Supramolecular complexation studies of [60]fullerene with calix[4]naphthalenes—a reinvestigation

Estimations of equilibrium or association constant (K_ASSOC) values reported by many other groups for the supramolecular complexation between [60]fullerene (‘C₆₀’) with different macrocyclic hosts, in solvents such as toluene or carbon disulfide, for example, is often conducted by UV-vis absorption and/or ¹H NMR spectroscopy. In this paper, the complexation behaviour of two calix[4]naphthalene hosts with C₆₀ in toluene and carbon disulfide has been re-examined, using both of these methods. An analysis is presented of the data newly obtained, in light of recent advances and understanding published by others of the limitations of, in particular, the absorption spectroscopic methods. The discussion presented is also intended to aid those who may be unfamiliar with the nuances and limitations of the analytic models involving C₆₀ supramolecular complexation. Also presented is a general mechanism for C₆₀ supramolecular complexation studies, which lay the groundwork for further experiments.     

Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C₆₀ and palladium two-component films, C₆₀/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C₆₀ reduction step. The incorporation of palladium particles into the structure of C₆₀/Pd polymers increases the polymer stability. The C₆₀/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C₆₀/Pd films.     

Synthesis of a linear benzo[3]phenylene-[60]fullerene dyad

The synthesis of a new linear benzo[3]phenylene-[60]fullerene dyad 1 is achieved over 10 steps in 15% overall yield by using an efficient sequence combining a double cobalt(I)-mediated cyclotrimerization with a Bingel reaction.     

Synthesis of a proline-rich [60]fullerene peptide with potential biological activity

A proline-rich [60]fullerene peptide was synthesized by use of (i) a 1,3-dipolar cycloaddition of an N-substituted glycine derivative to [60]fullerene, (ii) esterification of the isolated alcohol with the C-terminal amino acid of the desired peptide sequence, and finally (iii) coupling of the remaining hexapeptide to give the final product 8 as a TFA salt, with oxidized methionine. Product 8 was found to be biologically active against sera from MCTD and SLE patients (ELISA experiment).     

Synthesis of a novel [60]fullerene pearl-necklace polymer,poly(4,4′-carbonylbisphenylene trans-2-[60]fullerenobisacetamide)

A novel [60]fullerene pearl-necklace polymer, poly(4,4′-carbonylbisphenylene trans-2-[60]fullerenobisacetamide), was synthesized by a direct polycondensation of trans-2-[60]fullerenobisacetic acid with 4,4′-diaminobenzophenone in the presence of large excesses of triphenyl phosphite and pyridine. In the present polymer, [60]fullerene pearls and diamine linkers were attached to each other by methano-carbonyl connectors. The molecular weight M_w of the polymer was determined to be 4.5 × 10⁴ on the basis of the TOF-MS, and a GPC analysis of the polymer using polystyrene standards showed a weight-average molecular weight of 5.3 × 10⁴. The UV-vis spectrum of the resultant polymer in N,N-dimethylacetamide (DMAc) exhibited a broad absorption (λ_max 310 nm, ε 2.1 × 10⁴ L · mol⁻¹ · cm⁻¹), tailing to longer wavelengths, and a fluorenscence peak centered at 550 nm was observed in DMAc. There was observed a large downfield-shift of the cyclopropane methyne proton in the ¹H-NMR spectra from 4.57 ppm of the ethyl ester to 5.78 ppm of the polyamide. These observations indicate that the present polyamide is a high-molecular-weight [60]fullerene pearl-necklace polymer and that the cyclopropane rings are efficient to make the [60]fullerene cages and the diamine components conjugatable. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3632–3637, 1999     

Fabrication of anodic photocurrent generation systems by use of 6-O-dihydrophytylcellulose as a matrix or a scaffold of porphyrins

Langmuir-Blodgett (LB) films containing porphyrin molecules were fabricated by use of 6-O-dihydrophytylcellulose (DHPC) toward anodic photocurrent generation systems. To suppress the porphyrin aggregation, two different approaches were applied: (1) mixing a low-molecular-weight porphyrin having a diterpenoid carbon skeleton (DPor) with DHPC as a matrix (matrix fabrication) and (2) bonding porphyrin molecules to the hydroxyl groups of DHPC covalently, converting into 6-O-dihydrophytyl-2,3-di-O-[p-(10,15,20-triphenyl-5-porphyrinyl)-benzoyl]cellulose as a scaffold (scaffold fabrication). The structure and film properties of the monolayers and the LB films were investigated by the surface pressure (π)–area (A) isotherm measurements, atomic force microscopy, UV–Vis spectroscopy, and absorption dichroism measurements. The porphyrin aggregation in the LB film could be well suppressed only by the scaffold fabrication, leading to the improvement of the photocurrent quantum yields. The efficient photocurrent performance can be demonstrated by the isolation and the parallel orientation of porphyrin moieties due to the cellulose rigid scaffold. This paper was the subject of the Best Poster Award of the 235th edition of the ACS National Meeting, Cellulose and Renewable Materials.     

