Self-assembly of supramolecular polymers in water from tetracationic and tetraanionic monomers in water through cooperative electrostatic attraction and aromatic stacking

The cooperative electrostatic attraction and π-π stacking between tetrahedral tetrapyridinium and three tetraanionic tetraphenylethylenes led to the formation of a new series of supramolecular polymers in water.     

Structural fluctuation and concerted motions in F1‐ATPase: A molecular dynamics study

F₁‐ATPase is an adenosine tri‐phosphate (ATP)‐driven rotary motor enzyme. We investigated the structural fluctuations and concerted motions of subunits in F₁‐ATPase using molecular dynamics (MD) simulations. An MD simulation for the α₃β₃γ complex was carried out for 30 ns. Although large fluctuations of the N‐terminal domain observed in simulations of the isolated β_E subunit were suppressed in the complex simulation, the magnitude of fluctuations in the C‐terminal domain was clearly different among the three β subunits (β_E, β_TP, and β_DP). Despite fairly similar conformations of the β_TP and β_DP subunits, the β_DP subunit exhibits smaller fluctuations in the C‐terminal domain than the β_TP subunit due to their dissimilar interface configurations. Compared with the β_TP subunit, the β_DP subunit stably interacts with both the adjacent α_DP and α_E subunits. This sandwiched configuration in the β_DP subunit leads to strongly correlated motions between the β_DP and adjacent α subunits. The β_DP subunit exhibits an extensive network of highly correlated motions with bound ATP and the γ subunit, as well as with the adjacent α subunits, suggesting that the structural changes occurring in the catalytically active β_DP subunit can effectively induce movements of the γ subunit. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Oxymethylcrowned chromene: photoswitchable stoichiometry of metal ion complex and ion-responsive photochromism

Chromene derivatives bearing oxymethyl-12-crown-4 (1), -15-crown-5 (2), -18-crown-6 (3) ether moieties, and non-cyclic analogue (4) were synthesized, and their metal ion binding properties and photochromism were examined. NMR titration with alkali metal ions revealed that 1 formed a 1:2 complex (metal ion: ligand) with Na⁺, while Li⁺ afforded a 1:1 complex of 1. In cases of K⁺ and Rb⁺, the complexes were a mixture of 1:1 and 1:2 complexes, but the formation of 1:1 complex was observed again with Cs⁺. Under UV irradiation, however, the complex stoichiometry of 1 with all alkali metal ions was 1:1. As a comparison of NMR spectra between the Li⁺ and Na⁺ complexes of 1 indicated considerable upfield shift for the chromene moiety of the Na⁺ complex, π-π stacking of the chromene moiety seems to induce formation of the 1:2 complex. These results indicate that the chromene moiety is not only to show photochromism but also to induce aggregation to form the 1:2 complex resulted in switching of the complex stoichiometry by UV irradiation. The formation of 1:2 complex appeared only with 1 because flexibility of the crown moieties for 2 and 3 interfered the formation of 1:2 complex. Studies on photochromism in the presence of a metal ion demonstrated that the chromene derivatives bearing crown ether moieties show ion-responsive photochromism depending on the metal ion binding ability of their crown ether moieties.     

Synthesis, crystal structure and properties of cobalt(II) and nickel(II) coordination polymers supported by functionalized dicarboxylate ligands

Four new coordination polymers of cobalt(II) and nickel(II) with functionalized dicarboxylate ligands, namely, [Co^IIL¹(2,2′-bpy)(H₂O)] (1), [Ni^IIL¹(2,2′-bpy)(H₂O)]·H₂O (2), [Co^II₂(L²)₂(2,2′-bpy)₂(H₂O)] (3) and [Ni^II₂(L²)₂(2,2′-bpy)₂(H₂O)] (4), where H₂L¹ = 2,5-dibenzoylterephthalic acid, H₂L² = 4,6-bis(4-methylbenzoyl)isophthalic acid and 2,2′-bpy = 2,2′-bipyridine, were synthesized and characterized by elemental analysis, IR spectra and thermogravimetric analysis. Complex 1 exhibits a zigzag chain with a C–Hπ interaction between the phenyl ring proton and the phenyl ring of an adjacent chains to form a 2D supramolecular sheet. Complex 2 contains two helical chains which extend into 2D via a C–Hπ interaction between the pyridine ring proton and the pyridine ring. Complexes 3 and 4 are isomorphous with helical chains that extend in the same direction and further link to one another by supramolecular forces into a 2D structure. Moreover, magnetic and luminescence properties have been investigated for 1 and 2, respectively.     

