Structure of unsaturated fatty acids in 2D system

The behaviour of Langmuir monolayers corresponding to unsaturated fatty acids belonging to the omega-9 (oleic acid), omega-3 (α-linolenic and stearidonic acids) and omega-6 (linoleic, γ-linolenic and eicosadienoic acids) series was studied in order to get insight into the influence of various factors (such as subphase temperature, length, degree of unsaturation and position of the double bonds in the aliphatic chains) on the molecular conformation of these fatty acids spread at the A/W interface. The obtained results derived from the surface pressure - area isotherms, compressibility modulus and monolayer thickness prove that the lift-off and the limiting areas of investigated films increase both with the number of double bonds and length of the hydrocarbon chain. Also, the monolayers are more compressible (more fluid) upon increasing their tails unsaturation degree. However, eicosadienoic (EA) film is more rigid due to its longer acyl chain. Polyunsaturated fatty acids (PUFAs) monolayers, except for EA, exhibit anomalous temperature dependence (area contraction with increasing temperature), which was attributed to the increased solubility of PUFAs molecules with temperature. The recorded thickness values of the monolayers were compared with those estimated from theoretical molecular conformations in order to establish the orientation and configuration of molecules in different surface states of their monolayer.