo and EPX demonstrated a cosinelike circadian rhythm (log FeNo, p = 0.0001; log EPX, p = 0.0001) with lowest levels at 7 PM and highest at 7 AM. This was also the case for FEV1 % (p = 0.01). No difference in the amplitude of circadian rhythm was observed between asthmatic and healthy control children for log FeNo (p = 0.35), log EPX (p = 0.57), and FEV1 % (p = 0.17). A stratified analysis showed a significant circadian rhythm in the control group for log FeNo (p = 0.014) and log EPX (p = 0.0001). Our results therefore suggest a circadian rhythm of inflammatory markers, which peaks in the early morning. Rhythmicity of EPX excretion and FeNo in healthy children suggests a physiologic mechanism; however, pathologic effects during the night might occur under conditions of asthma-specific inflammation.

Adolescent↗