Novel coumarin-based containing denrons selective fluorescent chemosesor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a novel coumarin-based dendrons derivative CD and its chemical structure was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor CD showed an obvious “on-off” fluorescence quenching response toward Cu²⁺ with a maximum quenching efficiency of 99.8%. The CD-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions. The detection limit of the sensor CD was 0.29?×?10^?6?M to Cu²⁺ and 2.39?×?10^?9?M to PPi. In addition, the sensor CD showed a 1:1 binding stoichiometry to Cu²⁺ and the sensor CD-Cu²⁺ showed a 2:1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.2). The stable pH range of sensor CD to Cu²⁺ and CD-Cu²⁺ to PPi was from 3 to 8.     

Branched supramolecular polymers formed by bifunctional cyclodextrin derivatives

Branched supramolecular polymers have been prepared from the mixture of 3-cinnamamide-α-CD (1) and 3-N^α-cinnamamidehexancarbonyl-N^?-cinnamamide-lysinamide-α-CD (3) and from the mixture of 3-cinnamamidehexanamide-α-CD (2) and 3. Compounds 1 and 2 formed a linear supramolecular polymer, whereas compound 3 having two guest moieties formed a hyperbranched supramolecular polymer. Physical properties of these supramolecular polymers were studied by viscosity measurements in aqueous solutions. When compound 3 was added to the solution of compound 2, the η_sp/C value of the mixture of 2 and 3 was found to be much higher than that of compound 2. These results indicate that compound 3 functions as a branching moiety to increase the viscosity. Supramolecular polymers consisting of compound 2 or 3 did not show the viscosity increase, whereas the mixture of 2 and 3 gave highly viscous solutions and formed fibers from the concentrated aqueous solutions. It is caused by the branching of linear supramolecular polymers with compound 3 and hydrophobic and/or hydrogen bonding interactions between supramolecular polymers.     

A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a new coumarin based fluorescent chemosensor 1, in which tren and quinolone are introduced as receptors for sequential recognition of Cu²⁺ and PPi. The structure of chemosensor 1 was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. Sensor 1 showed an obvious “on-off” fluorescence quenching response toward Cu²⁺, and the quenching efficiency reached a maximum of 99.6% with the addition of 20 equiv. of Cu²⁺. The 1-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions, especially HPO₄^2? and H₂PO₄^?. The detection limit of sensor 1 was 1.9?×?10^?6?M to Cu²⁺ and 5.96?×?10^?8?M to PPi. In addition, sensor 1 showed a 1:1 binding stoichiometry to Cu²⁺ and sensor 1-Cu²⁺ showed a 2: 1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.4). The stable pH range of sensor 1 to Cu²⁺ and 1-Cu²⁺ to PPi was from 4 to 8.     

Two Isostructural Lanthanide Coordination Frameworks Assembled from H3nbtc as the Single Ligand: Syntheses, Crystal Structures, and Luminescence

Two new isostructural coordination polymers, namely, [Ln(nbtc)·2H₂O] _n [Ln = Eu (1), Tm (2)] (H₃nbtc = 5-nitrobenzene-1,2,3-tricarboxylic acid), have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. Both compounds are sandwich-like 2D layered network built by the 1D Ln-carboxylate chains and nbtc^3? linkers, displaying the same 3D supramolecular network via intermolecular hydrogen bonds. The photoluminescence and lifetime of 1 in the solid state has also been investigated.     

Inclusion of Ethyl Acetoacetate Bearing 7‐Hydroxycoumarin Dye by β‐Cyclodextrin and its Cooperative Assembly with Mercury(II) Ions: Spectroscopic and Molecular Modeling Studies

The inclusion of the fluorescent organic dye, ethyl 3‐(7‐hydroxy‐2‐oxo‐2H‐chromen‐3‐yl)‐3‐oxopropanoate ( 1 ) by the host β‐cyclodextrin (β‐CD), and its response toward mercuric ions (Hg²⁺), was studied by UV/Vis, fluorescence, and ¹H NMR spectroscopic analyses, mass spectrometry and molecular modeling studies. ¹H NMR measurements together with molecular modeling studies for dye 1 demonstrate that it exhibits two tautomeric forms (keto and enol); however, when the dye is included into the β‐CD cavity, the enol form predominates. Moreover, by using spectroscopic and spectrometry techniques, a 1:1 stoichiometry was determined for the complexes formed between dye 1 (enol form) and β‐CD, with a binding constant (K_b1=1.8×10⁴ m ^?1) and for the dye 1 (keto form)‐Hg²⁺ (K_b2=2.3×10³ m ^?1). Interestingly, in the presence of 1 –β‐CD complex and mercuric ions, a ternary supramolecular system (Hg– 1 –β‐CD complex) was established, with a 1:1:1 stoichiometry and a K_b3 value of 4.3×10³ m ^?1, with the keto form of the dye being the only one present in this assembly. The three‐component system provides a starting point for the development of novel and directed supramolecular assemblies.     

