Type Macrocycles Research Articles

Phenylene segments of zigzag carbon nanotubes synthesized by metal-mediated dimerization.

Well-studied cycloparaphenylenes (CPPs) correspond to the simplest segments of armchair CNTs, whereas the corresponding macrocyclic oligophenylene strip of zigzag CNTs is still missing. Herein, we present two series of conjugated macrocycles (CM2PP and CN2PP) containing two meta-phenylene or 2,7-naphthylene units facing each other in the strip. CM2PP and CN2PP can be regarded as the shortest cyclic primitive segments of zigzag CNTs. They were synthesized by gold-mediated dimerization and unambiguously characterized. They adopted the tubular structures and can further pack into one-dimensional supramolecular nanotubes. In particular, the supramolecular nanotube of CM2P4P mimics the CNT(9, 0) structure. Structural analysis and theoretical calculation accounted for the reduced ring strain in CM2PPs and CN2PPs. CM2PPs and CN2PPs exhibited a large optical extinction coefficient and high photoluminescence quantum yield. CN2P8P can accommodate fullerene C60, forming a Saturn-like C60@CN2P8P complex, a mimic structure of zigzag CNT peapods.

Mechanical interlocking of SWNTs with N-rich macrocycles for efficient ORR electrocatalysis.

Substitutional N-doping of single-walled carbon nanotubes is a common strategy to enhance their electrocatalytic properties in the oxygen-reduction reaction (ORR). Here, we explore the encapsulation of SWNTs within N-rich macrocycles as an alternative strategy to display electroactive sites on the surface of SWNTs. We design and synthesize four types of mechanically interlocked derivatives of SWNTs (MINTs) by combining two types of macrocycles and two types of SWNT samples. Comprehensive electrochemical characterization of these MINTs and their reference SWNTs allows us to establish structure–activity relationships. First, we show that all MINT samples are superior electrocatalysts compared to pristine SWNTs, which serves as general validation of our strategy. Secondly, we show that macrocycles displaying both N atoms and carbonyl groups perform better than those with N atoms only. Finally, we demonstrate that a tighter fit between macrocycles and SWNTs results in enhanced catalytic activity and stability, most likely due to a more effective charge-transfer between the SWNTs and the macrocycles. These results, focusing on the ORR as a testbed, show the possibility of understanding electrocatalytic performance of SWNTs at the molecular level and thus enable the design of more active and more stable catalysts in the future.

Structure analysis of inclusion crystals of diimide-based macrocycles with halocarbons

Inclusion crystals containing several halocarbons were formed by three types of diimide-based macrocycles. Iodomethane was encapsulated within the cavity of the macrocycle through halogen-related interactions.

Controlling chirality in the synthesis of 4 + 4 diastereomeric amine macrocycles derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine.

A few suitably long dialdehyde and primary diamine building blocks of a predetermined chirality have been designed and synthesized to enable controlled and efficient synthesis of all six possible diastereomers of 4 + 4 macrocyclic amine derived from trans-1,2-diaminocyclopentane (DACP) and 2,6-diformypyridine (DFP) units. Although two out of six diastereomers have been reported recently, their synthesis presented here is more direct and occurs with an improved yield. This family of 4 + 4 macrocycles contains one pair of homochiral enantiomers of identical RRRRRRRR and SSSSSSSS configurations of DACP units, two different meso forms (meso I of alternating RRSSRRSS and meso II of neighboring RRRRSSSS configuration of DACP moieties) as well as one pair of heterochiral enantiomers, where configuration of one diamine fragment is opposite to the other three diamine parts, RRRRRRSS and SSSSSSRR, respectively. The structures of each type of macrocycle in solid state have been confirmed by single crystal analyses of a macrocyclic amine in its suitable protonated form. The different symmetry of each type of macrocycle in solutions has been proved by 1H and 13C NMR spectra of their hydrochloride derivatives. The chiral nature of two different pairs of optically active enantiomers has been established by circular dichroism spectra. These chiral 4 + 4 diastereomeric macrocycles are receptors for chiral guests and recognize in solution 10-camphorsulfonic acid as well as chiral tartaric acid.

Entropy Effects in Intermolecular Associations of Crown-Ethers and Cyclodextrins with Amino Acids in Aqueous and in Non-Aqueous Media.

