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At least 631 records · Page 35Linked to original sources
PubMed1998

An antibody exo Diels-Alderase inhibitor complex at 1.95 angstrom resolution.

A highly specific Diels-Alder protein catalyst was made by manipulating the antibody repertoire of the immune system. The catalytic antibody 13G5 catalyzes a disfavored exo Diels-Alder transformation in a reaction for which there is no natural enzyme counterpart and that yields a single regioisomer in high enantiomeric excess. The crystal structure of the antibody Fab in complex with a ferrocenyl inhibitor containing the essential haptenic core that elicited 13G5 was determined at 1.95 angstrom resolution. Three key antibody residues appear to be responsible for the observed catalysis and product control. Tyrosine-L36 acts as a Lewis acid activating the dienophile for nucleophilic attack, and asparagine-L91 and aspartic acid-H50 form hydrogen bonds to the carboxylate side chain that substitutes for the carbamate diene substrate. This hydrogen-bonding scheme leads to rate acceleration and also pronounced stereoselectivity. Docking experiments with the four possible ortho transition states of the reaction explain the specific exo effect and suggest that the (3R,4R)-exo stereoisomer is the preferred product.

Antibodies, Catalytic↗
PubMed1992

Iron overload of the liver by trimethylhexanoylferrocene in rats.

Iron-deficient female Wistar rats were fed a diet, which contained 0.5% trimethylhexanoylferrocene, over a 56-week period. This dietary iron loading resulted in a progressive siderosis and enlargement of the liver with a maximum iron content of 947.0 +/- 148.0 mg (vs. 0.07 +/- 0.04 mg in iron deficiency) and a maximum organ weight of 39.4 +/- 6.6 g (vs. 6.9 +/- 1.4 g in iron-deficient control rats). Up to 43 weeks, whole liver iron rose by increase in iron concentration (max. 28.0 +/- 6.1 mg/g wet weight, w.w.) as well as by enlargement of the organ. Afterwards whole liver iron increased solely by ongoing hepatomegaly. At the commencement of iron loading, stainable iron was almost exclusively stored by hepatocytes equally throughout all areas of the liver lobule. Later, the distribution of iron-loaded hepatocytes became strikingly periportal, and, in addition, Kupffer cells as well as sinus-lining endothelia began to store iron. Animals with a liver iron concentration of more than 10.4 +/- 0.75 mg/g w.w. showed no further increase in ferritin and haemosiderin within hepatocytes. Iron-burdened Kupffer cells/macrophages, however, accumulated permanently, hereby forming intrasinusoidal and portal siderotic nodules and areas. First signs of liver damage such as necrosis of single hepatocytes and mild fibrosis began at a liver iron concentration of 14.7 +/- 1.4 mg/g w.w. With advancement of iron loading, focal necrosis of hepatocytes and iron-burdened macrophages took place, and significant perisinusoidal as well as portal fibrosis developed. Cirrhosis, however, the final stage of impairment in iron overload of the liver in humans, could not be induced in this animal model up to now.

Animals↗
PubMed1992

Iron overload of the bone marrow by trimethylhexanoyl-ferrocene in rats.

Iron-deficient female Wistar rats were fed a diet which contained 0.5% 3,5,5-trimethylhexanoyl (TMH)-ferrocene over a 57-week period. The state of iron deficiency was characterized by means of the absence of stainable iron in the bone marrow. After the first days on the iron-enriched diet, ferritin-containing siderosomes were found, in numerous erythroblasts up to orthochromatic normoblasts and in reticulocytes, i.e. the dispensed iron was used for haemoglobin synthesis. After 1 week the first macrophages showed a positive Perls' Prussian blue reaction. In the cytoplasm they stored the iron in the form of free ferritin molecules and lysosomally as aggregated ferritin and/or haemosiderin. The iron loading of the macrophages increased in both of the storage qualities proportionally with duration of the feeding period and reached a maximum after 38 weeks. Final stages showed extremely iron-loaded macrophages with high concentrations of free ferritin molecules and large siderosomes, partially flowing together to still greater units. Iron deposits within endothelial cells of bone marrow sinusoids can be observed for the first time after 4 weeks. In these cells the iron is stored as ferritin in siderosomes of relatively small and uniform size; free ferritin molecules in the cytosol were of only slight concentration. The TMH-ferrocene model of iron overload shows in the bone marrow: (1) an unimpeded utilization of the iron component for erythropoiesis, (2) development of excessive iron overload of the bone marrow in macrophages and endothelial cells of sinusoids and (3) a pattern of distribution of iron as seen in secondary haemochromatosis.

