title: Absolute configurational determination of an all-trans-retinal dimer isolated from photoreceptor outer segments.
abstract: An all-trans-retinal (ATR) dimer (1) isolated from photoreceptor outer segments was found to have a stereogenic center at C13' flanked by tetraene (295 nm) and hexaenal (438 nm) chromophores. Analytical chiral HPLC (Chiralcel OD) revealed that the isolated retinoid had formed in 13% enantiomeric excess. Using a combination of (1)H-(1)H NOESY constraints, molecular modeling, and CD exciton coupling analysis, it was determined that the favored enantiomer was 13'(R). Three low-energy conformers of the 13'(S) model were found with MMFF/DFT and were used to calculate the CD spectrum of the ATR dimer (DeVoe method). The Boltzmann weighted spectrum was found to exhibit a positive exciton couplet, in excellent agreement with the experimental spectrum for the first eluted enantiomer. This further suggested that despite the large energy difference between the two interacting chromophores, the dominant source of optical activity in the CD spectrum is the nondegenerate exciton mechanism.
authors.affiliation: Department of Chemistry, Columbia University, New York, NY 10027, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Fishkin
authors.forename: Gennaro
authors.initials: G
authors.lastname: Pescitelli
authors.forename: Janet R
authors.initials: JR
authors.lastname: Sparrow
authors.forename: Koji
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Nina
authors.initials: N
authors.lastname: Berova
mesh_terms: D019295:Computational Biology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry*; D012172:Retinaldehyde / Q000737:chemistry*; D012374:Rod Cell Outer Segment / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D012172:Retinaldehyde