Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Crystal structures of chloroform solvates of fullerenes

The chloroform solvates of C₆₀ and C₇₀ fullerenes and of the C₆₀/C₇₀ mixture were synthesized and investigated by X-ray powder diffraction.     

Charge transfer in complexes of C60 and C70 in solutions and solid state

Electronic absorption spectra of complexes of C₆₀ and C₇₀ fullerenes with donors, tetrathiafulvalene and pyranylidene derivatives, were studied in solutions and in the solid state. Charge transfer bands were found in the 680–1300 nm range. The charge transfer energies (hv _ct) for the C₆₀ and C₇₀ complexes in solutions are close and almost independent of the solvent polarity. For the C₆₀ complexes in the solid state, the dependence ofhv _ct on the ionization potential (IP) of donors was found to behv _ct=0.82IP–3.93 eV. In the C₆₀ complexes in the solid state, thehv _ct values are 0.15–0.20 eV lower than those in the solution. The linear dependences ofhv _ct onIP of donors for the C₆₀ complexes lie 0.6–0.7 eV higher than those in the complexes with tetracyanoethylene (TCNE). This is associated with lower values of the electron affinity of C₆₀ and the energy of the electrostatic interaction in the fullerene complexes as compared to those of the TCNE complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 478–483, March, 1999.     

Reactions of chlorofullerene C60Cl6 with N-substituted piperazines

It was shown for the first time that reactions of C₆₀ halides with aliphatic amines provide a facile route for the synthesis of aminofullerenes, valuable precursors for water-soluble cationic fullerene derivatives. Particularly, chlorofullerene C₆₀Cl₆ and N-substituted piperazines were investigated in this work. It was shown that substitution of chlorine atoms in C₆₀Cl₆ by amine groups is accompanied by partial elimination of addends from the fullerene cage that yields mixtures of di-, tetra- and, hexaaminofullerenes as the final products. Separation of these mixtures by column chromatography resulted in isolation of pure 1,4-diaminofullerenes; this procedure gives much higher and more reproducible yields of these compounds than direct oxidative photoaddition of secondary amines to C₆₀. ESI mass spectrometry and NMR spectroscopy data showed that hexaaminofullerene isomers are major components in inseparable mixtures of polyaddition products. Polyaminofullerenes were found to be readily soluble in aqueous acids; these solutions are unstable because of a facile substitution of protonated amine groups with hydroxyls. Nevertheless, the use of other amine substrates in the investigated reaction can potentially allow the preparation of more stable water-soluble cationic fullerene derivatives for biological studies.     

Harnessing Greenhouse Gases Absorption by Doped Fullerenes with Externally Oriented Electric Field

In this work, a theoretical investigation of the effects caused by the doping of C₂₀ with silicon (Si) atom as well as the adsorption of CO, CO₂ and N₂ gases to C₂₀ and C₁₉Si fullerenes was carried out. In concordance with previous studies, it was found that the choice of the doping site can control the structural, electronic, and energetic characteristics of the C₁₉Si system. The ability of C₂₀ and C₁₉Si to adsorb CO, CO₂ and N₂ gas molecules was evaluated. In order to modulate the process of adsorption of these chemical species to C₁₉Si, an externally oriented electric field was included in the theoretical calculations. It was observed that C₁₉Si is highly selective with respect to CO adsorption. Upon the increase of the electric field intensity the adsorption energy was magnified correspondingly and that the interaction between CO and C₁₉Si changes in nature from a physical adsorption to a partial covalent character interaction.     

Electrochemical behavior of fullerene C60 and substituted fullerenes immobilized on an electrode surface

The effect of substituents with different donor capabilities, which are inserted into a molecule of fullerene C₆₀, on the kinetics and thermodynamics of redox conversions of fullerenes that are immobilized on an electrode, is studied for the first time. To this end, redox conversions that occur with rubbed-on films of fullerene and fulleropyrrolidines are studied using cyclic voltammetry in 0.5 M KCl/H₂O and a 0.1 M (C₄H₉)₄NBF₄/AN solution in acetonitrile. A hypothesis that the kinetics of redox conversions occurring with films of individual fullerenes is defined largely by changes in the structure of initial films in the process of their cathodic doping is used. The effect of the substituents is explained in the framework of this hypothesis by a transition from a dense crystalline structure of nonsubstituted fullerene C₆₀ to an amorphous structure of substituted fullerenes. It is demonstrated that the formal potentials corresponding to redox conversions of fullerenes in a solid cationic lipid matrix are defined by the energy of interaction of anions, which are products of reduction of fullerenes, with cations of the matrix. As a result of this interaction, the formal potentials of the process of cathodic doping shift to less negative values. It is established that the insertion of a donor substituent and increase in its donor capability amplify the energy of interaction of the fullerene anions with the lipid cations.     