One-dimensional and two-dimensional coordination polymers constructed from copper(II) nodes and polycarboxylato spacers: Synthesis,crystal structures and magnetic properties

Four new coordination polymers were obtained by employing polycarboxylato spacers and cationic copper(II) complexes as nodes: ^∞₂[Cu₃(trim)₂(NH₃)₆(H₂O)₃] (1); ^∞₁[Cu(tmen)(dhtp)] (2), ^∞₁[Cu(tmen)(hitp)(H₂O)] (3), ^∞₁[Cu(tmen)(nitp)] (4). (H₃trim = trimesic acid, H₂dhtp = 2,5-dihydroxy-terephthalic acid; H₂hitp = 5-hydroxy-isophthalic acid, H₂nitp = 5-nitro-isophthalic acid; tmen = N,N,N′,N′-tetramethyl-ethylenediamine). The crystal structures of the four compounds have been solved. Compound 1 consists of 2D coordination polymers with heart-shaped meshes, while compounds 2–4 contain infinite zigzag chains. The role of the hydrogen bond interactions in sustaining the supramolecular solid-state architectures in compounds 1 and 3 is discussed. The cryomagnetic investigation of compounds 1, 2, and 4 reveals antiferromagnetic interactions between the copper ions.     

Toward supramolecular polymers incorporating double cavity cucurbituril hosts

We describe the synthesis of a series of guests (1-6) containing two adamantylammonium ions separated by xylylene spacing groups and their complexation properties toward double cavity cucurbituril host bis-ns-CB[10]. We observed the preferential formation of 1:1, 2:2, and oligomeric complexes rather than the desired n:n supramolecular polymers. Guest 7, which contains a longer biphenyl spacer successfully precludes the formation of the 1:1 complex but results in the formation of the 2:2 complex (bis-ns-CB[10]₂·7₂) rather than supramolecular polymer. Guest 8, which contains adamantylammonium, p-xylylene diammonium, and hexanediammonium ion binding regions is shown to reversibly form 2:2 and 1:2 complexes (bis-ns-CB[10]₂·8₂ and bis-ns-CB[10]·8₂) in response to changes in host:guest stoichiometry. Lastly, this equilibrium can be manipulated by the addition of exogenous CB[6], which selectively targets the hexanediammonium ion binding region of 8 and delivers the penta-molecular complex bis-ns-CB[10]·8₂·CB[6]₂.     

Metal coordination architectures of triazole-based ligands: Effect of the backbone of bridging ligands on the construction of polymers

In our efforts to investigate the influence of the backbone of different triazole-based bridging ligands on the structure of their metal complexes, four new coordination polymers, {[Cu(L¹)₂(H₂O)₂]Cl₂}_n (1), [Cu(L²)₂Cl₂]_n (2), [Co(L²)₂(SCN)₂]_n (3), and [Cu(L³)₂(NO₃)₂]_n (4), (L¹ = 1,2-bis(triazol-1-ylmethyl)benzene, L² = 1,3-bis(triazol-1-ylmethyl)benzene, L³ = 1,4-bis(triazol-1-ylmethyl)benzene), have been synthesized. All the complexes have been structurally characterized by IR, elemental analysis and single-crystal X-ray diffraction. Structural analyses show that 1 and 4 possess 2D coordination networks with (4,4) topology, and 1 shows a diagonal–diagonal inclined interpenetration. 2 and 3 are isostructural and feature 1D double chain, which further connected by C–H···Cl or π···π weak interactions to form 2D supramolecular frameworks. The results show that the structures of ligands (with different non-coordination backbone spacers) play important roles in the formation of such coordination architectures. Furthermore, EPR (Electron Paramagnetic Resonance) spectra of Cu^II complexes (1, 2, and 4) have been investigated in the solid state at room temperature.     

