Iodine solubility and speciation in glasses.

The study of iodine in glasses and melts is critical in many areas, from geosciences to materials science to waste management. Glasses in the ternary system Na2O-B2O3-SiO2 were studied with the goal of identifying a glass matrix able to dissolve large quantities of this element, and to identify the main parameters affecting the solubility of iodine. Two sets of experiments were carried out: the first one with the aim of determining the solubility limit of iodine, and the second one to identify the structural variations occurring within the glass network upon iodine incorporation, and to identify the parameters influencing the most both iodine solubility and speciation. We demonstrated that there is a strong dependence of iodine incorporation on bulk chemistry and glass physical properties. A solubility limit of ~5 mol% I has been assessed for B2O3-rich glasses and of ~1 mol% for SiO2-rich ones, and this composition dependence has been explained by considering the fragility parameter of the glass network. Structural variations in the iodine local environment and in the glass network were characterized by Raman, X-ray Absorption Spectroscopy, and 11B NMR. Spectroscopy data point out the coexistence of different I species within the glasses, with iodide being the predominant one, surrounded by Na+ ions.

Phosphorus solubility in basaltic glass: Limitations for phosphorus immobilization in glass and glass-ceramics.

The composition of sewage sludge from urban wastewater treatment plants is simulated using P-doped basalts. Electron microscopy analyses show that the solubility of P in the basaltic melt is limited by the formation of a liquid-liquid immiscibility in the form of an aluminosilicate phase and a Ca-Mg-Fe-rich phosphate phase. The rheological behavior of these compositions is influenced by both phase separation and nanocrystallization. Upon a thermal treatment, the glasses will crystallize into a mixture of inosilicates and spinel-like phases at low P contents and into Ca-Mg-Fe phosphate at high P contents. Hardness measurements yield values between 5.41 and 7.66 GPa, inside the range of commercial glasses and glass-ceramics. Leaching affects mainly unstable Mg2+-PO43- complexes.

A compositional tipping point governing the mobilization and eruption style of rhyolitic magma.

The most viscous volcanic melts and the largest explosive eruptions on our planet consist of calcalkaline rhyolites. These eruptions have the potential to influence global climate. The eruptive products are commonly very crystal-poor and highly degassed, yet the magma is mostly stored as crystal mushes containing small amounts of interstitial melt with elevated water content. It is unclear how magma mushes are mobilized to create large batches of eruptible crystal-free magma. Further, rhyolitic eruptions can switch repeatedly between effusive and explosive eruption styles and this transition is difficult to attribute to the rheological effects of water content or crystallinity. Here we measure the viscosity of a series of melts spanning the compositional range of the Yellowstone volcanic system and find that in a narrow compositional zone, melt viscosity increases by up to two orders of magnitude. These viscosity variations are not predicted by current viscosity models and result from melt structure reorganization, as confirmed by Raman spectroscopy. We identify a critical compositional tipping point, independently documented in the global geochemical record of rhyolites, at which rhyolitic melts fluidize or stiffen and that clearly separates effusive from explosive deposits worldwide. This correlation between melt structure, viscosity and eruptive behaviour holds despite the variable water content and other parameters, such as temperature, that are inherent in natural eruptions. Thermodynamic modelling demonstrates how the observed subtle compositional changes that result in fluidization or stiffening of the melt can be induced by crystal growth from the melt or variation in oxygen fugacity. However, the rheological effects of water and crystal content alone cannot explain the correlation between composition and eruptive style. We conclude that the composition of calcalkaline rhyolites is decisive in determining the mobilization and eruption dynamics of Earth's largest volcanic systems, resulting in a better understanding of how the melt structure controls volcanic processes.

Raman response of network modifier cations in alumino-silicate glasses.

