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Issue 14, 2015
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Structural insights into the cubic–hexagonal phase transition kinetics of monoolein modulated by sucrose solutions

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Abstract

Using DSC (differential scanning calorimetry), we measure the kinetics of the cubic–HII phase transition of monoolein in bulk sucrose solutions. We find that the transition temperature is dramatically lowered, with each 1 mol kg−1 of sucrose concentration dropping the transition by 20 °C. The kinetics of this transition also slow greatly with increasing sucrose concentration. For low sucrose concentrations, the kinetics are asymmetric, with the cooling (HII–cubic) transition taking twice as long as the heating (cubic–HII) transition. This asymmetry in transition times is reduced for higher sucrose concentrations. The cooling transition exhibits Avrami exponents in the range of 2 to 2.5 and the heating transition shows Avrami exponents ranging from 1 to 3. A classical Avrami interpretation would be that these processes occur via a one or two dimensional pathway with variable nucleation rates. A non-classical perspective would suggest that these exponents reflect the time dependence of pore formation (cooling) and destruction (heating). New density measurements of monoolein show that the currently accepted value is about 5% too low; this has substantial implications for electron density modeling. Structural calculations indicate that the head group area and lipid length in the cubic–HII transition shrink by about 12% and 4% respectively; this reduction is practically the same as that seen in a lipid with a very different molecular structure (rac-di-12:0 β-GlcDAG) that makes the same transition. Thermodynamic considerations suggest there is a hydration shell about one water molecule thick in front of the lipid head groups in both the cubic and HII phases.

Graphical abstract: Structural insights into the cubic–hexagonal phase transition kinetics of monoolein modulated by sucrose solutions

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Publication details

The article was received on 12 Jan 2015, accepted on 03 Mar 2015 and first published on 05 Mar 2015


Article type: Paper
DOI: 10.1039/C5CP00175G
Author version available: Download Author version (PDF)
Citation: Phys. Chem. Chem. Phys., 2015,17, 9194-9204
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    Structural insights into the cubic–hexagonal phase transition kinetics of monoolein modulated by sucrose solutions

    C. W. Reese, Z. I. Strango, Z. R. Dell, S. Tristram-Nagle and P. E. Harper, Phys. Chem. Chem. Phys., 2015, 17, 9194
    DOI: 10.1039/C5CP00175G

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