Studies on interaction of green silver nanoparticles with whole bacteria by surface characterization techniques

The use of silver nanoparticles (AgNPs) with their novel and distinct physical, chemical, and biological properties, has proven to be an alternative for the development of new antibacterial agents. In particular, the possibility to generate AgNPs coated with novel capping agents, such as phytomolecules obtained via a green synthesis (G-AgNPs), is attracting great attention in scientific research. Recently, we showed that membrane interactions seem to be involved in the antibacterial activity of AgNPs obtained via a green chemical synthesis using the aqueous leaf extract of chicory (Cichorium intybus L.). Furthermore, we observed that these G-AgNPs exhibited higher antibacterial activity than those obtained by chemical synthesis. In order to achieve the green AgNPs mode of action as well as their cellular target, we aimed to study the antibacterial activity of this novel green AgNPs against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The effect of the G-AgNPs on the bacterial surface was first evaluated by zeta potential measurements and correlated with direct plate count agar method. Afterwards, atomic force microscopy was applied to directly unravel the effects of these G-AgNPs on bacterial envelopes. Overall, the data obtained in this study seems correlate with a multi-step mechanism by which G-AgNPs-lipid membrane interactions is the first step prior to membrane disruption, resulting in antibacterial activity.Fil: Ferreyra Maillard, Anike Paula Virginia. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Gonçalves, Sónia. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; PortugalFil: Santos, Nuno C.. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; PortugalFil: López de Mishima, Beatriz A.. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Dalmasso, Pablo Roberto. Universidad Tecnologica Nacional. Facultad Regional Cordoba. Departamento de Ingenieria Quimica. Centro de Investigacion y Transferencia En Ingenieria Quimica.; ArgentinaFil: Hollmann, Axel. Universidad Nacional de Quilmes; Argentina. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; Portugal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Centro de Investigación en Biofísica Aplicada y Alimentos. - Universidad Nacional de Santiago del Estero. Centro de Investigación en Biofísica Aplicada y Alimentos; Argentin

Studies on interaction of green silver nanoparticles with whole bacteria by surface characterization techniques

The use of silver nanoparticles (AgNPs) with their novel and distinct physical, chemical, and biological properties, has proven to be an alternative for the development of new antibacterial agents. In particular, the possibility to generate AgNPs coated with novel capping agents, such as phytomolecules obtained via a green synthesis (G-AgNPs), is attracting great attention in scientific research. Recently, we showed that membrane interactions seem to be involved in the antibacterial activity of AgNPs obtained via a green chemical synthesis using the aqueous leaf extract of chicory (Cichorium intybus L.). Furthermore, we observed that these G-AgNPs exhibited higher antibacterial activity than those obtained by chemical synthesis. In order to achieve the green AgNPs mode of action as well as their cellular target, we aimed to study the antibacterial activity of this novel green AgNPs against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The effect of the G-AgNPs on the bacterial surface was first evaluated by zeta potential measurements and correlated with direct plate count agar method. Afterwards, atomic force microscopy was applied to directly unravel the effects of these G-AgNPs on bacterial envelopes. Overall, the data obtained in this study seems correlate with a multi-step mechanism by which G-AgNPs-lipid membrane interactions is the first step prior to membrane disruption, resulting in antibacterial activity.Fil: Ferreyra Maillard, Anike Paula Virginia. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Gonçalves, Sónia. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; PortugalFil: Santos, Nuno C.. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; PortugalFil: López de Mishima, Beatriz A.. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Dalmasso, Pablo Roberto. Universidad Tecnologica Nacional. Facultad Regional Cordoba. Departamento de Ingenieria Quimica. Centro de Investigacion y Transferencia En Ingenieria Quimica.; ArgentinaFil: Hollmann, Axel. Universidad Nacional de Quilmes; Argentina. Universidade Nova de Lisboa. Faculdade de Ciencias Medicas; Portugal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Centro de Investigación en Biofísica Aplicada y Alimentos. - Universidad Nacional de Santiago del Estero. Centro de Investigación en Biofísica Aplicada y Alimentos; Argentin

Kinetic Monte Carlo applied to the electrochemical study of the Li-ion graphite system

To delve deeper into the kinetics involved in the staging phenomena of lithium insertion into graphite, it is necessary to develop theoretical models that emulate the physical phenomenon involved. In the present work kinetic Monte Carlo simulations are used to carry out a thorough analysis of the Li-ion graphite system, with the twofold aim of providing atomistic support for interpretations based on several experimental electrochemical techniques commonly used in the laboratory and of making theoretical predictions for future experimental work. Cyclic voltammograms and chronoamperometric transients are obtained, and diffusion coefficients and exchange current densities are calculated at different Li loadings of graphite. These results are compared with selected experimental data from the literature. In this way, there emerge details that cannot be observed in ordinary experiments due to methodological/instrumental limitations. For example, it is found that chronoamperometric responses are different for intercalation and deintercalation, the latter being a faster process. The reason why these phenomena are different is revealed, supporting and widening experimental assumptions. The present results also suggest that the intrinsic hysteresis observed in experimental work (and in simulations) is due to kinetic factors.Fil: Gavilán Arriazu, Edgardo Maximiliano. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Química Teórica y Computacional; ArgentinaFil: Pinto, Oscar Alejandro. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: López de Mishima, Beatriz A.. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Barraco Diaz, Daniel Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Oviedo, Oscar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Leiva, Ezequiel Pedro M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Electrochemical and Spectrophotometric Methods for Polyphenol and Ascorbic Acid Determination in Fruit and Vegetable Extracts

