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At least 127 records · Page 7Linked to original sources
PubMed2003

Cerium(III) chloride-mediated reactions of sulfonamide dianions.

Presented here is the first report on the ability of cerium(III) chloride to mediate high-yielding and, oftentimes, highly diastereoselective additions of N-benzyl-alpha, N-dilithio methanesulfonamide to aldehydes and ketones of biological importance. Smooth addition was effected to base-sensitive substrates such as Fmoc-protected alaninal, citral, 5-cholesten-3-one, uridine 5'-aldehyde, 3'-ketouridine, and 3'-ketothymidine. The reaction was chemoselective for aldehydes in the presence of nitriles. Acetoxy groups are labile and thus not suitable protecting groups for alcohols under these conditions. N-Benzyl-alpha, N-dilithio methanesulfonamide was found to be of sufficient basicity to cause enolate formation with sensitive substrates, such as 1-phenylacetone. However, the addition of cerium(III) chloride mediated the basicity of the dianion and suppressed enolate formation in these cases. Further, cerium(III) has general utility for the addition of various N-aliphatic/aromatic methanesulfonamide dianions to 3'-ketouridine.

Journal Article↗
PubMed2001

HPLC analysis of complete BZ systems. Evolution of the chemical composition in cerium and ferroin catalysed batch oscillators: experiments and model calculations.

In the last few years many new reaction routes and intermediates have been discovered in the mechanism of the Belousov-Zhabotinsky (BZ) reaction with the aid of high performance liquid chromatography (HPLC). These previous HPLC studies, however, were limited to the Ce(4+)-organic substrate (malonic or bromomalonic acid) systems only. Very recently some measurements were made on a cerium catalysed full BZ system but only in its induction period. The present work follows the evolution of the main chemical components in a cerium and in a ferroin catalysed full BZ system from the start until the end of the oscillatory regime in a batch reactor. While recording the potential oscillations of a bromide selective electrode we measured from time to time the concentration of the following components: malonic and bromomalonic acids and bromate as main components; malonyl malonate, ethanetetracarboxylic and bromoethenetricarboxylic acids which are recombination products of organic free radicals; oxidized intermediates: tartronic, oxalic (OA) and mesoxalic (MOA) acids, and brominated products: dibromoacetic and tribromoacetic acids. Recombination products are generated in the intervals when the autocatalytic reaction is "switched off". In the course of the autocatalytic periods, however, the organic radicals react with the inorganic bromine dioxide radical mainly which leads to the formation of MOA and OA. Due to a very fast Ce(4+)-MOA reaction, MOA can be detected in the ferroin catalysed BZ system only. Our model calculations deal exclusively with the cerium catalysed system. The suggested new Marburg-Budapest-Missoula (MBM) model includes both negative feedback loops (bromous acid-bromide ion Oregonator type and bromine dioxide-organic free radicals Radicalator type feedback) and the recently discovered radical-radical recombination reactions. Comparison of the experimental data with the model calculations shows a good qualitative agreement but some open problems still remain. To overcome these problems oxygen atom transfer and other redox reactions are proposed.

Journal Article↗
PubMed2002

Solubility of cerium in LaCoO3-influence on catalytic activity.

The recent interest in the catalytic properties of lanthanum perovskites for methane combustion and three way catalysis has led to considerable debate as to their structure and defect chemistry. We have investigated the doping of LaCoO3 with the tetravalent cerium cation using atomistic simulation techniques. We have compared three routes for cerium insertion and identified the favoured doping mechanism, which explain experimental observations relating to the effect of cerium on catalytic activity.

Journal Article↗
PubMed2003

Cerium(III) dialkyl dithiocarbamates from [Ce[N(SiMe3)2]3] and tetraalkylthiuram disulfides, and [Ce(kappa2-S2CNEt2)4] from the Ce(III) precursor; Tb(III) and Nd(III) analogues.