Anemia, Hypochromic↗
PubMed1992

Transport of siderotic Kupffer cells to the lung and bronchial excretion of iron in experimental iron-overload.

In 3,5,5-trimethylhexanoylferrocene-induced iron overload of rats, three different types of iron-loaded macrophages and derivatives thereof were found in the lungs. On the basis of their localization and of their pattern of iron load it was possible to distinguish: (1) Resident macrophages, showing an alveolar localization and a moderate iron content represented by lysosomal ferritin and haemosiderin. (2) Liver-derived macrophages and giant cells, as well as fragments of them. They showed an exclusive localization in capillaries and alveolar septa, and high concentrations of free ferritin molecules in addition to polymorphous ferritin- and haemosiderin-containing siderosomes. (3) Monocyte-derived intravascular pulmonary macrophages. Initially, they contained iron only as lysosomal aggregates of ferritin and haemosiderin, as a result of phagocytosis of liver-derived macrophageal cell fragments. Later in iron overload, they also showed free ferritin molecules in the cytosol and fused intrapulmonarily to giant cells. The resident as well as the liver-derived siderotic pulmonary macrophages provide a way for iron excretion through the airways.

Animals↗
PubMed1994

Pattern of iron storage in the rat heart following iron overloading with trimethylhexanoyl-ferrocene.

Female Wistar rats with slight iron deficiency anemia were kept on a diet containing 0.5% trimethylhexanoyl (TMH)-ferrocene for up to 79 weeks. In the state of iron deficiency, the heart was free of light-microscopically detectable iron. After 7 weeks of the TMH-ferrocene diet, the first iron-positive granules appeared in perivascular macrophages. Further oral administration caused a progression of iron deposition in these cells, visible in the form of a granular staining but also as a diffuse iron staining of the cytoplasm. Accordingly, at the electron-microscopical level, the iron was stored partly as free ferritin molecules in the cytosol, and partly in lysosomes in the form of ferritin and/or hemosiderin. After 11 weeks, further iron-positive cells with relatively small dark-blue granules were found in the vicinity of capillaries, which could be identified as fibrocytes by means of electron microscopy. In addition, slight iron deposition occurred in the endothelial cells of the cardiac capillaries, likewise mainly in the form of small, uniform siderosomes. The myocytes showed no product of Perls' Prussian blue reaction during the whole period of investigation. From the 11th week onwards, discrete ferritin molecules were detected electron microscopically within lysosomes of these cells. Their amount increased slowly with progression of the TMH-ferrocene feeding period. Free ferritin molecules could be observed in the cytosol of fibrocytes, endothelial cells and myocytes in only very slight concentrations, whilst they were more plentiful in macrophages. In hereditary hemochromatosis and posttransfusional siderosis, the iron is found predominantly in myocytes and appears to cause cell damage, whilst this is not the case in experimental iron overload in rats.

Anemia, Iron-Deficiency↗
PubMed2003

Formation of carbon nanotubes without iron inclusion and their alignment through ferrocene and ferrocene-ethylene pyrolysis.

So far carbon nanotubes grown from the method most common method at present, that is, pyrolysis of ferrocene, invariably contains Fe inclusion. In addition, they are generally grown in random configurations. In the present investigations CNTs without Fe inclusion and in aligned configurations have been prepared by the pyrolysis of ferrocene (C10H10Fe) as well as pyrolysis of ferrocene in the presence of ethylene (C2H4). This has been achieved through optimization of growth parameters, for example, heating rate of ferrocene, pyrolysis temperature, and flow rates of carrier gas argon (Ar) and ethylene (C2H4). The as-synthesized samples have been characterized by transmission and scanning electron microscopic techniques. The optimum results relating to synthesis of carbon nanotubes without Fe inclusion and in aligned configurations have been obtained at 1000 degrees C pyrolysis temperature under flow rates of Ar of approximately 1000 sccm and of C2H4 of approximately 100 sccm. These carbon nanotubes have been found to have an outer diameter between approximately 20 and 60 nm and lengths between approximately 15 and 20 microns.

