2, Stevens Institute of Technology, Hoboken, New Jersey, United States
Conformational structures of proteins at the interfaces of zwitterionic polymer poly[2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide] (PMEDSAH), are examined to understand the role of protein-polymer interactions on the stability of proteins. In order to underpin the effect of interfacial hydration layer on the structures of physically adsorbed proteins, the strength of hydration layer of PMEDSAH brushes is controlled by varying the brush thickness and solution temperature. We measured that on 5-8 nm thick PMEDSAH brushes, all the proteins were more stable at 75°C than room temperature, indicating stronger hydration layer effect with the stretched chains. While on long brushes (15nm), proteins showed different behavior depending on their surface charges. Horseradish peroxidase with neutral isoelectric points had higher structural stability on 15nm brushes. Positively charged lysozyme and negatively charged streptavidin showed lower stability on 15nm brushes, implying the increasing electrostatic interactions of the stretched long chains can denature charged proteins. These results suggest that short polyzwitterionic brushes can facilitate improved biomaterial interactions that are essential for anti-fouling applications and biosensors performing at elevated temperatures.