Interactions between lignin and urea researched by molecular simulation

Abstract

Molecular simulations of interactions between urea molecules and lignin polymer have been carried out with the aim of understanding the mechanism of urea slow-release behaviours in lignin–urea materials. It has been found, by docking technology and natural bond orbital analysis, that H-bonds and π-electronic conjugation effect are the main driving forces to keep urea molecules adsorbed on the lignin. In the NPT (isothermal–isobaric ensemble) simulations, mean-squared displacement results show that water molecules can promote the urea molecules gradually away from the lignin. Furthermore, in NVT (canonical ensemble) molecular dynamic simulations, results on diffusion constants of urea molecules in lignin–urea system show that diffusion constant of urea molecules in a urea–water–lignin system increases with an increase in the water content. Conclusions gained from two different kinds of simulation are in agreement with each other and are consistent with the experimental observations.

Keywords:

• lignin
• urea
• molecular docking
• molecular simulation
• diffusion

Acknowledgements

Setting up models composed of lignin, urea and water was done in the Department of Chemistry in Georgetown University using Material Studio 4.3. This work was financially supported by the Natural Science Foundation of China (Grant No. 031070016).