The great stability of keratin results from the numerous disulfide bonds of cystine.
The formation of permanent waves in the beauty treatment of hair is based on partial reduction of the disulfide bonds of hair keratin by thioglycol, or some other mild reducing agent, and subsequent oxidation of the sulfhydryl groups (−SH) in the reoriented hair to disulfide bonds (−S−S−) by exposure to the oxygen of the air.
In proteins rich in cystine, the conformation of the peptide chain is determined to a considerable extent by the disulfide bonds (−S−S−) of cystine.
Similar interchain disulfide bonds have been found in the immunoglobulins.
For molybdenum the chief ore is molybdenite molybdenum disulfide, MoS2 but molybdates such as lead molybdate, PbMoO4 (wulfenite), and MgMoO4 are also found.
Molybdenum disulfide (MoS2), which resembles graphite, is used as a solid lubricant or as an additive to greases and oils.
In 1892 English chemists Charles F. Cross and Edward J. Bevan patented viscose, a solution of cellulose treated with caustic soda and carbon disulfide.
There are three general kinds of inorganic compounds that serve as solid lubricants: 1. Layer-lattice solids: materials such as graphite and molybdenum disulfide, commonly called molysulfide, have a crystal lattice structure arranged in layers.
Some important examples are galena (lead sulfide, PbS), blende (zinc sulfide, ZnS), pyrite (iron disulfide, FeS2), chalcopyrite (copper iron sulfide, CuFeS2), gypsum (calcium sulfate dihydrate, CaSO4∙2H2O) and barite (barium sulfate, BaSO4).
Commercially available systems of this type include lithium cobalt oxide, lithium nickel oxide, lithium manganese dioxide, and lithium molybdenum disulfide.
Examples of hazards identified in this manner include lung and nasal cancer among nickel workers, lung cancer in asbestos workers, and coronary heart disease among workers exposed to carbon disulfide (used in the manufacture of rayon).
