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Xenon solubility and formation of supercritical xenon precipitates in glasses under non-equilibrium conditions.

ABSTRACT: Estimates of noble gas solubility in glasses and minerals are important to understand the origin of these gases, particularly xenon, in the atmosphere. However, technical difficulties and ambiguities in quantifying the dissolved gases introduce large uncertainties in the solubility estimates. We present here the use of transmission electron microscopy (TEM) with in-situ noble gas ion implantation as a non-equilibrium approach for noble gas solubility estimates. Using a suitable Xe equation of state and Monte-Carlo simulations of TEM images, a clear distinction between Xe filled precipitates and empty voids is made. Furthermore, implantation-induced changes in the solubility are estimated using molecular dynamics simulations. These studies allow us to evaluate the xenon solubility of irradiated and pristine silica glasses and monitor in-situ the diffusion-mediated dynamics between the precipitates and voids - otherwise impossible to capture. On exceeding the solubility limit, supercritical xenon precipitates, stable at least up to 1155 K, are formed. The results highlight the high capacity of silicates to store xenon and, predict higher solubility of radiogenic xenon due to the accompanying radiation damage.

SUBMITTER: Mir AH

PROVIDER: S-EPMC6192981 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Oral administration of a solid dosage form requires drug dissolution in the gastrointestinal tract before absorption. Solubility is a key factor controlling dissolution, and it is recognized that, within the intestinal tract, this is influenced by the luminal fluid pH, amphiphile content, and composition. Various simulated intestinal fluid recipes have been introduced to mimic this behavior and studied using a range of different experimental techniques. In this article, we have measured equilibrium solubility utilizing a novel four component mixture design (4CMD) with biorelevant amphiphiles (bile salt, phospholipid, oleate, and monoglyceride) within a matrix of three pH values (5, 6, and 7) and total amphiphile concentrations (11.7, 30.6, and 77.5 mM) to provide a topographical and statistical overview. Three poorly soluble drugs representing acidic (indomethacin), basic (carvedilol), and neutral (fenofibrate) categories have been studied. The macroscopic solubility behavior agrees with literature and exhibits an overall increasing solubility from low pH and total amphiphile concentration to high pH and total amphiphile concentration. Within the matrix, all three drugs display different topographies, which can be related to the statistical effect levels of the individual amphiphiles or amphiphile interactions on solubility. The study also identifies previously unreported three and four way factor interactions notably between bile salt, phospholipid, pH, and total amphiphile concentration. In addition, the results also reveal that solubility variability is linked to the number of amphiphiles and the respective ratios in the measurement fluid, with the minimum variation present in systems containing all four amphiphiles. The individual 4CMD experiments within the matrix can be linked to provide a possible intestinal solubility window for each drug that could be applied in PBPK modeling systems. Overall the approach provides a novel overview of intestinal solubility topography along with greater detail on the impact of the various factors studied; however, each matrix requires 351 individual solubility measurements. Further studies will be required to refine the experimental protocol in order the maximize information garnered while minimizing the number of measurements required.

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Xenon solubility and formation of supercritical xenon precipitates in glasses under non-equilibrium conditions.

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