We report direct observation of entropic effect in determining the folding of a linear dicarboxylate dianion with a flexible aliphatic chain [–O2C-(CH2)6-CO2–] by photoelectron spectroscopy as a function of temperature (18 – 300 K) and degree of solvation from 1 to 18 water molecules. A folding transition is observed to occur at 16 solvent water molecules at room temperature, but at 14 solvent molecules below 120 K due to the entropic effect. The –O2C-(CH2)6-CO2–(H2O)14 hydrated cluster exhibits interesting temperature-dependent behaviors and its ratio of folded over linear conformations can be precisely controlled as a function of temperature, yielding the enthalpy and entropy differences between the two conformations. A folding barrier is observed at very low temperatures, resulting in kinetic trapping of the linear conformation. The current work provides a simple model system to study the dynamics and entropic effect in complex systems and may be important for understanding the hydration and conformation changes of biological molecules.
Revised: October 7, 2010 |
Published: January 17, 2008
Citation
Wang X.B., J. Yang, and L.S. Wang. 2008.Observation of Entropic Effect on Conformation Changes of Complex Systems Under Well-Controlled Temperature Condition.Journal of Physical Chemistry A 112, no. 2:172-175.PNNL-SA-57552.doi:10.1021/jp711205z