Preparation and identification of bis(formylmethano)[60]fullerene isomers: the first systematic study on bifunctionalized [60]fullerenes with dissymmetric addends

Fourteen isomers of bis(formylmethano)C₆₀ were isolated and characterized. A mixture of the bisadducts was obtained by the reaction of C₆₀ with an α-formylsulfonium ylide, and then separated into 15 fractions by preparative HPLC, preparative TLC, and recycling preparative HPLC. Fourteen of the fifteen fractions were found to consist of a single isomer, respectively, which were assigned to the trans-2 (3 diastereo-isomers), trans-3 (3 diastereo-isomers), trans-4 (3 diastereo-isomers), equatorial (2 diastereo-isomers), and cis-2 (3 diastereo-isomers) bisadducts by the comparison of their UV/vis spectra with those of the bisadducts obtained by the Bingel-Hirsch reaction. The ¹H and ¹³C NMR analysis, the transformation of the formyl groups, and the dipole moment calculation clarified the stereochemistry of the substituents on the two cyclopropane bridge-head carbons (in/in, in/out, and out/out).     

Supramolecular polymer networks based on calix[5]arene chained poly(p-phenyleneethynylene) and C60 fulleropyrrolidine

Abstract

A poly(p-phenyleneethynylene) polymer (PCF[5]), bearing two π-rich cone-like calix[5]arene cavities (assembling cores) attached to a rigid p-phenyleneethynylene spacer, was synthesised by a Pd-catalysed cross-coupling reaction. UV–vis absorption and fluorescence spectroscopies combined with dynamic light scattering measurements provide evidence for the self-assembly of PCF[5] (homopolytopic host molecule) with a complementary C₆₀ fulleropyrrolidine (C₆₀-Pyr) guest in solution, in the construction of a supramolecular polymer network. Atomic force microscopy analysis of PCF[5]/C₆₀-Pyr highlights the formation of a bicontinuous network consisting of a uniform distribution of prominent structures, within a polymeric background forming a biphasic structure.     

Production of reactive oxygen species induced by a new [60]fullerene derivative bearing a tetrazole unit and its possible biological applications

The wide range of physical and chemical properties of modified fullerenes has drawn increasing attention in the past few years. As part of this research, this paper describes the preparation, characterization, and photophysical properties of a new fullerene derivative chemically modified with a tetrazole. The photophysical properties were studied by EPR radical spin-trapping technique and showed that reactive oxygen species (ROS) can be produced through UVA photosensitization. EPR spin-trapping experiments with singlet oxygen (¹O₂) and superoxide (O₂⁻) inhibitors (β-carotene and superoxide dismutase, respectively) revealed also that: (i) the main ROS produced is ¹O₂ and (ii) ¹O₂ is being partially dismutated to O₂⁻. The results suggest that this derivative can be used in biological applications, as for example, in topic photodynamic therapy (PDT) as a photosensitizer.     

Regio/diastereo-controls of the Bingel-type biscyclopropanation of [60]fullerene by using bismalonates with a Tröger base analogue-derived tether

Four kinds of bismalonates tethered with a Tröger base derivative were synthesized and used for the double Bingel reaction of [60]fullerene. The regio/diastereoselectivities of the reaction were highly influenced by the structure of the Tröger base derivatives. Heteroaromatic analogues of the Tröger base were found to be applicable as the core of the tether.     

Supramolecular polymer materials based on pillar[5]arene: Ultrasensitive detection and efficient removal of cyanide

An ultrasensitive detection and effective removal material was successfully developed by using a pillar[n]arene-based supramolecular polymer gel (MTP5⊃HB). The MTP5⊃HB can ultrasensitively recognize Cu²⁺ and Fe³⁺, and the limits of detection (LODs) for Cu²⁺ and Fe³⁺ are 1.55 and 2.68 nmol/L, respectively. Additionally, the in-situ generated metallogel MTP5⊃HB-Cu can exclusively detect CN⁻, and the LOD for CN⁻ is 1.13 nmol/L. Noticeably, the xerogel of MTP5⊃HB-Cu can effectively remove CN⁻ from aqueous solution with 94.40% removal rate. Test kit based on MTP5⊃HB-Cu is also prepared for convenient detection of CN⁻.     

