Sulfolane desolvation by garlic sulfoxides: Potential link to plant survival upon uptake

Abstract

Previous studies report a positive correlation between contaminant hydrophobicity and accumulation in plants. We show that sulfoxides present in garlic, such as alliin, methiin and propiin, phase-separate (i.e., de-solvate, demix) sulfolane from aqueous solutions, as shown by optical microscopy during in vitro experiments conducted using garlic extracts. Sulfolane is a contaminant freely miscible in pure water. However, water interacts more strongly with the sulfoxides alliin, methiin and propiin than with sulfolane, as we demonstrated by computer simulations. This explains why garlic sulfoxides desolvate sulfolane, causing it to behave as a hydrophobic solvent. Garlic uptakes 10.5 ± 0.77 wt% sulfolane relative to water in its cloves from solutions prepared with 10 wt% sulfolane, during a two-week period at 18.5–19.5⁰C, as seen by Fourier transform infrared spectro-microscopy conducted on dissected garlic cloves. Under these conditions, it displays signs of stress and its shoots wilted, but it could nonetheless survive. In contrast, onion plants died. The algae Chlorella vulgaris and Raphidocelis subcapitata also died. They do not contain the sulfoxides found in garlic and did not phase-separate sulfolane from water.