Irene Domínguez

Stabilized Naked Sub-nanometric Cu Clusters within a Polymeric Film Catalyze C–N, C–C, C–O, C–S, and C–P Bond-Forming Reactions

Sub-nanometric Cu clusters formed by endogenous reduction of Cu salts and Cu nanoparticles are active and selective catalysts for C-N, C-C, C-O, C-S, and C-P bond-forming reactions. Sub-nanometric Cu clusters have also been generated within a polymeric film and stored with full stability for months. In this way, they are ready to be used on demand and maintain high activity (TONs up to 10(4)) and selectivity for the above reactions. A potential mechanism for the formation of the sub-nanometric clusters and their electronic nature is presented.

Electrochemical tomato (Solanum lycopersicum L.) characterisation using contact probe in situ voltammetry.

An in situ electrochemical contact probe methodology for characterising tomato samples is proposed. It is based on the record of the voltammetric response of antioxidant compounds when glassy carbon electrodes are inserted into the pericarp of fresh tomato specimens cut in half. The absence of pretreatment and in situ sampling avoid sample contamination and the oxidation of air-sensitive compounds thus increasing the representativity of the analytical data relative to conventional electrochemical analysis. Characteristic voltammetric responses recorded for such compounds, including rutin, chlorogenic acid, naringenin, naringenin chalcone and ascorbic acid have been obtained. A positive correlation between the (total phenolic compounds)/(ascorbic acid) ratio and peak intensity ratios has been found when analysing the voltammograms. This fact led us to differentiate between diverse tomato varieties and also tomatoes sample growth under different agronomic conditions and harvested at two ripeness stages.

Impact of bioactive packaging systems based on EVOH films and essential oils in the control of aflatoxigenic fungi and aflatoxin production in maize

Aspergillus flavus and A. parasiticus are the most common fungal species associated with aflatoxin (AF) contamination of cereals, especially maize, and other agricultural commodities. AFB1, the most frequent and toxic metabolite, is a powerful hepatotoxic, teratogenic and mutagenic compound. Effective strategies to control these fungal species and AFs in food and feed are required. Active packaging film containing essential oils (EO) is one of the most innovative food packaging concepts. In this study, ethylene-vinyl alcohol (EVOH) copolymer films incorporating EO from Origanum vulgare (ORE), Cinnamomum zeylanicum (CIN) or their major active constituents, carvacrol (CAR) and cinnamaldehyde (CINHO), respectively, were developed and assayed to control growth of A. flavus and A. parasiticus and AF production in maize grains under different aw and temperature regimens. EO doses assayed in cultures were in the range 0.25-4.0mg/Petri dish. The factors aw, temperature, type of EVOH-EO film and fungal species significantly influenced the ED50 values of all assayed films. Growth rate (GR) of both species was usually higher at 0.99 than at 0.96 aw and at 37°C than at 25°C. However, the contrary was found with regard to AF production. The order of efficacy of EVOH-EO films to control growth of both species and AF production was EVOH-CINHO>EVOH-CAR>EVOH-ORE>EVOH-CIN. The effective dose (ED50) (mg EO/plate) for EVOH-CINHO and EVOH-CIN films against A. flavus were in the ranges of 0.125 and 2.475-3.500 and against A. parasiticus in the ranges of 0.121-0.133 and 2.275-3.625, respectively. Under the assayed conditions, the ED90 for EVOH-CINHO film were 0.22-0.23mg/plate for both species. It was the most effective bioactive film to control fungal growth (vapour phase) and AF production, regardless of aw and temperature. This is the first study about the impact that interacting environmental conditions and bioactive EVOH-CINHO, EVOH-ORE, EVOH-CIN EVOH-CAR films have on the growth of aflatoxigenic fungi and on AF production in maize grains.

Influence of modified atmosphere and ethylene levels on quality attributes of fresh tomatoes (Lycopersicon esculentum Mill.).

Controlling storage atmosphere is a key factor for delaying postharvest fruit quality loss. The objective of this study is to evaluate its influence on physico-chemical, sensorial and nutritional quality attributes of two tomato fruit cultivars (Delizia and Pitenza) that respectively have a short- and long-storage life. To that end, the effect of two types of bags with different gas permeability, combined or not with an ethylene sorbent, on tomato organoleptic and nutritional properties were compared during fruit storage at 13°C. CO2 and O2 were critical factors for controlling tomato postharvest behaviour. Weight loss, firmness, color and visual quality were only affected by bag permeability just as total sugar content and acidity for Pitenza tomatoes. (trans)-2-Hexenal also appears to be related with CO2 and O2 levels. Lycopene, total phenols (TP) and ascorbic acid (AA) contents were also affected by the packaging form and the storage length. Ethylene removal in combination with MAP led to a higher content in TP and AA in the short-life tomato cultivar.

Contact probe voltammetry for in situ monitoring of the reactivity of phenolic tomato (Solanum lycopersicum L.) compounds with ROS.

