Non-enzymatic lipid peroxidation may change biomembrane structure and function. Here, we employed molecular dynamics simulations to study the effects of either phospholipid or cholesterol peroxidation individually, as well as the combined peroxidation of both components. When lipids were peroxidized, the generated OOH groups migrated to the membrane surface and engaged in H-bonds with each other and the phospholipid carbonyl ester groups. It caused the sn-2 acyl chains of phospholipid hydroperoxides to bend and the whole sterol backbone of cholesterol hydroperoxides to tilt. When phospholipids were kept intact, peroxidation of the sterol backbone led to a partial degradation of its condensing and ordering properties, independently of the position and isomerism of the OOH substitution. However, even in massively peroxidized membranes in which all phospholipids and cholesterol were peroxidized, the condensing and ordering properties of the sterol backbone were still significant. The possible implications for the formation of membrane lateral domains were discussed. Cholesterol peroxyl radicals were also investigated and we found that the OO groups did not migrate to the headgroups region.

Graphene oxide (GO)-based materials have been considered for potential energy storage applications, in particular supercapacitors. Here, for the first time, we present a detailed analysis of the properties of GO-based supercapacitors as a function of both chemical composition and charge density on the electrodes. Differential capacitance was determined and the effect of the degree of oxidation of the electrodes was taken into account. Also, structural and energetic details on the electrode–electrolyte interaction and, consequently, the double-layer electric structure were analyzed. The differential capacitance value for all supercapacitors is within the range of 1.5–5.4 μF cm–2 in the ±3 V window for the electrode potential and presents the highest value for the R20 system, which also had the highest mean integral capacitance. One important result is the gradual transition from bell-shaped to camel-shaped as the degree of oxidation increases. The results presented here provide the missing complement for a detailed and complete description of the properties of GO supercapacitors, indicating how they behave with the variation of charge density and degree of oxidation.

We report here density functional theory calculations and molecular dynamics atomistic simulations to determine the total capacitance of graphene-modified supercapacitors.

The amphiphilic character of graphene oxide was analysed in terms of its interfacial activities, using atomistic molecular dynamics. Graphene oxides at four different degrees of oxygenation were investigated considering both the effects of oxidation and carboxyl edge-functionalization. Solvation free energies are strongly negative and of increasing magnitude with the concentration for all systems, even in the toluene phase, indicating that GO presents a favourable solvation in both pure liquids as well as interfaces. The PMF results indicate that only the R20 system is slightly active at the water/vacuum interface, with a PMF minimum of about -2.6 kJ mol-1. Both analyses, free energy and PMF, indicate that all systems with higher oxygen concentrations have lower free energy in water than in toluene, while the R20 system opposes this tendency. Comparison between the reduced GOs (20%) shows that edge-functionalised systems were more active than basal-functionalized systems, indicating that oxygen concentration plays a more relevant role than the distribution of functional groups.

Hydration properties of graphene oxide (GO) are essential for most of its potential applications. In this work, we employ atomistic molecular dynamics simulations to investigate seven GO compositions with different levels of oxygenation. Two atomic charge models for GO are compared: (1, a simplified model) sp carbons are purely Lennard-Jones sites; (2, a CHELPG model) sp carbon charges are consistent with the CHELPG scheme. Structural properties were found to depend insignificantly on the charge model, whereas thermodynamics appeared very sensitive. In particular, the simplified model provides systematically stronger GO/water coupling, as compared to the more accurate model. For all GO compositions, hydration free energies are in the range of -5 to -45 kJ mol indicating that hydration is thermodynamically favourable even for modest oxidation degrees, thus differing drastically from the cases of pristine graphene and graphite. In general, it has been observed that as R increases the high oxidation degree obstructs the formation of new hydrogen bonds, which considerably affects their hydration properties. Although both the used charge models are qualitatively equivalent, the energy and number of hydrogen bonds have been shown to be sensitive to the charge set employed. In particular, the comparison shows that the simplified model tends to overestimate the GO/water interaction energy. The results and discussion presented herein provide a physical background for modern applications of GO, e.g. in electrodes of supercapacitors and inhibitors in processes involving biological molecules.

Molecular dynamics simulations were used to describe and quantify the role of edge groups on the hydrating properties of graphene oxide (GO). For this, six different oxygen concentrations were investigated, and in four of them, carboxyl groups were present. Structural analysis indicates a greater probability for the water solvation around the GO edges in detriment of the region of its basal plane, while hydrogen bonding analyses indicates that edge groups are very expressive, participating in about 60% of the total number of bonds. The impact of this bond network formed by edge groups is rationalized in energetic and thermodynamic terms. The resulting hydrophilicity observed, as expected, is of electrostatic origin and has a larger contribution from the edge groups that varies from 22 to 57% depending on the concentration. Hydration free energy and potential of mean force calculations support these findings. It was observed that the edge groups contribute up to 51% of the total hydration-free energy and that the PMF indicates the tendency for spontaneous aggregation at all investigated concentrations, being lower the higher the concentration of oxygen.

We report on DFT and MD simulations to investigate the contributions of quantum and double-layer capacitances in the total differential capacitance of functionalized graphene as the electrode material of aqueous-based supercapacitors. We consider the effects of nitrogen and oxygen incorporation in graphene quantum and double capacitance in four different supercapacitor models in the presence of aqueous electrolytes LiSO4 and LiTFSI. We found that the total differential capacitance is limited by the double-layer capacitance. Our best electrode/electrolyte model was obtained with a symmetric supercapacitor assembled with epoxy/hydroxyl-functionalized graphene electrodes filled with 1 M LiSO4 electrolyte. It achieved a higher double-layer capacitance among all investigated systems over the entire potential window, thus offering better performance in energy storage.

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