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Biomedical subjects

A Stierle

Publications and source records attributed to A Stierle.

14 recordsLinked to original sources
PubMed2006

Structure of Ag(111)-p(4 x 4)-O: no silver oxide.

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

Journal Article↗
PubMed2006

Initial corrosion observed on the atomic scale.

Corrosion destroys more than three per cent of the world's GDP. Recently, the electrochemical decomposition of metal alloys has been more productively harnessed to produce porous materials with diverse technological potential. High-resolution insight into structure formation during electrocorrosion is a prerequisite for an atomistic understanding and control of such electrochemical surface processes. Here we report atomic-scale observations of the initial stages of corrosion of a Cu3Au111 single crystal alloy within a sulphuric acid solution. We monitor, by in situ X-ray diffraction with picometre-scale resolution, the structure and chemical composition of the electrolyte/alloy interface as the material decomposes. We reveal the microscopic structural changes associated with a general passivation phenomenon of which the origin has been hitherto unclear. We observe the formation of a gold-enriched single-crystal layer that is two to three monolayers thick, and has an unexpected inverted (CBA-) stacking sequence. At higher potentials, we find that this protective passivation layer dewets and pure gold islands are formed; such structures form the templates for the growth of nanoporous metals. Our experiments are carried out on a model single-crystal system. However, the insights should equally apply within a crystalline grain of an associated polycrystalline electrode fabricated from many other alloys exhibiting a large difference in the standard potential of their constituents, such as stainless steel (see ref. 5 for example) or alloys used for marine applications, such as CuZn or CuAl.

Journal Article↗
PubMed2005

A surface x-ray study of the structure and morphology of the oxidized Pd001 surface.

The oxidation of Pd(100) and the formation of PdO was studied in situ using surface x-ray diffraction. A bulklike, epitaxial PdO film is formed at oxygen partial pressures beyond 1 mbar and sample temperatures exceeding 650 K. The main orientation is PdO(001)/Pd(001), based upon bulk reflections from the PdO film. By comparing with measurements from the Pd crystal truncation rods, we estimate an rms surface roughness of 6 A, in good agreement with previous high pressure scanning tunneling microscopy measurements. Finally, we observed the transformation from the (radical5 x radical5) surface oxide to PdO bulk oxide at 675 K and 50 mbar O(2) pressure.

Journal Article↗
PubMed2004

X-ray diffraction study of the ultrathin Al2O3 layer on NiAl110.

Ultrathin Al2O3 layers on alloys are used as templates for model catalysts, tunneling barriers in electronic devices, or corrosion-resistant layers. The complex atomic structure of well-ordered alumina overlayers on NiAl110 was solved by surface x-ray diffraction. The oxide layer is composed of a double layer of strongly distorted hexagonal oxygen ions that hosts aluminum ions on both octahedral and tetrahedral sites with equal probability. The alumina overlayer exhibits a domain structure that can be related to characteristic growth defects and is generated during the growth of a hexagonally ordered overlayer (Al2O3) on a body-centered cubic (110) substrate (NiAl).

Journal Article↗
PubMed2004

Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures.

The oxidation of the Pd(100) surface at oxygen pressures in the 10(-6) to 10(3) mbar range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions, we observe either a thin (sqrt[5]xsqrt[5])R27 degrees surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.

Journal Article↗
PubMed2000

Structural requirements for activity of the pheromones of Ustilago hordei.

Ustilago hordei, the cause of barley-covered smut, initiates mating with pheromones. Gene sequence analysis suggested that these pheromones, Uhmfa1 and Uhmfa2, would be farnesylated peptides. Although isolation of mating-type-specific activity was rarely possible, chromatographic separations of culture supernatants yielded fractions that stimulated or inhibited mating. Based on predicted amino acid sequences and mass spectra of stimulating fractions, a series of pheromone analogs were synthesized and their activities were determined. Underivatized Uhmfa1 (PGKSGSGLGYSTC) or Uhmfa2 (EGKGEPAPYC) peptides were inactive, while peptides that were farnesylated and/or methyl esterified specifically induced conjugation tubes by cells of the opposite mating type. Uhmfa1 truncated from the amino terminus beyond the lysine lost activity, while truncated Uhmfa2 remained partially active. In mating bioassays, a pheromone concentration-dependent default mating response was observed. In competition studies, shorter Uhmfa1 peptides lacking pheromone activity inhibited activity of full-length peptides most effectively when both had the same functional groups.

Chromatography, High Pressure Liquid↗
PubMed1999

Sphaeric acid, a new succinic acid derivative from a Sphaeropsis sp.

The structure of sphaeric acid (1), a novel succinic acid derivative isolated from the fermentation broth of a Sphaeropsis sp., was determined by spectral data and synthetic transformation to the diol of sphaeric acid and subsequently to a pair of gamma-lactones (2 and 3).

Fungi↗
PubMed1998

Trace element analysis on Si wafer surfaces by TXRF at the ID32 ESRF undulator beamline.

Synchrotron radiation total-reflection X-ray fluorescence (SR-TXRF) has been applied to the impurity analysis of Si wafers using a third-generation synchrotron radiation undulator source. A lower limit of detectability (LLD) for Ni atoms of 17 fg (1.7 x 10(8) atoms cm(-2)) has been achieved with an optical set-up based on an Si(111) double-crystal monochromator and a horizontal sample geometry. These first results are very promising for synchrotron radiation trace element analysis since we estimate that it is possible to lower the LLD by a factor of about 25 by employing appropriate optics and detectors. The use of a crystal monochromator opens new possibilities to perform absorption and scattering experiments (NEXAFS and X-ray standing-wave methods) for chemical and structural analysis of ultratrace elements.