Reactions of carbanions of bis(dialkoxyphosphoryl)bromomethane with fullerenes C60 and C70

The reactions of carbanions of bis(dialkoxyphosphoryl)bromomethanes with fullerenes C₆₀ and C₇₀ afforded new bis(dialkoxyphosphoryl)methanofullerenes C₆₀ and C₇₀, respectively, whose structures were established by spectroscopic methods.     

(Cyclopentadienyl)chromiumtricarbonyl dimers as a source of metal-centered free-radicals to form stable η-bonded spin-adducts with fullerenes

Spin-adducts (I, IIb-c) of C₆₀ and C₇₀ with metal-centered free radicals CpCr(CO)₃ (I, IIa) have been generated in toluene via interaction between fullerenes and the weakly metal-metal bonded dimeric complexes [CpCr(CO)₃]₂ (Cp = η⁵-C₅H₅ (I); Cp = η⁵-C₅Me₅ (II)). Their structures have been investigated using ESR spectroscopy and DFT-PBE calculations and η²-bonding to the CC bond between two hexagons in C₆₀ has been established. Calculations have been extended to investigate the nature of the intermediate η²-coordinated toluene chromium complexes (I, IId).     

Direct computation of second-order SCF properties of large molecules on workstation computers with an application to large carbon clusters

Summary The ab initio SCF computation of second-order properties of large molecules (with 50 atoms or more) on workstation computers is demonstrated for static dipole polarizabilities and nuclear magneting shieldings. The magnetic shieldings are calculated on the basis of gauge including atomic orbitals (GIAO). Algorithmic advances (semi-direct algorithms with efficient integral pre-screening, and use of a quadratically convergent functional for the polarizabilities) are presented together with an illustrative application to the fullerenes C₆₀ and C₇₀.     

Photo-labeling of C60 with 3-trifluoromethyl-3-phenyldiazirine

The photochemical reaction of C₆₀ with 3-trifluoromethyl-3-phenyldiazirine affords a photo-labeled C₆₀ derivative. The derivative was characterized by mass, UV-vis absorption, NMR spectroscopy, and X-ray crystallographic analysis. The redox potentials of this derivative were also investigated by means of CV and DPV. This photo-labeling method to the fullerene surface is expected to be effective for constructing various kinds of bio-functionalized fullerenes.     

Studies on novel cyclodextrans: Inclusion of C60 and C70

Cycloisomalto-heptaose (CI-7) and cycloisomalto-octaose (CI-8) are two novel cyclodextrans. Treatment with C₆₀ or C₇₀ by kneading leads to the formation of four distinct water-soluble inclusion complexes: CI-7/C₆₀ (2: 1), CI-8/C₆₀ (2: 1), CI-7/C₇₀ (2: 1) and CI-8/C₇₀ (2: 1). Their formation and structures have been examined by UV vis spectroscopy, X-ray powder diffraction and fluorescence spectral studies. The reaction is a reversible process.     

Binary and Ternary Complexes Between Lauryl Hexaoxyethylene, Benzoate and Cyclodextrin. Part I. α-CD

The characterization of binary and ternary complexes of benzoate, lauryl hexaoxyethylene (C₁₂E₆) and -CD is presented. Complexation was characterized by capillary zone electrophoresis and titration microcalorimetry. These techniques suggested that -CD formed two qualitatively different complexes with C₁₂E₆. The stoichiometric ratio of -CD : C₁₂E₆ in the individual complexes was 1 : 1 and 1.4 : 1, with stability constants of2.0 × 10³ M^-1 and 6.4 × 10⁵ M^-1.4, respectively. At higher concentrations of interacting species (10 mM), a precipitate formed. Addition of benzoate seemed to prevent precipitate formation and appeared to increase the stability constants of both binary complexes. Both techniques also indicated formation of ternary complexes between -CD, C₁₂E₆ and benzoate.     

