Antioxidant and prooxidant effects of α‐tocopherol in a linoleic acid‐copper(II)‐ascorbate system

The peroxidation of linoleic acid (LA) in the absence and presence of either Cu(II) ions alone or Cu(II)‐ascorbate combination was investigated in aerated and incubated emulsions at 37°C and pH 7. LA peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (aldehydes‐ and ketones‐like) oxidation products, detected by ferric‐thiocyanate and TBARS tests, respectively. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. Copper(II)‐ascorbate combinations generally led to distinct antioxidant behavior at low concentrations of α‐tocopherol and slight prooxidant behavior at high concentrations of α‐tocopherol, probably associated with the recycling of tocopherol by ascorbate through reaction with tocopheroxyl radical, while the scavenging effect of α‐tocopherol on lipid peroxidation was maintained as long as ascorbate was present. On the other hand, in Cu(II) solutions without ascorbate, the antioxidant behavior of tocopherol required higher concentrations of this compound because there was no ascorbate to regenerate it. Practical applications: Linoleic acid (LA) peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (e.g., aldehydes and ketones) oxidation products. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. The findings of this study are believed to be useful to better understand the actual role of α‐tocopherol in the preservation of heterogenous food samples such as lipid emulsions. Since α‐tocopherol (vitamin E) is considered to be physiologically the most important lipid‐soluble chain‐breaking antioxidant of human cell membranes, the results can be extended to in vivo protection of lipid oxidation.     

Liquefaction potential at Izmit Bay: comparison of predicted and observed soil liquefaction during the Kocaeli earthquake

The 1999 Kocaeli earthquake resulted in large-scale damage to structures and a death toll of more than 20,000. Numerous liquefaction and associated ground deformations caused by the earthquake were particularly observed along the southern coasts of Izmit Bay and Sapanca Lake, as well as the city of Adapazari. The paper discusses the soil liquefaction and lateral spreading along the southern coast of Izmit Bay. A microzonation map was created using the data from liquefaction susceptibility analyses and a liquefaction severity index. The predicted liquefiable zones showed good agreement with site observations. The assessment suggests that the amount of liquefaction-susceptible layers in the soil profile reduces away from the coastal zone.      

Modeling the kinetics of UV/hydrogen peroxide oxidation of some mono-, di-, and trichlorophenols

The decomposition of a number of chlorophenols (CPs), namely 2-CP, 2, 4-dichlorophenol and 2,4,6-trichlorophenol, has been studied in aqueous solution by UV-catalyzed oxidation with H(2)O(2) under UV radiation emitted by a 125-W medium pressure Hg lamp in an immersion well-type quartz photoreactor, and the organic-bound chlorine has been converted into the environmentally harmless inorganic chloride. For oxidant/CP mole ratios between 1:1 and 16:1, the reaction kinetics were modeled and the corresponding rate constants found by periodically measuring the remaining CP, hydrogen peroxide and converted chloride in solution. A theoretical model for the degradation pathway is proposed expressing the rate as a linear function of the concentrations of CP and oxidant. The rate constants for the pseudo-first order approximation of the CP degradation were compared. H(2)O(2), when combined with UV, is an effective photoactivated oxidant. The photodegradation order in terms of the initial rate of CPs destruction was: Cl(3).Ph>/=Cl(2).Ph>Cl.Ph.     

Electrochemical Determination of Food Preservative Nitrite with Gold Nanoparticles/p-Aminothiophenol-Modified Gold Electrode

Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Au_nano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Au_nano working electrode was prepared by coating the surface with the use of HAuCl₄ solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Au_nano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5–50 mg·L⁻¹ nitrite with a limit of detection (LOD) of 0.12 mg·L⁻¹. Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP‒modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO₂⁻ solution and in sausage sample solution, to which different concentrations of NO₂⁻ standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples.     

Quantification of Antioxidant Ability Against Lipid Peroxidation with an ‘Area Under Curve’ Approach

When oxygen is passed through a linoleic acid (LA) emulsion containing copper(II), primary (hydroperoxides) and secondary oxidation products (aldehydes and ketones) are formed, monitored by ferric thiocyanate (Fe(III)‐SCN) and thiobarbituric acid reactive substances (TBARS) colorimetry, respectively. As total antioxidant capacity (TAC) against lipid peroxidation was not quantified before, both methods were adapted to an ‘area under curve (AUC)’ approach. LA peroxidation followed pseudo‐first order kinetics in aerated emulsions. Absorbance changes as a function of incubation time exhibited sigmoidal curves, enabling the calculation of ‘area under curve’ (AUC) and net AUC = AUC_blank?AUC_sample, standard calibration curve as net AUC versus concentration, and trolox‐equivalent antioxidant capacity of the tested compounds. Garlic extract showed an antioxidative effect on hydroperoxide formation, but a prooxidative effect on TBARS. Although inhibition of lipid peroxidation was described qualitatively before, it was not evaluated quantitatively, e.g., the trolox‐equivalent antioxidant capacities (TEAC values) of antioxidants with respect to their inhibitive effect against lipid peroxidation were not calculated and compared. Additionally, real‐time monitoring of lipid oxidation products requires highly sophisticated but costly instrumental techniques, but no single oxidation product is a direct measure of lipid oxidation or its antioxidative prevention. The AUC approach is the first quantitative method measuring antioxidant protection against lipid oxidation, with a slightly different order of antioxidative effectiveness from reductive assays because of interfacial effects.     

An investigation on the mechanisms of instabilities and safe design of the south slope at a lignite pit (SW Turkey) based on a sensitivity approach

Turkey has significant lignite reserves which are generally being extracted using open pit mining methods. The Hüsamlar pit is one of the operated lignite pits in the well-known Mugla lignite province in SW Turkey. Some local failures and one large failure, which caused the evacuation of the Hüsamlar village located next to the slope crest and interruption in coal production, occurred along the south slope of this pit. This paper outlines the results of the field and laboratory geotechnical investigations associated with the causes and mechanisms of the instabilities, and assessments on the possible modifications in the current and planned final slope geometries to improve the stability of the south slope. Since no sufficient data on groundwater conditions in the pit were available, in order to reduce the uncertainty associated with groundwater, different pore pressure ratios (r _u) were considered and a sensitivity approach was used in the stability assessments. The back-analyses of the observed instabilities including one or more benches in the overburden indicated that the most critical modes of failure for the south slope are circular and composite sliding surfaces. Although kinematical analyses suggested that structurally controlled failures would not be expected, one local planar failure that occurred in the south slope emphasizes that the possibility of local planar sliding should be considered when the dip of bedding planes locally exceed 20° and pore pressure becomes high. In addition, the back-analyses revealed that r _u was probably between 0.3 and 0.4 and the residual shear strength along the bedding planes was critical when slope instabilities occurred along the south slope. The stability assessments for the current and the final south slope, which was planned by the mining organization operating the pit, indicated that some modifications in bench and slope geometries are necessary to achieve a factor of safety of 1.3, which is a commonly used value in open pit practice. In addition, these assessments also suggested that the most critical zone in the overburden was the thinly bedded marl in terms of stability, and at the thickest part of this material (30 m), the overall slope angles satisfying F = 1.3 at r _u values of 0.2, 0.3 and 0.4 should be 18°, 17° and 15°, respectively. Except those in the thinly bedded marl, bench widths in the overburden units and coal seam are reduced and steeper slopes with F ≥ 1.3 were achieved.     

Stress Distribution in an Infinite Body Containing Two Neighboring Locally Curved Nanofibers

In the present paper, the stress distribution in an infinite elastic body containing two neighboring nanofibers is studied. It is assumed that the midlines of the fibers are in the same plane. With respect to the location of the fibers according to each other the co-phase and anti-phase curving cases are considered. At infinity uniformly distributed normal forces act in the direction of the nanofibers, location. The investigations are carried out in the framework of the piecewise homogeneous body model with the use of the three-dimensional geometrically non-linear exact equations of the theory of elasticity. The normal and shear self-equilibrated stresses arising as a result of the nanofiber curving are analyzed. In particular, the influence of the interaction between the fibers on the distribution of these stresses is studied. A lot of numerical results on the effect of the geometrical non-linearity to the values of the self balanced shear and normal stresses are presented.     

Development of a silver nanoparticle-based method for the antioxidant capacity measurement of polyphenols

A sensitive colorimetric method for the detection of polyphenols (i.e., flavonoids, simple phenolic, and hydroxycinnamic acids) was proposed in this research based on the reduction of Ag(+) ions by polyphenols in the presence of citrate-stabilized silver seeds. The color of the stable suspension was controlled by varying the concentration of trisodium citrate, silver nitrate, and silver seeds. The reduction of Ag(+) to spherical silver nanoparticles (SNPs) by polyphenols in the presence of trisodium citrate and silver seeds produced a very intense surface plasmon resonance (SPR) absorption band of SNPs at 423 nm. The plasmon absorbance of SNPs allows the quantitative spectrophotometric detection of the polyphenols, and the developed method gave a linear response over a wide concentration range of standard polyphenolic compounds. In contrast to other reported NP-based antioxidant assays, it was established in this work that growth but not nucleation of SNPs gave a linear concentration-dependent response. The trolox equivalent antioxidant capacity (TEAC) values of various (hydrophilic and lipophilic) antioxidants using the developed method were comparable to those of the CUPRAC assay. Common food ingredients like oxalate, citrate, fruit acids, amino acids, and reducing sugars did not interfere with the proposed sensing method. This assay was validated through linearity, additivity, precision and recovery, demonstrating that the assay is reliable and robust. The developed method was used to screen total antioxidant capacity (TAC) of some commercial fruit juices and herbal teas without preliminary treatment, and showed a promising potential for the preparation of antioxidant inventories of a wide range of food plants.