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Results for “MAGNESIUM OXIDE”

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At least 307 records · Page 17Linked to original sources

PubMed2001

Activity of Basic Catalysts in the Meerwein-Ponndorf-Verley Reaction of Benzaldehyde with Ethanol.

The Meerwein-Ponndorf-Verley (MPV) reaction of benzaldehyde with ethanol in the liquid phase in the presence of basic catalysts consisting of magnesium oxide, calcium oxide, and mixed oxides obtained by calcination of layered double hydroxides, was studied. The catalysts were characterized using various techniques including X-ray diffraction and gas adsorption (viz nitrogen physisorption to determine textural properties and carbon dioxide chemisorption to elucidate surface basic properties). The catalyst consisting of calcium oxide, which was that possessing the highest density of basic sites, was found to be the most active in the process; the MPV reaction was accompanied by two other, competing reactions (viz aldol condensation and the Tishchenko cross-reaction). The MPV reaction of benzaldehyde with other alcohols was also examined, the highest conversion being obtained with secondary alcohols as hydrogen sources. Copyright 2001 Academic Press.

Journal Article↗

PubMed1982

Colon cleansing regimens. A clinical study in 1200 patients.

The purgative effect of bisacodyl, anthraquinone glycosides (Cascara), and sodium picosulfate, alone or in combination with a saline purge and a tap water enema, was studied in 1200 patients. The cleansing effect was scored with regard to retained fecal residue evident on double-contrast studies of the colon. The combination of a contact laxative and a saline purge produced good cleansing effect in 52%-80% of the patients. With an additional tap water enema given 1 hour before the colon examination, however, 96% of the colons were clean. The taste and the effects of the cleansing systems were tolerated favorably by more than 90% of the patients. However, 17% reported restriction in work capacity on the day of bowel cleansing.

Adult↗

PubMed2001

On the effect of catalyst status in the quantitative determination of platinum in Pt-Sn/MgO materials.

The development of an analytical method for the determination of platinum in MgO based Pt/Sn catalysts is described. Electrothermal atomic absorption spectroscopy (ETAAS) was chosen because of its high sensitivity and robustness against spectral interferences. All the sources of chemical interferences were statistically analyzed and corrections were adopted for the presence of magnesium oxide support. The effectiveness of different mineralization procedures was critically evaluated as a function of the chemical of the solid catalyst. Microwave digestion allowed recovery of metal of 100% for all the catalysts analyzed and exhibited significant better precision values than other digestion methods, which could nevertheless be utilized under proper conditions in selected cases.

Journal Article↗

PubMed1997

Primary hyperoxaluria type I: renal ultrasound before and after treatment.

Three patients with primary hyperoxaluria type I received therapy consisting of vitamin B6, magnesium oxide, and high oral fluid intake. Sonographic follow-up showed a variable response to treatment, ranging from normalization of renal tissue to no change at all. However, there is evidence of a correlation between laboratory findings and ultrasound findings during treatment.

Child↗

PubMed1992

Circadian variation in ventricular arrhythmias in hypertensive men.

Circadian patterns have been observed for various cardiovascular functions and events including sudden cardiac death. This study examined whether ventricular arrhythmias could be a pathophysiologic explanation for the increase in prevalence of sudden cardiac death observed between 6 A.M. and noon. Hypertensive men 35 to 70 years of age and without a history of symptomatic cardiac disease were withdrawn from diuretic treatment and received 1 month of oral electrolyte repletion with both 40 mmol of potassium chloride and 400 mg of magnesium oxide daily. Then continuous 24-hour Holter monitoring was performed and ventricular arrhythmias were classified by 6-hour time intervals. The interval from 6 A.M. to noon revealed a higher prevalence of complex or frequent ventricular arrhythmias than the interval from midnight to 6 A.M., as well as a higher mean number of ventricular premature complexes per hour. The differences were statistically significant (p less than 0.01) and amounted to increases of about one third. Ventricular arrhythmias during the other two 6-hour periods were intermediary in frequency. It is concluded that the increase in sudden cardiac death noted in the morning might be related, at least in part, to an increase in frequency of ventricular arrhythmias; the implications of this observation for preventive cardiology deserve further investigation.

Aged↗

PubMed1992

Silent myocardial ischemia in men with systemic hypertension and without clinical evidence of coronary artery disease.

