The energy spectra of ten isomers of trifluoromethyl derivatives of fullerenes C60(CF3)10 and C70(CF3)10 are calculated within the framework of the Hubbard model. Based on the obtained energy spectra, the optical absorption spectra of these compounds are modeled. The calculated optical absorption spectra are compared with the experimental spectra.

The evolution of the morphological properties of solutions of endohedral metallofullerene La@C82 in N,N-dimethylformamide in the presence of a coagulant was studied by dynamic and static light scattering methods. Based on the experimental results, the time evolution of the light scattering intensity, and the hydrodynamic radius of endohedral metallofullerene clusters, their association constants and aggregation rates are determined. Based on the analysis of the angular dependences of light scattering in solutions of endohedral metallofullerenes, the fractal dimension of La@C82 clusters in solutions of various concentrations at the initial and final stages of their aggregation was estimated.

The energy spectra of ten isomers of trifluoromethyl derivatives of fullerenes C 60 (CF 3 ) 10 and C 70 (CF 3 ) 10 are calculated within the framework of the Hubbard model. Based on the obtained energy spectra, the optical absorption spectra of these compounds are modeled. The calculated optical absorption spectra are compared with the experimental spectra. Keywords: trifluoromethyl derivatives, fullerene, Hubbard model, energy spectrum, optical absorption spectrum.

The antioxidant potential (capacity and activity) of aqueous fullerene dispersions (AFD) of non-functionalized C60, C70, and Gd@C82 endofullerene (in micromolar concentration range) was estimated based on chemiluminescence measurements of the model of luminol and generation of organic radicals by 2,2'-azobis(2-amidinopropane) dihydrochloride (ABAP). The antioxidant capacity was estimated by the TRAP method, from the concentration of half-suppression, and from the suppression area in the initial period. All three approaches agree and show that the antioxidant capacity of AFDs increased in the order Gd@C82 < C70 < C60. Mathematical modeling of the long-term kinetics data was used for antioxidant activity estimation. The effect of C60 and C70 is found to be quenching of the excited product of luminol with ABAP-generated radical and not an actual antioxidant effect; quenching constants differ insignificantly. Apart from quenching with a similar constant, the AFD of Gd@C82 exhibits actual antioxidant action. The antioxidant activity in Gd@C82 is 300-fold higher than quenching constants.

A green, scalable, and sustainable approach to prepare aqueous fullerene dispersions (AFD) C60, C70, endohedral metallofullerene Gd@C82, and their derivatives C60Cl6, C70Cl10, and supramolecular and ester-like derivatives, 10 fullerene species total, is proposed. For the first time, an immersed ultrasonic probe was used to preparing dispersions for pristine fullerenes without addends. Both ultrasound-assisted solvent-exchange and direct sonication techniques for AFD preparation using an immersed probe were tested. The average time for AFD preparation decreases 10?15 times compared to an ultrasound-bath-assisted technique, while final fullerene concentrations in AFDs remained at tens of ppm (up to 80 ppm). The aqueous dispersions showed long-term stability, a negatively charged surface with a zeta potential up to ?32 mV with an average nanocluster diameter of no more than 180 nm. The total anionic and cationic compositions of samples were found by inductively coupled plasma atomic emission spectroscopy and chromatographic techniques. The highlights and challenges of using an ultrasound probe for AFD production are discussed.

The antioxidant properties of unmodified aqueous fullerene dispersions (AFD) of C60, C70, Gd@C82 (in μM concentration range) were studied in the model of generation of organic radicals by 2,2’-azobis(2-amidinopropane) dihydrochloride (ABAP) and luminol. Purification protocols for AFDs are proposed. Based on chemiluminescence (CL) measurements, the concentration-dependent of the CL signal for any AFDs is revealed. Suppression of CL signals is up to 5 times better than Mexidol® antioxidant. The concentration of half-suppression increased in row C60

