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In this work, nanomembranes formed by the I

In this work, we observe the behavior of the dipole moment, atomic charges, solute-solvent interactions and NMR spectroscopy of aliphatic amino acids in a water solution via the computational simulations of classical molecular dynamics and DFT quantum calculations. Our results indicate that the convergence of the atomic charge of the solute, from an iterative process, together with the dipole moment of the amino acid, alters the lifetime of hydrogen bonds present in the first solvation shell, resulting in the modification of its structure and dynamics. Using GIAO-DFT-NMR calculations, we assessed the impact of these structural solute-solvent modifications on the magnetic shielding constants of the solute carbon atoms. In this sense, we evaluate the importance of an update in parameters that describe atomic charges present in the CHARMM36 force field.

The Sequential Monte Carlo/Quantum Mechanics approach was used for investigate the solvent effect on the solute-solvent structure and spectroscopic properties of Damascone derivatives, Carvone, Perillaldehyde and Menthadiene in water solution. Our in-water results have shown that the dipole moment increase of the compounds are between 36% and 84% when compared with the gas phase values and a solvatochromic shift between −20 and 14 nm whereas the magnetic properties studied have indicated an NMR shift close to 10 ppm for some carbon atoms and greater than 140 ppm for oxygen atoms.

In this paper, polypeptide membranes composed by surfactant-like peptides were studied by using molecular dynamics simulations. The studied membranes are composed by 15 amino acids, being a hydrophobic part consisting of 3 isoleucine (ILE - I), 3 valine (VAL - V), 3 alanine (ALA - A), 3 glycine (GLY - G), and a hydrophilic one formed by 3 lysine (LYS - K). These amino acids were linked into two different primary sequences, I3V3A3G3K3, with the charged lysine bounded at the C-terminus and K3G3A3V3I3, with the charged lysine bounded at the N-terminus. The density profiles results, the average number of hydrogen bonds, the Coulombic and van der Waals interactions between the peptide-water (PEP-Water) and between each group of peptide residues (PEP-PEP) indicate that, despite the occurrence of much water infiltration (especially in the I3V3A3G3K3 membrane, which has greater porosity than the K3G3A3V3I3 membrane), they still maintain a membrane structure. Our results allow a better understanding of the influence of the interactions between the peptides as well as the role of each group of amino acids residues, peptide terminus and solvent in membrane stability.

In this work, we propose and investigate numerically the electronic transitions of a new system useful for quantum information tasks composed by a graphene quantum dot (GQD) interacting with two Li+ ions in opposed facing directions. By changing the distance of the Li+ ions, we find a region in which only electronic transitions of GQD → Li+ are allowed. Notably, into this region emerges the possibility of controlled electronic transitions for both ions in the symmetric case via appropriate external electric fields. Finally, the robust entanglement generation arises since it is possible to inhibit the electronic transition back to GQD by grounding it.

In this article, we investigate the effects of the isoleucine (ILE)N amino acid chain growth, N = 1.0.6, the ILE conformational effect as well as the solvent presence on the electrical and magnetic spectroscopic properties when these compounds are in aqueous solution. Computational molecular dynamics simulations were performed to include the solvent medium and generate uncorrelated configurations involving solute-solvent structures. The charge point model for solvent was used to obtain the results for quantum mechanical calculation, in special DFT calculations, for (ILE)N structures. Our results for the magnetic shielding constant obtained via GIAO-DFT-NMR calculations show that there is evidence of a magnetic behavior that characterizes the number of peptide bonds and, therefore, how the N isoleucine polypeptide chain is composed. TD-DFT results also show an absorption band shift to larger wavelengths indicating a dependence on N growth.

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.

Development of efficient electrodes is one of the main ways to increase the performance of an electrochemical energy storage device. It is known that such performance is associated with the electrode specific area, which allows a much larger interfacial interaction with the electrolyte. In this work, molecular dynamics is employed to model C60/graphene composite electrodes that can expand the effective area by approximately 70% relative to a pure graphene electrode. Our simulations indicate that the performance of supercapacitors of C60/graphene electrodes is superior to those made of planar graphene, in some cases up to 150%. The inherent electrolyte asymmetry in the investigated supercapacitors has a negative effect on the total capacitance, indicating that even better results could be obtained after rational design of the fullerene density on the surface of the graphene as well as the choice of the ions in the liquid ionic composition.

