Investigation and optimisation of the drying of reduced glutathione by steered molecular dynamics simulation

Abstract

The drying of reduced glutathione from a series of aqueous–ethanol binary solutions at 300 K (below human body temperature) and 330 K (above human body temperature) was investigated in detail by steered molecular simulation and an umbrella sampling method with the Gromacs software package and Gromos96(53a6) united atomic force field. The results show that electrostatic interactions between glutathione and solvent represent the main resistance to drying. When the aqueous solution was gradually changed to pure ethanol, the energy of electrostatic interaction between glutathione and solvent molecules increased by 445.088 kJ/mol, and the drying potential of mean force (PMF) free energy also fell by 253.040 kJ/mol. However, an increase in temperature from 300 to 330 K in the aqueous solution only results in an increase of 23.013 kJ/mol in electrostatic interaction energy and a decrease of 34.956 kJ/mol in drying PMF free energy. Furthermore, we show that hydrogen bonding is the major form of electrostatic interaction involved, and directly affects the drying of glutathione. Therefore, choosing water-miscible solvents that minimise hydrogen-bond formation with glutathione will enhance its drying rate, and this is likely to be more efficient than increasing the temperature of the process. Thus, a power-saving technology can be used to produce the high bioactivity medicines.

Keywords::

• glutathione
• drying
• steered molecular simulation
• PMF free energy
• intermolecular interaction

Acknowledgements

This project was supported by the National Natural Science Foundation of China (Grant No. 51076108), Key Disciplines Program of Shanghai, China (Grant No. T0503 and P0502), the Innovation Funds for International Cooperation of the Shanghai Committee of Science and Technology, China (Grant No. 12430702000) and the Natural Science Foundation of Shanghai, China (Grant No. 12ZR1420400) as well as Alliance Program in Shanghai, China. We are grateful to Prof. Alan Tunnacliffe at University of Cambridge for comments on the manuscript and to Prof. Chen Chenglung at National Sun Yat-Sen University for insights into drying mechanism of glutathione.