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In this study, we observed the structural and energetic stability of a polypeptide nanosheet formed by a polypeptide skeleton of six alanines (ALA) or leucines (LEU) and a polar head composed of aspartic acid (ASP), lysine (LYS) or arginine (ARG). The six membrane structures A6D, A6K, A6R, L6D, L6K, and L6R were subjected to molecular dynamics simulations in an ionic liquid formed by the cholinium–glycine pair [CHO][GLY]. Our results show how the hydrogen bonds between the polypeptides and the ionic liquid are structured, the energetic behavior of the nanosheet, mobility of the IL, surface topology of the membrane and the stiffness of the structure when the extraction of a polypeptide from the macro structure is carried out. Different structural combinations were considered to verify the difference due to the electrostatic behavior in the systems. Our analysis aims to contribute information that can increase the use of these organic and biodegradable materials in other environments.

Recently, a series of organic structures formed by peptide self-assembly have been reported, among which stand out the peptide nanomembranes with promising applications in the energy storage field. In these applications, the nanomembranes can be subjected to high temperatures. Although the effects of temperature are well known in lipid membranes, in peptide ones they lack further investigation. In this sense, we present a study based on fully atomistic molecular dynamics simulation, which demonstrates the behavior of peptide membranes formed by Alanine (A) and Arginine (R) electrically charged and uncharged, A6R1+ and A6R, at temperatures of 300 K, 320 K, 340 K, 360 K, 380 K, 400 K, 420 K, 440 K, 460 K, 480 K, and 500 K. We report a detailed analysis based on the total average number of Hydrogen Bonds (HBs) between the residues and between the residues with the water molecules, as well as the average lifetime of each of these interactions. Our results demonstrate that a hydrogen-bond network is maintained in the range of temperature evaluated contributing to the stability of the peptide nanomembranes. The increase in temperature causes only a small variation in the total number of HBs, however, the HBs lifetime of these interactions is drastically affected by temperature, providing greater dynamics in the peptide-peptide interaction, favoring greater mobility of these molecules as the temperature rises, as confirmed by the Einstein's diffusion coefficient, also obtained in this study. The HBs results together with the Coulomb and vdW interactions, show that the membrane structures are quite stable in withstanding high temperatures, which may indicate a potential application in coatings, liquid separation, and especially in supercapacitors since the nanomembranes formed by A6R1+ and A6R peptide present pores in all 2D-material favoring a slight infiltration of ionic liquid in the material surface, which directly impacts energy storage efficiency.

We propose a computational Molecular Dynamic (MD) study to evaluate the interaction of C60 fullerene in contact with lipid membranes, as a function of the bilayers cholesterol content. Pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and DOPC/cholesterolXX (XX = 10%, 20% and 30%) membranes where investigated. An analysis involving umbrella pulling techniques to force the extraction of DOPC lipid and/or cholesterol molecules in comparison with an insertion of a fullerene C60 molecule into the lipid/cholesterol membranes was performed in order to verify the force/energy required for the C60@DOPC/cholesterol partitioning. In addition, electron spin resonance experiments using a lipid and an amphiphilic spin labels were performed to investigate the DOPC-cholesterol interactions and to mimic the C60 fullerene-membrane interactions. The spectroscopic results corroborated the MD ones and indicated that the presence of cholesterol in the lipid bilayers increased the membrane rigidity as well as the force required to C60 insertion/extraction.