RESUMO
The charge density mismatch concept was applied to the synthesis of high-charge-density silicoaluminophosphate SAPO-69 (OFF) and SAPO-79 (ERI) and zincoaluminophosphate PST-16 (CGS), PST-17 (BPH), PST-19 (SBS), and ZnAPO-88 (MER) molecular sieves. Combined alkali-organoammonium structure direction in these systems is thus enabled. Structure direction is treated from the perspective of stabilizing an ionic framework, the relationships between reaction charge density (OH- /H3 PO4 ), alkali and organoammonium content, and ionicity of tetrahedral framework atoms in successful structure direction are presented.
RESUMO
A solid understanding of the molecular-level mechanisms responsible for zeolite crystallization remains one of the most challenging issues in modern zeolite science. Here we investigated the formation pathway for high-silica LTA zeolite crystals in the simultaneous presence of tetraethylammonium (TEA(+)), tetramethylammonium (TMA(+)), and Na(+) ions as structure-directing agents (SDAs) with the goal of better understanding the charge density mismatch synthesis approach, which was designed to foster cooperation between two or more different SDAs. Nucleation was found to begin with the formation of lta-cages rather than the notably smaller sod and d4r-cages, with concomitant incorporation of TMA(+) and Na(+) into a very small amount of the solid phase with a low Si/Al ratio (ca. 2.5). The overall characterization results of our work demonstrate that sod-cages are first built around the preorganized lta-cages and that d4r-cages are in turn constructed by the progressive addition of low-molecular-weight (alumino)silicate species, which promotes the formation and growth of embryonic LTA zeolite crystals. We also show that the crystal growth may take place by a similar process in which TEA(+) is also incorporated, forming a single LTA zeolite phase with a higher Si/Al ratio (ca. 3.3).
RESUMO
BACKGROUND: NLRP3 (formerly known as CIAS1 or NALP3) encodes a key component of the inflammasome and is a strong candidate gene for Crohn's disease (CD) susceptibility. A recent study reported significant and internally replicated association between CD and six single nucleotide polymorphisms (SNPs) in a regulatory region 5.3 kb downstream of NLRP3. Independent replication is required to verify these findings. METHODS: In all, 1298 CD cases and 1244 healthy controls were genotyped for the six SNPs using Taqman. Single locus, haplotype, and subphenotype analyses were conducted using logistic regression-based methods and PLINK, respectively. RESULTS: No significant associations were found, either on single locus, subphenotype, or haplotype analysis. CONCLUSIONS: Given our high (>90%) power to replicate findings from the index study, our data suggest either a much smaller effect size for the association between NLRP3 and CD susceptibility than previously reported or the possibility of a false-positive result in the index study. Further studies in other populations are required to determine what role, if any, NLRP3 variants play in CD susceptibility.
