Interfacial and self-assembly properties of bolaamphiphilic compounds derived from a multifunctional oil

The self-assembly characteristics in aqueous solutions of cationic bolaamphiphiles with systematic changes in their chemical structure is described with respect to their interfacial properties within water and at the air/water interface. Six cationic bolaamphiphiles were synthesized from multifunctional vernonia oil with the following variations: (a) two different alkyl chain lengths connecting the head groups, (b) polar ester or hydrogen bonding amide groups within the hydrophobic domain, and (c) an acetylcholine cationic head group with different conjugation sites to the alkyl chain. Surface tension measurements were used for determining critical aggregation concentration (CAC) values and air/water interfacial parameters such as ‘effectiveness’, surface excess concentration and area occupied by one molecule in the air/water interface. Fluorescent studies with pyrene were used to characterize CAC properties within the aqueous volume and transmission electron microscopy (TEM) for determining the aggregate structure’s size, homogeneity and morphology. A bolaamphiphile molecular structure vs. interfacial property relationship was derived from this data which could be used to determine the molecular structure properties needed to generate interfacial forces to form either spherical vesicles or fibrous networks. The effects of the aliphatic chain length, head group orientation and functional groups within the hydrophobic domain on CAC, surface tension properties and self-aggregate morphology are described. Most bolaamphiphiles studied had CAC values in the 10–190 μM range, while two out of the six were found to assemble into MLM spherical vesicles with diameters ranging up to 120 nm suitable for drug delivery applications. Others formed a gelatinous network of fibers or multi-lamellar vesicles.

Self assembly characteristics, critical aggregation concentration and effect of molecular structure of cationic bolaamphiphiles derived from vernonia oil in aqueous solutions.Figure optionsDownload high-quality image (143 K)Download as PowerPoint slideHighlights
► CAC and interfacial characteristics of novel cationic bolaamphiphiles were studied.
► Configuration at air/water interface vs. bola structure and interfacial parameters.
► Molecular structure vs. self-aggregate geometry is discussed.
► Monolayered membrane vesicles and fibers are among the formed aggregate structures.
► Amides instead esters at the hydrophobic domain increase CAC value significantly.