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PubMedDate not supplied

Determination of elemental composition of substance lost following wear of all-ceramic materials.

PURPOSE: The aim of this study was to test the possible elemental release of four different all-ceramic materials in a wear machine to predict results about their long-term behavior in the oral environment. MATERIALS AND METHODS: Four different all-ceramic materials with different chemical compositions were selected for the wear testing. A total of 20 cylindric samples, five for each ceramic group, were prepared according to the manufacturers' instructions. These were subjected to two-body wear testing in an artificial saliva medium under a covered unit with a computer-operated wear machine. The artificial saliva solutions for each material were analyzed for the determination of amounts of sodium, potassium, calcium, magnesium, and lithium elements released from the glass-ceramic materials. The differences between and within groups were statistically analyzed with a one-way ANOVA, followed by Duncan tests. RESULTS: The statistical analyses revealed no significant differences among Na, K, Ca, or Mg levels (P > .05) released from the leucite-reinforced groups, while there was a significant (P < .05) increase in Li release from the lithium disilicate group. CONCLUSION: Considerable element release to the artifical saliva medium was demonstrated in short-term wear testing. The lithia-based ceramic was more prone to Li release when compared with other elements and materials.

Aluminum Silicates↗
PubMed2002

[Epidemiologic study of urinary calculi in Western France].

OBJECTIVES: An epidemiologic study of urinary calculi (N = 1843) was conducted in Western France: distribution according to the main chemical compounds, age and sex. Comparison with the results of a study with national recruitment (N = 10,617) and a study with regional recruitment (N = 1774). METHOD: The study involved 1843 stones characterized beforehand by morphological analysis associated with infra-red spectrophotometry (FTIR). If analysis of the composition of the stones was carried out on the totality of calculi, studies related to age and sex included only 1583 cases. Comparison of percentages was made using chi 2 test. RESULTS: The composition in main compounds of calculi was comparable with the results of other studies; minor significant compounds presented great differences, raising the problem of interpretation of the infra-red spectra of the latter. Hence, our work was directed towards the analysis of the major compounds and we showed, like most authors, that monohydrate calcium oxalate is predominant in male (46%) as well as in females (37%). Calculi average sex-ratio was 2.19 but dehydrated calcium oxalate sex-ratio was 4.42, suggesting that this compound is found mainly in men. Conversely, for the majority of phosphate stones, the sex-ratio was lower or equal to one, indicating that they predominate in women. Infectious calculi (particularly struvite calculi) appeared slightly more frequent in our population than in other studies, whereas the number of uric acid calculi was lower. This, however, remains to be confirmed. CONCLUSION: The population studied was not significantly different from the national population regarding lithiasis, except perhaps for uric acid and struvite calculi, despite specific regional differences in diet and the role of nutritional factors in lithogenesis.

Adolescent↗
PubMed2000

Fatal hypermagnesemia in a child treated with megavitamin/megamineral therapy.

We report a case of fatal hypermagnesemia resulting from the unsupervised use of high doses of magnesium oxide administered as part of a regimen of megavitamin and megamineral therapy to a child with mental retardation, spastic quadriplegia, and seizures. The treatment regimen was given at the recommendation of a dietician working as a private nutritional consultant without the involvement or notification of the child's pediatrician. Hypermagnesemia is an uncommon but serious side effect of the use of magnesium containing compounds. These compounds are widely used as laxatives and dietary supplements, and serious side effects are uncommon when used in appropriate dosages and with adequate supervision. The use of alternative medical therapies, including megavitamin/megamineral therapy, is widespread. Many patients use alternative medicine or seek care from alternative medicine practitioners without the recommendation or knowledge of their primary physicians. Despite unproved benefit, many alternative therapies may be safe. However, unsupervised use of generally safe treatments can result in serious side effects. This case report serves to illustrate the characteristic pathophysiologic changes of severe hypermagnesemia, an entity rarely seen in pediatric practice, and more importantly, it alerts primary care and subspecialty pediatricians to be aware of and monitor the use of alternative medical therapies in their patients.

Complementary Therapies↗
PubMedDate not supplied

[The effects of several factors on the growth of pure and mixed cultures of Azotobacter chroococcum and Bacillus subtilis].

