Temperature-Dependent Partitioning of C152 in Binary Phosphatidylcholine Membranes and Mixed Phosphatidylcholine/Phosphatidylethanolamine Membranes

Abstract

Time-resolved fluorescence and differential scanning calorimetry were used to determine the partitioning of coumarin 152 (C152) into large unilamellar vesicles composed of binary mixtures of two phosphatidylcholines (12:0/12:0 DLPC and 14:0/14:0 DMPC) and vesicles composed of binary mixtures of a phosphatidylcholine and a phosphatidylethanolamine (14:0/14:0 DMPC and 14:0/14:0 DMPE). Differential scanning calorimetry showed that both DLPC/DMPC and DMPC/DMPE are miscible in lipid vesicles. Time-resolved fluorescence indicated that C152 partitioning into DLPC/DMPC mixtures showed nearly ideal behavior that was described with weighted contributions from C152 partitioning into pure DLPC and pure DMPC vesicles. In contrast, C152 partitioning into DMPC/DMPE mixtures was distinctly nonideal. For DMPC/DMPE lipid vesicles having DMPC mole fractions between 10 and 80%, C152 partitioning into the bilayer was measurably enhanced near the melting temperature, relative to expectations based simply on weighted contributions from C152 partitioning into vesicles comprised of pure lipids. The origin of this behavior remains uncertain. For vesicles comprised of pure DMPE, C152 shows almost no partitioning into the membrane, with ≥80% of the solute remaining in the buffer solution at temperatures between 10 and 50 °C.

Coumarin Partitioning in Model Biological Membranes: Limitations of log P as a Predictor

“…Moreover, our results also identify where in the membrane solutes accumulate. This work extends the scope of previous studies that quantified the partitioning a 7-aminocoumarin, Coumarin 152 (or C152, 7-dimethylamino-4-(trifluoromethyl)­chromen-2-one) into lipid vesicle bilayers. − Specifically, the results presented below illustrate how small changes in solute structure can induce large changes in solute partitioning into biological membranes. Furthermore, the small differences in molecular architecture can create a large difference in the partitioning behavior which is not captured using a log P model.…”

Organic Enrichment at Aqueous Interfaces: Cooperative Adsorption of Glucuronic Acid to DPPC Monolayers Studied with Vibrational Sum Frequency Generation

“…Vesicle solutions were made using standard protocols. 45 Briefly, a ∼1 mg/mL solution of DPPC in chloroform was prepared in a round-bottom flask. The chloroform was removed with a rotary evaporator with a bath temperature that was ∼10 °C greater than T m of DPPC.…”

Quantifying Solute Partitioning in Phosphatidylcholine Membranes

“…5 Missing from this study, however, was any sort of description about where these solutes partitioned within a lipid membrane itself. Several other techniques have also been used to detect solute−membrane interactions, including immobilized lipid chromatography (ILC), 18 second harmonic generation (SHG), 11 Fourier transform infrared spectroscopy (FTIR), 19 NMR, 20 fluorescence emission, 21,22 and differential scanning calorimetry (DSC). 23 Partitioning of 12 anthracyclines, anticancer drugs, was studied through relating general fluorescence intensity to partitioning depth in the membrane.…”

“…Additional details of this analysis can be found in previous reports and in the Supporting Information. 22,26 Results presented below quantitatively measure C152 and C461 partitioning into phosphocholine membranes above and below each membrane's gel−liquid crystalline transition temperature. Furthermore, characteristic photophysical behaviors are used to clarify where solutes partition within a model membrane at different temperatures.…”

“…Fluorescence traces are fit to a multiexponential model, with three distinct lifetimes representing the solute in bulk buffer, near the polar lipid headgroups, and in the nonpolar lipid bilayer core. Additional details of this analysis can be found in previous reports and in the Supporting Information. , …”