C60 In Solution Research Articles

Effect of Centrifugal Field upon Hydrodynamic Characteristics of Fullerene C60 and Poly(N-vinylpyrrolidone) Complex in Aqueous Solutions

Velocity ultracentrifugation method was employed to study aqueous solutions of fullerene C60 and poly(N-vinylpyrrolidone) complex (PVP-C60). Strong dependence of sedimentation coefficient S 0 on ultracentrifuge rotor speed n was found. The S 0 value increases as the value of n decreases from that corresponding to isolated PVP-C60 macromolecules to the value that the clusters of PVP-C60 (registered by the light-scattering method) would have at n → 0. This dependence indicates that molar mass and size of clusters change depending on the centrifugal field applied.

Colloidal structure and stabilization mechanism of aqueous solutions of unmodified fullerene C60

Despite the inability of fullerenes to be directly dissolved in water, there are methods for preparing stable dispersions of fullerenes in water without any particular modifications of the fullerene or addition of stabilizers. The colloidal properties of such systems prepared by replacing the solvent and structural changes in them during coagulation have been studied. The coagulation dynamics has been investigated by spectroscopy and small-angle neutron scattering. The results obtained confirm the colloidal nature of such systems. During coagulation, particles retain a large volume of water around them, an indication of interaction between fullerene and water during solution stabilization.

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C60 in carbon disulfide CS2 have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 A in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.

Influence of dissolved oxygen on the thermal expansion and polyamorphism of fullerite C60

The temperature dependence of the coefficient of linear thermal expansion α of O2–C60 solutions with 20% and 80% filling of the octahedral cavities with oxygen is investigated in the temperature interval 2.2–24K. Hysteresis of α(T) is observed, attesting to the coexistence of two orientational glasses in these solutions. A comparison of the behavior of these glasses is made. The characteristic times for reorientation of the C60 molecules and for the phase transformations in the solutions are determined. When the temperature of the O2–C60 solution with 20mol.% oxygen is increased to 450°C, a chemical interaction of the oxygen with the C60 molecules is manifested. It proves possible to separate the influences of the chemical and physical sorption of oxygen on the thermal expansion of polycrystalline fullerite C60.

Aqueous dispersions of C60 fullerene

Stable aqueous colloidal dispersions of C60 fullerene are prepared. A solvatochromic effect is revealed upon the addition of C60 solution in chlorobenzene to a water-acetone mixture.

Observation of superluminal propagation at negative group velocity in C60 solution

The authors observed the superluminal propagation at negative group velocity in C60 toluene solution firstly. The theoretical analysis was made based on density matrix model of superluminal propagation. The simulation result was well consistent with experimental measurement. The largest time advancement of 3.58ms was got at 5.6×10−4mol∕l of sample concentration; the corresponding group velocity is −0.28m∕s.

Dynamics of Water in Solvation Shells and Intersolute Regions of C60: A Molecular Dynamics Simulation Study

We present dynamical characteristics of the solvent in various solvation shells of a C60 molecule as well as intersolute region between two fullerene molecules. Results are obtained from extensive atomistic molecular dynamics simulations of aqueous solutions of C60 in the isothermal−isobaric ensemble. Information about translational mobilities of water in and around fullerene molecules are obtained from velocity auto correlation function and mean square displacements as calculated from simulation data. Reorientational behavior also is investigated by analyzing first and second rank dipole−dipole correlation functions as calculated from simulation trajectories. Both the translational and rotational mobilities of water in the first solvation shell around a C60 molecule are found to be much slower than the same in the second and third solvation shells. Slower decay of the occupation time correlation function for the water in the first hydration shell indicates slower exchange of these water molecules with th...

Photoinduced quenching of the luminescence of singlet oxygen in fullerene solutions

The photoinduced quenching of the luminescence of singlet oxygen in solutions of C60 and C70 fullerenes in CCl4 is studied. It is shown that intense pumping of the solutions by ultraviolet and visible radiation leads to formation of relatively long-lived fullerene-oxygen complexes, which are effective quenchers of the 1Δg excited state of singlet oxygen. The behavior of these complexes depending on the experimental conditions (pumping intensity, concentration of fullerenes in the solution, and temperature) is studied. Decomposition of complexes with time is investigated. It is shown that, upon formation and gradual degradation of these complexes, the absorption spectra of the solutions change with time. The C60 fullerene is shown to be more stable to the intense pumping, its concentration being completely restored with the decomposition of the complexes. At the same time, C70 fullerene is partly irreversibly lost and the solution does not reach its initial concentration after decomposition of complexes.

