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1.
Synthesis and ion‐pair complexation properties of novel ditopic bis‐urea receptors based on dibenzo[21]crown‐7 ( R1 ) and dibenzo[24]crown‐8 ( R2 ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3/[D6]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb+ or Cs+, with the halide affinity increasing in order I?<Br?<Cl?. In solution, the rubidium complexes of both receptors have higher halide affinities compared to the caesium complexes. However, Rb+ and Cs+ complexes of R2 show stronger affinities toward all the studied anions compared to the corresponding cationic complexes of R1 . Similar selectivity of the receptors toward the studied ion pairs was also observed also in the gas phase by competition experiments with mass spectrometry. A total of eight crystal structures with different rubidium and caesium halides and oxyanions were obtained in addition to the crystal structure of R2?BaCl2 . The selectivity observed in solution and in the gas phase is explainable by the conformational differences observed in the crystal structures of ion‐pair complexes with R1 and R2 . In the solid state, R1 has an open conformation due to the asymmetric crown‐ether scaffold, whereas R2 has a compact, folded conformation. Computational studies of the ion‐pair complexes of R2 show that the interaction energies of the complexes increase in the order CsI<CsBr<CsCl<RbCl, supporting the selectivity observed in solution and the gas‐phase.  相似文献   

2.
A series of nucleobased polymers and copolymers were synthesized through atom transfer radical polymerization (ATRP). Biocomplementary DNA‐ and RNA‐like supramolecular complexes are formed in dilute DMSO solution through nucleobase recognition. 1H NMR titration studies of these complexes in CDCl3 indicated that thymine‐adenine (T‐A) and uracil‐adenine (U‐A) complexes form rapidly on the NMR time scale with high association constants (up to 534 and 671 M–1, respectively) and result in significant Tg increase. WAXD and differential scanning calorimetry analyzes in the bulk state indicate the presence of highly physical cross‐linked structures and provide further details into the nature of the self‐assembly of these systems. Furthermore, this study is of discussion on the difference in the hydrogen bond strength between T‐A and U‐A base pairs within polymer systems, indicating that the strength of hydrogen bonds in RNA U‐A pairs is stronger than that in DNA T‐A base pairs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6388–6395, 2009  相似文献   

3.
A new series of tris(2‐aminoethyl)amine (tren)‐based L ‐alanine amino acid backboned tripodal hexaamide receptors (L1–L5) with various attached moieties based on electron‐withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1–L5 with different anions, such as halides (F?, Cl?, Br?, and I?) and oxyanions (AcO?, BzO? (Bz=benzoyl), NO3?, H2PO4?, and HSO4?), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1–L4 invariably form 1:1 complexes with Cl?, AcO?, BzO?, and HSO4?, whereas L5 forms a 1:1 complex only with AcO?. In the case of Br?, I?, and NO3?, no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by 1H NMR spectroscopy. The ITC binding studies of F? and H2PO4? do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO? over Cl?, BzO?, and HSO4?. Solid‐state structural evidence for the recognition of Cl? by this new category of receptor was confirmed by single‐crystal X‐ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single‐crystal X‐ray diffraction clearly showed that the pentafluorophenyl‐functionalized amide receptor (L1) encapsulated Cl? in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion‐pair interactions to form a capped‐cleft orientation. To understand the role of the cationic counterpart in solution‐state Cl? binding processes with this series of receptors (L1–L4), a detailed Cl? binding study was carried out with three different tetraalkylammonium (Me4N+, Et4N+, and Bu4N+) salts of Cl?. The binding affinities of these receptors with different tetralkylammonium salts of Cl? gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion‐pair recognition by this series of receptors.  相似文献   

4.
Traditional micelle self‐assembly is driven by the association of hydrophobic segments of amphiphilic molecules forming distinctive core–shell nanostructures in water. Here we report a surprising chaotropic‐anion‐induced micellization of cationic ammonium‐containing block copolymers. The resulting micelle nanoparticle consists of a large number of ion pairs (≈60 000) in each hydrophobic core. Unlike chaotropic anions (e.g. ClO4?), kosmotropic anions (e.g. SO42?) were not able to induce micelle formation. A positive cooperativity was observed during micellization, for which only a three‐fold increase in ClO4? concentration was necessary for micelle formation, similar to our previously reported ultra‐pH‐responsive behavior. This unique ion‐pair‐containing micelle provides a useful model system to study the complex interplay of noncovalent interactions (e.g. electrostatic, van der Waals, and hydrophobic forces) during micelle self‐assembly.  相似文献   

