Chiral silicate zeolites

Abstract

Chiral zeolites are porous materials of prime importance because of their enantioselective potential applications in catalysis, in separation-science and in chromatography. We report a surprising observation made: as many as many 20 chiral silicate zeolites, none of which were recognized as such in their original publication, exist. In other words, the ''holy grail'' of having a library of such silicates was right under our nose. To be of practical use, such zeolites must reveal molecular level enantioselectivity; we show, for the first time, that chiral silicate zeolites are capable of enantioselective recognition of enantiomers, as revealed from comparative adsorption calorimetry experiments with either D-or L-histidine. The question of how to assign handedness to a chiral zeolite is addressed.

Life Origination Hydrate Theory (LOH-Theory) and the Explanation of the Biological Diversification

“…However, apparently, the chirality of the ribose-like radicals as such is not the only cause capable of initiating the observable chirality of the DNA-hydrate-matrix system. According to the recent works (Dryzun et al 2009;Dryzun and Avnir 2012), ''the proportion of non-biological chiral crystals is as high as 23 %; and only about 6 % of these are labeled as chiral,'' i.e., the natural crystals are chiral much more often than that it was earlier considered. This conclusion was made on the basis of detailed studies of different zeolites and quartzes; their chirality is determined by the imperfectness of the crystals or/and by the occurrence of structural and absorbed asymmetrical foreign particles within the crystal structures.…”

A Pure Silica Chiral Polymorph with Helical Pores

“…The importance of stereochemical control arises from the fact that chiral molecules typically provoke a different response in living beings depending on their chirality, a phenomenon already recognized by Pasteur over 150 years ago. [5] However, those chiral zeolites contain nonhelical pores, and it can be expected that these pores will impose less severe steric restrictions. 5 %) in a reaction catalyzed by a zeolite Beta synthesized using a chiral structure-directing agent (SDA), [4] there have only been significant advances in the last few years.…”

“…[3] Despite an early report claiming a minor enantiomeric excess (ee ca. [5] However, those chiral zeolites contain nonhelical pores, and it can be expected that these pores will impose less severe steric restrictions. The chiral nature of several zeolites had passed unnoticed until very recently, and calorimetric measurements on a natural zeolite indeed suggested a potential for use in processes that entail enantiomorphic molecular discrimination.…”

Exploring new methods and materials for enantioselective separations and catalysis

“…Recently, 20 other well-known zeolites have been identified as chiral, due to the fact that they have chiral asymmetric unit cells. [48] Three new chiral germanosilicate materials were synthesised recently: SOF, [49] STW [49] and ITQ-37. [50] These zeolites crystallise in chiral space groups, so they have a gyroidal structure.…”