Synthesis and anion binding properties of 2,5-diamidothiophene polypyrrole Schiff base macrocycles

[reaction: see text] Two easy-to-synthesize polypyrrolic 2,5-diamidothiophene Schiff base macrocycles are reported, along with their anion binding properties as determined via UV-vis spectroscopic titrations carried out in dichloroethane. There is a striking difference between the interactions with anions of the two macrocycles, a finding ascribed to differences in their rigidity. For example, the more flexible dipyrromethane-derived macrocycle displays a 1.2:1 hydrogen sulfate versus nitrate selectivity, while its more rigid bipyrrole-derived congener shows a 7.4:1 selectivity in favor to hydrogen sulfate.     

Synthesis and spectroscopic studies of binuclear metal complexes of a tetradentate N2O2 Schiff base ligand derived from 4,6-diacetylresorcinol and benzylamine

A tetradentate N2O2 donor Schiff base ligand, H2L, was synthesized by the condensation of 4,6-diacetylresorcinol with benzylamine. The structure of the ligand was elucidated by elemental analyses, IR, 1H NMR, electronic and mass spectra. Reaction of the Schiff base ligand with nickel(II), cobalt(II), iron(III), cerium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded binuclear metal complexes. Also, reaction of the ligand with several copper(II) salts, including Cl-, NO3-, AcO-, ClO4- and SO42- afforded different metal complexes that reflect the non-coordinating or weakly coordinating power of the ClO(4)(-) anion as compared to the strongly coordinating power of SO42- and Cl- anions. Characterization and structure elucidation of the prepared complexes were achieved by elemental and thermal analyses, IR, 1H NMR, electronic, mass and ESR spectra as well as magnetic susceptibility measurements. The metal complexes exhibited different geometrical arrangements such as square planar, octahedral, square pyramidal and pentagonal bipyramidal arrangements. The variety in the geometrical arrangements depends on the nature of both the anion and the metal ion.     

Selective Synthesis of [2＋2] Macrocyclic Schiff Bases from Chiral 1,4-Diamines

[2＋2] macrocyclic Schiff bases of three kinds have been synthesized from chiral 1,4-diamines by use of different methods. Macrocyclic Schiff bases 1a-1c have been selectively obtained based on a non-templated dilution method from chiral 1,4-diamines a-c and dialdehyde DA1, whereas macrocycles 2a-2c have been selectively produced from reaction of diamines a-c and dialdehyde DA2 in the presence of boric acid as templates. Macrocyclic Schiff bases 3a-3c have been afforded in high selectivity from diamines a-c and dialdehyde DA3 by means of sodium-template. All the titled compounds have been confirmed by ^1H NMR and ESI-MS analyses.     

Synthesis of Electron-Deficient Corona[5]arenes and Their Selective Complexation with Dihydrogen Phosphate: Cooperative Effects of Anion–π Interactions

Reported here are the syntheses, conformational structures, electrochemical properties, and noncovalent anion binding of corona[5]arenes. A (3+2) fragment coupling reaction proceeded efficiently under mild reaction conditions to produce a number of novel heteroatom- and methylene-bridged corona[3]arene[2]tetrazine macrocycles. Selective oxidation of the sulfur atom between two phenylene rings afforded sulfoxide- and sulfone-linked corona[5]arenes in good yields. All corona[5]arenes synthesized adopted similar 1,2,4-alternate conformational structures, forming pentagonal cavities. The cavity sizes and the electronic properties such as redox potentials, were measured with CV and DPV, and were influenced by the different bridging units. As electron-deficient macrocycles, the acquired corona[3]arene[2]tetrazines served as highly selective hosts, forming complexes with the hydrogen-bonded dimer of dihydrogen phosphate through cooperative anion–π interactions.     

Synthesis of Electron‐Deficient Corona[5]arenes and Their Selective Complexation with Dihydrogen Phosphate: Cooperative Effects of Anion–π Interactions

Reported here are the syntheses, conformational structures, electrochemical properties, and noncovalent anion binding of corona[5]arenes. A (3+2) fragment coupling reaction proceeded efficiently under mild reaction conditions to produce a number of novel heteroatom‐ and methylene‐bridged corona[3]arene[2]tetrazine macrocycles. Selective oxidation of the sulfur atom between two phenylene rings afforded sulfoxide‐ and sulfone‐linked corona[5]arenes in good yields. All corona[5]arenes synthesized adopted similar 1,2,4‐alternate conformational structures, forming pentagonal cavities. The cavity sizes and the electronic properties such as redox potentials, were measured with CV and DPV, and were influenced by the different bridging units. As electron‐deficient macrocycles, the acquired corona[3]arene[2]tetrazines served as highly selective hosts, forming complexes with the hydrogen‐bonded dimer of dihydrogen phosphate through cooperative anion–π interactions.     

