Biotransformation of patulin to hydroascladiol by Lactobacillus plantarum

Growth of Penicillium expansum, an ubiquitous mould found in stored fruit globallyt, was significantly restricted by exposure to 48 h cell-free supernatant of two strains of Lactobacillus plantarum (p < 0.001). In addition, the biotransformation of patulin, a toxic secondary metabolite formed by P. expansum, on exposure to L. plantarum cells and cell-free supernatant highlights the potential of this GRAS microbe as a biocontrol agent. Up to 80% of patulin was biotransformed following a 4 h incubation with 10¹⁰ cells ml⁻¹ (37 °C) forming E- and Z-ascladiol. The formation of these products was more pronounced at elevated pH and cell density. Exposure to cell free supernatant or sonicated cells resulted in complete patulin biotransformation with heat treatment inhibiting this effect. The ascladiol isomers were then further transformed over a 4-week cell-free incubation (4 °C) into the novel metabolite hydroascladiol (5-(2-hydroxyethyl)-4-(hydroxymethyl) furan-2(5H)-one) which produced a 2 amu difference across the main tandem mass fragments (113.1, 129.0, 139.0), compared to ascladiol (111.1, 127.0, 137.0). This suggests hydroascladiol could be a better biomarker of initial patulin levels in some food commodities. The in vitro biotransformation data and resistance of L. plantarum to highly elevated concentrations of patulin (≥100 μg ml⁻¹) suggest L. plantarum is a potential candidate for food preservation or remediation strategies and future work with fruit products is proposed.     

Effect of combination of ultraviolet light and hydrogen peroxide on inactivation of Escherichia coli O157:H7, native microbial loads,and quality of button mushrooms

Mushrooms are prone to microbial spoilage and browning during growing and processing. Ultraviolet light (254 nm, UV-C) has been used as an alternative technology to chemical sanitizersfor food products. Hydrogen peroxide (H₂O₂) is classified as generally recognized as safe for use in foods as a bleaching and antimicrobial agent, and could control the bacterial blotch and browning of mushrooms. This study investigated the effects of water wash (control), 3% H₂O₂ wash, 0.45 kJ m⁻² UV-C, and combination of H₂O₂ and UV-C (H₂O₂ + UV) on microbial loads and product quality of mushrooms during storage for 14 days at 4 °C. Additionally, the inactivation of Escherichia coli O157:H7 inoculated on mushrooms was determined. Results showed that water wash, H₂O₂, UV-C and H₂O₂ + UV resulted in 0.44, 0.77, 0.85, and 0.87 logs CFU g⁻¹ reduction of E. coli O157:H7, respectively. Hydrogen peroxide, UV-C and the combination reduced total aerobic plate counts on the surface of mushrooms by 0.2–1.4 logs CFU g⁻¹ compared to the control, while there was no significant difference among the three treatments during storage. After storage, UV-C treated mushrooms had similar L* and a* values as the control while H₂O₂ and H₂O₂ + UV-C treated mushrooms had higher L* (lighter) and lower a* (less brown) values than the control. Compared to water wash, all the treatments inhibited lesion development on the mushroom surface on day 14. The combination of H₂O₂ and UV achieved the best overall dual control of lesion and browning. There was no significant difference in ascorbic acid and total phenolic content among the treatments. Overall our results suggested that H₂O₂ + UV reduced microbial loads, and extended storage life by reducing lesion development without causing deterioration in nutritional quality of button mushrooms. Therefore, when properly utilized, H₂O₂ + UV could potentially be used for maintaining postharvest quality while marginally reducing populations of E. coli O157:H7 and background microflora.     

Modeling of sporicidal effect of hydrogen peroxide in the sterilization of low density polyethylene film inoculated with Bacillus subtilis spores

The sporicidal effect of hydrogen peroxide (H₂O₂) in the sterilization of low density polyethylene film (LDPE) was evaluated using a Central Composite Design (CCD). The effects of contact time (5-19s), bath temperature (23–70 °C) and concentration of H₂O₂ (0–35%) in an immersion bath were investigated. A 16 cm² film surface was evenly inoculated with 100 μL of the test microorganism Bacillus subtilis var. globigii ATCC9372 spores. The effective H₂O₂ sporicidal activity was demonstrated at concentrations from 18 to 35% and in a temperature range from 46 to 70 °C, resulting in 2–7 decimal reductions of B. subtilis spores. A quadratic mathematical model representative of the action of H₂O₂ on the B. subtilis spores was developed as a function of concentration, time and temperature. Test specimens sanitized with 28% H₂O₂ at 60 °C for 8 s showed 4 decimal reductions. In the same sterilization procedure, but extending the time to 16 s, this value increased to 7 decimal reductions, demonstrating the efficiency of H₂O₂ as a function of contact time. The sterilization system tested showed satisfactory performance in the sterilization of LDPE films, being capable of reaching up to 7 decimal reductions of the bacterial spore population.     

Salmonella enterica serovar Choleraesuis on fresh-cut cucumber slices after reduction treatments

Cucumber is a popular fruit around the world and has been implicated in Salmonella food poisonings. S. Choleraesuis is a serovar that can cause pig and human infections but was rarely examined in food safety context. To investigate S. Choleraesuis behavior on cucumber slices, it was inoculated, at 10⁴ colony forming units (CFU)/mL, onto fresh-cut cucumber slices and subjected to reduction with either high hydrostatic pressurization (HHP), hydrogen peroxide (H₂O₂), or Peredibacter sp. BD2GS treatment, its reduction and survival during 48 h storage at 4 °C and 25 °C were compared.Reduction tests revealed that 5% H₂O₂ was most effective in killing S. Choleraesuis, with 97.5% reduction after 15 min action, compared to 90.7%, 87.7%, 29.2% and 60.2% reduction rates with HHP, 2.5% H₂O₂, high- and low-dose BD2GS treatments, respectively.At the end of storage, contrast to no changes at 4 °C, S. Choleraesuis counts rose significantly (p < 0.05) at 25 °C. Compared to control that reached 7.1 ± 0.1 log CFU/g, HHP, 5% and 2.5% H₂O₂ attained 6.3 ± 0.1, 6.7 ± 0.1 and 6.4 ± 0.2 log CFU/g correspondingly, whereas high- and low-dose BD2GS attained 4.9 ± 0.1 and 5.9 ± 0.1 log CFU/g respectively. A shared growth peak of between 9 h and 12 h was noted in all treatments except high-dose BD2GS where it occurred in the first 3 h. Results of this study revealed the effectiveness of 5% H₂O₂ in the reduction of S. Choleraesuis, and demonstrated that if not stored properly, contaminated cucumber slices, though treated, can still have potentials to cause S. Choleraesuis outbreaks.     

Role of cellulose in protecting Shiga toxin producing Escherichia coli against oxidative and acidic stress

This study assessed the role of cellulose in protecting Shiga toxin-producing Escherichia coli (STEC) against environmental stress. Cellulose producing STEC strain 19B (O5:H-) and 49B (O103:H2) as well as their cellulose deficient derivates (19D and 49D) were subjected to oxidative (10, 20 and 30 mM H₂O₂) and acidic (pH 3.0, 3.5 and 4.5) stress. Approximately 4.25, 2.46 or 1.74 log CFU ml⁻¹ of the 19B cells survived a 2.5-h treatment with 10, 20 and 30 mM H₂O₂, respectively, while none of the 19D cells (8.02 logs) survived the same treatments. The population of 49D decreased from 7.70 to <0.60 log CFU ml⁻¹, whereas that of 49B decreased from 7.70 to 2.47 log CFU ml⁻¹ by a 2-h treatment with 30 mM H₂O₂. Approximately 2.63 log CFU ml⁻¹ of the 19B cells survived at pH 3.0 for 1 h and 4.75 log CFU ml⁻¹ of the 49B cells survived at pH 3.0 for 1.5 h, but the 19D and 49D cells did not survive these treatments. Results indicated that cellulose protected the selected STEC strains against oxidative treatments with 10-30 mM of H₂O₂ and acidic treatments at pH 3.0-3.5.     

