Association behaviors of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone)-grafted fullerenes in aqueous solution

Poly(N-vinylpyrrolidone) (PVP)-grafted fullerenes (PVP-C₆₀ and PVP-C₇₀) were synthesized by iniferter polymerization in order to fabricate water-soluble fullerene containing micelles. PVP-C₆₀ formed micelles with hydrodynamic diameters ranging from 15 to 33 nm. The solubilization of fullerene molecules into the core of the PVP-C₆₀ micelles was also found to control the size of the micelles. By increasing the amount of added fullerene, we gradually increased the micelle size before drastically increasing it to that of 200 nm in hydrodynamic diameter. The drastic change occurred at a critical value of the added C₆₀/PVP monomer ratio, almost independently of the molecular weight of PVP.     

Structure of poly(vinyl pyrrolidone) - C70 complexes in aqueous solutions

Aqueous solutions of poly(vinyl pyrrolidone)-fullerene complexes, PVP/C₇₀, have been studied using static and dynamic light scattering. Two diffusive processes were observed. The slow diffusion describes the motion of large PVP/C₇₀ clusters, whereas the fast diffusion is associated with the presence of single PVP molecules or small individual PVP/C₇₀ complexes of the order of a single PVP chain. The molar mass and the size of the PVP/C₇₀ clusters increase upon increasing the fullerene content. However, when the fullerene content is kept constant, an increase in the molar mass of the matrix PVP does not influence the mass and the size of the clusters. Dilution of the PVP/C₇₀ solutions has no effect on the clusters either. In PVP/C₇₀ there is a specific molar ratio of C₇₀ per repeating units of PVP that is same for all the samples studied.     

Static and dynamic light scattering study of strong intermolecular interactions in aqueous solutions of PVP/C60 complexes

The investigations of the dilute aqueous solutions of polyvinylpyrrolidone/fullerene (PVP/C₆₀) complexes by static (SLS) and dynamic (DLS) light scattering showed that strong intermolecular interactions, effective on the distances of about 45-50 nm, take place in the solutions. Two concentration ranges are well distinguished in these solutions. Above a critical concentration (c_cr) the fluctuations in the solutions are hindered and only one, diffusive, mode is observed in DLS experiments. Upon dilution (c<c_cr) this unified structure divides into large fragments (domains) and the slow mode attributed to long-range concentration fluctuations, gradually appears. The angular and concentration dependencies of the diffusion coefficient of the slow mode indicate the existence of strong intermolecular interactions.     

Separation of fullerenes C60 and C70 using a crystallization‐based process

A crystallization‐based process that separates pure fullerenes C₆₀ and C₇₀ from their mixture using o‐xylene as the solvent has been developed. Isothermal solid–liquid equilibrium phase diagrams of the C₆₀‐C₇₀‐o‐xylene ternary system for a number of temperatures were first determined at 1 atm. Taking advantage of the shift in solvent‐free composition of the C₆₀‐C₇₀ double saturation point with temperature and based on the solid solution‐forming phase behavior between C₆₀ and C₇₀, the flowsheet of a general crystallization process was then synthesized. It involved the fractionation of a C₆₀‐C₇₀ fullerene mixture into C₆₀‐rich and C₇₀‐rich solid solutions using temperature‐swing crystallization, followed by purification of the solid solutions with multistage crystallization into pure C₆₀ and C₇₀ solids. To demonstrate process feasibility, bench‐scale batch experiments were performed using a commercially available fullerene mixture that was pretreated by adsorption to remove higher fullerenes. C₆₀ and C₇₀ solids of purity higher than 99 wt % were obtained. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Mineralization of herbicide 3,6-dichloro-2-methoxybenzoic acid in aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

The mineralization of acidic aqueous solutions with 230 and 115 ppm of herbicide 3,6-dichloro-2-methoxybenzoic acid (dicamba) in 0.05 M Na₂SO₄ of pH 3.0 has been studied by electro-Fenton and photoelectro-Fenton using a Pt anode and an O₂-diffusion cathode, where oxidizing hydroxyl radicals are produced from Fenton's reaction between added Fe²⁺ and H₂O₂ generated by the cathode. While electro-Fenton only yields 60-70% mineralization, photoelectro-Fenton allows a fast and complete depollution of herbicide solutions, even at low currents, by the action of UV irradiation. In both treatments, the initial chlorine is rapidly released to the medium as chloride ion. Comparative electrolyses by anodic oxidation in the absence and presence of electrogenerated H₂O₂ give very poor degradation. The dicamba decay follows a pseudo-first-order reaction, as determined by reverse-phase chromatography. Formic, maleic and oxalic acids have been detected in the electrolyzed solutions by ion-exclusion chromatography. In electro-Fenton, all formic acid is transformed into CO₂, and maleic acid is completely converted into oxalic acid, remaining stable Fe³⁺-oxalato complexes in the solution. The fast mineralization of such complexes by UV light explains the highest oxidative ability of photoelectro-Fenton.     

