Rui Ferreira

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.

Exploring fungal activity in the presence of ionic liquids

In this work, the toxicological assessment towards filamentous fungi (Penicillium sp.) as model eukaryotic organisms of sixteen ionic liquids (containing an imidazolium, pyridinium, or cholinium cation) is presented. Amongst these fungi are members which show much higher tolerance towards ionic liquids than any other microorganism so far studied. Furthermore, guided by the paradigm that the choice of an ionic liquid as catalyst can alter the outcome of a given chemical reaction, the ability of ionic liquids to alter the metabolic profile in fungi was studied. The metabolic footprint, as investigated by electrospray ionisation mass spectrometry, revealed that fungal cultures respond to specific ionic liquids by changing their cell biochemistry, resulting in an altered pattern of secondary metabolites.

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 .

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.

Raman spectroscopic study of the vapor phase of 1-methylimidazolium ethanoate, a protic ionic liquid.

The gas phase over the ionic liquid 1-methylimidazolium ethanoate, [Hmim][O(2)CCH(3)], was studied by means of Raman spectroscopy. Raman spectra are presented, the species in the gas phase are identified, and their bands are assigned. The results are interpreted using ab initio quantum mechanical calculations that also predict vibrational spectra. The obtained data reinforce a previous interpretation, based on FT-ICR mass spectrometric data, that the vapor phase over [Hmim][O(2)CCH(3)] consists predominantly of two neutral molecules, monomeric ethanoic acid and 1-methylimidazole.

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.

Solubility of fluorinated compounds in a range of ionic liquids. Cloud-point temperature dependence on composition and pressure

In this work, we explore the mutual solubility of a number of mixtures of commonly used ionic liquids (imidazolium, pyridinium, phosphonium and ammonium ionic liquids) with partially fluorinated n-alcohols (C7 to C10) or perfluoroheptane. The corresponding T–x diagrams at atmospheric pressure were measured through cloud-point temperature determinations. For some selected systems under near-critical isopleth conditions, pressure effects were also studied. The results are discussed in terms of (i) shifts in the immiscibility envelopes as the cation alkyl-chain length is changed, (ii) the nature of the cation or the anion, (iii) the increasing length of the fluorinated/alkylic moiety of the partially fluorinated alcohol, or (iv) comparisons with similar systems involving normal alcohols.

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.

Solvation of Nucleobases in 1,3-Dialkylimidazolium Acetate Ionic Liquids: NMR Spectroscopy Insights into the Dissolution Mechanism

NMR studies of uracil, thymine, and adenine dissolved in 1-ethyl-3-methyl-imidazolium acetate ([C(2)mim][CH(3)COO]) and 1-butyl-3-methyl-imidazolium acetate ([C(4)mim][CH(3)COO]) show that hydrogen bonds (HB) dictate the dissolution mechanism and that both cations and anions participate in the solvation process. For that, the 1,3-dialkylimidazolium acetate ionic liquids (ILs) were considered to be bifunctional solvation ionic liquids. In the solvation of uracil and thymine, the [CH(3)COO](-) anion favors the formation of hydrogen bonds with the hydrogen atoms of the N1-H and N3-H groups of the nucleobases, while the aromatic protons in the bulky cations ([C(2)mim](+) and [C(4)mim](+)), especially the most acidic H2, interact with the oxygen atoms of the carbonyl groups. In the adenine solvation, while the [CH(3)COO](-) anion favors the formation of hydrogen bonds with the hydrogen atoms of the amino and N9-H groups of adenine, the aromatic protons in the bulky cations ([C(2)mim](+) and [C(4)mim](+)), especially the most acidic H2, prefer to interact with the unprotonated nitrogen atoms (N1, N3, and N7) of adenine. It is clearly demonstrated that hydrogen bonding is the major driving force in the dissolution of nucleobases in 1,3-dialkylimidazolium acetate ILs. Our results show that the ionic liquid must be a good hydrogen bond acceptor and a moderate hydrogen bond donor to dissolve nucleic acid bases. To strengthen the evidence of the proposed mechanism, NMR studies in the absence of deuterated cosolvents have been used, because the use of deuterated solvents could seriously hinder the dissolving capability of the IL for nucleobases.