Adsorptive and affinity linear sweep voltammetry for the determination of singulair in tablets and its interaction with human serum albumin

A new simple, sensitive and reliable adsorptive and affinity linear sweep voltammetric method at in situ mercury film electrode for the determination of singulair in tablets and its interaction with human serum albumin (HSA) was investigated. The solubility of singulair in aqueous media was enhanced by inclusion with hydroxypropyl-β-cyclodextrin (HPβCD). The nature of the electrochemical process of singulair was studied by affinity cyclic voltammetry (ACV). Reproducibility of the proposed method was checked giving interday precision of 0.073 standard deviation. The limit of detection and limit of quantification were 0.05 and 0.16 fg/L, respectively. In the present work, singulair was interacted with HSA by 1: 1 stoichiometry to form electroinactive supramolecular complex. The binding constant was precisely estimated by coupling affinity linear sweep voltammetry (ALSV) and ACV with non-linear regression analysis based on the shifting of analyte peak potentials. The proposed experiments and data analysis could be used to investigate the binding constant of drug with protein within one hour.     

Naphthalene-derived Al3+-selective fluorescent chemosensor based on PET and ESIPT in aqueous solution

A simple fluorescent chemosensor HL based on naphthalene with high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal cations in fully aqueous solution to enhance the potential applications of the fluorescent chemosensor was developed. HL exhibited a significant fluorescence enhancement at 475?nm in the presence of Al³⁺ over other competitive metal ions with a low detection limit of 0.43?μM due to the inhibition of the photo induced electron transfer (PET) and the excited-state intramolecular proton transfer (ESIPT). The 1:1 binding stoichiometry between HL and Al³⁺ was corroborated by the Job plot and the ESI-MS spectrum. Importantly, the reversible recognition process of HL to Al³⁺ will make HL could be used circularly and repeatedly in practical applications by addition of Na₂EDTA. In addition, the binding behavior and sensing mechanism of HL to Al³⁺ were illustrated in detail by the ¹H NMR titration experiment.     

Structure of benzo- and dibenzocrown ethers and their H-bonded adducts. 4. Structural motifs in the 2,4-dithiouracil complexes with 4-bromo- and 4-nitrobenzo-18-crown-6, [2.4]dibenzo- and thia[1.5]dibenzo-18-crown-6

Four novel complexes of 2,4-dithiouracil (pyrimidine-2,4(1H,3H)-dithione, DTU) with 18-membered benzo- and dibenzo-crown ethers were synthesized in approximately the same conditions and studied by single crystal diffraction. Hydrogen bonding was observed to be the most important for the complexation in the solid state but π–π interactions also contribute to it. The crystalline monohydrates of the 1:1:1 stoichiometry are recorded for 4-bromo- and 4-nitrobenzo-18-crown-6 (complexes 1 and 2), while complexes with [2.4]dibenzo- and thia[1.5]dibenzo-18-crown-6 (complexes 3 and 4) represent anhydrous adducts of the 2:2 ratio. The crystal structures reveal three supramolecular structural motifs: the alternative chain for the ternary complex 1 and two types of capsules for complexes 2?4 where the DTU dimers are encapsulated inside the space restricted by two crown molecules.     

Anion recognition through hydrogen bonding by adamantane-dipyrromethane receptors

Adamantane-dipyrromethane (AdD) receptors [di(pyrrole-2-yl)methyladamantane (1), 2,2-di(pyrrole-2-yl)adamantane (2), 1,3-bis[di(pyrrole-2-yl)methyl]adamantane (3), 2,2,6,6-tetra(pyrrole-2-yl)adamantane (4)] form complexes with F⁻, Cl⁻, Br⁻, AcO⁻, NO₃⁻, HSO₄⁻, and H₂PO₄⁻. The association constants of the complexes were determined by ¹H NMR titrations, whereas the geometries of complexes 1·F⁻ (2:1), 2·F⁻ (2:1), 2·Cl⁻ (2:1), 2·AcO⁻ (2:1), and 4·F⁻ (1:1) were determined by X-ray structural analysis. The most stable complexes are of 2:1 stoichiometry with F⁻ and AcO⁻. The stability constants are in accordance with the anion basicity and the ability of AdD receptors to place the hydrogen bonding donor groups in a tetrahedral fashion around anions. The binding energies of the complexes between receptors 1-4 and F⁻ anion are calculated using quantum chemical methods. The calculated results show that the solvent polarity is important for the complexation of fluoride ion with AdD receptors 1-4.     

Structures and properties of Sm(III) coordination polymers based on 2-(pyridin-4-yl)-1H-imidazole-4,5-dicarboxylate

Two novel 1D and 3D Sm(III) coordination polymers involving the 2-pyridin-4-yl-4,5-imidazoledicarboxylic acid (H₃PIDC) ligand have been characterized by infrared spectroscopy, elemental analysis and single-crystal X-ray diffraction. The coordination polymers were synthesized under hydrothermal conditions. Coordination polymer 1 gave a 1D zigzag chain, then forming 3D supramolecular structure through π?π stacking interactions and hydrogen bonds. Coordination polymer 2, in which oxalate was introduced as the second ligand gave a 3D framework with a 3,3-connected (4.8⁵)(4.8²) topology structure. But the luminescence of the coordination polymers has significant quenching.     

