Interaction of guanidinium and ammonium cations with phosphatidylcholine and phosphatidylserine lipid bilayers - Calorimetric, spectroscopic and molecular dynamics simulations study.

The ability of arginine-rich peptides to cross the lipid bilayer and enter cytoplasm, unlike their lysine-based analogues, is intensively studied in the context of cell-penetrating peptides. Although the experiments have not yet reconstructed their internalization mechanism, the computational studies have shown that the type or charge of lipid polar groups is one of the crucial factors in their translocation. In order to gain more detailed insight into the interaction of guanidinium (Gdm+) and ammonium (NH4+) cations, as important building blocks in arginine and lysine amino acids, with lipid bilayers, we conducted the experimental and computational study that tackles this phenomenon. The adsorption of Gdm+ and NH4+ on lipid bilayers prepared from a zwitterionic (DPPC) and an anionic (DPPS) lipid was examined by thermoanalytic and spectroscopic techniques. Using temperature-dependent UV-Vis spectroscopy and DSC calorimetry we determined the impact of Gdm+ and NH4+ on the thermotropic properties of lipid bilayers. FTIR data, along with molecular dynamics simulations, unraveled the molecular-level details on the nature of their interactions, showing the proton transfer between NH4+ and DPPS, but not between Gdm+ and DPPS. The findings originated from this work imply that Gdm+ and NH4+ form qualitatively different interactions with lipids of different charge which is reflected in the physico-chemical interactions that arginine-and lysine-based peptides establish at a complex and chemically heterogeneous environment such as the biological membrane.

Surface coating affects behavior of metallic nanoparticles in a biological environment.

Silver (AgNPs) and maghemite, i.e., superparamagnetic iron oxide nanoparticles (SPIONs) are promising candidates for new medical applications, which implies the need for strict information regarding their physicochemical characteristics and behavior in a biological environment. The currently developed AgNPs and SPIONs encompass a myriad of sizes and surface coatings, which affect NPs properties and may improve their biocompatibility. This study is aimed to evaluate the effects of surface coating on colloidal stability and behavior of AgNPs and SPIONs in modelled biological environments using dynamic and electrophoretic light scattering techniques, as well as transmission electron microscopy to visualize the behavior of the NP. Three dispersion media were investigated: ultrapure water (UW), biological cell culture medium without addition of protein (BM), and BM supplemented with common serum protein (BMP). The obtained results showed that different coating agents on AgNPs and SPIONs produced different stabilities in the same biological media. The combination of negative charge and high adsorption strength of coating agents proved to be important for achieving good stability of metallic NPs in electrolyte-rich fluids. Most importantly, the presence of proteins provided colloidal stabilization to metallic NPs in biological fluids regardless of their chemical composition, surface structure and surface charge. In addition, an assessment of AgNP and SPION behavior in real biological fluids, rat whole blood (WhBl) and blood plasma (BlPl), revealed that the composition of a biological medium is crucial for the colloidal stability and type of metallic NP transformation. Our results highlight the importance of physicochemical characterization and stability evaluation of metallic NPs in a variety of biological systems including as many NP properties as possible.