Self-recognition in helicate self-assembly: spontaneous formation of helical metal complexes from mixtures of ligands and metal ions.

Krämer, Roland; Lehn, Jean‐Maríe; Marquis-Rigault, Annie

doi:10.1073/pnas.90.12.5394

Cited by 533 publications

(308 citation statements)

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“…Even intrinsically weak interactions such as these can have a major effect on the product distribution of the cyclic-helicate-forming reaction (in this case, one handedness of helix being significantly thermodynamically favoured over the other), because ten such interactions are present per pentameric helicate complex. However, the driving force for helix formation is not sufficiently strong to bring about 'self-sorting' [41][42][43] : racemic 2g forms a mixture of oligomers and polymers rather than the two (M)-and (P)-[3g]Cl(PF 6 ) 9 cyclic helicates (Fig. 1).…”

Section: Resultsmentioning

confidence: 99%

A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

394

243

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Knots are being discovered with increasing frequency in both biological and synthetic macromolecules and have been fundamental topological targets for chemical synthesis for the past two decades. Here, we report on the synthesis of the most complex non-DNA molecular knot prepared to date: the self-assembly of five bis-aldehyde and five bis-amine building blocks about five metal cations and one chloride anion to form a 160-atom-loop molecular pentafoil knot (five crossing points). The structure and topology of the knot is established by NMR spectroscopy, mass spectrometry and X-ray crystallography, revealing a symmetrical closed-loop double helicate with the chloride anion held at the centre of the pentafoil knot by ten CH ... Cl -hydrogen bonds. The one-pot self-assembly reaction features an exceptional number of different design elements-some well precedented and others less well known within the context of directing the formation of (supra)molecular species. We anticipate that the strategies and tactics used here can be applied to the rational synthesis of other higher-order interlocked molecular architectures.K nots are important structural features in DNA 1 , are found in some proteins [2][3][4][5] and are thought to play a significant role in the physical properties of both natural and synthetic polymers 6,7 . Although billions of prime knots are known to mathematics 8 , to date the only ones to have succumbed to chemical synthesis using building blocks other than DNA are the topologically trivial unknot (that is, a simple closed loop without any crossing points) and the next simplest knot (featuring three crossing points), the trefoil knot 9,10 . A pentafoil knot-also known as a cinquefoil knot or Solomon's seal knot (the 5 1 knot in Alexander-Briggs notation 11 )-is a torus knot 12 with five crossing points, is inherently chiral, and is the fourth prime knot (following the unknot, trefoil knot and figure-of-eight knot) in terms of number of crossing points and complexity 8,11,12 .Sauvage reported the first molecular knot synthesis 13 , using a linear metal helicate 14 to generate the three crossing points required for a trefoil knot. Although other syntheses of trefoil knots have been reported [15][16][17][18][19][20][21][22] (as have composites of trefoil knots 23 and other molecular topologies such as catenanes [24][25][26][27][28] and Borromean links 29 ), higher-order molecular knots remain elusive. Here, we report on the synthesis of a molecular pentafoil knot that combines the use of metal helicates to create crossover points 30 , anion template assembly to form a cyclic array of the correct size [31][32][33] , and the joining of the metal complexes by reversible imine bond formation 34-37 aided by the gauche effect 38 to make the continuous 160-atom-long covalent backbone of the most complex non-DNA molecular knot prepared to date.So far, attempts to make molecular knots with more than three crossing points by extending the linear helicate strategy of Sauvage to ligands with more coordination sites...

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Section: Resultsmentioning

confidence: 99%

A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

394

243

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“…[16] In conclusion, the reaction of 1 and 2 with n-hexylamine (3) leads to a perfectly self-sorted and dynamic mixture of open circular helicates of different sizes, 4 and 5. Although this involves formation of imine bonds, it is effectively a cyclic version of the self-sorting experiment with linear helicates pioneered by Lehn and co-workers, [5] but instead of using ligand strands that sort according to the number of bidentate binding sites and overall length, 1 and 2 have the same number of binding sites and differ only by a one atom spacing of those binding sites within the strand. [14,15] Nonetheless, each ligand is able to effectively distinguish self from non-self in forming different-sized circular assemblies and the components are able to exchange in-and-out of the circular helicates in a facile manner.…”

Section: Methodsmentioning

confidence: 99%

“…[2] The use of orthogonal recognition elements is a convenient way to achieve sorting in artificial systems, [1,3] but other methods, [4] including subtle differences in ligand design, [5][6][7] can also be remarkably effective. A beautiful example is the classic experiment by Lehn and co-workers [5] in which a mixture of ligand strands containing two to five 2,2'-bipyridine groups spontaneously self-sort into linear double helicates, each containing two ligands with equal numbers of binding sites, in the presence of Cu I ions.We recently described the synthesis of a molecular Solomon link [8] (a doubly entwined [2]catenane [9] ) and a molecular pentafoil knot, [10] each formed through a combination of metal-ligand coordination, an anion template, and geometric restrictions. These closely related structures are derived from tetra- [8] and pentameric [10] circular helicate scaffolds, respectively, and are assembled from up to 20 common, or similar, components.…”

