Electrochemical oxidation of 3-substituted indoles.

2-Oxindoles are an abundant heteroaromatic motif in natural products and pharmaceuticals. An appealing method for accessing 2-oxindoles is by oxidation of the corresponding indole, a transformation currently executed using stoichiometric quantities of unsafe chemical oxidants that can also form unwanted side-products. Herein, we report that 3-substituted indoles undergo a logistically straightforward, electrochemical oxidation to the corresponding 2-oxindole in the presence of potassium bromide (>20 examples), with only traces of the oxidative dimer detected. Cyclic voltammetry and control studies infer that the reaction proceeds by electrochemical generation of elemental bromine (Br2) that upon reaction with indole, followed by hydrolysis, delivers the 2-oxindole. This procedure is an appealing alternative to existing methods used to access 2-oxindoles by oxidation of the parent indole.

Non-permanent primary food packaging materials assessment: Identification, migration, toxicity, and consumption of substances.

Almost all processed food comes packaged in either plastic, glass, metal, or paper and paperboard materials, and many packaging materials are disposed of after a single use (linear economy). Based on the concept of a circular economy, the recycling of food packaging materials has become one of the main targets for industries and regulators around the world. However, recycling presents particular challenges, mainly related to the recycled material composition, which determines its reusability, application, functionality, and chemical safety. In this latter matter, it has been demonstrated that the use of recycled food packaging materials increases the number and possible sources of substances that could be present in the packaging material, which is of concern as substances that can migrate into food and cause health hazards upon consumption. This review compiles information regarding substances detected in non-permanent food packaging materials, focusing mainly on plastics, paper, and paperboards. The compilation of literature studies (110 research articles) on the presence of intentionally added substances (IAS) and non-intentionally added substances (NIAS) in food packaging materials, their migration, toxicity, and dietary exposure has been summarized, evaluated, and discussed. In addition, current sustainable food packaging trends have been mentioned. Finally, approaches to reduce the presence, migration, and potential exposure to substances that have migrated from packaging materials into food have been reviewed.

Synthesis of 3-nitroindoles by sequential paired electrolysis.

3-Nitroindoles are synthetically versatile intermediates but current methods for the preparation hinder their widespread application. Herein, we report that nitroenamines undergo electrochemical cyclisation to 3-nitroindoles in the presence of potassium iodide. Detailed control experiments and cyclic voltammogram studies infer the reaction proceeds via a sequential paired electrolysis process, beginning with anodic oxidation of iodide (I-) to the iodine radical (I˙), which facilitates cyclisation of the nitroenamine to give a 3-nitroindolinyl radical. Cathodic reduction and protonation generates a 3-nitroindoline that upon oxidation forms the 3-nitroindole.

Green synthesis of akaganéite (ß-FeOOH) nanocomposites as peroxidase-mimics and application for discoloration of methylene blue.

This work reports an environmentally benign and readily scalable process for production of akaganéite (ß-FeOOH) nanocomposites by using abundant gallic acid or grape seed tannins and urea. Influences from those phytochemicals on the properties of ß-FeOOH nanocomposites were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, Thermogravimetric analysis, Scanning electron microscopy, Transmission electron microscopy, UV-Vis spectroscopy and Photoluminescence. The addition of 0.1% (w/v) grape seed tannins or gallic acid (640 mg L-1) solution yielded single-crystalline ß-FeOOH nanocomposites with reduced dimensions, increased porosities and BET surface area, and no oxidized impurities such as hematite (Fe2O3) were formed. The added grape seed tannins (S0.8) or gallic acid together with less urea (0.8 M) produced ß-FeOOH nanocomposites with higher activities as peroxidase mimics compared to those prepared with only urea (C0.8). Moreover, S0.8 was more efficient in methylene blue (MB) discoloration compared to C0.8 at all three pH values of 4, 7 and 11, and the S0.8-mediated MB degradation pathways at pH 4 and 7 were different from those at pH 11 due to the generation of different predominant oxidants. The overall MB discoloration efficacies by S0.8 at pH 4, 7 and 11 were combinative effects of both physical adsorption and chemical reactions. These ß-FeOOH nanocomposites possess great potential as peroxidase mimics for facile monitoring of excess hydrogen peroxide and applications in environmental remediation.

The Applications of Solid-State NMR to Conducting Polymers. The Special Case on Polyaniline.

