Phosphonium-based ionic liquids as antifungal agents for conservation of heritage sandstone

With a view to preventing fungal deterioration of historical stone artworks, we report the use of phosphonium-based ionic liquids (ILs) as potent antifungal agents against dematiaceous fungi commonly found on heritage stones. Three ILs: tributyldodecylphosphonium polyoxometalate [P-44412][POM], tributyltetradecylphosphonium polyoxometalate [P-44414][POM], and trihexyltetradecylphosphonium polyoxometalate [P-66614][POM] were prepared and their thermal stabilities and in vitro antifungal activities were evaluated. From the ramped temperature thermogravimetric analysis and antifungal experiments it can be clearly observed that the alkyl chain length of the tetraalkylphosponium cation has a significant influence on the thermal and antifungal properties. The thermal stability and antifungal activity decreased as the number of carbon atoms of the alkyl substituents increased and, thus, followed the order [P-44412][POM] > [P-44414][POM] > [P-66614][POM]. In addition, inoculation of four fungal species on IL-coated sandstone surfaces showed significant inhibition of fungal growth, endowing the materials with potential applications in heritage sandstone conservation.

Automated summary

In order to prevent fungal deterioration of historical stone artworks, phosphonium-based ionic liquids (ILs) were used as potent antifungal agents against dematiaceous fungi commonly found on heritage stones. The study found that the alkyl chain length of the tetraalkylphosponium cation had a significant influence on the thermal stability and antifungal activity of the ILs. Additionally, the ILs showed significant inhibition of fungal growth on sandstone surfaces, indicating their potential applications in heritage sandstone conservation.