The application of an in situ electrochemical contact probe methodology for monitoring reactivity of antioxidant polyphenolic compounds in tomato fruits is described. Upon electrochemical generation of reactive oxygen species (ROS), characteristic voltammetric responses were recorded for compounds resulting from the reaction of such species with tomato compounds. This suggests that new electrochemically oxidizable compounds are generated from the oxidation of highly reactive polyphenolic compounds with ROS. Therefore, an evaluation of the antioxidant capacity of such species could be made from voltammetric data for different tomato varieties.

Contact probe electrochemical characterization and metal speciation of silver LLDPE nanocomposite films

A contact probe methodology, based on the voltammetry of immobilized microparticle approach, is used for characterizing silver species present in linear low density polyethylene (LLDPE) films with different Ag(I)/Ag(0) ratios and silver nanoparticle features usable as food contact polymers. The films displayed characteristic voltammetric features in contact with aqueous acetate buffer, in particular signals for the stripping oxidation of nanoparticulate Ag systems. Significant differences between the studied films were also observed by means of electrochemical impedance spectroscopy and detected at the nanoscopic scale using electrochemical scanning microscopy. Differences in optical and thermal properties of the studied films are associated with the presence of silver nanoparticles. The silver oxidation state as well as nanoparticle size also had influence on the oxidative resistance of the LLDPE films; indeed, films containing cationic silver showed the lowest oxidation induction time value.

Disassembling Metal Nanocrystallites into Sub-nanometric Clusters and Low-faceted Nanoparticles for Multisite Catalytic Reactions

Metal nanocrystallites present saturated atoms, in planes, and unsaturated metal atoms, in corners and vertices, for catalytic applications. However, both sites are spatially complementary and simultaneously excluding for a given particle, thus their number cannot be independently maximized for a catalytic process. Here, it is shown that the independent dosage of Au clusters and metallic Au nanoparticles dramatically improves the catalytic activity of Au for the Sonogashira reaction, enabling the coupling of a wide range of iodo‐, bromo‐, and activated chloro‐derivatives with aromatic and aliphatic alkynes, and outperforming ligand‐free Pd and Cu catalysts. Mechanistic studies reveal that the unsaturated atoms of the cluster activate the alkyne and that the saturated atoms of the metallic nanoparticle preferentially activate the halide, to finally perform the coupling. Thus, a precise combination of sub‐nanometric metal clusters and metal nanoparticles, together, constitute a new catalytic strategy to substitute metal nanocrystallites in reactions in which both unsaturated and saturated atoms play a key role.

Chapter 22 – Antimicrobial Active Packaging Systems Based on EVOH Copolymers

Great attention is being paid to the potential applications of antimicrobial active packages that have resulted in diverse packaging systems commercialized for improved preservation of food products. This chapter reviews novel developments which make use of ethylene-vinyl alcohol copolymers (EVOH) as polymeric matrices for the design of antimicrobial active packages. EVOH copolymers are a family of materials that are widely used in package manufacturing, thanks to their excellent barrier properties to gases and organic vapors. They are highly hydrophilic and, in humid environments, tend to sorb large amounts of water, suffering a severe plasticization. This affects mechanical and barrier properties, and is commonly avoided by protecting EVOH between polyolefin layers. However, this water sensitivity can be beneficial, because plasticization can be used as a triggering mechanism in active packaging. Some of the antimicrobial active developments which make use of EVOH copolymers are reviewed in this chapter.

Use of EVOH for Food Packaging Applications

Ethylene vinyl alcohol copolymers (EVOH) are a family of thermoplastic polymers with application in many industrial sectors including packaging, especially, in food packaging. The main characteristic of EVOH copolymers for packaging applications is their outstanding barrier to gases (oxygen, carbon dioxide, etc.) and organic vapors (food aroma). EVOH is applied in multilayer structures for bags, trays, cups, bottles, squeezable tubes, or jars to protect oxygen-sensitive products. However, the hydrophilic nature of EVOH must be taken in consideration in package design to minimize water uptake and polymer swelling during thermal treatment processes such as retorting. This article reviews EVOH applications in barrier packaging and in active packaging.

Correction to “Stabilized Naked Sub-nanometric Cu Clusters within a Polymeric Film Catalyze C–N, C–C, C–O, C–S, and C–P Bond-Forming Reactions”

Page 3894. The first author’s surname should be “OliverMeseguer” (just one “s”). It is shown correctly in the list of authors here and on the title page of the revised Supporting Information file. Page 3899. In the Experimental Section, Typical Reaction Procedure, “diethyl ether” was used, not “dimethyl ether” (twice, lines 8 and 10 in the paragraph). The complete third sentence of this section should read as follows: “The vial was sealed, and the resulting mixture was placed in a pre-heated oil bath at 135 °C and magnetically stirred. After 24 h, slow addition of diethyl ether or dichloromethane (5 mL) and water (6 mL), separation of the organic layer, and two extractions of the aqueous layer with diethyl ether or dichloromethane were carried out before the combined organic layers were dried over MgSO4 and then filtered.” ■ ASSOCIATED CONTENT *S Supporting Information Additional Figures S1−S20, experimental procedures, and compound characterization, including NMR spectra (with title page corrected). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.5b03889. Addition/Correction