Translate this page to:
In JoVE (1)
Other Publications (46)
- Respiration Physiology
- Biochemical Pharmacology
- Biomedical Mass Spectrometry
- Biomedical Mass Spectrometry
- Journal of Neurochemistry
- Biomedical Mass Spectrometry
- Journal of Neurochemistry
- Journal of Neurochemistry
- Journal of Cancer Research and Clinical Oncology
- Recent Results in Cancer Research. Fortschritte Der Krebsforschung. ProgrÃ¨s Dans Les Recherches Sur Le Cancer
- Surgery, Gynecology & Obstetrics
- Cancer Research
- Cancer Research
- Life Sciences
- Cancer Research
- Xenobiotica; the Fate of Foreign Compounds in Biological Systems
- Physical Review. A
- Chemico-biological Interactions
- Applied and Environmental Microbiology
- Applied Microbiology and Biotechnology
- Der Chirurg; Zeitschrift Fur Alle Gebiete Der Operativen Medizen
- Physical Review Letters
- Physical Review Letters
- American Journal of Physiology. Renal Physiology
- Nano Letters
- Physical Review Letters
- Infection and Immunity
- Nano Letters
- Annals of Internal Medicine
- Nano Letters
- Journal of Physics. Condensed Matter : an Institute of Physics Journal
- Journal of Immunology (Baltimore, Md. : 1950)
- Physical Review Letters
- Nano Letters
- Nanoscale Research Letters
- Nanoscale Research Letters
- Nano Letters
- Advanced Materials (Deerfield Beach, Fla.)
- Journal of Immunology (Baltimore, Md. : 1950)
- Nature Communications
- Angewandte Chemie (International Ed. in English)
- Nano Letters
Articles by Andrea Geelhaar in JoVE
Culturing Primary Rat Inner Medullary Collecting Duct Cells
Dörte Faust1, Andrea Geelhaar1, Beate Eisermann1, Jenny Eichhorst2, Burkhard Wiesner2, Walter Rosenthal1,3, Enno Klussmann1
1Anchored Signalling, Max-Delbrück-Center for Molecular Medicine, 2Leibniz Institute for Molecular Pharmacology (FMP), 3Charité University Medicine Berlin
Arginine-vasopressin (AVP) controls fine-tuning of body water homeostasis through facilitating water reabsorption by renal principal cells. Here, we present a protocol for the cultivation of primary rat inner medullary collecting duct cells suitable for the elucidation of molecular mechanisms underlying AVP-mediated water reabsorption.
Other articles by Andrea Geelhaar on PubMed
Morphometric Estimation of Pulmonary Diffusion Capacity. 3. The Effect of Increased Oxygen Consumption in Japanese Waltzing Mice
Respiration Physiology. Mar, 1971 | Pubmed ID: 5573326
Biochemical Pharmacology. 1978 | Pubmed ID: 718729
Biomedical Mass Spectrometry. Jan, 1979 | Pubmed ID: 427258
Labeled gamma-aminobutyric acid was detected in mouse brain following intravenous injections of deuterium labeled 2-pyrrolidinone. [2H6]Pyrrolidinone was prepared by the reduction of [2H4]succinimide with lithium aluminum deuteride. Quantification was accomplished by a gas chromatography mass spectrometry assay method. gamma-Aminobutyric acid and internal standard, 5-aminovaleric acid, were converted to volatile derivatives by treatment with N,N-dimethylformamide dimethyl acetal. Quantitative estimates were derived from peak area measurements obtained from monitoring the parent ions of the gamma-aminobutyric acid and internal standard derivatives by repetitive scanning during the GC run. The conversion of pyrrolidinone to gamma-aminobutyric acid may provide a method for labeling central gamma-aminobutyric acid pools.
Applications of Deuterium Labeling in the Study of the in Vitro Conversion of Delta 1-pyrroline to 4-aminobutanoic Acid and 2-pyrrolidinone
Biomedical Mass Spectrometry. Nov, 1980 | Pubmed ID: 7194699
delta 1-Pyrroline is a putrescine metabolite that is biotransformed by rabbit liver preparations to 4-aminobutanoic acid and its lactam, 2-pyrrolidinone. Analysis of dilute aqueous solutions of delta 1-pyrroline by proton nuclear magnetic resonance indicated the the predominating species in the liver incubation preparations was delta 1-pyrroline monomer, although other species, such as 4-aminobutyraldehyde an delta 1-pyrroline timer, may exist in equilibrium with the monomer. [2H12]-delta 1-Pyrroline trimer was synthesized from [2H5]pyrrolidine by conversion to the N-chloro derivative followed by dehydrohalogenation. 4-Aminobutanoic acid was measured by a gas chromatographic mass spectrometric assay after derivatization with dimethylformamide dimethyl acetal. The 4-aminobutanoic acid homologue, 5-aminovaleric acid, served as internal standard. 2-Pyrrolidinone was hydrolyzed and measured as 4-aminobutanoic acid. A comparison of the amounts of product formed following incubation of labeled and unlabeled delta 1-pyrroline indicated a significant isotope effect in the formation of 2-pyrrolidinone. The influence of the label was much less on 4-aminobutanoic acid production. The results suggest that there are two separate pathways involved in the reaction.