含吡啶-2,6-二酰亚胺单元的大环化合物合成及性质

在硫酸催化作用下,用前体二醛1[1,3-二(2'-甲酰苯氧基)丙烷]和前体二胺2[N,N'-(2-胺基苯基)-2,6-二甲酰亚胺吡啶]合成了[1+1]席夫碱大环化合物3,进一步还原得到饱和大环4。 用¹H NMR、IR、元素分析和质谱等技术手段对大环3和4的组成进行了表征。 采用X射线衍射仪测定了大环3 和4的晶体结构。 用UV-Vis光谱仪对大环3和4与系列阴离子的作用分别进行了考察,结果表明,饱和大环4仅对F^-有明显的选择性作用,并测定了该配位反应的配位比和平衡常数,进一步考察了大环3和4对甲醇的吸附性能。     

Strong, size-selective, and electronically tunable C-H...halide binding with steric control over aggregation from synthetically modular, shape-persistent [34]triazolophanes

A series of shape-persistent [3(4)]triazolophanes bearing t-butyl or triethylene glycol (OTg) substituents on the phenylene linkers have been prepared in a modular manner from simple building blocks. Triazolophane-halide binding affinities were determined using UV titrations in order to help in understanding the driving forces behind the large receptor-anion binding strengths supported solely by CH hydrogen-bond donors. The fixed size of the central cavity provides a means for selective recognition of Cl(-) and Br(-) anions with large binding strengths (Ka > 1,000,000 M(-1); DeltaG > -8.5 kcal mol(-1)). The smaller F(-) and larger I(-) anions are bound less tightly by approximately 1 and approximately 3 orders of magnitude, respectively. The four triazole-based H-bond donors are believed to be of primary importance, while the four phenylene CH H-bond donors take on a secondary role. Consistent with this idea, the binding affinity can be tuned by as much as 1 kcal mol(-1) by changing the character of the four phenylene-based substituents from more (OTg) to less (t-butyl) electron-donating. Preorganization was also found to play a central role, on the basis of comparisons with a foldamer analogue that shows much-reduced binding. Aggregation was facilitated as the substituents were changed from t-butyl to OTg, increasing the degree of self-association from K(E) approximately = 0 to 230 M(-1) in CD2Cl2. Diffusion NMR experiments established aggregation as opposed to dimerization. These findings indicate the importance of the cavity size for selective anion recognition as well as the role of the phenylene linkers in tuning the binding strengths and modulating the aggregation of the [3(4)]triazolophanes.     

Zinc carboxylate cluster formation in conjugated metallomacrocycles: evidence for templation

A new [3 + 3] Schiff base macrocycle incorporating three N2O2 salphen-type binding sites and peripheral neopentyloxy substituents has been prepared. The incorporation of Zn2+ ions into this and related conjugated Schiff base macrocycles has been studied by NMR spectroscopy, mass spectrometry, and X-ray diffraction. When reacted with 7 equiv of zinc acetate, the macrocycles template the formation of heptanuclear complexes. Two tetranuclear Zn2+ complexes that are plausible intermediates in the assembly of the heptanuclear complexes have been isolated and structurally characterized. These reactive intermediates are promising substrates for the synthesis of polynuclear, mixed-metal clusters. We also demonstrate that this chemistry may be generalized to other bridging carboxylate ligands, such as methacrylate.     

Dipyrrolylmethane-based macrobicyclic azacryptand: synthesis, X-ray structures, conformational and anion binding properties

A new class of macrobicyclic azacryptand containing dipyrrolylmethane subunits with nitrogen bridgeheads was synthesized by the Mannich reaction of the dipyrrolylmethane in the presence of aqueous ammonia. The azacryptand exhibits a staggered conformation in the solid state, but is in a dynamic equilibrium with the eclipsed conformation in solution studied by the variable-temperature (1)H NMR methods. The azacryptand has a specific size suitable only for fluoride ion; large anions such as NO(3)(-) bind in the clefts of the macrobicycle as shown by the X-ray structures of its fluoride ion inclusion and the nitrate anion complexes. The anion binding studies showed that it has high selectivity and affinity for fluoride ion in acetone over other anions studied, which was supported by (1)H and (19)F NMR methods. The azacryptand has fast fluoride ion-mediated proton-deuterium exchanges with acetone-d(6) studied by the (19)F NMR method.     

Polarographic Studies on Anion Coordination Chemistry. Host–Guest Interactions of Hexacyclen and Pentacyclen with Pyrophosphate, Selenite, Selenate, Molybdate and Tungstate Anions

The complexation of protonated hexacyclen and pentacyclen with pyrophosphate, selenite, selenate, molybdate and tungstate anions was studied by differential pulse polarography at 25 °C. The stoichiometry and stability of the resulting anion complexes were evaluated from the pH and concentration-dependence of the peak potentials, respectively. The results established 1 : 1 anion receptor complexation in all cases. In the case of all anions studied, hexacyclen was found to form more stable anion complexes than pentacyclen. The fact that the anion-receptor complexation depends on the structural features of both the anions and the macrocycles used is indicative of a steric controlled interaction.     