Polyaniline is one of the most well studied conducting polymers due to its advanced electrical, chemical, redox and morphological properties. The high conductivity of regular polyaniline, when partially oxidized and doped under acidic conditions, has been associated with the formation of unique electronic states known as polarons and bipolarons. Alternative aniline oxidation products and interesting nanotube and nanorod forms have been observed as the synthesis conditions are varied. Solid-state NMR has offered great opportunities for structural investigations and the determination of molecular dynamics in such a complex and diverse material. This review summarizes various applications of solid-state NMR techniques to polyaniline and its derivatives and the information that can be obtained by solid-state NMR.

Enhanced antioxidant activity of polyolefin films integrated with grape tannins.

BACKGROUND: A natural antioxidant derived from an agro-waste of the wine industry, grape tannin, was incorporated by melt blending into three different polyolefins (high-density polyethylene, linear low-density polyethylene and polypropylene) to introduce antioxidant functionality. RESULTS: Significant antioxidant activity was observed at 1% tannin inclusion in all polymer blends. The antioxidant activity was observed to increase steadily with a greater concentration of grape tannins, the highest increases being seen with polypropylene. The mechanical and thermal properties of the polymer films following antioxidant incorporation were minimally altered with up to 3% grape tannins. All of the polyolefin-grape tannin films successfully passed the leachability test following USP661 standard protocol. CONCLUSION: Superior antioxidant activity was established in polyolefin thin films by utilization of a bulk grape extract obtained from winery waste. Significant increases in antioxidant activity were seen with 1% extract inclusion. This not only demonstrates the potential for food packaging applications of the polyolefin blends, but also valorizes the agro-waste. © 2015 Society of Chemical Industry.

Effects of post-fermentation addition of green tea extract for sulfur dioxide replacement on Sauvignon Blanc wine phenolic composition, antioxidant capacity, colour, and mouthfeel attributes.

This study examines the feasibility of replacing SO2 in a New Zealand Sauvignon Blanc wine with a green tea extract. The treatments included the control with no preservatives (C), the addition of green tea extract at 0.1 and 0.2 g/L (T1 and T2), and an SO2 treatment at 50 mg/L (T3). Five monomeric phenolic compounds were detected in the green tea extract used for the experiment, and their concentrations ranged in the order (-)-epigallocatechin gallate > (-)-epigallocatechin > (-)-epicatechin > (-)-epicatechin gallate > gallic acid. At the studied addition rates, these green tea-derived phenolic compounds contributed to ∼70% of the antioxidant capacity (ABTS), ∼71% of the total phenolic index (TPI), and âˆ¼ 84% of tannin concentration (MCPT) of the extract dissolved in a model wine solution. Among wine treatments, T1 and T2 significantly increased the wine's colour absorbance at 420 nm, MCPT, gallic acid and total monomeric phenolic content. TPI and ABTS were significantly higher in wines with preservatives (i.e., T2 > T1 â‰… T3 > C, p < 0.05). These variations were observed both two weeks after the treatments and again after five months of wine aging. Additionally, an accelerated browning test and a quantitative sensory analysis of wine colour and mouthfeel attributes were performed after 5 months of wine aging. When exposed to excessive oxygen and high temperature (50 °C), T1 and T2 exhibited ∼29% and 24% higher browning capacity than the control, whereas T3 reduced the wine's browning capacity by ∼20%. Nonetheless, the results from sensory analysis did not show significant variations between the treatments. Thus, using green tea extract to replace SO2 at wine bottling appears to be a viable option, without inducing a negative impact on the perceptible colour and mouthfeel attributes of Sauvignon Blanc wine.

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing.

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 µg/g based on our detected ten ɑ-dicarbonyls.

Could Collected Chemical Parameters Be Utilized to Build Soft Sensors Capable of Predicting the Provenance, Vintages, and Price Points of New Zealand Pinot Noir Wines Simultaneously?

Soft sensors work as predictive frameworks encapsulating a set of easy-to-collect input data and a machine learning method (ML) to predict highly related variables that are difficult to measure. The machine learning method could provide a prediction of complex unknown relations between the input data and desired output parameters. Recently, soft sensors have been applicable in predicting the prices and vintages of New Zealand Pinot noir wines based on chemical parameters. However, the previous sample size did not adequately represent the diversity of provenances, vintages, and price points across commercially available New Zealand Pinot noir wines. Consequently, a representative sample of 39 commercially available New Zealand Pinot noir wines from diverse provenances, vintages, and price points were selected. Literature has shown that wine phenolic compounds strongly correlated with wine provenances, vintages and price points, which could be used as input data for developing soft sensors. Due to the significance of these phenolic compounds, chemical parameters, including phenolic compounds and pH, were collected using UV-Vis visible spectrophotometry and a pH meter. The soft sensor utilising Naive Bayes (belongs to ML) was designed to predict Pinot noir wines' provenances (regions of origin) based on six chemical parameters with the prediction accuracy of over 75%. Soft sensors based on decision trees (within ML) could predict Pinot noir wines' vintages and price points with prediction accuracies of over 75% based on six chemical parameters. These predictions were based on the same collected six chemical parameters as aforementioned.

