Weiliang Cao

Relationship between Al/Mg Ratio and the Stability of Single-layer Hydrotalcite

Abstract On the basis of a single-layer hydrotalcite model, various computations with density functional theory (DFT) were carried out for the purpose of investigating the relationship between the Al/Mg molar ratio and the stability of single-layer hydrotalcite. With the increase in the Al/Mg molar ratio, both Al-O and Mg-O distances gradually became large and reached maximum at the ratio of 7:12. However, once the Al-O-Al triple was formed by continuously increasing the ratio, the case was dramatically different and the hydrotalcite structure phase dissolved. In consideration of the difference of the bond energy between Al-O and Mg-O, the structures formed at Al/Mg molar ratios of 6:13 and 7:12 were much more stable among all the constructed ones. In fact, if these results are extended to single layer hydrotalcite, high symmetry structures with ratios of 1:2 and 1:3 will be easily obtained in experiment. Therefore, in the case, where the formation of the Al-O-Al triple is avoided, the best synthesizing scheme may be heightening the ratio of Al/Mg.

Theoretical Study on the Conformational Conversion of 1,3-Dioxane Inside a Capsular Host

Abstract The mechanism for the conformational conversion of 1.3-dioxane guest encapsulated inside a capsular host was theoretically investigated using semiempirical PM3 method and DFT methods. The free-state process of the conformational conversion of 1,3-dioxane was also investigated to make a comparison between the two different states using the same theory. The influences of the inner phase of the capsule on the conformational conversion of guest molecule were discussed via analyzing the comparative results. It was found that the capsular host could accommodate 1,3-dioxane within its cavity by the weak attractive interactions between host and guest, and it responds to the conformational conversion of guest by the deformation of hydrogen-bonding seam at the middle of the capsule. When entrapped in the capsule, the guest molecule undergoes the conformational conversion from chair form to twist-boat form slower than that under the free condition. The deformation of the capsule is favorable to maximize the attractive interactions between host and guest.