Degree of exchange

Ion Exchange. The exchange behavior of nonframework cations in zeoHtes, eg, selectivity and degree of exchange, depends on the nature of... 

To determine how the degree of exchange between an extrinsic isotope and the intrinsic calcium in the food or meal is affected by the method of incorporating the isotope, the calcium source itself or foods fed with it. 

Increasing z increased the degree of exchange, as more than one sulfonate group can interact with a single cation. 

In addition, for solid samples or peptides in nonaqueous solvents, the amide II (primarily in-plane NH deformation mixed with C—N stretch, -1500-1530 cm-1) and the amide A (NH stretch, -3300 cm-1 but quite broad) bands are also useful added diagnostics of secondary structure 5,15-17 Due to their relatively broader profiles and complicated by their somewhat weaker intensities, the frequency shifts of these two bands with change in secondary structure are less dramatic than for the amide I yet for oriented samples their polarization properties remain useful 18 Additionally, the amide A and amide II bands are highly sensitive to deuteration effects. Thus, they can be diagnostic of the degree of exchange for a peptide and consequently act as a measure of protected or buried residues as compared to those fully exposed to solvent 9,19,20 Amide A measurements are not useful in aqueous solution due to overlap with very intense water transitions, but amide II measurements can usefully be measured under such conditions 5,19,20 The amide III (opposite-phase NH deformation plus C—N stretch combination) is very weak in the IR and is mixed with other local modes, but has nonetheless been the focus of a few protein-based studies 5,21-26 Finally, other amide modes (IV-VII) have been identified at lower frequencies, but have been the subject of relatively few studies in peptides 5-8,18,27,28 ... 

Table I lists the results of spectroscopic studies of iV,iV-dimethylaniline in zeolite samples 1, 2, 3, and 4. The spectral data show that the correlation of the number of different types of sites depends on the temperature of preliminary thermal activation, and the amount of different types of sites depends on the composition of crystals for various samples of zeolites treated at one temperature. Among the zeolites studied, sample 3 differs from samples 1,2, and 4 by its activity in the dark. The crystal compositions show that this sample has the highest degree of exchange of Na+ for NH4+.

To determine the influence of the degree of exchange on zeolite activity, studies were done on samples la, 2a, and 4a (degree of NH4+ exchange 90%). Results of spectroscopic investigations on the adsorption of iV,2V-dimethylaniline in samples la, 2a, and 4a showed that only sample 4a is as active in the dark as sample 3 after pretreatment at 350°, 450°, and 550°C. Samples la and 2a appeared to be inactive in the dark. Photoirradiation of samples la and 2a yielded almost the same results as for samples 1 and 2 except for a slight increase in intensity of the spectral bands for the former samples. 

Few systematic investigations of the behavior of the thermal stability of cation exchanged Y zeolites as a function of modul (Si02/Al203 mole ratio), cation type, degree of exchange, and activation conditions have been published. This work uses the results of IR and ESR spectroscopy to explain the behavior of thermal stability of modified Y zeolites. 

Conditions of Exchange. To prepare the modified samples (Table I) ion exchange was done at 70° C with 0.1 N nitrate solutions of the metal (ammonium) ions. The degree of exchange was determined by analyzing the solid for the amount of sodium and exchanged metal ions remaining. 

Figure 1. Thermal stability (°C) of cation-exchanged zeolites as a function of the degree of exchange (a) (a,b) and modul (c)...

Figure 2. Frequency of the D6-ring band vs. degree of exchange for ion-exchanged zeolites...

Figure S. IR spectra of CO adsorbed on ion-exchanged zeolites. Numbers are degree of exchange...

Figure 4 ESR spectrum (low eld components) of CuNaY zeolites dehydrated at 800° C and taken at room temperature in the X-hand as a function of degree of exchange (numbers on the left)...

In Table 3.1, the ionic compositions of the homoionic samples Na-HC, K-HC, Ca-HC, Mg-HC, and the original HC sample are displayed [18,28], The reported data reveal that Na and K are selectively exchanged in the clinoptilolite-containing zeolite rock, HC. On the other hand, the degree of exchange for the bivalent cations, Ca and Mg, is inferior than those reported for the monovalent cations. 

Structure VI is transformed into the more stable compound VII. This transformation is restricted to NaX zeolites. Although LiX and KX give rise to the formation of species VI at room temperature, carbonate structures were completely absent on CaX, SrX, and BaX at room temperature (280) but were formed at elevated temperatures (286). This behavior of various zeolites, which in detail depends on the degree of exchange, is explained by the location of the exchangeable cations on different sites in the zeolite framework (282). 

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