Raman scattering is performed in three sets of aluminosilicate glasses with light cations and concentrations varying from peralcaline to peraluminate domain. The depolarized spectra highlight two cation modes below ∼400 cm(-1). Comparison with infrared data reveals very stringent selection rules providing as much additional information for a vibrational analysis. The latter suggests in-phase (network-coupled) and out-of-phase (network-decoupled) displacements of the cations relative to their adjacent negatively charged structures. The low frequency vibration involves all cations whatever their role in the glass, network modifiers or charge compensators. Very interestingly, the second mode originates mostly from cations at modifier's places, providing thereby a new support for structural and chemical analysis of silicate glasses using Raman scattering.

Influence of short-chain fatty acids on iron absorption by proximal colon.

BACKGROUND: Short-chain fatty acids produced by bacterial fermentation in the colon enhance the local absorption of cations, such as calcium, that could be used to improve the bioavailability of iron if a significant colonic absorption of iron were to occur. METHODS: Iron (iron gluconate, 100 microM) absorption by the caecum of the rat was compared with that in proximal sites of the small bowel using the Ussing chamber model; the influence of probiotic bacteria (Propionibacterium freudenreichii) on iron absorption was assessed and compared with that of two of their fermentation products (acetic and propionic acids) using the Ussing chamber and the ligated colon with gamma emitting iron as experimental models. RESULTS: The caecum absorbed less iron than the duodenum, but significantly more than the jejunum and ileum. This occurred mainly through an enhanced mucosal transfer of iron uptake. Propionibacteria enhanced iron absorption from the proximal colon; the same effect was observed in the presence of viable bacteria, or the culture medium free of viable bacteria, or acetate and propionate or propionate alone. CONCLUSIONS: The proximal colon could be a significant site available for iron absorption; this absorption can be enhanced by local production of short-chain fatty acids such as propionate.

Inhibition of zinc absorption by iron depends on their ratio.

Previous studies upon zinc-iron interactions gave conflicting results that could come from differences in protocol design or in trace element status of subjects. The present work assessed the influence of zinc : iron ratio and iron deficiency upon zinc absorption. The digestive absorption of zinc sulphate (100 micromol Zn/l) in presence of iron gluconate was studied in perfused jejunal loops (n = 6/group) of normal rats (range 0-1000 micromol Fe/l) and iron deficient rats (200-750 micromol Fe/l). In normal rats no significant iron inhibition on zinc absorption occurred at Fe:Zn ratio below 2:1. At higher ratios zinc uptake and net absorption decreased significantly (p<0.05). Between 2:1 and 5:1 a dose dependent inhibition of zinc absorption occurred and reached a plateau beyond this ratio. In iron deficient animals no changes in zinc uptake, mucosal retention and absorption compared to normal animals occurred at ratio 2:1. At higher ratios differences were observed at every zinc absorption step except for mucosal retention at 7.5:1 ratio. Iron-zinc interactions depend on their ratio and on previous trace elements status of subjects. Due to the wide and unknown variations that were likely to occur between the subjects of previous human and experimental studies, these results could explain some of the discrepancies between their results.

Aluminium increases xanthine oxidase activity and disturbs antioxidant status in the rat.

The mechanisms responsible for the neurotoxic effects of Al remain poorly understood. In order to determine whether Al promotes oxidative stress in vivo, we measured the enzymatic activity of xanthine oxidase (XO), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione-S-transferase (GST) and glutathione reductase (GR) in four groups of rats after eight days of intraperitoneal administration of variable concentrations of Al (0, 5, 10, and 15 mg/kg body weight, respectively). XO activity was measured in both plasma and liver samples, and the activities of the remaining enzymes were further determined in the brain and red blood cells (RBC). The most significant changes were observed in XO and GPX activities, that were enhanced and depressed, respectively. In both instances, the enzyme activities were correlated with Al concentrations, either positively (XO) or negatively (GPX). Enhancement of XO and inhibition of GPX activity may lead to the accumulation of intermediate toxic compounds such as hydrogen peroxide and hydroxyl radicals, since SOD activity is increased as well. The latter finding must be taken with some caution because previous studies have shown contradictory results in this field. Our data suggest that Al toxicity could be mediated by its action on both pro- and anti-oxidant enzymes. The biological significance of these findings remains to be established.

