Characterization of HETEs and related conjugated dienes by UV spectroscopy

Three distinct pairs of HETEs can be distinguished on the basis of their UV spectra. We used hydroxy-linoleates (hydroxy-octadeca-cis-trans-dienoates) as a base for comparisons; both the 9- and 13-hydroxy isomers have identical chromophores with lambda max near 234 nm. The presence of a double bond three carbons removed from the conjugated diene (the chromophore of 9- and 11-HETE) causes a shift in the observed lambda max to near 235 nm. A double bond beta to the chromophore (5- and 15-HETE) gives a further shift of 1.5 nm, giving a lambda max between 236-236.5 nm. With double bonds in both these positions (8- and 12-HETE), the lambda max is observed near 237 nm. It is apparent that the exact lambda max of the cis-trans diene chromophore is influenced in a consistent way by the adjacent methylene interrupted cis double bonds.