|
Studies of the
Photochemical Properties of HIDD
Harper, Willa1
and Gaillard, Elizabeth1
Northern Illinois University1
Abstract-
A derivative of all-trans-retinal and ethanolamine, A2-E, is
the main fluorescent component of human lipofuscin. The accumulation
of lipofuscin has been correlated with exposure to ambient radiation
and loss of photoreceptors. A possible precursor to A2-E is the imine
formed from all-trans-retinal and ethanolamine. This compound,
(E,E,E,E)-2-[9-(2-hydroxyethyl)imino-3,7-dimethyl-1,3,5,7-decatrien-1-yl]-1,3,3-trimethylcyclohexene
(HIDD), has been synthesized and structurally characterized. The photophysical
and photochemical properties of HIDD (both the protonated and unprotonated
forms) have been investigated using steady state and time resolved methods.
Both HIDD and protonated HIDD are weakly fluorescent. HIDD forms a triplet
excited state upon direct excitation that decays with a decay rate constant
of 3.0 x 104 s-1. Intersystem crossing for the
protonated form is not observed under our experimental conditions, but
the triplet excited state can be sensitized with naphthalene and anthracene
and has a decay rate constant of 1.6 x 104 s-1.
The lifetime of the HIDD triplet excited state is observed to decrease
with increasing concentration of the well known hydrogen atom donors,
trimethylhydroquinone (TMHQ) and methylhydroquinone (MHQ), and the bimolecular
rate constants for these reactions are approximately 8.8 x 107
M-1s-1 and 6.7 x 107 M-1s-1,
respectively. These types of reactions may model photooxidative mechanisms
of damage in the retina.
Keywords: all-trans-retinal,
ethanolamine, age related macular degeneration, photooxidative damage
|
