Amino-acid derivatives of fullerene C60 behave as lipophilic ions penetrating through biomembranes

It was found using potential-sensitive probes that the water-soluble amino-acid derivatives of fullerene C₆₀, such as C₆₀-Pro, C₆₀-? aminocapronic acid, and C₆₀-Arg, possess a pronounced membranotropic activity. The first two cause concentration-dependent dissipation of the membrane potential (Δψ) of the symbiosomes of the nodules of the yellow lupine generated in the presence of ATP and Mg²⁺ ions. In contrast to the first two derivatives, C₆₀-Arg, which carries a strong positive charge at the physiological pH, has no effect on the dissipation of Δψ in this model. On the contrary, this derivative caused a noticeable dissipation of the K⁺ diffusion potential (“minus” inside) generated on the membrane of human erythrocytes with the help of the K⁺ ionophore of valinomycin. The regularities obtained indicate that the derivatives of C₆₀ are transported across biological membranes as lipophil ions, thus causing depolarization of the membranes.     

Simulation of the thermal fragmentation of fullerene C60

Defect formation and annealing processes in fullerene C₆₀ at T = (4000–6000) K are studied using molecular dynamics with a tight-binding potential. The cluster lifetime until fragmentation, which proceeds, as a rule, through the loss of a C₂ dimer, has been found as a function of temperature. The activation energy and the frequency factor in the Arrhenius equation for the fragmentation rate have been found to be E _a = (9.2 ± 0.4) eV and A = (8 ± 1) × 10¹⁹s^?1. It is shown that fragmentation can occur already after the C₆₀ cluster loses its spherical shape. This fact must be taken into account in theoretical calculations of E _a.     

Electron-impact induced fragmentation of fullerene ions

The C2 fragmentation of fullerene ions C(q+)(60) (q = 1,2,3) induced by electron impact was studied for the first time. The cross sections for the loss of a C2 fragment indicate the presence of two different processes. At low electron energies the projectile electron leads to the direct excitation of the giant plasmon resonance. At electron energies larger than 100 eV the fragmentation of the fullerene ions can be described as an unsuccessful ionization. Only this second part of the cross section shows a dependence on the charge state q of the precursor ion.     

Synthesis and EPR spectroscopy of nitroxyl derivatives of the C60 fullerene

The 2,2,5,5-tetramethyl-3-imidazoline-3-oxy-1-oxyl-4-(azidophenyl) derivatives of the C₆₀ fullerene with one (compound I), two (compound II), and three (compound III) nitroxyl groups are synthesized and studied by EPR spectroscopy. It is demonstrated that successive addition of nitroxyl radicals to C₆₀ leads to a decrease in the rotational mobility of molecules. Chromatographically inseparable isomers are found for compounds II and III.     

Vibronic resonance in spectra of frozen solutions of the C60 fullerene derivatives

This paper reports on a study by site-selective laser spectroscopy of low-temperature broadband fluorescence spectra of N-methyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-[C₆₀] fulleropyrrolidine (N-MBHPhFP fullerene) molecules embedded in the crystalline toluene matrix. It has been shown that monochromatic laser excitation in the region of vibrational satellites of the pure electronic absorption band initiates structurization of the emission band of a pure electronic transition, which suggests the existence of a set of impurity centers in the crystalline host matrix. An analysis has been made of the factors accounting for replacement of the wide, inhomogeneously broadened band by a series of narrow bands, with the most essential of them being the weakness of electron-phonon coupling in the impurity center, the absence of electronic excitation transfer between the centers, and the vibronic resonance in the excited state of the set of centers. Vibration frequencies of the N-MBHPhFP fullerene in the excited electronic state have been determined.     

Pressure-induced dimerization of C60 fullerene

The dimerization of C₆₀ fullerene under conditions of quasi-hydrostatic compression at temperatures above 293 K is investigated by IR spectroscopy, Raman scattering (RS) spectroscopy, and x-ray diffraction. The measured dimer (C₆₀)₂ content in the products of the polymerization of fullerite as a function of the pressure, temperature, and treatment time shows that dimerization occurs even at room temperature in the entire pressure range above ∼1.0 GPa. However, at least at temperatures above 400 K dimerization does not result in the formation of a dimer phase as a stable modification of the system, since the dimer is an intermediate product of the transformation. It is shown that increasing the holding time at 423 K decreases the content of the dimer fraction in the samples and results in the formation of linear (at 1.5 GPa) and two-dimensional (at 6.0 GPa) polymers, which are structure-forming elements of the orthorhombic and rhombohedral polymerized phases. Pis'ma Zh. éksp. Teor. Fiz. 68, No. 12, 881–886 (25 December 1998)     

Pressure-induced polycondensation of C60 fullerene

Modifications of carbon which are formed from C₆₀ fullerite at pressures up to 10.0 GPa and temperatures up to 1900 K are studied by x-ray diffraction, Raman spectroscopy, and atomic force microscopy methods. The pressures p and temperatures T at which atomic, molecular, and polymolecular structures form under conditions of quasihydrostatic compression are determined. It is shown that, together with polymerization, another type of chemical interaction of the molecules, called polycondensation, which leads to the formation of polymolecular structures with a shortest intermolecular distance of 0.65 nm, is possible in the system. Three-dimensional polycondensation of C₆₀ fullerene is explained by the special properties of the new carbon states. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 10, 778–783 (25 May 1996) The spelling of the authors names are presented here in English as requested by the Russian Editorial office.     

