Preparation and electrochemical performance of Li-rich layered cathode material,Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript>, for lithium-ion batteries

The Li-rich layered cathode material, Li[Ni_0.2Li_0.2Mn_0.6]O₂, was synthesized via a “mixed oxalate” method, and its structural and electrochemical properties were compared with the same material synthesized by the sol–gel method. X-ray diffraction (XRD) shows that the synthesized powders have a layered O₃–LiCoO₂-type structure with the R-3m symmetry. X-ray photoelectron spectroscopy (XPS) indicates that in the above material, Ni and Mn exist in the oxidation states of +2 and +4, respectively. The layered material exhibits an excellent electrochemical performance. Its discharge capacity increases gradually from the initial value of 228 mA hg⁻¹ to a stable capacity of over 260 mA hg⁻¹ after the 10th cycle. It delivers a larger capacity of 258 mA hg⁻¹ at the 30th cycle. The dQ/dV curves suggest that the increasing capacity results from the redox-reaction of Mn⁴⁺/Mn³⁺.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Electrochemical properties of amorphous Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>2</Subscript>O<Subscript>5−<Emphasis Type="Italic">y</Emphasis></Subscript> thin film deposited by r.f.-sputtering

The electrochemical properties of amorphous vanadium pentoxide (V₂O₅) thin films deposited by reactive r.f.-sputtering were investigated using galvanostatic charge/discharge cycling and galvanostatic intermittent titration technique (GITT). As x in Li _x V₂O_5−y increased (x = 0–2.0), the electromotive force of the lithium (Li)∣1 M LiClO₄–propylene carbonate∣Li _x V₂O_5−y cell decreased gradually without a potential plateau or an abrupt potential reduction, demonstrating that an irreversible structural change did not occur in the entire Li content. Chemical diffusivity of the Li ion in the Li _x V₂O_5−y thin film measured using GITT was determined to be 4 × 10⁻¹³–7 × 10⁻¹⁴ cm² s⁻¹ in the Li content range investigated.     

The effect of phase transition of crednerite/delafossite CuMn1−xCrxO2 on optical,thermal, and power factor properties

This study aims to investigate the effect of the phase transition of CuMn_1−xCr_xO₂ compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn_1−xCr_xO₂ samples were synthesized by a solid-state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO₂ to delafossite CuCrO₂ was confirmed by X-ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X-ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed-state Mn³⁺/Mn⁴⁺ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn_1−xCr_xO₂. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO₂ phase to the delafossite CuCrO₂ phase on CuMn_1−xCr_xO₂ compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties.     

DSA electrochemical treatment of olive mill wastewater on Ti/RuO<Subscript>2</Subscript> anode

The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO₂ anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO₂ anode. Experiments were conducted at 300–1,220 mg L⁻¹ initial chemical oxygen demand (COD) concentrations, 0.05–1.35 V versus SHE and 1.39–1.48 V versus SHE potential windows, 15–50 mA cm⁻² current densities, 0–20 mM NaCl, Na₂SO₄, or FeCl₃ concentrations, 80 °C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L⁻¹ and 50 mA cm⁻² leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L⁻¹) using lower current densities (15 mA cm⁻²) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L⁻¹ in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO₂ anode seems to be independent of the presence of salts in contrast with Ti/IrO₂ where addition of NaCl has a beneficial effect on decolorization.     

Determination of hydrogenation ability and exchange current of H<Subscript>2</Subscript>O/H<Subscript>2</Subscript> system on hydrogen-absorbing metal alloys

A detailed analysis of potential versus time measurements at galvanostatic charge/discharge conditions (external current change from −1 to +1 mA cm⁻²) for two La–Ni alloys in Ar-saturated 0.1 M KOH solution is presented. It is shown that passivation of the electrodes does not affect the potential jump as a result of current switching over. The value of potential jump allows to calculate the exchange current density for H₂O/H₂ system on the tested material. Anodic potential of the hydrogenated electrode (at i _a = const) linearly increases with logarithm of time which allows to evaluate precisely time necessary for oxidation of hydrogen absorbed during cathodic charging. The method described enables to determine effectiveness of hydrogen absorption by materials applied for negative electrodes of NiMH batteries.     

Improved catalytic hydrolysis of carboxy methyl cellulose using cellulase immobilized on functionalized meso cellular foam

Cellulase from Penicillium funiculosum was immobilized on functionalized MCF (Meso Cellular Foam) silica by imine bond formation followed by reduction using NaBH₄. The specific activities of free and immobilized enzyme were measured for hydrolysis of soluble carboxymethyl cellulose (CMC). The highest activity of MCF immobilized and native enzyme was obtained at optimum pH 5 and 4.5 respectively. Kinetic parameters, Michaelis–Menten constant (Km) and maximum reaction velocity (Vmax), were calculated as Km = 0.025 × 10⁻² mg/mL, Vmax = 5.327 × 10⁻³ U/mg for the free enzyme and Km = 0.024 × 10⁻² mg/mL, Vmax = 9.794 × 10⁻³ U/mg for MCF immobilized enzyme respectively. The reusability of immobilized enzymes showed that 66% of its activity is retained even after 15 cycles. The availability of polar groups (–NH–, –OH) and large pore size of surface modified MCF could be electrostatically stabilizing the cellulase. Functionalized MCF was found to be a promising material for stabilizing cellulase with 16.4 wt% loading of enzyme.     