The synthesis and characterisation of the first neutral cerium dialkyl dithiocarbamate complexes, using a novel oxidative displacement of the amido ligands of [Ce[N(SiMe3)2]3] by tetraalkylthiuram disulfides [R2NC(S)S]2(R = Me, Et) in thf solution, are reported. In the absence of other donors, the complexes [Ce(kappa2-S2CNMe2)3(thf)2] and Ce(kappa2-S2CNEt2)3) 3 were obtained. The addition of a polypyridyl ligand allowed easy access to a range of complexes of general formula [Ce(kappa2-S2CNR2)3(L[intersection]L)][R = Me and L([intersection])L = 2,2'-bipy (4), or 4,7-diphenyl-1,10-phenanthroline (6); or R = Et and L[intersection]L = 2,2'-bipy (5)]. Brief exposure of the Ce(III) dithiocarbamate to oxygen gas afforded in high yield the diamagnetic, crystalline Ce(IV) dithiocarbamate [Ce(kappa2-S2CNEt2)4)] 7. The neodymium (8) and terbium (10) complexes, isoleptic with 2, were prepared from the appropriate 4f metal (Ln) bis(trimethylsilyl)amide [Ln[pN(SiMe3)2]3][Ln = Nd or Tb (9)] and [Me2NC(S)S]2. The structures of the crystalline complexes, 2, 4, 6, 7, 9 and 10 have been determined by X-ray crystallography. Some evidence has been obtained for the formation of the cerium(IV) complex Ce[N(SiMe3)2]2(kappa2-S2CNMe2)2. The cerium(IV) complex 7 has the metal coordinated to eight sulfur atoms of four planar chelating S2CNC2 moities and its geometry is intermediate between dodecahedral and square prismatic; the mean Ce-S bond length of 2.803 A in 7 compares with the 2.950 A in the Ce(III) complex 2.

Journal Article↗
PubMed2005

Indirect determination of uranium by the on-line reduction and fluorimetric detection of cerium(III).

A novel flow injection method has been developed for the indirect determination of uranium by the on-line reduction and subsequent fluorimetric detection of cerium(III). A sample solution containing uranium(VI), prepared as a sulfuric acid solution, was injected into a sulfuric acid carrier solution and passed through a column packed with metal bismuth to reduce uranium(VI) to uranium(IV). The sample solution was merged with a cerium(IV) solution to oxidize uranium(IV) to uranium(VI) and the cerium(III) generated was then monitored fluorimetricaly. The present method is free from interference from zirconium, lanthanides, and thorium, and has been successfully applied to the determination of uranium in monazite coupled with an anion-exchange separation in a sulfuric acid medium to eliminate iron(III). The sample throughput was 25 per hour and the lowest detectable concentration was 0.0042 mg l(-1).

Journal Article↗
PubMed1998

[The influences of lanthanum,cerium and fluoride on the activity of glucosyltransferase(GTF) and adherence of oral cariogenic bacteria in vitro]

OBJECTIVE:Study of the influences of lanthanum,cerium and fluoride on the activity of flucosyltransferase(GTF) and adherence of oral cariogenic bacteria. METHODS: The influences of lanthanum,certium and fluoride on the acitivity of GTF and adherences of Steptococcus sobrinus 6715,Lactobacillus 4356 and Actinomycetes viscosus 19246 in vitro were investigated. RESULTS: Lanthanum and cerium can efficiently inhibit the acitivity of GTF than fluoride. CONCLUSION: The result was given a data that lanthanum and cerium could be used as a cariostatic agent in future.At the same time the inhibition of the bacterial adherence by these trace elements was also revealed.

Journal Article↗
PubMed1986

The influence of age on the efficiency of delayed therapy with Ca-DTPA for cerium in rats.

