Cyclic hydrocarbons, such as aromatics, alicyclics, and terpenes, interact with biological membranes, leading to structural and functional changes that impair microbial activity. These compounds are toxic to microorganisms, primarily affecting the cytoplasmic membrane. The study investigated the effects of cyclic hydrocarbons on liposomes made from Escherichia coli phospholipids. The partition coefficients of these compounds in the membrane and aqueous phase were determined, showing a strong correlation with their octanol-water partition coefficients. The accumulation of hydrocarbons in the membrane caused swelling and increased fluidity, leading to increased proton and carboxyfluorescein flux. In proteoliposomes containing cytochrome c oxidase, both components of the proton motive force (pH gradient and electrical potential) were dissipated, primarily due to increased proton permeability. The toxicity of cyclic hydrocarbons is closely related to their partitioning into the membrane, with higher partition coefficients correlating with greater toxicity. The study also showed that the effects of cyclic hydrocarbons on membrane integrity and function are directly related to their accumulation in the membrane, independent of their molecular structure. The results highlight the importance of understanding the interaction of cyclic hydrocarbons with biological membranes for assessing their toxicity and metabolism. The findings suggest that hydrophobic interactions with the membrane disrupt its function and the activity of membrane-embedded proteins, leading to microbial inhibition. The study provides a rationale for the observed correlation between the toxicity of lipophilic compounds to microorganisms and their partition coefficients in a standard octanol-water system.Cyclic hydrocarbons, such as aromatics, alicyclics, and terpenes, interact with biological membranes, leading to structural and functional changes that impair microbial activity. These compounds are toxic to microorganisms, primarily affecting the cytoplasmic membrane. The study investigated the effects of cyclic hydrocarbons on liposomes made from Escherichia coli phospholipids. The partition coefficients of these compounds in the membrane and aqueous phase were determined, showing a strong correlation with their octanol-water partition coefficients. The accumulation of hydrocarbons in the membrane caused swelling and increased fluidity, leading to increased proton and carboxyfluorescein flux. In proteoliposomes containing cytochrome c oxidase, both components of the proton motive force (pH gradient and electrical potential) were dissipated, primarily due to increased proton permeability. The toxicity of cyclic hydrocarbons is closely related to their partitioning into the membrane, with higher partition coefficients correlating with greater toxicity. The study also showed that the effects of cyclic hydrocarbons on membrane integrity and function are directly related to their accumulation in the membrane, independent of their molecular structure. The results highlight the importance of understanding the interaction of cyclic hydrocarbons with biological membranes for assessing their toxicity and metabolism. The findings suggest that hydrophobic interactions with the membrane disrupt its function and the activity of membrane-embedded proteins, leading to microbial inhibition. The study provides a rationale for the observed correlation between the toxicity of lipophilic compounds to microorganisms and their partition coefficients in a standard octanol-water system.