In this work, we have investigated the interactions of polypeptides composed of the sequence of six alanines and one arginine (A6R) grouped in three nanosheet structures with maximum, intermediate,...

Here we reported the impact of flexibility of solvent effects on the optical absorption, nuclear magnetic resonance (NMR) and electrical properties of A3R, a tetrapeptide compound derived from peptide bonds in the α-helix form of 3-alanines and one arginine, in aqueous environment. The in-water A3R configurations were generated by S-MM/QM and MD procedures and also using the PCM model. We have used the ASEC approach with 100 uncorrelated settings obtained from Monte Carlo simulation to achieve the convergence of the dipole moment for each in-water geometry in all steps between MC and QM calculations. The converged values of μ for A3R-MD geometries present increments between 69 and 392% in comparison with the gas phase value. Our results for optical absorption demonstrate the possibility of absorption in large range, with strong dependence of the geometric conformation of the A3R molecule. Our findings corroborate both the importance of the solute polarization and the geometric flexibility in the analyzed properties. Spectroscopic results obtained experimentally for the σ(13C) indicates that our A3R-MD geometry calculations are consistent with the adopted model.

We employ molecular dynamics (MD) simulations to assess the electrical behavior of the atomic charges of a fullerene immersed in an ionic liquid (and water). From solute-solvent configurations and DFT calculations, we obtained the atomic charges and the dipole moment in each stage of MD-simulation. Through an iterative process alternating MD-simulations and DFT calculations we obtained the convergence of the C60 dipole moment in solution. A complete analysis of the behavior of atomic charges is presented comparing the impact on the solute-solvent structure, where we highlight the importance of the complete polarization of the solute in solution. To observe the impact of electronic C60-solvente interaction on spectroscopy results we performed nuclear magnetic resonance (NMR) and absorption spectra quantum calculations, using GIAO-DFT and TD-DFT methodology. The results indicate a smaller chemical shift, δ ( 13 C ) and a more intense electronic transition band for the fully polarized C60 in solution.

In this work, we report results for the structural solute–solvent, electrical and magnetic properties of xanthine derivatives: caffeine, paraxanthine and theophylline, considering the effects of polarization in water that represents the achievement of electrostatic balance between solute and solvent. For this procedure, we performed atomistic computer simulations based on iterative and sequence applications of Classical Monte Carlo Simulations and Quantum Mechanics (S-QM/MM). We employ additional calculations using DFT to calculate the chemical shielding of xanthine molecules in the liquid environment, comparing the efficiency of various DFT-exchange and correlation functionals (B3LYP, CAM-B3LYP, BHandHLYP and PBE1PBE). The hydrogen bonds between the solute and the solvent were analyzed and the contribution of this structural property to the NMR spectrum was also carefully considered. Additionally, supramolecular models for xanthine-water in solution were also evaluated with the aim of evaluating whether such models can contribute to a better description of the magnetic signatures of carbon and hydrogen atoms.

We present a theoretical study of the solvent influence on ANR polypeptides, with N = 1, 2, 3, 4 and 5, in the gas phase and in water solution using the sequential MC/QM methodology combined with GIAO-DFT calculations. Our findings indicate a strong solvent effect on the dipole moment, exhibiting increases of up to 61% in the values of μ in the liquid phase when compared with the respective results in the gas phase. The spatial correlation between ANR polypeptides and water was also analyzed, as well as the solvent shells that are directly involved with solute–solvent interactions, like hydrogen bonds. In addition, we have reported the solvent influence on the magnetic shielding.