The influence of age on the effectiveness of chelation therapy starting 24 h after cerium administration was studied in 2- and 6-week-old rats. 141Ce was administered IP, followed after 24 and 48 h by IP administration of trisodium calcium diethylenetriaminepentaacetate (Ca-DTPA). The whole body and organ retention of 141Ce was determined 6 days after its administration. The chelation therapy significantly reduced cerium retention in both age groups but was more efficient in older animals. This age-related effect was, however, less pronounced than after immediate treatment with DTPA observed in our previous experiments, indicating that age as one of the factors which influence the efficacy of chelation treatment is probably more important in conditions of early than in conditions of delayed therapy.

Age Factors↗
PubMed1998

Cerium ions in the histochemical demonstration of second-messenger enzymes.

Second-messenger systems are involved in the regulation of numerous cellular processes. Adenylate cyclase (AC) and guanylate cyclase (GC) enzymes are in key positions in the regulation of these systems. The cerium method has been successfully applied to demonstrate amine- and neuropeptide-stimulated AC in rat nervous and adipose tissues and human sweat glands at the electron microscopic level. AC was also localized in cultured neurons. Nitric oxide compounds stimulated GC were demonstrated in rat hippocampal areas. Enzyme reactions were located in neurons pre- and postsynaptically in synapses; in addition, GC activity was seen intraneuronally and in glial cells. Adipocytes and eccrine glandular cells exhibited reaction products in their plasmalemmas. Optimal histochemical conditions are described, combined with control experiments. Some handicaps, related to the sensitivity of the enzymes to the fixatives, penetration problems of cerium salts, and especially the specificity of the method in phosphatase enzyme histochemistry in general are discussed.

Adenylyl Cyclase Inhibitors↗
PubMed1991

A new staining method for the detection of activities of H2O2-producing oxidases on gels and blots using cerium and 3,3'-diaminobenzidine.

Cerium chloride (CeCl3) was used to trap the hydrogen peroxide generated by several oxidases on native gels and blots. The pale yellow color of cerium perhydroxide formed is converted to a brown-black precipitate by the subsequent reaction with 3,3'-diaminobenzidine. The suitability of this method for the detection of the activity of several oxidases on gels and on blots under nondenaturing conditions, employing different electrophoretic systems and resolving techniques, is demonstrated. Moreover, this method has proven to be highly suitable for the assessment of the substrate and stereospecificity of oxidases, the determination of their molecular weights, and the isoelectric points of isoforms.

3,3'-Diaminobenzidine↗
PubMed1977

Studies of bone and soft-tissue tumours induced in rats with radioactive cerium chloride.

A colloidal suspension of radioactive cerium chloride was inoculated into the hind legs of Sprague Dawley rats. Bone and soft-tissue tumours were induced at the site of inoculation in 77% of the animals. All bone tumours were osteogenic osteosarcomas. Soft tissue tumours were mostly malignant and were of various histological types, predominantly fibrosarcomas, haemangiopericytomas, angiosarcomas and rhabdomyosarcomas. A kinetic study showed that the doubling time (DT) of tumours was closely correlated with the anatomical site of tumour development: bone tumours had a DT of 17.4 +/- 4.3 days and malignant tumours which developed in soft tissues had a DT ranging from 7.4 to 8.4 days with the exception of two haemangiosarcomas which had a long DT of 17 +/- 0.6 days. Pulmonary metastases were frequent for osteosarcomas and tumours of vascular origin. This model of induction of bone and soft-tissue tumours in rats by injection of a colloidal suspension of radioactive cerium chloride offers the possibility of more comprehensive physiopathological and kinetic studies of these tumours and may constitute a good model for their human counterparts.

Animals↗
PubMed1991

Immunoalkaline phosphatase with cerium-based cytochemistry for double staining at the transmission electron microscopic level.

Immunoelectron microscopic localization of surface antigens on lymphocytes is possible using alkaline phosphatase combined with cerium-based cytochemical methods. Distinctive electron-dense deposits are easily identified at sites of antibody binding. Mouse splenocytes showing surface immunoglobulin localization and human peripheral blood lymphocytes stained for the MHC-Class II antigen HLA-DR illustrate the results. Double staining for murine Ia antigen by the alkaline phosphatase procedure, combined with immunogold labeling of antigens identified on dendritic cells, i.e., NLDC-145, demonstrates the utility of the cerium cytochemical method.

