C11R6 assemblies have been measured working with nitrogen bases to estimate aqueous-equivalent pKa values.39 Unfortunately, this protocol impairs the precise determination of water content material by either Karl-Fischer titration or 1H NMR integration, and could not be utilized to differentiate the acidity of C11R6-A and C11R6-B. Thus, we investigate the potential of structure-dependent acidity to modulate the interaction strength with tri-n-butyl phosphine oxide (Bu3PO) as guest by means of 31P NMR (Figure 5).83,84 The encapsulation of Bu3PO was readily confirmed by 1 H NMR, displaying the development of broad upfield peaks ( = -2.0-0.5 ppm), ordinarily observed for encapsulated guests.24-38 The binding of Bu3PO inside the capsule was additional evidenced by 1H DOSY measurements (Figure S12), with equivalent diffusion for the C11R6 host and upfield peaks (log D = -9.0, see Figure 3b). A downfield chemical shift in 31P NMR is anticipated when a Bu3PO forms a PKCĪ¼ Compound hydrogen-bond adduct with a different species, which include when encapsulated inside C11R6 and the degree of this shift is proportionate to the acidity on the hydrogen-bond donor.83,84 3 peaks (31P 55.0-65.0 ppm) had been consistently observed in the 31P NMR spectra in the encapsulated Bu3PO (Figures S9 and S10). The upfield peak (31P 55.0-64.0 ppm) was assigned for the free Bu3PO by observed correlations towards the protons from the free of charge species by 1 H-31P HMBC (Figure S11). A low intensity peak (31P 64.0-65.0 ppm) was observed in all spectra, using a low intensity that waned with escalating water content. This spectral feature is specifically evident at a minimal water concentration (44.18 mM water, Figure S8), where the TIP60 Species majority in the Bu3PO (three.50 mM) was observed to be encapsulated. Unfortunately, twodimensional methods (e.g., HMBC) could not offer sufficient cross-peaks with which to recognize the originating species by other suggests. With more water this minor peak broadens and diverges in comparison with the big peaks, and wepubs.acs.org/JACSArticleFigure five. Chemical shift difference between totally free and encapsulated Bu3PO observed by 31P NMR at two concentrations, 3.50 mM (black) and 24.00 mM (red) within the presence of C11R6 (five.38 mM). Spectra have been obtained at water contents spanning 43.76-110.19 mM (3.50 mM Bu3PO) and 43.05-86.53 mM (24.00 mM Bu3PO), which were subsequently converted to the proportion of C11R6-B (B) by an empirical model (Figure S13). Inset, a 31P NMR spectrum displaying peaks corresponding to encapsulated (, green) and free (, blue) Bu3PO.infer that exchange between this minor species as well as the observed main peak is unlikely based on the diverging chemical shift. On the basis with the low intensity with the 31P signal, we surmise that this spectral feature doesn’t correspond for the totally free or encapsulated Bu3PO, and its identity is unlikely to interfere with measurements on the C11R6 capsule’s internal acidity. The remaining peak was attributed to the C11R6-associated Bu3PO (31P 60.0-64 ppm) depending on its apparent intensity (Figures S9 and S10). All three peaks had been observed to move in a concerted fashion with changes in water content, which we ascribe to changes in bulk dielectric on the solvent medium.85 The totally free and encapsulated Bu3PO afford distinct peaks in slow exchange (Figure 5, inset). Equivalent to observations produced with 1H NMR (Figure three), differentiation between phosphine oxide encapsulated within C11R6-A and C11R6-B was not observed by 31 P on account of the similarities on the magnetic environments knowledgeable by th