The importance of outlier rejection and significant explanatory variable selection for pinot noir wine soft sensor development.

Sensory attributes are essential factors in determining the quality of wines. However, it can be challenging for consumers, even experts, to differentiate and quantify wines' sensory attributes for quality control. Soft sensors based on rapid chemical analysis offer a potential solution to overcome this challenge. However, the current limitation in developing soft sensors for wines is the need for a significant number of input parameters, at least 12, necessitating costly and time-consuming analyses. While such a comprehensive approach provides high accuracy in sensory quality mapping, the expensive and time-consuming studies required do not lend themselves to the industry's routine quality control activities. In this work, Box plots, Tucker-1 plots, and Principal Component Analysis (PCA) score plots were used to deal with output data (sensory attributes) to improve the model quality. More importantly, this work has identified that the number of analyses required to fully quantify by regression models and qualify by classification models can be significantly reduced. Based on regression models, only four key chemical parameters (total flavanols, total tannins, A520nmHCl, and pH) were required to accurately predict 35 sensory attributes of a wine with R2 values above 0.6 simultaneously. In addition, for classification models to accurately predict 35 sensory attributes of a wine at once with prediction accuracy above 70%, only four key chemical parameters (A280nmHCl, A520nmHCl, chemical age and pH) were required. These models with reduced chemical parameters complement each other in sensory quality mapping and provide acceptable accuracy. The application of the soft sensor based on these reduced sets of key chemical parameters translated to a potential reduction in analytical cost and labour cost of 56% for the regression model and 83% for the classification model, respectively, making these models suitable for routine quality control use.

From energy storage to pathogen eradication: unveiling the antibacterial and antiviral capacities of flexible solid-state carbon cloth supercapacitors.

With the emergence of deadly viral and bacterial infections, preventing the spread of microorganisms on surfaces has gained ever-increasing importance. This study investigates the potential of solid-state supercapacitors as antibacterial and antiviral devices. We developed a low-cost and flexible carbon cloth supercapacitor (CCSC) with highly efficient antibacterial and antiviral surface properties. The CCSC comprised two parallel layers of carbon cloth (CC) electrodes assembled in a symmetric, electrical double-layer supercapacitor structure that can be charged at low potentials between 1 to 2 V. The optimized CCSC exhibited a capacitance of 4.15 ± 0.3 mF cm-2 at a scan rate of 100 mV s-1, high-rate capability (83% retention of capacitance at 100 mV s-1 compared to its value at 5 mV s-1), and excellent electrochemical stability (97% retention of the initial capacitance after 1000 cycles). Moreover, the CCSC demonstrated outstanding flexibility and retained its full capacitance even when bent at high angles, making it suitable for wearable or flexible devices. Using its stored electrical charge, the charged CCSC disinfects bacteria effectively and neutralizes viruses upon surface contact with the positive and negative electrodes. The charged CCSC device yielded a 6-log CFU reduction of Escherichia coli bacterial inocula and a 5-log PFU reduction of HSV-1 herpes virus. Antibacterial and antiviral carbon cloth supercapacitors represent a promising platform technology for various applications, including electronic textiles and electronic skins, health monitoring or motion sensors, wound dressings, personal protective equipment (e.g., masks) and air filtration systems.

Alternative Perspective on Rapid Wine Oxidation through Changes in Gas-Phase Volatile Concentrations, Highlighted by Matrix Component Effects.

A new perspective is presented to investigate the sensorially relevant gas-phase concentrations of volatile compounds in wine. This is achieved by measuring the partition coefficients and matrix-phase concentrations of volatiles using static headspace-gas chromatography-ion mobility spectrometry. Physicochemical properties that can contribute to the partition behaviors of 10 volatile esters, such as hydrophobicity and matrix temperature, are also discussed. Partition coefficients are then linked to quantitative measurements to obtain partial pressures, which describe the availability of volatile compounds in the gas phase. The concept of partition coefficients and partial pressure has then been applied to a time series of aroma changes due to oxidation in commercial wines. As a follow-up study, a full factorial design was devised to inspect the impact of three common wine matrix components, namely, copper, polyphenols, and ascorbic acid, on the partial pressure changes after 30-day oxidation treatment in either full-alcohol or low-alcohol simulated wine matrices. Interesting interactive effects between antioxidant behaviors and alcohol levels were elucidated, especially around the controversial use of ascorbic acid in winemaking. These results can guide winemakers who wish to minimize oxidative damage to wine aroma during wine storage or bulk transport, where ullage may be present or continual oxygen ingress may be occurring.