Alkaline Phosphatase↗
PubMed1991

Cerium depresses protein synthesis in cultured cardiac myocytes and lung fibroblasts.

The present study examined the effect of Cerium on protein synthesis in cultured cardiac myocytes and lung fibroblasts exposed to normal and markedly subnormal levels of Mg2+. Cerium was found to have a general inhibitory effect on protein synthesis in these cell types, including the synthesis of myofibrillar proteins in the cardiac myocytes. Further, the effect of the metal ion was more pronounced in cells exposed to the Mg2(+)-deficient medium. The possible implications of the observations are discussed.

Animals↗
PubMed1989

Light microscopical visualization of phosphatase activities demonstrated with the cerium method in resin sections of the kidney with the microwave oven.

The light microscopically invisible reaction product cerium phosphate in resin sections of rat kidney, that had been incubated for the demonstration of phosphatase activities before embedding, was converted into a visible reaction product by incubation for 10 min at 80 degrees C in alkaline lead citrate in a microwave oven. This method offers the possibility to study phosphatase activities with the cerium method in semithin Epon sections. Furthermore it is a suitable method to select areas with phosphatase activity to be studied with the electron microscope.

Adenosine Triphosphatases↗
PubMed1982

A cerium method for the ultracytochemical localization of monoamine oxidase activity.

A cytochemical method based on the complex formation between cerous ions and hydrogen peroxide is described for the ultrastructural localization of monoamine oxidase (MAO). First, the residual MAO activity after fixation was measured by a radiochemical assay technique and was found to be sufficiently retained for cytochemical detection. Although the Tris buffer used in the present method was found to be inhibitory to MAO, considerable activity was still retained after fixation and incubation in Tris. MAO activity, detected as precipitates of cerium perhydroxide, was observed in the mitochondrial outer compartment, mitochondrial cristae and perinuclear space of myocardial cells and endothelial cells of rat heart. MAO activity was also found along the plasma membrane of capillary endothelia. Omission of substrate from the incubation medium or pre-incubation with pargyline, a specific MAO inhibitor, drastically reduced the amount of deposits. The present cerium method seems promising because of its reproducibility and the high electron density of the reaction products.

Animals↗
PubMed1996

Quantitative assessment of primary cerium reaction product formed by glucose-6-phosphatase activity in a male rat liver: an image analysis study.

Glucose-6-phosphatase (G6Pase) activity has been determined in periportal and pericentral areas of the liver of normal male rats. Measurements were performed on unfixed cryostat sections mounted on semipermeable membranes. In the present study, the oxidized primary reaction product of a cerium-based histochemical method [Ce(IV)perhydroxyphosphate] instead of the final reaction product after a second-step incubation was measured. For quantification of the amount of Ce(IV)perhydroxyphosphate formed the digital image analyzing system Quantimet 500+ was used. Estimated values of optical densities of Ce(IV)perhydroxyphosphate over test areas were employed for calculation of kinetic parameters of (G6Pase). Highest activities of G6Pase (higher Km and Vmax levels) were found in periportal areas of the rat liver, indicating a higher amount of active enzyme molecules and a lower affinity for the substrate. Differences in values for both Km and Vmax between periportal and pericentral zones were highly significant and closely comparable to those for male fed rats. Correlations between Km and Vmax were significant for periportal as well for pericentral liver areas. The results of the present study thus allow the same biological implications as histochemical methods employing a final reaction for quantification of enzyme activities. The present method avoids the drawbacks of enhancement reactions and demonstrates the feasibility of in situ analysis of enzyme kinetic parameters by quantification of oxidized primary cerium reaction products.