We have investigated the solvent effects on the nonlinear and spectroscopic optical properties of some azo-enaminone molecules in the gas phase and in methanol and water solutions. Using the sequential Monte Carlo/Quantum Mechanics (S-MC/QM) approach, we have included the polarization of the solute due to the solvent medium. We have carried out TD-CAM-B3LYP/6-311++G(2d,2p) theoretical calculations for the electronic transitions. Solvatochromic deviations up to 25 nm in solution were observed for azo-enaminones in enol forms. Our CAM-B3LYP/6-311+G(d) calculations have indicated that the βHRS values may increase up to 100% when compared with the respective gas phase results. The magnetic signature of oxygen atoms was significantly affected by the inclusion of solvation effects.

In this work, we performed classical molecular dynamics simulations to evaluate laminar structures formed by peptides with the (RF)5 primary sequence. The alternating arginine (R) and phenylalanine (F) amino acids provide to the (RF)5 peptide a facially amphipathic sheets characteristic. Experimental studies report that the (RF)5 macromolecules can self-assembly into membrane-like or fiber-like nanostructures, however, our theoretical results indicate that the structures present more similarity with a laminar form. Our results demonstrate the existence of a dense mesh of hydrogen bonds that allows the separation of the hydrophilic and hydrophobic parts of the nanostructures in solution. Our theoretical results indicate properties that are perfectly compatible with experimental data. As an application, we noticed a dense charge distribution on the hydrophilic surfaces that allows efficient capture of ions in solutions.

In the present paper, we investigated the polarization effects on different amino acids (AAs) structures, i.e., Serine, Threonine, Cysteine, Methionine, Asparagine, and Glutamine. Initially, the AAs were modeled with CHARMM36 force field parameters and water molecules with TIP3P. Next, a polarization process was obtained from quantum calculations (using Density Functional Theory) of structures previously produced by simulations of Molecular Dynamics (MD) giving us improved values of the mean dipole moment and the new average atomic charges. Indeed, with these new values of the atomic charges we replace those ones used in previous MD-simulations and new MD-simulations stages are performed for each one of the structures under consideration. This process is repeated until the dipole moment and atomic charges presents a convergence. Finally, we analyze the hydrogen bonds, Coulombic and Lennard-Jones interaction energies, the mobility of AAs through the Einstein diffusion coefficient, nuclear magnetic resonance as well as the absorption spectrum. The results obtained for the improved (polarized) model are in full agreement with experimental results, which reinforces the feasibility of the present methodology.

Polyalanine chains have been extensively considered in the context of the development of peptides for self-organization of peptide nanostructures. Atomistic molecular dynamics simulations allowed us to analyze the structure and thermodynamics of the hydration of four polyalanines: A3, A6, A9 and A12. These chains have been considered to interact exactly as lipid in a peptide nanostructure, however our results show that such a view is inaccurate since alanine tails must interact strongly with each other, not only because of the hydrophobic interactions of side chains but also because of their hydrophilic groups. Our results show that the hydration free energy of such chains varies linearly with the length of the polyalanine, is strongly negative and is mostly driven by enthalpy. There is an entropic penalty, however, which is not enough to compensate for the enthalpic gain obtained in the hydration process.

We investigate the behavior of the spectroscopic properties of (α-)β-glucose and maltose in water solution using the S-MC/QM method. TD-CAM-B3LYP/6-311 ++G(2d,2p) and TD-B3LYP/6-311 ++G(2d,2p) electronic transitions show strong dependence with the solute polarization in water, indicating a blue shift of the λ water in comparison with λ gas – phase results. The NMR spectroscopy shows that the inclusion of the polarization effect and solvent medium - treated as point charge - is essential for a more appropriate description of the variation of the magnetic signature of oxygen atoms. Our results show variations up to 16 ppm on the solvent shift for σ( 17 O) values with CAM-B3LYP functional.

We develop a study using Molecular Dynamics and DFT to investigate the absorption spectrum of (Thr)n in-water. Results of MD-simulations characterize the solute-solvent interaction and indicate that Coulomb energy shown an increase of 61.41% between n = 1 and 6. Results confirm changes in the number of Hydrogen Bonds (per n) between solute-solvent, it is possible to observe values between 10.06 and 4.90 for n = 1 and 6. For absorption spectrum, our results demonstrate a difference of 60 nm between the maximum absorption obtained for the structures with n = 1 and 6.