Journal Article↗
PubMed1995

The search for a taxol-producing microorganism among the endophytic fungi of the Pacific yew, Taxus brevifolia.

Endophytic microbes associated with the Pacific yew tree, Taxus brevifolia, were examined as potential sources of the anticancer drug taxol [1], a secondary metabolite of the host organism. The first promising organism found was the novel fungus, Taxomyces andreanae, which was isolated from the inner bark of a yew tree growing in northwestern Montana. It appears to produce taxol and other taxanes in de novo fashion when grown in semi-synthetic liquid media. The presence of 1 in the fungal extract was confirmed by mass spectrometry, comparative chromatographic behavior with "yew" taxol, reactivity with taxol-specific monoclonal antibodies, and 9KB cytotoxicity studies. Both acetate-1-14C and phenylalanine UL-14C served as precursors of taxol-14C in fungal culture labeling studies, confirming the de novo synthesis of 1 by the fungus. Immunoassay techniques are currently being used to screen extracts of Taxomyces andreanae for new taxanes, and to determine if other endophytic fungi are taxol producers.

Antibodies, Monoclonal↗
PubMed1993

Taxol and taxane production by Taxomyces andreanae, an endophytic fungus of Pacific yew.

Taxomyces andreanae, a fungal endophyte, was isolated from the phloem (inner bark) of the Pacific yew, Taxus brevifolia. The fungus is hyphomyceteous and, when grown in a semi-synthetic liquid medium, produced taxol and related compounds. Taxol was identified by mass spectrometry, chromatography, and reactivity with monoclonal antibodies specific for taxol. Both [1-14C]acetic acid and L-[U-14C]phenylalanine served as precursors of [14C]taxol in fungal cultures. No taxol was detected in zero-time cultures or in the small agar plugs used to inoculate the culture flasks.

Antibodies, Monoclonal↗
PubMed1991

Apheresis-elutriation program for adoptive immunotherapy with autologous activated monocytes in cancer patients.

Human blood monocytes (Mo) and monocyte-derived macrophages (M phi) are known to be potent antitumor cytotoxic effector cells through activation with recombinant human interferon gamma (rIFN-gamma), bacterial muramyldipeptide or the synthetic derivative muramyltripeptide phosphatidylethanolamine entrapped in liposomes (L-MTP-PE). Large-scale generation of ex vivo activated Mo from the blood of cancer patients proved feasible. We report our experience with a fixed rotor speed counterflow centrifugation elutration (CEE) procedure using the newly available Beckman high capacity JE-5.0 rotor system that reproducibly isolates up to 1.0-1.5 x 10(9) Mo with greater than 90% purity, in suspension and functionally intact derived from peripheral blood mononuclear cell-enriched suspensions obtained by leukapheresis (LP) from healthy volunteers and cancer patients. The semiclosed, easy to handle CCE system, was adapted to a sterile technique that permitted clinical trials in adoptive monocyte immunotherapy. Freshly isolated Mo did not lose morphological or functional integrity and had no spontaneous activation. Their abilities to become activated to the cytotoxic state after 18-h stimulation with 500 U/ml rIFN-gamma or 1 microgram/ml L-MTP-PE and to differentiate into matured M phi in vitro were not altered. The system was therefore used to isolate large numbers of Mo for a phase I clinical trial of intraperitoneal immunotherapy with L-MTP-PE activated autologous Mo in nine patients with peritoneal carcinomatosis. Each patient received weekly Mo infusions (n = 5) with an intrapatient dose escalation schedule (from 10(7) to 10(9) Mo). Toxicities were mild including fever, chills and abdominal pain. There was no treatment-induced thromboembolic event or capillary leak syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1984

Effects of an extract of human brain containing growth factor activity on the proliferation of human vascular endothelial cells in primary culture.

Lesions of vascular human EC play an important role in the development of thrombi and atherosclerosis. The factors which control the repair of vascular lesions are not well known. In addition, they are difficult to study because vascular EC from large vessels are fastidious cells to grow in tissue culture. We have investigated some of the factors that may be important in human umbilical vein EC growth in primary culture. Because of reported species differences in EC culture, we have decided to culture human EC only in the presence of biological culture reagents of human origin. Human umbilical vein EC, at low seed density, can be grown to confluency on a human FN matrix or on human ECM providing the medium is supplemented with a high concentration (30%) of human serum. The optimal proliferation of EC (even when seeded at clonal density) is obtained if HBE is added. HBE cannot completely replace serum, but EC proliferate to a similar extent whether they are grown on FN or on ECM in the presence of 30% human serum of 10% human serum plus HBE. Thus, HBE contains a growth factor activity for human EC which stimulates cell growth and DNA replication. Further work is needed to purify HBE and to compare it to other endothelial cell growth factors isolated from bovine brain and bovine eye.

Blood Vessels↗
PubMed1982

Role of cyclic AMP in the inhibition of human platelet aggregation by quercetin, a flavonoid that potentiates the effect of prostacyclin.

Quercetin (3.3',4',5,7-pentahydroxyflavone) has previously been shown to inhibit cyclic nucleotide phosphodiesterases prepared from various cell homogenates and the function of intact human platelets. We now report that (1) high concentrations of quercetin raise platelet cAMP levels; and (2) quercetin potentiates the inhibitory effect of prostacyclin (PGI2) on ADP-induced washed human platelet aggregation and the elevation of platelet cAMP levels elicited by PGI2. These results suggest a role for cAMP in the mechanism of action of quercetin on blood platelets.

Adenosine Diphosphate↗