We studied the effect of a clay mineral, palygorskite, on the physiological activity of Azotobacter chroococcum and the phosphate-mobilizing bacterium Bacillus subtilis, as well as their mixed cultures, under various oxygen supply conditions during the utilization of phosphorus from readily and poorly soluble compounds (K2HPO4 x 3H2O) and (Ca3(PO4)2), respectively. During cultivation of the bacteria in a nutrient medium with Ca3(PO4)2, the number of microorganisms was higher than that observed in a medium with K2HPO4. An increase in oxygen mass transfer in the nutrient medium was followed by a rise in the number of Bacillus subtilis cells and an inhibition of Azotobacter chroococcum growth. An addition of palygorskite (5 g/l) into the nutrient medium stimulated the growth of both bacteria and stopped the decreasing growth of Azotobacter chroococcum at high values of oxygen mass transfer. The number of Bacillus and, particularly, Azotobacter cells was two to five times lower in a mixed culture than in a monoculture. These differences were less significant during the cultivation of mixed cultures in medium with palygorskite.

Azotobacter↗
PubMedDate not supplied

Determination of attapulgite and nifuroxazide in pharmaceutical formulations by sequential digital derivative spectrophotometry.

A new method for the sequential determination of attapulgite and nifuroxazide in pharmaceutical formulations by first- and second-derivative spectrophotometry, respectively, has been developed. In order to obtain the optimal conditions for nifuroxazide stability, studies of solvent, light, and temperature effects were performed. The results show that a previous hydrolysis of 2 h in 1.0 x 10(-1)M NaOH solution is necessary in order to obtain stable compounds for analytical purposes. Subsequently, the first- and second-derivative spectra were evaluated directly in the same samples. The sequential determination of the drugs can be performed using the zero-crossing method; the attapulgite determination was carried out using the first derivative at 278.0 nm and the nifuroxazide determination, using the second derivative at 282.0 nm. The determination ranges were 5.7 x 10(-6)-1.0 x 10(-4) and 3.7 x 10(-8) -1.2 x 10(-4)M for attapulgite and nifuroxazide, respectively. Repeatability (relative standard deviation) values of 1.2 and 3.0% were observed for attapulgite and nifuroxazide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets. Further, infrared spectroscopy and cyclic voltammetry studies were carried out in order to obtain knowledge of the decomposition products of nifuroxazide.

Anti-Infective Agents↗
PubMed2006

Kinetic study of the thermoluminescence of KMgF3:LaF3 compounds employing the general one trap model.

The parameters characterising the trap centres involved in the thermoluminescence of KMgF3:LaF3 compounds have been found by deconvolving the glow curve with the General One Trap model (GOT). For the fitting procedure the Levenberg-Marquardt method has been employed. Tm-T(stop) measurements along with initial rise measurements were performed in order to estimate the number of peaks the glow curve is made up of, and the corresponding activation energies. Instead of the Runge-Kutta method, a novel algorithm has been employed to integrate the differential equation of the GOT model, which reduces the computational time nearly 30 times with respect to the former when the glow curve is recorded with a lineal heating rate profile. The strong computational time reduction makes feasible a large number of runs with different guess values. An interesting result is that the concentration of disconnected deep traps is much less than the concentration of trap centres.

Computer Simulation↗
PubMedDate not supplied

LiF:Mg,Ti (MTT) TL detectors optimised for high-LET radiation dosimetry.

The properties of LiF:Mg,Ti (distributed as, e.g., TLD-100 or MTS-N), the most frequently used thermoluminescent detector, have been optimised for measurements of sparsely ionizing radiation (gamma rays), typically encountered in radiation protection or clinical dosimetry. However, these detectors need also to be applied in conditions of mixed-field dosimetry with a high-LET component, such as those encountered in heavy ion beams or in space. At the Institute of Nuclear Physics in Kraków a new type of LiF:Mg,Ti detector (named MTT) has been recently developed through modification of its dopant composition. This composition is intended to increase the detection efficiency after a dose of high-LET radiation. The concentration of dopants in the MTT material is: CMg=50 ppm, and CTi=120 ppm, i.e. about a three times less of magnesium and about 10 times more of titanium content, compared with the standard MTS-N. The MTT TL detectors feature an increased relative efficiency to high-LET radiation, which for 5 MeV alpha-particles is about twice that of standard LiF:Mg,Ti. The response of MTT detectors has been studied in charged particle beams of the HIMAC accelerator in Chiba, Japan and in Dubna, Russia. The main foreseen application of MTT detectors are dose measurements in space. The dose after high-LET exposure can be estimated from the difference of the response of MTS and MTT detectors. In the near future MTT detectors will be applied in the "Matroshka" experiment. Within this experiment a specially constructed human phantom will be exposed in free space (outside the International Space Station) for 1 year. The phantom will incorporate a few thousand measuring points enabling radiation doses to particular organs to be determined.