含2,6-二甲酰胺基吡啶单元的大环合成、结构及其对四面体构型阴离子的络合性质

采用前体二胺N,N’-(3-胺基苯基)-2,6-二甲酰亚胺吡啶(1)和5,5’-亚甲基双水杨醛(2)进行缩合反应得到含酚羟基的 [1+1] 席夫碱大环L1, 将其中席夫碱C=N双键还原得到环状骨架更具柔性的饱和大环L2. 通过1H NMR、FABMS和元素分析等对大环组成进行了表征, 并通过X射线单晶衍射解析了两个大环的晶体结构. 采用UV-Vis 光谱滴定技术对大环与系列阴离子的络合作用进行了考察, 结果表明席夫碱大环L1对四面体构型的阴离子H2PO4-、 HP2O73-和H2P2O72-有明显的选择性识别作用, 进一步通过UV-Vis 光谱、核磁滴定等技术获得了识别反应的配位比及平衡常数(K), L1对3个磷酸阴离子的络合能力依H2PO4-、HP2O73-和H2P2O72-顺序递增。     

Protonated macrobicyclic hosts containing pyridine head units for anion recognition

In this paper, we report two macrobicyclic receptors containing pyridine head units derived from 1,10-diaza-15-crown[5] (L1) or 4,13-diaza-18-crown[6] (L2) that can be protonated in MeCN and used for anion recognition. The interaction of these protonated lateral macrobicycles with different anions has been investigated by means of spectrophotometric titrations in MeCN. The association constants for the complexes of halide anions with the protonated macrobicycles follow the sequences Cl(-)>Br(-)>I(-)>F(-) (L1) and Cl(-)>F(-)>I(-)>Br(-) (L2), whereby an increase of more than two logarithmic units is observed from F(-) to Cl(-) for the binding constants of the receptor derived from L1. The association constants also indicate an important degree of selectivity of these macrobicyclic receptors for Cl(-) over Br(-) or I(-). The X-ray crystal structure analyses of the chloride and bromide complexes confirms the formation of the envisaged supramolecular complexes. Moreover, the binding constants indicate that these receptors present a high sulfate-to-nitrate binding selectivity. The stability trend observed for the recognition of halide anions by the macrobicycles presented herein as well as the sulfate-to-nitrate binding selectivity have been rationalised by means of DFT calculations at the B3LYP/LanL2DZ level. These studies indicate that the especially high binding selectivity for Cl(-) is the result of the optimum fit between the protonated macrobicyclic cavity and the size of the anion, whereas the sulfate-to-nitrate selectivity results from shape complementarity between the hydrogen-binding acceptor sites on sulfate and the hydrogen-bond donors of the macrobicycle.     

Anion‐binding properties of two calix[4]arene derivatives containing two ferrocene imine or ferrocene amine units at the upper rim

Calix[4]arene derivatives containing ferrocene units at the upper rim have been synthesized and their anion‐binding and sensing investigated towards anions such as chloride, bromide and hydrogen sulfate by cyclic voltammetry. Electrochemical studies show that these redox‐active ligands electrochemically recognize chloride and bromide anions. These compounds have excellent selectivity for chloride and bromide ions, in the comparison with hydrogen sulfate anion. With ferrocenyl Schiff base calix[4]arene 1 an anodic shift as large as 302 mV is observed on addition of four equivalents of Cl⁻ anion. Also electrochemical and UV–vis spectroscopic titrations ferrocenyl calix[4]arene derivatives 1 with chloride and bromide ions and 2 (only with Cl⁻) indicate a 1:1 binding‐stiochiometry. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of new azo containing Schiff base macrocycle

Fully conjugated Schiff base macrocycle has been prepared through a simple and mild condition,a one-pot cyclization procedure of four-component without using a template.The condensation reaction of related bis（hydroxybenzaldehyde） with phenylenediamines to prepare a conjugated[2 + 2]Schiff base macrocycle has been investigated and fluorescent[2 + 2]Schiff base macrocycles with N₂O₂ binding pockets has been prepared and characterized by elemental analysis,¹H NMR,IR,fluorescent,UV-visible and MALDI mass spectroscopies.     