New Octopus-like Phthalocyanines as Fullerene Receptors: Synthesis and Photophysical Investigation

Octopus-like zinc and magnesium phthalocyaninates bearing eight flexible benzylated diethylene glycol chains were synthesized and their interaction with fullerenes C₆₀ and C₇₀ was investigated by UV-Vis spectrophotometric titration, as well as by steady-state and time-resolved fluorescence spectroscopy in chloroform and toluene media. These measurements revealed a high affinity of receptors for C₆₀ and C₇₀, with selectivity to C₇₀: binding constants for C₇₀ are almost two times higher than for C₆₀. These results are interpreted by means of quantum-chemical calculations using the PM6-DH2 Hamiltonian. The binding constants also depend on both the nature of the metal ion in the receptor and the solvent. It is expected that the obtained molecules and supramolecular complexes can be used for further elaboration of optoelectronic donor-acceptor materials.     

Dilute solution properties of pullulan by dynamic light scattering

Summary Pullulan, produced by the fungus Aureobasidium, has been studied in dilute solution by viscometry, static low angle light scattering and dynamic light scattering at temperatures of 25, 40, 60 and 80 °C. The samples used were fractions obtained by partial hydrolysis of native pullulan and successive fractionation with ethanol. The mass-average molar mass, M_W, of the studied pullulans were in the range of 1.67*10⁵ to 1.0*10⁶ g/mol. The translational diffusion coefficient at infinite dilution, Do, was obtained from the reduced first cumulant of the intensity autocorrelation function of the light scattered by extrapolation to zero scattering angle and zero polymer concentration. The activation energy of diffusion, E_D, of pullulan macromolecules was calculated from Do=D^oexp(-E_D/RT). It was found that in the given temperature rangeE_D = 16.5 ± 0.5 kJmol⁻¹ for all samples. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

EXTRACTION OF COPPER(II) FROM ACID CHLORIDE SOLUTIONS BY N-DODECYL- AND N.N-DIHEXYLPYRIDINECARBOXAMIDES

ABSTRACT

N-dodecyl- and N,N-dihexylpyridinecarboxamides with amide group at 2, 3 or 4 position were synthesized. Model individual amides were used to recover copper(II) from chloride solutions at constant water activity and constant total concentration of dissolved species in aqueous solution. It was found, that pyridine-2-carboxamide forms with copper complexes (CuCl₂)_x (Ext)₂. Remaining amides form with copper complexes CuCl₂(Ext)₂. Monoalkylamides are not suitable for extraction because they and their complexes are slightly soluble in the hydrocarbon diluents. N,N-dialkylpyridinecarboxamides and their copper complexes are sufficiently soluble in the hydrocarbon phase to carry out extraction. However, they are strong extractants and extract efficiently copper already from dilute chloride solutions ([Cl] = 0.1 M). They extract also significant amounts of copper from concentrated (3-4M) nitrate solutions.     

Reversible photoreaction of C60-containing poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) was reacted with strong base NaH to convert its pendant hydroxy to oxy anions, followed with nucleophilic addition to buckminsterfullerene-C₆₀. The resulted PVA(C60−Na⁺)_n products were then converted to PVA(C₆₀H)_n by stirring with a strong acid cation exchanger of the H⁺ form. The reduced viscosities of PVA(C₆₀H)_n decreases with amount of C₆₀, and are between 0.38 and 0.66 dL/g compared to 1.97 dL/g of the original PVA. Repeated photocrosslinking under 300 nm light and photocleavage under 254 nm light of these C₆₀-containing PVAs were investigated in DMSO by tracing their UV absorption variations at 325 nm (maximum absorption of C₆₀H). It is confirmed that both PVA(C₆₀H)_n exhibit excellent reversibility at least under the observed three cycles. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 605–611, 1998     

Mechanism of electrodeposition of silicon from K2SiF6-flinak

Cyclic voltammetry data for stationary and rotating electrodes are presented for electrodeposition of silicon from solutions of K₂SiF₆ in the LiF/NaF/KF eutectic. It is concluded that electron transfer is the main rate-controlling mechanism but that solute diffusion cannot be neglected. The interface process is preceded by a chemical reaction, probably dissociation of polynuclear Si_nF_2n+2 complexes.     