Synthesis and characterization of difluoromethylene-homo[60]fullerene, C60(CF2)

Refluxing of the o-DCB solution of C60 with CF2ClCOONa and 18-crown-6 leads to formation of C60(CF2)n (n = 1-3); the monoadduct C60(CF2) has been found to consist of the main [6,6]- and minor [5,6]-isomers, both having an open structure.

Pristine Fullerene C60: Different Water Soluble Forms—Different Mechanisms of Biological Action

Aqueous fullerene preparations, namely complex of C60 with polyvinylpyrrolidone (C60/PVP) and molecular‐colloidal water solutions of C60 (FWS) exhibit virocidal activity due to different mechanisms: C60/PVP complexes act mainly on the lipid component of virus membranes, while the mechanism of virocidal action of FWS is mainly connected with the ability of fullerene to generate singlet oxygen under irradiation. In the first case, fullerene acts mainly as a membranotropic agent, whereas in the second case it acts mainly as a photosensitizer.

Comparison of Singlet Oxygen Generation Efficiency between Water‐Soluble C60‐Diphenylaminofluorene Conjugates and Molecular Micelle‐like FC4S

Amphiphilic C60‐diphenylaminofluorene conjugates C60 (>DPAF‐EGn) exhibit good water‐solubility and form self‐assembled bilayer vesicles in dilute aqueous solution. Their singlet oxygen generation efficiency in DMF or H2O was evaluated by using time‐resolved measurements of singlet oxygen luminescence at 1270 nm upon photoexcitation by nanosecond pulse laser operated at 523 nm. By the application of different bandpass filters to cut off certain emission at wavelength ranges outside 1270 nm, a distinguishable peak in medium to high integrated luminescence intensity was collected at wavelengths between 1240 and 1300 nm. It provided confirmation and close correlation of emitted photon counts measured for these fullerene derivatives to singlet oxygen. In contrast to apparently high singlet oxygen generation efficiency of FC4S in H2O, an observed low singlet oxygen production rate from aqueous solutions of C60 (>DPAF‐EG14) and C60 (>DPAF‐EG45) was interpreted as the result of the occurrence of competitive ultrafast intramolecular electron transfer going from DPAF moiety to C60 cage moiety. That eliminated largely the possibility of energy transfer process for fullerenyl intersystem crossing to generate 3C*60(>DPAF‐EGn). Instead, radical ion‐pairs containing molecules C60 −· [>(DPAF‐EGn)+·] were produced via the intramolecular electron transfer process in the photoexcited transient state.

Thermodynamic properties of fullerene C60 solutions in a mixture of tetrachloromethane and toluene

The solubility of fullerene C60 in the tetrachloromethane-toluene system is measured over the entire range of compositions of the mixed solvent in the temperature range 298.15–338.15 K. An equation is proposed for describing the solubility of C60 as a function of the temperature and the composition of the mixed solvent. The equation is used for calculating the thermodynamic characteristics of solution of the fullerene. It is found that, in the investigated C60-CCl4/C6H5CH3 system, two types of solid solvates of the fullerene with the solvent are formed. The enthalpies and temperatures of incongruent melting of the crystalline solvates are determined by differential scanning calorimetry. The thermodynamic characteristics of solution and solvation of C60 in CCl4 and C6H5CH3 are obtained. It is shown that the entropy factor plays a decisive role in the temperature dependence of the Gibbs energy of solvation of the fullerene.

Intense Photoluminescence from Mixed Solutions of C70 and Palladium Octaethylporphyrin: A Supramolecular Heavy Atom Effect

Unusually intense near-infrared (near-IR) photoluminescence has been observed from mixed solutions of C70 and palladium octaethylporphyrin (PdOEP). The novel emission has a spectrum similar to C70 phosphorescence and an intensity that is approximately 20 times greater than that of C70 fluorescence. The emitting species is identified as a noncovalently bound, short-lived triplet exciplex of C70 with PdOEP. The emission is essentially C70 phosphorescence intensified by spin-orbit coupling from the Pd atom in the nearby metalloporphyrin. This supramolecular heavy atom effect increases the C70 emissive quantum yield to approximately 1 x 10(-2) in degassed hexane solution at room temperature. The radiative rate constant is enhanced by a factor of 10(5), to approximately 7 x 10(4) s(-1), which is a value that exceeds the phosphorescence rate constant of PdOEP. Comparative studies in a rigid poly(methyl methacrylate) (PMMA) matrix show that the excited state of the static C70-PdOEP complex decays in approximately 150 ns. A Job's plot analysis shows that the complex has a 1:1 stoichiometry. It forms dynamically in solution and is relatively weakly bound, with an estimated equilibrium constant near 100 M(-1). Qualitatively similar supramolecular heavy atom effects were also observed for complexes of PdOEP with C60 and fullerene derivatives.

