The study investigates the interactions of cyclic hydrocarbons with biological membranes, focusing on their toxic effects on microorganisms. The primary site of toxicity is likely the cytoplasmic membrane, but the exact mechanism is not well understood. The researchers used liposomes prepared from Escherichia coli phospholipids to study the effects of various cyclic hydrocarbons. They found that these lipophilic compounds preferentially accumulate in the membrane, leading to membrane swelling and increased fluidity. This accumulation results in an increased passive flux of protons and carboxyfluorescein, which dissipates the proton motive force and electrical potential generated by cytochrome c oxidase. The toxicity of the hydrocarbons is correlated with their partition coefficients between the membrane and aqueous phase, suggesting that hydrophobic interaction with the membrane is the primary cause of microbial impairment. The study also highlights the importance of understanding the structural and functional changes in membranes caused by hydrocarbons, which can inform the toxicity of other lipophilic compounds.The study investigates the interactions of cyclic hydrocarbons with biological membranes, focusing on their toxic effects on microorganisms. The primary site of toxicity is likely the cytoplasmic membrane, but the exact mechanism is not well understood. The researchers used liposomes prepared from Escherichia coli phospholipids to study the effects of various cyclic hydrocarbons. They found that these lipophilic compounds preferentially accumulate in the membrane, leading to membrane swelling and increased fluidity. This accumulation results in an increased passive flux of protons and carboxyfluorescein, which dissipates the proton motive force and electrical potential generated by cytochrome c oxidase. The toxicity of the hydrocarbons is correlated with their partition coefficients between the membrane and aqueous phase, suggesting that hydrophobic interaction with the membrane is the primary cause of microbial impairment. The study also highlights the importance of understanding the structural and functional changes in membranes caused by hydrocarbons, which can inform the toxicity of other lipophilic compounds.