In nature, proteins have evolved sophisticated cavities tailored for capturing target guests selectively among competitors of similar size, shape, and charge. The fundamental principles guiding the ...molecular recognition, such as self-assembly and complementarity, have inspired the development of biomimetic receptors. In the current work, we report a self-assembled triple anion helicate (host 2) featuring a cavity resembling that of the choline-binding protein ChoX, as revealed by crystal and density functional theory (DFT)-optimized structures, which binds choline in a unique dual-site-binding mode. This similarity in structure leads to a similarly high selectivity of host 2 for choline over its derivatives, as demonstrated by the NMR and fluorescence competition experiments. Furthermore, host 2 is able to act as a fluorescence displacement sensor for discriminating choline, acetylcholine, L-carnitine, and glycine betaine effectively.The choline-binding protein ChoX exhibits a synergistic dual-site binding mode that allows it to discriminate choline over structural analogues. Here, the authors design a biomimetic triple anion helicate receptor whose selectivity for choline arises from a similar binding mechanism.
A series of dinuclear triple-stranded complexes, Fe2L3⊃XX6 X = BF4 – (1), ClO4 – (2), Fe2L3⊃SO42(SO4)5 (3), Fe2L3⊃Br(BPh4)6 (4), Fe2L3(NO3)Br6 (5), and Cu2L3⊃NO3(NO3)6 (6), which incorporate a ...central cavity to encapsulate different anions, have been synthesized via the self-assembly of iron(II) or copper(II) salts with the N,N′-bis5-(2,2′-bipyridyl)methylimidazolium bromide (LBr) ligand. X-ray crystallographic studies (for 1–4 and 6) and elemental analyses confirmed the cagelike triple-stranded structure. The anionic guest is bound in the cage and shows remarkable influence on the outcome of the self-assembly process with regard to the configuration at the metal centers. The mesocates (with different configurations at the two metal centers) have formed in the presence of large tetrahedral anions, while helicates (with the same configuration at both metal centers) were obtained when using the relatively smaller spherical or trigonal-planar anions Br– or NO3 –.
Self-assembly of the Fe(DABP)3SO4 (DABP = 5,5′-diamino-2,2′-bipyridine) or Fe(bipy)3SO4 (bipy = 2,2′-bipyridine) complex with a tripodal tris(3-pyridylurea) ligand (L) results in a layered structure ...that includes a sulfate anion in the cleft of one L molecule. The two compounds, Fe(DABP)3SO4⊂L·10H2O (2) and Fe(bipy)3SO4⊂L·9H2O (3), show very similar sheets formed by the anionic units SO4⊂L2− and cationic building blocks (Fe(DABP)32+ or Fe(bipy)32+). However, there are different water clusters that link the adjacent layers in the two products, that is, water parallelograms and quasi “water cubes” in 2 versus single water molecules, water dimers, and hexamers in 3. The half-encapsulation of sulfate by a single L molecule contrasts with the previously reported full-encapsulation of the sulfate ion by two L molecules in M(H2O)6SO4⊂L2 (1). This different anion encapsulation is traced to the hydrogen-acceptor properties of the pyridyl groups of L together with the hydrogen-bonding properties of the cation secondary coordination sphere for a solid-state packing optimization. In 1 the direct hydrogen bonding from the secondary coordination sphere of octahedral M(H2O)62+ to L-pyridyl helps in the formation of an octahedral cation−anion coordination in the NaCl-type structure. In 2 and 3, crystal water instead of the cations has to satisfy the hydrogen-accepting demands of L. Consequently, a non-spherical and only partly water-surrounded half-encapsulated SO4⊂L2− anion allows for a closer approach of the Fe(DABP)32+ or Fe(bipy)32+ cations than the SO4⊂L22− anion. Then, the similar cation and anion size in 2 and 3 with the Coulomb attraction confined to a two-dimensional plane leads to the formation of a hexagonal BN (or graphite) lattice. Competition experiments with different anions for compound 2 reveal that SO4 2− can be selectively crystallized against NO3 −, OAc−, or ClO4 −.