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confidence: 99%

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The Self‐Sorting Behavior of Circular Helicates and Molecular Knots and Links

et al. 2014

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We report on multicomponent self-sorting to form open circular helicates of different sizes from a primary monoamine, Fe II ions, and dialdehyde ligand strands that differ in length and structure by only two oxygen atoms. The corresponding closed circular helicates that are formed from a diamine-a molecular Solomon link and a pentafoil knotalso self-sort, but up to two of the Solomon-link-forming ligand strands can be accommodated within the pentafoil knot structure and are either incorporated or omitted depending on the stage that the components are mixed.The spontaneous segregation of molecular building blocks into discrete species within a mixture is known as selfsorting, [1] a phenomenon that helps to maintain structural control over complex dynamic systems in nature. [2] The use of orthogonal recognition elements is a convenient way to achieve sorting in artificial systems, [1,3] but other methods, [4] including subtle differences in ligand design, [5][6][7] can also be remarkably effective. A beautiful example is the classic experiment by Lehn and co-workers [5] in which a mixture of ligand strands containing two to five 2,2'-bipyridine groups spontaneously self-sort into linear double helicates, each containing two ligands with equal numbers of binding sites, in the presence of Cu I ions.We recently described the synthesis of a molecular Solomon link [8] (a doubly entwined [2]catenane [9] ) and a molecular pentafoil knot, [10] each formed through a combination of metal-ligand coordination, an anion template, and geometric restrictions. These closely related structures are derived from tetra- [8] and pentameric [10] circular helicate scaffolds, respectively, and are assembled from up to 20 common, or similar, components. Here we investigate the self-sorting behavior of both the closed molecular topologies and the open circular helicate scaffolds on which they are based (Figure 1). The study provides insights into the self-assembly processes of the individual species and reveals a subtle interplay between the driving forces and kinetic traps involved in their assembly.Despite their structural similarities (a difference of just two oxygen atoms in length), dialdehydes 1 and 2 react individually with a suitable monoamine and FeCl 2 to generate different-sized circular helicates: tetrameric [8] with 1 and pentameric [10] with 2. To investigate the self-sorting potential of the ligands, a 1:1 mixture of aldehydes 1 and 2 was allowed to react with FeCl 2 and n-hexylamine (3) in [D 6 ]DMSO at 60 8C for 18 h, followed by anion exchange through the addition of an aqueous solution of potassium hexafluorophosphate (Scheme 1). 1 H NMR spectroscopy (Figure 2 a, i) indicated the formation of both tetramer 4 and pentamer 5, the spectrum of the reaction outcome being a superimposition of the spectra from the reaction of the individual aldehydes under similar experimental conditions (Figure 2 a, ii and iii). Electrospray mass spectrometry (ESIMS) confirmed perfect self-sorting, with no detectable formation of...

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“…It is illustrated, for instance, in the self-selection of ligand strands in helicates (8) and building blocks in supramolecular cages, capsules (9-11), and polymers (12).…”

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confidence: 99%

Self-organization by selection: Generation of a metallosupramolecular grid architecture by selection of components in a dynamic library of ligands

Nitschke

Lehn

2003

Proc. Natl. Acad. Sci. U.S.A.

136

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Self-organization by selection is implemented in the generation of a tetranuclear [2 ؋ 2] grid-type metallosupramolecular architecture from its components. It occurs through a two-level self-assembly involving two dynamic processes: reversible covalent bound connection and reversible metal ion coordination. Thus, mixing the aminophenol 3, the dialdehyde 4, and zinc acetate generates the grid complex 1a(Zn) via the assembly of the ligand 2a by imine formation and of the grid by zinc(II) binding. When the same process is conducted in a solution containing a mixture of different aminophenol and carbonyl components, the generation of the grid 1a(Zn) drives the selection of the correct components in a virtual dynamic library of ligands, displaying an amplification factor of >100 and a selectivity of >99%. Component exchange as well as reversible protonic modulation of the assembly͞disassembly process display the dynamic character of the system and its ability to respond͞adapt to changes in environmental conditions. The processes described demonstrate the implementation of a two-level self-organization by selection operating on the dynamic diversity generated by a set of reversibly connected components and driven by the formation of a specific product in a ''self-design'' fashion.S elf-organization (1-7) of chemical entities of higher complexity from their components may be directed by the design of both these components and their mode of assembly, i.e., by the molecular information stored in the components and by the supramolecular processing of this information through the interactional algorithm (the interaction pattern) involved. Its sensitivity to changes in internal or external parameters defines the robustness, or conversely the adaptability, of the organizational program. The implementation of self-organization processes represents a major goal of supramolecular chemistry and rests on the design of adequately programmed chemical systems.The dynamic nature of supramolecular entities furthermore endows the system with selection, adaptation, and evolution features. Thus, in addition to self-organization by design, selforganization by selection may take place, provided a dynamic diversity of constituents is produced in the system on which selection may operate (7). Such diversity generation results when a collection of components undergoes continuous recombination of their connections to yield a set of interconverting constituents. It defines a constitutional dynamic chemistry operating on both the molecular and supramolecular levels (7).The latter involves noncovalent interactions, which are reversible by nature, and is therefore dynamic by essence. It is illustrated, for instance, in the self-selection of ligand strands in helicates (8) and building blocks in supramolecular cages, capsules (9-11), and polymers (12).The former covalent constitutional dynamic chemistry is dynamic by design because it requires the deliberate introduction of reversible covalent bonds to allow for constitutional variation through exc...

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Self-recognition in helicate self-assembly: spontaneous formation of helical metal complexes from mixtures of ligands and metal ions.

Cited by 533 publications

References 8 publications

A synthetic molecular pentafoil knot

A synthetic molecular pentafoil knot

The Self‐Sorting Behavior of Circular Helicates and Molecular Knots and Links

Self-organization by selection: Generation of a metallosupramolecular grid architecture by selection of components in a dynamic library of ligands

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