Search Results (32)

For decades, dendrimers have attracted the great interest of researchers, and continue to do so to this day. These compounds found a wide variety of applications in such areas as medicine, catalysis, and electronics. However, their synthesis is very expensive, and purification and isolation are difficult. In addition, dendrimers are often highly toxic. Toxic properties are significantly dependent on the generation and terminal group features. For the toxicity, decreasing the modification of dendrimer structure is widely used. This review discusses some examples of constructing dendrimers based on macrocyclic compounds—cyclophanes (pillararenes, resorcinarenes, and (thia)calixarenes). Preparation of these hybrids is not very difficult, and due to the presence of a hydrophobic macrocyclic platform, they acquire a number of practically useful properties that are not available to traditional dendrimers, such as additional opportunities for encapsulating substrates. Moreover, dendrimers acquire amphiphilic and chiral properties. This review is devoted to the features of the synthesis and properties of macrocyclic dendrimers based on cyclophanes. The review also demonstrates the prospects of using the resulting dendrimers for medicine, sensorics, catalysis and alternative energy sources. Full article

Radicals based on arylamine cyclophanes can be used as functional materials and show application potential in fields such as synthetic chemistry, molecular electronic components, organic light-emitting diodes, and catalytic chemistry. Using a Buchwald–Hartwig palladium-catalyzed aryl halide amination method, we synthesized a series of neutral hexaazacyclophane compounds 1–3 with different substituents in the meta–meta–meta positions of the phenyl rings. Three characteristic high-spin hexaazacyclophane diradical dications were obtained by two-electron oxidation using AgSbF₆: 1^2·+•2[SbF₆]⁻, 2^2·+•2[SbF₆]⁻, and 3^2·+•2[SbF₆]⁻. The electronic structures and physical properties of these compounds were then investigated by ¹H and ¹³C nuclear magnetic resonance spectroscopy, cyclic voltammetry, electron paramagnetic resonance spectroscopy, superconducting quantum interferometry, ultraviolet–visible spectroscopy, and density functional theory calculations. The findings provide new ideas for designing radical species with novel physical properties and electronic structures. Importantly, the obtained radical species are not sensitive to air, making them valuable functional materials for practical applications. Full article

Prismanes have been attracting interest for nearly 50 years because of their geometric symmetry, highly strained structures, and unique applications due to their high carbon densities and bulky structures. Although [3]-, [4]-, and [5]-prismanes have been synthesised, [6]-prismanes and their derivatives remain elusive. Herein, fluorine chemistry, molecular mechanics, molecular orbital package, and density functional theory calculations were used to design and implement the photoisomerisation of octafluoro[2.2]paracyclophane (selected based on the good overlap of its lowest unoccupied molecular orbitals and short distance between the benzene rings) into octafluoro-[6]-prismane. Specifically, a dilute solution of the above precursor in CH₃CN/H₂O/dimethyl sulfoxide (DMSO) (2:1:8, v/v/v) solution was irradiated with ultraviolet light, with the formation of the desired product confirmed through the use of nuclear magnetic resonance spectroscopy and gas chromatography–mass spectrometry. The product was thermally stable in solution but not under work-up conditions, which complicated the further analysis and single-crystal preparation. The key criteria for successful photoisomerisation were the presence of fluorine substituents in the cyclophane structure and DMSO in the solvent system. A more stable derivative design requires the isolation of prismane products. The proposed fluorination-based synthetic strategy is applicable to developing novel high-strain molecules/materials with three-dimensional skeletons. Full article

The main topic of the article is to provide the characteristics of individual intermolecular interactions present between three lantern-like superphanes and the ${\mathrm{H}}_2$O, ${\mathrm{NH}}_3$, HF, HCN, and MeOH molecules trapped inside them. Despite the large cavity, the freedom of the trapped molecules is significantly limited by the presence of numerous interaction sites on the side chains of the superphane molecule. It is shown that the molecule trapped inside the superphane is stabilized mainly by only one or, less often, two strong hydrogen bonds involving the imino nitrogen atom, but QTAIM calculations also suggest the presence of many other intermolecular interactions, mainly hydrogen bonds involving imino or central hydrogen atoms from the side chains of the superphane molecule. Moreover, it is also shown that the structural simplification of the side chains does not significantly affect both the size of the superphane molecule and the obtained encapsulation energies, which is important in modeling this type of carceplexes. Noticeably, the parent superphane considered here was previously synthesized by the group of Qing He, so the results obtained will help in understanding this type and similar systems. Full article

According to Bader’s quantum theory of atoms in molecules (QTAIM), the simultaneous presence of a bond path and the corresponding bond critical point between any two atoms is both a necessary and sufficient condition for the atoms to be bonded to one another. In principle, this means that this pair of atoms should make a stabilizing contribution to the molecular system. However, the multitude of so-called counterintuitive bond paths strongly suggests that this statement is not necessarily true. Particularly ‘troublesome’ are endohedral complexes, in which encapsulation-enforced proximity between the trapped guest (e.g., an atom) and the host’s cage system usually ‘produces’ many counterintuitive bond paths. In the author’s opinion, the best evidence to demonstrate the repulsive nature of the intra-cage guest⋯host interaction is the use of some trapping systems containing small escape channels and then showing that the initially trapped entity spontaneously escapes outside the host’s cage during geometry optimization of the initially built guest@host endohedral complex. For this purpose, a group of 24 Ng@[3${}_n$]cyclophane (3$\le n\le$6) endohedral complexes is used. As a result, arguments are presented showing that Bader’s topological bond path does not necessarily indicate a stabilizing interaction. Full article

Several new di- and tetracarboxylic [2.2]paracyclophane derivatives were obtained via Suzuki coupling between the appropriately brominated [2.2]paracyclophanes and 4-(methoxycarbonyl)phenylboronic acid. The reaction of one of these products, namely pp-bis(4-carboxyphenyl)[2.2]paracylophane (12), with zinc nitrate afforded a 2D coordination polymer comprising zinc-carboxylate paddlewheel clusters linked together by cyclophane cores. The zinc center is five-coordinated in a square-pyramidal geometry, with a DMF oxygen atom at the apex and four carboxylate oxygen atoms in the base. Full article

A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log K_b values in the range of 2.3–3.2 for pyrimidine nucleotides TMP (thymidine monophosphate), TTP (thymidine triphosphate) and CMP (cytidine monophosphate) and 3.8–5.0 for purine nucleotides AMP (adenosine monophosphate), ATP (adenosine triphosphate), and dGMP (deoxyguanosine monophosphate). Notably, in a neutral buffer solution, the fluorimetric response to the complex formation depends on the type of nucleotide. Hence, quenching of the already weak fluorescence was observed with the purine bases, whereas the association of the cyclophane with pyrimidine bases TMP, TTP, and CMP resulted in a significant fluorescence light-up effect. Thus, it was demonstrated that the styrylpyridine unit is a useful and complementary fluorophore for the development of selective nucleotide-targeting fluorescent probes based on alkylamine-linked cyclophanes. Full article

A study of cofacially arrayed π-systems is of particular importance for the design of functional materials for efficient long-range intra-chain charge transfer through the bulk semiconducting materials in the layers of photovoltaic devices. The effect of π-stacking between a pair of aromatic rings has been mainly studied in the form of cyclophanes, where aromatic rings are forced into a sandwich-like geometry, which extensively deforms the aromatic rings from planarity. The synthetic difficulties associated with the preparation of cyclophane-like structures has prevented the synthesis of many examples of their multi-layered analogues. Moreover, the few available multi-layered cyclophanes are not readily amenable to the structural modification required for the construction of D–spacer–A triads needed to explore mechanisms of electron and energy transfer. In this review, we recount how a detailed experimental and computational analysis of 1,3-diarylalkanes led to the design of a new class of cofacially arrayed polyfluorenes that retain their π-stacked structure. Thus, efficient synthetic strategies have been established for the ready preparation of monodisperse polyfluorenes with up to six π-stacked fluorenes, which afford ready access to D–spacer–A triads by linking donor and acceptor groups to the polyfluorene spacers via single methylenes. Detailed ¹H NMR spectroscopy, X-ray crystallography, electrochemistry, and He(I) photoelectron spectroscopy of F2–F6 have confirmed the rigid cofacial stacking of multiple fluorenes in F2–F6, despite the presence of rotatable C–C bonds. These polyfluorenes (F2–F6) form stable cation radicals in which a single hole is delocalized amongst the stacked fluorenes, as judged by the presence of intense charge-resonance transition in their optical spectra. Interestingly, these studies also discern that delocalization of a single cationic charge could occur over multiple fluorene rings in F2–F6, while the exciton is likely localized only onto two fluorenes in F2–F6. Facile synthesis of the D–spacer–A triads allowed us to demonstrate that efficient triplet energy transfer can occur through π-stacked polyfluorenes; the mechanism of energy transfer crosses over from tunneling to hopping with increasing number of fluorenes in the polyfluorene spacer. We suggest that the development of rigidly held π-stacked polyfluorenes, described herein, with well-defined redox and optoelectronic properties provides an ideal scaffold for the study of electron and energy transfer in D-spacer-A triads, where the Fn spacers serve as models for cofacially stacked π-systems. Full article

In this study, 28-membered macrocyclic 1,5(1,5)-di(1,5-diaza-3,7-diphosphacyclooctana)-2,4,6,8(1,4)-tetrabenzenacyclooctaphane were synthesized by condensation of pyridinephosphine, paraformaldehyde, and primary diamines (bis(4-aminophenyl)methane or -sulfide. The first representatives of binuclear copper(I) complexes of P,N-containing cyclophanes with two 1,5-diaza-3,7-diphosphacyclooctane rings incorporated into a macrocyclic core and intracavity location of unusual, developed angle Cu₂I moiety were obtained. The structure of one complex was established by X-ray diffraction analysis. The complexation led to a slight distortion of the cyclophane conformations. Full article

This paper reviews the most stable conformation of crystalline three-dimensional cyclophane (CP) achieved by self-assembling based on changing the type of aromatic compound or regulating the type and number of bridging groups. [3_n]cyclophanes (CPs) were reported to form supramolecular compounds with bind organic, inorganic anions, or neutral molecules selectively. [3_n]cyclophanes ([3_n]CPs) have stronger donor capability relative to compound [2_n]cyclophanes ([2_n]CPs), and it is expected to be a new type of electron donor for the progress of fresh electron conductive materials. The synthesis, conformational behavior, and properties of crystalline multi-bridge rings are summarized and discussed. Full article

Superphane, i.e., [2.2.2.2.2.2](1,2,3,4,5,6)cyclophane, is a very convenient molecule in studying the nature of guest⋯host interactions in endohedral complexes. Nevertheless, the presence of as many as six ethylene bridges in the superphane molecule makes it practically impossible for the trapped entity to escape out of the superphane cage. Thus, in this article, I have implemented the idea of using the superphane derivatives with a reduced number of ethylene linkers, which leads to the [2${}_n$] cyclophanes where $n<6$. Seven such cyclophanes are then allowed to form endohedral complexes with noble gas (Ng) atoms (He, Ne, Ar, Kr). It is shown that in the vast majority of cases, the initially trapped Ng atom spontaneously escapes from the cyclophane cage, creating an exohedral complex. This is the best proof that the Ng⋯cyclophane interaction in endohedral complexes is indeed highly repulsive, i.e., destabilizing. Apart from the ‘sealed’ superphane molecule, endohedral complexes are only formed in the case of the smallest He atom. However, it has been shown that in these cases, the Ng⋯cyclophane interaction inside the cyclophane cage is nonbonding, i.e., repulsive. This highly energetically unfavorable effect causes the cyclophane molecule to ‘swell’. Full article

Five novel tyrosine-decahydrofluorene analogues, xenoacremones D–H (1–5), each bearing a fused 6/5/6 tricarbocyclic core and a 13-membered para-cyclophane ring system, were isolated from the endophytic fungus Xenoacremonium sinensis. Compound 1 was a novel polyketide synthase–nonribosomal peptide synthetase (PKS–NRPS) tyrosine-decahydrofluorene hybrid containing a 6/5/6/6/5 ring system. Their structures were elucidated from comprehensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. All compounds were evaluated for their inhibitory activities on LPS-induced NO production in macrophages and their cytotoxicities against the NB4 and U937 cell lines. Compounds 3 and 5 exhibited potent anti-inflammatory activities in vitro. Compounds 1 and 3–5 displayed significant antiproliferative activity against the tumor cell lines (IC₅₀ < 20 µM). Full article

Background: Benzoxazole-containing ligands find many applications both in medicinal chemistry, catalysis and fluorescence chemosensing. Benzoxazole-containing macrocycles could be therefore a good strategy to achieve stable and selective fluorescent complexes with suitable metal ions. In this work, the synthesis, binding, and photochemical properties of a new fluorescent ligand (L) are reported. L is a cyclophane macrocycle containing the 1,3-bis(benzo[d]oxazol-2-yl)phenyl (BBzB) fluorophore and an aliphatic tetra-amine chain to form the macrocyclic skeleton. Methods: Spectrophotometric and spectrofluorimetric measurements, ¹H NMR analysis, and DFT calculations were performed. Results: L behaves as a PET-mediated chemosensor, being emissive at 390 nm at acidic pH and non-emissive at basic pH. The chemosensor is able to detect Zn²⁺ and Cd²⁺ in an aqueous medium (acetonitrile–water, 4:1 v/v) at neutral pH through a CHEF effect upon metal ion coordination. Paramagnetic metal ions (Cu²⁺) and heavy atoms (Pb²⁺, Hg²⁺) resulted in a quenching of fluorescence or very low emission. Conclusions: The new cyclophane macrocycle L was revealed to be a selective PET-regulated chemosensor for Zn²⁺ and Cd²⁺ in an aqueous medium, being able to bind up to two and one metal cations, respectively. The molecule showed a shifted emission towards the visible region compared to similar systems, suggesting a co-planar conformation of the aromatic fragment upon metal coordination. All these data are supported by both experimental measurements and theoretical calculations. Full article

The restricted rotation of chemical bonds may lead to the formation of stable, conformationally chiral molecules. While the asymmetry in chiral molecules is generally observed in the presence of one or more stereocenters, asymmetry exhibited by conformational chirality in compounds lacking stereocenters, called atropisomerism, depends on structural and temperature factors that are still not fully understood. This atropisomerism is observed in natural diarylether heptanoids where the length of the intramolecular tether constrains the compounds to isolable enantiomers at room temperature. In this work, we examine the impact tether length has on the activation free energies to isomerization of a diarylether cyclophane substructure with a tether ranging from 6 to 14 carbons. Racemization activation energies are observed to decay from 48 kcal/mol for a 7-carbon tether to 9.2 kcal/mol for a 14-carbon tether. Synthetic efforts to experimentally test these constraints are also presented. This work will likely guide the design and synthesis of novel asymmetric cyclophanes that will be of interest in the catalysis community given the importance of atropisomeric ligands in the field of asymmetric catalysis. Full article

Eight analogues of the bioherbicides macrocidin A (1) and Z (2) with structural variance in the size of the macrocycle, its para- or meta-cyclophane character, and its functional groups were synthesized on two modular routes and tested for herbicidal, antibiotic, and antibiofilm activities. Apart from the lead compounds 1 and 2, the structurally simplified dihydromacrocidin Z (3) and normacrocidin Z (4) showed high herbicidal activity in either thistles, dandelions or in both. The derivatives 2, 3, and dibromide 9 also inhibited the growth of Staphylococcus aureus biofilms by ca 70% when applied at subtoxic concentrations as low as ca 20 µM, which are unlikely to induce bacterial resistance. They also led to the dispersion of preformed biofilms of S. aureus, exceeding a similar effect by microporenic acid A, a known biofilm inhibitor. Compounds 3 and 9 showed no noticeable cytotoxicity against human cancer and endothelial cells at concentrations below 50 µM, making them conceivable candidates for application as anti-biofilm agents in a medicinal context. Full article