On the properties of the curcumin molecule in water. Exploration of the OPLS - United atom model by molecular dynamics computer simulation

A model for the curcumin molecule based on the united atom OPLS force field is proposed and studied by using molecular dynamics simulations in a vacuum and in water. The value of a dipole moment and its orientation with respect to the molecule symmetry axis in a vacuum are found to be close to the quantum chemical calculations and experimental estimates. We found that water affects shape of the curcumin molecule leading to a more bent conformation in comparison to a vacuum. The surrounding of the curcumin molecule in water is studied in terms of the pair distribution functions and the number of hydrogen bonds formed with water. Density distribution of water around single curcumin molecule is highly heterogeneous and reflects “drying” on the local scale. The number of the hydrogen bonds formed between the enol group of the curcumin acting as a donor and oxygens of water is found to depend strongly on the conformation of this group. An estimate for the self-diffusion coefficient for a single curcumin molecule in water is provided.