FT-IR investigation of the urea state in lecithin and sodium bis(2-ethylhexyl)phosphate reversed micelles

Fr-IR spectra of urea/lecithin/CCl4 and urea/sodium bis(2-ethylhexyl) phosphate (NaDEHP)/CCl4 systems as a function of the urea-to-surfactant molar ratio (R-urea) at a fixed surfactant concentration (0.1 mol kg(-1)) have been recorded at 25 degreesC. Analysis of the absorption spectra leads the to hypothesis that urea is confined within the hydrophilic micellar core of lecithin and NaDEHP reversed micelles. The encapsulation of urea involves some changes of the urea NH stretching band with respect to that of the pure solid urea, attributable to confinement effects. The stretching modes of the surfactant head group are affected by the presence of urea, indicating specific urea-surfactant head group interactions. On the other hand, analysis of the CO stretching band suggests that the urea CO groups are not engaged in urea-surfactant head group interactions. (C) 2003 Elsevier Science (USA). All rights reserved.