Cristina Silva Pereira

Novel biocompatible cholinium-based ionic liquids—toxicity and biodegradability†

The synthesis, characterisation and toxicological assessment of a new group of environmentally friendly ionic liquids are presented. Focussing on the toxic effect of the anion, the ionic liquids were designed by combining the benign cholinium cation, [NMe3(CH2CH2OH)]+, with a range of linear alkanoate anions ([CnH2n+1CO2]−, n = 1-9), as well as two structural isomers (n = 3 or 4). The toxicity of these ionic liquids was evaluated using filamentous fungi as model eukaryotic organisms. Surprisingly, most of the tested species showed active growth in media containing extremely high ionic liquid concentrations, up to molar ranges in some cases. The biodegradability of these ionic liquids was assessed, and new biotechnological applications for them are proposed, e.g. as solvents for biopolymers. This study leads to the better understanding of the anion influence on the ionic liquid toxicity, but its core is the recognition that conscious design of ionic liquids can be used to deliver truly biocompatible salts without adversely affecting one of the most striking of their properties—their outstanding solvent ability.

Dissolution of cork biopolymers in biocompatible ionic liquids

Classically, the best attempts to separate suberin from cork biopolymers have resulted in low efficiency; here, we report a class of biocompatible and biodegradable cholinium-based ionic liquids, the cholinium alkanoates, which show a highly efficient and specific dissolution of the suberin domains from cork biopolymers.

Impact of ionic liquids on extreme microbial biotypes from soil

This work aims at identifying, amongst extreme soil biotypes at locations of high salinity and high hydrocarbon load, microbial strains able to survive short or long-term exposure to the presence of selected ionic liquids. We have evaluated the impact of ionic liquids on the diversity of the soil microbiota to identify which microbial strains have higher survival rates towards ionic liquids, and consequently those which might possibly play a major role in their biotic fate. To the best of our knowledge, this is the first study of this kind. Soils, from a region in Portugal (Aveiro) were sampled and the bacterial and fungal strains able to survive after exposure to high concentrations of selected ionic liquids were isolated and further characterised. We have mainly focused on two types of cations: imidazolium – the most commonly used; and cholinium – generally perceived as benign. The surviving microbial strains were isolated and taxonomically identified, and the ionic liquid degradation was analysed during their cultivation. The continuing exposure of the microbial strains to petroleum hydrocarbons is likely to be the basis for their acquired resistance to some imidazolium salts; also, the higher capacity of fungi – compared to bacteria – to grow, even during their exposure to these liquid salts, became evident in this study.

Cholinium-based Supported Ionic Liquid Membranes: A Sustainable Route for Carbon Dioxide Separation

Aiming at full sustainability of CO2 separation processes, a series of supported ionic liquid membranes based on environmentally friendly cholinium carboxylate ionic liquids were successfully prepared. Their gas permeation properties were measured and high permselectivities were obtained for both CO2 /CH4 and CO2 /N2 .

Unravelling the mechanism of toxicity of alkyltributylphosphonium chlorides in Aspergillus nidulans conidia

The mechanism of toxicity of alkyltributylphosphonium chlorides [P4 4 4 n]Cl (n = 1, 3–8, 10, 12 or 14) in conidia of the filamentous fungus Aspergillus nidulans is reported. Systematic elongation of one of the alkyl substituents resulted generally in higher toxicity, as defined by their inhibitory and lethal effects. In this study, fluorescence microscopy is proposed as a direct method for assessing the impact of ionic liquids on the plasma membrane integrity. Data were complemented by microscopic evaluation of the conidia cell wall and morphology. The higher toxicity of phosphonium ionic liquids carrying long alkyl substituents is most likely due to their strong interaction with the conidia cellular boundaries.

Suberin isolation from cork using ionic liquids: characterisation of ensuing products

Cholinium alkanoates, a class of benign ionic liquids, were demonstrated to efficiently extract suberin domains from cork. A detailed characterisation of the extracted material has yet to be attained. In the present study the significance of the alkylic chain length of the anion and the ionic liquids basicity was investigated. The results obtained emphasise cholinium hexanoates selection; it proved to be a straightforward process, also ensuring the recyclability and reusability of the ionic liquid. The extracted suberinic material has been thoroughly characterised for the first time by ATR-FTIR, NMR, GC-MS and thermal analyses. Data showed that it is mainly composed of oligomeric or polymeric aliphatic esterified structures, resulting from suberin partial cleavage. More than 40 wt% of the extracted suberinic material was found to be cross-linked. Even though, the composing monomeric units were similar to those usually identified in suberin samples obtained by the conventional extraction processes. These data pave the way for advanced studies of suberin monomers/oligomers as building-blocks for the development of novel biopolymers and biomaterials.

