Adaptive binding and selection of compressed 1,ω-diammonium-alkanes via molecular encapsulation in water

Discrimination of Perfluorinated Arenes/Alkanes by Modulable Polyaromatic Capsules

Efficient and selective binding of perfluorocarbons (PFCs), comprising only fluorine and carbon atoms, unlike hydrocarbons, remains quite difficult owing to the repulsive nature of fluorine. Here we describe that a cavity modulation strategy enables metal-linked polyaromatic capsules to quantitatively bind PFCs with excellent selectivity. From a mixture of perfluoroarene and the corresponding perfluoroalkane (i.e., perfluoronaphthalene and perfluorodecalin), a Pt(II)-linked capsule exclusively binds the arenes in water at room temperature, via effective D-A-A-D π-stacking interactions. The size-selective binding toward perfluoroarenes (i.e., perfluoronaphthalene and perfluorobenzene) is improved by using the analogous N-doped capsule from 85% to quantitative selectivity. Furthermore, unlike the Pt(II)-capsule, an isostructural Pd(II)-linked capsule displays the unusual length/shape-selective binding of linear/cyclic perfluoroalkanes (i.e., perfluoroheptane and perfluorodecalin) under similar conditions. Recognition of substituted hydrogen atoms on perfluorobiphenyl can also be accomplished using the Pt(II)-capsule. Various PFCs are thus clearly distinguished for the first time by the modulable polyaromatic capsules under ambient aqueous conditions.

Size-dependent compression of threaded alkyldiphosphate in head to head cyclodextrin [3]pseudorotaxanes

The encapsulation of guests in a confined space enables unusual conformations and reactivities. In particular, the compression of akyl chains has been obtained by self-assembled molecular capsules but such an effect has not been reported in solution for pseudorotaxane architectures. By exploiting the tendency of cyclodextrin (CD) to form head to head [3]pseudorotaxanes and the hydrogen bonding abilities of phosphate groups, we have studied the effect of the CD dimer cavity on the conformation of threaded α,ω-alkyl-diphosphate axles. The formation of [2]pseudorotaxanes and [3]pseudorotaxanes was investigated by a combination of NMR, ITC and X-ray diffraction techniques. In the solid state, the [3]pseudorotaxane with a C₈ axle presents a fully extended conformation with both terminal phosphate groups interacting with hydroxyl groups of the primary rim of CDs. Such hydrogen bonding interactions are also present with the C₉ and C₁₀ axles resulting in a compression of the alkyl chain with gauche conformations in the solid state. NMR studies have shown that this effect is maintained in solution resulting in a size-dependent progressive compression of the alkyl chain by the CD [3]pseudorotaxane architecture for C₉, C₁₀ and C₁₁ axles.

Alkyl chain compression of alkanediphosphate guests was achieved by head-to-head cyclodextrin [3]pseudorotaxanes in a mechanostereoselective self-assembly process.

Studies of the hydrophobic interaction between a pyrene - containing dye and a tetra-aza macrocyclic gadolinium complex

An in vivo and in vitro investigation of the hydrophobic interaction between HPTS and gadolinium(III)-complex of tetra-aza macrocyclic ligand HP-DO3A‡ (Gd(HP-DO3A)) is reported. UV-spectra at variable pH showed that the...

Folding and Unfolding of Acetoxy Group-Terminated Alkyl Chains Inside a Size-Regulable Hemicarcerand

A resorcinarene-based hemicarcerand, which consists of two cavitands covalently linked to each other by four alkyl chains, allows structural expansion and contraction by demetalation and metalation of Cu(I) cations with a size change of approximately 12 Å. This metal-mediated switching of the two states regulates the conformations of acetoxy group-terminated alkyl chains. A guest binding study reveals the encapsulation of heptyl to undecyl chains in metal-free and Cu(I)-coordinated capsules. The chemical shifts of the acetoxy groups of the bound guests are the same in the metal-free capsule, while those in the Cu(I)-coordinated one differ from each other. This indicates that the metal-free capsule regulates its size to the bound guests, while the bound guests adopt their conformations to the cavity of the Cu(I)-coordinated capsules. ¹H NMR measurements and molecular mechanics calculations suggest that the bound guests have extended conformations in the metal-free capsule, while the Cu(I)-coordinated capsule forces the bound guests to adopt folded conformations. The presence of folded conformations is supported by the conformational study with structurally similar capsules and a nonsymmetric guest, allowing us to observe nuclear Overhauser effects stemming from the folded conformations of the guest in the cavity.

Progressive Folding and Adaptive Multivalent Recognition of Alkyl Amines and Amino Acids in p-Sulfonatocalix[4]arene Hosts: Solid-State and Solution Studies

Calix[4]arenes have the ability to encapsulate biomimetic guests, offering interesting opportunities to explore their molecular recognition, very close to biological scenarios. In this study, p-sulfonatocalix[4]arene (C4 A) anions and hydrated alkali cations have been used for the in situ recognition of cationic 1,ω-diammonium-alkanes and 1,ω-amino-acids of variable lengths. NMR spectroscopy illustrates that these systems are stable in aqueous solution and the interaction process involves several binding states or stabilized conformations within the C4 A anion, depending of the nature of the guest. DOSY experiments showed that monomeric 1 : 1 host-guest species are present, while the cation does not influence their self-assembly in solution. The folded conformations observed in the solid-state X-ray single-crystal structures shed light on the constitutional adaptivity of flexible chains to environmental factors. Futhermore, a comprehensive screening of 30 single crystal structures helped to understand the in situ conformational fixation and accurate determination of the folded structures of the confined guest molecules, with a compression up to 40 % compared with their linear conformations.

