Physicochemical and solubilization properties of N, N-dimethyl-N-(3-dodecylcarbonyloxypropyl)amineoxide: a biodegradable nonionic surfactant

The physicochemical characteristics of N,N-dimethyl-N-(3-dodecylcar- bonyloxypropyl)amineoxide (DDCPNO), a biodegradable analogue of a N, N-dimethylalkylamine-N-oxide, are compared with those of N, N-dimethyldodecylamine-N-oxide (DDNO) to establish the effect on the properties of DDNO of inserting a propoxy linker between the hydrophobic tail and hydrophilic head region. Surface tension measurements gave a critical micelle concentration of 0.33 mM for DDCPNO compared with a value of 1.57 mM for DDNO, suggesting that the former was the more hydrophobic surfactant. This result was confirmed by laser light scattering studies in which total intensity light scattering indicated the presence of DDCPNO micelles of aggregation number 85.0. Photon correlation spectroscopy studies yielded a limiting hydrodynamic diameter of 4.0 nm in comparison with values of 57.5 and 3.3 nm obtained for the aggregation number and the limiting hydrodynamic size, respectively, of DDNO micelles. Studies demonstrated that neither a dilute aqueous solution of DDCPNO or DDNO exhibited a cloud point within the temperature range 293-373 K. Solubilization studies showed that the capacity of DDCPNO micelles for a range of drugs of varying size and polarity was less than that observed with DDNO micelles at an equivalent surfactant concentration. As a further measure of solubilization, the ability of DDCPNO to form oil-in-water microemulsions with a range of ethyl ester oils was investigated and found to be slightly higher than that achieved with DDNO. Together these studies suggest that the presence of the semipolar linker significantly alters the properties of this low molecular weight surfactant.