Formation of secondary fullerene ozonides in the ozonolysis of C60 solutions and chemiluminescence upon their hydrolysis

The formation of secondary fullerene ozonides (SFOs) in the ozonolysis of C60 solutions in CCl4 has reliably been determined for the first time; SFOs are accumulated during the whole ozonolysis time as a suspension in CCl4. Hydrolysis of the SFOs results in chemiluminescence (CL) (Imax = 2.65·108 photon s−1 mL−1), whose spectra contain maxima at 558, 608, and 685 nm. The most probable CL emitters are excited fullerene polyketones. Hydrogen peroxide was identified as a stable hydrolysis product of the SFOs by the color reaction with diphenylcarbazide and CL arisen upon the addition of an aqueous solution of FeSO4·9H2O to the hydrolyzate of the SFO. Chemiluminescence upon hydrolysis is a selective test for SFOs and allows one to find them in a complex mixture of the ozonolysis products of C60. The rate constant and activation energy of SFO hydrolysis were determined from the kinetic measurements of CL. For SFO hydrolysis several probable reactions were proposed, including the formation of the CL emitters, and their heat effects were estimated using the PM3/RHF and AM1/RHF semiempirical methods for one-and two-cage model structures of SFOs.

Highly Enhanced Luminescence from Single-Crystalline C60·1m-xylene Nanorods

Single-crystalline C60·1m-xylene nanorods with a hexagonal structure were successfully synthesized by evaporating a C60 solution in m-xylene at room temperature. The ratio of the length to the diameter of the nanorods can be controlled in the range of ≈10 to over 1000 for different applications. The photoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that for pristine C60 crystals in air. Both UV and Raman results indicate that there is no charge transfer between C60 and m-xylene. It was found that the interaction between C60 and m-xylene molecules is of the van der Waals type. This interaction reduces the icosahedral symmetry of C60 molecule and induces strong PL from the solvate nanorods.

Diffusion Coefficients of C60 and C60– in Benzonitrile and Dichloromethane Solutions Containing Tetrabutylammonium Perchlorate, Measured by Potential-step Chronoamperometry

The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively.

Influence of fullerene C60 on the kinetics of toluene evaporation

The kinetic dependences of the relative weight loss of the solvent from dilute solutions of fullerene C60 in toluene under ambient conditions were determined. Evaporation of the pure solvent is slower than that of the same solvent from dilute solutions (≤0.01%).

Thermal expansion and polyamorphism of N2–C60 solutions

The linear coefficients α(T) of N2–C60 solutions with 9.9% and 100% of the C60 lattice thermal expansion interstitials filled with N2 are investigated in the interval 2.2–24K. The dependence α(T) has a hysteresis suggesting co-existence of two types of orientational glasses in these solutions. The features of the glasses are compared. The characteristic times of phase transformations in the solutions and reorientation of C60 molecules are estimated.

Thermal conductivity of nanoparticle suspensions

We describe an optical beam deflection technique for measurements of the thermal diffusivity of fluid mixtures and suspensions of nanoparticles with a precision of better than 1%. Our approach is tested using the thermal conductivity of ethanol-water mixtures; in nearly pure ethanol, the increase in thermal conductivity with water concentration is a factor of 2 larger than predicted by effective medium theory. Solutions of C60–C70 fullerenes in toluene and suspensions of alkanethiolate-protected Au nanoparticles were measured to maximum volume fractions of 0.6% and 0.35vol%, respectively. We do not observe anomalous enhancements of the thermal conductivity that have been reported in previous studies of nanofluids; the largest increase in thermal conductivity we have observed is 1.3%±0.8% for 4nm diam Au particles suspended in ethanol.

Effect of ultrasound treatment of C60 solutions on the crystalline structure of precipitated fullerite

The structure of fullerite precipitated from solutions of C60 in toluene, chlorobenzene, and 1,2-dichlorobenzene by adding isopropanol was studied. It was demonstrated that, irrespective of the nature of the solvent, the parameter of the fcc lattice of precipitated fullerite decreases markedly when the process occurs in the presence of a ultrasound field. No effect of ultrasound sonication on the size of the precipitated crystallites was observed.