PHYSICAL-PROPERTIES OF INSECT CUTICULAR HYDROCARBONS - THE EFFECTS OFCHAIN-LENGTH, METHYL-BRANCHING AND UNSATURATION

The waterproofing abilities of insect cuticular lipids, consisting mai nly of hydrocarbons, are thought to depend upon their biophysical prop erties. However, little is known regarding the effects of specific str uctural changes upon cuticular lipid properties. We examined the phase behavior of pure hydrocarbons differing in chain length, methyl-branc hing pattern, and unsaturation, using Fourier transform infrared spect roscopy. Melting temperatures (T-m) of 21-40 carbon n-alkanes increase d by 1-3 degrees C for an increase in backbone chain length of one car bon atom. The effects of methyl-branching on hydrocarbon properties de pended upon the location of the methyl group along the molecule. Melti ng temperatures of 25-carbon long methylpentacosanes decreased by over 30 degrees C as the location of the methyl moiety was shifted from th e terminal portion of the molecule to more internal positions. Additio n of a second methyl branch had additional effects on T-m. Unsaturatio n decreased T-m by 50 degrees C or more.