Screening pentachlorophenol degradation ability by environmental fungal strains belonging to the phyla Ascomycota and Zygomycota

Pentachlorophenol (PCP) bioremediation by the fungal strains amongst the cork-colonising community has not yet been analysed. In this paper, the co- and direct metabolism of PCP by each of the 17 fungal species selected from this community were studied. Using hierarchical data analysis, the isolates were ranked by their PCP bioremediation potential. Fifteen isolates were able to degrade PCP under co-metabolic conditions, and surprisingly Chrysonilia sitophila, Trichoderma longibrachiatum, Mucor plumbeus, Penicillium janczewskii and P. glandicola were able to directly metabolise PCP, leading to its complete depletion from media. PCP degradation intermediates are preliminarily discussed. Data emphasise the significance of these fungi to have an interesting potential to be used in PCP bioremediation processes.

Ex Situ Reconstitution of the Plant Biopolyester Suberin as a Film

Biopolymers often have unique properties of considerable interest as a basis for new materials. It is however not evident how to extract them from plants without destroying their chemical skeleton and inherent properties. Here we report the ex situ reconstitution of the biopolyester suberin as a new waterproof and antimicrobial material. In plant cell walls, suberin, a cross-linked network of aromatic and aliphatic monomers, builds up a hydrophobic protective and antimicrobial barrier. Recently we succeeded in extracting suberin from the plant cell wall using the ionic liquid cholinium hexanoate. During extraction the native three-dimensional structure of suberin was partially preserved. In this study, we demonstrate that this preservation is the key for its ex situ reconstitution. Without any chemical additives or purification, the suberin composing macromolecules undergo self-association on the casting surface forming a film. Suberin films obtained show barrier properties similar to those of the suberin barrier in plants, including a potentially broad bactericidal effect.

Unveiling the dual role of the cholinium hexanoate ionic liquid as solvent and catalyst in suberin depolymerisation

Disruption of the three-dimensional network of suberin in cork by cholinium hexanoate leads to its efficient and selective isolation. The reaction mechanism, which likely involves selective cleavage of some inter-monomeric bonds in suberin, was still unanswered. To address this question, the role of the ionic liquid during suberin depolymerisation and during cleavage of standard compounds carrying key chemical functionalities was herein investigated. A clear demonstration that the ionic liquid catalyses the hydrolysis of acylglycerol ester bonds was attained herein, both experimentally and computationally (DFT calculations). This behaviour is related to cholinium hexanoate capacity to activate the nucleophilic attack of water. The data showed also that the most favourable reaction is the hydrolysis of acylglycerol ester bonds, with the C2 position reporting the faster kinetics, whilst most of the linear aliphatic esters remained intact. The study emphasises that the ionic liquid plays the dual role of solvent and catalyst and leads to suberin efficient extraction through a mild depolymerisation. It is also one of the few reports of ionic liquids as efficient catalysts in the hydrolysis of esters.

Degradation pathway of pentachlorophenol by Mucor plumbeus involves phase II conjugation and oxidation–reduction reactions

Environmental pollution by pentachlorophenol (PCP) is a critical concern worldwide and fungal bioremediation constitutes an elegant and environment-friendly solution. Mucorales from the Zygomycota phylum are often observed to be competitive in field conditions and Mucor plumbeus, in particular, can efficiently deplete PCP from media. The pathway for PCP degradation used by this fungus has not been investigated. In this study, PCP-derived metabolites were identified by liquid chromatography coupled with quadrupole time-of-flight mass spectrometry, including tetra- and tri-chlorohydroquinones and phase II-conjugated metabolites. Amongst the latter are the previously reported glucose, sulfate and ribose conjugates, and identified for the first time in fungi sulfate-glucose conjugates. A PCP transformation pathway for M. plumbeus is proposed, which excludes the involvement of cytochrome P-450 and extracellular ligninolytic enzymes.