Journal of Neurochemistry. Apr, 1982 | Pubmed ID: 7062030
delta 1-Pyrroline, 5-methyl-delta 1-pyrroline, and 5,5-dimethyl-delta 1-pyrroline have been identified as substances metabolized to gamma-aminobutyric acid (GABA), 4-aminopentanoic acid (methylGABA), and 4-amino-4-methylpentanoic acid (dimethylGABA), respectively. An enzyme system residing in the soluble fraction of rabbit liver catalyzes the conversion of delta 1-pyrroline to GABA and its lactam, 2-pyrrolidinone. Acetaldehyde, allopurinol, and cyanide inhibited the reaction. Incubation of deuterium-labeled delta 1-pyrroline with mouse brain homogenates produced deuterated GABA. Mouse liver 10,000 g supernatant and mouse brain homogenates converted 5-methyl-delta 1-pyrroline to methylGABA, and 5,5-dimethyl-delta 1-pyrroline to dimethylGABA. Four hours after intraperitoneal injection of 5-methyl-delta 1-pyrroline (200 mg/kg), methylGABA was detected in mouse brain (0.27 mumol/g). DimethylGABA (1.21 mumol/g) was determined in mouse brain 30 min after intraperitoneal administration of 5,5-dimethyl-delta 1-pyrroline (200 mg/kg). Neither methylGABA nor dimethylGABA penetrated into the central nervous system when administered in the periphery. The present studies suggest that pyrrolines may represent a chemical class of brain-penetrating precursors of pharmacologically active analogues of GABA.
Biomedical Mass Spectrometry. Mar, 1984 | Pubmed ID: 6426542
The deamination of putrescine catalysed by diamine oxidase was carried out in deuterium oxide and deuterated buffers. Enamine and alpha, beta-unsaturated intermediates were excluded, based on the observation that deuterium was not incorporated into delta 1-pyrroline during its enzymatic formation in deuterium oxide. When the reaction mixture was buffered with phosphate, isolated delta 1-pyrroline contained two deuterium atoms at C-3, indicating that a phosphate-promoted, non-enzymatic isotope exchange had occurred. Using 5,5-dimethyl-delta 1-pyrroline as a model compound, the nature of the non-enzymatic deuterium exchange was studied and a bifunctional catalysis mechanism proposed. The results suggest that the choice of buffer could alter the conclusions drawn from enzyme mechanism studies involving imine-enamine tautomerism .
Journal of Neurochemistry. Dec, 1984 | Pubmed ID: 6436440
1-Piperideine, 5-aminopentanoic acid, and its lactam, 2-piperidone, were identified as metabolites of cadaverine in 10,000 g mouse liver supernatants to which diamine oxidase had been added. Both metabolites were also found when the cadaverine metabolite 1-piperideine was incubated with the preparation which suggested that 1-piperideine is an intermediate in the formation of 5-aminopentanoic acid and 2-piperidone. Identification of the metabolites was based on gas chromatography-mass spectrometric analysis in comparison to authentic standards. Mouse brain homogenates converted 1-piperideine to 5-aminopentanoic acid. The results suggest that the metabolic fate of cadaverine may provide precursors of pharmacologically active analogues of GABA.
1-Piperideine As an in Vivo Precursor of the Gamma-aminobutyric Acid Homologue 5-aminopentanoic Acid
Journal of Neurochemistry. Sep, 1985 | Pubmed ID: 4031870
Intraperitoneal injection of the cyclic imine 1-piperideine in mice resulted in measurable quantities of 5-aminopentanoic acid in brain. 5-Aminopentanoic acid is a methylene homologue of gamma-aminobutyric acid (GABA) that is a weak GABA agonist. 5-Aminopentanoic acid formed in the periphery was ruled out as the source of brain 5-aminopentanoic acid based on the absence of detection in brain following injection of 100 mg/kg of 5-aminopentanoic acid. Deuterium-labeled 1-piperideine was prepared by exchange in deuterated phosphate buffer. Injection of [3.3-2H2]1-piperideine yielded [2.2-2H2]5-aminopentanoic acid in brain. The results are consistent with uptake of 1-piperideine into brain and oxidation of the precursor to 5-aminopentanoic acid. Inhibition of GABA catabolism by pretreatment with aminooxyacetic acid increased brain concentrations of 5-aminopentanoic acid formed from 1-piperideine, suggesting that 5-aminopentanoic acid is an in vivo substrate of 4-aminobutyrate:2-oxoglutarate aminotransferase.
Experiments on the Efficacy and Toxicity of Locoregional Chemotherapy of Liver Tumors with 5-fluoro-2'-deoxyuridine (FUDR) and 5-fluorouracil (5-FU) in an Animal Model
Journal of Cancer Research and Clinical Oncology. 1986 | Pubmed ID: 2936747
For the investigation of locoregional chemotherapy of liver neoplasms we developed a standardized animal model in the rat. Continuous infusion therapy or repeated bolus injections of FUDR or 5-FU were given via the hepatic artery, the portal vein or the vena cava in tumor-bearing animals. The efficacy of the treatment was determined by measuring the tumor volume 3 weeks after tumor cell implantation. For the evaluation of the local and systemic toxicity serum GOT, GPT, and total bilirubin were determined. DNA single strand breaks were assessed in isolated liver and bone marrow cells. Inhibition of colony formation of bone marrow stem cells was determined by CFU-C and CFU-S bioassay. A significant reduction of tumor growth was observed only after continuous infusion of FUDR via the hepatic artery. Systemic toxicity was lowest in this group for both compounds while the local liver toxicity was only slightly elevated.
