Cation C60 Research Articles

Interaction of a pyrene derivative with cationic [60]fullerene in phospholipid membranes and its effects on photodynamic actions.

We have reported that upon visible light irradiation, ferrocene-porphyrin-[60]fullerene triad molecules yield long-lived charge-separated states, enabling the control of the plasma membrane potential (V m) in living cells. These previous studies indicated that the localization of the triad molecules in a specific intra-membrane orientation and the suppression of the photodynamic actions of the [60]fullerene (C60) moiety are likely important to achieve fast and safe control of V m, respectively. In this study, by mimicking our previous system of triad molecules and living cells, we report a simplified model system with a cationic C60 derivative (catC60) and a liposome with embedded 1-pyrenebutyric acid (PyBA) to demonstrate that the addition of PyBA was important to achieve fast and safer control of V m.

Cellular Uptake, Organelle Enrichment, and In Vitro Antioxidation of Fullerene Derivatives, Mediated by Surface Charge.

Hydrophilic fullerene derivatives get notable performance in various biological applications, especially in cancer therapy and antioxidation. The biological behaviors of functional fullerenes are much dependent on their surface physicochemical properties. The excellent reactive oxygen species-scavenging capabilities of functional fullerenes promote their outstanding performances in inhibiting pathological symptoms associated with oxidative stress, including neurodegenerative diseases, cardiovascular diseases, acute and chronic kidney disease, and diabetes. Herein, fullerene derivatives with reversed surface charges in aqueous solutions are prepared: cationic C60-EDA and anionic C60-(EDA-EA). Under the driving force of membrane potential (negative inside) in the cell and mitochondria, C60-EDA is much rapidly taken in by cells and transported into mitochondria compared with C60-(EDA-EA) that is enriched in lysosomes. With high cellular uptake and mitochondrial enrichment, C60-EDA exhibits stronger antioxidation capabilities in vitro than C60-(EDA-EA), indicating its better performance in the therapy of oxidation-induced diseases. It is revealed that the cellular uptake rate, subcellular location, and intracellular antioxidation behavior of fullerene derivatives are primarily mediated by their surface charges, providing new strategies for the design of fullerene drugs and their biological applications.

Stage-1 cationic C60 intercalated graphene oxide films

A “stage-1” intercalated film has been made by the ion exchange of pyrrolidinium-functionalized C60 (C60(Py)n+) into centimeter-wide, micrometer-thick air-dried graphene oxide (G-O) films composed of tens of thousands of layers of stacked/overlapping G-O platelets, denoted [C60(Py)n+]G-O films. Spontaneous intercalation by ion exchange of one layer of C60(Py)n+ between adjacent G-O layers expands the interlayer spacing of the films from 0.74 nm to 1.46 nm. The films remain intact in water and various organic solvents, which is likely due to a strong affinity between C60(Py)n+ and G-O. Membranes made of the films showed a 6.8 times faster water vapor permeation rate (allowing the vapor to transport through the membrane almost freely) and a 10.5 times faster liquid water permeation rate than G-O membranes. Heating the films at 2000 °C under applied pressure or at 2700 °C without physical confinement converted them into highly graphitized structures.

Anionic behavior and single-molecule crystal in fullerene confinements: A contribution from DFT energy decomposition and cooperativity analyses.

The recently proposed systems of various anions (A) confined inside C60 , A- @ C60 , which in turn behave as large and stable anions, (A @ C60 )- , can find potential applications in various fields. On the other hand, it has earlier been shown that from the dihalogens (X2 ) encapsulated C60 , X2 @ C60 , only F2 @ C60 can be introduced as a system in which the cage acts as a cation C60 + and interacts with an endohedral anion, F2 - , forming the F2 - @ C60 + as a single-molecule crystal compound. In this work, two density functional theory energy decomposition analysis (EDA) schemes, where in one of them the noninteracting kinetic, electrostatic, and exchange-correlation energies come into play while another scheme, called as EDA-SBL, includes the steric, electrostatic, and quantum effects as essential ingredients (S. Liu, J. Chem. Phys. 2007, 126, 244103), are utilized to find out what energetic components govern the unique characteristics of the (A @ C60 )- and X2 @ C60 confinements. It is shown that the noninteracting kinetic energy and steric energies have important contributions to the total interaction energies for the considered systems. However, there are other confinements for which the electrostatic and exchange-correlation contributions play also imperative roles. Furthermore, we find reasonable correlations between interaction energies and their components as well as the energetic components themselves, leading to an alternative EDA scheme including the noninteracting kinetic, steric, and electrostatic energies for investigations on other endohedral fullerenes. Extending our analyses to large size confinements, Cl- @ Cn with n up to 90 as illustrative examples, the quantitative cooperativity concept is also explored, where the positive and negative cooperativity profiles unveil a specific size of the anionic confinements to form the most stable large anion.