A fully complementary tris(urea) receptor for phosphate and sulfate anions has been developed by mimicking the scaffold of terpyridine which shows very high affinities and selectivities toward the ...tetrahedral anions.
The reaction of a ditopic diiminopyridine ligand 2,6-bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L) with group 12 metal salts in various solvent systems afforded 12 ...metal−organic coordination complexes, including zero-dimensional (0D) metallomacrocycle, one-dimensional (1D) chain, and two-dimensional (2D) network structures: Zn4Cl8L2·2C7H8·2CH3COCH3·3H2O (1a), {Zn2Cl4L·2CH3OH·2CHCl3·2H2O} n (1b), {ZnCl2L·0.5CH2Cl2·0.5H2O} n (1c), {ZnBr2L·CH2Cl2} n (2), ZnI2L n (3), {Zn(NO3)2L2·2C7H8} n (4), {CdCl2L2·2CH2Cl2} n (5), {Cd(NO3)2L2·CH2Cl2} n (6), {Cd(ClO4)2L2·CH2Cl2} n (7), {Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6·2H2O} n (8), {HgBr2L·CH3CN·0.5CH2Cl2} n (9), and {HgI2L·0.5CH2Cl2} n (10). In these complexes, the semirigid ligand L exhibits four kinds of coordination modes (syn, syn, syn), (syn, syn, anti), (anti, anti, syn), (anti, anti, anti), leading to the formation of various supramolecular structures. Complex 1a is a tetranuclear metallomacrocycle. 1b contains 1D zigzag chains propagating along two different directions, which further pack into a noninterpenetrated three-dimensional (3D) framework by hydrogen-bonding interactions. Complexes 1c, 2, 3, 9, and 10 exhibit a 1D helical chain structure, while 4, 5, 6, and 7 are 1D looped-chain coordination polymers. Complex 8 displays an unprecedented pentanuclear Hg(II)-based 2D network with both HgCl2 and Hg2Cl2 bridges. It is noteworthy that 1a and 1b are supramolecular isomers formed in different solvent systems. The effects of the solvent, metal center, and anion on the different conformations adopted by the ligand and the structure of the products have been discussed. Additionally, the luminescent properties of the complexes have been investigated in the solid state, which display increased ligand-based fluorescence emission at room temperature.
A series of dinuclear chloride‐binding foldamers – (TEA)2L1Cl2·Et2O (1), (TEA)2L2Cl2 (2), (TBA)2L3Cl2 (3), (TBA)2L4Cl2 (4), K(18‐crown‐6)2L4Cl2·H2O (5), and (TBA)2L5Cl2·H2O (6) – have been ...synthesized from naphthyl‐ and anthracenyl‐decorated oligoureas (tetrakisurea to hexakisurea, L1–L5). In the crystal structures of 1–6, the oligoureas adopt helical conformations and two chloride anions are bound inside by the urea groups. The solution binding properties of L1–L5 toward chloride ion were investigated by 1H NMR and fluorescence spectroscopy. Upon binding of the anions, characteristic downfield shifts of the NH signals and enhanced fluorescent emission relative to the free ligands were observed. In DMSO solution, the ligands each display a 1:1 binding ratio to chloride, with association constants of K = 1.16–7.58 × 102 M–1, which contrasts with the 1:2 (host to guest) binding mode in the crystal structures. However, the formation of dinuclear foldamers in the less polar solvent CHCl3 was indicated by the HRMS (ESI) spectra.
A series of dinuclear chloride‐binding foldamers have been synthesized from naphthyl‐ and anthracenyl‐decorated, ortho‐phenylene‐bridged oligoureas (tetrakisurea to hexakisurea).
The location of intermolecular lone pair atom contacts with C6F5X, where X = any atom, was evaluated using the Cambridge Structural Database (CSD). The results establish that it is not possible to ...distinguish the distribution of lone pair atoms in contact with this arene surface from an isotropic distribution of van der Waals contacts. In other words, the CSD provides no evidence for either the directionality or the existence of the lone pair−π interaction with this electron-deficient arene. The current findings are in stark contrast to prior reports that crystal structure data provide (i) examples of lone pair−π interactions and (ii) evidence that lone pair−π interactions are strongly directional. Examination of the previous CSD analyses reveals that in every case the data had been misinterpreted. The most common mistake involves using search criteria to select subsets of contacts and then attaching significance to these selected contacts without the context of the entire contact distribution.
