-ine is a suffix used in chemistry to denote two kinds of substance. The first is a chemically basic and alkaloidal substance. It was proposed by Joseph Louis Gay-Lussac in an editorial accompanying a paper by Friedrich Sertürner describing the isolation of the alkaloid "morphium", which was subsequently renamed to "morphine". Examples include quinine, morphine and guanidine. The second usage is to denote a hydrocarbon of the second degree of unsaturation. Examples include hexine and heptine. With simple hydrocarbons, this usage is identical to the IUPAC suffix -yne.
The suffix is usually pronounced either /iːn/ or /ɪn/ depending on the word it appears in and the accent of the speaker. In a few words (for example, quinine and strychnine), the /aɪn/ sound is normal in some accents. Gasoline ends with /iːn/; glycerine more often with /ɪn/ than with /iːn/.
The suffix -in (/ɪn/) is etymologically related and overlaps in usage with -ine. Many proteins and lipids have names ending with -in: for example, the enzymes pepsin and trypsin, the hormones insulin and gastrin, and the lipids stearin (stearine) and olein.