The prevalence, characteristics and circadian pattern of silent myocardial ischemia, and its association with ventricular arrhythmias was studied in hypertensive men aged 35 to 70 years (mean 61) without clinical cardiac disease. Participants were withdrawn from diuretic treatment and received 1 month of oral electrolyte repletion with 40 mmol of potassium chloride, and 400 mg of magnesium oxide daily. Twenty-four-hour Holter monitoring was then performed. Episodes of silent myocardial ischemia occurred in 50 of 186 men (27%) and lasted from 2 to 289 minutes (mean 30 and median 18). Statistical analysis comparing the interval from midnight to 6 A.M. with each of the other three 6-hour time intervals revealed that participants were less likely to have silent myocardial ischemia in this period (p less than 0.01 for each comparison) than at other times of the day. There was little difference in the proportion of men with a frequent or complex ventricular arrhythmia during the entire day or within 1 hour of the silent myocardial ischemic episode (or during a comparable time period) comparing those with to those without silent myocardial ischemia. These findings indicate that silent myocardial ischemia occurs in approximately 25% of an older population of hypertensive men without history of symptomatic cardiac disease. The circadian pattern of frequency of silent ischemic events in men free of clinical cardiac disease is similar to that reported for patients with cardiac disease and coincides with that reported for sudden death. There was no significant association between silent myocardial ischemia and ventricular arrhythmias.

Adult↗

PubMed1985

Microassay for ammonium by determination of ammonia nitrogen in a nitrogen analyzer.

The method described comprises the transformation of ammonium into ammonia, the rapid and gentle liberation of the ammonia followed by the measurement of the nitrogen in a Dohrmann nitrogen analyzer. Untreated biological samples (1-50 microliters) were pipetted onto magnesium oxide tablets at 130 degrees C and the ammonia liberated was transferred by a continuous stream of nitrogen carrier gas into the nitrogen analyzer. There the ammonia was determined by oxidative pyrolysis and subsequent chemiluminescence measurement of the excited NO2. The result could be read in nanograms ammonia nitrogen within 6.5 min. Apart from volatile amines, which are usually negligible in biological samples, the method was specific for ammonia because under the given conditions of volatilization the labile groups of glutamine and asparagine did not interfere. The assay was sensitive in the range of 1.5-150 nmol ammonia and suitable for the routine analysis of small samples.

Ammonia↗

PubMed1984

Metabolism of [4-14C]androstenedione by cells cultured from human amniotic fluid.

The conversion of [14C]androstenedione by human fibroblast (F) and amniotic fluid (AF) cells obtained by amniocentesis was investigated using human dermal fibroblasts (DF) as controls. Cell suspensions were incubated with [14C]androstenedione in the presence of a NADPH generating system. Steroid reaction products were separated from unreacted substrate by chromatography on micro-columns of magnesium oxide, partially resolved by partition chromatography on celite and further characterized by thin-layer chromatography and recrystallization to constant specific activity. In the case of F cells the pattern of metabolism was qualitatively similar to that of DF cells; the predominant metabolite was testosterone and several uncharacterized metabolites were detectable. However testosterone was the only metabolite isolated from incubations with AF cells. The results demonstrate distinct differences in the capacity of AF and F type cells to metabolize [14C]androstenedione and support the view that F cells resemble typical fibroblasts from dermis or other connective tissues.

Amniotic Fluid↗

PubMed1989

An improved head-and-neck phantom for radiation dosimetry.

To obtain accurate estimates of radiation doses within the head and neck, a phantom was constructed. The osseous structures were represented by a human skull and cervical vertebrae with Mix D simulating the soft tissues originally with the bone. The soft tissues of the head and neck were also represented by this mixture of wax, plastic, magnesium oxide, and titanium dioxide with the x-ray absorption and scattering properties nearly equal to water and soft tissue. Soft tissue thicknesses and facial contours were based on depths reported in the literature and supplemented by cadaver measurements. Air passages, air cells, sinuses, and the oral cavity were left open to accurately simulate the patient. The locations of 16 anatomic sites were based on cadaver dissection and measured relationships to osseous landmarks and the skin surface. To confirm the accuracy of the phantom, doses were measured with lithium fluoride thermoluminescent dosimeters and compared with the results of other investigations reported in the literature.

Cervical Vertebrae↗

PubMed1993

The strengthening mechanism of a magnesia core ceramic.

A high-expansion core material containing magnesia and forsterite may be used to make all-ceramic dental crowns with porcelain-fused-to-metal body porcelains. The purpose of this study was to investigate the strengthening mechanism for the magnesia core material. Six batches of the magnesia core material were made by reacting magnesia with a silica glass with holding times ranging from 17 to 120 min. The flexural strength was measured using three-point loading according to the ISO specification for dental ceramics. The forsterite content was measured using quantitative x-ray diffraction. A statistically significant correlation was found between the forsterite content and flexural strength. The proposed mechanism for strengthening is the precipitation of fine forsterite crystals in the glass matrix surrounding unreacted magnesia. Longer reaction times produced more dissolution of magnesia and subsequent precipitation of forsterite. This method results in a new strengthening mechanism for dental ceramics which have previously relied on the incorporation of alumina, leucite or ceramic whiskers.