Endohedral metal fullerene are potential nanopharmaceuticals for MRI; thus, it is important to study their effect on reactive oxygen species (ROS) homeostasis. Superoxide anion radical is one of the key ROS. The reactivity of aqueous dispersions of pristine (non-functionalized) fullerenes and Gd@C82 endofullerene have been studied with respect to superoxide in the xanthine/xanthine oxidase chemiluminescence system. It was found that C60 and C70 in aqueous dispersions react with superoxide as scavengers by a similar mechanism; differences in activity are determined by cluster parameters, primarily the concentration of available, acting molecules at the surface. Gd endofullerene is characterized by a significantly (one-and-a-half to two orders of magnitude) higher reactivity with respect to C60 and C70 and is likely to exhibit nanozyme (SOD-mimic) properties, which can be accounted for by the nonuniform distribution of electron density of the fullerene cage due to the presence of the endohedral atom; however, in the cell model, Gd@C82 showed the lowest activity compared to C60 and C70, which can be accounted for by its higher affinity for the lipid phase.

The photoexcitation energy transfer in donor–acceptor (DA) systems formed from a mixture of semiconductor polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with fullerene C 60 and endohedral metallofullerene Ho@C 82 have been investigated. It is established that the migration of excitons between polymer segments significantly affect the quenching of MEH-PPV luminescence. The Forster radii of nonradiative energy transfer are estimated for the DA systems under study. It is shown that the DA system formed using endohedral metallofullerenes is most efficient. Model photovoltaic cells with different C 60 and Ho@C 82 doping levels are formed based on MEH-PPV. The spectral sensitivity of photovoltage and kinetics of rise in the photovoltage signal under pulsed irradiation are measured for the formed cells. The charge carrier mobility in the polymer composites under study is estimated. It is established that a change in the endohedral metallofullerene concentration within 1–2% makes it possible to change the effective free-carrier mobility of the polymer heterojunction.

The influence of silicon atoms in the graphite electric arc zone on the formation efficiency of higher fullerenes C76, C78, C80, C82, C84, C86, etc. was studied. Additives of silicon carbide from 0 to 6.3 wt. % of composite graphite electrodes and optimization of the conditions of their evaporation make it possible to obtain soot with a content of higher fullerenes up to 15.5 wt.% in the extract and at the same time with a high total yield of fullerenes 10.5 wt.%.

The photoexcitation energy transfer was studied in donor-acceptor systems (DA) formed from a mixture of the semiconductor polymer poly [2-methoxy-5- (2`-ethylhexyloxy) -1,4-phenylenevinylene] (MEH-PPV) with C60 fullerene and endohedral metallofullerene Ho@C82. A significant effect of the exciton migration between the polymer units on the quenching of MEH-PPV luminescence has been established. The Foerster radii of nonradiative energy transfer for the investigated DA systems are estimated. It is shown that the DA system formed using endohedral metallofullerenes is the most effective. Based on MEH-PPV, model photovoltaic cells with different doping levels C60 and Ho@C82 were formed. For the formed cells, the spectral sensitivity of the Photo-EMF and the kinetics of the increase in the Photo-EMF signal under pulsed irradiation were measured. The mobility of charge carriers in the studied polymer composites was estimated. It was found that a change in the concentration of endohedral metallofullerene within 1-2% allows you to change the effective mobility of free carriers of the polymer heterojunction.

The effects that the presence of silicon atoms in the zone of electric arc used for evaporation of graphite electrodes has on the efficiency of formation of higher fullerenes C 76 , C 78 , C 80 , C 82 , C 84 , C 86 , etc., are studied. Optimization of the evaporation conditions and the use of composite graphite electrodes containing silicon carbide, the additive, in the range of 0 to 6.3 wt % enables us to produce soot with the fullerene content at up to 15.5 wt % in a soot extract and, at the time, achieve a high net fullerene yield of 10.5% of the soot weight.