The effect of cysteine and 2,4-dinitrophenol on heme and nonheme absorption in a rat intestinal model.

Previous studies have showed that purified heme iron forms insoluble polymers that are poorly absorbed. The presence of peptides and of amino acids maintaining heme iron in a soluble form could improve its bioavailability. The digestive uptake and transfer of a concentrated hydrolysate of heme peptides (HPH) and of iron gluconate (Gluc) at 100 µM were compared in vitro in a Ussing chamber. The effects of an enhancing amino acid (L-cysteine) on the uptake and transfer of both forms were assessed. An inhibitor of the oxidative phosphorylation (2,4-dinitrophenol; DNP) was used to differentiate the active and passive mechanisms of the absorption. The mucosal uptake (%Tot) and enterocyte transfer (%S) of the two sources of iron did not differ. DNP significantly reduced %Tot and %S of both forms. Cysteine significantly enhanced %Tot and %S of HPH and Gluc, partly corrected the inhibition exerted by DNP on %Tot of HPH and %S of both forms, and fully restored %Tot of Gluc. In presence of peptides produced by globin hydrolysis, the absorption of hemoglobin iron was efficient; it was mostly energy dependent and, therefore, should have occurred by a regulated transcellular pathway. Cysteine enhanced the passive uptake of iron and the passive processes involved in the enterocyte transfer of the common pool made of both sources (heme and nonheme) of iron. These results showed that heme iron can be purified and concentrated without impairing its digestive absorption, provided it remains in presence of peptides or amino acids.

Long-term effects of iron:zinc interactions on growth in rats.

The influence of iron (Fe) on the bioavailability and functional status of zinc (Zn) was studied in young rats using metabolic balances and tissue dosages, which were compared to growth. Diets supplied adequate intakes of Fe (45 and 300 mg/kg diet) and Zn (14 and 45 mg/kg) for 2 mo. Two metabolic balance determinations were performed that were correlated for Zn and Fe during the first and the last weeks of the study. A significant effect of Fe supply, but not of Zn was displayed on Fe absorption; both Fe and Zn diet concentrations had a significant influence on Zn absorption. Fe and Zn organ contents were significantly correlated with the amount absorbed during the two metabolic balances. There was a positive correlation between liver and muscle Fe and Fe absorption, and Fe absorption and muscle Zn, as well as a negative one with liver Zn; a positive correlation was displayed between Zn absorption and Zn organ content. No correlation was found between Zn absorption and Fe tissue content. Growth was correlated with Zn, but not with Fe absorption during both balances. A positive correlation was displayed between growth and Zn liver content, and a negative one with Fe liver content. Care must be taken to give growing subjects balanced diets or supplementation, since the negative interactions between these trace elements are likely to persist as long as the diet is given.

Mechanisms of absorption of caseinophosphopeptide bound iron.

Binding iron (Fe) to the 1-25 caseinophosphopeptide obtained from enzyme hydrolysis of beta casein (beta CPP) improves Fe bioavailability in the rat. To assess the mechanisms involved in its absorption, a perfused, vascularized duodenal rat loop model was used in controls and in Fe-deficient (bleeding of 25% blood volume) rats. Inhibitors of oxidative phosphorylation [2-4 dinitrophenol (DNP)] and/or of endocytosis [phenylarsine oxide (PAO)] were added to the perfusion solution containing 50 microM Fe as beta CPP bound Fe (Fe-beta CPP) or gluconate (Fe Gluc). Fe-beta CPP enhanced Fe uptake, reduced mucosal storage, and improved net absorption both in controls and in deficient animals. DNP reduced uptake, mucosal storage, and net absorption by the same percentage in Fe-beta CPP and Fe Gluc perfused rats in both control and Fe-deficient animals. PAO decreased uptake, mucosal storage, and net absorption of Fe-beta CPP but not of Fe Gluc. At the end of the experiment Fe serum levels were increased only in Fe Gluc animals. These results confirm the improved bioavailability of beta CPP bound Fe. They suggest that at least part of its absorption can occur by a different pathway than usual Fe salts. Fe-beta CPP can be taken up by endocytosis and absorbed bound to amino acids or peptides.