Animals↗
PubMed2003

Production of hydrogen peroxide in situ in cardiac myocytes during hypoxia-reoxygenation as assessed with cerium.

Free radicals have been implicated in myocardial reperfusion injury. Hydrogen peroxide (H(2)O(2)) is one possible source of reactive oxygen intermediates. We studied the formation and toxicity of H(2)O(2) in isolated myocytes during hypoxia-reoxygenation with the use of cerium. This method involves formation of an electron-dense precipitate when H(2)O(2) reacts with cerium chloride (CeCl(3)). Single myocytes were obtained from rat hearts by collagenase digestion. Isolated myocytes were reoxygenated for 15 min after 30 min of hypoxia. The cells were treated with digitonin to increase the permeability of the plasma membrane, and CeCl(3) was added to detect intracellular H(2)O(2) on electron microscopy. In the nonhypoxia control group, the ultrastructure of cells was well preserved, and no dense deposits were found in myocytes. In the hypoxia-reoxygenation group, precipitates, i.e., Ce-H(2)O(2) reaction products, were found inside and along swollen mitochondria, and cell viability was reduced to 72.3% of control. These results indicate that endogenous H(2)O(2) is generated by mitochondria and that its release into the cytosol may lead to myocyte death under pathological situations such as hypoxia-reoxygenation.

Animals↗
PubMed1993

The use of cerium nitrate-silver sulphadiazine as a topical burns dressing.

Infection remains the major cause of morbidity and mortality following the shock phase in the burn patient. Measures to reduce the risk of wound infection and subsequent sepsis include early excision where possible, and the use of topical antimicrobial creams such as silver sulphadiazine. Studies from the USA and Europe suggest the addition of cerium nitrate to this commonly used agent may improve its efficacy. We present the findings of a pilot study which investigated the action of a commercial preparation of cerium nitrate/silver sulphadiazine mixture (Flammacerium, Duphar B. V. Holland) on 20 patients considered unsuitable for surgery. There were no episodes of cellulitis or septicaemia. Flammacerium was noted to produce an adherent eschar that was easy to shave and which received split skin grafts well.

Administration, Topical↗
PubMed1990

Cerium chloride as a histochemical marker of hydrogen peroxide in reperfused ischemic hearts.

Hydrogen peroxide (H2O2) has been implicated in cardiac damage due to ischemia and reperfusion. We adapted an electron microscopic, histochemical method for demonstrating H2O2 produced by isolated cells to isolated, buffer-perfused rabbit hearts. The method involves formation of an electron-dense precipitate when H2O2 reacts with cerium chloride (CeCl3). We perfused hearts retrograde via the aorta with well-oxygenated bicarbonate-buffered solution, followed by one in which bicarbonate was replaced with imidazole (IPSS) to prevent precipitation of bicarbonate and CeCl3. Some hearts were made globally ischemic (30 min, 37 degrees C), reperfused 5 min with well-oxygenated IPSS containing 1 mM CeCl3, then processed for electron microscopy. Others were perfused with IPSS containing catalase (300 U/ml) or albumin before ischemia and upon reperfusion, followed by CeCl3 administration. Nonischemic control hearts perfused with IPSS (+/- catalase) were also studied. Electron micrographs were assessed visually and by computer for precipitate localization and amount. There was abundant precipitate on the luminal face of the coronary vascular endothelium in ischemic-reperfused, cerium-treated hearts, including those treated with albumin. There was significantly less in reperfused catalase-treated or nonischemic control hearts. X-ray microbeam analysis of the endothelial precipitate indicated the presence of Ce. This appears to be the first visual demonstration of a CeCl3-H2O2-dependent reaction product in intact isolated ischemic hearts. The data indicate that at the time of reperfusion some H2O2 is accessible to the vascular space, and that its amount can be reduced by perfused catalase. Further modifications this technique may be useful for assessing the sites and pathways by which H2O2 is generated by hearts or other buffer-perfused organs subjected to stresses such as ischemia or hypoxia.

Animals↗