Synthesis,structure and properties of supramolecular Mn,Co, Ni and Zn complexes containing Salen-type bisoxime ligands

Four supramolecular complexes [MnL¹(H₂O)₂] (1), {[CoL²(OAc)(H₂O)]₂Co}·5CH₃CH₂OH (2), {[NiL³(OAc)(CH₃OH)]₂Ni}·2CH₃COCH₃·2CH₃OH (3) and {[ZnL²(OAc)]₂Zn}·CHCl₃ (4), have been synthesized and characterized by elemental analyses, IR, UV–Vis spectra and X-ray diffraction techniques. All the complexes have the trinuclear configuration except for Mn^II complex being mononuclear configuration. Every trinuclear complex contains two acetate ions coordinate to the three metal ions via a familiar M–O–C–O–M (M = Co, Ni, Zn) coordinated mode. Although complexes 1 and 3 display 1D supramolecular chains, the different coordination environments (mononuclear in 1, trinuclear in 3) provoke divergence in the structures and aggregations of the chain subunits. Complex 2 forms a 3D hydrogen-bonding supramolecular networks possessing a channel composing of six O–H···O hydrogen bonds, while complex 4 exhibits a 2D hydrogen-bonding supramolecular networks with the formation of “grottos” occupied by chloroform molecules through intermolecular hydrogen-bond interactions. The spectral properties of the title complexes have been further discussed in detail.     

A highly selective fluorescent probe for nanomolar detection of ferric ions in the living cells and aqueous media

A dipodal fluorescent probe 3, with imine and hydroxyl moieties as binding sites, has been synthesized and characterized with spectroscopic methods, single-crystal X-ray techniques, and DFT. The synthesized probe 3 (φ = 0.0028) showed highly sensitive and highly specific fluorescent ‘turn-on’ effect (λ_em = 453 nm) for the 1:1 binding with Fe³⁺ ions to form probe 3.Fe³⁺ complex (φ = 0.203) in semi-aqueous medium (acetonitrile:water (50:50; v/v)) and live cells. The 1:1 binding stoichiometry of probe 3 and Fe³⁺ ions was proposed by DFT calculations and confirmed by the NMR spectroscopy, crystal structures of probe 3 and 3.Fe³⁺ complex, and mass spectrum of probe 3.Fe³⁺ complex. The stability of probe 3.Fe³⁺ complex in a wide pH range (pH 2–12) and reversibility for binding with Fe³⁺ ions in the presence of EDTA indicates that it can be an effective chemosensor for the detection of Fe³⁺ ions in various samples, including living cells. Importantly, with the LOD of 21.5 nM for the detection of Fe³⁺ ions, probe 3 did not show any interference from potentially competing ions even at a 1:3 ratio, indicates its biocompatibility. The nanomolar limit of detection (21.5 nM), cell permeability, and low cytotoxicity allows the probe 3 to be an excellent tool for the live-cell imaging and detection of ferric ions in live cells.     

System-pH-dependent supramolecular isomers of puckered three-dimensional layered hydrogen-bonded networks: Syntheses, characterization and fluorescent properties

Two true supramolecular isomers (1 and 2) formulated as [Zn(bipy)(H₂btc)₂]_n (bipy=2,2′-bipyridine, H₃btc=benzene-1,3,5-tricarboxylic acid) have been hydrothermally prepared through systematically changing the pH value of reaction mixture, and characterized by single-crystal X-ray diffraction, element analysis, infrared spectra (IR), and differential scanning calorimetry (DSC). Isomer 1 crystallizes in triclinic space group P-1, tetrahedral Zn(ΙΙ) ions possess four-coordinated environment, while isomer 2 crystallizes in monoclinic space group C2/c and the distorted octahedral Zn(II) ions adopt six-coordinated fashion. 1 and 2 can be regarded as supramolecular structural isomers, the formation of which should be undoubtedly attributed to the preference for pH-dependent crystallization leading to multiple connectivity (monodentate and chelating bidentate) of organic ligand despite the same stoichiometry employed. The supramolecular chemistry, which organizes the coordination complexes into three-dimensional (3D) layered open structure, is driven by a combination of hydrogen-bond and π-π interactions. Moreover, 1 emits fluorescence at 350.1 nm () and 2 exhibits fluorescent property at about 351.4 nm ().