Browsing by Author "Alves, Luis"
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- Cellulose-based edible films for probiotic entrapmentPublication . Singh, Poonam; Magalhaes, Solange; Alves, Luis; Antunes, Filipe; Miguel, Maria; Lindman, Bjorn; Medronho, BrunoEncapsulation with edible films is a promising approach that may solve the disadvantages associated with the use of bioactive compounds as food additives. This is particularly relevant in the case of probiotics, since their stability in food matrices and in the gastrointestinal tract may be rather poor. Therefore, new cellulose-based edible films have been successfully developed and characterized. Sodium carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) were used for the film preparation and cross-linked with citric acid (CA) under reasonably mild conditions. Model probiotic bacteria (Lactobacillus rhamnosus GG) were incorporated in the films either during the film formation and casting or after the film synthesis, via bacteria diffusion and adsorption. The later approach could efficiently entrap and preserve viable bacteria. The mechanical properties and swelling ability could be tuned by varying the HEC/CMC ratio and the amount of CA. Moreover, the surface area and total pore volume of the films considerably decreased after cross-linking. Overall, these novel films are regarded as promising inexpensive and friendly matrices for food protection and packaging applications.
- Dissolution state of cellulose in aqueous systems. 1. Alkaline solventsPublication . Alves, Luis; Medronho, Bruno; Antunes, Filipe E.; Topgaard, Daniel; Lindman, BjornThe understanding of the state of dissolution of cellulose in a certain solvent is a critical step forward in the development of new efficient solvent systems for cellulose. Nevertheless, obtaining such information is not trivial. Recently, polarization transfer solid-state NMR (PTssNMR) was shown to be a very promising technique regarding an efficient and robust characterization of the solution state of cellulose. In the present study, combining PTssNMR, microscopic techniques and X-ray diffraction, a set of alkaline aqueous systems are investigated. The addition of specific additives, such as urea or thiourea, to aqueous NaOH based systems as well as the use of an amphiphilic organic cation, is found to have pronounced effects on the dissolution efficiency of cellulose. Additionally, the characteristics of the regenerated material are strongly dependent on the dissolution system; typically less crystalline materials, presenting smoother morphologies, are obtained when amphiphilic solvents or additives are used.
- Dissolution state of cellulose in aqueous systems. 2. Acidic solventsPublication . Alves, Luis; Medronho, Bruno; Antunes, Filipe E.; Topgaard, Daniel; Lindman, BjornCellulose is insoluble in water but can be dissolved in strong acidic or alkaline conditions. How well dissolved cellulose is in solution and how it organizes are key questions often neglected in literature. The typical low pH required for dissolving cellulose in acidic solvents limits the use of typical characterization techniques. In this respect, Polarization Transfer Solid State NMR (PT ssNMR) emerges as a reliable alternative. In this work, combining PT ssNMR, microscopic techniques and X-ray diffraction, a set of different acidic systems (phosphoric acid/water, sulfuric acid/glycerol and zinc chloride/water) is investigated. The studied solvent systems are capable to efficiently dissolve cellulose, although degradation occurs to some extent. PT ssNMR is capable to identify the liquid and solid fractions of cellulose, the degradation products and it is also sensitive to gelation. The materials regenerated from the acidic dopes were found to be highly sensitive to the solvent system and to the presence of amphiphilic additives in solution. (C) 2016 Elsevier Ltd. All rights reserved.