Analysis of Variance↗

PubMed1991

'Special effects' burn injuries.

Three patients are presented with significant flame burns, resulting from accidents occurring during 'special effects' situations in the entertainment industry. These occurred as a result of the spontaneous combustion of various materials, during events in live theatre (gun powder), a television commercial (artificial 'rocket fuel'), and a video presentation (magnesium oxide). All three patients sustained flash burns to the face and hands. One patient sustained a significant bilateral corneal injury, a gamekeeper's thumb, and a permanent continuous right-sided high frequency tinnitus, in addition to his burn injury. Photographic documentation of all three patients is presented. The total loss of time from work for all patients was 6 months. All these injuries were potentially preventable.

Accidents, Occupational↗

PubMed2004

Physicochemical characterization of interfaces.

Reversed-flow inverse gas chromatography (RF-IGC) was used to measure, directly from experimental data, adsorption energies, local adsorption isotherms, the probability density function for the adsorption energies, and lateral interaction parameters, as distributed over experimental time. Local isotherms and the distribution energy function were correlated with adsorption energy. The results obtained are comparable to those calculated on the basis of the well-known integral equation. The RF-IGC method was used with the two most common hydrocarbons, acetylene and 1-butene, as probe gases, in the presence and absence of ozone, and with magnesium oxide and silicon oxide as solid adsorbents.

Journal Article↗

PubMed2006

Stabilisation/solidification of synthetic petroleum drill cuttings.

This paper presents the results of an experimental investigation into the use of stabilisation/solidification (S/S) to treat synthetic drill cuttings as a pre-treatment to landfilling or for potential re-use as construction products. Two synthetic mixes were used based on average concentrations of specific contaminates present in typical drill cuttings from the North Sea and the Red Sea areas. The two synthetic drill cuttings contained similar chloride content of 2.03% and 2.13% by weight but different hydrocarbon content of 4.20% and 10.95% by weight, respectively; hence the mixes were denoted as low and high oil content mixes, respectively. A number of conventional S/S binders were tested including Portland cement (PC), lime and blast-furnace slag (BFS), in addition to novel binders such as microsilica and magnesium oxide cement. Physical, chemical and microstructural analyses were used to compare the relative performance of the different binder mixes. The unconfined compressive strength (UCS) values were observed to cover a wide range depending on the binder used. Despite the significant difference in the hydrocarbon content in the two synthetic cuttings, the measured UCS values of the mixes with the same binder type and content were similar. The leachability results showed the reduction of the synthetic drill cuttings to a stable non-reactive hazardous waste, compliant with the UK acceptance criteria for non-hazardous landfills: (a) by most of the binders for chloride concentrations, and (b) by the 20% BFS-PC and 30% PC binders for the low oil content mix. The 30% BFS-PC binder successfully reduced the leached oil concentration of the low oil content mix to inert levels. Finally, the microstructural analysis offered valuable information on the morphology and general behaviour of the mixes that were not depicted by the other tests.

Adsorption↗

PubMed1990

Optimization of the postcolumn hydrolysis reaction on solid phases for the routine high-performance liquid chromatographic determination of N-methylcarbamate pesticides in food products.

Various solid-phase materials were evaluated as catalysts for the postcolumn hydrolysis of N-methylcarbamate pesticides in a high-performance liquid chromatographic (HPLC) method for food products. Inexpensive magnesium oxide has been used for the first time in HPLC as a very efficient catalyst and as a good alternative for, e.g., expensive anion-exchange resins. The reaction mechanism and kinetics were studied through measurement of the reaction band broadening, which depends on the stationary phase, mobile phase composition and flow-rate, and reaction temperature. Also, relationships between carbamate structure and reactivity were examined. The usefulness of the optimized postcolumn system was thoroughly tested by application to crop sample analysis during an extended period of time. The range of application of the solid-phase reaction was extended to 22 carbamate pesticides and ten of their metabolites. For crop sample analysis, limits of determination in the range 1-10 ppb were obtained.

Carbamates↗

PubMed2002

Alarming atrioventricular block and mitral valve prolapse in the Kearns-Sayre syndrome.