Extraterrestrial Environment↗
PubMed1996

Ab initio characterization of MgCCH, MgCCH+, and MgC2 and pathways to their formation in the interstellar medium.

A study of Mg-bearing compounds has been performed in order to determine molecular properties which are critical for planning new astronomical searches and laboratory studies. The primary focus of the work is on MgCCH, MgCCH+, and the isomers of MgC2. Only MgCCH has been identified in laboratory studies. Additional calculations have been carried out on MgH, MgNC, MgCN, and their cations in an effort to evaluate pathways to the formation of MgCCH and MgCCH+ in the interstellar medium (ISM) or in circumstellar envelopes. Correlated ab initio methods and correlation-consistent basis sets have been employed. Properties including structures, rotational constants, dipole moments, and harmonic frequencies are reported. A transition state between linear MgCC and cyclic MgC2 has been characterized and was found to yield a minimal barrier (approximately 0.5 kcal mole-1), indicating easy interconversion to the cyclic form. Direct reactions in the ISM between Mg or Mg+ and HCCH are precluded by energetic considerations, but a number of ion-molecule or neutral-neutral exchange reactions between CCH and various Mg-containing species offer plausible pathways to MgCCH or MgCCH+. Weakly bound MgH may react with CCH to form MgCCH, but MgH has not been detected. Both MgNC and MgCN have been observed, but reactions with CCH are slightly endothermic by 1-3 kcal mole-1. Although MgH+, MgNC+, and MgCN+ have not been detected, their reactions with CCH to form MgCCH+ are all exothermic. With only a small barrier separating linear MgCC and cyclic MgC2, the dissociative recombination of MgCCH+ with an electron is expected to yield cyclic MgC2 and regenerate Mg and CCH. New astronomical searches for MgCCH, MgCCH+, cyclic MgC2, MgNC+, and MgCN+ will provide further insight into organo-magnesium astrochemistry.

Astronomy↗
PubMed2005

Raman spectroscopy of synthetic and natural iowaite.

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.

Air↗
PubMed2005

Formation and stability of polychlorinated biphenyl Pickering emulsions.

An emulsion stabilized by colloidal suspensions of finely divided solids is known as a Pickering emulsion. The potential for polychlorinated biphenyls (PCBs) to form Pickering emulsions ex situ when in contact with powdered solids, such as clays and metal oxides, is investigated here. Bentonite, iron oxide and magnesium oxide dispersions proved to be robust Pickering emulsion stabilizers, whereas manganese oxide dispersions were not. Batch experiments revealed that emulsions can be formed using a moderately low energy input and can be stabilized with solid concentrations as low as 0.5 wt.%. For the base conditions (volumetric oil fraction (phi(oil))=30 vol.%; solid concentration (chi)=2 wt.%), the formed emulsions were indefinitely stable and the initial average droplet diameters varied from 80 to 258 mum, depending on the solid used in the colloidal dispersion. The average droplet size varied at early time, but for most conditions stabilized to a steady-state value 1 week after preparation. The effect of Ostwald ripening was limited. At greater than 0.5 wt.% concentration, the efficiency of the solid dispersion as a stabilizer was dependant on the volumetric oil fraction but not on the solid concentration. Generally, systems with volumetric oil fractions outside of the 20-70 vol.% range were unstable. The emulsions' droplet stability, average droplet size and size distribution were observed to vary as a function of the amount of energy provided to the system, the volumetric oil fraction, and the concentration of the solid in the aqueous dispersion. It is hypothesized that drilling through fractured rock in the immediate vicinity of dense, non-aqueous phase liquid (DNAPL) PCBs may provide both the energy and solid material necessary to form Pickering emulsions.