Fullerenes against COVID-19: Repurposing C60 and C70 to Clog the Active Site of SARS-CoV-2 Protease

The persistency of COVID-19 in the world and the continuous rise of its variants demand new treatments to complement vaccines. Computational chemistry can assist in the identification of moieties able to lead to new drugs to fight the disease. Fullerenes and carbon nanomaterials can interact with proteins and are considered promising antiviral agents. Here, we propose the possibility to repurpose fullerenes to clog the active site of the SARS-CoV-2 protease, M^pro. Through the use of docking, molecular dynamics, and energy decomposition techniques, it is shown that C₆₀ has a substantial binding energy to the main protease of the SARS-CoV-2 virus, M^pro, higher than masitinib, a known inhibitor of the protein. Furthermore, we suggest the use of C₇₀ as an innovative scaffold for the inhibition of SARS-CoV-2 M^pro. At odds with masitinib, both C₆₀ and C₇₀ interact more strongly with SARS-CoV-2 M^pro when different protonation states of the catalytic dyad are considered. The binding of fullerenes to M^pro is due to shape complementarity, i.e., vdW interactions, and is aspecific. As such, it is not sensitive to mutations that can eliminate or invert the charges of the amino acids composing the binding pocket. Fullerenic cages should therefore be more effective against the SARS-CoV-2 virus than the available inhibitors such as masinitib, where the electrostatic term plays a crucial role in the binding.     

Thermal Stability of C60-Methylnaphthalenes Solvates

The crystalline solvates containing fullerenes and (di)methylnaphthalenes were investigated by thermal analyses and X-ray diffraction methods. It was found that C₆₀ with (di)methylnaphthalenes forms two types of stable solvates: either at the molar ratio 1:2 decomposing at temperatures close to 100°C or at 1:1 molar ratio decomposing in the temperature range 120–214°C. Crystalline lattice and thermal stability of the solvates depends on the structure of the solvent molecules. The strong solute-solvent interaction is also manifested by the modification of the C₆₀ absorption spectra in solution. The results are discussed using semiempirical quantum chemistry methods. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some applications of thermal analysis to fullerenes

Thermal analysis is a convenient means of characterizing the soot used as a source of the carbon clusters, the extracted mixture of fullerenes, and the individual clusters themselves. TG in an inert atmosphere will rapidly assay the volatile fractions, presumably the lower molecular weight clusters. TG in oxygen indicates — a slight weight gain for the soots and clusters prior to their combustion.DSC in oxygen is used to determine the heat of combustion for the separated C₆₀ and C₇₀ materials. The combustion occurs around 300°C for the clusters. There is a small exothermic peak before this which is attributed to the oxidation associated with the slight weight gain. The heats of combustion measured are –18.7 and –21.0 kJ·mol^–1 for the C₆₀ and C₇₀ respectively.MS-EGA indicates the loss of small amounts of water and argon at temperatures around 250°C in vacuum and of solvent at about 350°C prior to sublimation.

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Zusammenfassung Thermoanalyse ist ein praktisches Hilfsmittel zur Charakterisierung von Ruß als Quelle für Kohlenstoffcluster, extrahierte Gemische von Fullerenen und die individuellen Cluster an sich. TG in einer inerten Atmosphäre ergibt schnell die flüchtigen Fraktionen, wahrscheinlich die niedermolekularen Cluster. TG in Sauerstoff zeigt einen leichten Gewichtszuwachs für Ruß und Cluster vor ihrer Zersetzung.DSC in Sauerstoff wurde angewendet, um die Verbrennungswärme der getrennten C₆₀ und C₇₀ Materialien zu ermitteln. Die Verbrennung erfolgt für die Cluster bei etwa 300°C. Davor kann ein kleiner exothermer Peak beobachtet werden, welcher der Oxidation in Verbindung mit dem geringen Gewichtszuwachs zugeschrieben wird. Die gemessenen Verbrennungswärmen betragen –18.7 und –21.0 kJ·mol^–1 für C₆₀ bzw. C₇₀.MS-EGA zeigt den Verlust von geringen Mengen an Wasser und Argon bei Temperaturen von etwa 250°C in Vakuum und von Lösungsmittel bei etwa 350°C, bevor die Sublimation eintritt.

     

C4H4Y (Y＝O, S, Se)与BX3 (X＝H, F, Cl)作用的计算化学研究

采用量子化学的密度泛函B3LYP和二阶微扰MP2(full)方法对C₄H₄Y (Y＝O, S, Se)与BX₃ (X＝H, F, Cl)形成的电子授受型复合物进行了研究, 所得18个复合物的构型包括BX₃位于C＝C双键上方的π-p作用型和B与O, S, Se直接作用的n-p作用型. 体系C₄H₄Y-BH₃以n-p作用型较为稳定, 体系C₄H₄Y-BF₃, C₄H₄Y-BCl₃的π-p和n-p作用型复合物稳定性相当. 对各复合物的几何构型、振动频率和自然键轨道分析表明, 复合物的形成过程中均存在几何构型的改变、电荷的转移和振动频率的变化, 它们的变化规律与复合物稳定性的变化规律基本一致, 即按H, F, Cl的顺序依次降低.     