The analysis of the ratios of entropy and enthalpy characteristics and their contributions to the change in the Gibbs energy of intermolecular interactions of crown ethers and cyclodextrins with amino acids is carried out. Two different types of macrocycles were chosen for examination: crown ethers with a hydrophilic interior and cyclodextrins with a hydrophobic inner cavity and a hydrophilic exterior. The thermodynamics of complex formation of crown ethers and cyclodextrins with amino acids in water and aqueous-organic solvents of variable composition was examined. The contributions of the entropy solvation of complexes of 18-crown-6 with glycine, alanine, phenylalanine to the change in the entropy of complexation in water-ethanol and water-dimethyl sulfoxide solvents was calculated and analyzed. It was found that the ratios of the entropy and enthalpy solvation of the reagents for these systems have similar trends when moving from water to aqueous-organic mixtures. The relationship between the thermodynamic characteristics and structural features of the complexation processes between cyclodextrins and amino acids has been established. The thermodynamic enthalpy–entropy compensation effect was revealed, and its features for complexation of cyclodextrins and 18-crown-6 were considered. It was concluded that, based on the thermodynamic parameters of molecular complexation, one could judge the mode of the formation of complexes, the main driving forces of the interactions, and the degree of desolvation.

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

All are aromatic: A 3D globally aromatic cage containing five types of 2D aromatic macrocycles

Calix[3]-Type Macrocycles: The Missing Family Member

Calix[3]-Type Macrocycles: The Missing Family Member

Calix[3]pyrrole: A Missing Link in Porphyrin-Related Chemistry.

A long-standing question in porphyrin chemistry is why pyrrole monomers selectively form tetrapyrrolic macrocycles, whereas the corresponding tripyrrolic macrocycles are never observed. Calix[3]pyrrole, a tripyrrolic porphyrinogen-like macrocycle bearing three sp3-carbon linkages, is a missing link molecule that might hold the key to this enigma; however, it has remained elusive. Here we report the synthesis and strain-induced transformations of calix[3]pyrrole and its furan analogue, calix[3]furan. These macrocycles are readily accessed from cyclic oligoketones. Crystallographic and theoretical analyses reveal that these three-subunit systems possess the largest strain energy among known calix[n]-type macrocycles. The ring-strain triggers transformation of calix[3]pyrrole into first calix[6]pyrrole and then calix[4]pyrrole under porphyrin cyclization conditions. The present results help explain the absence of naturally occurring three-pyrrole macrocycles and the fact that they are not observed as products or intermediate during classic porphyrin syntheses.

Pillararene-based supramolecular systems for theranostics and bioapplications

As an emerging type of important macrocycles for supramolecular chemistry, pillararenes and their derivatives have been widely studied and applied in numerous fields, which intensively promotes the development of chemistry, materials science and biology. Pillararene-based theranostic systems are of special interest in the biological and medical areas as they have shown very promising results. Owing to easy preparation, reliable guest affinity, good biocompatibility and stability, pillararenes are frequently used to construct functional biomaterials. On one hand, pillararenes can either be used individually or form diversiform self-assemblies such as micelles, nanoparticles and vesicles to increase water solubility and biocompatibility of drugs. On the other hand, it is promising to modify solid materials like framework materials, silica nanoparticles and graphene oxides with pillararene derivatives to enhance their functions and controllability. In this review, we summarize recent endeavors of pillararene-based supramolecular systems with theranostics and other biological applications comprising drug delivery/chemotherapy, photodynamic/photothermal therapy, antimicrobials, bioimaging, etc. By introducing several typical examples, the design principles, preparation strategies, identifications and bio-applications of these pillararene-based supramolecular systems are described. Future challenges and directions of this field are also outlined.

Self-assembly of novel copper(II) macrocyclic and luminescent europium(III) triple-stranded supramolecules with new anthracene-based bis-β-diketonate ligands

Two novel bis-(β-diketonate) ligands, 1,1′-(anthracene-1,8-diyl)bis(butane-1,3-dione) (H2L1), 1,1′-(anthracene-1,5-diyl)bis(4,4,4-trifluorobutane-1,3-dione) (H2L2) have been designed and synthesized for self-assembly of the luminescent supramolecular coordination compounds with transition and lanthanide metals. Two neutral dinuclear supramolecular assemblies Cu(II)-bis-β-diketonate macrocyclic complex [Cu2(L1)2](CH3OH)2 (1·2CH3OH) and Eu(III) bis-β-diketonate triple-stranded complex [Eu2(L2)3](CH3OH)4 (2·4CH3OH) have been characterized by various spectroscopic techniques. Their photophysical properties were further investigated. X-ray single crystal structural analysis revealed that complex 1·2CH3OH adopts a 1D chain arrangement which is constructed with a pitch of 1.951 Å through intermolecular hydrogen bonds along the b axis. The slightly distorted parallelogram of 1 is a neutral [M2L2]-type macrocycle with a size of 5.40 Å × 8.40 Å. The triple-stranded helicate CPK (Corey-Pauling-Koltun) diagram was calculated using Scigress 2.6 program.

Rh(III)-Catalyzed mild straightforward synthesis of quinoline-braced cyclophane macrocycles via migratory insertion.