Experiments on the Toxicity of Locoregional Liver Chemotherapy with 5-fluoro-2'-deoxyuridine and 5-fluorouracil in an Animal Model
Recent Results in Cancer Research. Fortschritte Der Krebsforschung. ProgrÃ¨s Dans Les Recherches Sur Le Cancer. 1986 | Pubmed ID: 2942992
Surgery, Gynecology & Obstetrics. Jun, 1986 | Pubmed ID: 3715689
Ten parameters, including delayed cutaneous hypersensitivity testing (DCH), were evaluated with regard to their predictive value in instances of postoperative septic complications. In 302 patients undergoing surgical treatment, 45 complications, including wound infection, abscess, pneumonia and sepsis, were seen postoperatively in 42 patients. When these patients were compared with 260 patients without complications, hemoglobin, leukocyte count, serum albumin, total protein, blood sedimentation rate, age and sex were found not to contribute to the prediction of postoperative complications. In DCH testing, the complication rate increased from 7.5 per cent in normergic patients to 20.6 per cent in anergic patients. With increasing length and severity of operation, the complication rate increased from 6.5 to 26.4 per cent and from 6.5 to 31.8 per cent, respectively. Only in severe, long lasting operations could DCH testing differentiate the complication risk. Normergic patients had a 8.6 per cent complication rate; hypoergic patients, 36.6 per cent, and anergic patients, 37.5 per cent. The results of DCH testing did not correlate with the complication rate in any of the other operative groups. In conclusion, the predictive value of DCH testing is clearly greater in groups of patients highly affected by the operative trauma. The results of this study show that it is important to consider both host defense mechanisms and environmental factors in the assessment of operative risks.
Identification of Metabolites of the Cell-differentiating Agent Hexamethylene Bisacetamide in Humans
Cancer Research. Oct, 1986 | Pubmed ID: 3756851
Hexamethylene bisacetamide, a compound which in vitro induces differentiation in a wide variety of human and animal cancer cell lines, is being investigated in phase I clinical trials. After i.v. administration of hexamethylene bisacetamide to humans, urine contained the parent compound and at least five metabolites formed by deacetylation and oxidation pathways. Identification of urinary metabolites was accomplished by gas chromatography-mass spectrometric analysis after isolation by ion exchange chromatography or extraction with ethyl acetate. Metabolites with amino or alcohol groups were trifluoroacetylated and acidic functional groups were esterified with 2,2,2-trifluoroethanol or methanol. The structure of each metabolite was confirmed by comparison with authentic standards. Metabolites identified included the major metabolite, 6-acetamidohexanoic acid; the monodeacetylated product, N-acetyl-1,6-diaminohexane; the bis-deacetylated diamine, 1,6-diaminohexane; and the amino acid, 6-aminohexanoic acid and its lactam, caprolactam.
Cancer Research. Nov, 1987 | Pubmed ID: 3664514
In order to further understand the clinical toxicities of hexamethylene bisacetamide (HMBA) and to allow appropriate in vitro studies, we developed a suitable gas chromatographic assay and quantified plasma concentrations and urinary excretion of four metabolites which we had previously identified in urine of patients receiving 5-day HMBA infusions at 4.8-43.2 g/m2/day. 6-Acetamidohexanoic acid (AcHA) was the major plasma metabolite and reached steady state concentration (Css) by 24 h. AcHA Css increased from 0.12 +/- 0.02 (SD) mM at 4.8 g/m2/day to 0.72 mM at 43.2 g/m2/day. The Css AcHA:Css HMBA ratio decreased with increasing HMBA dosage. At dosages below 24 g/m2/day plasma Css of N-acetyl-1,6-diaminohexane (NADAH), the initial metabolite of HMBA, were below the limit of detection of our assay. With HMBA infusions of 24, 33.6, and 43.2 g/m2/day, Css of NADAH were 0.16 +/- 0.05, 0.14 +/- 0.06, and 0.19 +/- 0.04 mM, respectively. Css NADAH:Css HMBA ratios at 24, 33.6, and 43.2 g/m2/day were 0.18 +/- 0.06, 0.08 +/- 0.02, and 0.31 +/- 0.05, respectively. Plasma Css of 1,6-diaminohexane and 6-aminohexanoic acid were below the limit of detection of our assay. Each patient's urinary excretion of NADAH, AcHA, and 1,6-diaminohexane was consistent from day to day. The fraction of dose excreted in urine as AcHA was not affected by HMBA dosage and accounted for 12.7 +/- 3.9% of the daily dose. The percentage of daily HMBA dose accounted for by excretion of NADAH decreased with increasing HMBA dosage (10.8 +/- 6.0% at 4.8 g/m2/day to 4.2 +/- 1.2% at 33.6 g/m2/day). Urinary excretion of 1,6-diaminohexane always accounted for less than 3% of the daily dose. Our results indicate that: (a) plasma concentrations of AcHA alone cannot explain the degree of acidosis observed with toxic doses of HMBA; (b) NADAH is present in plasma at concentrations that we have found to cause differentiation in vitro; and (c) the probable rate-limiting step in HMBA metabolism is the initial deacetylation.