Determination of polystyrene-carbon dioxide-decahydronaphthalene solution properties by high pressure dynamic light scattering

The diffusion coefficients of polystyrene (PS) in decahydronaphthalene (DHN) and in solutions of carbon dioxide (CO₂) and DHN were measured for dilute PS solutions over a range of temperatures and CO₂-DHN ratios using high pressure dynamic light scattering. Infinite dilution diffusion coefficients (D₀) of PS and dynamic second virial coefficients (k_D) were determined for essentially monodisperse 308 kDa PS. At a system pressure of 20.7 MPa, PS diffusion coefficients increased by a factor of 2.5, and the activation energy of diffusion decreased by approximately 16% when DHN was “expanded” with 44 mol% CO₂. However, the hydrodynamic radius of PS at a given temperature was not particularly sensitive to the CO₂ concentration. Solvent quality, as measured by k_D, decreased at higher CO₂ concentrations. The addition of CO₂ to polymer solutions may offer a way to “tune” the properties of the solution to facilitate the heterogeneous catalytic hydrogenation of polymers.     

Concentration dependence of the diffusion coefficient in polymer solution and molecular weight distribution determined by the diffusion method

The effects of the concentration dependence of the diffusion coefficient of a polymer solution (polystyrene in benzene and cyclohexane) in determining molecular weight distribution by the diffusion method are briefly discussed. The value of the ratio D_m0/D_A0 in a good solvent was found to be close to 1.0 for a polydisperse polymer and less than 1.0 for monodisperse polymers. Molecular weight distribution curves of the polydisperse sample were obtained by the diffusion method in cyclohexane and benzene, respectively. The molecular weight distribution curve obtained for the polymer used in benzene solution looked as if the polymer had a narrow molecular weight distribution. The phenomena cited above were interpreted in the light of the concentration dependence of the diffusion coefficient of polymer solutions.     

Polymeric fullerene oxide (fullerene ozopolymers) produced by prolonged ozonation of C60 and C70 fullerenes

The prolonged ozonation of C₆₀ and C₇₀ fullerene produces light brown to brown amorphous solids which are insoluble in chlorinated and hydrocarbon solvents but which are readily soluble in water, acetone and ethanol where they give dark-brown solutions. The polymeric and polyelectrolytic nature of these solids has been shown by viscosimetric and cryoscopic measurements. Due to the polymeric nature the solids have been called ‘ozopolymers’. The reactivity and the ozone uptake have been measured quantitatively during the ozonation of C₆₀ and C₇₀ fullerene in CCl₄. Three different C₆₀ ozopolymer samples have been produced at different degrees of ozonation: at O₃/C₆₀ molar ratio of 8, 14 and 26. The C₇₀ ozopolymer has been produced at an O₃/C₇₀ molar ratio of 30. All the samples have been studied by FT-IR spectroscopy and the C₆₀ ozopolymers have been easily reduced by the action of Zn dust and acetic acid or by the action of H₂S and studied by FT-IR. The action of oxidizing agents has been studied as well. C₆₀ ozopolymer is a polyelectrolyte rich in carboxyl groups and for this reason it possesses a high metal binding capacity similar to that of humic acids. The thermal stability of C₆₀ ozopolymer and its reduced derivatives as well as the thermal stability of C₇₀ ozopolymer has been checked by thermogravimetric analysis in nitrogen and air flow. Finally, the electrical conductivity of C₆₀ ozopolymer was found to be σ=2.8×10⁻⁸ S/cm which is three orders of magnitude lower than that of pure C₆₀.     

Light-stimulated oxidation reactions of tris(1,10-phenanthroline), tris (2,2′-dipyridine) and bis(2,2′,2″-tripyridine)iron(II) complexes

The oxidation reactions of Fe(phen)²⁺₃, Fe(dipy)²⁺₂ were investigated electrochemically under the irradiation of visible light and in the dark. Two arrests in current were observed at 0.5 and 0.9 V (vs sce) in the anodic polarization curves of these complexes. The initial and the second arrests were ascribed to the oxidations of the aquo-ferrous ion and FeL²⁺_n, respectively. The oxidation of these complexes was stimulated by irradiation with light. It was concluded that d electrons were excited to antibonding ligand orbitals, on absorbing visible light and then the electrochemical oxidation of these complexes proceeded more favourably under the irradiation of light than in the dark.     

Insight into dynamics of polyelectrolyte chains in salt-free solutions by laser light scattering and analytical ultracentrifugation

We have investigated the dynamics of xanthan aqueous solutions with and without added salt (NaCl) by using laser light scattering (LLS) and analytical ultracentrifugation (AUC) via sedimentation velocity (SV). The fast and slow modes are observed in salt-free and low-salt xanthan solutions by dynamic light scattering (DLS). The scattering ratio (KC/R_s(q)) and apparent diffusion coefficient (D_s,app(q)) of the slow mode is linearly related to scattering vector (q²), indicating that it is related to the diffusion of scattering objects. The intensity contribution (α_s) of the slow mode is independent of scattering angles, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length. However, the slow mode disappears in SV experiments, indicating that it arises from the temporal aggregates due to long range electrostatic interactions between chains, which can be destroyed in centrifugal field. The diffusion coefficient measured by SV is close to that of the fast mode in DLS measurements, indicating that it is the coupling diffusion of macroions and counterions. The present studies also demonstrate that the chain stiffness does not change the characteristics of the dynamics of polyelectrolyte in solutions.     