Pozadina istraživanja. Svježe rezano voće i povrće smatra se dobrim izvorom antioksidacijskih spojeva. Međutim, njihova trajnost je ograničena zbog smanjenja kakvoće proizvoda, nutritivnih vrijednosti i sigurnosti. Stoga su u posljednje vrijeme razvijeni različiti postupci obrade i čuvanja hrane te određivanja antioksidacijskih spojeva koji nakon konzumacije imaju višestruko povoljan učinak na zdravlje. Svrha je ovoga rada bila usporediti rezultate analize sastava polifenola i askorbinske kiseline u ekstraktima voća (patlidžan), jestivog korijenja (mrkva) i lišća (radič, zelena salata i blitva) dobivene elektrokemijskom i spektrofotometrijskom metodom, te procijeniti njihovu mogućnost detekcije neznatne promjene sastava antioksidacijskih spojeva u ekstraktu ploda patlidžana izloženom UV-C svjetlosti različitog intenziteta. Eksperimentalni pristup. Polifenolni spojevi i askorbinska kiselina određeni su elektrokemijskom i spektrofotometrijskom metodom. Za određivanje polifenolnih spojeva elektrokemijskom metodom korišten je enzimski biosenzor, a za određivanje askorbinske kiseline nanokompozitni biosenzor. Za spektrofotometrijska mjerenja korištene su sljedeće metode: Folin-Ciocalteu i metoda koju su razvili Kampfenkel i suradnici. Rezultati i zaključci. Rezultati dobiveni pomoću ove dvije, različite metode usporedivi su i u skladu s očekivanjima. Obje metode mogu poslužiti za određivanje udjela askorbinske kiseline i polifenola u ekstraktima voća i povrća. Osim toga, obje su metode detektirale promjenu u koncentraciji analita u uzorcima izloženim različitom intenzitetu UV-C zraka i vremenu skladištenja. Naposljetku, opaženo je da antioksidacijski kapacitet ovisi o vrsti hrane, postupku obrade te vremenu skladištenja. Novina i znanstveni doprinos. Obje su metode prikladne za kvantifikaciju analita; međutim, elektrokemijski su senzori bili specifičniji i selektivniji, mogli su se primijeniti na različite uzorke voća i povrća, te su pomoću njih dobiveni precizniji rezultati u kraćem vremenskom razdoblju i manjem volumenu uzorka, što smanjuje troškove radi manje potrošnje reagensa.Research background. Fresh-cut fruits and vegetables are considered sources of antioxidant compounds. However, their shelf life is limited due to nutritional, quality and safety deterioration. Therefore, in recent decades, various methods have been reported for food processing and preservation, as well as for the determination of antioxidant compounds, due to their many benefits when consumed. The aim of the present work is to compare the performance of electrochemical and spectrophotometric methods in the analysis of the content of polyphenolic compounds and ascorbic acid in extracts from fruits (eggplant), edible roots (carrot) and leaves (rocket, lettuce and chard), and evaluate their capability to detect small changes in the antioxidant content in the eggplant extracts previously irradiated with different UV-C light intensities. Experimental approach. Polyphenolic compounds and ascorbic acid were determined by electrochemical and spectrophotometric methods. An enzymatic biosensor and a nanocomposite sensor were used for polyphenolic compounds and ascorbic acid, respectively, in electrochemical measurements, while Folin-Ciocalteu and Kampfenkel methods were used for spectrophotometric measurements. Results and conclusion. Results obtained through the different methodologies were comparable and consistent with each other. Both methods allowed determining the content of ascorbic acid and polyphenolic compounds in the fruit and vegetable extracts. Moreover, both techniques enable the detection of the analyte concentration changes in samples exposed to different UV-C intensities and storage days. Finally, it was observed that the antioxidant capacity depends on the type of food, treatment and storage period. Novelty and scientific contribution. Both methodologies were suitable for the quantification of analytes; however, the electrochemical sensors provided higher specificity and selectivity, applicable to different fruit and vegetable matrices, obtaining results with higher precision, in shorter time and with a smaller sample volume, minimizing the economic costs because of the lower consumption of reagents

Extracción de naringina de Citrus paradisi L. estudio comparativo y optimización de técnicas extractivas

