PubMed · 508329
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P I Lelkes. 1979-09-27. Potential dependent riigidity changes in lipid membrane vesicles.. https://doi.org/10.1016/0006-291x(79)91285-3
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A lipophilic dye consisting of a (1E,3E,5E)-1,6-diphenyl-1,3,5-hexatriene (DPH) fluorophore attached to a phosphate diester was prepared, and its fluorescence behavior in different solvent systems and in a liposomal membrane bilayer was examined. The key step in the synthesis of the functionalized end of the dye is a Sonogashira coupling of protected iodophenol with propargyl alcohol; the remaining phenyl ring and double bonds of the all-trans polyene core arise from a Wittig reaction with trans-cinnamaldehyde. Like DPH itself, the emission intensity of its phosphorylated derivative is quenched in polar media.
The fluorescence polarization technique was used to measure the microviscosity of a series of phospholipid-based emulsions. Fourteen different oil-in-water emulsions containing 20% medium chain length triglycerides, various concentrations and types of phospholipids, and 2.2% glycerin were prepared by microfluidization and pH-adjusted to 4.0 or 7.4. Microviscosity was measured by determining the anisotropy of a fluorophore probe (1,6-phenyl 1,3,5-hexatriene) which was found to obey Perrin's equation as has been previously reported for liposomes and membrane bilayers. Moreover the method was validated by comparing viscosities of phospholipid-oil mixtures measured by rheometry and fluorescence polarization. The viscosities determined by fluorescence polarization were within 6% of the values obtained by classic rheometry. Emulsions were also subjected to thermal stress at 121 degrees C. The droplet growth rate was estimated by measuring the time-dependent mean droplet diameter using photon correlation spectroscopy. The logarithm of the droplet growth rate was found to be directly proportional to the interfacial rigidity (i.e., the inverse microviscosity) which suggested that coalescence rather than molecular diffusion is the primary mechanism of droplet growth under these conditions of thermal stress.
The potential contamination of binary bags by traces of fat emulsion stemmed from ternary bags prepared just before, led us to determine traces of lipids into the line set of the automated compounder MM23. Diphenylhexatriene (DPH) was chosen as fluorescence probe due to its strong fluorescence enhancement in a lipid environment. Optimization of experimental conditions (i.e. DPH amounts, pH of fat emulsion samples, ultrasounds use, light, temperature and contact duration) for fluorescence measurement and validation of analytical method were performed. This method was linear over 0.5-8.0 mg l(-1) (r=0.999) of fat emulsion. The intra-day and inter-day precisions were inferior to 2% for the 2.0 and 8.0 mg l(-1) standards. Under optimized conditions, the detection limit and quantitation limit were 0.10 and 0.29 mg l(-1) of lipids respectively. Compared to the colorimetric method using sodium dichromate, it is at least 100 times more sensitive. The proposed method permitted to rapidly measure fat emulsion traces in automated compounder line set for parenteral nutrition solutions and thus, to assess the risk of contamination of binary bags by lipids. At last, this method was shown to be conveniently applied to the analysis of fat emulsion in the final total parenteral nutrition bag.