5.
A novel and facile approach to manipulate the morphology of Cu2+‐ion‐specific assembly of conjugated polymer by coordinative interaction at an oil–water two‐phase interface is present. The application of increasing importance is the use of π‐conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self‐rolling of a strained ionic bilayer film at the oil/water interface.  相似文献   

6.
The rod‐coil molecules with n‐shaped rod building block, consisting of an anthracene unit and two biphenyl groups linked together with acetylenyl bonds at the 1,8‐position of anthracene as a rigid rod segment, and the alkyl or alkyloxy chains with various length (i.e., methoxy‐ ( 1 ), octyl‐ ( 2 ), hexadecyl‐ ( 3 )) at the 10‐position of anthracene and poly(ethylene oxide) with the number of repeating units of 7 connected with biphenyl as coil segments were synthesized. The molecular structures were characterized by 1H NMR and MALDI‐TOF mass spectroscopy. The self‐assembling behavior of new type of molecules 1–3 was investigated by means of DSC, POM, and SAXS at the bulk state. These molecules with a n‐shaped rod building block segment self‐assemble into supramolecular structures through the combination of π–π stacking of rigid rod building blocks and microphase separation of the rod and coil blocks. SAXS studies reveal that molecules 1 and 2 show hexagonal columnar and rectangular columnar structures in the liquid crystalline phase, respectively; meanwhile, molecules 1–3 self‐organize into lamellar structures in the crystalline state. In addition, self‐assembling studies of molecules 1–3 by DLS and TEM indicated that these molecules self‐assemble into elongated nanofibers in aqueous medium. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1415–1422, 2010  相似文献   

7.
A new heteroditopic calix[4]diquinone triazole containing receptor capable of recognising both cations and anions through Lewis base and C? H hydrogen‐bonding modes, respectively, of the triazole motif has been prepared. This ion‐pair receptor cooperatively binds halide/monovalent‐cation combinations in an aqueous mixture, with selectivity trends being established by 1H NMR and UV/Vis spectroscopy. Cation binding by the calix[4]diquinone oxygen and triazole nitrogen donors enhances the strength of the halide complexation at the isophthalamide recognition site of the receptor. Conversely, anions bound in the receptor’s isophthalamide cavity enhance cation recognition. 1H NMR investigations in solution suggest that the receptor’s triazole motifs are capable of coordinating simultaneously to both cation and anion guest species. Solid‐state X‐ray crystallographic structural analysis of a variety of receptor ion‐pair adducts further demonstrates the dual cation–anion binding role of the triazole group.  相似文献   

8.
Two self‐complementary {2}‐metallocryptates, differing in methyl and phenyl substituents, respectively, have been studied by X‐ray analysis, and solid‐state and solution NMR. Mixed Mg/Cs metal methyl complex 2 is a linear polymer in the solid state. The two different Cs sites are confirmed by 133Cs‐solid‐state NMR. By contrast, the analog mixed Mg/Cs metal phenyl complex 4 is a meandering polymer as shown by an actual X‐ray analysis. The four non‐equivalent Cs‐sites in 4 are reflected in the solid‐state NMR spectra. Solution 133Cs‐NMR spectra of 4 reveal two independent dynamic processes: a fast exchange of Cs within contact ion‐pairs and solvent‐separated ion‐pairs (CIP, SSIP), and a slower exchange of ‘inside’ endo Cs, surrounded by three ligands, and ‘outside’ exo Cs involved in the CIP/SSIP equilibrium. Complete line‐shape analysis of variable‐temperature 133Cs‐NMR spectra of 4 yield kinetic parameters of =10.8 kcal/mol for the fast SSIP‐CIP exchange and =13.2 kcal/mol for the slower endo/exo exchange of Cs. DOSY‐NMR Measurements confirm the monomeric nature of 4 in solution.  相似文献   

