Solution Properties of Tadpole-type Cationic Amphiphilic Dendrimers Consisting of an Alkyl Chain, a Quaternary Ammonium, and a Poly(amidoamine) Dendron

Abstract

Tadpole-type amphiphilic dendrimers consisting of an alkyl chain, a quaternary ammonium bromide (qb) and a poly(amidoamine) dendron (den) (C_nqbdenGm, where n represents an alkyl chain with a length of 10,14, or 18 carbons; m is the generation number G of dendron taking the value –0.5, 0.5, or 1.5) were synthesized using N, N-dimethylethylenediamine as a central scaffold. Electrical conductivity, surface tension, pyrene fluorescence, and dynamic light scattering measurements were used to characterize the properties of the dendrimers. In addition, the effect of the alkyl chain length and the generation number of a dendron on these properties was evaluated through a comparison with those of the corresponding previously reported amphiphilic dendrimers with lactobionamide sugar terminal groups (C_nqbdenGmLac) and conventional cationic monomeric surfactants (C_nTAB). Both critical micelle concentration (cmc) and surface tension (except for C₁₈ series) were lower than those of C_nqbdenGmLac and C_nTAB with the same alkyl chain length, indicating that the synthesized amphiphilic dendrimers have an excellent micelle-forming ability in solution and high adsorption ability at the air/water interface, in spite of the large bulky dendron structure. When the alkyl chain length and the generation number of the amphiphilic dendrimers were increased, the surface tension became high because of the curved long alkyl chain and the bulky structure of dendron. Further, C_nqbdenGm formed micelles with a small size in solution, and the micelles of C_nqbdenG(–0.5) had almost a constant size despite the changes in the concentration, while those of C_nqbdenG0.5 and C_nqbdenG1.5 became smaller with increasing concentration. The difference in the behavior results from the difference in the number of amide groups in the low- and high-generation dendrons.