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

We dissolve C₆₀, C₇₀ or C₈₄ molecules in benzene and change the fluid state from a gas–liquid two-phase region (25.0 °C) to the critical point (289.0 °C) and from the critical point to the original state (25.0 °C) along the gas–liquid coexistence curve. We find that particle-like and whisker-like nano/micro clusters, which are composed of C₆₀ molecules, deposit on the surface of a silicon substrate placed vertically in C₆₀/benzene solution during the temperature change, whereas no appreciable clusters are detected on the silicon substrate in either C₇₀/benzene or C₈₄/benzene solutions. The clusters, in which fcc lattice structures are formed by C₆₀ molecules, remain stable in the solution. The present result suggests that C₆₀ molecules can be separated and extracted from a mixture of C₆₀, C₇₀ and C₈₄ molecules dissolved in benzene.     

Electrochemical Study of Core-Shell Microgels

Core and core-shell microgels are synthesized by aqueous free radical precipitation polymerization and their solvent release effects characterized. Dynamic light scattering (DLS) reveals hydrodynamic radii (Rh) decrease sharply at lower critical solution temperature (LCST) of 32 ^oC. Electrochemical properties of microgels were also investigated using cyclic voltammetry (CV) and chronoamperometry (CA) with electroactive probes: Fc(MeOH)₂, uncharged and Ru(NH₃)₆Cl₃, positively charged. By measuring the effect of temperature change on the diffusion coefficients, I estimated the electrostatic interactions in varying solutions: aqueous (without migrogels), 25% core microgel and 25 % core-shell microgel solution systems. The diffusion coefficient of uncharged ferrocenedimethanol Fc(MeOH)₂was found to increase as temperature increases, in both core or core-shell solutions. Positive charged Ru(NH₃)₆Cl₃ shows a different behavior in both 25% core and 25% core-shell systems. In aqueous solution, increasing temperature brings increased diffusion coefficients. With the addition of core and core-shell microgel solution systems, diffusion coefficients fall sharply above LCST. This suggests that there is some amount of electrostatic interactions between negatively charged core and core-shell microgels and positively charged Ru(NH₃)₆Cl₃.     

Thermal decomposition of solid oxygenated complexes formed by coal oxidation at low temperatures

Solid oxygenated complexes formed by coal oxidation play an important role in low-temperature oxidation of coal. Using an isothermal-flow reactor, the decomposition behaviour of solid oxygenated complexes was examined under pure nitrogen, at temperatures between 60 and 110 °C. The production of CO₂ and CO during thermal decomposition of the complexes was quantified by an on-line dual-column micro GC. Experiments show that the production rates of CO₂ and CO depend on temperature, but are independent of the particle size of the samples, indicating that the thermal decomposition process is dominated by chemical kinetics rather than diffusion. It was also found that the rates of formation of carbon oxides follow the Elovich equation and the activation energies for the production of CO₂ and CO are 52.1±6.3 and 72.0±5.8 kJ/mol, respectively, indicating two separate reaction pathways proceeding in the decomposition of solid oxygenated complexes.     

Polyelectrolyte complexes based on chitosan and poly(L‐glutamic acid)

Polyelectrolyte complexes (PECs) were prepared by mixing aqueous solutions of chitosan (CS) and poly(L ‐glutamic acid) (PLGA) at various pH. It was found that the stoichiometry of the PECs depends on pH. An investigation of the PECs using Fourier transform infrared spectroscopy proved that the formation of the complexes is due to electrostatic interaction between ? NH₃⁺ groups of CS and ? COO^? groups of PLGA. The solid PECs were characterized using wide‐angle X‐ray diffraction, which suggested that a strong interaction occurs between the two polymers at pH = 4 or 5 and relatively weak interaction at pH = 3. These results were further confirmed by thermogravimetric analysis data. Transmission electron microscopy showed that the complexes have a spherical shape. The effect of ionic strength on the size of the PECs was also studied using dynamic light scattering. It was found that the size of the PECs is dependent on pH. Copyright © 2007 Society of Chemical Industry     

Synthesis and fluorescent properties of Eu and Tb complexes with a series of new diamide ligands

A series of new diamide ligands were introduced into the complexes of Eu(NO₃)₃ and Tb(NO₃)₃ so as to improve the fluorescent properties. The fluorescent properties of the resulting complexes were investigated. It was found that the complexes subject to the excitation of UV light showed characteristic emission of europium and terbium ions, in particular, the Tb complexes had very much intense fluorescence.