Browsing by Subject "Solubility"

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    Increase on the initial soluble heme levels in acidic conditions is an important mechanism for spontaneous heme crystallization in vitro
    (Public Library of Science, 2010) Stiebler, Renata; Hoang, Anh N; Egan, Timothy J; Wright, David W; Oliveira, Marcus F
    BACKGROUND: Hemozoin (Hz) is a heme crystal that represents a vital pathway for heme disposal in several blood-feeding organisms. Recent evidence demonstrated that β-hematin (βH) (the synthetic counterpart of Hz) formation occurs under physiological conditions near synthetic or biological hydrophilic-hydrophobic interfaces. This seems to require a heme dimer acting as a precursor of Hz crystals that would be formed spontaneously in the absence of the competing water molecules bound to the heme iron. Here, we aimed to investigate the role of medium polarity on spontaneous βH formation in vitro . METHODOLOGY/PRINCIPAL FINDINGS: We assessed the effect of water content on spontaneous βH formation by using the aprotic solvent dimethylsulfoxide (DMSO) and a series of polyethyleneglycols (PEGs). We observed that both DMSO and PEGs (3.350, 6.000, 8.000, and 22.000) increased the levels of soluble heme under acidic conditions. These compounds were able to stimulate the production of βH crystals in the absence of any biological sample. Interestingly, the effects of DMSO and PEGs on βH formation were positively correlated with their capacity to promote previous heme solubilization in acidic conditions. Curiously, a short chain polyethyleneglycol (PEG 300) caused a significant reduction in both soluble heme levels and βH formation. Finally, both heme solubilization and βH formation strongly correlated with reduced medium water activity provided by increased DMSO concentrations. CONCLUSIONS: The data presented here support the notion that reduction of the water activity is an important mechanism to support spontaneous heme crystallization, which depends on the previous increase of soluble heme levels.
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    Solubilisation properties of phosphatidylcholine
    (1966) Taylor, Patria Maria; Leisegana E C; Linder P W
    The solubilisation of glucose and related sugars by thoroughly-purified phosphatidylcholine (lecithin) in benzene solution has been studied. The extent of solubilisation of the sugar has been found to depend on the concentration of lecithin, the structure of the sugar and the presence of cholesterol as a co-solute. The limiting solubility of glucose was achieved at low lecithin concentrations and corresponds to a 1:1 molar ratio of glucose to lecithin. Osmometric evidence indicated that, at higher concentrations, glucose was carried within the lecithin micelle. For other suiars, solubilisation was found to depend on the size of the sugar molecule relative to that of the lecithin micelle and on the number and acidity of its free hydroxyl groups. Enthalpy and entropy of solubilisation were determined for glucose and the results are consistent with an interaction mechanism involving hydrogen bonding via the free hydroxyl groups. Cholesterol, when present as a co-solute, competed for available hydrogen bonding sites on the lecithin molecule and thus decreased the amount of glucose solubilised, but in benzene solutions lecithin exhibited a 5:1 preference for glucose hydroxyl over cholesterol hydroxyl. In aqueous-ethanolic solutions inversion of the lecithin micelle occured and accordingly cholesterol could be solubilised. As the dielectric constant of the medium was decreased by the addition of ethanol, the micellar weight decreased and the uptake of cholesterol increased. In 90% ethanol the limiting solubility of cholesterol corresponded to a 1:1 cholesterol/lecithin ratio. In 70% ethanol the uptake of cholesterol corresponded to a 1:9 cholesterol/lecithin ratio, and this ratio was independent of lecithin concentration below 7.0 mg/ml. In media of higher dielectric constant lecithin formed an opalescent sol rather than a solution and the uptake of cholesterol decreased further, but the cholesterol/lecithin molar ratio continued to be independent of the lecithin concentration of the sol. In none of the aqueous solutions was glucose found to have any effect on the uptake of cholesterol. It is possible that these results may have biological significance.