Molecular dynamics simulations. The octa-anionic, apo Octacid4 neutralized with 8 sodium ions (or an Octacid4 in a different configuration) was manually solvated with 150 copies of a guest (xylene, dioxane, or naphthalene) using PyMOL V1.7.0.3 () and tLEaP of the AmberTools 16 package (University of California, San Francisco) and then energy-minimized for 100 cycles of steepest-descent minimization followed by 900 cycles of conjugate-gradient minimization to remove close van der Waals contacts using SANDER of the AMBER 11 package (University of California, San Francisco), FF12MClm , and a cutoff of 8.0 Å for noncovalent interactions. The resulting system was slowly heated to 298/340/363/370 K in 30 steps under constant temperature and constant volume, and then equilibrated for 10 6 timesteps under constant temperature of 298/340/363/370 K and constant pressure of 1 atm employing isotropic molecule-based scaling. Finally, a set of 20/40/100 distinct, independent, unrestricted, unbiased, and classical isobaric-isothermal MD simulations was performed for the resulting system using PMEMD of the AMBER 14/16/18 package (University of California, San Francisco), FF12MClm , and a periodic boundary condition at 1 atm and Carbon and oxygen are in orange and red, respectively. Hydrogen, counter ion, and the naphthalene in the bulk phase are not displayed for clarity. The noncovalent interaction gradient isosurfaces show the intermolecular interactions using a blue-red scale with blue indicating strong attractions and red indicating strong repulsions. All conformations shown here were obtained directly (no energy minimization) from Simulation 34 of the 100 6,320-ns simulations at 298 K. The isosurfaces reveal no major repulsion but increasing attraction between the two molecules throughout the pathway. . The linear regression analysis was performed using the PRISM 5 program.