Synthesis and physicochemical studies of methyl-12-[1 '-beta-d-lactosyl]-octadec-9-ene-1-oate: A novel biosurfactant analog

Synthesis of a new glycolipid and biosurfactant analog, methyl-12-[1'-beta- D-lactosyl]-octadec-9-ene-1-oate (LOD), has been done from easily accessibl e renewable resources, namely, lactose and ricinoleic acid from castor oil. Surface and thermodynamic properties at the air/water interface including critical micelle concentration (CMC), aggregation number (<N>), maximal den sities (Gamma(max)), minimal area per molecule (A(min)), surface pressure a t the CMC (Pi(CMC)), free energy of adsorption (Delta G(ad)(0)), and free e nergy of micelle formation per mole of monomer unit (Delta G(m)(0)) were in vestigated. The results indicate that this particular glycolipid, because o f branching in the hydrophobic chain, has a comparatively large A(min) valu e and hence a very low CMC, aggregation number, and less free energy of mic ellization and adsorption at the air/water interface than molecules with a straight hydrophobe, for example, n-dodecyl-beta-D-maltoside. The effects o f electrolytes (NaCl, KCl, CaCl2, and AlCl3) of the same ionic strength and of increasing ionic strength on the interfacial microenvironment of LOD we re also investigated. For the same anion, Cl-, and the same ionic strength, different cations were found to have different effects on the CMC of LOD. With increasing ionic strength, different electrolytes were found to have d ifferent effects on the interfacially located, highly hydrated aqueous laye r of the LOD micelle. The water structure-making or -breaking ability of di fferent cations from the interfacial microenvironment of LOD was found to d epend on the charge/radius ratio of the cations.