title: Direct observation of atoms entering and exiting L-alanyl-L-valine nanotubes by hyperpolarized xenon-129 NMR.
abstract: The kinetics of gas --> channel and channel --> gas exchange of Xe in self-assembled L-alanyl-L-valine (AV) nanotubes was facilitated by continuous flow hyperpolarized xenon-129 two-dimensional exchange NMR spectroscopy. Cross-peaks due to gas atoms entering or exiting were observed at Xe pressures of 92, 1320, and 3300 mbar, corresponding to Xe fractional occupancies ranging from 0.047 to 0.64. At each pressure, the rate of desorption from the channels was determined by fitting the mixing time dependence of the cross-peak and diagonal-peak signals to a magnetization exchange model, assuming steady-state Langmuir adsorption under hyperpolarized gas flow conditions. The observed rate constant for desorption of Xe from AV nanotubes decreased from 4.5 s-1 to 2.0 s-1 over the occupancy range studied, a finding that is consistent with a decrease in the diffusivity in the channels.
authors.affiliation: Chemistry Department, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Chi-Yuan
authors.initials: CY
authors.lastname: Cheng
authors.forename: Clifford R
authors.initials: CR
authors.lastname: Bowers