Involvement of Monoamine Oxidase and Diamine Oxidase in the Metabolism of the Cell Differentiating Agent Hexamethylene Bisacetamide (HMBA)
Life Sciences. 1988 | Pubmed ID: 3137409
We have previously demonstrated a number of metabolites of hexamethylene bisacetamide (HMBA) in the urine of patients treated with HMBA. These include N-acetyl-1,6-diaminohexane (NADAH), 6-acetamidohexanoic acid (6AcHA), 1,6-diaminohexane (DAH) and 6-aminohexanoic acid (6AmHA). Because these compounds have potential roles in the dose-limiting metabolic acidosis and neurotoxicity associated with HMBA therapy, and are similar in structure to known substrates of monoamine oxidase (MAO) and diamine oxidase (DAO), we investigated the activities of these enzymes in the metabolic interconversion of HMBA metabolites. NADAH (5 mM) was incubated with MAO and aldehyde dehydrogenase. 6AcHA production was verified by gas chromatography-mass spectrometry and quantified by gas chromatography. 6AcHA production was linear for up to 4 hr. Complete inhibition of MAO activity was observed with 2 mM tranyl-cypromine or pargyline. Mouse liver microsomes, which do not contain MAO, did not convert NADAH to 6AcHA and, in control experiments, did not degrade 6AcHA. The HMBA metabolite, DAH, was a substrate for DAO, producing 3,4,5,6-tetrahydro-2H-azepine. Participation of DAO in the metabolism of HMBA implies potential interaction of HMBA and metabolites with polyamine metabolism and may represent a mechanism for HMBA's effects on cellular growth and differentiation. Metabolism of NADAH, also a differentiator, by MAO implies that concurrent use of HMBA and an MAO inhibitor may be clinically useful.
Induction of Differentiation of Human Promyelocytic Leukemia Cells (HL60) by Metabolites of Hexamethylene Bisacetamide
Cancer Research. Jul, 1988 | Pubmed ID: 3163938
We studied the ability of five metabolites of hexamethylene bisacetamide (HMBA), which we had previously identified in patient urine, to induce differentiation or to influence differentiation induced by HMBA of a human promyelocytic cell line. Differentiation of HL60 cells was quantified by morphological changes and by the ability to reduce nitroblue tetrazolium. N-Acetyl-1,6-diaminohexane (NADAH), the deacetylated, first metabolite of HMBA, was a more potent inducer of HL60 differentiation than was HMBA. NADAH produced 20-30% differentiation at 0.25 mM and 30-40% differentiation at 0.5 mM. NADAH (1 mM) induced 2-3-fold more differentiation than did 1 mM HMBA. HL60 differentiation, induced by various combinations of HMBA and NADAH, reflected a combined effect of the two compounds. In contrast, 1,6-diaminohexane, at 0.5-5 mM, failed to induce HL60 differentiation. Similarly, 0.5-5 mM 6-acetamidohexanoic acid, the major metabolite of HMBA, and 6-aminohexanoic acid failed to induce differentiation of HL60 cells. However, 6-acetamidohexanoic acid, when combined with HMBA or NADAH at various concentrations and ratios, enhanced the differentiation of HL60 cells induced by these two compounds. This enhancement was most apparent with addition of 0.50-3.0 mM 6-acetamidohexanoic acid to HL60 cells incubated with 1.0-3.0 mM HMBA or 0.25-1.0 mM NADAH. 6-Aminohexanoic acid similarly enhanced HMBA-induced differentiation of HL60 cells. These in vitro results have implications in terms of the clinical application of HMBA and interpretation of the results of clinical trials performed to date and may provide some insight into the mechanism of HMBA-induced cellular differentiation.
A Cyclic Imine Intermediate in the in Vitro Metabolic Conversion of 1,6-diaminohexane to 6-aminohexanoic Acid and Caprolactam
Xenobiotica; the Fate of Foreign Compounds in Biological Systems. Jan, 1989 | Pubmed ID: 2502880
1. 3,4,5,6-Tetrahydro-2H-azepine is an intermediate in the enzyme-catalyzed conversion of 1,6-diaminohexane to 6-aminohexanoic acid and its corresponding lactam, caprolactam, by mammalian liver aldehyde oxidase. 2. Identification of metabolites was based on analysis by gas chromatography-mass spectrometry and confirmed by comparison with the properties of authentic standards. 3. The results indicate that the cell differentiating agent hexamethylene bisacetamide is converted into 1,6-diaminohexane, and its metabolism therefore involves diamine oxidase. 4. The metabolic fate of 1,6-diaminohexane is similar to that of putrescine and cadaverine in that a cyclic imine is an intermediate in the formation of metabolites with ring (lactam) and chain (amino acid) structures.
Physical Review. A. Aug, 1990 | Pubmed ID: 9904311
Isotopically Sensitive Regioselectivity in the Oxidative Deamination of a Homologous Series of Diamines Catalyzed by Diamine Oxidase
Chemico-biological Interactions. Nov, 1992 | Pubmed ID: 1458548
The equivalence of aminomethylene groups in selected diamine substrates of diamine oxidase was exploited for the determination of intramolecular isotope effects. In the series of substrates, [1,1-2H2]-1,3-diaminopropane, [1,1-2H2]-1,5-diaminopentane, [1,1-2H2]-1,6-diaminohexane, [1,1-2H2]-1,7-diaminoheptane and [alpha,alpha-2H2]-4-(aminomethyl)benzylamine, the preference of the enzyme for reaction at the unlabeled methylene was found to vary from 1.45 to 10.5-fold. The observed partitioning ratios go through a minimum value with 1,5-diaminopentane, the best substrate of diamine oxidase of the compounds tested. The results suggest that fast substrates have less opportunity to reorient into alternate binding conformations while bound to the active site of the enzyme. On the other hand, diamine substrates tested that cannot exist in energetically favorable conformations with internitrogen distances of about 7-8 A showed larger intramolecular isotope effects.