Se realizó el estudio comparativo de distintas técnicas extractivas de naringina utilizando cáscaras de pomelo (Citrus paradisi). Las mejores condiciones de preparación previa del material son el fragmentado de cáscara fresca y el secado en estufa con posterior fragmentado. Para cáscara fresca resulta más conveniente la extracción con etanol puro por Soxhlet (obteniéndose 26g/kg de peso fresco), mientras que para cáscara seca los mejores resultados se obtienen en la extracción con la mezcla etanol-agua en las proporciones 70:30 por maceración (20g/kg de peso fresco) y reflujo (22g/kg de peso fresco). Se observaron evidencias de la importancia del agua en el proceso de extracción. Se determinaron los valores de concentración de naringina en cáscaras de distintas variedades de Citrus paradisi de la región del Noroeste Argentino

Interaction of green silver nanoparticles with model membranes: Possible role in the antibacterial activity

Silver nanoparticles (AgNPs) constitute a very promising approach for overcoming the emergence of antibiotic resistance bacteria. Although their mode of action could be related with membrane damage, the AgNPs-lipid membrane interaction is still unclear. In this sense, the present work investigated the interaction of model lipid membranes with AgNPs coated with different capping agents such as citrate (C-AgNPs) and phytomolecules (G-AgNPs) obtained via a green synthesis. The AgNPs-membrane interactions were evaluated studying i) the surface pressure changes on both zwitterionic (DMPC) and negatively charged (DMPC:DMPG) lipid monolayers, ii) the zeta potential and DLS of DMPC:DMPG liposomes and iii) Zeta potential on Escherichia coli membranes, incubated with this nanomaterials. The results showed that both negatively charged-AgNPs can interact with these lipid monolayers inducing an increase in the surface pressure but G-AgNPs presented a significantly higher affinity toward both monolayers in comparison with C-AgNPs. Zeta potential data confirmed again the interaction event showing that both DMPC:DMPG liposomes and E. coli bacteria became more negative with the addition of G-AgNPs. This increased net negative charge of the liposomes and E. coli allows to indicate an interfacial interaction where the green nanometal should keep adsorbed to the membrane via the insertion of aromatic/hydrophobic moieties of capping agents on the surface of AgNPs into the lipid bilayer. Summarizing, the AgNPs-membrane interaction should be an essential step in the antibacterial activity either because the membrane is the main target or by increasing the local concentration of silver from G-AgNPs accumulation which could cause the bactericidal effect.Fil: Ferreyra Maillard, Anike Paula Virginia. Universidad Nacional de Santiago del Estero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Dalmasso, Pablo Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: López de Mishima, Beatriz A.. Universidad Nacional de Santiago del Estero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hollmann, Axel. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentin

Studies on interaction of green silver nanoparticles with whole bacteria by surface characterization techniques

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Electrostatically mediated layer-by-layer assembly of a bioinspired thymine polycation and gold nanoparticles

In this work, we built self-assembled structures of gold nanoparticles (AuNPs) using a new polyelectrolyte formed by copolymerization of the monomers 4-vinylbenzyl thymine (VBT) and 4-vinylbenzyl triethylammonium chloride (VBA). For the synthesis, a monomer ratio of 1 mol of VBT to 16 mol of VBA was used to obtain the polycation [(VBT)1:(VBA)16]16+ with a charge density suitable for the electrostatic adsorption of citrate stabilized AuNPs. The objective of this work was to explore the optical and electrochemical properties of the structure built on gold and quartz substrates with a view to its potential application as a (bio)sensor for optical and electrochemical detection. The polycation adsorption process was studied by surface plasmon resonance, which allowed us to select the appropriate concentration and adsorption time for the polymer and verify the formation of the self-assembly. Characterization of the system by atomic force microscopy allowed determining that AuNPs are distributed in isolation, such as dimers, trimers, tetramers, or bigger aggregates. The analysis of the resonance of the localized surface plasmons (LSPR) of the AuNPs, as well as the increase in the intensity of the polycation Raman signals revealed the electromagnetic coupling between close nanoparticles. In addition, the electrochemical impedance spectroscopy study of gold electrodes modified with the ([(VBT)1:(VBA)16]16+/AuNPs)n multilayer showed that incorporation of the AuNPs in the structure produced an increase in the apparent heterogeneous charge transfer constant. This fact indicates that the structure of the film and the nanoparticles distribution favor the electronic conduction mediated by AuNPs. The observed properties indicate that this multilayer represents a very interesting platform for the development of (bio)sensors based on optical or electrochemical detection.Fil: Gulotta, Florencia Alejandra. Universidad Nacional de Santiago del Estero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; ArgentinaFil: Paz Zanini, Veronica Irene. Universidad Nacional de Santiago del Estero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santiago del Estero. Universidad Nacional de Santiago del Estero. Centro de Investigaciones y Transferencia de Santiago del Estero; ArgentinaFil: López de Mishima, Beatriz A.. Universidad Nacional de Santiago del Estero. Instituto de Bionanotecnología del Noa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Bionanotecnología del Noa; ArgentinaFil: Martino, Debora Marcela. Universidad Nacional del Litoral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Linarez Pérez, Omar Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Ferreyra, Nancy Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin