Enantiomeric resolution of supramolecular helicates with different surface topographies

Abstract

The enantiomeric resolution of an extended range of di-metallo supramolecular triple-helical molecules are reported. The ligands for all complexes are symmetric with two units containing an aryl group linked via an imine bond to a pyridine. Alkyl substituents have been attached in different positions on the ligand backbone. Previous work on the parent compound, whose molecular formula is [Fe(2)(C(25)H(20)N(4))(3)]Cl4, showed that it could be resolved into enantiomerically pure solutions using cellulose and 20 mM aqueous sodium chloride. In this work a range of mobile phases have been investigated to see if the separation and speed of elution could be increased and the amount of NaCl co-eluted with the compounds decreased. Methanol, ethanol and acetonitrile were considered, together with aqueous NaCl : organic mixtures. Effective separation was most often achieved when using 90% acetonitrile : 10% 20 mM NaCl (aq) w/v, which gives scope for scaling up to incorporate the use of HPLC. The overall most efficient (i.e. fastest) separation was generally achieved where the cellulose column was packed with 20 mM NaCl (aq) and the column first eluted with 100% acetonitrile, then with 75% ethanol : 25% 20 mM NaCl (aq) until the M enantiomer had fully eluted and finally with 90% acetonitrile : 10% 20 mM NaCl (aq) until the P enantiomer had been collected. The sequence of eluents ensured minimum NaCl accompanying the enantiomers and minimum total solvent being required to elute the enantiomers, especially the second one, from the column. No helicate with a methyl group on the imine bond could be resolved and methyl groups on the pyridine rings also have an adverse effect on resolution.

Formation of Metal‐Assisted Stable Double Helices in Dimers of Cyclic Bis‐Tetrapyrroles that Exhibit Spring‐Like Motion

“…In most cases the optical resolution of such racemic mixtures, which would provide various valuable chiral clusters, is not easy to achieve, [7] especially in the case of metal-assisted helices, because of fairly weak metal-ligand interactions.…”

Chiral Metallo–Supramolecular Complexes Selectively Induce Human Telomeric G‐Quadruplex Formation under Salt‐Deficient Conditions

“…[10,32] The enantiomerically pure [Ni 2 L 3 ]Cl 4 was obtained by using a cellulose (ca. 20 mm, Aldrich) column and eluting with 20 mm NaCl aqueous solution.…”

Structural Diversity on Copper(I) Schiff Base Complexes

“…Upon excitation at 360 or 470 nm, 35 display a single broad emission band with the maxima at 540 nm in methanol at room temperature [30]. In recent years, Hannon et al have systematically studied on helical metallo-supramolecular arrays with multidentate Schiff bas ligands L 47 -L 50 [27,28,40,71,72]. For this kind of compounds, the ligand must offer sufficient flexibility for multiple strands to wrap around two or more metal centers, and it should also be sufficiently rigid to impose the same stereochemistry as both metals [27,28].…”

“…Until now, many examples of both single and double-stranded architectures have now been reported [92]. Studies on inorganic helical complexes containing transition metal ions have attracted much attention recently [27][28][29]40,[67][68][69][70][71][72]. In these supramolecular self-assembleies, the formation of the helicates can be described as the result of reading molecular information stored in the ligands by metal ions following the coordination algorithm such as tetrahedral.…”

“…The basic bis-bidentate Schiff base ligands have two arms connected via a ring, or C-C bond, as for example, shown in Schemes 10 -14 [27][28][29][30]32,[35][36][37][38][39][40][66][67][68][69][70][71][72].…”