- Effect of ethyleneoxide groups of anionic surfactants on lipase activityPublication . Magalhães, Solange S.; Alves, Luis; Sebastião, Marco; Medronho, Bruno; Almeida, Zaida L.; Faria, Tiago Q.; Brito, Rui M. M.; Moreno, Maria J.; Antunes, Filipe E.The use of enzymes in laundry and dish detergent products is growing. Such tendency implies dedicated studies to understand surfactant-enzyme interactions. The interactions between surfactants and enzymes and their impact on the catalytic efficiency represent a central problem and were here evaluated using circular dichroism, dynamic light scattering, and enzyme activity determinations. This work focuses on this key issue by evaluating the role of the ethyleneoxide (EO) groups of anionic surfactants on the structure and activity of a commercial lipase, and by focusing on the protein/surfactant interactions at a molecular level. The conformational changes and enzymatic activity of the protein were evaluated in the presence of sodium dodecyl sulfate (SDS also denoted as SLE0S) and of sodium lauryl ether sulfate with two EO units (SLE2S). The results strongly suggest that the presence of EO units in the surfactant polar headgroup determines the stability and the activity of the enzyme. While SDS promotes enzyme denaturation and consequent loss of activity, SLE2S preserves the enzyme structure and activity. The data further highlights that the electrostatic interactions among the protein groups are changed by the presence of the adsorbed anionic surfactants being such absorption mainly driven by hydrophobic interactions. (c) 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1276-1282, 2016
- From a new cellulose solvent to the cyclodextrin induced formation of hydrogelsPublication . Medronho, Bruno; Duarte, Hugo; Magalhaes, Solange; Alves, Luis; Valente, Artur J. M.; Romano, AnabelaA new efficient solvent for cellulose dissolution was developed based on the mixture of aqueous tetrabutylammonium hydroxide, TBAH(aq) and an organic co-solvent, dimethylsulfoxide (DMSO). Clear cellulose solutions were readily obtained at mild conditions in a few minutes. The viscoeleastic properties of the dopes formed are found to be dependent on the cellulose content and TBAH(aq)/DMSO ratio. Additionally, stiff hydrogels are formed when adding beta-cyclodextrin (beta-CD) to the cellulose dopes. The formation of a host-guest complex between the beta-CD and the tetrabutylammonium cations (TBA(+)), which presumably destabilizes the cellulose solution state triggering the hydrogel formation, is suggested as mechanism. The robust hydrogels formed have been characterized regarding their viscoelasticity, microscopic morphology and release properties. The kinetics and released amount of the TBA(+) from the cellulose gel matrixes are found to be strongly dependent on the balance between average pore diameter, surface area and free volume of the hydrogels. (C) 2017 Elsevier B.V. All rights reserved.
- New deep eutectic solvent assisted extraction of highly pure lignin from maritime pine sawdust (Pinus pinaster Ait.)Publication . Fernandes, Catarina; Melro, Elodie; Magalhaes, Solange; Alves, Luis; Craveiro, Rita; Filipe, Alexandra; Valente, Artur J. M.; Martins, Gabriela; Antunes, Filipe E.; Romano, Anabela; Medronho, BrunoLignocellulosic biomass is a renewable and sustainable feedstock, mainly composed of cellulose, hemicellulose, and lignin. Lignin, as the most abundant natural aromatic polymer occurring on Earth, has great potential to produce value-added products. However, the isolation of highly pure lignin from biomass requires the use of efficient methods during lignocellulose fractionation. Therefore, in this work, novel acidic deep eutectic solvents (DESs) were prepared, characterized and screened for lignin extraction from maritime pine wood (Pinus pinaster Ait.) sawdust. The use of cosolvents and the development of new DES were also evaluated regarding their extraction and selectivity performance. The results show that an 1 h extraction process at 175 ?C, using a novel DES composed of lactic acid, tartaric acid and choline chloride, named Lact:Tart:ChCl, in a molar ratio of 4:1:1, allows the recovery of 95 wt% of the total lignin present in pine biomass with a purity of 89 wt%. Such superior extraction of lignin with remarkable purity using a ?green? solvent system makes this process highly appealing for future large-scale applications. ? 2021 Elsevier B.V. All rights reserved.
- New insights on the role of urea on the dissolution and thermally-induced gelation of cellulose in aqueous alkaliPublication . Alves, Luis; Medronho, Bruno; Filipe, Alexandra; E. Antunes, Filipe; Lindman, Björn; Topgaard, Daniel; Davidovich, Irina; Talmon, YeshayahuThe gelation of cellulose in alkali solutions is quite relevant, but still a poorly understood process. Moreover, the role of certain additives, such as urea, is not consensual among the community. Therefore, in this work, an unusual set of characterization methods for cellulose solutions, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR) and diffusion wave spectroscopy (DWS) were employed to study the role of urea on the dissolution and gelation processes of cellulose in aqueous alkali. Cryo-TEM reveals that the addition of urea generally reduces the presence of undissolved cellulose fibrils in solution. These results are consistent with PTssNMR data, which show the reduction and in some cases the absence of crystalline portions of cellulose in solution, suggesting a pronounced positive effect of the urea on the dissolution efficiency of cellulose. Both conventional mechanical macrorheology and microrheology (DWS) indicate a significant delay of gelation induced by urea, being absent until ca. 60 °C for a system containing 5 wt % cellulose, while a system without urea gels at a lower temperature. For higher cellulose concentrations, the samples containing urea form gels even at room temperature. It is argued that since urea facilitates cellulose dissolution, the high entanglement of the cellulose chains in solution (above the critical concentration, C*) results in a strong three-dimensional network.
