# A Wide-Ranging NMR Probe for Multiscale Structures
## 5 Applications
### Liquids, Mixtures, and Solutions
In this case, MD studies proved that xenon interacted significantly with the flexible and hydrophobic (due to the large charge delocalization) anion. In addition to that, some anions were observed to diffuse in the alkyl domains, making nanosegregation much less defined than in [C\({}_{\text{n}}\)C\({}_{\text{1}}\)im][Cl] ILs. The blurred nanodomain separation and, consequently, the possibility for xenon to explore all the possible environments, made its diffusion dependent on the properties of the overall ionic liquid matrix. Thus, the \({}^{129}\)Xe diffusion coefficient decreased with increasing viscosity, following the typical trend of the diffusion of small species in liquids. The formation of nanosegregated domains has also been recently demonstrated for an hexane/perfluorohexane mixture [66] and for different perfluoroalkylalkanes, which are diblock molecules with the general formula F(CF\({}_{\text{2}}\))\({}_{\text{n}}\)(CH\({}_{\text{2}}\))\({}_{\text{m}}\)H [67]. A theoretical chemical shift of dissolved xenon was calculated assuming a coordination sphere representative of the composition of the bulk, or, in other words, containing a proportion of functional groups interacting with xenon equal to their bulk concentration. Experimental data showed systematic deviations from these values, indicating a shift in the local composition of the mixture compared to the average composition. This, in turn, indicated the nanosegregation between fluorinated and hydrogenated domains, with xenon atoms interacting preferentially with the latter. These results were also confirmed by molecular dynamics simulations. A thorough study on the liquid organization of a series of hydrocarbons has been performed with \({}^{129}\)Xe NMR by [PERSON] and co-workers [68]. The chemical shift of dissolved xenon in 21 different molecules (among \(n\)-alkanes, cycloalkanes, and branched alkanes) was obtained in a wide temperature range. The results were interpreted in terms of solvent density and organization of the chemical groups in the vicinity of the xenon atoms, with the aid of molecular dynamics simulations. For \(n\)-alkanes, the Xe chemical shift depended on the number and proportion of -CH\({}_{\text{3}}\)/-CH\({}_{\text{2}}\) groups, with the former showing the greatest influence. For the branched counterparts, \(\delta\) also depended on the position of these groups. Lastly, for cycloalkanes, it was determined that the various -CH\({}_{\text{2}}\) groups did not interact  
Figure 1: \({}^{129}\)Xe nuclear magnetic resonance (NMR) spectra of xenon dissolved in 1-butyl-3-methylimidazolium-based ionic liquids. The anions are indicated on the left. Reprinted with permission from reference [19]. Copyright 2013 American Chemical Society. equally with xenon, leading to overall lower chemical shifts compared to the corresponding linear or branched counterparts. [PERSON] et al. used xenon NMR to analyze the cavities of \(\alpha\)-cyclodextrintrin [69]. A series of solutions in H\({}_{2}\)O/D\({}_{2}\)O 80:20 and dimethyl sulfoxide (DMSO) with various \(\alpha\)-CD concentrations were analyzed, and the resulting chemical shifts were interpreted with a three-site model comprising a 1:1 complex between Xe and \(\alpha\)-CD, Xe in close environment with the host, and bulk xenon. Fitting of the data to this model provided the true chemical shift of xenon in the host-guest complex, as well as the equilibrium constant of its formation. The latter was an order of magnitude smaller in DMSO compared to the H\({}_{2}\)O/D\({}_{2}\)O mixture, in agreement with the higher solubility of xenon in this solvent with respect to water. Another study on the complexation of xenon was conducted by [PERSON] and co-workers on different modified cryptophanes, soluble in water at biological pH [70]. The chemical shift of bound xenon decreased with increasing the cavity size. Moreover, binding constants were extracted from both \({}^{129}\)Xe and \({}^{1}\)H spectra by signal integration and assuming the formation of a 1:1 complex.