Bentonite↗
PubMed1988

The interaction of amines with the occluded state of the Na,K-pump.

We have studied the effect of various amines on the rate of release of 86Rb from the occluded state of dog kidney Na,K-ATPase formed by pre-incubation of the enzyme with 86Rb. In the presence of MgPi, various amines act like K+ or Rb+ in blocking the release of 86Rb from one of two sites for occlusion (the "s" site). Of 38 amines tested, tetrapropylamine and various benzyl amines exhibit the highest affinity; the K1/2 for these compounds is 2-5 mM. In the presence of ATP, when 86Rb is presumably released towards the intracellular face of the pump in the normal mode of operation, 86Rb release is blocked by the presence of amine, but only if the amine is also included in a preincubation with MgPi. The data are consistent with a model in which the interaction of amine with one of the transport sites (the "f" site) prevents the E2----E1 transformation that is stimulated by ATP. When 86Rb deocclusion from the f site has occurred in the presence of amine, the lone 86Rb at the s site can be released in the presence of ATP if the amine is removed from the medium. This suggests that a single 86Rb ion at the s site can be released to the intracellular face of the membrane, and therefore that transport can occur with only one K+ site occupied. The amine that blocks release of one 86Rb ion does not itself become occluded: (a) The interaction of amine and ATP is only seen when both ligands are present in the medium; (b) the effects of amines are not "remembered" after a brief exposure to a rinse medium; (c) with the vanadate-inhibited enzyme, benzyltriethylamine and tetrapropylamine are only weakly effective in blocking 86Rb release from the s site; and (d) organic cations exhibit very low affinity in competition with 86Rb for occlusion at equilibrium. Thus the results are consistent with the idea that monofunctional amines block by binding to the f site but that, unlike K+ and Rb+, they do not become occluded. In contrast, at equilibrium ethylenediamine prevents 86Rb occlusion in a competitive manner, suggesting the possibility of occlusion of the bifunctional amine.

Adenosine Triphosphate↗
PubMed1999

Newer drug therapy for congestive heart failure.

BACKGROUND: The management of congestive heart failure has undergone a number of modifications over the past 5 to 10 years. METHODS: These include assaying the role of inotropic drugs, evaluating the role of phosphodiesterase inhibitors, considering the role of intermittent inotropic infusion in ambulatory patients, and recognizing the importance of angiotensin-converting enzyme inhibitors. Very recently, the important role of angiotensin II receptor blocking agents and the use of beta blockade have provided additional modalities for the control of congestive heart failure. The relative usefulness of such therapy has been reviewed in this article. CONCLUSION: The management of congestive heart failure has undergone considerable change with the use of newer and more effective drugs.

Adrenergic beta-Antagonists↗
PubMed2006

Magnesium for acute traumatic brain injury.

BACKGROUND: Acute traumatic brain injury is a leading cause of death and disability in young adults. Magnesium had been considered as a potential therapeutic tool because of its activity on NMDA-receptors, calcium channels and neuron membranes. Animals studies have indicated a beneficial effect of magnesium on outcome after brain injury, but its efficacy in humans is unknown. OBJECTIVES: To quantify the effect of magnesium administration on mortality and morbidity in patients with acute traumatic brain injury. SEARCH STRATEGY: We searched the Cochrane Injuries Group's specialised register, Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, National Research Register, Current Controlled Trials, SIGLE, LILACS, Zetoc. The searches were conducted in July 2005. SELECTION CRITERIA: We included all randomized controlled trials comparing any magnesium salt with no magnesium or with placebo, in patients following acute traumatic brain injury. DATA COLLECTION AND ANALYSIS: Two authors independently screened search results and assessed the full texts of potentially relevant studies for inclusion. Data were extracted and methodological quality was examined. MAIN RESULTS: Three studies met the inclusion criteria, one of which is an ongoing study. Two studies were included in the analysis. No data on mortality were available. For Glasgow Outcome Score at six months the pooled WMD = 0.55 (95% CI -0.15 to 1.26), P = 0.12. AUTHORS' CONCLUSIONS: There is currently no evidence to support the use of magnesium salts in patients with acute traumatic brain injury.

