Fig 1.
Process scheme of the paper reinforcement method.
Process as described by Krupp et al. [18] and based on Maier [5]. Cellulose fibers are solubilized in IL (green triangles) and DMSO (orange circles) as co-solvent (left). Upon solvent exchange with HMDSO (blue circles; arrows indicate solvent replacement), cellulose fibers precipitate at cellulosic surfaces, thereby adding mechanical strength to the cellulosic documents while incorporating IL molecules (and other co-solvents).
Fig 2.
Chemical structures of known antifungals and ILs.
Clotrimazole (a) and Miconazole (b) as known antifungals with polar protic imidazolium groups (blue) and a rather nonpolar, (derivatized) aliphatic molecule region (green) causing overall asymmetrical molecule properties. Ionic liquids tested for antifungal activity in this study were: 1-butyl-3-methylimidazolium with (c) chloride (BC) and (d) acetate (BA) as counter ions as well as (e) 1-allyl-3-methylimidazolium-chloride (AC) and (f) 1-hexyl-3-methylimidazolium-chloride (HC). All four ILs contain an aprotic imidazolium group (blue) as well as nonpolar tails (green) varying in size and hydrophobicity.
Fig 3.
Principal investigation and comparison of antifungal IL activity.
(a) shows the exemplary result of the initial antifungal activity screening of all tested ILs including DMSO as a negative and Clotrimazole as a positive control on densely inoculated MM-CMC plates for P. glabrum, spotted following scheme (b), after seven days of incubation. c) and d) demonstrate the molar potency comparisons of the four ILs, using P. glabrum spot dilution series of HC (c) and the halo radius plot for all four ILs (d) as representative data for all tested fungi. e) MIC and MGIC concentration analysis in the microtiter scale growth assay for P. glabrum and for the most susceptible fungal strain in this study, T. capillare (f).
Fig 4.
Fungal growth tests on IL-treated paper samples.
T. capillare spores inoculated on BA-treated (right) or untreated (left) paper and incubated on water agar (a) or under saturated humidity conditions in a high humidity chamber (b) did not show growth impairment or inhibition effects after paper treatment.