The Ability of Functionalized Fullerenes and Surface‐Modified TiO2 Nanoparticles to Photosensitize Peroxidation of Lipids in Selected Model Systems

Photochemical properties of a new class of inorganic nanoparticles, namely a cationic C60 fullerene substituted with three quaternary pyrrolidinium groups (BB6) and a surface-modified nanocrystalline TiO2 with bromopyrogallol red (Brp@TiO2 ) were examined for their effectiveness in photogenerating singlet oxygen and free radicals. In particular, their ability to photosensitize peroxidation of unsaturated lipids was analyzed in POPC:cholesterol liposomes and B16 mouse melanoma cells employing a range of spectroscopic and analytical methods. Because melanoma cells typically are pigmented, we examined the effect of melanin on the photosensitized peroxidation of lipids in liposomes and B16 melanoma cells, mediated by BB6 and Brp@TiO2 nanoparticles. The obtained results suggest that peroxidation of unsaturated lipids, photosensitized by BB6 occurs mainly, although not exclusively, via Type II mechanism involving singlet oxygen. On the other hand, if surface-modified TiO2 is used as a photosensitizer, Type I mechanism of lipid peroxidation dominates, as indicated by the predominant formation of the free radical-dependent cholesterol oxidation products. The protective effect of melanin was particularly evident when BB6 was used as a photosensitizer, suggesting that melanin could efficiently interfere with Type II processes.

Buckyball Difluoride F2 - @C60 + -A Single-Molecule Crystal.

We report the F2 @C60 system as the first example of an endohedral fullerene in which C60 acts as a cation C60 + interacting with endohedral anion, F2 - . Our state-of-the-art computations reveal that in F2 @C60 , despite of the known high electron affinity of C60 , an electron is transferred from C60 to F2 resulting in the F2 - @C60 + system. The F-F bond length in F2 @C60 is substantially longer than in free F2 , which is the result of electron-transfer to the antibonding σu molecular orbital of F2 . Interestingly, although there is a full charge-transfer of one electron between C60 and F2 , only negligible delocalized covalent interactions are found between F2 - and C60 + which is a reminiscent of ionic crystals. Therefore, F2 - @C60 + can be considered as a single-molecule crystal. The other encapsulated halogens in C60 do not show such behavior.

Buckyball Difluoride F2−@C60+—A Single‐Molecule Crystal

AbstractWe report the F2@C60 system as the first example of an endohedral fullerene in which C60 acts as a cation C60+ interacting with endohedral anion, F2−. Our state‐of‐the‐art computations reveal that in F2@C60, despite of the known high electron affinity of C60, an electron is transferred from C60 to F2 resulting in the F2−@C60+ system. The F−F bond length in F2@C60 is substantially longer than in free F2, which is the result of electron‐transfer to the antibonding σu molecular orbital of F2. Interestingly, although there is a full charge‐transfer of one electron between C60 and F2, only negligible delocalized covalent interactions are found between F2− and C60+ which is a reminiscent of ionic crystals. Therefore, F2−@C60+ can be considered as a single‐molecule crystal. The other encapsulated halogens in C60 do not show such behavior.

