Cancrinite

Figure C2.12.4. Typical polyhedra found in zeolites (a) sodalite cage found in sodalite, zeolite A or faujasite (b) cancrinite or a-cage found in cancrinite, erionite, offretite or gmelinite (c) the 5-ring polyhedron found in ZSM-5 and ZSM-11 (d) the large cavity of the faujasite stmcture and (e) the a-cage fonning the large cavity in zeolite A.

Study of the antacid properties of carbonated disordered cancrinite and its intermediate phase... 

Keywords disordered cancrinite intermediate phase antacid pepsin zeolite. 

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

Due to blockage of the main zeolite channels by anions present in the structure, few applications have been reported for these tectosilicates. However, the presence of carbonate anions could make them suitable as antacids. Our group has worked with a series of natural minerals as antacids, such as clays [4], modified carbons [5] and zeolites[6]. In this way, a carbonated cancrinite and its intermediate phase were tested as an antacid with a synthetic gastric juice. 

Disordered cancrinite and the intermediate phase were synthesized by the previously reported procedure [6], The parameters and the results of the syntheses are summarized in Table 1. 

According to Table 1, our results showed that disordered cancrinite can also be formed by using a medium carbonate concentration (0.86 mol. L"1) and a low temperature (80°C), but higher reaction times (96 and 336 h) are necessary. A low temperature and low NaOH concentration (80°C, 3.07 mol. L"1) and short reaction times (96 h) did not allow the dissolution of the starting material. On the contrary, a high NaOH and carbonate concentration totally dissolved the starting material and any solid phase is determined in this experiment. 

IR spectra did not show differences between the intermediate phase and the disordered cancrinite. Therefore, IR techniques fail when were used to identify these phases. One more effective way to identify disordered cancrinite and the intermediate phase is by using X-ray diffraction (XRD). Fig 1 shows the diffractogram of both tectosilicates. In the intermediate phase, the observed peaks correspond with those reported in the literature[4]. The main differences between both spectra correspond to those peaks placed between 25°<20<35°, which are more intense for the disordered cancrinite [9]. Likewise, the results of specific surface area for the intermediate phase (sample 5) and the disordered cancrinite (sample 6) were 35 and 41 m2/g respectively. The antacid capacity test was carried out with the samples 5 and 6. Fig. 2 shows the relationship between experimental pH versus the mass content of the tectosilicates. The neutralization capacity of these solids is related with its carbonate content which reacts with the synthetic gastric juice to neutralize it. In general, the behaviour of solids is similar the pH increases as the weight of the studied solid is increased. However, a less disordered cancrinite mass amount must be employed to reach a pH= 4 in comparison... 

Figure 1. XRD spectra of the intermediate phase (sample 5) and disordered cancrinite (sample 6)...

In Fig. 3, the pepsin dissolved in HC1, without interaction with any solid, showed a maximum at 272 nm. After interaction with the disordered cancrinite and the intermediate phase, a small decrease in the absorbance maximum of the pepsin spectrum was observed. This small decrease is due to the pepsin adsorption on the solid surfaces. The pepsin activity was also determined by the proteolysis reaction of a denatured haemoglobin solution at different times. Fig. 4 shows the obtained results. One can see, that the enzymatic activities (determined as absorbance), presented by the tested solids were very similar among them. These results show that pepsin enzymatic activity is not lost after the contact the pepsin with the tested solids. Therefore, the absorbance decrease observed in Fig. 4, is produced by the pepsin adsorption on the tectosilicate surface, and not by chemical reactions between pepsin and the tectosilicates... 

This paper represents an effective study of the synthesis, characterization and antacid test of the disordered cancrinite and the intermediate phase. So, it was possible to synthesize the disordered cancrinite in soft temperature conditions. By XRD, IR and the BET surface area confirmed the synthesis of the disordered cancrinite and the intermediate phase. Neutralization tests indicated that disordered cancrinite was more effective than the intermediate phase. Furthermore, the disordered cancrinite was able to keep a pH plateau between 3 and 4 in higher extension than the intermediate phase. The enzymatic activity of pepsin was preserved when the tested solids were contact with it. Finally, these tectosilicates could be used as effective antacid drugs. 

Figure 3 Cross-section depicting the smallest steps present on the surface of each face of crystals with aspect ratios 1.5. Where 1 i) shows the position of the cross-section, lii) shows the cross-section and the corresponding heights and 1 iii) shows a schematic of the possible cancrinite unit of attachment onto the hexagonal face. Where 2i) shows the position of the cross-sections, 2ii) and iv) show the cross-sections and the corresponding heights and 2iii) and v) show schematics of the possible cancrinite unit of attachment onto the side walls.

In summary, zeolite L was found to grow via cancrinite cage incorporation, although different mechanisms of incorporation were observed depending on the face of the crystal. When the crystal habit was modified, the features observed on the hexagonal face varied considerably, suggesting growth had been modified. It is possible that this was caused by the occurrence of defects in the crystal. 

Extraframework cations are needed in anionic zeolites for charge balance, and for several zeolite topologies their locations are well investigated [281, 282]. Different cations have been investigated by solid state NMR in the past with different NMR properties and different project targets. We restrict this section to a tutorial example on sodium cation motion in sodalite and cancrinite structures [283-285], 23Na has a nuclear electric quadrupole moment, and quadrupolar interaction is useful to investigate jump processes, especially when they are well defined. 

The hopping process in the cancrinite cage is only of local nature, and long-range conductivity has been observed only for the sodium cations in the onedimensional 12-ring channels, where the chromate ions are also located [283]. 

Harvey et al. [43] reported the synthesis of alkali beryUophosphate molecular sieves with the RHO, GIS, EDI and ANA shucture topologies and a novel structure, BPH. Simultaneously, the first beryUophosphate mineral species were reported hptopite [with the cancrinite (CAN) topology] by Peacor et al. [50] and pahasapaite (with the RHO topology) by Rouse et al. [51]. 

Peacor, D.R., Rouse, R.C., and Ahn, J.H. (1987) Crystal structure of tiptopite, a framework beryllophosphate isotypic with basic cancrinite. Am. Mineral., 71, 816-820. 

Fig. 13. The nuclear magnetic spin-lattice relaxation rate for water protons as a function of magnetic field strength reported as the proton Larmor frequency at 298 K for 5% suspensions of the particulate stabilized in a 0.5% agar gel presented as the difference plot (A) Zeolite 3A (B) Zeolite 13X (C) Zeolite NaY (D) kaolin with 7 s added to each point to offset the data presentation (E) Cancrinite with 9 s added to each point to offset the data presentation and (F) 0.5% agar gel profile with 10 s added to each point. The solid lines are fits to a power law (68).

The rocks of the NS-N dyke group range from nepheline syenite to sodalite-bearing nephelinolite. The primary phases in the NS-N dyke group are k-feldspar and nepheline, with variable abundances of amphibole, plagioclase, phlogopite, calcite, sodalite, titanite, cancrinite, apatite, clinopyroxene, zircon, chlorite, quartz, pyrochlore, and opaque phases. 

---