Effect of stabilising amino acids on the digestive absorption of heme and non-heme iron.

We used the Ussing chamber model to study heme iron absorption by rat duodenal mucosa. Heme iron was obtained by enzymic digestion of bovine haemoglobin and concentration of heme (HPH). Its uptake and mucosal transfer was compared to iron gluconate (Gluc), at 100 microM and 1 mM. At 100 microM iron uptake (Qtot), mucosal retention (Qm) and transfer across the mucosa (Qs) was similar for the two sources of iron. Qs was significantly higher at 1 mM for Gluc but not for HPH, and was associated with higher levels of Qm. Addition of L-histidine did not improve iron absorption and indeed it decreased it if iron was provided as Gluc. L-cysteine increased the transfer of iron of both sources. In the in vitro model using rat digestive mucosa, heme iron appeared to be an efficiently used source of iron, which might prevent its accumulation by gut when supplied in excess.

Effect of small variations of aluminum intake on calcium metabolism in young rats.

BACKGROUND: While in the adult Al intoxication requires high dosages, little is known on the threshold level of Al toxicity in the young. METHODS: Weaning rats were fed for 90 days ore of four diets differing by their content in Ca (7.5 vs < 0.5 g/< g diet)(Ca+/-) and Al (10.6 vs 8.4 mg/kg)(Al+/-); Al supplementation was 30% above the standard level of diet. Ca and Al levels were measured in liver, bone (femur), and brain. RESULTS: Ca- had a significant negative effect on growth which was further reduced by Al+; in Ca sufficient/Al+ animals, Al concentrations were significantly increased in bone and brain and tended to increase in liver; Ca decreases observed in these three organs were only significant in brain. Ca deficiency further enhanced the Al deposit in bone at both levels of Al intakes, and reduced Ca concentrations in these three organs in Al+ animals; in Ca-/Al- animals, the decrease in Ca displayed in the three tissues reached a significant level in brain. CONCLUSIONS: This study suggests that in the growing subject the side effects of small variations of Al intake can be enhanced when they are combined with other mineral imbalances.

Chromium and parenteral nutrition in children.

Chromium (Cr) dosage was assayed in i.v. nutrition, serum, and losses of five children on total parenteral nutrition for > or = 4 weeks. The Cr supply (4.7 +/- 1.2 micrograms/kg/day) was above recommended levels (0.5 microgram/kg/day). Serum (18.2 +/- 1.8 micrograms/L) and urine (37.4 +/- 10.5 micrograms/L) were also higher than control values (0.7-0.9 microgram/L and 0.2-0.8 microgram/L, respectively). Serum and urine Cr concentrations displayed a positive correlation. Serum Cr and Fe showed a negative correlation. These results confirm the potential toxicity of Cr previously reported in animals. Cr levels of i.v. nutrition solutes should be checked thoroughly.

A cross-sectional study of plasma and urinary aluminum levels in term and preterm infants.

High aluminum levels have been reported in sick and intravenously fed premature infants; however, aluminum is a ubiquitous pollutant of food. This study compares the usual aluminum levels of healthy newborns from birth to the third month of life with those of enterally fed premature infants free of renal failure. Plasma and urine concentrations were determined 66 times in full-term newborns (n = 58), 56 times in a group of preterm infants whose gestational age at birth was 28 to 32 weeks (n = 36) and 54 times in another group of preterm infants whose gestational age at birth was 33 to 36 weeks (n = 50). Daily aluminum intakes (+/- SE) of the full-term infants and the two groups of preterm infants were 0.42 +/- 0.05, 0.64 +/- 0.03, and 0.52 +/- 0.03 mumol/kg per day, respectively (p = .05). Plasma aluminum levels were 0.29 +/- 0.05, 0.49 +/- 0.06, and 0.39 +/- 0.05 mumol/L (p = .007); urine excretion levels were 0.80 +/- 0.12, 0.77 +/- 0.21, and 0.78 +/- 0.2 mumol of aluminum/mmol of creatinine (p value not significant). Although the metabolic consequences of the high aluminum intakes and blood levels we have observed in very low birth weight infants remain to be assessed, these results suggest that more attention should be paid to the aluminum status and intake of healthy premature babies.

