Induced chirality of cage metal complexes switched by their supramolecular and covalent bindingстатья
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Дата последнего поиска статьи во внешних источниках: 18 февраля 2018 г.
Аннотация:An ability of the ribbed-functionalized iron(II) clathrochelates to induce a CD output in interactions with a
protein, covalent bonding or supramolecular interactions with a low-molecular-weight chiral inductor,
was discovered. The interactions of CD inactive, carboxyl-terminated iron(II) clathrochelates with serum
albumin induced their molecular asymmetry, causing an appearance of strong CD signals in the range of
350–600 nm, whereas methyl ester and amide clathrochelate derivatives remained almost CD inactive.
The CD spectra of carboxyl-terminated clathrochelates on supramolecular interactions or covalent
bonding with (R)-(+)-1-phenylethylamine gave a substantially lower CD output than with albumin,
affected by both the solvent polarity and the isomerism of clathrochelate’s ribbed substituents. In supramolecular
assemblies, the bands were most intensive for ortho-substituted carboxyl-terminated clathrochelates.
The ortho- and meta-phenylethylamide cage complexes in tetrachloromethane inverted the
signs of their CD bands compared with those in acetonitrile. It was suggested that the tris-dioximate
metal clathrochelates possess a Russian doll-like molecular system. Because of the distorted TP–TAP
geometry, their coordination polyhedron had no inversion centre and possessed an inherent chirality
together with the equiprobability of its left(Λ)- and right(Δ)-handle twists. The selective fixation of one of
these C3-distorted conformations resulted in the appearance of the CD signal in the range of their visible
metal-to-ligand charge transfer bands. Calculations by DFT methods were used to illustrate the possible
conformations of the macrobicyclic molecules, as well as the intramolecular interactions between the
cage framework and optically active distal substituents responsible for the chirality induction of the
metal-centred coordination polyhedra.