Current developments of nanoscale insight into corrosion protection by passive oxide films

Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified.Comment: Current Opinion in Solid State and Materials Science, Elsevier, final accepted preprin

A study of the antioxidant capacity of oak wood used in wine ageing and the correlation with polyphenol composition

The antioxidant capacity of oak wood used in the ageing of wine was studied by four different methods: measurement of scavenging capacity against a given radical (ABTS, DPPH), oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP). Although, the four methods tested gave comparable results for the antioxidant capacity measured in oak wood extracts, the ORAC method gave results with some differences from the other methods. Non-toasted oak wood samples displayed more antioxidant power than toasted ones due to differences in the polyphenol compositon. A correlation analysis revealed that ellagitannins were the compounds mainly responsible for the antioxidant capacity of oak wood. Some phenolic acids, mainly gallic acid, also showed a significant correlation with antioxidant capacity

Pretreatment of citrus by-products affects polyphenol recovery:a review

A large amount of citrus waste is generated annually. This waste is of great economic worth, since it contains high levels of polyphenols, which have attracted scientific interest due to their potent antimicrobial and antiradical activities. Pretreatment is a crucial step that precedes the extraction process and influences the yields and quality of polyphenols. This review emphasizes the effect of different drying processes, such as freeze drying, hot-air drying, vacuum drying, microwave drying, infrared drying, and high-speed drying, on the polyphenol retention in citrus by-products. Further treatments of the dried citrus by-products for assisting the liberation of bound polyphenols are also provided and comprehensively discussed

Antiviral and antioxidant activity of a hydroalcoholic extract from Humulus lupulus L.

A hydroalcoholic extract from female inflorescences of Humulus lupulus L. (HOP extract) was evaluated for its anti-influenza activity. The ability of the extract to interfere with different phases of viral replication was assessed, as well as its effect on the intracellular redox state, being unbalanced versus the oxidative state in infected cells. The radical scavenging power, inhibition of lipoperoxidation, and ferric reducing activity were assayed as antioxidant mechanisms. A phytochemical characterization of the extract was also performed. We found that HOP extract significantly inhibited replication of various viral strains, at different time from infection. Viral replication was partly inhibited when virus was incubated with extract before infection, suggesting a direct effect on the virions. Since HOP extract was able to restore the reducing conditions of infected cells, by increasing glutathione content, its antiviral activity might be also due to an interference with redox-sensitive pathways required for viral replication. Accordingly, the extract exerted radical scavenging and reducing effects and inhibited lipoperoxidation and the tBOOH-induced cytotoxicity. At phytochemical analysis, different phenolics were identified, which altogether might contribute to HOP antiviral effect. In conclusion, our results highlighted anti-influenza and antioxidant properties of HOP extract, which encourage further in vivo studies to evaluate its possible application

A Review on the Bulk and Surface Chemistry of Iron in Atmospherically-relevant Systems Containing Humic Like Substances (HULIS)

As the fourth most abundant element by mass in the Earth’s crust, iron is ubiquitous and its chemistry is rich and interdisciplinary in nature. This review synthesizes the current state of knowledge of iron chemistry in multicomponent atmospheric aerosols, which is also applicable to other atmospherically-relevant systems that include iron-containing anthropogenic nanodust, ocean surfaces and buildings. Because of the abundance of humic-like substances (HULIS) in these systems, studies on their chemistry with iron and those used as models for HULIS are the focus of this review. Findings from field measurements and laboratory studies are summarized to highlight major themes in iron chemical reactivity that varies depending on the solubility, redox conditions, absence and presence of UV-visible light and reactive oxygen species, pH, and temperature. The review also highlights key differences between bulk and surface chemistry of iron-containing materials, which varies considerably because of the structure of interfacial water and solvent cage effect. Additional laboratory, field, and modeling studies are needed to better understand the contributions of transition metals chemistry to secondary organic aerosol formation and chemistry, uptake, and release of trace gas phase species. This information will improve the predictive power of models that incorporate aerosols chemistry and physics

Electrochemical determination of gallic acid in food matrices using novel materials.