Anisotropy↗
PubMed2004

Carbon nanotubes grafted on silicon oxide nanowires.

In this article, we report the grafting of multi-walled carbon nanotubes on silica nanowires by directly growing nanotubes on the surfaces of the nanowires via chemical vapor deposition (CVD) using ferrocene and xylene as Fe catalyst precursor and carbon source, respectively. The grafted carbon nanotubes are a few micrometers long with diameters of 10 to approximately 30 nm, and grow uniformly along the lengths of the nanowires. The distribution density of the grafted carbon nanotubes on the silica nanowires can be tuned by simply adjusting the CVD growth temperature. Our method provides a simple approach for synthesizing nanometer scale grafted heterostructures between nanotubes and nanowires, which could be used to design and construct high-performance filters, chemical sensors and reinforced composites.

Carbon↗
PubMed2004

Synthesis of bamboo-shaped carbon-nitrogen nanotubes using acetonitrile-ferrocene precursor.

We report the formation of bamboo-shaped carbon-nitrogen nanotubes by employing a simple, one-step and economically viable spray pyrolysis technique using new precursor; acetonitrile and ferrocene solution. By varying the concentration of ferrocene with respect to acetonitrile, it has been found that the optimum concentration of ferrocene in acetonitrile is 5 mg/ml. The special feature of the as-synthesized bamboo-shaped carbon-nitrogen nanotubes bundles is that they are produced in a high yield (1.25 gms/run). They also have long linear extents (approximately 430 microm) and are very clean. The average composition of carbon-nitrogen nanotubes comes out to be C26N.

Acetonitriles↗
PubMed2004

Temperature effects on resistance of aligned multiwalled carbon nanotube films.

Electrical transport in vertically aligned films of multiwalled carbon nanotubes has been investigated in the -150 degrees C to 300 degrees C temperature range (all the tests were conducted in air at atmospheric pressure). In all the cases, the nanotube film exhibited a semi-conducting behavior, with the film resistance decreasing with increasing temperature. Removal of amorphous carbon contamination (via plasma etching) significantly improved the nanotube film's sensitivity to temperature changes (particularly in the 20 degrees C to 200 degrees C temperature range). All the of films tested in this study showed a consistent, repeatable behavior that was independent of the nanotube film length. The temperature sensitivity of the nanotube films was also found to be independent of the heating/cooling rates and without hysteresis. Because of the excellent repeatability and stability of the results, it is conceived that miniaturized temperature sensors could be designed using such aligned multiwalled nanotube films.

Carbon↗
PubMed2005

Effect of ferrocene concentration on the synthesis of bamboo-shaped carbon-nitrogen nanotube bundles.

We have investigated the effect of ferrocene concentration on the synthesis of carbon-nitrogen (C-N) nanotubes. The bamboo-shaped carbon-nitrogen nanotubes were synthesized by spray pyrolysis of Fe(C5H5)2 and CH3CN solution using argon as a carrier gas at the optimum temperature of approximately 900 degrees C. The effect of ferrocene concentration on the length and concentration of nitrogen in nanotubes was studied. Micro-structural features of the nanotubes were monitored employing scanning and transmission electron microscopic techniques. SEM studies reveal that with decreasing ferrocene concentration from 25 mg ml(-1) to 5 mg ml(-1), the length of the nanotubes vary from 80 microm to 430 microm. A feasible growth model has been described and discussed. X-ray photoelectron spectroscopic studies have confirmed the formation of nitrogen-doped carbon nanotubes. These studies reveal that the nitrogen concentration in the nanotubes decreases with the increase of ferrocene concentration. The present synthesis route also provides means of producing carbon nanotubes with different concentrations of nitrogen.

Crystallization↗
PubMed2006

Synthesis and characterization of uncapped gamma-Fe2O3 nanoparticles prepared by flame pyrolysis of ferrocene in ethanol.