C60 fullerene binding to DNA

Fullerenes have attracted considerable attention in various areas of science and technology. Owing to their exceptional physical, chemical, and biological properties, they have many applications, particularly in cosmetic and medical products. Using the Lennard-Jones 6-12 potential function and the continuum approximation, which assumes that intermolecular interactions can be approximated by average atomic surface densities, we determine the binding energies of a C₆₀ fullerene with respect to both single-strand and double-strand DNA molecules. We assume that all configurations are in a vacuum and that the C₆₀ fullerene is initially at rest. Double integrals are performed to determine the interaction energy of the system. We find that the C₆₀ fullerene binds to the double-strand DNA molecule, at either the major or minor grooves, with binding energies of ?4.7 eV or ?2.3 eV, respectively, and that the C₆₀ molecule binds to the single-strand DNA molecule with a binding energy of ?1.6 eV. Our results suggest that the C₆₀ molecule is most likely to be linked to the major groove of the dsDNA molecule.     

Interaction of polymers with fullerene C60

The fundamentals of the method for estimating the fullerene-binding power of polymer macromolecules and supramolecular formations are developed for fullerene C₆₀. Polymers with covalently attached anthracene groups (one group per macromolecule) whose luminescence decreases in the presence of fullerene in solution in direct proportion to the stability of the fullerene-polymer complex are used. The effect of the anthracene mark on the fullerene-binding power of a luminescent-marked polymer is taken into account or discarded on the basis of an analysis of the interaction between fullerene and low-molecular models of luminescent marks.     

Pressure-induced dimerization kinetics of fullerene C60

Dimerization kinetics was studied for fullerene C₆₀ by IR spectroscopy at a pressure of 1.5 GPa in the temperature range 373–473 K. The kinetic curves for the formation of a dimer (C₆₀)₂ were obtained using its analytical IR band at 796 cm^?1. Under the assumption that pressure-induced C₆₀ dimerization is a second-order irreversible reaction, the reaction rate constants were determined at different temperatures. The corresponding activation energy and preexponential factor were found to be 134±6 kJ/mol and (1.74± 0.24)×10¹⁴ s^?1, respectively. The specific features of the solid-phase C₆₀ dimerization in simple cubic and face-centered cubic fullerite phases are discussed.     

纳秒激光诱导C60分子碎裂中轻碎片离子C+n(n《30)的产生机理研究

采用飞行时间质谱计测量了纳秒激光诱导C60分子碎裂中轻碎片离子C n(n≤11)的初始平均动能,结果显示轻碎片离子具有相同的初始平均动能(约为0.34 eV),并且该动能在一定范围内不随激光通量的变化而明显改变.结合前人的实验结果,对纳秒激光诱导C60分子碎裂中轻碎片离子C n(n<30)的主要产生模式作了新的阐述,即C60分子级联发射15个C2分子和一个电子形成自身不稳定的C 30离子,在皮秒时间尺度内C 30离子的笼形结构塌陷,进而轻碎片离子产生.     

Hydrogen migration on the C60 fullerene

We investigate the migration barriers, transition states, and optimum migration paths of hydrogen on the C₆₀ fullerene using the ab initio density functional theory. Calculated energy barriers tend to be higher for non-local exchange-correlation functionals. We find that the migration between adsorption sites with the same energy has high migration barriers, and thus the initial stages of the H nucleation requires desorption–adsorption cycles. The migration barrier is reduced near another H adsorbate. The migration may be involved more in the later stages of the regio-selective hydrogenation of C₆₀. We find that the migration barriers are reduced by the presence of hydrogen sources, and the hydrogenating agents in the environment are required in order to reach the regio-selective hydrogenation of the C₆₀ fullerene.     

Multiple ionization and fragmentation of negatively charged fullerene ions by electron impact

Cross sections for the electron-impact multiple ionization and fragmentation of negatively charged fullerene ions C(-)(n) ( n = 60, 70) to C(q+)(n-m) ( q = 1,2,3 and m = 0,2,4) have been measured for electron energies up to 1 keV. In the case of pure ionization all threshold energies are about 10 eV higher than the values expected. This shift, however, is not observed for the fragment ions. The experimental data indicate that there is no strong electron-electron interaction between the incident electron and the attached electron. A novel ionization mechanism is proposed which can be expected to be valid for all negatively charged molecular or cluster ions which are able to shield the attached electron from the incident electron.     

Totally symmetric vibrational modes of fullerene C60

Semiempirical molecular orbital calculations are carried out for the totally symmetric vibrations of the C₆₀ molecule. The calculated equilibrium geometry coincides with the precision experimental data to within measurement error. The ratio of force constants calculated for the two different types of C-C bonds in fullerene is equal to 1.389. A comparison of the computational results with the Raman scattering data indicates that there may be Fermi resonance between the totally symmetric vibrations.