An efficient Rh(III)-catalyzed straightforward strategy is developed for the synthesis of quinoline braced cyclophane macrocycles via methyl (sp3) C-H functionalization. The method is mild, simple and regioselective with various ring sizes and has good functional group tolerance. The method proceeds via C8-methyl metalation, metal-carbene formation and a subsequent migratory insertion. High dilution is not necessary for this macrocyclization and the only byproduct is nitrogen. A preliminary investigation shows that the C-H metalation step is the rate-determining step.

Construction of Hydrocarbon Nanobelts.

Linearly fused hydrocarbon nanobelts are a unique type of double-stranded macrocycles that would serve as not only the powerful hosts in supramolecular science but also the templates to grow zig-zag carbon nanotubes with defined diameters. Fully conjugated hydrocarbon nanobelts such as belt[n]arenes would also possess unique physical and chemical properties. Despite the importance, both fully conjugated and (partially) saturated hydrocarbon nanobelts remain largely unexplored because of the lack of cyclization methods. Reported here is the construction of nanometer sized H12 -belt[12]arenes based on the strategy to close up all fjords of resorcin[6]arene by means of six-fold intramolecular alkylation reactions of resorcin[6]arene derivatives. All resulting H12 -belt[12]arenes produce a very similar nanobelt core structure with six benzene rings and six boat 1,4-cyclohexadiene rings being alternately linear-fused to give a nearly equilateral hexagonal cylinder. The average long diagonal is around 1 nm and the height of the cylinder is about 0.3 nm. The acquired H12 -belt[12]arenes would be the potential precursors to various hydrocarbon nanobelts including fully conjugated belt[12]arenes.

A new spirofluorene-based nonplanar PBI-dyad and its utilization in the film-based photo-production of singlet oxygen

Traditional photosensitizers are predominantly based on various types of polypyrrole macrocycles, which are generally used in homogeneous and/or suspension states. In the present study, a new non-polypyrrole-based photosensitizer (LW-PBI) was developed via the introduction of a nonplanar spirofluorene into a derivative of perylene bisimides (PBI) containing two longalkyl chains. Photophysical studies demonstrated that the compound shows good solubility in common organic solvents, great photochemical stability, and high absorption efficiency in the visible light region. Due to containing of two energetically matchable, independent fluorescent units, the compound as prepared displays strong tendency to form non-fluorescent charge-separated states under light irradiation in polar solvents. Based on the merits, LW-PBI was examined for its catalytic property in the photo-production of singlet oxygen in film state. Luckily, the compound is an effective photosensitizer in the generation of the active oxygen species as verified by its unique reaction with uric acid (UA). Further studies revealed that the effective photo-production of singlet oxygen can be also realized via the utilization of a tiny and low-price LED lamp as a light source and as a film support. Detailed studies on the application of the conceptual device as a medical instrument for photodynamic therapy (PDT) are in progress.

Reactions of anions [(μ-PhSe)(μ-CO)Fe2(CO)6]− and {[μ-SeZSe-μ][(μ-CO)Fe2(CO)6]2}2− with various electrophiles to give the corresponding new linear and macrocyclic cluster complexes

To develop the butterfly Fe/E (E = S, Se) cluster chemistry, the following four types of new butterfly Fe/E cluster complexes have been synthesized and structurally characterized. The first type of such complexes involves the linear type of (diphosphine)Pt-bridged double-butterfly Fe/E clusters [(μ-PhSe) (μ-S=CS)Fe2(CO)6]2[Pt(diphosphine)] (1–3, diphosphine = dppe, dppv, dppb), while the second type of complexes involves the linear type of butylene-bridged double-butterfly Fe/E clusters [μ-Se(CH2)4Se-μ][(μ-R)Fe2(CO)6]2 (4–6, R = PhCH2SC=S; PhNHC = S; PhC = NC6H4Me-p). More interestingly, the third and fourth types of complexes include the macrocyclic type of (diphosphine)Pt-bridged double-butterfly Fe/E clusters [μ-Se(CH2)3Se(CH2)3Se-μ][(μ-S=CS)Fe2(CO)6]2[Pt(diphosphine)] and the macrocyclic type of quadruple-butterfly Fe/E clusters {[μ-Se(CH2)3Se-μ][(μ-S=CS)Fe2(CO)6]2}2[Pt(diphosphine)]2 (7a,b−8a,b, diphosphine = dppe, dppv), respectively. While the possible pathways for production of the four types of new butterfly Fe/E complexes are briefly described, their structures are characterized by elemental analysis and various spectroscopic methods, and particularly for their representatives by X-ray crystallography.

A donor-acceptor type macrocycle: toward photolyzable self-assembly.

A water-soluble macrocyclic host is reported, composed of alkoxyanthracene as the donor (D), and 4,4-bipyridinium as the acceptor (A). The intramolecular D-A structure renders the host highly photostable. However, the introduction of a strong electron-donating guest promotes the photodecomposition of alkoxyanthracene, yielding photolyzable host-guest complexes or aggregates.

