Differential scanning calorimetry lipid mixtures

Differential scanning calorimetry was used for evaluating the interaction between model mixtures of stratum corneum lipids and gel-state PC. The mixing of the systems was complete in about 24 h.21 The slow interaction of gel-state PC may also apply to its topical application in vivo. 

Mabrey S, Sturtevant JM. Investigation of the phase transitions of lipids and lipid mixtures by high sensitivity differential scanning calorimetry. Proc. Natl. Acad. Sci. U.S.A. 1976 73 3862-3866. 

The first set of experiments involved fluorescence resonance energy transfer (FRET) between the naphthalene and pyrene-laheled polymers. A 5 1 mixture of PNIPAM-Py to PNIPAM-Na was used. When assembled in micelles, the pyrene acts as a quencher to the naphthalene, leading to high pyrene fluorescence and low naphthalene fluorescence. When the mixture is added to DMPC (liquid phase) or DSPC (gel phase) vesicles at room temperature, naphthalene fluorescence is increased, while pyrene fluorescence is dramatically decreased. This effect is not seen with the PNIPAM-Py-Na polymer, so the reduction in FRET is not due to the hydrophobic environment. This means that the hydrophobic anchors of the PNIPAM-Py and the PNIPAM-Na likely enter the membrane and the dyes are moved apart from one another. The fact that the anchor appeared to insert into the gel-phase DSPC membrane was somewhat surprising. The authors attribute the effect to defects between crystalline domains in the membrane. To test if the LCST transition still occurs when the polymers are anchored to the membrane, differential scanning calorimetry (DFC) was used. The LCST transition of the PNIPAM-Py/PNIPAM-Na mixture in solution was observed in the DFC ttace. When combined with DSPC or DMPC vesicles, the same peak was observed, indicating that the transition does indeed stiU occur, even in the presence of the lipid. 

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