Gallic acid (GA), as an endogenous polyphenol, has shown many different important properties that have influenced its use in the food and pharmaceutical industry. These properties include its antioxidant, anti-cancer, anti-tumor, anti-HIV and anti-ulcerogenic activities. The most commonly used GA determination techniques have been the spectrophotometric and chromatographic techniques. However, these techniques have shown some drawbacks; they are expensive, labour intensive, time-consuming and are not suitable for in-situ measurements. Electrochemical methods using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at inert glassy carbon electrode (GCE) or carbon paste electrodes (CPE) have also been used in the determination of GA. However, despite their easy application and fast result generation, their sensitivity and selectivity have been relatively inadequate for the analysis of GA found in beverages and pharmaceutical products. The aim of this study is therefore to investigate and develop novel nanomaterials-based electrochemical sensors for determination and analysis of GA that is fast, sensitive, cost-effective and selective. In this study, the detection of GA in red and white wines was achieved using CV, through the development of carbon-based working electrodes modified with graphene oxide nanoparticles and other metal oxide nanoparticles. The synthesised metal oxide nanoparticles were characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and Zetasizer (for particle size analysis). Meanwhile, characterisation of the developed electrodes was carried out using CV, DPV and electrochemical impedance spectroscopy. The electrochemical effects of the electrodes were analysed. This thesis presents the results of a novel graphene oxide nanocolloids-SiO2 nanoparticles combination used for the electrochemical determination of GA. The results show enhanced peak currents, with high sensitivity and selectivity. The anodic peak current was enhanced from 241 µA (for the bare GCE) to 411 µA (for the modified GCE) - with a limit of detection (LOD) of 2.09 x 10-6 mol L-1, within a concentration range of 6.25 x 10-6 to 1.0 x 10-3 mol L-1. The thesis also proposes that there is a synergistic effect between SiO2 nanoparticles and graphene oxide nanocolloids in the determination of GA. Synthesised amorphous zirconium oxide nanoparticles were used for the modification of a carbon paste electrode and used for the determination of GA. The electrode modification enhanced the electrochemical activity of GA, with increased sensitivity and selectivity. The modified electrode produced an enhanced anodic peak from 260 µA (for the bare electrode) to 451 µA (for the modified electrode) - with an LOD of 1.24 x 10-7 mol L-1, within a range of 1 x 10-6 to 1.0 x 1 x 10-3 mol L-1. The thesis additionally makes a novel proposal for the interaction and effect of the amorphous zirconia nanoparticles on the graphite in the CPE. Zinc oxide nanoparticles and cobalt oxide nanoparticles were also used individually for the modification of carbon paste electrodes. The modified electrodes showed an enhanced effect on GA oxidation. This enhanced effect was an increase in anodic peak current from 261 µA to 414 µA, when the CPE was modified. The LOD produced by the ZnO nanoparticles-modified CPE was 1.86 x 10-7 mol L-1, within a concentration range of 1 x 10-3 to 5 x 10-2 mmol L-1. Meanwhile, the effect of scan rate and the effect of pH show that the electrodes were more effective in acidic pH, and that the GA-electrode interaction was an adsorption-controlled process. Cobalt oxide nanoparticles were also synthesised, characterised and used for the modification of CPE. The modified electrode produced an enhanced anodic peak current from 302 µA (for the bare CPE) to 404 µA (for the modified electrode). The LOD of the modified electrode was studied and found to be 1.52 x 10-6 mol L-1, at a concentration range of 1 x 10-4 to 1 x 10-3 mol L-1. The modified electrodes were successfully used for the determination of GA in real samples of red and white wine. Based on the electrochemical activities of the different electrodes made, the Zirconium dioxide nanoparticles-modified carbon paste electrode seems to have produced the best results. The zirconium dioxide-modified CPE showed increased sensitivity and better limit of detection for GA

