Synthesis, X-ray Structure, and Anion-Binding Properties of a Cryptand-Like Hybrid Calixpyrrole (original) (raw)
Industrial & Engineering Chemistry Research, 2000
The synthesis and chemical properties of a variety of chemically modified calix[4]pyrroles are described. The effects of structural changes, specifically the presence and absence of substituents on the meso-like and-pyrrolic carbons, on anion affinities are detailed as is their effect on macrocycle conformation. Also described are unsymmetrical systems, bearing an aliphatic and aromatic substituent on each of the four meso-like carbon atoms. In this case, the properties of the resulting configuration isomers are discussed in terms, again, of the resulting effects on macrocycle conformation and substrate binding affinity. Finally, the use of appropriately functionalized calix[4]pyrrole systems as rudimentary fluorescence-based anion sensors is presented.
Calix[6]pyrrole and Hybrid Calix[n]furan[m]pyrroles (n+m=6): Syntheses and Host–Guest Chemistry
Chemistry - A European Journal, 2002
Calix[6]pyrrole 2 and the ™hybrid systems∫ calix[3]furan[3]pyrrole 12, calix[2]furan[4]pyrrole 13, and calix[1]furan[5]pyrrole 14, have been synthesized by increasing conversion of the furan units present in the readily accessible calix[6]furan 3 to pyrroles. The host ± guest chemistry of these novel macrocycles towards a number of anions, including halogen ions, dihydrogen phosphate, hydrogen sulfate, nitrate, and cyanide has been investigated in solution by 1 H NMR titration techniques and/or phase transfer experiments. The solid-state structures of the free receptors 2, 12, and 13, the 1:1 complexes of calix[6]pyrrole 2 with chloride and bromide, and the 1:1 complex of 14 with chloride are also reported.
Calix[4]pyrroles with bulky substituents and their anion binding studies
TURKISH JOURNAL OF CHEMISTRY, 2017
Calix[4]pyrrole derivatives with bulky substituents at their meso-positions were synthesized via mixed condensation of pyrrole with cyclohexanone and acetophenone derivatives. Anion binding studies, carried out by isothermal titration calorimetry in 1,2-dichloroethane with Cl − and CH 3 CO − 2 anions in the form of their tetrabutylammonium salts, revealed that these new calix[4]pyrrole derivatives can bind the aforementioned anions as effectively as the unsubstituted "parent" system, octamethylcalix[4]pyrrole (1). Structural characterizations of new calix[4]pyrroles were carried out by using 1 H and 13 C NMR spectroscopy corroborated with mass spectrometry.
Anion Binding Modes in meso-Substituted Hexapyrrolic Calix[4]pyrrole Isomers
Journal of the American Chemical Society, 2014
We report on the synthesis of a new receptor for anions, mesosubstituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole's core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis-and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion−π interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cisisomer 1 displays higher affinity (10 5 −10 6 M −1) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.
Anion Binding Modes in meso-Substituted Hexapyrrolic Calix[4]pyrrole Isomers
Journal of the American Chemical Society, 2014
We report on the synthesis of a new receptor for anions, mesosubstituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole's core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis-and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion−π interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cisisomer 1 displays higher affinity (10 5 −10 6 M −1) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.
Synthesis, Structure, Anion Binding, and Sensing by Calix[4]pyrrole Isomers
Journal of the American Chemical Society, 2006
The synthesis, structure, and anion binding properties of chromogenic octamethylcalix[4]pyrroles (OMCPs) and their N-confused octamethylcalix[4]pyrrole isomers (NC-OMCPs) containing an inverted pyrrole ring connected via R′-and -positions are described. X-ray diffraction analyses proved the structures of two synthesized isomeric pairs of OMCPs and NC-OMCPs. The addition of anions to solutions of chromogenic OMCPs and NC-OMCPs resulted in different colors suggesting different anion-binding behaviors. The chromogenic NC-OMCPs showed significantly stronger anion-induced color changes compared to the corresponding chromogenic OMCP, and the absorption spectroscopy titrations indicated that chromogenic OMCPs and NC-OMCPs also possess different anion binding selectivity. Detailed NMR studies revealed that this rather unusual feature stems from a different anion-binding mode in OMCPs and NC-OMCPs, one where the -pyrrole C-H of the inverted pyrrole moiety participates in the hydrogenbonded anion-NC-OMCP complex. Preliminary colorimetric microassays using synthesized chromogenic calixpyrroles embedded in partially hydrophilic polyurethane matrices allow for observation of analytespecific changes in color when the anions are administered in the form of their aqueous solutions and in the presence of weakly competing anions.
