Thiols
Thiol and Disulfide conversion
Two thiols can react together under a mild oxidation, lose two hydrogen atoms, and form a disulfide linkage. If a reaction occurs and two hydrogen atoms are added to the disulfide in a reduction, the two thiols can once again be made.
This is an important biochemical reaction. Proteins are made up of many amino acids. Cysteine is one of these amino acids. It contains a thiol group.
To hold proteins in their folded shapes, the cysteine thiols often link up to form disulfide bridges. If a chemist wants to reduce the disulfides of a protein, to have it relax and lose its folded shape, a reducing agent must be used. The reducing agents we have used in the past (NaBH4 and LAH) are usually not very effective at performing the reduction of disulfides. Instead, biochemists usually reduce disulfides in proteins by adding DTT, dithiothreitol, to their buffer solutions. A biochemist does this to keep proteins unfolded – perhaps to measure their size in gel electrophoresis.
Human hair is a protein. The cysteines make disulfide linkages in the hair protein, which helps give your hair its structure- whether it is curly or straight. A process to make hair curly is called a hair permanent, or perm. In a perm, a mild reducing agent, usually sodium thioglycolate, is places on the hair, causing the disulfide linkages to break and become thiols. The hair protein is then wrapped around curlers followed by the application of a mild oxidizer, usually hydrogen peroxide, to reform the disulfide linkages. The disulfide linkages help hold the hair in its new configuration, making it curlier. The same process can be used to straighten hair.
A mild oxidizer forms disulfide linkages from thiols, but a strong oxidizer like nitric acid or KMnO4 forms sulfonic acids.
Sulfonic acids do not stink like thiols. One home remedy for being sprayed by a skunk is to use hydrogen peroxide in a mixture of soap and baking soda to try to oxidize the thiols to sulfonic acids so there is less of an odor. Let’s be clear, it would not be a good idea to spray nitric acid on a skunk sprayed victim. It might reduce the smell but would do terrible damage to their skin.