9.
A set of dendritic‐linear copolymers, poly(maleic anhydride‐grafted‐3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate))‐random‐polystyrene (PMA‐APM‐r‐PS), was successfully prepared by copolymerization of the novel dendritic macromonomer, 4‐(4‐(bis(3‐(4‐(bis(3‐methoxy‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐4‐oxobut‐2‐enoic acid (MA‐APM), with styrene monomer. The dendritic MA‐APM macromonomer dendron 3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate) (APM) was then grafted by using the divergent growth method. FTIR, 1H NMR, and 13C NMR spectra were used to identify the structures of the dendron, the dendritic macromonomer, and the dendritic‐linear PMA‐APM‐r‐PS copolymer. Furthermore, microporous dendritic‐linear PMA‐APM‐r‐PS copolymer films were prepared by using solvent‐induced phase separation at room temperature. We investigated the phase separation behavior and morphological structures of the dendritic‐linear copolymer film as functions of dendritic GMA‐HPAM segments in the content using SEM. Self‐assembly of the dendritic‐linear PMA‐APM‐r‐PS copolymer in the MG2‐X system, which represented the second generation dendron containing X wt % of the dendritic MA‐APM segment, resulted in submicron phase segregation. Interestingly, the submicron phase segregation morphology of the MG2–43 sample presented a uniform size distribution of ordered‐array structures. The results of this study demonstrate that controlling the appropriate macromonomer content via the grafting of a three‐dimensional structure results in a self‐assembly process that is capable of providing an ordered‐array microporous morphology in a polymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3290–3301, 2010  相似文献   

10.
A second‐generation supramolecular dendrimer has been prepared by orthogonal multiple hydrogen bonding. In the first (inner) recognition domain, the interaction of one bis‐isocyanuric acid ( 25 ) with two branching units ( 21 ) that carry complementary Hamilton receptors has been exploited. In the second (outer) generation, the two ADDA (A=hydrogen‐bond acceptor, D=donor) receptors of each branching unit ( 21 ) have bound complementary DAAD units ( 4 ). The problem of limited solubility of the building blocks has been overcome by the introduction of branched ethylhexyl residues and by the use of flexible alkylene or oligo(ethylene glycol) linking chains. The orthogonal binding of the two hydrogen‐bonding pairs was elucidated by chemical induced shift NMR titrations, which proved that the two pairs, isocyanuric acid with the Hamilton receptor and ADDA with DAAD, bind preferentially. The formation of the supramolecular self‐assembled 1:2:4 dendrimer with a molecular weight of 5065 g mol?1 was investigated by diffusion NMR spectroscopy.  相似文献   

11.
This article describes a DNA‐like polymer that exhibits the ability to self‐assemble through hydrogen bonding. We synthesized poly[1‐(4‐vinylbenzyl)thymine] (PVBT) and 9‐hexadecyladenine (A‐C16) through an atom transfer radical polymerization (ATRP) and alkylation, respectively. Biocomplementary PVBT/A‐C16 hierarchical supramolecular complexes formed in dilute DMSO solution through nucleobase recognition, that is, hydrogen bonding interactions between the thymine (T) groups of PVBT and the adenine (A) group of A‐C16; evidence for this molecular recognition was also gained from dynamic light scattering studies. 1H NMR titration studies in CDCl3 showed that T–A complexes formed rapidly on the NMR time scale with high association constants (up to 534 M?1). Moreover, FTIR spectroscopic, differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering analyses provided further details into the nature of the self‐assembly of these systems. In the bulk state, these complexes self‐assemble into well‐ordered lamellar structures; the changing d‐spacing distance (ranging from 4.98 to 2.32 nm) at different A‐C16 loadings reveals that the molecular structures of the PVBT/A‐C16 complexes are readily tailored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6416–6424, 2008  相似文献   

12.
A full account of our studies of 2,4,6‐trinitrophenol (TNP) sensing is provided. A series of chemosensors 2 , 3 , 4 , 5 with a variety of aromatic chromophores for specific recognition of TNP has been designed and then realized through the fluorescence “on/off” mechanism. These chemosensors demonstrated highly selective, sensitive, and fluorescent quenching of TNP with remarkable visual changes through the intramolecular charge‐transfer (ICT) process. Their host–guest interactions were investigated by 1H NMR spectroscopic titrations and their corresponding co‐crystal structures, which showed that the 1:1 host–guest complexes were formed by multiple hydrogen‐bond interactions in solution or in the solid state. The origins of the significant affinity demonstrated during the fluorescence recognition process were further disclosed through DFT calculations of corresponding compounds.  相似文献   