Denitration of Glycerol Trinitrate by Resting Cells and Cell Extracts of Bacillus Thuringiensis/cereus and Enterobacter Agglomerans
Applied and Environmental Microbiology. Jul, 1995 | Pubmed ID: 7618866
A number of microorganisms were selected from soil and sediment samples which were known to have been previously exposed to nitrate ester contaminants. The two most effective bacteria for transforming glycerol trinitrate (GTN) were identified as Bacillus thuringiensis/cereus and Enterobacter agglomerans. For both isolates, denitration activities were expressed constitutively and GTN was not required for induction. Dialysis of cell extracts from both isolates did not affect denitration, which indicates that dissociable and depletable cofactors are not required for denitration. With thin-layer chromatography and high-performance liquid chromatography, the denitration pathway for both isolates was shown to be a sequential denitration of GTN to glycerol dinitrate isomers, glycerol mononitrate isomers, and ultimately to glycerol. GTN was observed to be completely converted to glycerol during a long-term incubation of cell extracts.
Applied Microbiology and Biotechnology. May, 1996 | Pubmed ID: 8785037
In previous studies, bacterial cultures were isolated that had the ability to degrade the nitrate ester glyceryl trinitrate (i.e., nitroglycerin). The goal of the present study was to examine the ability of resting cells and cell-free extracts of the isolate Bacillus sp. ATCC 51912 to degrade the more recalcitrant nitrate ester propylene glycol dinitrate (PGDN). It was observed that the PGDN-denitrating activity was expressed during growth even when cells were cultured in the absence of nitrate esters. This indicates that nitrate esters are not required for expression of denitration activity. Using cell-free extracts, PGDN was observed to be sequentially denitrated to propylene glycol mononitrate (PGMN) and propylene glycol with the second denitration step proceeding more slowly than the first. Also it was observed that dialysis of the cell-free extracts did not affect denitration activity indicating that regenerable cofactors [e.g., NAD(P)H or ATP] are not required for denitration.
Der Chirurg; Zeitschrift Fur Alle Gebiete Der Operativen Medizen. Jan, 1999 | Pubmed ID: 10068835
Cryophlebectomy, a more recent technique in varicose veins surgery, was evaluated in comparision with conventional techniques. Group IA: Microphlebectomy, invaginative stripping of the long saphenous vein, tourniquet, n = 90; group IB: only microphlebektomie and tourniquet, n = 72. Group IIA: Cryostripping of the long saphenous vein in combination with cryosurgical distal avulsion of varicosities and microphlebectomy, n = 112; gr. IIB: only cryosurgical distal avulsion of varicosities and microphlebectomy. Data were compared regarding duration of operation and hospitalisation and cosmetic outcome. Hospital stay (gr. IA: 9.1 +/- 5.1 d vs. gr. IIA: 6.1 +/- 2.1 d, gr. IB: 5.5 +/- 2.3 d vs. gr. IIB: 4.8 +/- 2.5 d) and duration of operation (gr. IA: 113.6 +/- 35 min vs. gr. IIA: 67 +/- 21.3 min, gr. IB: 74.4 +/- 35.3 min vs. gr. IIB: 53.3 +/- 15.5 min) were found to be significantly shorter and cosmetic result and postoperative discomforts improved in the cryophlebectomy-group. We conclude that the use of this combination of methods reduces invasivity, rises the patient's well-being and helps in cost-reduction.
Physical Review Letters. Jan, 2001 | Pubmed ID: 11136107
The stoichiometric GaAs(114) surface has been prepared using molecular beam epitaxy followed by annealing in ultrahigh vacuum. Based on in situ scanning tunneling microscopy measurements and first-principles electronic-structure calculations, we determine the surface reconstruction which we call alpha2(2x1). Contrary to what is expected for a high-index surface, it is surprisingly elementary. The (2x1) unit cell contains two As dimers and two rebonded Ga atoms. The surface energy is calculated as 53 meV/Ã…(2), which falls well within the range of low-index GaAs surface energies.
Physical Review Letters. Apr, 2001 | Pubmed ID: 11329331
The atomic structure of GaAs(2 5 11), a hitherto unknown stable surface, has been determined by in situ scanning tunneling microscopy and first-principles electronic structure calculations. This orientation is located within the stereographic triangle, i.e., far away from all low-index surfaces. A low-energy ( 1x1) reconstruction containing arsenic dimers forms on the surface. The analysis of the surface structure shows that, for semiconductor surfaces, the gain in stability due to minimization of the number of dangling bonds is more important than the gain from rendering a semiconducting ground state.
American Journal of Physiology. Renal Physiology. Jan, 2003 | Pubmed ID: 12388395
The water permeability of the renal collecting duct is regulated by the insertion of aquaporin-2 (AQP2) into the apical plasma membrane of epithelial (principal) cells. Using primary cultured epithelial cells from the inner medulla of rat kidney (IMCD cells), we show that osmolality and solute composition are potent regulators of AQP2 mRNA and protein synthesis, as well as the classical cAMP-dependent pathway, but do not affect the arginine vasopressin-induced AQP2 shuttle. In the presence of the cAMP analog dibutyryl cAMP (DBcAMP, 500 microM), NaCl and sorbitol, but not urea, evoked a robust increase of AQP2 expression in IMCD cells, with NaCl being far more potent than sorbitol. cAMP-responsive element-binding protein phosphorylation increased with DBcAMP concentrations but was not altered by changes in osmolality. In the rat and human AQP2 promoter, we identified a putative tonicity-responsive element. We conclude that, in addition to the arginine vasopressin/cAMP-signaling cascade, a further pathway activated by elevated effective osmolality (tonicity) is crucial for the expression of AQP2 in IMCD cells, and we suggest that the effect is mediated via the tonicity-responsive element.
