Structure, Dynamics, and Interaction of the Stationary Phase and Xenon Atoms in the Zorbax SB-C18 HPLC Column Material Studied by Solid State NMR and ¹²⁹Xe NMR

Abstract

This research applied the techniques of CP MAS 29 Si and 13 C, MAS high power decoupling 13 C, and MAS 1 H solid-state NMR, variable-temperature dependent 1 H NMR, 129 Xe NMR, low temperature 1 H diffusion, and two-dimensional exchange 129 Xe NMR to study the structure, dynamics, and interaction of the stationary phase and the xenon atoms in the Zorbax SB-C18 HPLC column material. The solid-state NMR experimental results showed the single binding type of alkylsilane groups, -Si(CH 2 -CH-(CH 3 ) 2 ) 2 (CH 2 ) 17 CH 3 , and the mobile alkyl chains on the silica surface at room temperature. The VT 1 H NMR and 1 H spin diffusion experiments suggested that at low temperatures a large portion of the alkyl chain molecules became immobile in the area where the density of the alkyl chains could be higher, while the rest of the alkyl chains remained somehow mobile in the areas with possibly lower density. The results of the VT 129 Xe NMR experiments showed the solvation of the xenon atoms in the stationary phase, the spatial occupation of the xenon atoms in the void spaces of the column material, and the diffusion of the xenon atoms in the column material. The two-dimensional exchange 129 Xe NMR results at low temperatures displayed the slow xenon diffusion between the pores and the voids between the particles. The two-dimensional exchange 129 Xe NMR spectra also indicate that the amorphous areas of the alkyl chains in the stationary phase experienced slow motions even at a temperature of -140 °C. This research illustrated that solid-state NMR of the stationary phase and 129 Xe NMR of the mobile phase give complementary information concerning the structure, dynamics, and interaction of column materials.

Variability in the Structures of Luminescent [2‐(Aminomethyl)pyridine]silver(I) Complexes: Effect of Ligand Ratio, Anion, Hydrogen Bonding, and π‐Stacking

“…[42] All excitation and emission spectra were recorded at concentrations of 1 × 10 -4 m in acetonitrile glasses at 77 K. The low-temperature solution luminescence was collected to give a general representation of what the solidstate excitation and emission would be, given that in the 77 K glasses there is substantial complex character (polymeric character in the case of compounds 6 and 7). [18,43,44] Luminescence spectra of representative compounds are displayed in Figure 11. A more complete collection of spectra are available in the supporting information.…”

129Xe: A Wide-Ranging NMR Probe for Multiscale Structures

“…HPLC columns are constituted by silica-based materials, often functionalized to enhance their capability to retain apolar compounds, making separation processes more efficient. Some functionalized HPLC materials have been studied employing 129 Xe NMR by the group of Ba [98]. In their study, xenon was chosen as a probe molecule representative of a possible mobile phase, and the structure of the stationary phase along with its interaction with xenon was analyzed.…”