13.
New tripodal squaramide‐based hosts have been synthesised and structurally characterised by spectroscopic methods. In 2.5 % (v/v) [D6]DMSO in CDCl3, compound 4 formed dimeric assemblies [log Kdim=3.68(8)] as demonstrated by 1H NMR spectroscopy and UV dilution experiments. AFM and SEM analyses revealed the formation of a network of bundled fibres, which indicates a preferential mechanism for aggregation. These C3‐symmetric tripodal hosts exhibited two different and mutually exclusive modes of binding, each one easily accessible by simultaneous reorientation of the squaramide groups. In the first, a convergent disposition of the NH squaramide protons allowed the formation of an array of N? H???X? hydrogen bonds with anions. In the second mode, reorientation of carbonyl squaramide groups allowed multiple C?O???H interactions with ammonium cations. The titration of 4 with different tetraalkylammonium iodides persistently showed the formation of 1:1 complexes, as well as 1:2 and 1:3 complexes. The corresponding stoichiometries and binding affinities of the complexes were evaluated by multi‐regression analysis. The formation of high‐order complexes, supported by ROESY, NOESY and mass spectrometry experiments, has been attributed to the insertion of NR4I ion pairs between the carbonyl and NH protons of the squaramide groups located in adjacent arms of 4 . The observed effects reflect the induction of significant conformational changes in the hosts, mainly in relation to the relative orientation of the squaramide groups adapting their geometries to incoming ion‐pair complementary substrates. The results presented herein identify and fully describe two different modes of ion‐pair recognition aimed at directing conformational transitions in the host, therefore establishing a base for controlling more elaborate movements of molecular devices through ion‐pair recognition.  相似文献   

14.
Programmed nucleic acid sequences undergo K+ ion‐induced self‐assembly into G‐quadruplexes and separation of the supramolecular structures by the elimination of K+ ions by crown ether or cryptand ion‐receptors. This process allows the switchable formation and dissociation of the respective G‐quadruplexes. The different G‐quadruplex structures bind hemin, and the resulting hemin–G‐quadruplex structures reveal horseradish peroxidase DNAzyme catalytic activities. The following K+ ion/receptor switchable systems are described: 1) The K+‐induced self‐assembly of the Mg2+‐dependent DNAzyme subunits into a catalytic nanostructure using the assembly of G‐quadruplexes as bridging unit. 2) The K+‐induced stabilization of the anti‐thrombin G‐quadruplex nanostructure that inhibits the hydrolytic functions of thrombin. 3) The K+‐induced opening of DNA tweezers through the stabilization of G‐quadruplexes on the “tweezers’ arms" and the release of a strand bridging the tweezers into a closed structure. In all of the systems reversible, switchable, functions are demonstrated. For all systems two different signals are used to follow the switchable functions (fluorescence and the catalytic functions of the derived hemin–G‐quadruplex DNAzyme).  相似文献   

15.
An effective route to novel 4‐(alkylamino)‐1‐(arylsulfonyl)‐3‐benzoyl‐1,5‐dihydro‐5‐hydroxy‐5‐phenyl‐2H‐pyrrol‐2‐ones 10 is described (Scheme 2). This involves the reaction of an enamine, derived from the addition of a primary amine 5 to 1,4‐diphenylbut‐2‐yne‐1,4‐dione, with an arenesulfonyl isocyanate 7 . Some of these pyrrolones 10 exhibit a dynamic NMR behavior in solution because of restricted rotation around the C? N bond resulting from conjugation of the side‐chain N‐atom with the adjacent α,β‐unsaturated ketone group, and two rotamers are in equilibrium with each other in solution ( 10 ? 11 ; Scheme 3). The structures of the highly functionalized compounds 10 were corroborated spectroscopically (IR, 1H‐ and 13C‐NMR, and EI‐MS), by elemental analyses, and, in the case of 10a , by X‐ray crystallography. A plausible mechanism for the reaction is proposed (Scheme 4).  相似文献   

16.
A new high‐speed counter‐current chromatography method for semi‐preparative separation and purification of alkaloids from embryo of the seed of Nelumbo nucifera Gaertn was developed by using pH‐gradient elution mode. Diethyl ether was used as the stationary phase of the two‐phase solvent system and Na2HPO4/NaH2PO4 buffer solution with pH values of 7.5 and 7.2 in gradient mode as the mobile phase. Consequently, 33 mg of liensinine, 42 mg of isoliensinine, and 67 mg of neferine were obtained from 200 mg of crude extracts. The purities of them were all over 98% as determined by HPLC area normalization method, and the structures were identified by 1H‐NMR and 13C‐NMR.  相似文献   

