Proton localized

For the clusters containing three A1 atoms, there are still two similar possibilities, OH-III and OH-III, with the proton localized between Si and A1 or betweeen two A1 atoms. Thus, since the H forms of A zeolites are unstable, the existence of the following five types of structural hydroxyls may be expected, with acidity decreasing in the given sequence OH-I, OH-II, OH-III and OH-II, OH-III for each subset. 

In asymmetrically substituted cations, the NMe2 groups are non-equivalent and they are observed as two doublets with different values of the /nmb,nh coupling constants (Table 8). It was suggested that the relationship between these constants can be used for estimating the IHB asymmetry via the proton localization index (PL)98, which is calculated in accordance with equation 6. 

Figure 31. Schematic behavior of the functions v t,(x), v tr(x), v tR(x), and (x2 — Xq), where v iL(x) and v tR(x) are wave functions of a proton localized in the left and right wells of the two-well potential, respectively xq are coordinates of the minimums of the right and the left wells.

Both spin-lattice (motional) and spin-spin processes contribute to TjpCC). Experimental cross-polarization transfer rates from protons in the local dipolar field to carbons in an applied rf field can be used to determine the relative contributions quantitatively. This measurement also requires a determination of the proton local field. Methods for making both measurements have been developed in the last few years [1,2]. For polystyrenes, the spin-lattice contribution to TjpCCO s is by far the larger. This means that the TipCCVs can be interpreted in terms of rotational motions in the low-to-mid-kHz frequency range. 

Thus, the selective broadening of the lines of the protons localized at the surface of the membrane, testifies unambiguously to the localization of the paramagnetic moieties of the CigV" cation radicals near the surface of the lipid bilayer (Fig. 8). 

In the initial state, shown on the left-hand side, the excess is proton localized on the Eigen cation, and the excess proton charge is centered at the position of the donor oxygen atom Od- The free energy profile of the proton as a function of 8jj+ exhibits a nonsymmetric double-well character. 

Ganapathy, S., Kumar, R., Delevoye, L., and Amoureux, J.P. Identification of distinct Brpnsted acidic sites in zeolite mordenite by proton localization and [ A1]- H READPOR NMR spectroscopy. Chem. Commun. 2003, 2076-2077. 

As we have indicated, solids generally give very broad, featureless NMR spectra whilst liquids may give very sharp lines, some times narrower. This would be true, for example, for the proton resonance in ice and liquid water at 273 K. Why is this The answer can only be in the fact that in the liquid the nuclear spins are undergoing much faster and more developed relative motions, i.e., rotations, translations, etc., and this must clearly lead to an averaging away of the dipolar proton-proton local fields responsible for the broad line in the ice. This indeed is the reason and we should then ask ourselves how fast do the motions have to be and about what directions in space must they occur in order that averaging will take place. 

A nonmobile proton localized on an arginine side chain... 

Langer, U, Hoelger, C, Wehrle, B., Latanowicz, L, Vogel, E, and Limbach, H.H. (2000) A N NMR study of proton localization and proton transfer thermodynamics and kinetics in polycrystalline porphycene. /. Phys. Org. Chem., 13, 23-34. 

Fig. 6.13 Proton conduction in water-containing BaCeOs. As oxygen ions move towards each other on account of lattice vibrations, the activation energy for the proton jump is lowered, and the proton changes partner. The initi d situation was shown in Fig. 5.5 (page 116) (however with the proton localized in the centre of the figiu-e). FVom Ref. [120].

---