Biocompatible Microemulsions Based on Limonene: Formulation, Structure, and Applications

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• 作者：Vassiliki Papadimitriou ; Stergios Pispas ; Stauroula Syriou ; Anastasia Pournara ; Maria Zoumpanioti ; Theodore G. Sotiroudis ; Aristotelis Xenakis
• 刊名：Langmuir
• 出版年：2008
• 出版时间：April 1, 2008
• 年：2008
• 卷：24
• 期：7
• 页码：3380 - 3386
• 全文大小：75K
• 年卷期：v.24,no.7(April 1, 2008)
• ISSN：1520-5827

文摘

The preparation of biocompatible (w/o) microemulsions based on R-(+)-limonene, water, and a mixture of lecithinand either 1-propanol or 1,2-propanediol as emulsifiers was considered. The choice of the compositions of themicroemulsions used was based on the pseudo-ternary phase diagrams of the four-component system determined at30 C for different weight ratios of the components. When 1-propanol was considered as co-surfactant, the area ofthe microemulsion zone was remarkably increased. Interfacial properties and the dynamic structure of the emulsifier'smonolayer were studied by electron paramagnetic resonance (EPR) spectroscopy using the spin-labeling technique.The rigidity and polarity of the interface were affected by the nature of the alcohol used as co-surfactant. When1-propanol was used, the emulsifier's interface was much more flexible, indicating a less tight packing of lecithinmolecules than in the case of 1,2-propanediol. In addition, the membrane's polarity was decreased when the diol wasadded as co-surfactant in the microemulsion system. To evaluate the size of the dispersed aqueous domains as afunction of water content and other additives concentration, dynamic light scattering (DLS) measurements were carriedout. Radii in the range from 60 to 180 nm were observed when 1-propanol was used as co-surfactant, and the watercontent varied from 0 to 12% w/w. Electrical conductivity measurements of R-(+)-limonene/lecithin/1-propanol/watermicroemulsions with increasing weight fractions of water indicated the appearance of a percolation threshold at watercontent above 4% w/w. Lipase from Rhizomucor miehei was solubilized in the aqueous domains of the biocompatiblemicroemulsions, and the esterification of octanoic, dodecanoic, and hexadecanoic acids with the short-chained alcoholsused as co-surfactants for the formulation of microemulsions was studied. The enzyme efficiency was affected bythe chain length of the carboxylic acids and the nature of the alcohol. In the case of 1-propanol, a preference for thelong-chain carboxylic acids was observed. On the contrary, when 1,2-propanediol was used formulation of thecorresponding esters was not observed. This behavior could be possibly attributed to either the specificity of the lipasetoward the alcohol employed for the esterification of the acids or the structural changes induced in the system when1-propanol was replaced by 1,2-propanediol.