Henri S. Schrekker

Preparation, cation-anion interactions and physicochemical properties of ether-functionalized imidazolium ionic liquids

A set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium ionic liquids 2-4 ([CxOyMIm]+[Anion]- or [CxMIm]+[Anion]-, where MIm = 3-methylimidazolium; CxOy = 1-alkyl ether, C7O3 = -(CH2)2O(CH2)2O(CH2)2OCH3 (A), C3O1 = -(CH2)2OCH3 (B); Cx = 1-alkyl, C10 = C10H21 (C), C4 = C4H9 (D); and [Anion]- = H3CSO3- (2), BF4- (3) or PF6- (4)) was prepared and characterized. The cation-anion hydrogen bonding strength showed to be mainly anion dependent and decreased in the order H3CSO3- > BF4- > PF6-. All methanesulfonate ionic liquids 2 possessed a strongly deshielded H2 imidazolium ring proton. 1-Alkyl ether functionalized ionic liquids showed higher densities in comparison to their 1-alkyl equivalents. The salts 2a-b, 3a-d and 4a-b are room-temperature ionic liquids. All 1-alkyl ether functionalized ionic liquids (except 4b) are completely amorphous. The widest liquid ranges were obtained with the tetrafluoroborate ionic liquids due to their late solidification and excellent thermal stability. These data provide important information for the understanding of their application scope and the preparation of task-specific ionic liquids.

The multifunctional role of ionic liquids in the formation of epoxy-silica nanocomposites

This work addresses the use of ionic liquids (ILs) as additives for formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. The application of different methylimidazolium based ILs allows controlling the silica structure and modifying interphase interaction, thus producing hybrids with diverse morphologies and improved mechanical properties. Both the anionic and cationic components of the ILs affected the hybrid formation and the final properties. The application of 1-decyl-3-methylimidazolium tetrafluoroborate ionic liquid together with HCl as an acid catalyst promotes both hydrolysis and condensation in the sol–gel process as well as the self-assembly ordering of the IL. This system produces a very fine hybrid morphology with well dispersed silica nanodomains and a significantly increased rubbery modulus due to physical crosslinking by the ordered domains of decyl-substituents.

Imidazolium salts as antifungal agents: strong antibiofilm activity against multidrug-resistant Candida tropicalis isolates

The in vitro activity of the imidazolium salt C16MImCl against planktonic and biofilm cells of multidrug‐resistant isolates of Candida tropicalis was evaluated, both in solution and applied on a commercial catheter surface. This was determined by inhibition and susceptibility assays of biofilm and planktonic cells. In both cases, C16MImCl prevented in vitro biofilm formation of C. tropicalis strains, including multidrug‐resistant ones. Outstanding performances were observed, even at extremely low concentrations. Furthermore, this is the first report of the antifungal lock property of C16MImCl, using a tracheal catheter as the test specimen to mimic a clinical in vivo condition. As such, C16MImCl has been identified as a promising antimicotic pharmaceutical candidate for the treatment of candidiasis infections.

Imidazolium Salts as Antifungal Agents: Activity Against Emerging Yeast Pathogens, Without Human Leukocyte Toxicity

This study demonstrates the excellent in vitro antifungal activity profile of imidazolium ionic liquids (ILs) against species of opportunistic human mycoses. Several ILs were identified as more effective and less harmful than commercially available antifungal medications. Frequently, emerging yeast pathogens are resistant against commercial antifungal agents and, as a consequence, this class of imidazolium ILs represents a promising breakthrough in their treatment.

Tunable reinforcement of epoxy-silica nanocomposites with ionic liquids

Imidazolium ionic liquids (ILs) have the capacity to exert multiple functions as additives for the formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. This study addresses the effect of ILs on the reinforcement of tensile properties in rubbery epoxy-silica nanocomposites, allowing property tailoring. The use of ILs together with the coupling agent 3-glycidyloxypropyltrimethoxysilane (GTMS) created a synergic action between physical and chemical interfacial bonding, enabling an increase in toughness without a considerable loss of stiffness. The best tensile property balance was obtained with IL 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate and GTMS. The rubbery nanocomposite produced was remarkably both stiffer and tougher than the unmodified epoxy-silica system, displaying ca. 6 times higher modulus and tensile strength as well as more than 10 times higher energy to break.

Imidazolium salts with antifungal potential against multidrug-resistant dermatophytes.

