Crystallization- and Metal-Driven Selection of Discrete Macrocycles/Cages and Their Metallosupramolecular Polymers from Dynamic Systemic Networks

Reversible imine- and metal-coordination reactions are dynamic enough to produce complex libraries of macrocycles, cages, and supramolecular polymers in solution, from which amplification effects have been identified in solution or during crystallization in response to ligand- and metal-driven selection modes. Crystallization-driven selection can lead to the amplification of unexpected metallosupramolecular architectures. The addition of Ag+ triggered the change of the optimal components, so that the crystallization process showed different ligand preferences than in solution. The most packed constituents are amplified in the solid state, taking into account the optimal coordination of metal ions together with non-specific non-covalent interactions between the macrocycle packed in dimers or trimers in the solid state.

Metal Cation-Driven Dynamic Covalent Formation of Imine and Hydrazone Ligands Displaying Synergistic Co-catalysis and Auxiliary Amine Effects

Optimizing C=N bond formation and C/N component exchange has major significance in Dynamic Covalent Chemistry (DCC). Imine and hydrazone generation from their aldehyde, amine and hydrazine components showed large accelerations in presence of AgOTf or Zn(OTf)₂ , up to 10⁴ for the Zn(II)-(p-anisidine)imine complex. Zn(OTf)₂ and auxiliary p-anisidine together accelerated 630 times the formation of the Zn(II)-hydrazone complex, revealing a strong synergistic effect, traced to very fast initial formation of the reactive Zn(II)-imine complex presenting a C=N bond metallo-activated towards reaction with the hydrazine component. Reactions involving more entities showed kinetically faster and thermodynamically simpler outputs due to dynamic competition within a mixture of higher complexity. Catalytic amounts of metal salts and auxiliary amine gave similar marked rate accelerations and turnover, indicating true catalysis. The synergistic effect achieved by combining metallo- and organo-catalysis points to a powerful co-catalysis strategy of bond-formation in DCC through interconnected chemical transformations.

Self-sorting of porous Cu4L2L'2 metal-organic cages composed of isomerisable ligands

We report the self-sorting of a dynamic combinatorial library (DCL) of metal-organic cages composed of a rotationally isomerisable ligand. Convergence of the DCL occurs upon crystallisation and leads to low-symmetry Cu4L2L'2 cages that display differing porosities based on their overall shape and ligand configuration.

Kinetic and Thermodynamic Modulation of Dynamic Imine Libraries Driven by the Hexameric Resorcinarene Capsule

The composition of dynamic covalent imine libraries (DCL) adapts to the presence of the hexameric resorcinarene capsule. In the presence of the self-assembled capsule, a kinetic and thermodynamic modulation of the imine constituents of the DCLs was observed, which was induced by an unusual predatory action of the capsule on specific imine constituents. More complex 2 × 2 DCLs also adapt to the presence of the hexameric capsule, showing a thermodynamic and kinetic modulation of the constituents induced by the predatory action of the capsule. By cross-referencing experimental data, a good selectivity (up to 66%) for one constituent can be induced in a 2 × 2 DCL.

Chiral superstructures from homochiral Zn2+ , Co2+ , Fe2+ -2,6-bis (aryl ethylimine)pyridine complexes

We report the hierarchical supramolecular organization of metallosupramolecular homochiral complexes 1-Λ-(S,S,S,S)-M²⁺ /1-∆-(R,R,R,R)-M²⁺ and 2- Λ-(S,S,S,S)-M²⁺ /2-∆- (R,R,R,R)-M²⁺ of M²⁺ = Co²⁺ , Fe²⁺ , Zn²⁺ metal ions with chiral pseudo-terpyridine-type ligands: 1-(S,S) or 1-(R,R) = 2,6-bis (naphthyl ethylimine)pyridine and 2-(S,S) or 2-(R,R) = 2,6-bis (phenyl-ethylimine)pyridine. Circular dichroism measurements in solution were used to confirm the enantiomeric nature of all twelve complexes. For crystal structures of 1- Λ- (S,S,S,S)-M²⁺ or 1-∆- (R,R,R,R)-M²⁺ complexes, absolute configurations {∆ (or P), Λ (or M)} were confirmed by refinement of the Flack parameter x: -0.007 ≤ x ≤ 0.11 for the single crystals of 1-Λ-(S,S,S,S)-M²⁺ /1-∆- (R,R,R,R)-M²⁺ , 2- Λ- (S,S,S,S)-Fe²⁺ , and 2-∆- (R,R,R,R)-Co²⁺ .

Amino-ether macrocycle that forms CuII templated threaded heteroleptic complexes: a detailed selectivity, structural and theoretical investigations

Self-sorting behavior of a newly synthesized macrocycle with divalent metal ions and aromatic ligands via pseudorotaxane formation has been described.

Crystallisation-Driven Self-Sorting of H-Bonded Guanidinium or Sodium Sulfonate Constitutional Molecular Frameworks

Four single crystal structures were obtained in order to better understand the difference between the crystallisation-driven formation of solid state organo-sulfonate guanidinium superstructures and their sodium salt analogues. 5-Formyl-2-furfuryl sulfonate and 4,4′-diamino-2,2′-biphenyl disulfonate were chosen as anions due to functional and geometrical considerations together with guanidinium, aminoguanidinium, and sodium cations. 5-Formyl-2-fufuryl sulfonate reacts with aminoguanidinium cation in water leading to an imino-zwitterionic compound, able to form on its own a guanidinium-sulfonate superstructure in crystalline state.

Experimental and theoretical methods for the analyses of dynamic combinatorial libraries

Progresses in spatial and temporal analytical tools open new avenues for the study and control of increasingly complex chemical systems.

Self-sorting of dynamic metallosupramolecular libraries (DMLs) via metal-driven selection

“Metal-driven” selection between finite mononuclear and polymeric metallosupramolecular species can be quantitatively achieved.

Antifungal vanillin-imino-chitosan biodynameric films

Vanillin-chitosan biodynamers have been prepared and structure-morphology correlations revealed the pathway of progressive incorporation of the aldehyde onto chitosan backbones. Such dynamic biopolymers or biodynamers, generated from reversibly interacting components, offer the possibility to address the dynamic covalent behaviour of the reversible imine-bond formation/hydrolysis equilibria between vanillin and chitosan polymeric backbones. The reaction takes place with very low conversion in acidic aqueous solutions (7-12%), but the imine bond formation is amazingly improved (∼80%) when the reaction takes place while solution-solid state transition and solid state phase-organization events occur. The chitosan-vanillin biopolymeric films described here present interesting Candida albicans antifungal activity compared with other common bacterial strands, which suggests the implementation of these biocompatible materials as thin layer protecting systems for medical devices.

The use of electrospray mass spectrometry to determine speciation in a dynamic combinatorial library for anion recognition

The composition of a dynamic mixture of similar 2,2'-bipyridine complexes of iron(II) bearing either an amide (5-benzylamido-2,2'-bipyridine and 5-(2-methoxyethane)amido-2,2'-bipyridine) or an ester (2,2'-bipyridine-5-carboxylic acid benzylester and 2,2'-bipyridine-5-carboxylic acid 2-methoxyethane ester) side chain have been evaluated by electrospray mass spectroscopy in acetonitrile. The time taken for the complexes to come to equilibrium appears to be dependent on the counteranion, with chloride causing a rapid redistribution of two preformed heteroleptic complexes (of the order of 1 hour), whereas the time it takes in the presence of tetrafluoroborate salts is in excess of 24 h. Similarly the final distribution of products is dependent on the anion present, with the presence of chloride, and to a lesser extent bromide, preferring three amide-functionalized ligands, and a slight preference for an appended benzyl over a methoxyethyl group. Furthermore, for the first time, this study shows that the distribution of a dynamic library of metal complexes monitored by ESI-MS can adapt following the introduction of a different anion, in this case tetrabutylammonium chloride to give the most favoured heteroleptic complex despite the increasing ionic strength of the solution.

Adaptation of dynamic covalent systems of imine constituents to medium change by component redistribution under reversible phase separation

A dynamic covalent library of interconverting imine constituents, dissolved in an acetonitrile/water mixture, undergoes constitutional reorganization upon phase separation induced by a physical stimulus (heat) or a chemical effector (inorganic salt, carbohydrate, organic solvent). The process has been made reversible, regenerating the initial library upon phase reunification. It represents the behavior of a dynamic covalent library upon reversible phase separation and its adaptation to a phase change, with up-regulation in each phase of the fittest constituents by component selection. Finally, the system exemplifies the splitting of a 2D (square) constitutional dynamic network into a 3D (cube) one.

Impact of the level of complexity in self-sorting: Fabrication of a supramolecular scalene triangle

The impact of the level of complexity in self-sorting was elaborated through the fabrication of various scalene triangles. It turned out that the self-sorting system with a higher level of complexity was far superior to less complex sorting algorithms.

In situ evaluation of lipase performances through dynamic asymmetric cyanohydrin resolution

A dynamic resolution process based on multiple reversible cyanohydrin formation coupled to lipase-mediated transesterification is demonstrated. The resulting process resulted in the efficient evaluation of complex lipase performances in asymmetric cyanohydrin acylate synthesis. Dynamic systems were generated and resolved in situ, and the effects of the reaction conditions could be directly monitored for the overall system. By this concept, the enzyme activity, chemo- and stereoselectivity for all involved substrates could be simultaneously evaluated.

{2,6-Bis[(4-bromo-phen-yl)imino-meth-yl]pyridine-κN,N',N''}trichlorido-chromium(III)

In the title compound, [CrCl₃(C₁₉H₁₃Br₂N₃)], the Cr³⁺ ion is coordinated by the tridentate 2,6-bis­[(4-bromo­phen­yl)imino­meth­yl]pyridine Schiff base ligand in a fac-octa­hedral geometry. The dihedral angles between the pyridine and benzene rings are 23.9 (6) and 70.7 (1)°.

From 2-fold completive to integrative self-sorting: a five-component supramolecular trapezoid

The amalgamation of two incomplete self-sorting processes into a process that makes quantitative use of all members of the library is described by 2-fold completive self-sorting. Toward this goal, individual metal-ligand binding scenarios were optimized for high thermodynamic stability and best selectivity, by screening a variety of factors, such as steric and electronic effects, pi-pi interactions, and metal-ion specifics. Using optimized, heteroleptic metal-ligand binding motifs, a library of four different ligands (1, 2, 3, 4) and two different metal ions (Zn(2+), Cu(+)) was set up to assess 2-fold completive self-sorting. Out of 20 different combinations, the self-sorting library ended up with only two metal-ligand complexes in basically quantitative yield. To demonstrate the value of 2-fold completive self-sorting for the formation of nanostructures, the optimized, highly selective binding motifs were implemented into three polyfunctional ligands. Their integrative self-sorting in the presence of Zn(2+) and Cu(+) led to the clean formation of the supramolecular trapezoid T, a simple but still unknown supramolecular architecture. The dynamic trapezoid T consists of three different ligands with four different donor-acceptor interactions. Its structure was established by (1)H NMR spectroscopy, electrospray ionization mass spectroscopy, and differential pulse voltammetry (DPV) and by exclusion of alternative structures.