Influence of Conformational Change and Interligand Hydrogen Bonding in a Chiral Metal–Organic Cage

Abstract

We report about the coordination-driven self-assembly of a chiral bis-pyridyl ligand (1), synthesized from steroidal cholic acid, with Pd­(II) ions to form a chiral metal–organic Pd2(1)4 cage. The self-assembly of the cage was facilitated by favorable conformational change in the alkyl chain of the cholic acid. Interligand hydrogen bonding played a crucial role in directing the formation of a C 4 symmetric cage among different possible isomers, as suggested by DFT studies, and control experiments with different ligands.

Increasing structural and functional complexity in self-assembled coordination cages

“…13, isomer A) was reported by Natarajan et al based on the chiral steroid cholic acid. 93 Another example has been recently reported by the group of Chand, where the self-assembly of naked and cis-protected Pd II ions combined with a non-symmetric ligand having pyridine and aniline donor groups was investigated. Among all the possible assembly products, a combination of NMR and DFT studies proved the selective formation of a cis-[Pd 2 L 4 ] structure with a "two up two down" arrangement of the non-symmetric ligand (Fig.…”

Metallo‐Supramolecular Self‐Assembly with Reduced‐Symmetry Ligands

“…Repeating the self-assembly with ligands lacking one or both of these hydroxyl groups resulted in formation of isomeric mixtures, confirming the importance of the additional noncovalent interactions in driving biased isomer formation. [80] If the energy difference between isomers of self-assembled systems is insufficiently large, a mixture of metallosupramolecular architectures is likely to result. Whilst on the face of it this may be assumed to be an undesirable outcome, it does provide the opportunity to bias isomer formation through the influence of stimuli.…”

A New Mechanically‐Interlocked [Pd2L4] Cage Motif by Dimerization of two Peptide‐based Lemniscates

“…Natarajan et al. have assembled [Pd 2 L 4 ] “cages on steroids” from cholic acid derivatives [22] . We equipped both faces of DNA G‐quadruplexes with pyridine ligands, allowing to bind square‐planar Cu II cations whose distance across the bio‐hybrid helicate could be determined by EPR methods [23] .…”

“…[21] Natarajan et al have assembled [Pd 2 L 4 ] "cages on steroids" from cholic acid derivatives. [22] We equipped both faces of DNA G-quadruplexes with pyridine ligands, allowing to bind square-planar Cu II cations whose distance across the bio-hybrid helicate could be determined by EPR methods. [23] The integration of biocompatible motifs into artificial molecules and assemblies bears application potential for the (multitopic) binding to proteins or other biopolymers.…”