- Revisiting the dissolution of cellulose in H3PO4(aq) through cryo-TEM PTssNMR and DWSPublication . Alves, Luis; Medronho, Bruno; Filipe, Alexandra; Romano, Anabela; Rasteiro, Maria G.; Lindman, Bjorn; Topgaard, Daniel; Davidovich, Irina; Talmon, YeshayahuCellulose can be dissolved in concentrated acidic aqueous solvents forming extremely viscous solutions, and, in some cases, liquid crystalline phases. In this work, the concentrated phosphoric acid aqueous solvent is revisited implementing a set of advanced techniques, such as cryo-transmission electronic microscopy (cryo-TEM), polarization transfer solid-state nuclear magnetic resonance (PTssNMR), and diffusing wave spectroscopy (DWS). Cryo-TEM images confirm that this solvent system is capable to efficiently dissolve cellulose. No cellulose particles, fibrils, or aggregates are visible. Conversely, PTssNMR revealed a dominant CP signal at 25 degrees C, characteristic of C-H bond reorientation with correlation time longer than 100 ns and/or order parameter above 0.5, which was ascribed to a transient gel-like network or an anisotropic liquid crystalline phase. Increasing the temperature leads to a gradual transition from CP to INEPT-dominant signal and a loss of birefringence in optical microscopy, suggesting an anisotropic-to-isotropic phase transition. Finally, an excellent agreement between optical microrheology and conventional mechanical rheometry was also obtained.
- The relevance of structural features of cellulose and its interactions to dissolution, regeneration, gelation and plasticization phenomenaPublication . Lindman, Bjorn; Medronho, Bruno; Alves, Luis; Costa, Carolina; Edlund, Hakan; Norgren, MagnusCellulose is the most abundant polymer and a very important renewable resource. Since cellulose cannot be shaped by melting, a major route for its use for novel materials, new chemical compounds and renewable energy must go via the solution state. Investigations during several decades have led to the identification of several solvents of notably different character. The mechanisms of dissolution in terms of intermolecular interactions have been discussed from early work but, even on fundamental aspects, conflicting and opposite views appear. In view of this, strategies for developing new solvent systems for various applications have remained obscure. There is for example a strong need for using forest products for higher value materials and for environmental and cost reasons to use water-based solvents. Several new water-based solvents have been developed recently but there is no consensus regarding the underlying mechanisms. Here we wish to address the most important mechanisms described in the literature and confront them with experimental observations. A broadened view is helpful for improving the current picture and thus cellulose derivatives and phenomena such as fiber dissolution, swelling, regeneration, plasticization and dispersion are considered. In addition to the matter of hydrogen bonding versus hydrophobic interactions, the role of ionization as well as some applications of new knowledge gained are highlighted.
- The role of cyclodextrin-tetrabutylammonium complexation on the cellulose dissolutionPublication . Medronho, Bruno; Duarte, Hugo; Alves, Luis; Antunes, Filipe E.; Romano, Anabela; Valente, Artur J. M.Cellulose dissolution is a challenging process which is typically very sensitive to the solvent characteristics such as pH, temperature or presence of additives. Regarding the later aspect, it is here reported the interaction between cc-cyclodextrin (alpha-CD) and beta-cyclodextrin (beta-CD) with the tetrabutylammonium cation (TBA(+)) by H-1 NMR titration experiments. The analysis by the continuous variation method suggests the formation of 1:1 CD:TBA+ complexes. However, the computed apparent association constants reveal that the interaction of MA+ with the beta-CD (K=1580 M-1) is unexpectedly stronger than with alpha-CD (K=106 M-1). In both CD cases, the formation of CD:TBA(+) complexes decrease the dissolution efficiency of the solvent and this has been rationalized as an effective decrease in the concentration of the amphiphilic cation and concomitant weakening of the hydrophobic interactions in solution influencing the overall performance of the solvent. Additionally, the data also supports the fact that amphiphilic species in solution are beneficial for the enhancement of cellulose solubility. (C) 2015 Elsevier Ltd. All rights reserved.