Wash water disinfection of a full-scale leafy vegetables washing process with hydrogen peroxide and the use of a commercial metal ion mixture to improve disinfection efficiency

Hydrogen peroxide (H₂O₂) was used to maintain the microbial wash water quality of a full-scale leafy vegetables (radicchio, sugar loaf, curled endive, lollo, lollo rosso) wash water process. Despite addition of 300 L/h of 1.8% H₂O₂ to a 450 L washing bath (333 ± 50 kg/h fresh-cut produce introduction speed), the H₂O₂ quickly decreased and a lower wash water contamination of aerobic psychrotrophic plate count (APC) and enterococci than without addition of H₂O₂ could not be maintained. There was no significant difference between the APC on fresh-cut leafy vegetables washed with H₂O₂ and those washed with water.In a second part, lab-scale experiments were performed to assess the impact of a commercial metal ion formulation (Bacsan^®, containing a. o. Cu²⁺, Zn²⁺, Ag⁺) on the stability of H₂O₂ in artificial wash water, made from iceberg lettuce and tap water. Bacsan improved the stability of H₂O₂ in artificial lettuce wash water and fresh-cut leafy vegetables wash water from a processing company and synergistically increased the disinfection efficiency of APC and Escherichia coli (E. coli) compared to H₂O₂ or Bacsan. Increasing chemical oxygen demand (COD) had detrimental effect on the H₂O₂ stability and disinfection efficiency. Addition of Ag⁺ to Bacsan further synergistically enhanced the H₂O₂ stability.H₂O₂ is not suited as an in situ wash water disinfectant to avoid cross-contamination in fresh-cut leafy vegetables washing processes due to the slow water disinfection kinetics and the rapid H₂O₂ consumption. However, H₂O₂/Bacsan shows potential for use in off-line processes.     

Effect of binder on the physical stability and bactericidal property of titanium dioxide (TiO2) nanocoatings on food contact surfaces

TiO₂ is a promising photocatalyst for use in food processing environment as an antimicrobial coating. The purpose of this study was to determine the effect of different binding agents on the physical stability and bactericidal property of TiO₂ nanocoatings created on stainless steel surfaces. A total of six different coating suspensions were prepared by mixing TiO₂ (Aeroxide^® P-25) nanoparticles (NPs) with three different types of binders (Shellac (A), polyuretahne (B), and polycrylic (C)) at a 1:4 to 1:16 NP to binder weight ratio. Bactericidal activity of these TiO₂ coatings against Escherichia coli O157:H7 (5-strain) was determined at three different UV-A light intensities (0.25, 0.50 and 0.75 mW/cm²) for 3 h. The type of binder used in the coating had a significant effect on the log reduction of E. coli O157:H7. TiO₂ coatings with binder C showed highest reduction (>4 log CFU/cm²) followed by TiO₂ coating with binder B and A. Increasing the binder concentration in the formulation from a 1:4 to 1:16 weight ratio decreased the log reduction of E. coli O157:H7. Increasing the UV-A light intensity from 0.25 to 0.75 mW/cm² increased the log reduction of bacteria for all the TiO₂ coatings. The physical stability of the TiO₂ coatings was determined using ASTM procedures. TiO₂ coatings with binder B showed highest adhesion strength and scratch hardness when compared to coatings with other binders. However, on repeated use experiments (1, 3, 5, and 10 times), TiO₂ coatings with binder C were found to be physically more stable and able to retain their original bactericidal property. The results of this study showed promise in developing durable TiO₂ coatings with strong photocatalytic bactericidal property on food contact surfaces using appropriate binding agents to help ensure safe food processing environment.     

