Molecular Dynamics Simulation Study of Chlorophyll a in Different Organic Solvents.

Herein, we present a new model of chlorophyll a for molecular dynamics simulations based on the optimized potentials for liquid simulations force field. The new model was used to study the structural and dynamic properties of the molecule in three different solvents: water, methanol, and benzene. The results of the simulations show that structural and dynamic properties of the chlorin ring are similar in both methanol and benzene. In methanol and water, the magnesium in the chlorin ring binds the oxygen of the solvent molecules with residence times of 2566 and 1300 ps, respectively. In both methanol and benzene, the phytol tail shows a worm-like chain distribution with a larger persistence length for the molecule in benzene. On the contrary, chlorophyll a in water adopts a more compact structure with the phytol chain folded onto the chlorin ring. This conformation is consistent with the expected conformation of the aggregates of chlorophyll a in aqueous environments. Finally, the rotational time constants obtained with our model from the simulations in methanol (125 ps) and benzene (192 ps) are in good agreement with the value extrapolated from the experimental data.