Nano Letters. Dec, 2006 | Pubmed ID: 17163684
Schottky barrier field effect transistors based on individual catalytically-grown and undoped Si-nanowires (NW) have been fabricated and characterized with respect to their gate lengths. The gate length was shortened by the axial, self-aligned formation of nickel-silicide source and drain segments along the NW. The transistors with 10-30 nm NW diameters displayed p-type behaviour, sustained current densities of up to 0.5 MA/cm2, and exhibited on/off current ratios of up to 10(7). The on-currents were limited and kept constant by the Schottky contacts for gate lengths below 1 microm, and decreased exponentially for gate lengths exceeding 1 microm.
Compositional Correlation and Anticorrelation in Quaternary Alloys: Competition Between Bulk Thermodynamics and Surface Kinetics
Physical Review Letters. Nov, 2007 | Pubmed ID: 18233164
We analyze the atomistic mechanisms driving the compositional correlation of In and N in the quaternary Inx Ga1-xAs1-yNy alloys combining atomic scale chemical analysis in transmission electron microscopy and density-functional theory calculations. Our results show that for typical growth conditions surface kinetics prevail over bulk thermodynamics resulting in a hitherto unexpected compositional anticorrelation between In and N.
Gastroenterology. Jan, 2010 | Pubmed ID: 19664628
Whipple's disease is a chronic multisystemic infection caused by Tropheryma whipplei. Host factors likely predispose for the establishment of an infection, and macrophages seem to be involved in the pathogenesis of Whipple's disease. However, macrophage activation in Whipple's disease has not been studied systematically so far.
Infection and Immunity. Nov, 2010 | Pubmed ID: 20696822
Whipple's disease is a chronic multisystemic infection caused by Tropheryma whipplei that is characterized by arthritis, weight loss, and diarrhea. The immunological defects in the duodenal mucosa, the site of major replication of the agent underlying the pathogenesis of Whipple's disease, are poorly understood. Mucosal immunoglobulins are essential for the defense against intestinal pathogens; therefore, we analyzed the B-cell response in duodenal specimens and sera of Whipple's disease patients. Whereas systemic immunoglobulin production was affected only marginally, duodenal biopsy specimens of Whipple's disease patients contained reduced numbers of immunoglobulin-positive plasma cells and secreted less immunoglobulin compared to healthy controls but showed a weak secretory IgA response toward T. whipplei. This T. whipplei-specific intestinal immune response was not observed in controls. Thus, we were able to demonstrate that general mucosal immunoglobulin production in Whipple's disease patients is impaired. However, this deficiency does not completely abolish T. whipplei-specific secretory IgA production that nonetheless does not protect from chronic infection.
Nano Letters. Sep, 2010 | Pubmed ID: 20715843
We investigate the nucleation of Ni-induced GaN nanowires by in situ and ex situ experiments. Three nucleation stages are evidenced. In the first two stages, different crystal structures of the Ni collectors are identified. Real-time monitoring of the Ga desorption allows the amount of Ga incorporated in the collectors to be quantified. A transition of their crystal structure prior to nanowire growth is found to be in agreement with the thermodynamically stable phase sequence of the relevant phase diagrams.
Annals of Internal Medicine. Dec, 2010 | Pubmed ID: 21135294
Whipple disease, which is caused by infection with Tropheryma whipplei, can be treated effectively with antimicrobials. Occasionally, inflammation reappears after initial improvement; this is often interpreted as refractory or recurrent disease. However, polymerase chain reaction for T. whipplei in tissue is sometimes negative during reinflammation, indicating absence of vital bacteria, and this reinflammation does not respond to antimicrobials but does respond to steroids.
Nano Letters. Mar, 2011 | Pubmed ID: 21319838
The incorporation of Au during vapor-liquid-solid nanowire growth might inherently limit the performance of nanowire-based devices. Here, we assess the material quality of Au-assisted and Au-free grown GaAs/(Al,Ga)As core-shell nanowires using photoluminescence spectroscopy. We show that at room temperature, the internal quantum efficiency is systematically much lower for the Au-assisted nanowires than for the Au-free ones. In contrast, the optoelectronic material quality of the latter is comparable to that of state-of-the-art planar double heterostructures.
Journal of Physics. Condensed Matter : an Institute of Physics Journal. Mar, 2011 | Pubmed ID: 21378442
The reversal processes of magnetization in epitaxial MnAs nanotubes prepared by an overgrowth on the sidewall of GaAs nanowires having a diameter of 26Â nm are investigated. While the magnetic hard axis is aligned in the direction of the nanowire axis, we apply an external magnetic field perpendicular to the axis to examine the flipping characteristics of magnetic moments. We determine the contributions from the substrate by a direct measurement in order to extract the magnetization of the core-shell heterostructures. The abrupt change in the thus-obtained magnetization due to a flip when the field is varied exhibits an overshoot at about 0.4Â kOe for samples with a thickness of the ferromagnetic shell (40-50Â nm) larger than the diameter of the core. Moreover, the peak value exceeds the value when the field is swept in the opposite direction. The magnetic hysteresis loop consequently involves line crossings. We speculate that the spin textures of domain walls in such thick hollow cylinders and their movement at the magnetization flip are affected by the geometry and magnetostatic interactions of various origins, giving rise to the anomalous behaviour.