Investigation on the sonocatalytic degradation of nitrobenzene using heterogeneous nanostructured catalysts in absence and presence of surfactant

Because of the extensive use and excessive release of various NB, economical and efficient methods for the treatment of wastewater and cleanup of petrochemical compounds are needed. This study focused on the sonocatalytic degradation of NB in aqueous solution assisted with H₂O₂ oxidant and nanostructured metal oxide catalysts, prepared in the absence of CTAB (series I), (Fe₂O₃-I, CuO-I, NiO-I, and Co₃O₄-I) and nanostructured metal oxide catalysts prepared in the presence of CTAB (series II), (Fe₂O₃-II, CuO-II, NiO-II, and Co₃O₄-II). The physicochemical properties of these catalysts were investigated via X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and point of zero charge (PZC).The potential degradation feasibility for NB in US/nano metal oxide (series I and or series II)/H₂O₂ systems was measured by GC analysis at regular time intervals. Otherwise, some operational parameters such as ultrasonic irradiation time, solution pH value, H₂O₂ concentration, different weights of the nano-sized catalysts, NB concentration, leaching of the nano-sized catalysts, and reaction kinetics had been examined. It was found that H₂O₂ oxidant can effectively assist the sonocatalytic degradation of NB in the presence of nano-sized oxides (series I) and with more efficiency in the presence of nano-sized oxides (series II), and the effect of efficiency in degradation was changed in the order of (Fe₂O₃ > CuO > NiO > Co₃O₄). Therefore, oxides prepared in micellar solution were found to upgrade the economic aspect of NB degradation.     

Efficacy of natural antimicrobials to prolong the shelf-life of minimally processed apples packaged in modified atmosphere

Minimally processed fruit are susceptible to microbial proliferation and to a fast loss of sensory quality. In this experimental work, in order to increase shelf-life and quality parameters (texture and colour) maintenance of sliced apples (Malus communis, var. Golden delicious), the use of natural antimicrobials was proposed as alternative to the traditional sanitization methods. Citron EO, hexanal, 2-(E)-hexenal, citral and carvacrol, alone or in combination, were employed. As control, apples washed only with 0.5% of ascorbic and 1% of citric acid were used. The apples were dipped with traditional or natural antimicrobial solutions according to a defined protocol. After the treatment, apples were packaged in active modified atmosphere (7% O₂ and 0% CO₂₎, into medium permeability bags. The products were stored at 6 °C and, immediately after washing and during storage, the yeast cell loads were monitored until the spoilage threshold (6 log CFU/g). In addition, the volatile profiles, electronic nose analyses, colour and texture analyses were monitored during the storage. In all the samples the spoilage yeast threshold was not attained within the 35 days of storage independently on the substance or mixture of substances supplemented. Samples treated with the combinations citral/2-(E)-hexenal and hexanal/2-(E)-hexenal showed a good retention of colour parameter during storage. Among investigated samples, hexanal/2-(E)-hexenal treatment promoted the best retention of firmness throughout 35 days of storage. These results evidence the potentiality of dipping treatment based on these natural antimicrobials to strongly prolong the shelf-life of fresh-cut apples.     

Catalytic performance of organically templated nano nickel incorporated-rice husk silica in hydroconversion of cyclohexene and dehydrogenation of ethanol

