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Phenol as a Slimicide

Phenol is a Bronsted-Lowry acid; a saturated solution of phenol in water has a pH of about 5.5. A mildly acidic solution. The saturation concentration of phenol in water is around 84g per litre; pretty soluble.

Phenol is lipophilic (both hydrophilic and hydrophobic). The hydrophilic-lipophilic balance (HLB) value of phenol in water is 9.95, meaning it’s an effective oil-in-water emulsifier.

Actually, looking at it, it’s likely more of a co-surfactant. It’s unlikely to form micelles by itself, for example. That’s me being a molecular psychologist, in case you’re wondering. You can’t do this unless you understand both the kinetics and thermodynamics of both reactive and passive multiphase chemical systems.

The lipophilic property of phenol allows it to pass through cell membranes, which are themselves lipophilic in nature, and then into the cell interiors, where it can “denature” proteins, ultimately leading to cell death and necrosis.

Usually the polar components of a protein are on the outside of the protein, which makes the protein soluble in water. [This is my guess here] Phenol, being a small (in molecular volume) surfactant and quite soluble in water, easily gets to and then into the protein volume and causes “folding changes” by solubilising the more hydrophobic components of the protein and desolubilising the more hydrophilic components.

The smart person asks why typical cell membrane surfactants (e.g. phospholipids) don’t also have this effect on proteins. My gut feeling is that they’re just a lot bigger than phenol and less soluble in water, and can’t get to and into the protein volume as readily. The cell structure evolved just so.

The amino acid sequence of a protein determines its 3D structure. A protein’s function depends on its shape, and when protein structure goes awry, the resulting misshapen proteins cause problems that range from bad, when proteins neglect their important work, to ugly, when they form a sticky, clumpy mess inside of cells. That is, proteins have to be in their correct native structure in order to function properly. Incorrect structure (folding) produces inactive or toxic proteins that malfunction.

I write this because bio types don’t understand physical chemistry and they haven’t and can’t put this into simple-to-understand terminology. I know because I looked.

You can thank me later.