Asymmetric channel properties

The individual chemical species with chiral catalytic properties, such as complex, organometallic compounds, organic ligands or molecules, anchored or grafted into the channels of microporous and mesoporous materials, and some microporous compounds possessing chiral channels or their pore structures composed of the chiral motifs, all promise further development and potential application in microporous chiral (asymmetric) catalysis and separations. It is an important frontier direction in the zeolite catalytic field at present. Therefore, the synthesis and assembly of chiral microporous compounds and materials are of particular interest for researchers engaged in porous materials. This is a research field in rapid development. 

Wahlund, K.-G. Giddings, J.C. Properties of an asymmetrical flow field-flow fractionation channel having one permeable wall. Anal. Chem. 1987, 59, 1332-1339. 

The Efimov trimers influence the three-body scattering properties. When an Efimov state intersects the continuum threshold for a < 0 three-body recombination loss is enhanced [79,80], as the resonant coupling of three atoms to an Efimov state opens up fast decay channels into deeply bound dimer states plus a free atom. Such an Efimov resonance has been observed in an ultracold, thermal gas of Cs atoms [77]. For fl > 0 a similar phenomenon is predicted, namely an atom-dimer scattering resonance at the location at which an Efimov state intersects the atom-dimer threshold [81,82]. Resonance enhancement of P has been observed in a mixture of Cs atoms and Cs2 halo dimers [78] see Figure 9.15. The asymmetric shape of the resonance can be explained by the background scattering behavior, which here is a linear increase as a function of a. 

Nevertheless, photoactive MOFs also show unique photocatalytic properties that other materials cannot compete with, especially in organic synthesis applications. MOFs create the opportunity to combine photocatalyst with organocatalyst. One example is the chiral MOF, namely, Zn-PYIl, which exhibits high selectivity for photocatalytic asymmetric a-alkylation of aldehydes, as demonstrated in Fig. 4.13c. The Zn-PYll has also been synthesised via a PSM process of the parent MOF Zn-BClPl (top of Fig. 4.13c), which has been synthesised via solvothermal reaction from L-N-tert-butoxycarbonyl-2-(imidazole)-l-pyrrolidine (l-BCIP) [58]. The key point of the PSM process is the removal of the protective tert-butoxycarbonyl (Boc) moiety to expose active sites, which are likely to be the N — H of pyrrolidine of the L-BCIP molecules that is located within the channels according to dye adsorption test. This has been realised by microwave irradiation in dry lV,lV-dimethyl-formamide solution. The activated Zn-PYIl shows a high reaction efficiency (74 % in yield) and excellent enantioselectivity (92 % ee) in photocatalytic a-alkylation of aliphatic aldehydes compared to that of other MOFs. 

---