Emerging subject for chiral separation science: Cluster boron compounds

Abstract

The structural chirality is an inherent feature of fully synthetic boron cluster compounds that sometimes exhibit unique biochemical effects. HPLC studies with zwitter-ionic cluster boron compounds and electrophoretic studies with boron cluster anions reveal that the chiral separability of these species is remarkably dissimilar to that of organic species, if uncharged cyclodextrins are used as chiral selectors. Furthermore, marked differences were found between the analytical characteristics of the chiral separations of the boron cluster species and those of the organic species with uncharged cyclodextrins. The present-day experimental database indicates that the rules valid for the chiral separations of the organic species cannot be applied to the chiral separations of the boron cluster species without experimental verification. The current extent of research work devoted to the investigation of chirality and chiral separations of boron cluster species is negligibly small in comparison with that devoted to the investigation of chirality and chiral separations of organic species. This makes difficult a reliable explanation of both the particularities observed in chiral separations of boron cluster species with cyclodextrins as chiral selectors and the strange effects related to these separations at the moment.

Chiral separability of boron cluster species studied by screening approaches utilizing polysaccharide‐based chiral stationary phases

“…Zwitterions 1 and 3, whose cluster can tightly contact the stationary phase, have been separated at least once, while enantiomer 2 with substituents on the opposite side of its cluster was never separated. The listed steric indications on the importance of the cluster size, the number of exo‐skeletal substituents and their mutual orientation correspond with the findings from electrophoretic chiral separations of boron cluster anions with native cyclodextrins (Horáková et al ., ).…”

“…Anions 17 and 20 were detected on LC-2, LC-1 and LA-2 with at least one mobile phase within 1 h, but eluted as one peak. Considering the earlier reported photometric detectability of all boron cluster anions listed in Table 1 (Horáková et al, 2004(Horáková et al, , 2011, there are three possibilities for the absence of detection of the anions: irreversible adsorption on the used chiral phases; insolubility in the mobile phases; and elution of peaks after the end of the run (linked to first possibility). The used mobile phases only contained 10% (v/v) of either ethanol or isopropanol, while it is known that methanol and acetonitrile are more powerful solvents for boron cluster species.…”

“…Chiral discrimination can be characterized as a result of coordination of gently tuned intermolecular interactions, which have q mutually rigid arrangement in space. Until now, only structurally chiral boron cluster species, which are free of chiral atoms and other structural elements that cause chirality of organic species, have been separated (Horáková et al, 2011). For such compounds, the rigidity of their three-dimensional clusters guaranteed the rigid space arrangement of participating interactions.…”

“…Chiral species therefore dominate among boron cluster species even if they are free of chiral atoms and other structural elements, which are responsible for the chirality of organic species. Until now, only cyclodextrins have been investigated as selectors in their chiral separations (Horáková et al, 2011); however, they had an efficacy that was surprisingly lower in some cases than what is standardly seen in chiral separations of organic species. Cyclodextrins proved to be highly efficient in HPLC separations of zwitterionic species.…”

Diglycolamide-functionalized task specific ionic liquids for nuclear waste remediation: extraction, luminescence, theoretical and EPR investigations

“…are highly appreciated due to their ability to form strong noncovalent complexes with cyclodextrins. For example, the hostguest interaction between bCD and carborane is used for chromatographic separation 21,22 and for the solubilization of carborane complexes containing platinum(II)-based DNA intercalators. 23,24 Here we use 1,2-closo-carborane (Cb) as a monovalent supramolecular guest molecule for the efficient non-covalent immobilization of biologically active peptides on bCD surfaces (Fig.…”