Direct-hydrothermal synthesis of LiFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> cathode materials

Carbon free LiFe_1−x Mn _x PO₄ (x = 0, 0.05, 0.1, 0.2, 0.4) cathode materials were prepared by a direct-hydrothermal process at 170 °C for 10 h. The structural and electrochemical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge–discharge experiments, cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The electrochemical performance of LiFePO₄ prepared in this manner showed to be positively affected by Mn²⁺-substitution. Among the Mn²⁺-substitution samples, the LiFe_0.9Mn_0.1PO₄ exhibited an initial discharge capacity of 141.4 mA h g⁻¹ at 0.1 C, and the capacity fading is only 2.7% after 50 cycles.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

A new class of Sol–gel derived LiM1xM2yMn2?x?yO3.8F0.2 (M1?=?Cr, M2?=?V; x?=?y?=?0.2) cathodes for lithium batteries

A series of LiM_1xM_2yMn_2−x−yO_3.8F_0.2 (M₁ = Cr, M₂ = V; x = y = 0.2) cathodes, viz., LiMn₂O_3.8F_0.2, LiCr_0.2Mn_1.8O_3.8F_0.2 and LiCr_0.2V_0.2Mn_1.6O_3.8F_0.2 along with native LiMn₂O₄ have been synthesized by Citric Acid assisted Modified (CAM) sol–gel method, with a view to understand the effect of synthesis methodology and the effect of dual category dopants, viz., anion and/or cation upon spinel cathodes individually. An acceptable capacity retention (94%) observed up to 50 cycles for native LiMn₂O₄ cathodes is attributed to the significance of CAM sol–gel method. Similarly, the encouraging charge–discharge results of LiMn₂O_3.8F_0.2 (130 mAh g⁻¹) and LiCr_0.2Mn_1.8O_3.8F_0.2 (142 mAh g⁻¹) cathodes revealed a possible augmentation in the reversible capacity behavior of the spinels upon F⁻ substitution at 32e site and the simultaneous substitution of Cr³⁺ and F⁻ at 16d and 32e sites respectively.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Temperature programmed desorption of oxygen from Pd films interfaced with Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZrO<Subscript>2</Subscript>

The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y₂O₃–stabilized–ZrO₂ (YSZ), an O²⁻ conductor, under high-vacuum conditions and temperatures between 50 and 250 °C. Oxygen was adsorbed both via the gas phase and electrochemically, as O²⁻, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300 °C (state β₁) and 340–500 °C (state β₂). The creation of the low temperature peak is favored at high exposure times (exposure >1 kL) and low adsorption temperatures (T_ads < 200 °C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450 °C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O²⁻ pumping to the Pd catalyst film show two peaks (at 350 and 430 °C) corresponding to spillover O_ads and according to the reaction:

Synthesis, Characterization, Conductivity, Band Gap, and Thermal Analysis of Poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol and Its Polymer–Metal Complexes

Oxidative polycondensation reaction conditions of [(2-mercaptophenyl)iminomethyl]-2-naphthol (2-MPIM-2N) were studied using oxidants such as air and NaOCl in an aqueous alkaline medium between 40 °C and 90 °C. The structure of poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol (P-2-MPIM-2N) was characterized by ¹H- ¹³C NMR, FT-IR, and UV–Vis spectroscopy, size exclusion chromatography (SEC), and elemental analysis. At optimum reaction conditions, the yield of P-2-MPIM-2N was found to be 78 and 82% for air and NaOCl oxidants, respectively. From SEC measurements, the number-average molecular weight (M _n ), weight-average molecular weight (M _w ) and polydispersity index (PDI) of P-2-MPIM-2N are 2900, 3500 g mol⁻¹ and 1.207; 2200, 2500 g mol⁻¹ and 1.136, for air and NaOCl oxidants, respectively. Polymer–metal complexes were synthesized by the reaction of P-2-MPIM-2N with Co²⁺, Cu²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ ions. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrochemical band gaps (E^￠_g E^{\prime}_{g} ) of 2-MPIM-2N and P-2-MPIM-2N were −5.97, −2.66 and 3.31 eV and −5.82, −2.68 and 3.14 eV, respectively. The conductivity of polymer and polymer–metal complexes were determined in the solid state. Conductivity measurements of doped and undoped Schiff base polymer and polymer–metal complexes were carried out at room temperature and atmospheric pressure by the four-point probe technique using an electrometer. The conductivities of the polymer and polymer–metal complexes increased when iodine was used as doping agent.     

Emissions of N<Subscript>2</Subscript>O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N₂O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N₂O ha⁻¹ year⁻¹ for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N₂O ha⁻¹ year⁻¹. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N₂O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N₂O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N₂O emissions such as groundwater level. In this paper we report on the relations between N₂O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N₂O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N₂O–N ha⁻¹ year⁻¹ and 11.6 kg N–N₂O ha⁻¹ year⁻¹ for the dry and wet conditions, respectively. Especially under dry conditions, measured N₂O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N₂O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R ² = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.     

Biocatalytic Properties of Lipase from Walnut Seed (<Emphasis Type="Italic">Juglans regia</Emphasis> L.)

Lipase (E.C. 3.1.1.3) from walnut seed was purified 28.6-fold with 31% yield using Sephadex G-100 gel chromatography. Olive oil served as good substrate for the enzyme. The optimum pH and temperature were 9.0 and 70 °C, respectively. The lipase was stable between 30 and 80 °C for 5 min. K _m and V _max values were determined as 48 mM and 23.06 × 10⁻³ U/min mg for triolein as substrate. Lipase activity was slightly reduced by Cu²⁺, Ca²⁺, Hg²⁺, Mn²⁺, and Ni²⁺ ions, while Mg²⁺ and Zn²⁺ had no effects. Anionic surfactant sodium dodecyl sulfate stimulated lipase activity while non-ionic surfactants Tween-80 and Triton X-100 had negligible effects on enzymatic activity. The enzyme activity was not affected by 50 mM urea and thioacetamide. Potassium ferricyanide, n-bromosuccinamide and potassium cyanide reduced the enzyme activity. The enzyme showed a good stability in organic solvents, the best result being in n-hexane (113% residual activity). The activity of dialysate was maintained approximately 80% for 1 year at −20 °C.     

Preparation and characterization of crednerite glass–ceramics in the MnO·CuO·SiO2 system

Nanoscale crednerite (CuMnO₂) was prepared in the system MnO·CuO·SiO₂, using glass–ceramics technique for the first time. Based on obtained data from differential thermal analysis (DTA), the prepared samples were heat-treated at 700 and 800 °C for 2 h. The presence of crystalline phases after and before heat treatment was investigated by X-ray diffraction analysis. Crystallization of crednerite (CuMnO₂), manganese silicate (Mn₂SiO₄) and traces of cuprite (Cu₂O) and cristobalite (SiO₂) phases were recognized. Transmission electron microscopy showed nanoscale crystals in the range 5–10 nm. The prepared glass–ceramics showed ferrimagnetic properties with wide range coercivity from 53 to 2217 Hci and magnetization saturation from 0.21708 to 1.2 emu/g. From IR reflection data; the reflection intensity of the light is high in the range of orange–red color and violet–blue colors and low in the range of green color.     

Electrochemical promotion of CO<Subscript>2</Subscript> hydrogenation on Rh/YSZ electrodes

The electrochemical promotion of the CO₂ hydrogenation reaction on porous Rh catalyst–electrodes deposited on Y₂O₃-stabilized-ZrO₂ (or YSZ), an O²⁻ conductor, was investigated under atmospheric total pressure and at temperatures 346–477 °C, combined with kinetic measurements in the temperature range 328–391 °C. Under these conditions CO₂ was transformed to CH₄ and CO. The CH₄ formation rate increased by up to 2.7 times with increasing Rh catalyst potential (electrophobic behavior) while the CO formation rate was increased by up to 1.7 times with decreasing catalyst potential (electrophilic behavior). The observed rate changes were non-faradaic, exceeding the corresponding pumping rate of oxygen ions by up to approximately 210 and 125 times for the CH₄ and CO formation reactions, respectively. The observed electrochemical promotion behavior is attributed to the induced, with increasing catalyst potential, preferential formation on the Rh surface of electron donor hydrogenated carbonylic species leading to formation of CH₄ and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation.     

Kinetic Study of the Prooxidant Effect of α-Tocopherol. Hydrogen Abstraction from Lipids by α-Tocopheroxyl Radical

A kinetic study of the prooxidant effect of α-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by α-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k _p) obtained are <1 × 10⁻² M⁻¹ s⁻¹ for 1, 1.90 × 10⁻² M⁻¹ s⁻¹ for 2, 8.33 × 10⁻² M⁻¹ s⁻¹ for 3, 1.92 × 10⁻¹ M⁻¹ s⁻¹ for 4, and 2.43 × 10⁻¹ M⁻¹ s⁻¹ for 5 at 25.0 °C. Fatty acid esters 3, 4, and 5 contain two, four, and six –CH₂– hydrogen atoms activated by two π-electron systems (–C=C–CH₂–C=C–). On the other hand, fatty acid ester 2 has four –CH₂– hydrogen atoms activated by a single π-electron system (–CH₂–C=C–CH₂–). Thus, the rate constants, k _abstr/H, given on an available hydrogen basis are k _p/4 = 4.75 × 10⁻³ M⁻¹ s⁻¹ for 2, k _p/2 = 4.16 × 10⁻² M⁻¹ s⁻¹ for 3, k _p/4 = 4.79 × 10⁻² M⁻¹ s⁻¹ for 4, and k _p/6 = 4.05 × 10⁻² M⁻¹ s⁻¹ for 5. The k _abstr/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction.