Per-Alkoxy-pillararenes as Electron Donors: Electrochemical Properties of Dimethoxy-Pillararene and Its Corresponding Rotaxane.
ABSTRACT: 1,4-dimethoxypillararene undergoes reversible multielectron oxidations forming stable radical cations, a property retained when incorporated in rotaxanes, suggesting that pillararenes can be employed as viable, yet unreported, electron donors.
Project description:The pillararene mono- and di(oxyalkoxy)benzoic acids were successfully prepared in high yields by sequential alkylation of ?-bromoalkoxy-substituted pillararenes with methyl or ethyl p-hydroxybenzoate followed by a hydrolytic reaction under basic conditions. Under catalysis of HOBt/EDCl, the amidation reaction of pillararene mono(oxybutoxy)benzoic acid with monoamido-functionalized pillararenes afforded diamido-bridged bis-pillararenes. 1H NMR and 2D NOESY spectra clearly indicated that rotaxanes were formed by insertion of longer diaminoalkylene unit into the cavity of one pillararene with another pillararene acting as a stopper. The similar catalysed amidation reaction of pillararene di(oxybutoxy)benzoic acid with monoamido-functionalized pillararenes resulted in the diamido-bridged tris-pillararenes, which successfully form the unique bis-rotaxanes bearing longer than diaminopropylene diamido bridges.
Project description:Pillar[n]arenes are a new type of macrocyclic compounds, which were first reported in 2008 by Ogoshi. They not only have cylindrical, symmetrical, and rigid structures, but also have many advantages, including easy functionalization and rich host-guest properties. On the other hand, mechanically interlocked molecules (MIMs) exist extensively in nature which have been artificially synthesized and widely applied in the fields of nanotechnology and biology. Although pillararene-based MIMs have been investigated much over recent years, pillararene-based rotaxanes are very limited. In this report, we synthesized a series of amide-linked pillararene-based rotaxanes with ferrocene unit as the stopper. Under the catalysis of HOBT/EDCL, the mono-amido-functionalized pillararenes were amidated with ferrocene carboxylic acid to constructed ferrocene-based rotaxanes, respectively. The structure of the rotaxanes were characterized by 1H NMR, 13C NMR, 2D NMR, mass spectroscopy, and single-crystal X-ray structural determination. In the experiment, the monofunctionalized pillararene was synthesized with a self-inclusion property, which allows for forming a pseudo-rotaxane. The key role is the length of the imine chain in this process. The formation of a rotaxane was realized through amidation of ferrocene dicarboxylic acid, which acted as a plug. In addition, due to the ferrocene units, the pillararene-based rotaxanes perform electrochemically reversible property. Based on this nature, we hope these pillararene-based rotaxanes can be applied in battery devices in the future.
Project description:Two types of mono-ester-functionalized pillararenes, P1 and P2, bearing different side-chain groups, were synthesized. Their host-guest complexation and self-inclusion properties were studied by 1H NMR and 2D nuclear overhauser effect spectroscopy (NOESY) NMR measurements. The results showed that the substituents on their phenolic units have a great influence on the self-assembly of both pillararenes, although they both could form stable pseudorotaxanes at room temperature. When eight bulky 4-brombutyloxy groups were capped on the cavity, instead of methoxy groups, pseudorotaxane P1 became less stable and its locked ester group in the inner space of cavity was not as deep as P2, leading to distinctly different host-guest properties between P1 and P2 with 1,6-dibromohexane. Moreover, pillararene P1 displayed effective molecular recognition toward 1,6-dichlorohexane and 1,2-bromoethane among the guest dihalides. In addition, the self-complex models and stabilities between P1 and P2 were also studied by computational modeling and experimental calculations.
Project description:A series of mono-amide-functionalized pillararenes with different lengths of N-?-aminoalkyl groups as the side chain on the rim were designed and synthesized, which all formed pseudorotaxanes in the crystal state. And these pseudorotaxanes could be transformed into rotaxanes or open forms in the crystal state. In addition, they were also studied in solution by (1)H NMR spectroscopy.
Project description:A synthetic approach combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self-assembly to prepare rotaxanes) gave easy access to a large variety of sophisticated rotaxane heteroglycoclusters. Specifically, compounds combining galactose and fucose have been prepared to target the two bacterial lectins (LecA and LecB) from the opportunistic pathogen Pseudomonas aeruginosa.
Project description:A new approach for the reduction of aryl ammonium salts to arenes or aryl silanes using nickel catalysis is reported. This method displays excellent ligand-controlled selectivity based on the N-heterocyclic carbene (NHC) ligand employed. Utilizing a large NHC in non-polar solvents generates aryl silanes, while small NHCs in polar solvents promote reduction to arenes. Several classes of aryl silanes can be accessed from simple aniline building blocks, including those useful for cross-couplings, oxidations, and halogenations. The reaction conditions are mild, functional group tolerant, and provide efficient access to a variety of benzene derivatives.
Project description:The development of an efficient synthetic route toward rim-differentiated C5-symmetric pillararenes (Ps), whose two rims are decorated with different chemical functionalities, opens up successive transformations of this macrocyclic scaffold. This paper describes a gram-scale synthesis of a C5-symmetric penta-hydroxy P precursor, and a range of highly efficient reactions that allow functionalizing either rim at will via, e.g., sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or Suzuki-Miyaura coupling. Afterward, BBr3 demethylation activates another rim for similar functionalizations.
Project description:The synthesis of "rim-differentiated" C5-symmetric pillararenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a "preoriented" synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C5-symmetric tiara-like pillararene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillararene derivatives with C5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.
Project description:Subcellular organelle-specific reagents for simultaneous targeting, imaging and treatment are highly desirable for cancer therapy. However, it remains a challenge to fabricate a single molecular platform containing a targeting group, imaging and therapeutic agents through traditional synthesis. Due to their superior sensitivity and photostability, fluorescent probes with aggregation-induced emission (AIE) characteristics have attracted more and more attention in studying the process of translocation, drug release, and excretion of nanomedicines in vitro or in vivo. We construct a pillararene-based rotaxane (R1) by employing tetraphenylethene (TPE) and triphenylphosphonium (TPP) moieties as stoppers; the TPE unit retains the aggregation-induced emission (AIE) attribute and the TPP group is used as a mitochondria-targeting agent. R1 exhibits enhanced AIE, high specificity to mitochondria, and superior photostability. By introducing doxorubicin (DOX) into R1, prodrug R2 is constructed as a dual-fluorescence-quenched Förster resonance energy transfer (FRET) system, in which the TPE-based axle acts as a donor fluorophore and the DOX unit acts as the acceptor. Upon hydrolysis of R2 in endo/lysosomes, the fluorescences of the carrier and the drug recover. R1 is further utilized as a drug delivery platform to conjugate other anticancer drugs containing amine groups through imine formation to prepare prodrugs. The anticancer drugs are released from these prodrugs in the cells upon hydrolysis of the pH-responsive imine bonds.
Project description:Rotaxane building blocks bearing 3,5-bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillararene derivative, 3,5-bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10-decanediol and 1,12-dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers.