• Ice Nucleation Activity of Perfluorinated Organic Acids.

      Schwidetzky, Ralph; Sun, Yuling; Fröhlich-Nowoisky, Janine; Kunert, Anna T; Bonn, Mischa; Meister, Konrad (ACS Publications, 2021-03-31)
      Perfluorinated acids (PFAs) are widely used synthetic chemical compounds, highly resistant to environmental degradation. The widespread PFA contamination in remote regions such as the High Arctic implies currently not understood long-range atmospheric transport pathways. Here, we report that perfluorooctanoic acid (PFOA) initiates heterogeneous ice nucleation at temperatures as high as −16 °C. In contrast, the eight-carbon octanoic acid, perfluorooctanesulfonic acid, and deprotonated PFOA showed poor ice nucleating capabilities. The ice nucleation ability of PFOA correlates with the formation of a PFOA monolayer at the air−water interface, suggesting a mechanism in which the aligned hydroxyl groups of the carboxylic acid moieties provide a lattice matching to ice. The ice nucleation capabilities of fluorinated compounds like PFOA might be relevant for cloud glaciation in the atmosphere and the removal of these persistent pollutants by wet deposition.
    • Ice Recrystallization Inhibition Is Insufficient to Explain Cryopreservation Abilities of Antifreeze Proteins

      Sun, Yuling; Maltseva, Daria; Liu, Jie; Hooker II, Theordore; Mailänder, Volker; Ramløv, Hans; DeVries, Arthur, L.; Bonn, Mischa; Meister, Konrad (American Chemical Society, 2022-01-26)
      Antifreeze proteins (AFPs) and glycoproteins (AFGPs) are exemplary at modifying ice crystal growth and at inhibiting ice recrystallization (IRI) in frozen solutions. These properties make them highly attractive for cold storage and cryopreservation applications of biological tissue, food, and other water-based materials. The specific requirements for optimal cryostorage remain unknown, but high IRI activity has been proposed to be crucial. Here, we show that high IRI activity alone is insufficient to explain the beneficial effects of AF(G)Ps on human red blood cell (hRBC) survival. We show that AF(G)Ps with different IRI activities cause similar cell recoveries of hRBCs and that a modified AFGP variant with decreased IRI activity shows increased cell recovery. The AFGP variant was found to have enhanced interactions with a hRBC model membrane, indicating that the capability to stabilize cell membranes is another important factor for increasing the survival of cells after cryostorage. This information should be considered when designing novel synthetic cryoprotectants.
    • Toward Understanding Bacterial Ice Nucleation

      Lukas, Max; Schwidetzky, Ralph; Eufemio, Rosemary J.; Bonn, Mischa; Meister, Konrad (American Chemical Society, 2022-01-27)
      Bacterial ice nucleators (INs) are among the most effective ice nucleators known and are relevant for freezing processes in agriculture, the atmosphere, and the biosphere. Their ability to facilitate ice formation is due to specialized ice-nucleating proteins (INPs) anchored to the outer bacterial cell membrane, enabling the crystallization of water at temperatures up to −2 °C. In this Perspective, we highlight the importance of functional aggregation of INPs for the exceptionally high ice nucleation activity of bacterial ice nucleators. We emphasize that the bacterial cell membrane, as well as environmental conditions, is crucial for a precise functional INP aggregation. Interdisciplinary approaches combining high-throughput droplet freezing assays with advanced physicochemical tools and protein biochemistry are needed to link changes in protein structure or protein–water interactions with changes on the functional level.