Yumiko Mukai

Transient Raman spectra of the all-trans and 7-, 9-, 11- and 13-mono-cis isomers of retinal and the mechanism of the cis-trans isomerization in the lowest excited triplet state

Transient Raman studies of isomeric retinals reveal that the photoexcitation and subsequent intersystem crossing results (except for 13-cis) in an identical relaxed triplet species which gives exclusively the all-trans conformer in the ground state. The 13-cis isomer yields another relaxed triplet species. A scheme for the mechanism of the isomerization in T 1 is proposed in which the cis-trans partitioning takes place in the vibrationally, excited levels of the cis T 1 manifold and in which an efficient intersystem crossing occurring in these levels plays an essential role.

Picosecond time-resolved absorption study of all-trans- and 9-cis-retinal: configurational relaxation in the triplet state

Abstract Picosecond time-resolved absorption spectra of all-trans- and 9-cis-retinal in n -hexane solution have been measured by using an Nd 3+ :YAG laser photolysis system. A drastic change of the T n ← T 1 ] absorption spectrum of the 9-cis isomer has been observed in the picosecond to nanosecond time region, which should reflect the configurational relaxation in the triplet state.

Isolation by high-pressure liquid chromatography, configurational determination by 1H-NMR, and analyses of electronic absorption and raman spectra of isomeric spheroidene

A set of cis-trans isomers of spheroidene (all-trans, 9′-cis, 13′-cis, 9-cis, 13-cis, 5,9′-cis, 9,13′-cis, and 5,13-cis + 13,9′-cis) were isolated from an isomeric mixture which was obtained by iodine-sensitized photoisomerization of the all-trans isomer by means of high-pressure liquid chromatography (HPLC) using a calcium hydroxide column. The 15-cis isomer was isolated from the reaction center (RC) of Rhodobacter sphaeroides 2.4.1. The configurations of the above isomers were determined by 1H-nuclear magnetic resonance (NMR) spectroscopy. The order of elution of the isomers in HPLC is explained in terms of the interaction between the extended all-trans part of the various cis-trans configurations of the conjugated backbone and the flat surface of calcium hydroxide at the molecular level. A systematic change from a peripheral-cis toward a central-cis isomer was found, for mono-cis isomers except for 15-cis, in the wavelength of the 1Ag− 1Bu+ absorption and in the relative intensity of the C10(single bond)C11 (C10′(single bond)C11′) vs. C14(single bond)C15 (C14′(single bond)C15′) stretching Raman lines.

Transient raman spectra of all-trans, 7-cis, 9-cis, 11-cis and 13-cis retinylideneacetaldehyde. Structures of triplet species as revealed by Raman spectroscopy

Abstract Transient Raman spectra of retinylideneacetaldehyde in the triplet state produced from the all-trans, 7-cis, 9-cis, 11-cis and 13-cis isomers, by 355 nm flash photolysis in n -hexane solution, have been recorded. All the isomers produced ‘all-trans’ triplet species in common, but the 9-cis isomer additionally produced its own ‘9-cis’ triplet. The structures of those triplet species are discussed, by using key Raman lines, together with ‘all-trans’ and ‘13-cis’ triplet of retinal and ‘all-trans’ triplet of β- ionylidenecrotonaldehyde.

COMPARISON OF THE PATHWAYS AND QUANTUM YIELDS OF DIRECT PHOTOISOMERIZATION OF UNPROTONATED AND PROTONATED N-BUTYLAMINE SCHIFF BASES OF ISOMERIC RETINYLIDENEACETALDEHYDE WITH THOSE OF SCHIFF BASES OF ISOMERIC RETINAL: RATIONALIZATION OF THE SELECTION OF THE RETINYLIDENE CHROMOPHORE BY RETINOCHROME

Abstract— The pathways and quantum yields of direct photoisomerization of unprotonated and pro‐tonated n‐butylamine Schiff bases (SB and PSB) of isomeric retinylideneacetaldehyde (C22 aldehyde) were determined in n‐hexane, acetonitrile and methanol for the former and in acetonitrile and methanol for the latter. The results are compared with those of the Schiff bases of isomeric retinal (C20 SB and C20 PSB) reported previously (Koyama et al., Photochem. Photobiol. 54, 433–443, 1991). The isomerization pathways and quantum yields of C22 SB are more or less similar to those of C20 SB, but conspicuous differences in the isomerization pathways are found between C22 PSB and C20 PSB. The homogeneous (exclusive) isomerization of the retinylidene chromophore from all‐trum to 11‐cis in retinochrome is rationalized not by C22 PSB but by C20 PSB.

ISOMERIZATION OF THE RETINYLIDENE CHROMOPHORE OF BACTERIORHODOPSIN IN LIGHT ADAPTATION: INTRINSIC ISOMERIZATION OF THE CHROMOPHORE AND ITS CONTROL BY THE APO‐PROTEIN

Abstract— The dependence of the isomeric configuration of the retinylidene chromophore of bacteriorhodopsin on the pH value and on the wavelength of irradiation (in a photostationary state) were examined by high performance liquid chromatographic analyses of extracted retinal. The process of isomerization of the chromophore during light adaptation was also traced. More than 93% of all‐trans and less than 5% of 13‐cis retinal were extracted in the photostationary state for irradiation at 560 nm in the pH region of5–9 as well as for irradiation in the wavelength region of 400–650 nm at pH 7. Comparison of the above photostationary state composition with that of protonated n‐butylamine Schiff base of retinal indicates that strong constraint is applied to the chromophore by the apo‐protein. The constraint can be changed at low or high pH by a partial denaturation or transition of the apo‐protein, which results in the generation of 11‐cis retinal in the extract. At higher photon density, the isomerization process of the chromophore during light adaptation at pH 7 was characterized, as extracted isomeric retinal, by (1) the initial decrease in 13‐cis and increase in all‐trans, (2) a subsequent, transient toward the above photostationary state composition. The results are discussed in terms of both the photoisomerization pattern inherent in the retinylidene chromophore and the control by the apo‐protein.