The EDIBLES survey II. The detectability of C60+ bands

Gas phase spectroscopic laboratory experiments for the buckminsterfullerene cation C60+ have resulted in accurate rest wavelengths for five C60+ transitions that have been compared with diffuse interstellar bands (DIBs) in the near infra-red. Detecting these in astronomical spectra is difficult because of the strong contamination of ground-based spectra by atmospheric water vapor, to the presence of weak and shallow stellar lines and/or blending with other weak DIBs. The detection of the two strong bands has been claimed by several teams, and the three additional and weaker bands have been detected in a few sources. Certain recent papers have argued against the identification of C60+ based on spectral analyses claiming (i) a large variation in the ratio of the equivalent widths of the 9632 and 9577 Å bands, (ii) a large redshift of the 9632 Å band for the Orion star HD 37022, and (iii) the non-detection of the weaker 9428 Å DIB. Here we address these three points: (i) We show that the model stellar line correction for the 9632 Å DIB overestimates the difference between the strengths of the lines in giant and dwarf star spectra, casting doubts on the conclusions about the ratio variability. (ii) Using high quality stellar spectra from the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES), recorded with the ESO/Paranal Ultraviolet Echelle Spectrograph (UVES) in about the same atmospheric conditions, we find no wavelength shift in the 9632 Å band toward HD 37022. (iii) Using EDIBLES spectra and data from the Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) at CFHT we show that the presence of a weak 9428 Å band cannot be ruled out, even in the same observations that a previous study claimed it was not present.

Water-soluble PPV and C60 nanocomposite with enhanced miscibility and enhanced photo-induced charge transfer through ground state electrostatic interactions

We report the preparation of highly charged nanocomposites comprised of water-soluble, anionic fullerene and cationic poly-phenylenevinylene (PPV) derivatives. The nanocomposites display high fluorescence quenching efficiency (99%) presumably due to enhanced miscibility between cationic PPV and anionic C60 via electrostatic interactions. We show that complexation between the cationic PPV and anionic C60 derivatives leads to formation of nanocomposites with optical and electronic properties distinct from individual components without preferential electrostatic interactions. Photo-induced charge transfer quenches fluorescence from the PPV component is consistent with the frontier energy offsets of PPV and C60, and cyclic voltammetry and UV–Vis spectroscopy measurements. This result confirms high miscibility between donor and acceptor and resonance Raman spectra indicate a conformational changes of the PPV backbone upon complex formation.

Cyclodextrin complexed [60]fullerene derivatives with high levels of photodynamic activity by long wavelength excitation.

We have evaluated the photodynamic activities of C60 derivative·γ-cyclodextrin (γ-CDx) complexes and demonstrated that they were significantly higher than those of the pristine C60 and C70·γ-CDx complexes under photoirradiation at long wavelengths (610-720 nm), which represent the optimal wavelengths for photodynamic therapy (PDT). In particular, the cationic C60 derivative·γ-CDx complex had the highest photodynamic ability because the complex possessed the ability to generate high levels of (1)O2 and provided a higher level of intracellular uptake. The photodynamic activity of this complex was greater than that of photofrin, which is the most widely used of the known clinical photosensitizers. These findings therefore provide a significant level of information toward the optimization of molecular design strategies for the synthesis of fullerene derivatives for PDT.

Spherical aromaticity of Jahn–Teller active fullerene ions

Density functional theory was applied to com- pute the nucleus-independent chemical shifts of fullerene (C60), the fullerene ion C60 10? , and the Jahn-Teller active fullerene anion C60 - and cation C60 ? . Positioning a 3 He nucleus inside the cage of each of these fullerene species facilitates investigations of the substantial differences among them, 3 He NMR chemical shifts can provide important data on the aromatic behavior of these molecular cages. Thus, we also calculated the NMR chemical shift of a 3 He atom positioned at the center of each fullerene spe- cies investigated (C60 ,C 60 10? ,C 60 - , and C60 ? ). The data obtained revealed significant differences in the aromatic behavior of the C60 (moderately aromatic) and C60 10? (highly aromatic) species. The values of the nucleus- independent chemical shift parameters were also scanned along the intrinsic distortion path for the C60 - and C60 ? species. In both cases, antiaromatic character decreases with increasing deviation from high-symmetry structures to low-symmetry global minimum points, resulting in the antiaromatic C60 - and weakly aromatic C60 ? .