Dinuclear silver(i) complexes with a pyridine-based macrocyclic type of ligand as antimicrobial agents against clinically relevant species: the influence of the counteranion on the structure diversification of the complexes.

New dinuclear silver(i) complexes with N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc), [Ag2(NO3)(tpmc)]NO3·1.7H2O (1), [Ag2(CF3SO3)2(tpmc)] (2), and [Ag2(tpmc)](BF4)2 (3) were synthesized and characterized by NMR (1H and 13C), IR and UV-Vis spectroscopy, cyclic voltammetry and molar conductivity measurements. The molecular structures of the complexes were determined by single-crystal X-ray diffraction analysis. The spectroscopic and crystallographic data showed that the structure of the complexes strongly depends on the nature of the counteranion of silver(i) salt used for their synthesis. The antimicrobial activity of complexes 1-3 was examined against Gram-positive and Gram-negative bacteria and different species of unicellular fungus Candida spp. The ability of these complexes to inhibit the formation of Candida biofilms and to eradicate the already formed biofilms was tested in the standard microtiter plate-based assay. In addition, a bioelectrochemical testing of the antimicrobial activity of complex 1 against early biofilm was also performed. The obtained results indicated that complexes 1-3 showed increased activity toward Gram-negative bacteria and Candida spp. and could inhibit the formation of biofilms. In most cases, these complexes had positive selectivity indices and showed similar or even better activity with respect to the clinically used silver(i) sulfadiazine (AgSD). The values of the binding constants for complexes 1-3 to bovine serum albumin (BSA) were found to be high enough to indicate their binding to this biomolecule, but not so high as to prevent their release upon arrival at the target site. Moreover, the positive values of partition coefficients for these complexes indicated their ability to be transported through the cell membrane. Once inside the cell, complexes 1-3 could induce the formation of the reactive oxygen species (ROS) in C. albicans cells and/or interact with DNA. Taken together, silver(i) complexes with the tpmc ligand could be considered as novel antimicrobial compounds with favourable pharmacological properties, being safer than AgSD.

Supramolecular-Macrocycle-Based Crystalline Organic Materials.

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Enantioselective Solid-Liquid Extraction of Native Saccharides with Chiral BINOL-Based Pyridine-Phenol Type Macrocycles.

A chiral 1,1'-bi-2-naphthol (BINOL)-containing pyridine-acetylene-phenol macrocycle and a pyridine-BINOL alternating macrocycle were developed for enantioselective recognition of saccharides. In solid-liquid extraction of native saccharides, these macrocycles selectively extracted one enantiomer from each of a racemic mixture of d/l-fructose, d/l-glucose, and d/l-mannose into a lipophilic solvent. This is the first example in which native saccharides, especially such important hexoses, were enantioselectively extracted with artificial host molecules.

Introduction of polar or nonpolar groups at the hydroquinone units can lead to the destruction of the columnar structure of Pillar[5]arenes

Pillar[5]arenes, a type of novel macrocycles containing di-substituted hydroquinone units linked by methylene bridges in para-positions, have attracted extensive attention in supramolecular chemistry as interesting candidates to be used in the preparation of host-guest complexes. Functionalization by means of rim substitution and sustaining an ordered substituent arrangement on both sides of the rim is important for the development of new pillararene-based materials. In order to achieve this, the rim inversion process of rotating the hydroquinone units through the pillar[5]arenes has to be controlled. In this context we have studied the effect of different types of hydroquinone substituents on the rotational energy profile using density functional theory combined with the hybrid M06-2X functional. The influence of polar (CH2F, CH2Cl, CH2OH, CH2SH, CH2NH2) and nonpolar alkyl (CH3, CH2CH3, CH2CH2CH3, CH(CH3)2 and CH2CH2CH2CH3) substituents on the on the energy barriers of the rotation mechanism, and different local minima was investigated. The stabilization of the intermediate structures by non-covalent van der Waals and interactions and also by hydrogen bonds constitute a major factor affecting barrier heights. In case of polar substituents, the largest barriers were found for CH2OH and CH3 substitutions and the lowest ones for CH2SH and CH2NH2. For the alkyl series, the barrier decreased significantly up to propyl due to increasing stabilizing dispersion interactions while it increased again for n-butyl since the chain did not fit in well the cavity to rotate through.

Atropisomer-based construction of macrocyclic hosts that selectively recognize tryptophan from standard amino acids.

A syn-atropisomer of naphthalene diimide as a highly preorganized precursor was used to construct a type of trapezoid-shape macrocycle, namely 'trapezoid' molecular boxes (TBox). As supramolecular hosts, TBox can bind electron-rich guests and selectively recognize free tryptophan and tryptophanyl residues from 20 standard amino acids.