Solubility Of Small Molecules Research Articles

Novel method to estimate solubility of small molecules in cis-polyisoprene by molecular dynamics simulations

A novel method to predict gas solubility in cis-1,4-polyisoprene is developed using molecular dynamics (MD) simulations under constant particle number, constant pressure and constant temperature (NPT) conditions. Analogous to the experimental sorption technique, the binary-phase model constructed of gas/polymer was prepared. In order to maintain external pressure of the whole system during long NPT-MD runs, the vapor phase was filled with virtual liquid which has no interaction with the gas molecules and has only a repulsive interaction with the polymer. After attaining equilibration of the system, the solubility of oxygen and carbon dioxide in the polymer phase were estimated in the temperature range from 273 K to 373 K by counting the number of gas molecules inside the polymer phase. The average solubility linearly increased with the increase in the external pressure, indicating that Henry’s Law was satisfied. The solubility coefficient obtained from the present method showed good agreement with the experimental data. Concentration profiles of gas molecule showed that it was significantly higher near the interface than both in the gas phase and inside the polymer phase. The distinction between “adsorbed” and “absorbed” gas molecules and also their effect on the solubility was discussed.

A molecular simulation study on gas diffusion in a dense poly(ether–ether–ketone) membrane

Results of molecular dynamics (MD) simulations on transport and solubility of small molecules in amorphous cardo poly–ether–ether–ketone membranes are discussed. Atomistic simulation techniques have proven to be a useful tool for the understanding of structure–property relationships of materials. Although MD are still not an ideal tool for the quantitative prediction of gas permeation properties, this methodology can be used for a detailed description of the complex morphologies and transport mechanisms associated with rigid glassy structures.The diffusion process results from jumps of penetrant molecules between adjacent holes in the polymer matrix. The free volume and the occurring jump mechanism are characterized and visualized with different methods. Constants of diffusion and solubility coefficients have been calculated by the Transition State Gusev–Suter Monte Carlo method revealing a considerable agreement between simulated and calculated data.

Small Molecule Diffusion and Solubility in Adhesives Used for Transdermal Drug Delivery: Infrared-Attenuated Total Reflectance (IR-ATR) Studies.

AbstractA key factor in designing a drug-in-adhesive transdermal drug delivery system is to understand the rate at which the drug and small-molecule excipients can diffuse in the adhesive matrix. The solubility of these components in the adhesive matrix is also of great importance. Results will be presented discussing the use of infrared-attenuated total reflectance (IR-ATR) spectroscopy as a method to measure both diffusion and solubility of small molecules in adhesives. In this method, the donor layer is either a doped adhesive or a free liquid that is placed in contact with a receptor layer which is an undoped adhesive in contact with an IR-ATR crystal. The IR-ATR crystal detects as a function of time any molecules that diffuse from the donor layer into and through the receptor layer.Examples will be discussed of several different experiments that can be performed with this technique. Diffusion coefficients are presented here for testosterone and terpineol in an isooctyl acrylate based adhesive using a doped adhesive donor layer. Diffusion and solubility of liquids in several adhesives has been determined using the experiment where a free liquid is used as the donor. Solubility and diffusion coefficients determined using an oversaturated doped layer containing dispersed, as well as dissolved solute, are presented here for testosterone and for progesterone. Finally diffusion from a doped layer of one adhesive to an undoped layer of a different adhesive was performed as a partition measurement. The parameters that can be extracted from each of these experiments, as well as the limitations of each type of experiment will be discussed.

Solubility of Small Molecules and Their Mixtures in Polyethylene

The solubility of small molecules and their mixtures in polyethylene is studied using a recently proposed united atom force field.1 By comparing the simulation results with experimental data on solubility of small molecules in semicrystalline polyethylene, it is found that crystallinity can severely effect the solubility of a solute, especially if it is highly soluble in the polymer of interest. It is also observed that small molecules form aggregates within the polymer in the liquid phase.

The Sensitivity of Small Molecule Sorption to Annealing in Glassy Liquid Crystalline Polymers

ABSTRACTThe sorption of organic penetrants is found to be sensitive to thermal annealing conditions in a series of glassy, nematic, thermotropic, random copolyesters. Controlled thermal annealing of two polymers in this series permitted a systematic variation of chain packing and, presumably, higher order molecular suprastructure, ranging from a disordered amorphous morphology to More ordered nematic liquid crystalline and semi-crystalline morphologies. The development of liquid crystalline order appears to reduce or preclude small molecule solubility in nematically ordered forms of these polymers.