Journal of Immunology (Baltimore, Md. : 1950). Oct, 2011 | Pubmed ID: 21918190
Classical Whipple's disease (CWD) is caused by chronic infection with Tropheryma whipplei that seems to be associated with an underlying immune defect. The pathognomonic hallmark of CWD is a massive infiltration of the duodenal mucosa with T. whipplei-infected macrophages that disperse systemically to many other organ systems. An alleviated inflammatory reaction and the absence of T. whipplei-specific Th1 reactivity support persistence and systemic spread of the pathogen. In this article, we hypothesized that regulatory T cells (T(reg)) are involved in immunomodulation in CWD, and we asked for the distribution, activation, and regulatory capacity of T(reg) in CWD patients. Whereas in the lamina propria of CWD patients before treatment numbers of T(reg) were increased, percentages in the peripheral blood were similar in CWD patients and healthy controls. However, peripheral T(reg) of CWD patients were more activated than those of controls. Elevated secretion of IL-10 and TGF-Î² in the duodenal mucosa of CWD patients indicated locally enhanced T(reg) activity. Enhanced CD95 expression on peripheral memory CD4(+) T cells combined with reduced expression of IFN-Î³ and IL-17A upon polyclonal stimulation by CD4(+) cells from untreated CWD patients further hinted to T(reg) activity-related exhaustion of effector CD4(+) T cells. In conclusion, increased numbers of T(reg) can be detected within the duodenal mucosa in untreated CWD, where huge numbers of T. whipplei-infected macrophages are present. Thus, T(reg) might contribute to the chronic infection and systemic spread of T. whipplei in CWD but in contrast prevent mucosal barrier defect by reducing local inflammation.
Physical Review Letters. Nov, 2011 | Pubmed ID: 22181912
This work elucidates the role of the Schottky junction in the electronic transport of nanometer-scale transistors. In the example of Schottky barrier silicon nanowire field effect transistors, an electrical scanning probe technique is applied to examine the charge transport effects of a nanometer-scale local top gate during operation. The results prove experimentally that Schottky barriers control the charge carrier transport in these devices. In addition, a proof of concept for a reprogrammable nonvolatile memory device based on band bending at the Schottky barriers will be shown.
Nano Letters. Jan, 2012 | Pubmed ID: 22142481
The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited carriers, as well as to spatially control exciton recombination in GaAs-based nanowires (NWs) on a subns time scale. The experiments are carried out in core-shell NWs transferred to a SAW delay line on a LiNbO(3) crystal. Carriers generated in the NW by a focused laser spot are acoustically transferred to a second location, leading to the remote emission of subns light pulses synchronized with the SAW phase. The dynamics of the carrier transport, investigated using spatially and time-resolved photoluminescence, is well-reproduced by computer simulations. The high-frequency contactless manipulation of carriers by SAWs opens new perspectives for applications of NWs in opto-electronic devices operating at gigahertz frequencies. The potential of this approach is demonstrated by the realization of a high-frequency source of antibunched photons based on the acoustic transport of electrons and holes in (In,Ga)As NWs.
Lattice Parameter Accommodation Between GaAs(111) Nanowires and Si(111) Substrate After Growth Via Au-assisted Molecular Beam Epitaxy
Nanoscale Research Letters. 2012 | Pubmed ID: 22315928
Using out-of-plane and in-plane X-ray diffraction techniques, we have investigated the structure at the interface between GaAs nanowires [NWs] grown by Au-assisted molecular beam epitaxy and the underlying Si(111) substrate. Comparing the diffraction pattern measured at samples grown for 5, 60, and 1,800 s, we find a plastic strain release of about 75% close to the NW-to-substrate interface even at the initial state of growth, probably caused by the formation of a dislocation network at the Si-to-GaAs interface. In detail, we deduce that during the initial stage, zinc-blende structure GaAs islands grow with a gradually increasing lattice parameter over a transition region of several 10 nm in the growth direction. In contrast, accommodation of the in-plane lattice parameter takes place within a thickness of about 10 nm. As a consequence, the ratio between out-of-plane and in-plane lattice parameters is smaller than the unity in the initial state of growth. Finally the wurtzite-type NWs grow on top of the islands and are free of strain.
Nanoscale Research Letters. 2012 | Pubmed ID: 22583747
: The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport.
Nanotechnology. Aug, 2012 | Pubmed ID: 22751267
We study the mechanism of lattice parameter accommodation and the structure of GaAs nanowires (NWs) grown on Si(111) substrates using the Ga-assisted growth mode in molecular beam epitaxy. These nanowires grow preferentially in the zincblende structure, but contain inclusions of wurtzite at the base. By means of grazing incidence x-ray diffraction and high-resolution transmission electron microscopy of the NW-substrate interface, we show that the lattice mismatch between the NW and the substrate is released immediately after the beginning of NW growth through the inclusion of misfit dislocations, and no pseudomorphic growth is obtained for NW diameters down to 10 nm. NWs with a diameter above 100 nm exhibit a rough interface towards the substrate, preventing complete plastic relaxation. Consequently, these NWs exhibit a residual compressive strain at their bottom. In contrast, NWs with a diameter of 50 nm and below are completely relaxed because the interface is smooth.
Correlation Between In Content and Emission Wavelength of In(x)Ga(1-x)N/GaN Nanowire Heterostructures
Nanotechnology. Nov, 2012 | Pubmed ID: 23085638
GaN nanowire ensembles with axial In(x)Ga(1-x)N multi-quantum-wells (MQWs) were grown by molecular beam epitaxy. In a series of samples we varied the In content in the MQWs from almost zero to around 20%. Within the nanowire ensemble, the MQWs fluctuate strongly in composition and size. Statistical information about the composition was obtained from x-ray diffraction and Raman spectroscopy. Photoluminescence at room temperature was obtained in the range of 2.2 to 2.5 eV, depending on In content. Contrary to planar MQWs, the intensity increases with increasing In content. We compare the observed emission energies with transition energies obtained from a one-dimensional model, and conclude that several mechanisms for carrier localization affect the luminescence of these three-dimensional structures.
