Abstract

Abstract The temperature dependence of carbon-13 chemical shifts has been studied for retinal isomers, N-all-trans-retinylidenebutylamine(all-trans-NRB) and N-all-trans-retinylidenebutylammonium chloride (all-trans-NRB·HCl). The change in the chemical shift was discussed in terms of the temperature dependences of the polarizability and conformation of the polyene-chain. In 11-cis-retinal, the coplanarity between the two parts of polyene-chain separated by the cis bond increases with a lowering of the temperature. The equilibrium between 12-s-cis and 12-s-trans conformers in 11-cis-retinal was studied and it was shown the latter conformer is preferable at low temperatures. In all-trans-NRB and all-trans-NRB·HCl, the temperature dependences of the chemical shifts are similar to those in all-trans-retinal. The extents of the chemical shift changes are in the following order: NRB·HCl<NRB<retinal. This trend can be correlated with the order of the red shifts of the absorption spectra.

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