Degradation of cyanidin-3-O-glucoside induced by antioxidant compounds in model Chinese bayberry wine: Kinetic studies and mechanisms.

The degradation kinetic of cyanidin-3-O-glucoside was determined in combination with different antioxidants, namely ascorbic acid, cysteine, reduced glutathione, and sodium sulfite at different concentrations and temperatures (4, 20, and 37 °C) in model Chinese bayberry wine. Ascorbic acid, cysteine, and reduced glutathione accelerated cyanidin-3-O-glucoside degradation; half-life times decreased by ca. 46 âˆ¼ 93%, 0.39 âˆ¼ 88%, and 1.6 âˆ¼ 92% respectively when the concentrations of antioxidants were 0.1 âˆ¼ 5 mM. Thiols with more -SH groups lead to faster degradation of cyanidin-3-O-glucoside. Interactions of oxidized cyanidin-3-O-glucoside with antioxidants were evaluated in aqueous solution and methanol to investigate the degradation mechanism of anthocyanin after oxidation. An anthocyanin-cysteine adduct was identified by LC-MS and formation pathways are proposed, along with mechanisms of anthocyanin degradation induced by antioxidants.

Electrochemical Methods for the Analysis of Milk.

The milk and dairy industries are some of the most profitable sectors in many countries. This business requires close control of product quality and continuous testing to ensure the safety of the consumers. The potential risk of contaminants or degradation products and undesirable chemicals necessitates the use of fast, reliable detection tools to make immediate production decisions. This review covers studies on the application of electrochemical methods to milk (i.e., voltammetric and amperometric) to quantify different analytes, as reported over the last 10 to 15 years. The review covers a wide range of analytes, including allergens, antioxidants, organic compounds, nitrogen- and aldehyde containing compounds, biochemicals, heavy metals, hydrogen peroxide, nitrite, and endocrine disruptors. The review also examines pretreatment procedures applied to milk samples and the use of novel sensor materials. Final perspectives are provided on the future of cost-effective and easy-to-use electrochemical sensors and their advantages over conventional methods.

Polyhydroxybutyrate (PHB) produced from red grape pomace: Effect of purification processes on structural, thermal and antioxidant properties.

Red grape pomace was used as a source for poly(3-hydroxybutyrate) (PHB) production, which was then subject to a range of purification processes. The different PHB biopolymers were characterized for chemical structure, crystallinity, thermal properties, colour, release of compounds into different food simulants and antioxidant inhibition, and comparisons were made with a commercially available PHB. An increase in purification steps did not have a significant effect on the high thermal stability of the extracted biopolymer, but it decreased the degree of crystallinity and the presence of amino acids and aromatic compounds. With additional purification, the PHB powders also whitened and the number of components released from the biopolymer into food simulants decreased. The released compounds presented antioxidant inhibition, which has not been previously reported in the literature or with commercially available polyhydroxyalkanoates. This is of great interest for food packaging and biomedical industries where the addition of antioxidant additives to improve PHB functional properties may not be necessary and could be avoided.

Volatile-Based Prediction of Sauvignon Blanc Quality Gradings with Static Headspace-Gas Chromatography-Ion Mobility Spectrometry (SHS-GC-IMS) and Interpretable Machine Learning Techniques.

The analytical scope of static headspace-gas chromatography-ion mobility spectrometry (SHS-GC-IMS) was applied to wine aroma analysis for the first time. The method parameters were first fine-tuned to achieve optimal analytical results, before the method stability was demonstrated, in terms of repeatability and reproducibility. Succinct qualitative identification of compounds was also realized, with the identification of several volatiles that have seldom been described previously in Sauvignon Blanc wine, such as methyl acetate, ethyl formate, and amyl acetate. Using the SHS-GC-IMS data in an untargeted approach, computer modeling of large datasets was applied to link aroma chemistry via prediction models to wine sensory quality gradings. Six machine learning models were compared, and artificial neural network (ANN) returned the most promising performance with a prediction accuracy of 95.4%. Despite its inherent complexity, the ANN model offered intriguing insights on the influential volatiles that correlated well with higher and lower sensory gradings. These findings could, in the future, guide winemakers in establishing wine quality, particularly during blending operations prior to bottling.

Effects of antioxidant and elemental sulfur additions at crushing on aroma profiles of Pinot Gris, Chardonnay and Sauvignon Blanc wines.

