PubMed Health⌕ Search

Biomedical subjects

S Heinze

Publications and source records attributed to S Heinze.

At least 19 recordsLinked to original sources
PubMed2002

Magnetization-direction-dependent local electronic structure probed by scanning tunneling spectroscopy.

Scanning tunneling spectroscopy (STS) of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different. This experimental result is explained on the basis of first-principles calculations. A detailed analysis reveals that the spin-orbit induced mixing between minority d(xy+xz) and minority d(z(2)) spin states depends on the magnetization direction and changes the local density of states in the vacuum detectable by STS. As a consequence nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips.

Journal Article↗
PubMed2002

Triple point of nuclear deformations.

We show that the second-order phase transition between spherical and deformed shapes of atomic nuclei is an isolated point following from the Landau theory of phase transitions. This point can occur only at the junction of two or more first-order phase transitions which explains why it is associated with one special type of structure and requires the recently proposed first-order phase transition between prolate and oblate nuclear shapes. Finally, we suggest the first empirical example of a nucleus located at the isolated triple-point.

Journal Article↗
PubMed2002

Carbon nanotubes as schottky barrier transistors.

We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.

Journal Article↗
PubMed2001

Resolving complex atomic-scale spin structures by spin-polarized scanning tunneling microscopy.

The spin-polarized scanning tunneling microscope (SP-STM) operated in the constant current mode is proposed as a powerful tool to investigate complex atomic-scale magnetic structures of otherwise chemically equivalent atoms. The potential of this approach is demonstrated by successfully resolving the magnetic structure of Cr/Ag(111), which is predicted on the basis of ab initio vector spin-density calculations to be a coplanar noncollinear periodic 120 degrees Néel structure. Different operating modes of the SP-STM are discussed on the basis of the model of Tersoff and Hamann.

Journal Article↗
PubMed2001

Experimental evidence for intra-atomic noncollinear magnetism at thin film probe tips.

The energy-dependent spin-density orientation (SDO) at the apex of thin magnetic film tips is studied by spin-polarized scanning tunneling spectroscopy (SP-STS) at different bias voltages. At most energies the SDO is collinear with the tip magnetization resulting in a domain or domain-wall contrast in SP-STS images of out-of-plane magnetized samples measured with Gd or Fe coated tips, respectively. For some bias voltages, however, the SDO of the tip is found to be almost perpendicular to its magnetization. This result is explained in terms of intra-atomic noncollinear magnetism.

Journal Article↗
PubMed2001

Disclosure of new and recurrent microbial metabolites by mass spectrometric methods.

The application of modern mass spectrometry methods (SI-CID-MS/MS; MSn) in the disclosure of new and recurrent microbial metabolites is discussed. Spray ion (SI) sources coupled to different kinds of mass analyzers enable the determination of molecular weights and chemical formulas of given samples even in mixtures. Diagnostic fragment formation by collision-induced dissociation (CID-MS/MS) and MSn experiments using ion trap mass analyzers are shown as another indispensable source of structural information. Due to the development of benchtop-type mass spectrometers coupled to high-performance liquid chromatography (HPLC), MS can be practised in almost every laboratory as a powerful tool in natural product analysis. Examples are given for special MS applications in identification of bioactive metabolites from screening strains.

Bacteria↗
PubMed2000

Real-space imaging of two-dimensional antiferromagnetism on the atomic scale

A two-dimensional antiferromagnetic structure within a pseudomorphic monolayer film of chemically identical manganese atoms on tungsten(110) was observed with atomic resolution by spin-polarized scanning tunneling microscopy at 16 kelvin. A magnetic superstructure changes the translational symmetry of the surface lattice with respect to the chemical unit cell. It is shown, with the aid of first-principles calculations, that as a result of this, spin-polarized tunneling electrons give rise to an image corresponding to the magnetic superstructure and not to the chemical unit cell. These investigations demonstrate a powerful technique for the understanding of complicated magnetic configurations of nanomagnets and thin films engineered from ferromagnetic and antiferromagnetic materials used for magnetoelectronics.

Journal Article↗
PubMed1998

New macrodiolide antibiotics, 11-O-monomethyl- and 11, 11'-O-dimethylelaiophylins, from Streptomyces sp. HKI-0113 and HKI-0114.

Elaiophylin (1) and two new methyl derivatives, 11-O-monomethylelaiophylin (2) and 11,11'-O-dimethylelaiophylin (3), were isolated from the mycelium cake of Streptomyces strains HKI-0113 and HKI-0114. The structures of 2 and 3 were determined by mass spectrometric and NMR investigations. Compounds 2 and 3 display antimicrobial and moderate cytotoxic activities.

Animals↗
PubMed1997

Lipohexin, a new inhibitor of prolyl endopeptidase from Moeszia lindtneri (HKI-0054) and Paecilomyces sp. (HKI-0055; HKI-0096). I. Screening, isolation and structure elucidation.

Lipohexin was isolated as a novel lipohexapeptide (I) (C39H68N6O9) from three fungal strains, Moeszia lindtneri HKI-0054, Paecilomyces sp. HKI-0055 and Paecilomyces sp. HKI-0096. The structure was elucidated by detailed mass spectrometric and NMR experiments. The proline-containing peptide displays moderate antibacterial activity against Bacillus subtilis ATCC 6633 and inhibits competitively the prolyl endopeptidase from human placenta.

Anti-Bacterial Agents↗
PubMed1997

Lipohexin, a new inhibitor of prolyl endopeptidase from Moeszia lindtneri (HKI-0054) and Paecilomyces sp. (HKI-0055; HKI-0096). II. Inhibitory activities and specificity.

The new proline-containing lipohexapeptide lipohexin (I) isolated from three fungal strains, Moeszia lindtneri (HKI-0054) and Paecilomyces sp. (HKI-0055 and HKI-0096) is a competitive inhibitor of prolyl endopeptidase (PEP) from human placenta with IC50 of 3.5 microM. Specificity of lipohexin (I) is indicated by the much weaker inhibitory activity against bacterial prolyl endopeptidase from Flavobacterium meningosepticum (IC50 25 microM). No effect of lipohexin (I) was found on the activity of mechanistically related proteases such as proline specific proteases and other serine proteases.

Animals↗
PubMed1997

Ampullosporin, a new peptaibol-type antibiotic from Sepedonium ampullosporum HKI-0053 with neuroleptic activity in mice.

Ampullosporin (I; Ac-Trp-Ala-Aib-Aib-Leu-Aib-Gln-Aib-Aib-Aib-Gln-Leu-Aib-Gln-Leuol) was isolated from the mycelium of Sepedonium ampullosporum as a new 15-membered peptaibol-type antibiotic. The structure was determined by mass spectrometric and two-dimensional NMR experiments. Ampullosporin displays narrow-spectrum antibacterial and antifungal activity, induces pigment formation by Phoma destructiva, causes hypothermia and decreased spontaneous locomotor activity in mice in dosages > 1 mg/kg.

Animals↗