Synthesis and photophysical properties of polyamides containing in-chain porphyrin and [60]fullerene

Conjugated polyamides containing porphyrin and [60]fullerene (C60) in the main chain were prepared by a direct polycondensation of the 3′H,3″H-dicyclopropa[1, 9:16, 17] [5, 6]fullerene-C60-Ih-3′,3″-dicarboxylic acid and 5,15-bis(4-aminophenyl)-10,20-bis(3,5-dialkoxyphenyl)porphyrin in the presence of triphenyl phosphite and pyridine. Gel permeation chromatography (GPC) analysis of the polyamides showed the weight-average molecular weight was about 23,626–23,736, and the temperature at 5% weight loss determined by thermogravimetric analysis (TGA) was above 216 °C. The transmission electron microscopy (TEM) images displayed the regular one-dimensional linear arrays of the polyamides with lengths exceeded 200 nm. The photoinduced electron transfer from porphyrin to C60 in the polyamides was observed in nanosecond laser-flash photolysis experiments at ambient temperature, which produced a charge-separated state (porphyrin radical cation–C60 radical anion pair) with a lifetime as long as 40 μs. The calculated ratio of kCS/kCR was found to be 2.1 × 104. They could have potential applications for photoelectronic devices, organic solar cells and so on.

Visible Light Sensitized Inactivation of MS-2 Bacteriophage by a Cationic Amine-Functionalized C60 Derivative

Recently, we reported the successful synthesis of various hexakis C60 derivatives (i.e., C60 with six functional groups containing NH3+-, CO2H-, or OH-terminals) with enhanced stability in water for aqueous phase application (Lee et al., Environ. Sci. Technol. 2009, 43, pp 6604-6610). Among these newly synthesized C60 derivatives, the cationic hexakis C60 derivative with amine functionality, C60(CR2)6 (R=CO2(CH2)2NH3+CF3CO2-), was found to exhibit remarkable efficiency to inactivate Escherichia coli and MS-2 bacteriophage under UVA irradiation. Herein, we report that this amine-functionalized C60 derivative is also photoactive in response to visible light from both commercial fluorescence lamps and sunlight. Efficient production of 1O2, facile reaction of 1O2 with proteins in MS-2 phage capsid and electrostatic attraction between positively charged C60 derivative and negatively charged MS-2 phage collectively contributed to high efficiency of MS-2 phage inactivation in this photocatalytic disinfection system. The rate of 1O2 production was evaluated using a probe compound, furfuryl alcohol, and 1O2 CT (the product of 1O2 concentration and exposure time) required to achieve a target level of virus inactivation was quantitatively analyzed. The unique visible-light sensitized virucidal property makes this C60 derivative highly desirable for the development of sustainable disinfection strategies that do not require continuous chemical addition nor an external energy source other than ambient light.

Photovoltaic Cells Based on Sequentially Adsorbed Multilayers of Conjugated Poly(p-phenylene ethynylene)s and a Water-Soluble Fullerene Derivative

We describe the layer-by-layer (LBL) fabrication of multilayer films and photovoltaic cells using poly(phenylene ethynylene)-based anionic conjugated polyelectrolytes as electron donors and water-soluble cationic fullerene C60 derivatives as acceptors. LBL film deposition was found to be linearly related to the number of bilayers as monitored by UV-vis absorption. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) of the multilayer films revealed an aggregated but relatively uniform morphology devoid of any long-range phase separation. The maximum incident monochromatic photon to current conversion efficiency (IPCE) of the photovoltaic cells was 5.5%, the highest efficiency reported to date for cells fabricated by using the LBL fabrication technique, and since the thin film cells do not provide complete absorption of the incident light, the current generation per photon absorbed may be as much as 10%. The cells exhibited open circuit voltages of 200-250 mV with highest measured short circuit currents up to 0.5 mA/cm2 and fill factors around 30%. The power conversion efficiencies measured at AM 1.5 solar conditions (100 mW/cm2) varied between 0.01 and 0.04%, and similar to the IPCE results, the efficiency is a function of the thickness of the PV active layer.

Artifacts in the electron paramagnetic resonance spectra of C60 fullerene ions: inevitable C120O impurity.