The antioxidants sulfur dioxide (50 ppm) and ascorbic acid (100 ppm) were added to grapes soon after harvest at crushing. The chemical composition and sensory profile of Sauvignon Blanc, Pinot Gris and Chardonnay wines were examined, made from grapes collected at three different sites for each variety. With good antioxidant protection of the juices, reflected in low absorbances at 420 nm, remarkable increases in the polyfunctional mercaptans, 3-mercaptohexanol (3MH) and its acetate ester (3MHA), were seen in the wines. Moreover, high levels of these compounds were produced in the Pinot Gris and Chardonnay wines, equally high as with Sauvignon Blanc. The Pinot Gris wines maintained varietal characteristics in sensory profiles, even with high levels of polyfunctional mercaptans. When elemental sulfur was included with the grapes at crushing, extra increases in polyfunctional mercaptans were observed. However, this led to the production of unwanted reductive aroma compounds in some wines.

Electrochemical Preparation of Poly(3,4-Ethylenedioxythiophene) Layers on Gold Microelectrodes for Uric Acid-Sensing Applications.

Two different methods for the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) on gold electrodes are described, using electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in an aqueous and an organic solution. Cyclic voltammetry (CV) was used in the synthesis of PEDOT thin layers. Lithium perchlorate (LiClO4) was used as a dopant in both aqueous (aqueous/acetonitrile (ACN)) and organic (propylene carbonate (PC)) solvent systems. After the PEDOT layer was created in the organic system, the electrode surface was acclimatized by successive cycling in an aqueous solution for use as a sensor for aqueous samples. The use of an aqueous-based electropolymerization method has the potential benefit of removing the acclimatization step to have a shorter sensor preparation time. Although the aqueous method is more economical and environmentally friendly than the organic solvent method, superior PEDOT formation is obtained in the organic solution. The resulting PEDOT electrode surfaces were characterized by scanning electron microscopy (SEM), which showed the constant growth of PEDOT during electropolymerization from the organic PC solution, with rapid fractal-type growth on gold (Au) microelectrodes.

Solvent Effect in Imidazole-Based Poly(Ionic liquid) Membranes: Energy Storage and Sensing.

Polymerized ionic liquids (PILs) are interesting new materials in sustainable technologies for energy storage and for gas sensor devices, and they provide high ion conductivity as solid polymer electrolytes in batteries. We introduce here the effect of polar protic (aqueous) and polar aprotic (propylene carbonate, PC) electrolytes, with the same concentration of lithium bis(trifluoromethane) sulfonimide (LiTFSI) on hydrophobic PIL films. Cyclic voltammetry, scanning ionic conductance microscopy and square wave voltammetry were performed, revealing that the PIL films had better electroactivity in the aqueous electrolyte and three times higher ion conductivity was obtained from electrochemical impedance spectroscopy measurements. Their energy storage capability was investigated with chronopotentiometric measurements, and it revealed 1.6 times higher specific capacitance in the aqueous electrolyte as well as novel sensor properties regarding the applied solvents. The PIL films were characterized with scanning electron microscopy, energy dispersive X-ray, FTIR and solid state nuclear magnetic resonance spectroscopy.

Free and Glycosidic Volatiles in Tamarillo (Solanum betaceum Cav. syn. Cyphomandra betacea Sendt.) Juices Prepared from Three Cultivars Grown in New Zealand.

This study investigated the free and glycosidic-bound volatiles in the juice samples of three tamarillo cultivars (i.e. Amber, Mulligan, and Laird's Large) that are widely grown in New Zealand. Juice samples were prepared from fruits at different ripening stages (green, middle, and ripe). Headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was applied to analyze the free volatiles in the samples. A total of 20 free volatiles were detected. Among the samples, the ripe Mulligan juice gave the highest contents of free terpenoids (424 µg/L) and esters (691 µg/L). The glycosidic-bound volatiles were prepared by solid-phase extraction. The matrix effect was evaluated based on the recovery rate of analytes containing multiple aglycone classes. From the results, phenyl ß-d-glucopyranoside was selected to compensate the matrix effect caused by insufficient acquisition of glycosidic volatiles during analyte preparation. In all the ripe-fruit juice samples, the aglycones 4-hydroxy-2,5-dimethyl-3(2H)-furanone and trans-2, cis-6-nonadienal were found to give high odor activity values. According to multivariate statistical analysis, 11 free volatiles and 22 glycosidic volatiles could be potentially applied as volatile makers to distinguish the juice samples. This study has provided a comprehensive understanding of the flavor chemistry of tamarillo juices, with a focus on the potential role of glycosidic aglycones as aroma contributors to tamarillo products.