Rice husk silica (RHS) was extracted from local rice husk by acid digestion and burning at 650 °C. RHS-Ni catalyst was prepared by dissolving RHS in 1 N NaOH and titrating with 3 N HNO₃ containing 10 wt.% Ni²⁺. The organic modifiers, either p-amino benzoic acid (A) or p-phenylenediamine (PDA) were incorporated in 5 wt.% and reduced in H₂ flow. Investigation of the three catalysts, (RHS-Ni)_R350, (RHS-Ni–A)_R350 and (RHS-Ni–PDA)_R350, confirmed good dispersion of Ni nanoparticles; all catalysts were amorphous. The BET surface areas increased in the order: (RHS-Ni)_R350 < (RHS-Ni–A)_R350 < (RHS-Ni–PDA)_R350 with controlled pore sizes. The as-prepared catalysts were applied for both hydroconversion of cyclohexene with molecular H₂ and ethanol dehydrogenation, using a flow-type reactor, at different temperatures. The activity in cyclohexene hydroconversion and selectivity to cyclohexane depended upon the reaction temperature; at t < 150 °C, the increased hydrogenation activity was referred to the formed SiO₂–Ni–amine complex, pore regulation as a prime requirement for H₂ storage and homogeneous distribution of incorporated Ni nanoparticles. At t > 150 °C, the backward dehydrogenation pathway was more favored, due to unavailability of H₂; the process became structure-sensitive. In ethanol conversion, the prevailing dehydrogenation activity of organically modified catalyst samples was encouraged by improved homogeneous distribution of Ni nanoparticles and created micropre system.     

Experimental and theoretical investigation of a new triazole derivative for the corrosion inhibition of carbon steel in acid medium

A new triazole derivative, (E)-4-(4-(dimethylamino)benzylideneamino)-5-(pyridin-4-yl)-2H-1,2,4-triazole-3(4H)-thione (DPT), was synthesized and characterized using spectral data. The electrochemical experimental techniques were utilized to evaluate the inhibition efficiency (IE) of DPT for the corrosion of C1018 carbon steel. The studies revealed that, DPT is highly efficient with IE value 90% at 250 ppm. Further, the addition of DPT resulted in the decrease of cathodic as well as anodic current densities which is the indication of mixed-type inhibition. Also, the studies inferred the Langmuir model for DPT-metal adsorption. The surface morphological studies of C1018 carbon steel with and without DPT was investigated using SEM, EDX, and XPS, which indicated the strong adsorption of metal-DPT. Monte-Carlo simulation and Density functional theory approaches had been employed for correlating the structure of DPT and its corrosion inhibition ability. The high IE values of DPT observed in experimental studies were in agreement with the theoretical studies, and hence DPT acts as good inhibitor for the corrosion of C1018 steel.     

Optimization of HPLC conditions for quantitative analysis of aflatoxins in contaminated peanut

The main objective of present study was to investigate the effect of HPLC conditions namely mobile phase composition (X₁), flow rate (X₂) and temperature (X₃) on peak area of four target aflatoxins (i.e. B₁ (Y₁), B₂ (Y₂), G₁ (Y₃) and G₂ (Y₄)) from the spiked peanut. The significant nonlinear response surface models with high coefficient of determinations (R²) ranging from 0.958 to 0.995 were fitted to evaluate the detection value of target aflatoxins as a function of HPLC variables. Flow rate had the most significant (p < 0.05) effect on quantification value of target aflatoxins. The highest quantification value for target aflatoxins could be obtained under the following HPLC conditions: the mobile phase composition of ACN/H₂O/MeOH: 8/54/38, temperature of 24 °C and flow rate of 0.4 mL/min. The recommended optimum HPLC conditions provided higher peak area for all target aflatoxins by 1–2.5 fold compared to two other conditions (A: mobile phase (ACN/H₂O/MeOH: 23/54/23), ambient temperature (28–32 °C), flow rate 1 mL/min; B: mobile phase (ACN/H₂O/MeOH: 17/54/29), temperature 30 °C, flow rate 1 mL/min).     

Effect of hydrogen peroxide vapor treatment for inactivating Salmonella Typhimurium,Escherichia coli O157:H7 and Listeria monocytogenes on organic fresh lettuce

In this study, the efficacy of hydrogen peroxide vapor (HPV) for reducing Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on lettuce was investigated as well as its effect on lettuce quality. Lettuce was inoculated with a cocktail containing three strains of each pathogen then treated with vaporized hydrogen peroxide for 0, 2, 4, 6, 8 and 10 min. The concentrations of hydrogen peroxide used were 0, 1, 3, 5 and 10%. With increasing treatment time and hydrogen peroxide concentration, HPV treatment showed significant (P < 0.05) reduction compared to the control (0%, treated with vaporized distilled water). In particular, vaporized 10% hydrogen peroxide treatment for 10 min was the most effective combination for reducing the three pathogens on lettuce. The reduction levels of S. Typhimurium, E. coli O157:H7 and L. monocytogenes on lettuce were 3.12, 3.15 and 2.95 log₁₀ CFU/g, respectively. Furthermore, there were no significant (P > 0.05) quality changes (color and texture) of lettuce among all tested samples, and hydrogen peroxide residues were not detected after 36 h storage time in any of the treated samples. These results suggest that HPV treatment could be an alternative method for reducing S. Typhimurium, E. coli O157:H7 and L. monocytogenes on fresh produce.     

A novel antimicrobial substance produced by Lactobacillus rhamnous LS8

Superbugs or multi-drug resistant pathogens are not only clinical issue but also highlighted in food safety. However, development of new antibiotics and safe preservatives is declining. A novel workflow was used to purify antimicrobial substance produced by Lactobacillus rhamnosus LS-8, in which ethyl acetate extraction, polypeptide column and HPLC were involved in the purification process. Subsequently, a novel antimicrobial substance was purified and identified as 4,6-dimethyl-1,2,5-triazepane-3,7-dione (C₆H₁₁N₃O₂) by mass spectrum, ¹H NMR and ¹³C NMR analysis. Fortunately, it has significant inhibitory effect on both gram-positive and gram negative strains including multi-drug resistance pathogens. Also it had good heat stability and resistant to proteolytic enzymes, however, it was only active in acidic condition. The results of scanning electron microscopy (SEM) and transmission electron microscope (TEM) showed that LS-8-25 destroyed the ultrastructure of S. aureus and E. coli. The discovery is adding a new variety of antimicrobial substance produced by lactic acid bacteria.     

Adsorption and inhibition behavior of a novel Schiff base on carbon steel corrosion in acid media

In this study, the inhibition effect of 2,2′-(heptane-1,7-diylbis(azanylylidene)bis-(methanylylidene))diphenol (HAMD) on carbon steel corrosion in 0.5 mol L⁻¹ H₂SO₄ solution was studied. Weight loss and electrochemical techniques such as open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to inspect the efficiency of HAMD as corrosion inhibitor. Scanning electron microscopy (SEM) and energy dispersion X-ray (EDAX) were used to characterize the steel surface. Polarization measurements indicated that, the studied inhibitor acts as mixed-type inhibitor. The adsorption of HAMD molecules on the carbon steel surface obeys Langmuir adsorption isotherm.     

Influence of sunflower oil based nanoemulsion (AUSN-4) on the shelf life and quality of Indo-Pacific king mackerel (Scomberomorus guttatus) steaks stored at 20 °C

The influence of nanoemulsion (AUSN-4) on the microbiological, proximal, chemical, and sensory qualities of Indo-Pacific king mackerel (Scomberomorus guttatus) steaks stored at 20 °C was studied for a time period of 72 h. AUSN-4 treatment showed initial reduction (P > 0.05) in the heterotrophic, H₂S and lactic acid bacterial populations in 12 h, followed by a gradual increase in their respective populations. Irrespective of treatments, reduction in total carbohydrate, protein, and fat contents were observed in all samples with an increase in storage time (h), with AUSN-4 treated steaks having the lowest reduction. AUSN-4 treatment significantly (P < 0.05) decreased the values of chemical indicators of spoilage throughout the storage period. Organoleptic evaluation revealed that AUSN-4 treated steaks showed an extension of shelf life of 48 h, when compared with control and antibiotic treated samples, respectively. Based on the results obtained in our present study we conclude that sunflower oil based nanoemulsion preservative technique is able to extend the shelf life and maintain the quality of S. guttatus steaks during storage.     

Assessment of trace elements in fishes of Japanese foods marketed in São Paulo (Brazil)

In recent years, there has been increasing fish consumption in Brazil, largely due to the popularity of Japanese cuisine. No study, however, has previously assessed the presence of inorganic contaminants in species used in the preparation of Japanese food. In this paper, we determined total arsenic, cadmium, chromium, total mercury, and lead contents in 82 fish samples of Tuna (Thunnus thynnus), Porgy (Pagrus pagrus), Snook (Centropomus sp.), and Salmon (Salmo salar) species marketed in São Paulo (Brazil). Samples were mineralized in HNO₃/H₂O₂ for As, Cd, Cr and Pb, and in HNO₃/H₂SO₄/V₂O₅ for Hg. Inorganic contaminants were determined after the validation of the methodology using Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES); and for Hg, an ICP-coupled hydride generator was used. Concentration ranges for elements analyzed in mg kg^?1 (wet base) were as follows: Total As (0.11–10.82); Cd (0.005–0.047); Cr (0.008–0.259); Pb (0.026–0.481); and total Hg (0.0077–0.9681). As and Cr levels exceeded the maximum limits allowed by the Brazilian law (1 and 0.1 mg kg^?1) in 51.2 and 7.3% of the total samples studied, respectively. The most contaminated species were porgy (As = 95% and Cr = 10%) and tuna (As 91% and Cr = 10%). An estimation of As, Cd, Pb, and Hg weekly intake was calculated considering a 60 kg adult person and a 350 g consumption of fish per week, with As and Hg elements presenting the highest contribution on diets reaching 222% of provisional tolerable weekly intake (PTWI) for As in porgy and 41% of PTWI for Hg in tuna.     

Cyclic voltammetric studies of carbon steel corrosion in chloride-formation water solution and effect of some inorganic salts

The influence of sulfide, sulfate and bicarbonate anions on the pitting corrosion behavior of carbon steel in formation water containing chloride ions were analyzed by means of cyclic voltammetry technique and complemented by X-ray diffraction (XRD) investigation. The anodic response exhibits a well-defined anodic peak A, followed by a passive region. A pronounced increase in the anodic current density is observed in the passive region at pitting potential (E_pit). On the other hand, the cathodic sweep shows two cathodic peaks CI and CII. The data show that the presence of chloride ions causes pitting corrosion of carbon steel in formation water. It was found that both the pitting potential E_pit and the repassivation potential (E_pro) decreased with increase in Cl^? ions concentration. Data clearly show that the presence of Na₂S with 0.3 M of chloride ions has a strong accelerating effect on the active dissolution and pitting corrosion of carbon steel in formation water, while the presence of Na₂SO₄ and NaHCO₃ with chloride ions has an inhibiting effect on the active dissolution and pitting corrosion.     

Degradation of alkyl radicals via C-H bond dissociation: Kinetic parameters and transition state geometry

Experimental data on the decomposition of alkyl radicals in the gas phase of the type RCH₂C^.H₂ → RCH=CH₂ + H^. were analyzed in terms of the method of crossing parabolas. The parameters characterizing such decomposition were calculated. The activation energy E _e0 for the thermoneutral degradation reaction was shown to depend on the radical structure. The degradation of the radicals RCH₂C^.H₂, CH₂=CRC^.H₂, PhC^.HCH₂R, and CH₂=C^.CH₂R is characterized by E _e0 = 81.6, 85.9, 85.9, and 115.2 kJ mol^?1, respectively. The semiempirical algorithm for calculation of geometric parameters of the transition state for reactions of hydrogen atom addition to olefins was extended to the degradation reactions of alkyl, aminoalkyl, and ketyl radicals. The kinetic (activation energies) and geometric (interatomic distances in the transition state) reaction parameters were calculated for the decomposition reactions of various alkyl, alkylaromatic, aminoalkyl, and ketyl radicals.