Vibrational spectra of cyclooctatetraenyl alkali metal complexes [C8H8M2 (M = Na, K)]: A theoretical study

The cyclooctatetraenyl dianion (C₈H₈²⁻) π-conjugated system forms a stable complex system with alkali and some transition metals. The results of vibrational analysis for C₈H₈M₂ (M = Na, K) complexes were reported here. The geometries of C₈H₈M₂ (M = Na, K) were optimized using ab initio (HF, MP2, CCSD(T)) and DFT (B3LYP) methods with 6-311G** and 6-311++G** basis sets and the harmonic frequencies were obtained. To reproduce and compare with the experimental values the structurally similar molecules C₅H₅M (M = Na, K) and benzene were studied. The scale factors obtained from these systems were applied to predict the experimental frequencies of C₈H₈M₂ (M = Na, K). The force field and vibrational spectra are analyzed and the most probable assignments are proposed for all the fundamentals based on the potential energy distribution.     

Thiophene separation from aliphatic hydrocarbons using the 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid

The ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate has been tested as solvent for the separation of thiophene from aliphatic hydrocarbons. Liquid–liquid equilibrium data have been determined for ternary systems containing the ionic liquid, thiophene and C₆, C₇, C₁₂ or C₁₆ alkanes at T = 298.15 K. The performance of the ionic liquid as solvent in such systems has been evaluated. The experimental data were correlated using the NRTL and UNIQUAC equations, and the binary interaction parameters have been reported. The phase diagrams for the ternary mixtures including both the experimental and calculated tie-lines have been presented.     

Molecular mechanics on bonding and non-bonding interactions in (atom@C60)

The interactions between the embedded atom X (X = Li, Na, K, Rb, Cs; F, Cl, Br, I) andC60 cage in the endohedral-form complexes (X@C₆₀) are calculated and discussed according to molecular mechanics from the point of view of the bonding and non-bonding. It is found from the computational results that for atoms with radii larger than Li’s, their locations with the minimum interaction in (X@C₆₀) are at the cage center, while atom Li has an off-center location with the minimum interaction deviation of ~0.05 nm, and the cage-environment in C₆₀ can be regarded as syhero-symmetry in the region with radiusr of ~0.2 nm. It is shown that the interaction between X and C₆₀ cage is of non-bonding characteristic, and this non-bonding interaction is not purely electrostatic. The repulsion and dispersion in non-bonding interactions should not be neglected, which make important contribution to the location with minimum interaction of X, at center or off center. Some rules about the variations of interactions with atomic radii have been obtained. Project supportt:d by the National Natural Science Foundation of China.     

Spectroscopic and electrochemical studies on the interaction of an inclusion complex of β-cyclodextrin/fullerene with bovine serum albumin in aqueous solution

The potential effect of human exposure to carbonaceous nanomaterials (e.g., fullerenes or their derivatives) in the environment has become a concern. In the current study, we report the interaction of one water-soluble fullerene with bovine serum albumin using spectroscopic and electrochemical methods under aqueous solutions. The novel supramolecular inclusion complex of the water-soluble fullerene (β-CD)₂/C₆₀ was synthesized and characterized. In the mechanism discussed, the spectroscopic methods such as fluorescence quenching and ultraviolet-visible absorption, proved that the fluorescence quenching of BSA by (β-CD)₂/C₆₀ was the result of the formation of (β-CD)₂/C₆₀-BSA complex and that the mechanism of quenching might be a static quenching procedure. The binding constants K_a, the number of binding sites n, and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy, then as an auxiliary method, the electrochemical impedance spectroscopy (EIS) experiments confirmed this conclusion. The results indicated that the electrostatic interactions play a major role in (β-CD)₂/C₆₀-BSA association. The circular dichroism spectra show the conformation change of the effect of (β-CD)₂/C₆₀ on the conformation of BSA, which was confirmed by the results of the three-dimensional fluorescence spectra. Site marker competitive experiments indicate that the binding of (β-CD)₂/C₆₀ to BSA primarily took place in site I. The distance r between donor (BSA) and acceptor ((β-CD)₂/C₆₀) was obtained according to fluorescence resonance energy transfer (FRET). This work aims to demonstrate the mechanisms of the formation of the complex between water-soluble fullerene and protein under physiological conditions, as well as the remediation for the possible unwarranted biological effects of water-soluble fullerene.