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.

Experimentally observed all-boron fullerene, B-80, inspires systematic investigation of its physical chemical properties and search for possible applications. We hereby report density functional theory calculations to characterize interactions of B-80 with the selected imidazolium room-temperature ionic liquids (RTILs), dimethylimidazolium nitrate and dimethylimidazolium hexafluorophosphate. Whereas the imidazolium cation exhibits a rather poor affinity to B-80, the inorganic anions form polar covalent bonds with the boron atom occupying a central position within a B-6 hexagon. Attachment of the RTIL ion pairs leads to a significant alteration of the electronic spectra, charge density distribution, valence and conduction molecular orbitals. The total binding energies keeping the RTIL@B 80 complexes together range 200–250 kcal mol −1 , being higher than the energies of many interactions in chemistry. The observed phenomenon predicts an excellent solubility of B-80 in the considered RTILs, but may also reveal a poor stability of B-80 in the polar media. Our results motivate further efforts in studying the behavior of the all-boron fullerene in polar environments.

Atomistic molecular dynamics simulations were used to study the interaction of AnK peptides (with n = 3, 6 and 9) in contact with two different types of lipid membranes, DPPC and DPPG. PMF calculations and their decomposition into enthalpic and entropic components allowed a detailed thermodynamic analysis of the energy profile associated with the adsorption and penetration of the peptides through the lipid membranes. Our simulations indicated a drastic difference between the interactions of the peptides with both membranes. For the peptide A6K the interaction with the DPPG and DPPC membranes were −222 kJ mol−1 and −16 kJ mol−1, respectively. PMF for the DPPC membrane did not show any minimum in the interface region, that is, no favorable interaction with its surface. On the other hand, the interaction with the DPPG membrane showed a clear minimum near the surface. This minimum, although shallow, −10 kJ mol−1, indicates that the adhesion of the AnK peptides on the surface of the DPPG membranes is a favorable process.

Binding energy (BE) is an important descriptor in chemistry, which determines thermodynamics and phase behavior of a given substance. BE between two molecules is not directly accessible from the experiment. It has to be reconstructed from cohesive energies, vaporization heats, etc. We report BE for the excited states of two semiconductor molecules – boron-dipyrromethene (BODIPY) and graphene quantum dot (GQD) – with water. We show, for the first time, that excitation increases BE twofold at an optimal separation (energy minimum position), whereas higher separations lead to higher differences. Interestingly, the effects of excitation are similar irrespective of the dominant binding interactions (van der Waals or electrostatic) in the complex. This new knowledge is important for simulations of the excited semiconductors by simplified interaction functions.

In this theoretical work we develop simulations of classical molecular dynamics sequentially combined with quantum calculations to obtain an update of the atomic charges of the aromatic amino acids: Phenylalanine, Tryptophan and Tyrosine in water solution. The charge point model was used to describe the solvent medium and obtain new atomic charges as the aromatic amino acids' dipole moment convergence into solution. Additionally, we developed quantum calculations for GIAO-NMR and absorption spectrum (TD-DFT) spectroscopy to verify the influence of electrical distribution adjustment on the spectroscopic properties of these amino acids in water. Our results show that, in fact, a new electronic distribution of the amino acids is obtained and updates the CHARMM36's atomic charges. In this way the solute-solvent interaction is modified and indicates deviations on the magnetic shielding spectroscopy signature up to −6.9 ppm for carbon atoms, −4.4 ppm for nitrogen atoms and −13.4 ppm for oxygen atoms. Electronic absorption spectrum demonstrates a change in the distribution of electronic transitions.

Here we present calculations of electrical, energetic and magnetic properties of the amino acids arginine, aspartic acid, glutamic acid, histidine and lysine in water solution. The molecules have charged NH31+ and COO1− terminations. The objective is to verify if the atomic charges of the CHARMM36 force field accurately describe the interactions between these amino acids and water, using Molecular Dynamics simulations. For this, the molecules were polarized in solvent medium and we have obtained new atomic charges after the simulations. A comparison of the properties of interest was made using the two charge models and the results show that, in some situations, the updated charge model can better describe the interactions between the analyzed amino acids and the water molecules.