Mixed Explicit-Implicit Solvation Approach for Modeling of Alkane Complexation in Water-Soluble Self-Assembled Capsules

The host-guest binding properties of a water-soluble resorcinarene-based cavitand are examined using density functional theory methodology. Experimentally, the cavitand has been observed to self-assemble in aqueous solution into both 1:1 and 2:1 host/guest complexes with hydrophobic guests such as n-alkanes. For n-decane, equilibrium was observed between the 1:1 and 2:1 complexes, while 1:1 complexes are formed with shorter n-alkanes and 2:1 complexes are formed with longer ones. These findings are used to assess the standard quantum chemical methodology. It is first shown that a rather advanced computational protocol (B3LYP-D3(BJ)/6-311+G(2d,2p) with COSMO-RS and quasi-rigid-rotor-harmonic-oscillator) gives very large errors. Systematic examination of the various elements of the methodology shows that the error stems from the implicit solvation model. A mixed explicit-implicit solvation protocol is developed that involves a parametrization of the hydration free energy of water such that water cluster formation in water is predicted to be thermoneutral. This new approach is demonstrated to lead to a major improvement in the calculated binding free energies of n-alkanes, reproducing very well the 1:1 versus 2:1 host/guest binding trends.

“Calix[4]-box” cages promote the formation of amide bonds in water in the absence of coupling reagents

Calix[4]box cages promote template synthesis via accelerated amide bond formation upon encapsulation in water.

Pyrene-box capsules for adaptive encapsulation and structure determination of unstable or non-crystalline guest molecules

“Pyrene-box” cages easily crystallize from aqueous solutions and readily encapsulate compounds of biological interest.

Chiral and achiral crystals, charge-assisted hydrogen-bond patterns and self-organization of selected solid diaminium thiosulfates

A series of diaminium thiosulfates, derivatives of diamines: NH₂CH₂CH(CH₃)NH₂ (1) and NH₂(CH₂)_nNH₂, n = 3-6 [(2)-(5)] and thiosulfuric acid were prepared and their structures determined by single-crystal X-ray diffraction analysis. Compounds (1), (2) and (4) turned out to be hydrates. The crystal structure of 1,2-propylenediaminium thiosulfate is chiral and exhibits spontaneous resolution. Crystals for both enantiomers [(1a) and (1b)] were obtained with high enantiometric excess and examined. An extended network of strong, charge-assisted hydrogen bonding of the ⁺N-H...O^- type (also O-H...O and O-H...S for hydrates) is most likely the main factor defining crystal packing and the variable conformation of the cations. The formation of chiral hydrogen-bond motifs - distorted cubans - seems to induce the formation of chiral solid-state structure from achiral components in the case of (4). Diaminium thiosulfates with an odd number of C atoms in the alkyl chain [compounds (1), (2) and (4)] form three-dimensional supramolecular networks, while in the case of diaminium salts with an even number of C atoms [(3) and (5)], two-dimensional layers of hydrogen-bond domains are observed. The aminium thiosulfates were also characterized by elemental analysis, NMR and Fourier transform (FT)-IR spectroscopy. The conformations of α,ω-alkyldiaminium cations in the solid state are discussed and rationalized by DFT calculations.

Adaptive Encapsulation of ω-Amino Acids and Their Guanidinium-Amide Congeners

The binding and the encapsulation of the 6-aminohexanoic acid (1) and 11-aminoundecanoic acid (2) are achieved in aqueous solution and in crystalline Pyrene-box cages. Unexpectedly, the amino-guanidinium AG⁺ and the amino acids 1 or 2 are reacting in aqueous solution in the absence and in the presence of Pyrene-box cages. The formation of an amide bond between a carboxylic acid and the amino-guanidine unit under mild acidic conditions in water without the use a coupling reagent is extremely interesting and unexpected. The resulted adducts AG1 and AG2 show adaptive binding behaviors and compressions.

Protein Camouflage: Supramolecular Anion Recognition by Ubiquitin

Progress in the field of bio-supramolecular chemistry, the bottom-up assembly of protein-ligand systems, relies on a detailed knowledge of molecular recognition. To address this issue, we have characterised complex formation between human ubiquitin (HUb) and four supramolecular anions. The ligands were: pyrenetetrasulfonic acid (4PSA), p-sulfonato-calix[4]arene (SCLX4), bisphosphate tweezers (CLR01) and meso-tetrakis (4-sulfonatophenyl)porphyrin (TPPS), which vary in net charge, size, shape and hydrophobicity. All four ligands induced significant changes in the HSQC spectrum of HUb. Chemical shift perturbations and line-broadening effects were used to identify binding sites and to quantify affinities. Supporting data were obtained from docking simulations. It was found that these weakly interacting ligands bind to extensive surface patches on HUb. A comparison of the data suggests some general indicators for the protein-binding specificity of supramolecular anions. Differences in binding were observed between the cavity-containing and planar ligands. The former had a preference for the arginine-rich, flexible C terminus of HUb.

New "pyrene box" cages for adaptive guest conformations

The possibility of controlling the compression extent and the coiling shape of the 1,12-diammoniumdodecane guest is shown by changing the dimensions of the internal space of the host guanidinium 1,3,5,8 pyrene-tetrasulfonate PTS(4-) crystalline capsules by using guanidinium (G(+)), amino-guanidinium (AG(+)), and diaminoguanidinium (A2G(+)) cations.

Molecular amorphous glasses toward large azomethine crystals with aggregation-induced emission

Imine compounds containing rigid cores and soft aliphatic tails have been designed to generate molecular glasses and large crystals displaying aggregation-induced emission, which makes them interesting candidates for optoelectronic applications.