Anion binding in aqueous media by a tetra-triazolium macrocycle

Three tetra-triazole macrocycles were synthesized in good yields by the copper(i)-catalysed cycloaddition of bis-triazole azides and bis-alkynes. One of these was alkylated to give a cyclic tetra-triazolium receptor, which complexes anions strongly in competitive DMSO-water mixtures. In 1?:?1 DMSO-water, the tetracationic receptor exhibits a preference for the larger halides, bromide and iodide, with all halides associating more strongly than the oxoanion, acetate. The sulfate dianion is complexed far more strongly than any of the monobasic anions (K(a) > 10(4) M(-1)). Quantum mechanics/molecular mechanics simulations corroborate the experimentally determined anion binding selectivity trends.     

High‐Fidelity Multistate Switching with Anion–Anion and Acid–Anion Dimers of Organophosphates in Cyanostar Complexes

The acid–base switching of complexes formed from anti‐electrostatic anion–anion homodimers of organophosphates and cyanostar macrocycles was investigated for the first time. High‐fidelity 2:2 complexes were selected by using suitably sized organo substituents. Reversible and direct switching occurs with triflic acid and hydroxide base. An unexpected acid⋅⋅⋅anion heterodimer was discovered with weaker picric acid, which helped reveal some of the elementary steps. Switching can also proceed in a cooperative (strong anion then weak acid) or stepwise manner (weak acid then strong anion).     

Effect of loop distortion on the stability and structural dynamics of DNA hairpin and dumbbell conjugates

The thermal stability and conformational dynamics of DNA hairpin and dumbbell conjugates having short A-tract base pair domains connected by tri- or hexa(ethylene glycol) linkers is reported. The formation of stable base-paired A-tract hairpins having oligo(ethylene glycol) linkers requires a minimum of four or five A-T base pairs. The formation of base-paired dumbbells having oligo(ethylene glycol) linkers by means of chemical ligation of nicked dumbbells requires a minimum of two A-T base pairs on either side of the nick. Molecular modeling indicates that the hexa(ethylene glycol) linker is sufficiently long to permit formation of strain-free loop regions and B-DNA base pair domains. In contrast, the tri(ethylene glycol) is too short to permit Watson-Crick base pairing between the bases attached to the linker. The shorter linker distorts the duplex, resulting in fluxional behavior in which the base pairs adjacent to the linker and at the open end of the hairpin dissociate on the nanosecond time scale. The loss of interstrand binding energy caused by these fluctuations leads to a difference of approximately 5 degrees C in melting temperature between EG3 and EG6 hairpins. An analysis of the fluxional behavior of the EG3 adjacent base-pair has been used to study the pathways for base flipping and base stacking, including the identification of rotated base (partially flipped) intermediates that have not been described previously for A-T base pairs.     

Novel chiral "calixsalen" macrocycle and chiral robson-type macrocyclic complexes

A family of novel chiral "calixsalen" Schiff base macrocycles R,R-H(3)L4, R,R-H(3)L5, containing three chiral diamino moieties were synthesized by an efficient self-assembly and characterized by (1)H and (13)C NMR, mass spectrometry, and X-ray diffraction. The systematic synthesis, structure, and coordination properties of the [2 + 2] and [3 + 3] Robson-type Schiff base macrocyclic mono-, di-, tri-, and tetranuclear metal complexes were explored.     

Schiff base macrocycles containing pyrroles and pyrazoles

A double nucleophilic substitution reaction of 3,5-bis(chloromethyl)pyrazole with pyrroles generates a novel pyrrole-pyrazole hybrid building block, the pyrazole analogue to tripyrrane. Vilsmeier-Haack formylation produces the corresponding dialdehyde, which was used in the formation of a series of nonaromatic Schiff base macrocycles. NMR and UV/Vis spectroscopy and single-crystal diffractometry were used to characterize the novel macrocycles. The solid-state structures of select free bases and protonated members of this class of macrocycles display a range of intra- and intermolecular hydrogen-bonding patterns that suggest their use in molecular-recognition systems. They also contain an acid-sensitive chromophore. Their acid-base and anion-recognition properties were ascertained; alas, only modest anion-selective spectroscopic signatures could be detected by using UV/Vis and (1)H NMR spectroscopy. The macrocycles proved resistant toward oxidation to their aromatic congeners. The pyrrole-pyrazole building blocks presented are potentially useful for the synthesis of a range of pyrazole analogues of all-pyrrole macrocycles.     

Donor effect on supramolecular structures of silver(I) perchlorate complexes of macrocycles with O2S2X (X=S, O and NH) donor sets

By virtue of simple one donor variations of O(2)S(2)X-donor macrocycles (L(1): X=S, L(2): X=O and L(3): X=NH) towards silver(I) perchlorates, four supramolecular complexes (1-3) with different topologies have been isolated; L(1) afforded solvent- and anion-free sandwich complex (1), otherwise L(2) and L(3) gave the dimeric (2a), 1-D polymeric (2b), and tetrameric bowl-type (3) complexes with solvent or anion coordination.