17.
This paper presents results from a series of pulsed field gradient (PFG) NMR studies on lipophilic guanosine nucleosides that undergo cation‐templated assembly in organic solvents. The use of PFG‐NMR to measure diffusion coefficients for the different aggregates allowed us to observe the influences of cation, solvent and anion on the self‐assembly process. Three case studies are presented. In the first study, diffusion NMR confirmed formation of a hexadecameric G‐quadruplex [G 1 ]16 ? 4 K+ ? 4 pic? in CD3CN. Furthermore, hexadecamer formation from 5′‐TBDMS‐2′,3′‐isopropylidene G 1 and K+ picrate was shown to be a cooperative process in CD3CN. In the second study, diffusion NMR studies on 5′‐(3,5‐bis(methoxy)benzoyl)‐2′,3′‐isopropylidene G 4 showed that hierarchical self‐association of G8‐octamers is controlled by the K+ cation. Evidence for formation of both discrete G8‐octamers and G16‐hexadecamers in CD2Cl2 was obtained. The position of this octamer–hexadecamer equilibrium was shown to depend on the K+ concentration. In the third case, diffusion NMR was used to determine the size of a guanosine self‐assembly where NMR signal integration was ambiguous. Thus, both diffusion NMR and ESI‐MS show that 5′‐O‐acetyl‐2′,3′‐O‐isopropylidene G 7 and Na+ picrate form a doubly charged octamer [G 7 ]8 ? 2 Na+ ? 2 pic? 9 in CD2Cl2. The anion's role in stabilizing this particular complex is discussed. In all three cases the information gained from the diffusion NMR technique enabled us to better understand the self‐assembly processes, especially regarding the roles of cation, anion and solvent.  相似文献   

18.
Anion complexes of anion‐responsive π‐electronic molecules can behave as pseudo π‐electronic anions providing various ion pairs in combination with countercations. In this study, single crystals of ion‐pairing assemblies comprising porphyrin–AuIII complexes and Cl? complexes of dipyrrolyldiketone BF2 complexes were prepared from 1:1 mixtures of anion receptors and the Cl? salts of cationic porphyrins in solution. In the solid state, the ion pairs formed characteristic assemblies, depending on the substituents of the anion receptors and porphyrin–AuIII complexes. Theoretical calculations on the ion pairs revealed that the stacking structures are stabilized by compensating positive and negative charges as well as π–π interactions.  相似文献   

19.
In the present investigation, the first incorporation of both ferrocene scaffold and 1,2‐dihydro‐2‐oxopyridine‐3‐carbonitrile pharmacophore leading to a series of structurally novel ferrocene‐based hybrids has been achieved, involving the condensation reaction of ferrocenyl substituted chalcones with 2‐cyanoacetamide in a freshly prepared EtONa solution at 70°. The molecular structures of these newly synthesized products were confirmed by IR, and 1H‐ and 13C‐NMR analyses.  相似文献   

20.
The controlled secondary self‐assembly of amphiphilic molecules in solution is theoretically and practically significant in amphiphilic molecular applications. An amphiphilic β‐cyclodextrin (β‐CD) dimer, namely LA‐(CD)2, has been synthesized, wherein one lithocholic acid (LA) unit is hydrophobic and two β‐CD units are hydrophilic. In an aqueous solution at room temperature, LA‐(CD)2 self‐assembles into spherical micelles without ultrasonication. The primary micelles dissociates and then secondarily form self‐assemblies with branched structures under ultrasonication. The branched aggregates revert to primary micelles at high temperature. The ultrasound‐driven secondary self‐assembly is confirmed by transmission electron microscopy, dynamic light scattering, 1H NMR spectroscopy, and Cu2+‐responsive experiments. Furthermore, 2D NOESY NMR and UV/Vis spectroscopy results indicate that the formation of the primary micelles is driven by hydrophilic–hydrophobic interactions, whereas host–guest interactions promote the formation of the secondary assemblies. Additionally, ultrasonication is shown to be able to effectively destroy the primary hydrophilic–hydrophobic balances while enhancing the host–guest interaction between the LA and β‐CD moieties at room temperature.  相似文献   

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