1,720,993 research outputs found
Hydrophobic eutectic solvent with antioxidant properties: application for the dispersive liquid-liquid microextraction of fat-soluble micronutrients from fruit juices
Full text linkDespite the great interest devoted to eutectic solvents with significant negative deviations from ideality (namely, deep eutectic solvents), many hydrophobic liquid mixtures are ideal or quasi-ideal systems. In this regard, we propose the introduction of a hydrophobic eutectic solvent based on l-menthol and butylated hydroxytoluene, blended in a molar ratio of 3:1. The physicochemical characterization by means of differential scanning calorimetry and infrared spectroscopy has identified that it is an ideal eutectic solvent. Compared to other hydrophobic mixtures, this one represents an advanced solvent system due to its intrinsic antioxidant activity, which makes it an ideal green choice for the extraction and preservation of easily oxidizable lipophilic compounds. In order to evaluate its efficiency, it was applied for the first time as an extractant for the dispersive liquid-liquid microextraction of carotenoids and fat-soluble vitamins from fruit juices, carried out at 298 K. All extracts were analyzed by high-performance liquid chromatography-tandem mass spectrometry. The developed method was then validated, providing precise (4-8%) and accurate (4-6%) results on a commercial fruit juice containing declared values of β-carotene and α-tocopherol acetate. Recoveries were ≥70%, while the detection limits were 0.05 μg L-1 for β-carotene and 0.28 μg L-1 for α-tocopherol acetate. Here, we also propose an original approach to properly determine the antioxidant activity of eutectic mixtures since the available commercial kits cannot be applied to such systems without altering their nature. Last but not least, a circular process of reuse of this ideal eutectic solvent has been developed using a low-cost activated carbon material obtained from coconut shells
Twofold Facet of Kinetics of Glass Aging
No full textWe employ fast scanning calorimetry to monitor the isothermal aging kinetics in glassy polymers, complemented with measurements on other glasses. Apart from following the time evolution of the glass enthalpic state, we monitor the aging kinetics of the devitrification width on heating, Delta Tdev. We find that significantly below the glass transition temperature, Tg, the glass enthalpy attains equilibrium earlier than Delta Tdev, which evolves at long aging times toward enhanced heterogeneity. Hence, our results indicate that the description of time dependent evolution in glassy materials requires information beyond the mere description of its enthalpic state
Glass transition and molecular dynamics in polystyrene nanospheres by fast scanning calorimetry
No full textWe employ fast scanning calorimetry (FSC) to characterize the glass transition of polystyrene (PS) nanospheres. We observe suppression of the glass transition temperature (Tg) in comparison to bulk PS, both in terms of limiting fictive temperature (Tf) and temperature range of vitrification. At the same time, the polymer molecular mobility is found to be independent of the nanospheres diameter and bulk-like. Importantly, apart from the fact that this result has been obtained on the same samples and experiments and at comparable time scales, in all cases, a perturbation of the entropy is induced. Hence, to understand these results, the conceptual difference between vitrification kinetics and molecular mobility is highlighted. The main consequence of the outcome of the present study is that arguments beyond those based on the modification of the molecular mobility must be accounted for to explain Tg suppression in polymer glasses subjected to nanoscale confinement
Liquid structure of a choline chloride-water natural deep eutectic solvent: A molecular dynamics characterization
Full text linkThe liquid structure of a representative of the first water-in-salt (WiS) Natural Deep Eutectic Solvents (NADES), hereinafter indicated as aquoline, a mixture of choline chloride (ChCl) and water with molar ratio 1:3.33, is ex- plored at ambient conditions. Using Molecular Dynamics (MD) simulation tools, we extract structural informa- tion at atomistic level on the nature of inter-correlations between the different moieties. Despite being a very fluid liquid, with much lower viscosity than other common ChCl-based DES, aquoline turns out to be very struc- tured. Computed X-ray and neutron weighted scattering patterns (the latter also on selectively deuterated mix- tures) highlight the existence of mesoscopic organization that is rationalised in terms of choline vs. water/ chloride structural alternation. The study shows that choline cations are highly coordinating the surrounding en- vironment: strong hydrogen bonding mediated correlations between the hydroxyl group and water or chloride are detected. In addition, the ammonium group drives the formation of a complex solvating environment, with water, chloride and hydroxyl moieties approaching it, between the hindering methyl groups. Strong hydrogen- bonding interactions between water molecules and between water and anions are detected and, while water cannot create a bulk water-like environment around itself, its network with neighbour water or anions develops long chains across the bulk phase. This is a first study that will be extended based on complementary experimen- tal work as a function of water content and temperature/pressure, to explore structural and dynamic properties of this class of materials
Choline chloride-water mixtures as new generation of green solvents: a comprehensive physico-chemical study
Full text linkNatural deep eutectic solvents (NADES) are an increasingly appreciated class of mixtures composed by eco-sustainable and environmentally responsible components with hydrogen bonding (HB) donor and acceptor capabilities that enable the establishment of an extended HB network. The latter eventually leads to a substantial drop in the mixture melting point with respect to the one of the ideal mixture. Water-based NADES represent an exciting system that responds to the above mentioned criteria and contain water as a major component, rather than as an impurity or a deliberately added minor ingredient. Choline Chloride (ChCl, a well known HB acceptor in DES systems) forms NADES when mixed with water, which plays the role of HB donor. Several applications have already been identified for this system, but chemical physical properties of choline-rich mixtures, including the DES concentration, are not well established, yet. In order to overcame this limitation and introduce a subsequent, more systematic investigation of atomistic organization in these mixtures, here we report results from a series of chemical physical characterizations of water:ChCl with ratio ranging from 2 to 10 between ca. 280 and 330 K. Calorimetric measurements, density, viscosity, electric conductivity, refractive index, X-ray diffraction patterns and several 1H and 35Cl NMR spectroscopy observables are reported and compared with literature (when available). The deep eutectic nature of the water: ChCl 4:1 mixture is assessed, leading to the individuation of aquoline, as the corresponding DES. The other chemical physical properties are observed to vary, upon water content, in a monotone way, without abrupt changes across the eutectic concentration, thus providing support for the exploitation of the ChCl/water class of solvents, with tunable chemical-physical properties across their wide liquid range
Anatomy of a deep eutectic solvent: structural properties of choline chloride : sesamol 1 : 3 compared to reline
No full textThe structural properties of the deep eutectic solvent (DES) formed by choline chloride (ChCl) and sesamol in 1 : 3 ratio have been investigated and compared to those of reline (ChCl : urea 1 : 2). An integrated approach combining small and wide angle X-ray scattering with molecular dynamics simulations has been employed and the simulation protocol has been validated against the experimental data. In the ChCl : sesamol DES, strong hydrogen bonds (HBs) are formed between the chloride anion and the hydroxyl groups of the choline and of sesamol molecules. Conversely, choline-choline, choline-sesamol and sesamol-sesamol interactions are negligible. A more extended interplay between the constituents is observed in reline where, besides the HBs involving the chloride anion, the eutectic formation is favored also by strong choline-urea and urea-urea interactions. The three-dimensional arrangement around the individual components shows that, in the ChCl : sesamol DES, the cholinium cations and the sesamol molecules are packed in such a way to maximize the interactions with the chlorine anion. This structural arrangement may favor the pi-pi interactions between the sesamol molecules and the aromatic species mediated by the chloride ions, providing an interpretation for the high separation rates previously observed for phenolic DESs towards aromatic compounds
Surface modification of polyester films with polyfunctional amines: Effect on bacterial biofilm formation
