Molecular flexibility of retinoic acid under white fluorescent light.

Among the series of metabolic analogs of the eccentric cleavage pathway of beta-carotene with different side chain lengths, retinoic acid was shown to have exceedingly higher molecular flexibility to undergo photoisomerization into the geometrical isomers under white fluorescent light. When irradiated with white fluorescent lamps (1,200 lx), the velocity of photoisomerization of all-trans-retinoic acid (8.4 x 10(-7) mol/L.min) was exceedingly higher than those of the other analogs: ionylideneacetic acid (4 x 10(-8) mol/L.min), ionylidenecrotonic acid (3.0 x 10(-7) mol/L.min), all-trans-beta-apo-14'-carotenoic acid (1.7 x 10(-7) mol/L.min), all-trans-beta-apo-12'-carotenoic acid (1.3 x 10(-7) mol/L.min), and all-trans-beta-apo-8'-carotenoic acid (0.1 x 10(-7) mol/L.min). beta-Carotene did not undergo photoisomerization under the experimental conditions. The molecular flexibility of retinoic acid is assumed to be an important basis of the mechanism of action of retinoic acid.