The design of controlled grafting copolymers is critical in synthesizing effective artificial cellular matrices because of their regulatory role in cellular behavior. However, it is unclear whether poly(2-aminoethyl methacrylate) grafted onto chitosan generated by gamma-radiation-induced graft polymerization in different solvents can influence the physicochemical properties and biotech applicability of the copolymer. This work aims to demonstrate for the first time the effect of various solvents on the synthesis, properties, and biological performance of grafted chitosan using the simultaneous irradiation method. The results proved that the solvent is one of the critical factors affecting the properties of the modified polysaccharide. The degree of grafting showed a solvent-dependent profile. Hexane presented utmost importance concerning the degree of grafting. Ethyl acetate showed the best results in grafting extent and human dermal fibroblast growth. These findings indicate that proper solvent selection determines the possible copolymer use for in vitro engineered skin substitute models.
Chitosan , Chitosan/chemistry , Humans , Methacrylates , Polymerization , Polymers/chemistry , Solvents
Molecular dynamics simulations are performed to study carbonates and ethers that are widely used as electrolytes in energy storage devices. The first type contains in their molecular geometry a hydrocarbon tail of ethylene, propylene, and butylene whereas in the second type, the tail comprises 1,2-dimethoxyethane and 1,2-diethoxyethane. The evaluation of optimized potential for liquid simulations (OPLS), CHARMM, and GROMOS force fields for some of the solvents shows poor agreement with experimental thermodynamic and transport properties leading us to parameterize those solvents using the OPLS parameters as the starting point. A systematic procedure that uses the solubility of the solvents as the target property in simulations with explicit water is applied. The transferability of the parameters of the smallest cyclic or linear molecules was used to simulate systems with longer hydrocarbon chains. The optimized parameter reproduce the experimental solubility of butylene carbonate and 1,2-diethoxyethane in water. The interaction parameters were used to obtain the self-diffusion coefficients of ions of the salt LiPF6 at 1 M concentration in mixtures with ethylene carbonate or propylene carbonate. The simulation results for pure components and mixtures with the new parameters are in excellent agreement with the experimental data.
A new procedure, based on electronic structure calculations that only requires a dipole moment value for a given molecule as input and, from which the charges for all the atoms in it are uniquely determined, is developed and applied to the study of molecular fluids with classical dynamics. The dipole moment value considered for the isolated molecule is the one that reproduces the dielectric constant of its corresponding fluid. Following previous work, the Lennard-Jones parameters are determined to reproduce the liquid density and the surface tension at the liquid-vapor interface. The force field thus obtained leads to a reasonable description of several properties such as heats of vaporization, self-diffusion coefficients, shear viscosities, isothermal compressibilities, and volumetric expansion coefficients of pure substances.
The transferable potential for a phase equilibria force field in its united-atom version, TraPPE_UA, is evaluated for 41 polar liquids that include alcohols, thiols, ethers, sulfides, aldehydes, ketones, and esters to determine its ability to reproduce experimental properties that were not included in the parametrization procedure. The intermolecular force field parameters for pure components were fit to reproduce experimental boiling temperature, vapor-liquid coexisting densities, and critical point (temperature, density, and pressure) using Monte Carlo simulations in different ensembles. The properties calculated in this work are liquid density, heat of vaporization, dielectric constant, surface tension, volumetric expansion coefficient, and isothermal compressibility. Molecular dynamics simulations were performed in the gas and liquid phases, and also at the liquid-vapor interface. We found that relative error between calculated and experimental data is 1.2% for density, 6% for heat of vaporization, and 6.2% for surface tension, in good agreement with the experimental data. The dielectric constant is systematically underestimated, and the relative error is 37%. Evaluating the performance of the force field to reproduce the volumetric expansion coefficient and isothermal compressibility requires more experimental data.
A new strategy to develop force fields for molecular fluids is presented. The intermolecular parameters are fitted to reproduce experimental values of target properties at ambient conditions and also the critical temperature. The partial charges are chosen to match the dielectric constant. The Lennard-Jones parameters, εii and σii, are fitted to reproduce the surface tension at the vapor-liquid interface and the liquid density, respectively. The choice of those properties allows obtaining systematically the final parameters using a small number of simulations. It is shown that the use of surface tension as a target property is better than the choice of heat of vaporization. The method is applied to molecules, from all atoms to a coarse-grained level, such as pyridine, dichloromethane, methanol, and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) at different temperatures and pressures. The heat of vaporization, radial distribution functions, and self-diffusion coeficient are also calculated.
Current force fields underestimate significantly the dielectric constant of formamide at standard conditions. We present a derivation of an accurate potential for formamide, with a functional form based on the OPLS/AA force field. Our procedure follows the approach introduced by Salas et al. ( J. Chem. Theory Comput. 2015 , 11 , 683 - 693 ) that relies on ab initio calculations and molecular dynamics simulations. We consider several strategies to derive the atomic charges of formamide. We find that the inclusion of polarization effects in the quantum mechanical computations is essential to obtain reliable force fields. By varying the atomic charges and the Lennard-Jones parameters describing the dispersion interactions in the OPLS/AA force field, we derive an optimum set of parameters that provides accurate results for the dielectric constant, surface tension, and bulk density of liquid formamide in a wide range of thermodynamic states. We test the transferability of our parameters to investigate liquid/liquid mixtures. We have chosen as case study an equimolar mixture of formamide and hexan-2-one. This mixture involves two fluids with very different polar characteristics, namely, large differences in their dielectric constants and their performance as solvents. The new potential predicts a liquid/liquid phase separation, in good agreement with experimental data, and highlights the importance of the correct parametrization of the pure liquid phases to investigate liquid mixtures. Finally, we examine the microscopic origin of the observed inmiscibility between formamide and hexa-2-one.
Molecular dynamics simulations to study the behavior of an anionic surfactant close to TiO(2) surfaces were carried out where each surface was modeled using three different crystallographic orientations of TiO(2) (rutile), (001), (100) and (110). Even though all three surfaces were made with the same atoms the orientation was a key to determine adsorption since surfactant molecules aggregated in different ways. For instance, simulations on the surface (100) showed that the surfactant molecules formed a hemicylinder structure whereas the molecules on the surface (110) were attached to the solid by forming a hemisphere-like structure. Structure of the aggregated molecules and surfactant adsorption on the surfaces were studied in terms of tails and headgroups density profiles as well as surface coverage. From density profiles and angular distributions of the hydrocarbon chains it was possible to determine the influence of the solid surface. For instance, on surfaces (100) and (001) the surfactant molecules formed molecular layers parallel to the surface. Finally, it was found that in the solids (100) and (110) where there are oxygen atoms exposed on the surface the surfactant molecules were attached to the surfaces along the sites between the lines of these oxygen atoms.
Sodium Dodecyl Sulfate/chemistry , Surface-Active Agents/chemistry , Titanium/chemistry , Adsorption , Molecular Dynamics Simulation , Water/chemistry
