AbstractsChemistry

At head of first title: "Part 1"; at head of second title: "Part 2." Title of second work on added title page: Preparation and properties of a series of lower homologs of β-carotene. "December 1995." Typescript. Microfiche. 167 leaves ill. 28 cm Part I: A new synthetic route, starting from 3-hydroxy-B-ionone, was developed for the synthesis of hindered 7-cis isomers of 3-dehydroretinal which led to six 7-cis isomers of 3dehydroretinal and four 7-cis isomers of 3-hydroxyretinal. The structures of these isomers were characterized with UV-Vis and 1H-NMR. HyperChem program was used to calculate structural data such as dihedral angels, charge density, total energy of the 3-dehydroretinal isomers and synthetic intermediates to account for the observed UV properties and photochemistry. The 7-cis isomers were found to have a C5-C6-C7-C8 dihedral angel in the range of 60 -70° while the 7-trans isomers have the corresponding dihedral angles in the range of 40-50° . The binding of these new isomers with bovine opsin was investigated. While the 7-cis and 7,9-dicis isomers of 3-dehydroretinal and 3-hydroxyretinal formed pigments with opsin without isomerization, the 7,13-dicis, 7,9, 13-tricis, 7,1l-dicis and 7,9,1l-tricis isomers of 3-dehydroretinal all showed instability in the binding media and isomerized during the binding process. The Spectra Calc software package was employed to analyze the pattern of isomerization and the likely configuration of the chromophore in the pigments formed. 7,13-Dicis and 7,9,13-tricis 3-dehydroretinal have been shown to isomerize to 7cis and 7,9-dicis during the binding process and the newly formed pigments are of 7-cis and 7,9-dicis configuration. The analysis of binding curves of 7,ll-dicis 3-dehydroretinal indicates that two pigments were likely formed during the binding process, one with 7,11dicis configuration, the other with 7-cis configuration. 7,9,1l-Tricis 3-dehydroretinal was shown to form a pigment of the 7,9-dicis configuration. Part II. A series of lower B-carotene homologs (dubbed mini-carotenes) were prepared and their properties and photostationary states were investigated. The cis isomer of the mini-3, lowest member of this series, showed dynamic NMR behavior at much lower temperature than the 7-cis compounds in the retinal series. It also showed thermall,7-H-shift reaction, which was rarely observed in the retinal series. The unusual red-shifted UV absorption of cis-mini-S has been attributed to the secondary orbital overlap in its spiral structure. Photochemistry of both cis-mini-S and trans-mini-S was studied. The cis-trans isomerization was found to be accompanied by other irreversible sigmatropic 1,5-H-shift and electrocyclization reactions to give complex mixtures. Photostationary state of mini-5 consists of about 60% 9-cis isomer and 40% all trans isomers. No7-cis isomers were detected. Preliminary work with mini-7 indicated that it is relatively inactive toward light.