Highly water-soluble, pH sensitive and biocompatible PAMAM 'dendrizyme' to maintain catalytic activity in complex medium.

The dendrimer based synthetic mimetic enzyme has been drawing great attention. However, this mimetic enzyme is different from the natural enzymes, which are pH sensitive, biocompatible and keep their catalytic activity in biological complex medium. A single zwitterionic layer composed by primary amine and carboxyl groups may be a useful method to obtain these properties. Herein, we report a novel facile method to prepare a mimetic enzyme. The complexes of generation 5 poly(amido amine) dendrimers (G5 PAMAM) with free hemin (G5Hs) were modified by the maleic anhydride and cysteamine. Results showed that the mimetic enzymes (G5HMCs) had pH sensitivity and good stability by varying the pH from 4 to 9, while significant precipitation was observed for free hemin at pH5 after two days. The G5HMC (3:1) showed optimal catalytic activity at its isoelectric point. Furthermore, G5HMCs displayed excellent biocompatibility. The G5HMCs incubated with fibrinogen were stable for 24h, while G5Hs immediately formed large aggregates. G5HMC (3:1 2mg/mL) displayed little cytotoxicity with HeLa cells or A549 cells for 24h, while G5H (3:1) had serious cytotoxicity, which was also demonstrated by cell morphology observation. At last, G5HMCs fully preserved their catalytic activity in bovine serum albumin (BSA) solution compared with phosphate buffer saline (PBS) solution, while hemin decreased to 73.5-81.5% catalytic activity in BSA solution, which was caused by the less interaction with BSA for G5HMCs than free hemin. The surface functionalization schemes described in this report would represent a versatile method to prepare water-soluble, pH sensitive, biocompatible, and efficient artificial enzymes for biomedical related applications.