Nanoparticles of iron(III) oxide were synthesized by spontaneous combustion of ferrocene in ethanol solution using a simple spirit lamp. X-ray powder diffraction and electron diffraction analysis of the powder suggested the formation of gamma-Fe2O3 (Maghemite phase) having lattice constant 8.3539 +/- 0.0209 A. Transmission Electron Micrograph suggested the formation of spherical particles with an average diameter of 24.7 +/- 1.6 nm. A sextet with an isomeric shift of 0.328 mm s(-1) seen in the Mossbauer spectrum recorded at room temperature, further supports the formation of gamma-Fe2O3. The particles were dispersed freely in the polar solvents like ethanol, dimethyl sulfoxide, and water. Infra Red spectrum gave bands at 400, 432, 565, and 638 cm(-1), which confirms the presence of gamma-Fe2O3 phase.

Crystallization↗
PubMed2006

Modified electrodes prepared from ferrocene functionalized silicate xerogels: analysis of the electrochemical response in isotropic and fractal structural systems.

New xerogels functionalized by ferrocenes as redox probes have been prepared using various types of catalysis. The analysis of the electrochemical response in the case of modified electrodes allows us to get an insight into the gel nanostructure which has been found to be isotropic in the case of acidic catalysis, and fractal in the case of fluoride catalysis, provided that the amount of functionalized silanes is not too high. Indeed the results of electrochemical measurement prove that the fractality of functionalized hybrid silica is general in the case of basic catalysis, except in the case of very high functional moieties loading, where the electrode become essentially organic and isotropic. On the other hand, in the case of acidic catalysis, whatever the amount of organic material, the hybrid gel remains isotropic, and a classical electron pseudo-diffusive behaviour is observed. The diffusion coefficient values extracted from the current-time slopes do not vary monotonically with the amount of redox probe in the case of fractal xerogel structures, which is indicative that not all the functional moieties are electroactive in that case.

Electrochemistry↗
PubMed2006

Assessment of Plasmodium falciparum resistance to ferroquine (SSR97193) in field isolates and in W2 strain under pressure.

BACKGROUND: Ferroquine (FQ), or SSR97193, is a novel antimalarial drug currently in phase I clinical trials. FQ is a unique organometallic compound designed to overcome the chloroquine (CQ) resistance problem. FQ revealed to be equally active on CQ-sensitive and CQ-resistant Plasmodium falciparum laboratory strains and field isolates. FQ is also curative on rodent malaria parasites. As FQ will be tested in patients, the potential for resistance to this drug was evaluated. METHODS: The relationship between CQ-resistant transporter gene genotype and susceptibility to FQ were studied in 33 Cambodian P. falciparum field isolates previously studied for their in vitro response to CQ. In parallel, the ability of the CQ-resistant strain W2, to become resistant to FQ under drug pressure was assessed. RESULTS: The IC50 values for FQ in field isolates were found to be unrelated to mutations occurring in the P. falciparum chloroquine resistance transporter (PfCRT) or to the level of expression of the corresponding mRNA. In vitro, under a drug pressure of 100 nM of FQ, transient survival was observed in only one of two experiments. CONCLUSION: Field isolates studies and experimental drug pressure experiments showed that FQ overcomes CQ resistance, which reinforces the potential of this compound as a new antimalarial drug.

Amino Acid Sequence↗
PubMed2000

Ferrocene-Mediated carbon paste electrode modified with D-fructose dehydrogenase for batch mode measurement of D-fructose.

A mediated modified carbon paste and renewable surface electrode for fructose amperometric measurement based on D-fructose dehydrogenase (FDH) was prepared and optimized. Commercially available ferrocene (FcH) and hydroxymethyl ferrocene (FcCH2OH) were used as mediators. The substituted FcH showed better linearity and higher sensitivity. The influence of different experimental parameters was studied for optimum analytical performance. The final FDH-modified electrode showed good analytical performance for batch mode measurements of fructose.

Beverages↗
PubMedDate not supplied

Biosensor for determination of glucose and sucrose in fruit juices by flow injection analysis.

