Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates

Abstract

'Chirality switching' is one of the most important chemical processes controlling many biological systems. DNAs and proteins often work as time-programmed functional helices, in which specific external stimuli alter the helical direction and tune the time scale of subsequent events. Although a variety of organic foldamers and their hybrids with natural helices have been developed, we highlight coordination chemistry strategies for development of structurally and functionally defined metal helicates. These metal helicates have characteristic coordination geometries, redox reactivities and spectroscopic/magnetic properties as well as complex chiralities. Several kinds of inert metal helicates maintain rigid helical structures and their stereoisomers are separable by optical resolution techniques, while labile metal helicates offer dynamic inversion of their helical structures via non-covalent interactions with external chemical signals. The latter particularly have dynamically ordered helical structures, which are controlled by the combinations of metal centres and chiral ligands. They further function as time-programmable switches of chirality-derived dynamic rotations, translations, stretching and shape flipping, which are useful applications in nanoscience and related technology.

Synthesis, structure, stability and antimicrobial activity of a ruthenium(II) helicate derived from a bis-bidentate “click” pyridyl-1,2,3-triazole ligand

“…Inspired by this work we carried out a preliminary investigation of the antimicrobial properties of the ligand 1a, the corresponding rac-ruthenium(II) helicate 2a along with Hannon's rac-[Fe 2 L 3 ](Cl) 4 helicate and corresponding pyridylimine ligand L ( Table 2 and Supporting information). 4 An initial in vitro screen of these compounds, against both Gram positive (S. aureus) and Gram negative (E. coli) microorganisms, was carried out using agar-based disk diffusion assays (Supporting information). The Ru(II) complex (2a) displayed small zones of inhibition against both S. aureus and E. coli indicating that it had some antimicrobial activity (Table 2).…”

“…In particular helicates [4][5][6][7][8][9][10] have been extensively examined. Pioneering work by Hannon et al showed that a triply-stranded [Fe 2 L 3 ] 4+ (L = N,N 0 -(methanediyldibenzene-4,1-diyl)bis[1-(pyridin-2-yl)methanimine]) helicate [11] had extremely interesting biological properties [12,13].…”

Supramolecular Chirality in Dynamic Coordination Chemistry

“…Metalloporphyrins and coordinatively unsaturated lanthanide complexes are typical examples for chirality induction exhibiting chirality sensing of external substrates via dynamic coordination [29][30][31]. Furthermore, the metal complexes can function as chiral building units for a variety of molecular geometries including linear, triangular, tetrahedral, octahedral, and higher polyhedral structures [32][33][34][35], some of which are easily converted to each other in response to environmental conditions. Their stereoisomers often have similar free energy, which results in labile metal complexes being generated as a racemate and/or coexisting in solution ( Figure 1).…”

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…To date, various types of chemical and other stimuli have been used to achieve dynamic helicity inversion of the helical structures such as polymers, metal helicates, etc. [18][19][20][21][22][23][24]. …”

“…Since the P and M forms are in dynamic equilibrium, we can change the P/M equilibrium ratio by the addition/removal or modification of the chiral auxiliary. This would lead to responsive helicity changes and inversions as described the Section 1.3, which are recognized as one of the hot topics in functional molecular chemistry [18][19][20][21][22][23][24]. ( Figure 3a), we have to convert the enantiomer pair into a diastereomer pair by the introduction of a chiral auxiliary.…”