Structural aspects of the clustering of curcumin molecules in water. Molecular dynamics computer simulation study

Abstract

We explore clustering of curcumin molecules in water by using the OPLS-UA model for the enol conformer of curcumin (J. Mol. Liq., 223, 707, 2016) and the SPC-E water model. With this purpose, solutions of 2, 4, 8, 12, 16 and 20 curcumin molecules in 3000 water molecules are studied by using extensive molecular dynamics computer simulations. Radial distributions for the centers of mass of curcumin molecules are evaluated and the running coordination numbers are analyzed. The formation of clusters on time is elucidated. The internal structure of molecules within the cluster is described by using radial distributions of the elements of the curcumin molecule, the orientation descriptors, the order parameter and the radius of gyration. The self-diffusion coefficient of solute molecules in clusters is evaluated. The distribution of water species around clusters is described in detail. A comparison of our findings with computer simulation results of other authors is performed. A possibility to relate predictions of the model with experimental observations is discussed.

Aspects of the microscopic structure of curcumin solutions with water-dimethylsulfoxide solvent. Molecular dynamics computer simulation study

“…We begin with the description of the radial distribution of the center of mass (COM) of curcumin species in the solvent of variable composition. From the left-hand panel of figure 4, we learn that 12 curcumin molecules self-assembly into a cluster or clusters, in close similarity to the pure water solvent case in [30], if the solvent contains a small fraction of DMSO molecules, because the radial distributions shown in this panel decay to zero at a certain interparticle separation.…”

“…The chemical structure of the molecule is given in figure 1. The "ball-and-stick" schematic representation of the molecule had been already presented in [27,29,30]. Still, for the sake of convenience of the reader, we show it here again in figure 2.…”

“…Technical details of the simulation procedure are the same as in [29,30]. The geometric combination rules were applied to determine the parameters for the cross interactions (rule 3 of GROMACS software).…”

“…We apply the geometric definition for a cluster. Namely, taking into account the behaviour of the radial distribution of curcumin molecules in pure water explored by us recently [30], we choose here the "cut-off" COM-COM distance 𝑅 c = 0.75 nm, as a criterion for the cluster definition. Hence, all the curcumin molecules satisfying this geometric criterion during the production run are counted as belonging to a cluster.…”