Acute Disease↗
PubMed1988

A retrospective cohort mortality study of males mining and milling attapulgite clay.

To evaluate the possible health effects of occupational exposure to a nonasbestos mineral fiber, a cohort of 2,302 males employed for at least 1 month between 1940 and 1975 at an attapulgite (clay fiber) mining and milling facility was followed through 1975. A significant deficit of mortality (SMR = 43, 90% CI 23-76) from nonmalignant respiratory disease (NMRD) was observed for the cohort based on age-, calendar year-, and race-specific rates for U.S. males. A marked deficit of NMRD was seen regardless of presumed dust exposure level, induction-latency period, or duration employed. A statistically significant excess of mortality from lung cancer was observed among whites (SMR = 193, 90% CI 121-293), but a deficit occurred among nonwhites (SMR = 53, 90% CI 21-112). Lung cancer risk in either race was not altered substantially with presumed dust exposure level, induction-latency period, or duration employed with one exception-those employed for at least 5 years in high-exposure-level jobs.

Dust↗
PubMed2006

Safety and efficacy of bioabsorbable magnesium alloy stents in porcine coronary arteries.

OBJECTIVE: We aimed to determine the safety and efficacy of biobasorbable magnesium alloy stents in porcine coronary arteries. Bioabsorbable magnesium stents carry the potential to overcome the limitations posed by permanent metallic stents such as chronic inflammation, late stent thrombosis, prolonged antiplatelet therapy, and artifacts when imaged by multislice-computed tomography or magnetic resonance imaging. METHODS: Magnesium alloy stents or stainless steel stents were randomly deployed in coronary arteries of domestic or minipigs. Domestic pigs were sacrificed at 3 days (n = 2) or 28 days, and minipigs at 3 months. RESULTS: At 3 days, magnesium alloy stents were intact, but started to show signs of degradation by 28 days. There was no evidence of stent particle embolization, thrombosis, excess inflammation, or fibrin deposition. At 28 days and 3 months, neointimal area was significantly less in magnesium alloy stent segments (2.44 +/- 0.88 mm(2) and 1.16 +/- 0.19 mm(2)) as compared with the stainless steel stent segments (5.03 +/- 1.5 mm(2) and 1.72 +/- 0.68 mm(2), P < 0.001 and 0.02). Quantitative coronary analysis indicates that percentage area stenosis and percentage diameter stenosis in magnesium alloy stent segments improved significantly at 3 months as compared to 28 days. Despite decreased neointimal hyperplasia, lumen area of the magnesium alloy stented vessels did not improve significantly. CONCLUSION: Magnesium alloy stents are safe and are associated with less neointima formation; however, reduced neointima did not result in larger lumen.

Absorbable Implants↗
PubMed2004

Cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic and benzylic Grignard reagents and their application to tandem radical cyclization/cross-coupling reactions.

Details of cobalt-catalyzed cross-coupling reactions of alkyl halides with allylic Grignard reagents are disclosed. A combination of cobalt(II) chloride and 1,2-bis(diphenylphosphino)ethane (DPPE) or 1,3-bis(diphenylphosphino)propane (DPPP) is suitable as a precatalyst and allows secondary and tertiary alkyl halides--as well as primary ones--to be employed as coupling partners for allyl Grignard reagents. The reaction offers a facile synthesis of quaternary carbon centers, which has practically never been possible with palladium, nickel, and copper catalysts. Benzyl, methallyl, and crotyl Grignard reagents can all couple with alkyl halides. The benzylation definitely requires DPPE or DPPP as a ligand. The reaction mechanism should include the generation of an alkyl radical from the parent alkyl halide. The mechanism can be interpreted in terms of a tandem radical cyclization/cross-coupling reaction. In addition, serendipitous tandem radical cyclization/cyclopropanation/carbonyl allylation of 5-alkoxy-6-halo-4-oxa-1-hexene derivatives is also described. The intermediacy of a carbon-centered radical results in the loss of the original stereochemistry of the parent alkyl halides, creating the potential for asymmetric cross-coupling of racemic alkyl halides.

Alkylation↗