Fullerene is a nanosized carbon structure with potential drug delivery applications. We studied the bioeffects of a water-soluble fullerene derivative, fullerenol, with 10-12 oxygen groups (F10-12); ...its structure was characterized by IR and XPS spectroscopy. A bioluminescent enzyme system was used to study toxic and antioxidant effects of F10-12 at the enzymatic level. Antioxidant characteristics of F10-12 were revealed in model solutions of organic and inorganic oxidizers. Low-concentration activation of bioluminescence was validated statistically in oxidizer solutions. Toxic and antioxidant characteristics of F10-12 were compared to those of homologous fullerenols with a higher number of oxygen groups:F24-28 and F40-42. No simple dependency was found between the toxic/antioxidant characteristics and the number of oxygen groups on the fullerene’s carbon cage. Lower toxicity and higher antioxidant activity of F24-28 were identified and presumptively attributed to its higher solubility. An active role of reactive oxygen species (ROS) in the bioeffects of F10-12 was demonstrated. Correlations between toxic/antioxidant characteristics of F10-12 and ROS content were evaluated. Toxic and antioxidant effects were related to the decrease in ROS content in the enzyme solutions. Our results reveal a complexity of ROS effects in the enzymatic assay system.
Gd@C82OxHy endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a mixture of ...graphite and Gd2O3 oxide. The Gd@C82 endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@C82O8(OH)20. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole C82 cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the C82 cage causes the formation of Gd@C82O28H20, with a breakdown of the integrity of the parent C82 cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@C82O6(OOH)2(OH)18 endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.
A kinetic model of fullerene formation in the carbon-helium plasma of an arc discharge was proposed. In the model, in addition to the coagulation of carbon clusters, the cluster isomerization and ...their cooling with a buffer gas were taken into account. The simulation results of the fullerene formation are in qualitatively agreement with the experimental data, i.e., the fraction of higher fullerenes increases at high pressures in the fullerene mixture.
We show that in a carbon–helium high-frequency (66kHz) arc discharge the fullerene yield and composition can be controlled by changing the helium pressure. By emission spectroscopy we could derive ...the excitation temperature within the arc. We found that the radial temperature gradient of the arc plasma increases with increasing pressure. We further found that with increasing pressure the yield of fullerenes reaches a maximum of 12.6wt.% at 0.12MPa pressure and in the range from 0.16 to 0.38MPa the fullerene content in the carbon soot stays within the limits of 7.2–7.0wt.%. The content of С70 and higher fullerenes relative to the total amount of extractable fullerenes increases with pressure. Our results suggest that in the carbon–helium plasma fullerenes are mainly formed in a top-down process by the decay and annealing of large, hot precursor carbon molecules.
The results of the effect of helium pressure in the chamber on the amount and composition of the produced fullerenes (C
60
, C
70
, etc.) synthesized in the arc plasma with graphite electrodes are ...presented. The findings obtained when the arc is powered by a direct (DC) and alternating (AC) currents of low frequency were compared in the same chamber with the electrodes located at the same angle to each other. These two methods are drastically different. The complete conversion of graphite into fullerene soot in AC occurs, but a part of the graphite is converted into a cathode deposit that does not contain fullerenes in DC, the relative amount of which increases when decreasing the helium pressure in the chamber. The highest fullerene content in fullerene soot of 10.2 wt.% is produced at a pressure of 127.5 kPa in AC arc, but in DC arc, the highest content of fullerenes in fullerene soot of 8.3 wt.% is produced at a pressure of 33.3 kPa.
Gd endohedral complexes of C82 fullerenols were synthesized and mass spectrometry analysis of their composition was carried out. It was established that the synthesis yields a series of fullerenols ...Gd@C82Ox(OH)y (x = 0, 3; y = 8, 16, 24, 36, 44). The atomic and electronic structure and properties of the synthesized fullerenols were investigated using the density functional theory calculations. It was shown that the presence of endohedral gadolinium increases the reactivity of fullerenols. It is proposed that the high-spin endohedral fullerenols are promising candidates for application in magnetic resonance imaging.
The paper presents the results of experimental measurements of constitutive and electrophysical properties in hydroxylated endohedral metallofullerene with gadolinium sample. We extracted endohedral ...metallofullerene from carbon condensate, synthesized in high-frequency arc discharge plasma. Later hydroxyl groups were added. Via methods of infrared and x-ray photoelectronic spectroscopy, it was established that the molecules of hydroxylated endohedral metallofullerene have the Gd@C82Ox(OH)y, x + y=(40–42) composition. The method of measuring the electrical impedance in the frequency range from 100 Hz to 100 MHz shows that the resulting hydroxylated fullerene is an ion conductor. The measured frequency dependences of the dielectric permittivity and conductivity of hydroxylated fullerene are explained based on the assumption of an inhomogeneous distribution of electric charges in the material volume. Dielectric-hysteresis loops in the frequency range of 25 Hz–1 MHz and temperature range of 80–300 K, and volt-ampere characteristics were measured. The obtained results imply the appearance of residual polarization induced by the electric field in hydroxylated fullerene. However, the constant dipole moment is absent.
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•Proton conductivity of Gd@C82Ox(OH)y (x + y = 40–42) is 10−10 S/cm.•At temperatures below 260 K the residual polarization amount up 3.3·10−4 μC/cm2•A large number of O and OH groups affect on the amount of residual polarization.•Reach-through conductivity suppresses polarization at temperatures above 260 K.
The paper presents results of fullerenes and endohedral metallofullerenes extracts studies, isolated from the graphite rods carbon soot spray, and containing Y
2
O
3
in a high frequency arc ...discharge. Two ways of extraction were applied and compared - (1) the classic method of Soxhlet extraction, and (2) the one developed by our team - extraction based on mechanical action combined with filtration. To implement the method, we used a laboratory version of installation, embodying technical solutions for rapid extraction. Chromatographic and mass spectrometry studies of fullerene extracts obtained by these methods revealed that by combining mechanical action with simultaneous filtration, we can significantly intensify and reduce the process of extracting fullerenes and endohedral metallofullerenes compared to the Soxhlet extraction method. This is especially evident in the release of endohedral metallofullerenes. Our method allows to reduce the release time of fullerenes from 10 g of carbon soot on laboratory installation up to 15 minutes, against the Soxhlet extraction method taking 18 hours. Whilst, the total number of fullerenes extracted by both methods almost coincides (the extraction method using mechanical action allowed us to extract 0.2-0.4 wt. % more), the composition of the isolated fullerene mixtures is different. The relative content of higher fullerenes and endohedral metallofullerenes exceeds when the mechanical action-based extraction method applied.
Gd@C
O
H
endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a mixture of ...graphite and Gd
O
oxide. The Gd@C
endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@C
O
(OH)
. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole C
cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the C
cage causes the formation of Gd@C
O
H
, with a breakdown of the integrity of the parent C
cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@C
O
(OOH)
(OH)
endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.
The article presents, for the first time, the results of the research on composite film obtained from hydroxylated endohedral metallofullerenes (EMF) Y@C
82
, Y
2
@C
82,
with Y
2
C
2
@C
82
and ...highest fullerenes as dopant. The composite film has been established to have electric conductivity and to be a ferroelectric with the value of residual polarization of ∼0.75 μC/cm
2
. The impedance spectroscopy of this sample allowed us to determine dispersion of dielectric permittivity and conductivity in the range of frequencies of 0.5 Hz-100 MHz. It is stated that the value of the high-frequency dielectric permittivity of films is ε′
∞
= 2.8. However, with reduction in the electric field frequency, real and imaginary parts of ε increase to values ∼10
4
-10
5
. Such increase in dielectric permittivity is connected with increase in polarizing caused by accumulation of mobile electric charges (electrons of ions, protons) on boundaries of the structural defects of a film, which are divided by thin dielectric interlayers. The film is solid electrolyte with the ionic conductivity of ∼5 × 10
−7
S/cm.
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