Nanotechnology. Nov, 2012 | Pubmed ID: 23092897
Light emitting diodes (LEDs) have been fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy. Electron-beam-induced current analysis, cathodoluminescence as well as biased Î¼-photoluminescence spectroscopy, transmission electron microscopy, and electrical measurements indicate that the electroluminescence of such LEDs is governed by the differences in the individual current densities of the single-NW LEDs operated in parallel, i.e. by the inhomogeneity of the current path in the ensemble LED. In addition, the optoelectronic characterization leads to the conclusion that these NWs exhibit N-polarity and that the (In, Ga)N quantum well states in the NWs are subject to a non-vanishing quantum confined Stark effect.
Nano Letters. Dec, 2012 | Pubmed ID: 23130785
We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and whether their formation has to be induced by defects. For this purpose, we prepare smooth and coherently strained AlN layers on 6H-SiC(0001) and SiC(0001Ì…) substrates to ensure a well-defined polarity and an absence of structural and morphological defects. On N-polar AlN, a homogeneous and dense N-polar GaN nanowire array forms, evidencing that GaN nanowires form spontaneously in the absence of defects. On Al-polar AlN, we do not observe the formation of Ga-polar GaN NWs. Instead, sparse N-polar GaN nanowires grow embedded in a Ga-polar GaN layer. These N-polar GaN nanowires are shown to be accidental in that the necessary polarity inversion is induced by the formation of Si(x)N. The present findings thus demonstrate that spontaneously formed GaN nanowires are irrevocably N-polar. Due to the strong impact of the polarity on the properties of GaN-based devices, these results are not only essential to understand the spontaneous formation of GaN nanowires but also of high technological relevance.
Advanced Materials (Deerfield Beach, Fla.). Feb, 2013 | Pubmed ID: 23108727
The first experimental demonstration of a spin amplifier at room temperature is presented. An efficient, defect-enabled spin amplifier based on a non-magnetic semiconductor, Ga(In)NAs, is proposed and demonstrated, with a large spin gain (up to 2700% at zero field) for conduction electrons and a high cut-off frequency of up to 1 GHz.
Journal of Immunology (Baltimore, Md. : 1950). Mar, 2013 | Pubmed ID: 23365082
During antimicrobial treatment of classic Whipple's disease (CWD), the chronic systemic infection with Tropheryma whipplei, immune reconstitution inflammatory syndrome (IRIS), is a serious complication. The aim of our study was to characterize the immunological processes underlying IRIS in CWD. Following the definition of IRIS, we describe histological features of IRIS and immunological parameters of 24 CWD IRIS patients, 189 CWD patients without IRIS, and 89 healthy individuals. T cell reconstitution, Th1 reactivity, and the phenotype of T cells were described in the peripheral blood, and infiltration of CD4(+) T cells and regulatory T cells in the duodenal mucosa was determined. During IRIS, tissues were heavily infiltrated by CD3(+), predominantly CD45RO(+)CD4(+) T cells. In the periphery, initial reduction of CD4(+) cell counts and their reconstitution on treatment was more pronounced in CWD patients with IRIS than in those without IRIS. The ratio of activated and regulatory CD4(+) T cells, nonspecific Th1 reactivity, and the proportion of naive among CD4(+) T cells was high, whereas serum IL-10 was low during IRIS. T. whipplei-specific Th1 reactivity remained suppressed before and after emergence of IRIS. The findings that IRIS in CWD mainly are mediated by nonspecific activation of CD4(+) T cells and that it is not sufficiently counterbalanced by regulatory T cells indicate that flare-up of pathogen-specific immunoreactivity is not instrumental in the pathogenesis of IRIS in CWD.
Nature Communications. 2013 | Pubmed ID: 23612292
Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (~150 Gauss) and nuclear spin polarization (~15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in <5 Î¼s at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications.
Angewandte Chemie (International Ed. in English). Jun, 2013 | Pubmed ID: 23740565
Patterns of communication: Reinitzer's discovery of liquid crystals in 1888 was followed by 30 years of scholarly dispute. One hundred years later, Pierre-Gilles de Gennes was awarded the Nobel Prize in Physics for his contribution to this scientific revolution. The commercial success of liquid crystals was achieved in display applications. Today more than 4 billion people use them in mobile communication devices. Painting: Detail from Raphael's School of Athens fresco.
Nano Letters. Jun, 2013 | Pubmed ID: 23758601
We investigate the axial and radial growth of GaN nanowires upon a variation of the Ga flux during molecular beam epitaxial growth. An increase in the Ga flux promotes radial growth without affecting the axial growth rate. In contrast, a decrease in the Ga flux reduces the axial growth rate without any change in the radius. These results are explained by a kinetic growth model that accounts for both the diffusion of Ga adatoms along the side facets toward the nanowire tip and the finite amount of active N available for the growth. The model explains the formation of a new equilibrium nanowire radius after increasing the Ga flux and provides an explanation for two well-known but so far not understood experimental facts: the necessity of effectively N-rich conditions for the spontaneous growth of GaN nanowires and the increase in nanowire radius with increasing III/V flux ratio.