In this work, structural and energetic properties of five peptide membranes are investigated via fully atomistic molecular dynamics simulations. The membranes are made up of peptides with the Ac-I3XGK (X = glutamine (Q), serine (S), asparagine (N), glycine (G) or leucine (L)) amino acid primary sequence. That is, peptides with a charged polar head, composed of one lysine residue, and a neutral tail (I3XG). This work seeks to understand how the insertion of polar amino acids (Q, S, or N) in the peptide neutral tail, at the X position, changes the energetic and structural properties of the peptide membranes, contrasting with membranes composed of just non-polar amino acids (G or L) at this position. We report the results of hydrogen bonds, Coulombic, and van der Waals interactions between the membranes' peptide residues, as well as between each peptide residue and water. It was seen that the I3QGK, I3SGK, and I3NGK membranes perform more hydrogen bonds between their residues than the I3GGK and I3LGK ones. Besides, an important observation is that the polar amino acids would allow the appearance of hydrogen bonds between the peptide β-sheet side chains (forming polar zipper) instead of just between the peptide main chains. This work elucidate importance results that can help in the interpretation of experimental investigations, and the construction of structures in a bottom-up process by given a detailed understanding of the polar zippers formation, which can allow the emergence of flat and wide structures.

In this work, Molecular Dynamics simulation (MD), GIAO-DFT-NMR, and TD-DFT results are obtained to study structural, energetic, dynamics, and spectroscopy properties of polypeptide membranes composed of 6 alanine residue (A6) attached to one histidine residue (H). The histidine residue is simulated with a hydrogen atom bonded in different positions on the aromatic ring: at the epsilon (HSE), or delta (HSD) nitrogen. The results are presented for the A6H(SE or SD) peptide in monomer and membrane configurations to contrast the effects of an organized structure on the peptides' properties studied. Spectroscopy properties are acquired using DFT quantum mechanics calculations combined with MD classical configurations. From 25,000 MD configuration, 100 of them were selected for the calculation of spectroscopic properties. For the A6HSE and A6HSD membranes, in every 100 MD-configurations, we selected just one peptide in the center of the simulation box for quantum mechanics calculation, the other peptides, and water molecules, were considered as charge points. Our results indicate how the absorption spectrum spectroscopy and magnetic shielding constant signature of the A6H(SE or SD) polypeptides are affected when the structure goes from a free monomer in-water solution to a monomer inside a membrane structure in-water solution. The NMR results, acquired at an atomic and molecular level via theoretical studies, reproduce the performance experimentally observed, indicating the reliability of our data. This way, endorsing the methodology used to verify the spectroscopic properties of membranes from a unit monomer.

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.

We present calculations of nuclear magnetic shieldings of the nucleic acids adenine, cytosine, guanine e thymine in liquid water environment in normal thermodynamic condition. The study is based on a sequential approach, where a classical Monte Carlo simulation of the solvated system is performed to generate the different solute–solvent configurations to be used in the following quantum mechanics calculations of magnetic properties. We find that the environment polarization effect shields the unprotonated nitrogens, with solvent shifts for the magnetic shieldings between +10.52 and +48.95 ppm. Protonated and amino nitrogens are less shielded by amounts of −17.77 and +0.22 ppm. The results obtained from supermolecule calculations show that protonated and amino nitrogen magnetic shieldings are particularly sensitive to the hydrogen bond interactions, with solvent shifts between −5.48 and −33.42 ppm, when the first microsolvation shell is explicitly considered. In addition, the supermolecular calculations also show a marked deshielding effect for the hydrogens of the protonated nitrogens, with solvent shifts between −2.43 and −5.12 ppm. There is an overall agreement between the theoretical predictions for the 1H and 15N chemical shifts and the available experimental results.

