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.     

Microwave-assisted extraction of C60 and C70 from fullerene soot

Microwave-assisted extraction (MAE) was examined as an alternative to the traditional Soxhlet method of extracting C₆₀ and C₇₀ from fullerene soot. MAE of 0.20 g of fullerene soot with 95:5 toluene–acetonitrile yielded greater than 7.8 mg of C₆₀ and greater than 0.54 mg of C₇₀ in 4 min with no further increase in yield after 30 min of irradiation. By comparison, exhaustive Soxhlet extraction of the same size sample with the same solvent yielded 7.1 mg of C₆₀ and 0.58 mg of C₇₀ in 340 min. Reextraction by MAE of soot initially extracted by Soxhlet increased the yield of Soxhlet alone. Although MAE was limited to less than 0.5-g sample per extraction vessel, multiple samples were extracted with minimal increased extraction time and no reduction in the amount of material recovered.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Geometry and stability of fullerene cages: C24 to C70

The electronic structures and geometries of all even carbon fullerenes were investigated theoretically using density functional theory (DFT) at the B3LYP/6‐31G* level. Based on geometries, energies, and aromaticities, the potential relationship between geometry factors and stability has been investigated systematically. The extra stability of C₆₀ has been confirmed by the shorter average bond length, smaller angle strain, widest energy gap, larger binding energy, and dissociation energy. Furthermore, C₃₂ and C₅₀ are predicted to have higher aromaticity due to larger negative nucleus independent chemical shift (NICS) values, whereas C₆₀ displays a weak aromaticity. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Flow-injection determination of creatine in animal tissues

After deproteination of samples with trichloroacetic acid, creatine is determined by reaction with 1-naphthol and biacetyl, based on a stopped-flow method. The calibration graph is linear over the range 0–250 mg l^?1, and recoveries from muscle samples are quantitative.     

Synthesis and reaction of fullerene C70 encapsulating two molecules of H2

New endohedral fullerene C(70) encapsulating one and two H(2) molecule(s) has been synthesized by organic reactions, the so-called "molecular surgery" method, and the first organic derivatization of H(2)@C(70) and (H(2))(2)@C(70) has been conducted. Although the interaction between inner H(2) and outer C(70) is rather weak, (H(2))(2)@C(70) exhibits smaller equilibrium constants in the Diels-Alder reaction with 9,10-dimethylanthracene than those of H(2)@C(70).     

Construction and photophysical properties of hypocrellin A/fullerene C70 supramolecular assembly

Interaction of hypocrellin A (HA), a naturally perylenequinonoid, with fullerene C₇₀ has been studied by UV–vis and fluorescence spectra, and the results show that HA and C₇₀ can form a supramolecular assembly HA/C₇₀ with a 2:1 stoichiometry in organic solvents and buffer solution containing poly(vinylpyrrolidone) (PVP). The triplet lifetime of HA and C70 are reduced due to the formation of supramolecular complex. Electron paramagnetic resonance (EPR) studies suggest that photoinduced electron transfer from N,N,N′N′-tetramethyldiethyleneamine (TMEDA) to the excited HA induces the generation of anion radical of HA (HA^?), followed by further electron transfer from HA^? to C₇₀. HA can mediate the electron transfer from TMEDA to C₇₀ and significantly enhance the intensity of characteristic Near-IR absorption transition of C₇₀^?, through efficient electron-transfer processes. Upon visible light irradiation, HA/C₇₀ exhibits stronger photodamage ability on calf thymus DNA under anaerobic condition than HA and C₇₀.     

An analysis of the structure of fullerene C70 by quantum-chemical methods

Hartree-Fock and density functional theory calculations showed that the B, C, D, and E fullerene C₇₀ cycles were not coplanar. The interrelation between acoplanarity and pyramidality of atoms was studied. The bond lengths, valence and torsion angles, and charges and chemical shifts of fullerene C₇₀ atoms were jointly analyzed. Most attention was given to the acoplanarity of hexagons E in the aromatic belt.     

Kinetics and stoichiometry of the reaction between ozone and C70 fullerene in CCl4

The kinetics and stoichiometry of the reaction between C₇₀ fullerene and ozone have been studied. The reaction obeys a bimolecular rate law. The stoichiometric coefficients of the reaction are 1: 12 to 1: 22, depending on reaction conditions. The rate constant at 22°C is 5 × 10⁴ l mol^?1 s^?1 for the first stage of fullerene conversion and (0.8–0.6) × 10⁴ l mol^?1 s^?1 for the subsequent stages. Since the stages differ in terms of reaction rate, the original C₇₀ molecules are first involved in the reaction, whereas, at the subsequent stages, all molecules are involved with equal probabilities, irrespective of the number of preceding reaction events in which they have participated.     

Trace metal determination in animal tissues: an interlaboratory comparison

Two dried and powdered preparations of narwhal liver and muscle were distributed to 13 laboratories for analysis for Cu, Cd, Zn, Pb, Hg, and Se. Laboratories chose their own methods, using atomic-absorption spectrometry, atomic-emission spectrometry with a direct-current or inductively-coupled plasma, anodic stripping voltammetry (ASV), neutron activation analysis (NAA), and gas chromatography. The coefficients of variation ranged from 2 to 5% for Cu, Cd, Zn, Hg in liver, but were somewhat higher for Zn by ASV and NAA. In muscle, the precision for Zn was similar to that for liver, but was poorer for Cu (8.8%) and Cd (19%). For Pb, the overall precision was 15% and 21% for liver and muscle respectively. Selenium in both tissues was determined with an overall precision of 6-7%, except by NAA, for which it was considerably worse, at 21-26%.     