Kearns-Sayre syndrome (KSS) is a multisystem mitochondrial disorder characterized by the invariant triad: onset before 20, progressive external ophthalmoplegia and pigmentary retinal degeneration, plus at least one of the following: complete (or not) heart block, cereberal dysfunction and CSF protein above 100 mg/dl. Autopsies from patients with KSS revealed widespread tissue distribution mtDNA deletions. These deletions result in significantly lower activities of the enzymes of the respiratory chain. The same deletion of mitochondrial DNA present in skeletal muscle is found in myocardial tissue. An 18-year-old girl diagnosed with the KSS was admitted to our hospital because of an upper respiratory tract infection and dysphagia. ECG showed cardiac conduction defects. The patient had no history of syncope. At her surface ECG there was a complete RBBB (QRS duration approximately 130 ms), a clockwise rotation with an axis of approximately 90 degrees and a slight QT prolongation (420 ms). Echocardiography showed prolapse with thickening and degeneration of both mitral valve leaflets but without mitral regurgitation. The patient was started on a diet rich in potassium and pharmaceutical therapy with magnesium oxide (240 mg of elemental Mg p.o. per day), 1 g of calcium carbonate t.i.d., vitamin D (calcitriol 0.25 microg p.o. per day) and coenzyme Q(10) 100 mg daily and discharged 6 days later with slightly improved biochemical profile but apparent clinical improvement. Urgent pacemaker implantation was decided but unfortunately the patient died due to acute cardiac arrest 10 days later.

Adolescent↗

PubMed2000

Development of omeprazole buccal adhesive tablets with stability enhancement in human saliva.

To develop an omeprazole buccal adhesive tablet, the absorption of omeprazole solutions from human oral cavity was evaluated and the physicochemical properties such as the bioadhesive forces of various omeprazole tablet formulations composed of bioadhesive polymers and alkali materials, and the stability of omeprazole tablets in human saliva were investigated. About 23% of the administered dose was absorbed from the oral cavity at 15 min after the administration of omeprazole solutions (1 mg/15 ml). A mixture of sodium alginate and HPMC was selected as the bioadhesive additive for the omeprazole tablet. Omeprazole tablets prepared with bioadhesive polymers alone had the bioadhesive forces suitable for buccal adhesive tablets, but the stability of omeprazole in human saliva was not satisfied. Among alkali materials, only magnesium oxide could be an alkali stabilizer for omeprazole buccal adhesive tablets due to its strong waterproofing effect. Two tablets composed of [omeprazole/sodium alginate/HPMC/magnesium oxide (20/24/6/50, mg/tab)] and [(20/30/0/50, mg/tab)] were suitable for omeprazole buccal adhesive tablets which could be attached to human cheeks without collapse and could be stabilized in human saliva for at least 4 h. It was concluded that these two formulae were potential candidates for the subject of further study for the development of omeprazole buccal adhesive tablets.

Absorption↗

PubMed1976

High resolution shadowing for electron microscopy by sputter deposition.

The sputtering process by an ion beam well collimated and highly accelerated provides a valuable means of high resolution shadowing, replication of a fine object by a combination of pre-shadowing and deposition as well as a preparation of supporting films. High resolution shadowing and films with grains smaller than 1 nm can be obtained by argon ion-sputtering targets of tungsten and tungsten/tantalum alloy. The resolution of carbon replicas pre-shadowed with tungsten/tantalum is determined from the radius of curvature of replicated magnesium oxide crystal corners.

Alloys↗

PubMed1999

Trace analysis of ethosuximide in human plasma with a chemically removable derivatizing reagent and high-performance liquid chromatography.

A simple and sensitive liquid chromatographic method is described for the determination of ethosuximide in human plasma, as a highly sensitive derivative. Ethosuximide spiked in plasma was extracted with toluene and derivatized with a chemically removable derivatizing reagent, 2-(2-naphthoxy)ethyl 2-[1-(4-benzyl)piperazyl]ethanesulfonate, in a homogeneous system, using magnesium oxide as base catalyst. The resulting derivative was separated on a LiChrospher diol column with 1.2% isopropanol in n-hexane as the mobile phase and using coumarin as the internal standard. Several parameters affecting the extraction/derivatization of ethosuximide from spiked plasma were investigated. The linear range for the determination of ethosuximide in spiked plasma was over 30-700 nmol/ml. For ethosuximide in plasma, the detection limit (signal-to-noise ratio=3; sample size, 10 microl) was about 9 pmol; the relative standard deviation was 6.4% for intra-day assay (n=6) and 9.2% for inter-day assay (n=6) and the relative recovery was found greater than 94%.

Anticonvulsants↗