To investigate the antidermatophytic action of a complementary set imidazolium salts (IMS), determining structure‐activity relationships and characterizing the IMS toxicological profiles.

Epoxy–silica nanocomposite interphase control using task-specific ionic liquids via hydrolytic and non-hydrolytic sol–gel processes

Carboxylic-functionalized task-specific imidazolium ionic liquids (carboxylic-ILs) presented selective high reactivities with epoxy-functionalized compounds, even in highly complex epoxy–silica nanocomposite systems. The carboxylic-ILs induced the in situ covalent bonding with epoxy based materials and tuning of the nanocomposites’ filler–matrix interphase when applied either via hydrolytic or non-hydrolytic sol–gel processes. Structural modifications in the carboxylic-ILs allowed fine morphology control and promoted the formation of well dispersed silica nanodomains. This approach resulted in nanocomposites with improved mechanical properties, without a negative effect on the glass transition temperature, for both rubbery and glassy epoxy–silica nanocomposite systems with a very small IL content (∼0.2 wt%). The best properties were achieved with the application of IL 1-carboxypropyl-3-methylimidazolium chloride, which produced a toughness increase of more than 7 times for the rubbery and almost twice for the glassy epoxy systems, when compared to their IL-free equivalents. These easy and quick procedures to produce imidazolium functionalized materials have the potential to open up a broad range of new conductive, responsive, smart and tunable reinforced materials.

Is the emergence of fungal resistance to medical triazoles related to their use in the agroecosystems? A mini review.

Triazole fungicides are used broadly for the control of infectious diseases of both humans and plants. The surge in resistance to triazoles among pathogenic populations is an emergent issue both in agriculture and medicine. The non-rational use of fungicides with site-specific modes of action, such as the triazoles, may increase the risk of antifungal resistance development. In the medical field, the surge of resistant fungal isolates has been related to the intensive and recurrent therapeutic use of a limited number of triazoles for the treatment and prophylaxis of many mycoses. Similarities in the mode of action of triazole fungicides used in these two fields may lead to cross-resistance, thus expanding the spectrum of resistance to multiple fungicides and contributing to the perpetuation of resistant strains in the environment. The emergence of fungicide-resistant isolates of human pathogens has been related to the exposure to fungicides used in agroecosystems. Examples include species of cosmopolitan occurrence, such as Fusarium and Aspergillus, which cause diseases in both plants and humans. This review summarizes the information about the most important triazole fungicides that are largely used in human clinical therapy and agriculture. We aim to discuss the issues related to fungicide resistance and the recommended strategies for preventing the emergence of triazole-resistant fungal populations capable of spreading across environments.

Ionic liquids as dynamic templating agents for sol-gel silica systems: synergistic anion and cation effect on the silica structured growth

This work presents a detailed investigation about the influence of a complementary set of imidazolium ionic liquids (IL: [C4MIm][BF4]–[C10MIm][BF4]–[C7O3MIm][BF4]–[C4MIm][NTf2]–[C10MIm][NTf2]–[C7O3MIm][NTf2]) in the preparation of hydrolytic sol–gel silica wet gels and xerogels, providing insights into their hierarchical structures, morphologies of primary particles and aggregation domains. The reported IL decreased dramatically the gelation time (up to ~500 times), evolving the systems to transparent or opalescent wet gels with distinct consistencies, or silica powders. Characterization of the obtained silica xerogels was performed by transmission and scanning electron microscopy, atomic force microscopy, X-ray diffraction, small-angle X-ray scattering and thermogravimetric analysis. In general, the IL allowed controlling the silica particle size, color, compactness, structures and morphology. The xerogels showed homogenous and ordered structures (spherical or triangular) of different sizes and with distinct microporosities, depending on the IL applied. These results highlight the key role of IL in the sol–gel silica synthesis with controlled properties, which can be further tuned for specific applications by changing small process parameters.Graphical Abstract

“Unrolling” multi-walled carbon nanotubes with ionic liquids: application as fillers in epoxy-based nanocomposites

This work describes a straightforward procedure for the preparation of graphene by opening multi-walled carbon nanotubes (CNT), using ionic liquids (IL) as lubricating and stabilizing agents. The sequential application of vacuum and sonication allows the successful opening and unrolling of the CNT, and the final nanocarbon morphology is IL-dependent. This enabled the preparation of epoxy-based nanocomposites with morphologically distinct carbon nanofillers. The CNT–IL mixtures and nanocomposites obtained were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy.