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American Society for Testing and Materials

https://www.elsevier.com/__data/assets/pdf_file/0005/96971/Application-of-corrosion-inhibitors-for-steels-in-acidic-media.pdf

Application of corrosion inhibitors for steels in acidic media for the oil and gas industry: A review

Ionic liquids (ILs), in particular imidazolium-based ILs, have proven to be suitable media for the generation and stabilisation of soluble metal nanoparticles (NPs). Indeed, transition-metal NPs with small sizes, narrow size distribution and different shapes have been prepared by reduction of organometallic compounds with molecular hydrogen, decomposition of transition-metal complexes in the zero-valent state, metal bombardment or simple transfer for previously prepared water- or classical organic solvent-soluble colloids to the ILs. The formation and stabilisation of NPs in these highly hydrogen bonded organised supramolecular fluids occur with the re-organisation of the hydrogen bond network and the generation of nanostructures with polar and non-polar regions, including the NPs. The IL forms a protective layer, which is probably composed of imidazolium aggregates located immediately adjacent to the nanoparticle surface, which provides both steric and electronic protection against aggregation and/or agglomeration. These stable transition-metal NPs immobilised in the ILs have proven to be efficient green catalysts for several reactions in multiphase conditions and also novel materials for chemical sensors. In this critical review, the structural/surface properties of these soluble metal NPs dispersed in ILs and their application in catalysis and as chemical sensors are discussed, with particular attention paid to the stabilisation models proposed to explain the stability and properties of these metal NPs (219 references).

On the structural and surface properties of transition-metal nanoparticles in ionic liquids

Rapid progress in identifying biomarkers that are hallmarks of disease has increased demand for high-performance detection technologies. Implementation of electrochemical methods in clinical analysis may provide an effective answer to the growing need for rapid, specific, inexpensive, and fully automated means of biomarker analysis. This Review summarizes advances from the past 5 years in the development of electrochemical sensors for clinically relevant biomolecules, including small molecules, nucleic acids, and proteins. Various sensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms into point-of-care solutions.

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Electrochemical Methods for the Analysis of Clinically Relevant Biomolecules

Oxidative stress, a result of an overproduction and accumulation of free radicals, is the leading cause of several degenerative diseases such as cancer, atherosclerosis, cardiovascular diseases, ageing and inflammatory diseases. Polyphenols form an important class of naturally occurring antioxidants, having innumerable biological activities such as anticancer, antifungal, antibacterial, antiviral, antiulcer and anticholesterol, to name a few. Among various polyphenols, gallic acid (3,4,5-trihydroxybenzoic acid), a naturally occurring low molecular weight triphenolic compound, has emerged as a strong antioxidant and an efficient apoptosis inducing agent. Starting from the bioavailability and the biosynthetic pathway of gallic acid, this review includes various in vitro, in vivo and in silico studies providing the mode of action, radical scavenging activity, ability to inhibit lipid peroxidation, maintenance of endogenous defense systems and metal ion chelation by this triphenolic molecule, along with a comprehensive overview of factors responsible for its high antioxidant activity. Gallic acid derivatives have also been found in a number of phytomedicines with diverse biological and pharmacological activities, including radical scavenging, interfering with the cell signaling pathways and apoptosis of cancer cells. The diverse range of applications of this simple polyphenol is due to a fine amalgam between its antioxidant and prooxidant potential. The existing literature on this dual behavior of gallic acid and its derivatives is reviewed here. This is followed by an account of their potential clinical and industrial applications.

Gallic acid: a versatile antioxidant with promising therapeutic and industrial applications

Evaluation of the inhibitor effect of l-ascorbic acid on the corrosion of mild steel

Caffeic acid as a green corrosion inhibitor for mild steel

We investigated the antioxidant activity of phenylpropionic acids – caffeic (CAF), ferulic (FER), para-coumaric (COU) and cinnamic (CIN) – and phenolic acids and related compounds – gallic (GAL), methyl gallate (meGAL), vanillic (VAN) and gentisic (GEN) – using visible spectroscopy, inhibition of nitroblue tetrazolium (NBT) reduction, and electrochemical methods including cyclic voltammetry and potentiometry. In the spectroscopic assays, only CAF, GAL and meGAL were able to inhibit NBT reduction. The same compounds showed the lowest oxidation potentials (Epa) and the highest redox potentials ∆E) in the cyclic voltammetric and potentiometric studies, respectively. In addition, it was observed that the greater the number of hydroxyls linked to the aromatic ring, the greater was the antioxidant activity of the analysed compounds. The correlations of Spermann – used to compare the methods between themselves and the methods with the relationship structure–antioxidant activity – were r = -0.9762 for th...

Antioxidant capacity of phenolic and related compounds: correlation among electrochemical, visible spectroscopy methods and structure–antioxidant activity

The electrochemistry of quercetin hydro-alcoholic solutions of pH 2.2 to 9.2 was studied by cyclic voltammetry, controlled-potential electrolysis and UV-Vis spectroscopy. Cyclic voltammograms for quercetin showed three oxidation peaks and one reduction peak depending on the experimental conditions. The two-electron two-proton oxidation process at the first peak led to the formation of the corresponding ortho-quinone, which is an electrochemically active and unstable species, as evidenced by the dependence of the cyclic voltammogram profile on the applied scan rate, in agreement with the EC mechanism. Controlled-potential electrolysis yielded three products as characterized by UV-Vis spectroscopy. A reaction scheme comprising electrochemical and chemical steps was proposed for the electro-oxidation of the quercetin in hydro-alcoholic solutions on basis of experimental evidences obtained in this work and elsewhere.

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Electrochemical oxidation of quercetin in hydro-alcoholic solution

Two sulfonamides, namely sulfadiazine and sulfamethoxazole, were independently quantified in pharmaceutical products by square-wave voltammetry (SWV) using a boron-doped diamond (BDD) electrode. The electroanalytical determination of sulfadiazine was carried out in ethanol + 0.5 mol L −1 H 2 SO 4 50/50 (v/v) and of sulfamethoxazole in ethanol + pH 6.0 phosphate buffer 50/50 (v/v) solutions. Both analytes showed one well-resolved irreversible oxidation peak at around +1.1 V, which served as the analytical response. Calibration curves were obtained in the concentration ranges of 8.01 × 10 −6 to 1.19 × 10 −4  mol L −1 ( r  = 0.9995) for sulfadiazine and 6.10 × 10 −6 to 6.01 × 10 −5  mol L −1 ( r  = 0.9995) for sulfamethoxazole, with respective detection limits of 2.19 × 10 −6 and 1.15 × 10 −6  mol L −1 . For both sulfonamides, recovery values were in the range of 95–104% for all samples, indicating no matrix interference effects on the analytical results. The accuracy of the electroanalytical methodology reported herein was compared to the standard HPLC method, and the values for the relative error between the proposed and standard methods were −4.31% for sulfadiazine and −0.79% for sulfamethoxazole. The data suggest a potential and interesting alternative method for the electroanalytical determination of sulfa drugs in pharmaceuticals and other products.

Almir Spinelli

Papers

Evaluation of the inhibitor effect of l-ascorbic acid on the corrosion of mild steel

Caffeic acid as a green corrosion inhibitor for mild steel

Antioxidant capacity of phenolic and related compounds: correlation among electrochemical, visible spectroscopy methods and structure–antioxidant activity

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Electroanalytical determination of sulfadiazine and sulfamethoxazole in pharmaceuticals using a boron-doped diamond electrode