The work considers a possibility of creating standard reference samples of aqueous dispersions of unmodified fullerenes and endohedral fullerenes. Procedures for preparing highly concentrated dispersions and methods for determining the concentration of the main component, elemental impurity composition, organic composition, and dimensional characteristics are discussed. Commercially available fullerenes C60 and C70 and endohedral fullerene Y@C82 (C2v isomer) synthesized by the electric arc method were used as the starting materials. Aqueous fullerene dispersions (AFDs) were prepared by replacing the organic solvent (toluene) under additional ultrasonic treatment. The maximum concentrations of fullerenes C60, C70, and Y@C82 were 150 ± 3, 55 ± 2, and 2.8 ± 0.1 mg/L, respectively. The long-term stability of solutions (more than 5 years) on storage was found. A set of methods and procedures that enable the determination of the main components of AFDs (fullerenes) and accompanying components (impurities of organic solvents and metals at the level of trace concentrations) is discussed. The sizes of fullerene clusters in solutions (from 100 to 120 nm for all solutions) are characterized; the stability of dispersions is estimated based on the electrokinetic potential (ca. –40 mV). The combined use of spectrophotometry, determination of total organic carbon, inductively coupled plasma atomic emission spectrometry, headspace gas chromatographic analysis, and HPLC offers a complete description of the physicochemical properties of AFDs, which further ensures the validation of AFDs as standard reference samples.

Aqueous dispersions of an unmodified (pristine) (AFD) nY@C-82 (symmetry C-2v) endofullerene were produced with a nearly 100% yield relative to the initial toluene solution of the endofullerene. To the best of our knowledge, this is the first report of this kind of endofullerene aqueous dispersions. The solvent-exchange ultrasound-assisted procedure requires no modification of the endofullerene surface or addition of any stabilizing agents into the aqueous phase. The procedure is applicable to any endohedral metallofullerene aqueous dispersions suitable for biomedical applications. The resulting dispersions are stable for at least 6months. For the produced aqueous dispersions of Y@C-82, the zeta potential of ca. -42mV shows good stability; the average diameter of clusters was as small as ca. 120nm. Techniques for purification and purity control of nY@C-82 and of the intermediate toluene solution of Y@C-82 were developed. The residual quantity of organic compounds was less than 1 ppb after the purification. Based on ICP-AES, headspace GC-MS, and MALDI-TOF, a procedure to assess endofullerene concentrations in the aqueous phase was proposed.

Solutions of endohedral Gd@C82(C 2v ) and Ho@C82(C 2v ) metallofullerenes are studied by means of visible and near-IR spectroscopy upon their conversion from neutral to the anionic form via a redox reaction with the electron donor potassium perchlorotriphenylmethide K(18-crown-6)[C(C6Cl5)3]. The concentrations of the studied solutions of endohedral Gd@C82(C 2v ) and Ho@C82(C 2v ) metallofullerenes in o-dichlorobenzene were determined from the spectroscopic data, and their molar extinction coefficients are calculated.

The energy spectrum of C 82 fullerene (isomer no. 3 of C 2 symmetry) is calculated within the Hubbard model in the approximation of static fluctuations. Based on the energy spectrum, optical absorption spectra of this isomer in neutral and anionic states with one, two, three, and four additional electrons are simulated. The calculated optical spectra in neutral and monoanionic states are compared with known experimental spectra.

В рамках модели Хаббарда в приближении статических флуктуаций вычислен энергетический спектр фуллерена C82 (изомер N 3 симметрии C2). На основе энергетического спектра смоделированы спектры оптического поглощения данного изомера в нейтральном и анионных состояниях c одним, двумя, тремя и четырьмя дополнительными электронами. Проведено сравнение расчетных оптических спектров в нейтральном и моноанионном состояниях с известными экспериментальными спектрами. Работа выполнена при финансовой поддержке РФФИ (проекты N 14-08-00824-a, 16-03-00810-a) и гранта МарГУ N 2014-003a. DOI: 10.21883/FTT.2017.01.43974.194

Электродуговой синтез сажи с высоким содержанием высших фуллеренов в "параллельной" дуге

Soot with a relatively high content of higher fullerenes (C76, C78, C80, C82, C84, C86, etc.) is synthesized in a parallel arc upon evaporation of pure carbon electrodes. The content of higher fullerenes in soot extract amounts to 13.8 wt % when two electrodes are simultaneously burnt in electric-arc reactor. Such a content is comparable with the content obtained upon evaporation of composite graphite electrodes with potassium carbonate impurity.