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 λ 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 λ max to near 235 nm. A double bond β to the chromophore (5‐ and 15‐HETE) gives a further shift of 1.5 nm, giving a λ max between 236–236.5 nm. With double bonds in both these positions (8‐ and 12‐HETE), the λ max is observed near 237 nm. It is apparent that the exact λ max of the cis‐trans diene chromophore is influenced in a consistent way by the adjacent methylene interrupted cis double bonds.