The Design, Synthesis of Thermo and pH Sensitive Poly(amidoamine) Dendrimer Derivatives
|Keywords||PAMAM dendrimer pH and temperature sensitivity N-isopropylamide N, N-diethylamide|
The temperature-sensitive functional structure units were introduced to the surface of the relatively lower generation PAMAM dendrimer to endow the dendrimer itself with pH and temperature responsibility. The functional structure units included N-isopropylamide (NIPAM), N, N-diethylamide (DEA) and N, N- dimethylaminoethyl carboxylate (DMA) groups, which are considered to play an important role in the temperature dependent solubility change in their linear temperature sensitive polymer.G2.5 and G3.5 PAMAM dendrimers were chosen to be modified. In order to increase the density of the terminal groups of PAMAM dendrimer, the ester-terminated groups of PAMAM dendrimer were converted into the terminal hydroxyls by the addition of TRIS (tri(hydroxymethyl) amino methane), which transfered one ester into three terminal hydroxyls. By using EDC.HCl as coupling agent and DMAP as catalyst, through esterification reaction the functional structure units were conjugated to the surface of PAMAM-TRIS dendrimer. The obtained PAMAM-TRIS-NIPAM and PAMAM -TRIS-DEA conjugates exhibited temperature and pH sensitivity, and the LCST of PAMAM-TRIS-NIPAM in PBS of different pH values were around the physiological temperature. All the conjugates didn’t induce haemolysis.Using indomethacin as a model drug, dissolution test of drug from the complex in different pH at 37℃was studied. Unfortunately, the PAMAM-TRIS-NIPAM conjugates didn’t show the capability of controlling drug release, although they exhibited the capability of sustained release.The interaction between drug moleculars and the dendrimer was also discussed. The entrapment of drug in the dendrimers’cavities resulted in a more expanded conformation, and the acidic guest molecules caused the protonation of the tertiary amino groups. The LCST of the dendrimer derivatives increased because of the charge-charge repulsion and the bulk effect.