The interior construction of vesicles fashioned solely by mannosylerythritol lipid-A (MEL-A), a glycolipid produced by basidiomycetous yeasts of the genus Pseudozyma, was visualized by liquid cell and cryogenic transmission electron microscopy. Furthermore, it was proven for the primary time that their morphology will be managed by dicarboxylic acids performing as molecular alerts, mixed with the pH of the answer. MEL-A fashioned nano-sized unilamellar vesicles (200 nm diameter, 5 nm bilayer thickness) at pH 7 and pH 4 with out dicarboxylic acids. Upon addition of dicarboxylic acids at pH 7, divalent dicarboxylate anions interact with the hydroxyl teams of the erythritol moiety in MEL-A, driving the expansion of unilamellar vesicles with diameters of 250–300 nm. At pH 4, the addition of dicarboxylic acids (oxalic, maleic, fumaric or malonic acids), which exist predominantly as monoanions, induced the growth to micro-sized vesicles (0.8–2.1 µm in diameter) and the transition right into a multilamellar construction consisting of as much as 18 layers. For oxalic acid, the vesicular membrane exhibited a thickness of 80 nm and consisted of 16 layers, of which each the outermost and the innermost layer thickness was 5 nm. Vesicle multilayering in MEL-A assemblies is pushed by cooperative dissociated/undissociated carboxyl interactions in dicarboxylate monoanions.