Prolongation of the lifetime of the charge-separated state at low temperatures in a photoinduced electron-transfer system of [60]fullerene and ferrocene moieties tethered by rotaxane structures

A rotaxane tethering both fullerene (C60) and ferrocene (Fc) moieties (abbreviated as (C60;Fc)rotax+) was synthesized in a good yield by the urethane end-capping of pseudorotaxane based on the crown ether-secondary amine motif. In (C60;Fc)rotax+, the C60 group serving as an electron acceptor is attached to the crown ether wheel, through which the axle with a Fc group acting as an electron donor on its end penetrates. The intrarotaxane photoinduced energy-transfer and electron-transfer processes between C60 and Fc in (C60;Fc)rotax+ have been investigated by time-resolved transient absorption and fluorescence measurements with changing solvent polarity. Nanosecond transient absorption measurements of the rotaxane demonstrated that the charge-separated state (C60*-;Fc*+)rotax+ is formed mainly via the excited triplet state of C60 in polar solvents. The lifetime of (C60*-;Fc*+)rotax+ was evaluated to be 20 ns in dimethylformamide (DMF) at room temperature. With lowing temperature, the lifetime of (C60*-;Fc*+)rotax+ extends to 270 ns in DMF at -65 degrees C, due to the structural changes leaving C60*- and Fc*+ at a relatively long distance in the low-temperature region.     

Probing traces of hydrogen peroxide by use of a biosensor based on mediator-free DNA and horseradish peroxidase immobilized on silver nanoparticles

A new electrochemical biosensor for determination of hydrogen peroxide (H₂O₂) has been developed by immobilizing horseradish peroxidase (HRP) on silver colloids (nanosilver) and use of a DNA-functionalized interface. In the presence of the DNA and the nanosilver the immobilized HRP gives a pair of well-defined redox peaks with an electron-transfer rate constant of 3.27 ± 0.91 s⁻¹ in pH 7.0 PBS. The presence of DNA also provides a biocompatible microenvironment for enzyme molecules, greatly amplifies the amount of HRP molecules immobilized on the electrode surface, and improves the sensitivity of the biosensor. Under optimum conditions the biosensor has electrocatalytic activity in the reduction of hydrogen peroxide with linear dependence on H₂O₂ concentration in the range 1.5 × 10⁻⁶ to 2.0 × 10⁻³ mol L⁻¹; the detection limit is 5.0 × 10⁻⁷ mol L⁻¹ at a signal-to-noise ratio of 3. The value of HRP in the composite membrane was found to be 1.62 mmol L⁻¹. These results suggest that the properties of the complex film, with its bioelectrochemical catalytic activity, could make it useful for development of bioelectronic devices and for investigation of protein electrochemistry at functional interfaces.     

Highly Enhanced Fluorescence of Supramolecular Polymers Based on a Cyanostilbene Derivative and Cucurbit[8]uril in Aqueous Solution

Supramolecular polymers (SPs) have received great attention because of their potential for various practical applications. As part of our search for SPs that are highly fluorescent in aqueous media, we designed a system based on a cucurbit[8]uril (CB[8]) host and a newly designed cyanostilbene guest. Fluorescence quantum yields of ≈0 % in the disassembled monomer state and 91 % in the CB[8]‐induced SP state were obtained. The intriguing photophysical properties of the SP are elucidated through detailed experimental and computational analysis, paving the way towards a fascinating class of water‐soluble fluorescent SPs.     

Solubilization of C60 by micellization with a thermoresponsive block copolymer in water: Characterization,singlet oxygen generation,and DNA photocleavage

Water‐soluble diblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly(N‐vinyl‐2‐pyrroridone) (PNIPAM_m‐b‐PNVP_n), was found to associate with fullerene (C₆₀), and thus C₆₀ can be solubilized in water. The 63C₆₀/PNIPAM_m‐b‐PNVP_n micelle formed a core‐shell micelle‐like aggregate comprising a C₆₀/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C₆₀‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and ¹H NMR techniques. The hydrodynamic radius (R_h) of the C₆₀‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). ¹H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C₆₀‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C₆₀‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C₆₀‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis of a [60]fullerene‐functionalized poly(vinyl chloride) derivative by stereospecific chemical modification of PVC

The covalent attachment of [60]fullerene (C₆₀) to two poly(vinyl chloride) (PVC) samples with different isotactic content is achieved by direct reaction in o‐dichlorobenzene (o‐DCB) solution in the presence of AIBN. The extent of fullerenation is controlled by varying the C₆₀ feed ratio. The pendant C₆₀‐chemically modified PVC polymers are soluble in tetrahydrofuran (THF) and have been characterized by UV–vis, NMR, FTIR, DSC, TGA, cyclic voltammetry, and SEM. The quantitative microstructural analysis after covalent attachment of the bulky C₆₀ moiety to the PVC has been followed by ¹³C NMR spectroscopy. From the results it can be concluded that the modification of PVC by graft reaction through free radical reaction proceeds by a stereoselective mechanism. This conclusion has been confirmed on the basis of the increase of the glass‐transition temperature (T_g) and the thermal stability of the C₆₀‐chemical modified PVC samples. The fullerenated PVCs obtained show good electron acceptor properties, as evidenced by electrochemical investigations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5408–5419, 2007     

Supramolecular hydrogen-bonded liquid–crystalline polymer complexes. Design of side-chain polymers and a host–guest system by noncovalent interaction

Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.