Carbon Nanomaterials in Biological Systems

ABSTRACT This thesis intends to present, from the biophysical viewpoint, my study on understanding carbon nanomaterials in biological and environmental systems. Carbon nanotubes and fullerenes represent a major family of carbon nanoparticles which possess distinct electrical, optical and mechanical properties. However, the major hurdle for making carbon nanomaterials bioavailable lies in their tendency toward bundling, driven by hydrophobic interaction, van der Waals force, and pi-stacking. To overcome this problem, we used non-covalent binding of zwitterionic lysophopholipids (LPL) onto the external surfaces of single-walled carbon nanotubes (SWNTs). This method affords superior SWNT solubility in aqueous solution. The stability of SWNT-LPL complex has been found to be dependent on the pH of the solvent, but independent of solvent temperature. Based on this method, the translocation of rhodamine-lysophosphoethanolamine-SWNT (Rd-LPE-SWNT) complex across cell membranes, as well as the dissociation of Rd-LPE from SWNTs in the cellular environment was detected using the technique of fluorescence resonance energy transfer (FRET). Towards understanding the environmental impact of carbon nanomaterials, we have studied the biomodification of SWNT-lyso-phosphatidylcholine (SWNT-LPC) by aquatic organism Daphnia magna. Through normal feeding behavior, Daphnia magna ingested SWNT-LPC and stripped out the lipids as food source. SWNTs rebundled inside the guts of daphnia and were excreted into the water column. Acute toxicity was observed only in the highest test concentrations of 0.5 mg/L under starvation conditions. Regarding fullerenes, C70, the shortest \u27SWNT\u27, was solubilized in water by gallic acid, a natural anti-oxidant and anticancer agent. The suparmolecular complex of C70-gallic acid, assembled through pi-stacking, emitted green fluorescence in aqueous solution. Utilizing this optical property, we succeeded in labeling biological systems at cellular, tissue and living organism levels. We have further discovered that the fluorescence of C70 is far more resistant to photobleaching than calcein AM, a conventional dye for bioimaging. Using confocal fluorescence microscopy we have obtained the first real-time observation of nanoparticle translocation across cell membranes. In summary, the objectives of this thesis are: Solubilizating SWNT in aqueous solution afforded by different solvating agents, including DOPA, sodium dodecyl sulfate (SDS) and LPC, and testing the stability of the solution at different temperatures, pH and ionic strengths; Using SWNT as a transporter for lipid delivery across cell membranes; Understanding the fate of SWNT in aquatic organism Daphnia magna; and Coating C70 with gallic acid and utilizing the optical properties of C70 for detecting its cell translocation. The studies documented in this thesis further our understanding of the interactions between carbon nanomaterials and biological and environmental systems. Water soluble carbon nanomaterials enable future field studies in imaging, sensing, drug delivery, nanotoxicity, nanomedicine, and environmental science and engineering

Inhibitory effect of tannic acid and its derivative (gallic acid) against cisplatin–induced thiobarbituric acid reactive substances (TBARS) production in rat kidney – in vitro

Increasing amounts of evidence suggests tannic acid (TA) and its derivative, gallic acid (GA) has beneficial effects against nephrotoxicity. The aim of this study was to investigate the effect of TA and GA (two structurally related phenolic acids) against cisplatin-induced thiobarbituric acid reactive substances (TBARS) production in rat kidney in vitro. The effect of both phenolic acids on kidney TBARS level in the presence of cisplatin, an antineoplastic drug used in the treatment of many solid-tissue cancers which has its chief side effect in nephrotoxicity, was assessed. Thereafter, the antioxidant properties were also determined. Incubation of the kidney tissue homogenate in the presence of cisplatin (1 mM) caused a significant (P<0.05) increase in the TBARS level. However, both phenolic acids caused a significant (P<0.05) decrease in the TBARS content of the kidney in a dose dependent manner (0 – 12.5 µM). Nevertheless, TA had a significantly higher (P<0.05) inhibitory effect on TBARS production than gallic acid judging by their IC50 value. Furthermore, TA possesses stronger antioxidant properties than GA as revealed by their scavenging, chelating and reducing ability. The inhibition of cisplatin–induced thiobarbituric acid reactive substances (TBARS) production in rat kidney by both TA and GA could be due to their antioxidant properties and this provide further insight into the mechanism of action for their nephroprotective properties from previous reported experimental studies. However, the study revealed that hydrolysis of TA reduces its potenc

Screening the effect of four ultrasound-assisted extraction parameters on hesperidin and phenolic acid content of aqueous citrus pomace extracts

Polyphenols of citrus by-products, due to their antioxidant and antimicrobial activities, could be valorized by pharmaceutical and food industries, adding a value to the citrus processing companies. A number of studies have investigated the effect of ultrasound-assisted extraction (UAE) conditions on the recovery of phenolics derived from citrus waste using both organic solvents or mixed aqueous solvent systems. To maximize efficiency, UAE conditions should be tailored to the physical parameters of the solvent(s) employed. The aim of this study was to investigate the effect of four UAE parameters: particle size (1.40–2.80 mm), extraction time (10–60 min), extraction temperature (23–50 °C) and ultrasonic power (150–250 W) on the simultaneous recovery of p-coumaric acid, caffeic acid, chlorogenic acid, and hesperidin from citrus waste using pure water as a solvent. High-performance liquid chromatography (HPLC) was employed for the identification and quantification of the cited compounds. Particle size was determined to be an important parameter affecting compound recovery, with the exception of chlorogenic acid. A particle size of 1.40 mm resulted in the highest recovery of p-coumaric and caffeic acids (0.25 and 0.58 mg/g, respectively), while higher hesperidin yields were achieved from the particle sizes of 2.00 and 1.40 mm (6.44 and 6.27 mg/g, respectively). Extraction temperature significantly affected only the recovery of the flavanone glycoside (P&lt;0.05). As the extraction temperature increased from 30 to 50 °C the recovery of hesperidin increased from 6.59 to 7.84 mg/g, respectively. Neither extraction time nor ultrasonic power significantly affected the recovery of any individual phenolic compound