Pishchalnikov Roman Y, Yaroshevich Igor A, Zlenko Dmitry V, Tsoraev Georgy V, Osipov Evgenii M, Lazarenko Vladimir A, Parshina Evgenia Yu, Chesalin Denis D, Sluchanko Nikolai N, Maksimov Eugene G
Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov Str., 38, Moscow, Russia, 119991.
Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia, 119991.
Photosynth Res. 2023 Apr;156(1):3-17. doi: 10.1007/s11120-022-00955-2. Epub 2022 Sep 5.
Our analysis of the X-ray crystal structure of canthaxanthin (CAN) showed that its ketolated β-ionone rings can adopt two energetically equal, but structurally distinct puckers. Quantum chemistry calculations revealed that the potential energy surface of the β-ionone ring rotation over the plane of the conjugated π-system in carotenoids depends on the pucker state of the β-ring. Considering different pucker states and β-ionone ring rotation, we found six separate local minima on the potential energy surface defining the geometry of the keto-β-ionone ring-two cis and one trans orientation for each of two pucker states. We observed a small difference in energy and no difference in relative orientation for the cis-minima, but a pronounced difference for the position of trans-minimum in alternative pucker configurations. An energetic advantage of β-ionone ring rotation from a specific pucker type can reach up to 8 kJ/mol ([Formula: see text]). In addition, we performed the simulation of linear absorption of CAN in hexane and in a unit cell of the CAN crystal. The electronic energies of [Formula: see text] transition were estimated both for the CAN monomer and in the CAN crystal. The difference between them reached [Formula: see text], which roughly corresponds to the energy gap between A and B pucker states predicted by theoretical estimations. Finally, we have discussed the importance of such effects for biological systems whose local environment determines conformational mobility, and optical/functional characteristics of carotenoid.
我们对视黄基丁二酮（CAN）的X射线晶体结构分析表明，其酮化的β-紫罗兰酮环可呈现两种能量相等但结构不同的褶皱。量子化学计算表明，类胡萝卜素中共轭π-体系平面上β-紫罗兰酮环旋转的势能面取决于β-环的褶皱状态。考虑到不同的褶皱状态和β-紫罗兰酮环旋转，我们在势能面上发现了六个独立的局部最小值，它们定义了酮基-β-紫罗兰酮环的几何结构——两种褶皱状态下各有两个顺式和一个反式取向。我们观察到顺式最小值在能量上有微小差异，相对取向没有差异，但反式最小值在不同褶皱构型中的位置有明显差异。从特定褶皱类型进行β-紫罗兰酮环旋转的能量优势可达8 kJ/mol（[公式：见原文]）。此外，我们对CAN在己烷和CAN晶体晶胞中的线性吸收进行了模拟。对CAN单体和CAN晶体中的[公式：见原文]跃迁的电子能量进行了估计。它们之间的差异达到[公式：见原文]，这大致对应于理论估计预测的A和B褶皱状态之间的能隙。最后，我们讨论了此类效应对于生物系统的重要性，这些生物系统的局部环境决定了类胡萝卜素的构象流动性以及光学/功能特性。