Glucose and sucrose were measured with an amperometric method by using the flow injection analysis technique. A carbon paste electrode with a renewable surface containing glucose oxidase, horseradish peroxidase, and ferrocene was used in combination with the soluble enzymes invertase and mutarotase. The effect of invertase, mutarotase, and ascorbic acid on the electrode response was examined. Glucose and sucrose concentrations were determined with < 3% errors. The proposed method for glucose and sucrose measurements was validated in real samples of fruit juices. The results were also compared with those obtained with the ultraviolet method.

Ascorbic Acid↗
PubMed2002

The lipophilic iron compound TMH-ferrocene [(3,5,5-trimethylhexanoyl)ferrocene] increases iron concentrations, neuronal L-ferritin, and heme oxygenase in brains of BALB/c mice.

Mismanagement of intracellular iron is a key pathological feature of many neurodegenerative diseases. Our long-term goal is to use animal models to investigate the mechanisms of iron neurotoxicity and its relationship to neurodegenerative pathologies. The immediate aim of this experiment was to determine regional distribution of iron and cellular distribution of iron storage proteins (L- and H-ferritin) and an oxidative stress marker (heme oxygenase-1) in brains of mice fed the lipophilic iron compound (3,5,5-trimethylhexanoyl) (TMH)-ferrocene. We fed male and female weanling BALB/cj mice diets either deficient in iron (0 mg Fe/kg diet), adequate in iron (35 mg Fe/kg diet; control mice), or adequate in iron and supplemented with 0.1 or 1.0 g TMH-ferrocene/kg diet for 8 wk. Iron concentrations in cerebrum were higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p < 0.05). Liver iron concentrations were eightfold higher in mice fed 1.0 g TMH-ferrocene/kg diet than in control mice (p < 0.0001). L-Ferritin and heme oxygenase-1 expression were elevated in striatum in mice fed 1.0 g TMH-ferrocene/kg diet. We conclude that administration of the lipophilic iron compound TMH-ferrocene leads to subtle perturbations of cellular iron within the brain, potentially representing a model of iron accumulation similar to that seen in various neuropathological conditions.

Animals↗
PubMed2001

Electrochemical behavior of catechol and 3,4-dihydroxytoluene in acetonitrile at a platinum-disk electrode modified with a tyrosinase containing polyacrylamide film.

A modified platinum-disk electrode coated with a non-plasticized polyacrylamide (PAA) membrane was used to study electrochemically an enzymatic reaction between tyrosinase in the PAA membrane and catechol and 3,4-dihydroxytoluene in acetonitrile (AN). Tyrosinase, a hydrophilic biofunctional material, was immobilized in the thin PAA membrane, which adhered to the platinum-disk electrode and was stable in AN. The enzymatic activity of tyrosinase in the PAA membrane to the above substrates in AN was confirmed by cyclic voltammetry and amperometry. The apparent maximum velocities (Vmaxapp) and the apparent Michaelis constants (Kmapp) were determined from the amperometric results; the apparent turnover numbers were also determined. The reduction potentials of the substrates were reported vs. the cathodic peak potential of ferrocene in AN to improve the reliability of the potential data and to make possible a comparison of the potentials in different solvents. The electrochemical system discussed in this report can be used for tracing enzymatic reactions with substrates dissolving in aprotic dipolar solvents and for investigating solvent effects on enzymatic activities.

Acetonitriles↗
PubMed2001

Electrochemical sensing for the determination of activated cyclic AMP-dependent protein kinase.

A novel electrochemical system has been developed for monitoring the cyclic AMP-dependent protein kinase (PKA) activity. In this method, PKA activity was monitored as the change in the redox current of a ferrocene-pendant PKA substrate peptide (Fe-LRRASLG) on a gold electrode, which had been modified with thioctic acid, using cyclic voltammetry. The phosphrylation of the ferrocene-pendant substrate with PKA changed the net charge from +1 to -1. This caused a decrease in the redox current of the ferrocene unit due to an electrostatic repulsion between the substrate and the anionic surface of the electrode. We expect that this method is potentially useful for monitoring the enzyme activity in medical or pharmacological fields.

Biosensing Techniques↗