The Bowers Group - University of California at Santa Barbara






		Theoretical Dynamics Data for PEG, PPG, and PTMEG - obtained using molecular mechanics methods

		Theoretical cross-sections of Na⁺PPG5, Na⁺PPG14, Na⁺PTMEG5, and Na⁺PTMEG11 plotted as a function of temperature and time as determined by MD simulations. The molecular dynamics simulations were begun at 200 K and run for 1000 ps. Every ps, the resulting structure was saved and its cross-section calculated. At the end of the simulation the temperature was increased by 100 K and the process repeated. The average cross-sections at each temperature are given as the "theory" points in the plots comparing experimental and theoretical cross-sections. For Na⁺PPG5, the maximum variance in cross-section is ±5 Å² throughout the entire dynamics run. There is also a slight, steady decrease in cross-section from 300 K to 600 K that follows the trend observed in the experimental data. For Na⁺PTMEG5, the maximum variance in cross-section is ±10 Å² at 600 K (twice that of Na⁺PPG5). The average cross-section remains essentially constant from 400 K to 600 K, again in agreement with the trend observed in the experimental data. In both of these oligomers, all 6 available oxygens remain coordinated to the Na⁺ ion throughout the entire dynamics run, essentially holding the oligomer in place. The only difference is in the increased motion involved with the "ring" surrounding the Na⁺ ion. For Na⁺PPG14 and Na⁺PTMEG11, the maximum spread in cross-section increases from ~±10 Å² at 200 K to ±27 Å² (for Na⁺PPG14) and ±35 Å² (for Na⁺PTMEG11) at 600 K. The average cross-section also increases steadily from 400 K to 600 K. In these simulations, the part of the oligomer that is coordinated to the Na⁺ ion remains in place but the part that is remote from the Na⁺ ion unravels at higher temperatures, thus increasing the average "size" or cross-section of the oligomer.