Institut für Physikalische Chemie, Friedrich-Schiller-Universität Jena, Jena, Germany.
Chemphyschem. 2001 Nov 19;2(11):665-71. doi: 10.1002/1439-7641(20011119)2:11<665::AID-CPHC665>3.0.CO;2-O.
Semiempirical AM1 studies on phycocyanobilin, the most abundant chromophore in the light-harvesting phycobiliproteins and a suitable model of the phytochrome chromophore, have been carried out. For the all-Z isomer, the structures and energies of all possible conformers, which arise from rotation about the single bonds of the exocyclic methine bridges, were calculated. In addition, the rotational barriers between the different conformers were deduced from the computed energy hypersurfaces. The cyclic helical SSS conformation is the most stable structure. Other minimum-energy structures with well-separated local minima on the energy hypersurface are the partially extended ASS and SAS conformations, although the conformational situation is characterized by a high degree of kinetic flexibility. The energy of the different conformers is mainly governed by intramolecular hydrogen bonding and steric repulsion of the substituents at the tetrapyrrolic backbone. It is very likely that the energetically most favorable conformers, SSS, ASS, and SAS, correspond with the three ground-state conformers of phycocyanobilin detected in previous time-resolved absorption studies.
已经对藻蓝胆素（phycocyanobilin）进行了半经验 AM1 研究，藻蓝胆素是在捕光藻胆蛋白中含量最丰富的发色团，也是植物色素发色团的合适模型。对于全 Z 异构体，计算了由外环甲叉桥的单键旋转引起的所有可能构象的结构和能量。此外，从计算的能量超曲面上推导出了不同构象之间的旋转势垒。环状螺旋 SSS 构象是最稳定的结构。其他具有能量表面上分离良好局部最小值的最低能量结构是部分伸展的 ASS 和 SAS 构象，尽管构象情况的特点是高度的动力学灵活性。不同构象的能量主要受分子内氢键和四吡咯骨架上取代基的空间排斥的控制。很可能，能量上最有利的构象 SSS、ASS 和 SAS，与先前时间分辨吸收研究中检测到的藻蓝胆素的三种基态构象相对应。