Chromatographic Behavior of C60 and C70 Fullerenes at Subambient Temperature with n-Alkanes Mobile Phases

The influence of temperature on the retention and separation of C60 and C70 fullerenes was studied under HPLC conditions. Particularly, chromatographic experiments were conducted using moderate carbon loaded octadecylsilica stationary phase and homologous series of n-alkanes including n-pentane, n-hexane and n-heptane as the mobile phases. All studies were performed across wide range of subambient temperature from −80 to +20 °C. From practical point of view the best chromatographic conditions for baseline separation of the components of interest were selected. The retention of analytes was strongly affected by temperature and below minus 30 °C strong deviation from van't Hoff behavior was observed. To explore this phenomenon selected thermodynamic parameters including changes of enthalpy (ΔH^o) and changes of entropy (ΔS^o) were estimated. Positive values of the ΔH^o and ΔS^o at low temperature region may indicate the lack of the interaction with the stationary phase ligands. A possible retention mechanism at different temperatures for C60 and C70 molecules has been discussed.     

分离富勒烯的新型高效液相色谱固定相

从分子结构与分子间作用力的关系出发，以富电子性化合物甲苯、α－二甲苯、α－甲基萘修饰的聚苯乙烯－二乙烯苯（ＰＳ－ＤＶＢ）树脂作为固定相分离Ｃ６０、Ｃ７０混合物，获得很好的结果，其中以α－甲基萘修饰ＰＳ－ＤＶＢ和为固定相分离效果最理想。     

Experimental and theoretical analysis of the reorientational dynamics of fullerene C70 in various aromatic solvents

A previous study of C70 in deuterated chlorobenzene generated evidence suggesting C70 was experiencing unique reorientational behavior at given temperatures. The present study explores the possibility that this behavior is present across other solvents. The 13C spin-lattice relaxation rates for four carbon resonances in C70 were analyzed in benzene-d6, chlorobenzene-d5, and o-dichlorobenzene-d4, and as a function of temperature, to probe the reorientational dynamics of this fullerene. Anisotropic behavior was observed at the lowest (283 K) and highest temperatures (323 K), isotropic diffusion was seen between 293 and 303 K, and quasi-isotropic at 313 K. When anisotropic motion was present, diffusion about the figure axis was seen to be higher than diffusion of the figure axis. Experimentally obtained diffusion coefficients generated reorientational correlation times that were in excellent agreement with experimental values. Theoretical predictions generated by a modified Gierer-Wirtz model provided acceptable predictions of the diffusion constants; with DX usually being more closely reproduced and DZ values generally being underestimated. Overall, the results indicate that the factors affecting rotational behavior are complex and that multiple solvent factors are necessary to characterize the overall motion of C70 in these solvents. Although a solvent's viscosity is normally sufficient to characterize the tumbling motion, the spinning motion is less sensitive to solvent viscosity but more responsive to solvent structure. The balance and collective influence of these factors ultimately determines the overall rotational behavior.     

Preparation and NMR characterization of C70H10: cutting a fullerene pi-system in half

Three isomers of C70H10 were prepared by Zn(Cu) reduction of C70. Three chromatographic bands were identified as C70H10 species by MALDI-FT mass spectrometry, and these compounds were isolated by repeated HPLC treatments. The major isomer (2) was characterized by 1H and 13C NMR, while the minor isomers 3-4 were isolated in such small quantities that only 1H NMR analysis was possible. 1H-coupled and 1H-decoupled 13C NMR of 2 established a 7,8,19,26,33,37,45,49,53,63-substitution pattern. This assignment was confirmed by HMBC and DFQ-COSY experiments. This structure is completely reasonable, as we found that 2 results exclusively from reduction of the 7,19,23,27,33,37,44,53-C70H8 that is formed in the course of the Zn(Cu) reduction of C70.     

The determination of zirconium in animal tissues by neutron activation and γ-spectrometry

A neutron activation method has been developed for determining microgram and submicrogram quantities of zirconium in animal tissue. The procedure uses phosphate to aid in the separation of zirconium from interfering radio-isotopes. Tissues are dried, sealed in quartz vials, irradiated at a high flux, and wet-ashed; the zirconium is precipitated as ZrO(H₂PO₄), redissolved, and precipitated as BaZrF₆. This procedure effectively removed interfering radioactive elements. Chemical oxidation and the simple separation procedure were checked by radiotracer experiments, and by processing tissues to which known quantities of zirconium had been added. The detection limit of the method for a 100-h irradiation at 1 × 10¹⁴ n cm^-2 s^-1 followed by radiochemical processing is 10 ng, based on 2 σ counting statistics. The error is estimated to be ± 5–10%.     

The polarographic determination of zinc and manganese in plant and animal tissues and soils

A method is proposed whereby microgram quantities of zinc and manganese may be simultaneouly extracted with excess sodium diethyldithiocarbamate in the presence of tartrate at pH 5.5, the extracts decomposed and the metals polarographed in a lithium chloride supporting electrolyte. Iron must first be removed with cupferron, and the interference by cobalt and nickel is overcome by the use of dimethylglyoxime prior to the extraction. The method may be applied to the digests of animal tissues, plant materials or soils.