Effects of solvent polarity and temperature on the conformational statistics of a simple macrocyclic polyether

In this work, we present NPT Monte Carlo simulations of the simplest macrocyclic polyether (18-crown-6) in water and carbon tetrachloride solutions at various temperatures. The three-dimensional structure of the ring polyether plays a significant role in determining its binding characteristics. Thus, we study the conformations adopted by the cyclic polyether in various distinct environments. We find that temperature and solvent polarity have an important influence on the crown structure. Our results show that several different conformations are populated in solution. However, the conformational statistics are such that the D_3d structure is the dominant conformation in water, and the C_i structure is the dominant one in CCl₄ solutions. We find that the effect of temperature on the conformational statistics is more pronounced in CCl₄ solutions. Additionally, we determine the structuring of solvent molecules around the crown and find indications of hydrogen bonding in the case of water. We compare our results with experiment and discuss the implications for ammonium cation binding.