Effect of Saline and Non-Specific Insulin Binding on the Phase Behavior of Poly(Ethylene Glycol)-Grafted Phosphoethanolamine-Succinyl Model Membranes

ii Poly (ethylene glycol)-grafted membrane-mimetic surfaces bearing negatively charged phospholipid headgroups have gained significant attention due to their promising contributions in numerous biomedical applications. The conformational properties of PEG chains have been mainly studied at the air/water interface, which does not elucidate much about its behavior at the physiological pH ~ 7.4. In this contribution, binary mixtures of a phosphoethanolamine-Succinyl bearing C16 aliphatic chains, DPPE-Succinyl, and a PEG-phospholipid conjugate bearing a PEG chain of 2000 Da, DPPE-PEG2000, have been used as ideal models of bio-nonfouling membrane-mimetic surfaces. The effect of PBS with pH ~7.4 as well as each of its individual constituents including Na2HPO4, KCl, KH2PO4, and NaCl on the biophysical properties of model membrane was examined. Our findings suggest that saline and each of its individual constituents play a pivotal role in the phase and conformational behavior of PEG-grafted membrane models. Insulin as a model protein was then selected to further investigate the effect of phase and conformation behavior of PEG-grafted membrane models on protein/membrane interactions. The insulin/membrane interactions were quantified in terms of monolayer area expansion, ΔA, penetration area, Ap, as well as protein binding degree, χp. To the best of our knowledge, this study provides the first insight into mechanistic aspects of protein interactions with model negatively charged PEG-grafted membranes. This knowledge, may aid in understanding the in-vivo performance of advanced targeted therapeutic carriers. ii