The diffusion coefficient of cucurbituril (CB) and cucurbituril (CB) was determined using pulsed gradient spin−echo nuclear magnetic resonance spectroscopy. Both CB and CB diffuse faster through H2O than D2O with increasing temperature, consistent with the Stokes−Einstein equation where diffusion is proportional to temperature divided by viscosity. The activation energy (EA) was also determined and is larger for CB[n] in 90 % H2O/10 % D2O v/v than in D2O. Both compounds aggregate with increasing concentration between (0.25 and 2)·10−3 mol·L−1. The pH of the solution does not significantly affect the diffusion coefficient of CB and CB, except at very low pH where protonation of the carbonyl groups induces aggregation, which slows their rate of diffusion.
- diffusion coefficient
Grant, M., Wheate, N. J., & Aldrich-Wright, J. R. (2009). Diffusion coefficient of cucurbit[n]urils (n = 6 or 7) at different concentrations, temperatures and pH. Journal of Chemical and Engineering Data, 54(2), 323-326. https://doi.org/10.1021/je800347u