We report a novel strategy for reversible modulation of the supramolecular chirality based on guest‐facilitated heteroleptic assembly of helical anionocages. Two triple‐stranded helical anionocages ...including a chiral cage 1 (A2L13) and a crown ether functionalized achiral cage 2 (A2L23) were synthesized by anion coordination of bis‐monourea‐based ligands and PhPO32−. Both cages exhibited favorable binding with tetraethylammonium TEA+ and cobaltocenium Cob+ (endo‐guest, bound in the cavity). Additionally, cage 2 could reversibly release and recapture the guests through binding the exo‐guest potassium ions (K+) in the crown ethers and subsequent removal of the K+ by 2,2,2‐cryptand. The circular dichroism (CD) spectrum of cage 1 was not significantly affected by guest encapsulation or mixing with the “empty” cage 2. However, in the presence of both cage 2 and an endo‐guest/exo‐guest, the Cotton effects were reversed at 391 nm and significantly enhanced at 310 nm. This observation was attributed to the guest‐facilitated formation of heteroleptic cages that enabled effective chirality transfer from the chiral to the achiral ligands. The CD changes induced by K+ could be fully reversed by removing it with 2,2,2‐cryptand. Sequential addition and removal of K+ allowed reversible modulation of the chirality for at least 10 cycles without significant attenuation.
Guest‐facilitated heteroleptic assembly of helical anionocages has proved effective for chirality modulation of a supramolecular system, which was induced by effective chirality transfer from the chiral to achiral ligands. While both the endo‐guest (bound in the cavity) and exo‐guest (K+, bound in the crown ethers) are effective for chirality modulation, only that induced by K+ could be reversibly switched.
Inspired by the signal transduction function of organophosphates in biological systems, bioactive organophosphates were utilized for the first time as chiral nodes to dictate the stereoselective ...assembly of hydrogen‐bonded anionic cages. Phosphonomycin (antibiotics), tenofovir (antivirals), adenosine monophosphate (natural product, AMP) and clindamycin phosphate (antibiotics) were assembled with an achiral bis‐monourea ligand, thereby leading to the stereoselective formation of quadruple or triple helicates. The extent of the stereoselectivity could be enhanced by either lowering the temperature or adding stronger‐binding cations as templates. With the chiral anionic cages as the host, some enantioselectivity was achieved when binding chiral quaternary ammonium cations.
Organophosphates are critically involved in biological signal transduction, and they can play a similar role in supramolecular systems. Organophosphates have now been utilized as chiral nodes to transfer asymmetry information to hydrogen‐bonded anionic cages, with the supramolecular chirality readily modulated by encapsulated achiral guests, temperature, and protonation/deprotonation of the anions.
In many critical biological processes, host–guest chemistry of protein receptors is regulated by effector molecules to realize cascaded delivery of messenger molecules between different targets. ...Mimicking these natural processes with artificial receptors remains a challenge. Herein, we report a cascaded guest delivery between two anionocages (anion‐coordination‐driven cages), in a reversible manner, wherein binding of K+ ions by a crown ether functionalized, heteroleptic A2L3 (A=anion, L=ligand) anionocage triggers the release and delivery of a TEA+ (tetraethylammonium) guest to another A2L3 anionocage that is a weaker and less K+‐sensitive receptor. Elimination of the K+ with 2,2,2‐cryptand enables recapture of the TEA+ by the crown ether functionalized anionocage and thus realizes a reversed guest delivery. Moreover, integrative self‐sorting of anionocages is firstly reported, leading to heteroleptic cages with enhanced guest binding affinities.
Potassium‐responsive anionocages were developed for cascaded guest delivery in a reversible manner. Binding of K+ by a crown ether functionalized, heteroleptic anionocage triggers the release and delivery of a TEA+ (tetraethylammonium) guest to another anionocage that is a weaker and less K+‐sensitive receptor. This process could be fully reversed by elimination of the K+ with 2,2,2‐cryptand.
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