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1 September 2003 A Photochemical Study of (E,E,E,E)-2-[9-(2-Hydroxyethyl)imino-3,7-dimethyl-1,3,5,7-decatrien-1-yl]-1,3,3-trimethylcyclohexene, a Derivative of all-trans-retinal and Ethanolamine
Willa S. Harper, Elizabeth R. Gaillard
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A derivative of all-trans-retinal (RAL) and ethanolamine, A2-E, is the main fluorescent component of human retinal 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 RAL 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 and its protonated form, HIDD-H , have been investigated using steady-state and time-resolved methods. Both HIDD and HIDD-H are weakly fluorescent, and the fluorescence lifetime and quantum yield for HIDD are ca 0.6 ns and 4.0 ± 0.5 × 10–4, respectively. HIDD forms a triplet excited state on direct excitation that decays with kd = 3.4 × 104 s–1. The extinction coefficient and quantum yield of intersystem crossing for the HIDD triplet are measured as 7.6 ± 1.3 × 104 M–1cm–1 and 0.055 ± 0.006, respectively. The triplet excited state of HIDD-H can be sensitized by triplet energy transfer and has a decay rate constant of 1.6 × 104 s–1. The lifetime of the HIDD triplet excited state is observed to decrease with increasing concentration of the well-known electron or hydrogen atom donors, 2,3,5,6-tetramethyl-1,4-phenylenediamine and 2,3,5-trimethylhydroquinone, and the bimolecular rate constants for these reactions are approximately 5.4 × 106 M–1s–1 and 1.7 × 108 M–1s–1, respectively. These types of reactions may model photooxidative mechanisms of damage in the retina.

Willa S. Harper and Elizabeth R. Gaillard "A Photochemical Study of (E,E,E,E)-2-[9-(2-Hydroxyethyl)imino-3,7-dimethyl-1,3,5,7-decatrien-1-yl]-1,3,3-trimethylcyclohexene, a Derivative of all-trans-retinal and Ethanolamine," Photochemistry and Photobiology 78(3), 298-305, (1 September 2003).<0298:APSOEA>2.0.CO;2
Received: 2 April 2003; Accepted: 1 June 2003; Published: 1 September 2003

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