Chromium status of full-term and preterm newborns.

In order to obtain reference values from normal babies, Cr status of full-term newborns has been studied. Plasma and urine values were (mean +/- SEM) 0.7 +/- 0.1 micrograms/L and 0.9 +/- 0.3 micrograms/L, respectively, for the first month of life (n = 19), and 0.6 +/- 0.1 micrograms/L and 0.8 +/- 0.2 micrograms/L for the second-to-third-month period (n = 31). Premature newborns (gestational age 28-36 wk) were compared to these control values; concentrations were 0.9 +/- 0.1 micrograms/L and 1.1 +/- 0.2 micrograms/L for the first month (n = 47), and 1.0 +/- 0.2 micrograms/L and 1.5 +/- 0.3 micrograms/L for the second to third months (n = 27). For the whole group, there was a positive correlation between plasma and urine concentrations (p = 0.0001); multiple regression analysis was performed between plasma levels and gestational age at birth (p = -0.002) and postnatal age (NS). Plasma levels of prematures and full terms were statistically different (p = 0.03) only for the second- to third-month period. It is suggested that these high Cr levels result from high dietary intakes and/or high absorption rates.

Plasma chromium concentrations in normal infants and cystic fibrosis patients.

Plasma Cr concentrations have been studied in normal children aged 0-14 yr. Levels ranged from 0.65 to 0.88 microgram/l and did not change with age. Plasma concentrations of CF patients given 0.5-0.75 microgram Cr/kg/d in addition to their diet were similar to normal values. There was no correlation between these plasma values and growth retardation.

[Changes in the amount of fatty acids produced by Melosira dastei culture on synthetic medium]. / Variations de la quantité des acides gras élaborés par le Melosira dastei au cours de la culture sur un milieu synthétique.

Some of fatty acids contents of the marine Diatom, Melosira dastei, were characterized. The major constituents of them are palmitic, palmitoleic and eicosapentaenoic acids. Linolenic acid type appeared to be a minor constituent. When that Diatom is cultured on an artificial medium, it might be considered as a potential source of valuable eicosapentaenoic acid. Even when the cells concentration is low, in batch cultures, eicosapentaenoic acid constitutes up to 5% of the dry weight and reaches about 20% of the triglycerids content. This level might be improved.

[Preventive action on stable exercise-induced angina of a topical nitroglycerin gel and of an oral slow-release nitroglycerin compound (Lénitral) in low and high dosage (author's transl)]. / Action préventive dans l'angor d'effort stable, d'un gel de trinitrine à absorption cutanée et de doses faibles et fortes de trinitrine à libération intestinale progressive (Lénitral).

A nitroglycerin gel applied to the skin in doses of 15 to 30 mg prevents or delays the anginal pain induced by an excise tolerance test. The effects of the drug after a single application lasted 3 hours irrespective of the dose. Improvement in terms of increased heart rate, decreased S-T segment displacement and increased exercise capacity was the same as that observed after 0,75 mg sublingual nitroglycerin. A single 2.5 mg dose of an oral compound slowly released from the intestine (Lénitral) had no measurable effect during a 3-hour observation period. In contrast, a single 7.5 mg dose of the same compound produced, after 3 hours, the same overall improvement as that obtained with 0.75 mg sublingual nitroglycerin.

[First attempts to synchronize cell division in the diatom Navicula ostrearia (Gaillon) Bory in axenic culture]. / Premiers essais de synchronisation des divisions cellulaires chez la diatomée Navicula ostrearia (Gaillon) Bory en culture axénique

The diatom Navicula ostrearia, grown under small quantities, was synchronized in diurnally intermittent illuminations of 16 hour light and 8 hour dark. Under these experimental conditions, the doubling of the population only occurs during the dark period and the fission time is about 6 hours.