Coordination Chemistry Reviews, 2006
This is a first review devoted to N-confused calix[4]pyrroles (NCCPs). NCCPs are a relatively recent arrival to the family of the pyrrole-based anion binding macrocycles, being for the first time identified in 1999. Yet, in a relatively short time these calix[4]pyrrole (CP) isomers attracted attention of the community of research groups interested in anion binding and sensing. This is because they are relatively easy to synthesize, but mainly because they posses anion-binding properties that are different from that of regular calix[4]pyrroles. The difference in anion-binding properties stems from a different binding mode between the NCCP and anion. While the regular CPs adopt in the complex an ideal cone-like conformation where all four pyrroles-NHs engage in hydrogen bonding to the anion, the inverted pyrroles do not allow forming the cone. NCCPs bind anions via a confused cone (CC), by three NH hydrogen bonds with an anion and a CH-anion contact. This different binding mode results also in different anion-binding affinity and selectivity compared to regular CPs. Also, the inverted pyrroles offer a unique possibility for selective chemical modification of the receptor. The corresponding colorimetric sensors were tested for anion binding applications. The results of colorimetric assays for anions are presented and potential applications discussed.
Anion Binding Studies of Fluorinated Expanded Calixpyrroles
The Journal of Organic Chemistry, 2005
The anion binding properties of fluorinated calix[n]pyrroles (n ) 4-6) in aprotic solvents (acetonitrile and DMSO) and modified reaction conditions allowing for the synthesis and isolation of the hitherto missing dodecafluorocalix[6]pyrrole from the condensation of 3,4-difluoro-1H-pyrrole and acetone are described. In acetonitrile solution containing 2% water, the association constants for the 1:1 binding interaction between octafluorocalix[4]pyrrole and chloride anion obtained with isothermal titration calorimetry (ITC) and 1 H NMR titration methods were found to match reasonably well. As compared to its nonfluorinated congener, octafluorocalix[4]pyrrole was found to display enhanced binding affinities for several representative anions in pure acetonitrile as judged from ITC analyses. Similar analyses of the fluorinated calix[n]pyrroles revealed an increase in the relative affinity for bromide over chloride with increasing macrocycle size, as manifest in a decrease in the binding ratio K a(Cl) /K a(Br) . Anion binding studies in the solid state, involving single-crystal X-ray diffraction analyses of the chloride and acetate anion complexes of octafluorocalix[4]pyrrole and decafluorocalix-[5]pyrrole, respectively, confirmed the expected hydrogen bond interactions between the pyrrolic NH protons and the bound anions.
Inversion of selectivity in anion recognition with conformationally blocked calix[4]pyrroles
Organic & Biomolecular Chemistry, 2012
Two calixpyrrole derivatives were synthesised. A p-dimethylaminobenzoyl group was electronically attached to a pyrrole ring, establishing an intramolecular hydrogen bond in a 1,3-alternate conformation. The formation of the H-bond was corroborated by IR, NMR, and X-ray measurements. NMR titration studies reveal that the H-bond is strong enough to block the conversion to a cone conformation, allowing them to only acquire a partial cone conformation. Affinity constants for several anions were calculated, and a noticeable increase was observed for tridentate tetrahedral anions, while the K a of spheric or bidentate anions decreased. In the presence of several acids, the synthesised compounds can act as chemosensors by a double process: protonation of the amino group and coordination of the generated anion. In addition, a displacement approach gives rise to a proof of concept for sulphonate recognition. † Electronic supplementary information (ESI) available: 1D and 2D NMR spectra of compounds 1 and 2. IR of 1, 2, 3 and 1·TBACl, NMR titration data, crystallographic data of compounds 1 and 2. CCDC 879852 (1) and 879855 (2). For ESI and crystallographic data in CIF or other electronic format see
Molecules
This manuscript reports the improved synthesis of the α,α,α,α isomer of tetra-p-iodophenyl tetra-methyl calix[4]pyrrole and the X-ray characterization of two solvate polymorphs. In the solid state, the calix[4]pyrrole receptor adopts the cone conformation, including one acetonitrile molecule in its aromatic cavity by establishing four convergent hydrogen bonds between its nitrogen atom and the four pyrrole NHs of the former. The inclusion complexes pack into rods, displaying a unidirectional orientation. In turn, the rods form flat 2D-layers by alternating the orientation of their p-iodo substituents. The 2D layers stack on top of another, resulting in a head-to-head and tail-to-tail orientation of the complexes or their exclusive arrangement in a head-to-tail geometry. The dissimilar stacking of the layers yields two solvate polymorphs that are simultaneously present in the structures of the single crystals. The ratio of the two polymorph phases is regulated by the amount of aceton...
A simple synthesis of 2,2′-bipyrroles from pyrrole
Tetrahedron Letters, 2008
a b s t r a c t 2,2 0 -Bipyrroles, which are obvious precursors for the synthesis of 2,2 0 -bipyrrole-based natural products, are synthesized in three steps from pyrrole employing known pyrrolyl ketoalcohols by a sequential alcohol oxidation and Paal-Knorr pyrrole synthesis.
Calixphyrins. Hybrid macrocycles at the structural crossroads between porphyrins and calixpyrroles
Pure and Applied Chemistry, 2001
Calixphyrins are a class of hybrid molecules that lie at the structural crossroads between porphyrins and calixpyrroles. Porphyrins, long known for their versatile metal cation coordination chemistry, are macrocycles that contain only sp 2 -hybridized bridging meso carbon atoms within their framework. Calix[n]pyrroles, on the other hand, are porphyrin analogs that contain pyrroles bridged exclusively by sp 3 meso carbon centers, and in recent years have been shown to display remarkable anion-binding properties. Calix[n]phyrins bear analogy to both the porphyrins and calixpyrroles and are macrocyclic analogs that contain a mixture of sp 2 -and sp 3 -hybridized meso carbon bridges. This leads to partial interruptions in the conjugation pathway of the molecule, introduces novel structural features, and leads to interesting anion and cation recognition properties. It also allows for modular syntheses. In the present paper, the chemistry of calix[n]phyrins, still at an early stage of exploration, is reviewed.
Organic Letters
Two new expanded calix[4]pyrroles 3 and 4 were synthesized by '2 þ 2' cyclocoupling of easily prepared diboryldipyrromethane 7 (by Ir-catalyzed CH-bond activation) with appropriate diiodoarenes using the Suzuki protocol. Owing to the unique design, both macrocycles exhibited extended π-conjugation and enhanced fluorescence. Upon complexation with anions (fluoride and acetate), receptor 3 displayed turn-on sensing of fluorescence, whereas 4 showed turn-off sensing.
Chromogenic anion molecular probes based on β,β’-disubstituted calix[4]pyrroles
Sensors and Actuators B: Chemical, 2014
The reaction of octamethylcalix[4]pyrrole with 3-(dimethylamino)prop-2-enal and POCl 3 affords a mixture of isomeric calix[4]pyrroles bearing two formylethenyl groups at the ˇ-pyrrolic positions. These dialdehydes were used in Knoevenagel reactions with malononitrile and indene-1,3-dione leading to new chromogenic anion molecular probes. The binding ability of the new receptors was investigated by UV-vis spectroscopy and NMR, indicating the formation of supramolecular 1:2 host:guest complexes with high affinity constants.
Anion Sensing by Fluorescent Expanded Calixpyrroles
Chemistry (Weinheim an der Bergstrasse, Germany), 2018
Expanded calixpyrrole-type macrocycles, calix[2]benzo[4]pyrroles, bearing fluorescent moieties attached via conjugated vinyl spacers, have been synthesized from the corresponding formyl derivatives through Knoevenagel condensation. The anion-binding properties of the resulting fluorescent macrocycles have been studied by means of NMR, UV/Vis, and fluorescence spectroscopies. Our main focus has been on dicarboxylates matching the size of the binding cavity of the calix[2]benzo[4]pyrrole skeleton. The observed anion-binding properties were compared with those of the regular calix[4]pyrroles bearing identical fluorophores. Surprisingly, the parent calix[4]pyrroles appear to be equally efficient, if not more so, for sensing anions such as dicarboxylates. Affinity constants determined for various anions and dianions show the sensors S1-S5 to be highly cross-reactive. The cross-reactivity of the sensors was utilized in a microchip-based array, which showed perfect (100 %) classification o...