Thermosensitive properties of poly(amidoamine) dendrimers with peripheral phenylalanine residues.

Dendrimers are unique polymers with globular shapes and well-defined structures. We previously prepared poly(amidoamine) (PAMAM) dendrimers having phenylalanine (Phe) residues at every chain end of the dendrimer as efficient gene carriers. In this study, we found that Phe-derivatized PAMAM dendrimers change their water solubility depending on temperature. The dendrimers were soluble in aqueous solutions at low temperatures, but they became water-insoluble at temperatures above a specific threshold, which is termed the lower critical solution temperature (LCST). Although the LCST of Phe-modified dendrimers decreased with increasing dendrimer generation, these dendrimers exhibited an LCST of 20-30 degrees C under physiological conditions. In addition, the LCST of the dendrimers was controlled by introducing isoleucine (Ile) residues at chain ends of dendrimers at varying ratios with respect to Phe residues. The PAMAM dendrimers are known to encapsulate various drug molecules. For these reasons, temperature-sensitive dendrimers might be useful as efficient drug carriers with controlled size and temperature-responsive properties.