Aspects of the electron paramagnetic resonance (EPR) spectra of C60n- fulleride ions (n = 2, 3) and the EPR signal observed in solid C60 are reinterpreted. Insufficient levels of reduction and the unrecognized presence of C120O, a ubiquitous and unavoidable impurity in air-exposed C60, have compromised most previously reported spectra of fullerides. Central narrow line width signals ("spikes") are ascribed to C120On- (n = odd). Signals arising from axial triplets (g approximately 2.0015, D = 26-29 G) in the spectrum of C602- are ascribed to C120On- (n = 2 or 4). Their D values are more realistic for C120O than C60. Less distinct signals from "powder" triplets (D approximately 11 G) are ascribed to aggregates of C120On- (n = odd) arising from freezing nonglassing solvents. In highly purified samples of C60, we find no evidence for a broad approximately 30 G signal previously assigned to a thermally accessible triplet of C60(2-). The C60(2-) ion is EPR-silent. Signals previously ascribed to a quartet state of the C60(3-) ion are ascribed to C120O4-. Uncomplicated, authentic spectra of C60- and C60(3-) become available when fully reduced samples are prepared under strictly anaerobic conditions from freshly HPLC-purified C60. Solid off-the-shelf C60 has an EPR signal (g approximately 2.0025, DeltaH(pp) approximately 1.5 G) that is commonly ascribed to the radical cation C60*+. This signal can be reproduced by exposing highly purified, EPR-silent C60 to oxygen in the dark. Doping C60 with an authentic C60*+ salt gives a signal with much greater line width (DeltaH(pp) = 6-8 G). It is suggested that the EPR signal in air-exposed samples of C60 arises from a peroxide-bridged diradical, *C60-O-O-C60* or its decomposition products rather than from C60*+. Solid-state C60 is more sensitive to oxygen than previously appreciated such that contamination with C120O is almost impossible to avoid.

Synthesis of Various Water-Soluble G60 Derivatives and Their Superoxide-Quenching Activity

In order to examine the utility of fullerene as a medicinal application, we evaluated the reaction between fullerene derivatives and active oxygen species in vitro. This paper describes the synthesis of various water-soluble C60 derivatives (cationic and anionic) and evaluation of their superoxide (O2 −) quenching activity. Cationic C60 derivatives showed fairly high efficiency.

Synthesis of Various Water-Soluble C60 Derivatives and Their Superoxide-Quenching Activity

In order to examine the utility of fullerene as a medicinal application, we evaluated the reaction between fullerene derivatives and active oxygen species in vitro. This paper describes the synthesis of various water-soluble C60 derivatives (cationic and anionic) and evaluation of their superoxide (O2 −) quenching activity. Cationic C60 derivatives showed fairly high efficiency.

The first complex of C60 fullerene with bis(ethylenedithio)tetrathiafulvalene radical cation: C60·(BEDT-TTF·I3)

The complex of C60 fullerene containing the radical cation of the organic donor,viz., C60·(BEDT-TTF·I3), where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene, was synthesized for the first time. Single crystals of the complex were grown in benzonitrile. The crystals of this compound belong to the monoclinic system with a base-centered lattice. The unit cell parameters are as follows:a=17.419(6),b=9.997(4),c=13.499(1) A, β=99.00 (1)o. The IR and electronic spectra of single crystals of the complex have absorption bands characteristic of the BEDT-TTF.+ radical cation and neutral C60. The ESR spectrum has a signal withg=2.0074 and δH pp=23 G belonging to BEDT-TTF.+. The position of the 13d5/2 peak in the X-ray photoelectron spectrum confirms the formation of the I3 − anion.

ESR spectra of C60 in concentrated sulfuric acid

On dissolution of C60 in concentrated sulfuric acid, ESR spectra of paramagnetic species, which were identified as dimers (C120 +) or oligomers (nC60)+, were recorded. The ESR spectra recorded upon the reaction of a toluene solution of C60 with sulfuric acid were assigned to the radical cation C60 +.

Formation of radical adducts of C60 with alkyl and halo-alkyl radicals. Transient absorption and emission characteristics of the adducts

C60 is known to undergo addition reactions with several radicals. Laser flash photolysis and pulse radiolysis studies have been carried out on C60 solutions containing various halocarbons. Transient absorption peaks observed in pulse radiolysis experiments at 460 and 640 nm are attributed to different radical adducts between C60 and halocarbon radicals. No evidence is obtained for the radical cation C60˙+. On a longer timescale (ca. 30 µs), a unique strong emission is observed with a maximum at 745 nm which is attributed to the excited state of C60 radical adducts generated owing to absorption of the strong probe light. Rate constants for the formation and decay of the radical adducts have been estimated and compared with some reported values.