Magnetic shielding constants for an isolated fullerene C60, cucurbituril CB[9], and the host-guest complex C60@CB[9] were calculated as a function of separation of the monomers. Our results in the gas phase and water indicate a significant variation of the magnetic properties for all atoms of the monomers in the complex and after liberation of fullerene C60 from the interior of the CB[9] cavity. The interaction between the two monomers results in a charge transfer that collaborates with a redistribution of electron density to deshield the monomers. Graphical Abstract NMR spectroscopy alteration on C60@CB[9] host-guest mutual interactionsᅟ.

Magnetic shielding constants for an isolated fullerene C

Stable all-boron fullerene B80 supplements a family of elemental cage molecules. These molecules may initiate a drastic rise to intriguing new chemistry. The principal stability of B80 was recently demonstrated using photoelectron spectroscopy. We report the systematic investigation of different aspects of B80 interactions with small gas molecules—such as carbon dioxide, molecular hydrogen, hydrogen sulfide, hydrogen fluoride, ammonia and sulfur dioxide—employing density functional theory. We found peculiar interactions between B80 and ammonia resulting in the formation of a weak boron–nitrogen covalent bond in one of their local-minimum configurations. Hydrogen fluoride maintains a weak hydrogen bond with B80. The boron fullerene was found to be strongly polarizable, with its electron density distribution changing significantly even in the presence of low-polar gases. The binding energies of the gas molecules to B80 are generally in direct proportion to their dipole moments. Valence bands are predominantly localized on B80. According to the present findings, one of the prospective applications of B80 in future may be gas capture and separation.

We investigate the nuclear isotropic shielding constants and spin-spin coupling for oxygen and carbons atoms of isomers of tartaric acid in gas phase and water solutions by Monte Carlo simulation and quantum mechanics calculations using the GIAO-B3LYP approach. Solute polarization effects are included iteratively and play an important role in the quantitative determination of shielding constants. Our MP2/aug-cc-pVTZ results show substantial increases of the dipole moment in solution as compared with the gas phase results (61-221%). The solvent effects on the {\sigma}(13C) [J(C-C)] values are in general small. More appreciable solvent effects can be seen on the {\sigma}(17O) and J(C-O).

We investigate the first absorption band and the 13C and 17O magnetic shieldings of vitamin E models in chloroform and in water using the S-MC/QM methodology in combination with the TD-DFT and GIAO approaches. The results show that the solvent effects on these spectroscopic properties are small but a proper description of the solvent shift for 17O magnetic shielding of the hydroxyl group in water requires the use of explicit solute–solvent hydrogen bonds. In addition, the effect of the replacement of hydrogen atoms by methyl groups in the vitamin E models only affects magnetic shieldings.

Small monovalent ions are able to polarize carbonaceous nanostructures significantly. We report a systematic investigation of how monovalent and divalent ions influence valence electronic structure of graphene. Pure density functional theory is employed to compute electronic energy levels. We show that the lowest unoccupied molecular orbital (LUMO) of an alkali ion (Li(+), Na(+)) fits between the highest occupied molecular orbital (HOMO) and LUMO of graphene, in such a way as to tune the bottom of the conduction band (i.e., band gap). In turn, Mg(2+) shares its orbitals with graphene. The corresponding binding energy is ca. 4 times higher than that in the case of alkali ions. The reported insights provide inspiration for engineering electrical properties of the graphene-containing systems.

Atomistic molecular dynamics was employed to characterize the stability of nanosheets formed by bolaamphiphilic polypeptides. Two different nanosheets (based on RFL4FR and EFL4FE peptide sequences) were simulated to quantify the impact of the bolaamphiphilic nature of the peptides on the structure and energetics of the formed nanostructures. Our results corroborate the structural results obtained experimentally, indicating consistent values for the separation between the peptide planes as well as for nanosheet thickness. Energy analysis indicates that in general the stability of the nanosheets is dominated by electrostatic interactions and nanosheet-water environment interactions contribute considerably to stability. In general, the nanosheets were found to be very stable especially the EFL4FE system that presents a greater energy of interaction between the components of the system. PMF calculations indicate that the free energy required to remove a peptide from the nanosheet is greater than 250 kJ mol-1 reaching the highest value of 310 kJ mol-1 for the extraction of the peptide in the EFL4FE nanosheet.