No full textThe development of materials with antifouling properties is crucial in many areas, including medicine and food packaging. In this study, 2D-matrices made of polylactic acid (PLA), polyhydroxybutyrate (PHB), or polyhydroxybutyrate-co-valerate (PHB-HV) were surface functionalized through aminolysis with three poly- functional amines, 1,6-hexamethylenediamine (HDA), tetraethylenepentamine (TEPA), and polyallylamine hy- drochloride (PAH). The aminolysis procedure was thoroughly studied to ensure a high amount of amine groups while preserving the structural properties of the films. Interestingly, PHB and PHB-HV were found to be more sensitive to aminolysis than PLA, and the highest amino group density was achieved in surfaces etched with PAH. A decrease in the contact angle from ca. 85◦ to ca. 70◦ was revealed for polymers functionalized with HDA and TEPA and a drastic reduction in Staphylococcus epidermidis adhesion was observed for PHB-HV functionalized with the polymeric amine PAH. Polymer antimicrobial activity was found to be related to the degree of surface functionalization. The functionalized, cationic polymer surfaces were supposed to act upon contact with bacteria, without releasing any antimicrobial agent. The developed bioactive surfaces may have potential applications as flexible films for food packaging
Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment
No full textIntroductionOnce dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.MethodsBy combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi (R) - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.Results and DiscussionThe phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment
Fate of a deep eutectic solvent upon cosolvent addition: choline chloride-sesamol 1:3 mixtures with methanol
Full text linkThe changes upon methanol (MeOH) addition in the structural arrangement of the highly eco-friendly deep eutectic solvent (DES) formed by choline chloride (ChCl) and sesamol in 1:3 molar ratio have been studied by means of attenuated total reflection Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering (SWAXS), and molecular dynamics simulations. The introduction of MeOH into the DES promotes the increase of the number of Cl–MeOH hydrogen bonds (HBs) through the replacement of sesamol and choline molecules from the chloride anion coordination sphere. This effect does not promote the sesamol–sesamol, choline–choline, and sesamol–choline interactions, which remain as negligible as in the pure DES. Differently, the displaced sesamol and choline molecules are solvated by MeOH, which also forms HBs with other MeOH molecules, so that the system arranges itself to keep the overall amount of HBs maximized. SWAXS measurements show that this mechanism is predominant up to MeOH/DES molar ratios of 20–24, while after this ratio value, the scattering profile is progressively diluted in the cosolvent background and decreases toward the signal of pure MeOH. The ability of MeOH to interplay with all of the DES components produces mixtures with neither segregation of the components at nanoscale lengths nor macroscopic phase separation even for high MeOH contents. These findings have important implications for application purposes since the understanding of the pseudophase aggregates formed by a DES with a dispersing cosolvent can help in addressing an efficient extraction procedure
Silver- and Zinc-Decorated Polyurethane Ionomers with Tunable Hard/Soft Phase Segregation
Full text linkSegmented polyurethane ionomers find prominent applications in the biomedical field since they can combine the good mechanical and biostability properties of polyurethanes (PUs) with the strong hydrophilicity features of ionomers. In this work, PU ionomers were prepared from a carboxylated diol, poly(tetrahydrofuran) (soft phase) and a small library of diisocyanates (hard phase), either aliphatic or aromatic. The synthesized PUs were characterized to investigate the effect of ionic groups and the nature of diisocyanate upon the structure–property relationship. Results showed how the polymer hard/soft phase segregation was affected by both the concentration of ionic groups and the type of diisocyanate. Specifically, PUs obtained with aliphatic diisocyanates possessed a hard/soft phase segregation stronger than PUs with aromatic diisocyanates, as well as greater bulk and surface hydrophilicity. In contrast, a higher content of ionic groups per polymer repeat unit promoted phase mixing. The neutralization of polymer ionic groups with silver or zinc further increased the hard/soft phase segregation and provided polymers with antimicrobial properties. In Particular, the Zinc/PU hybrid systems possessed activity only against the Gram-positive Staphylococcus epidermidis while Silver/PU systems were active also against the Gram-negative Pseudomonas aeruginosa. The herein obtained polyurethanes could find promising applications as antimicrobial coatings for different kinds of surfaces including medical devices, fabric for wound dressings and other textiles
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