Conformational flexibility of phycocyanobilin: Monte-Carlo and DFT study

A scan of the potentia I-energy surface (PES) for phycocyanobilin has been performed by Monte-Carlo Multiple Minimum (MCMM) searching method using the force field of MMFFs. The resulting most stable/populated structures are then reoptimized with ab initio methods and density functional theory (DFT) using HF/6-31G and B3LYP/6-31G levels of theory, and all possible conformers of phycocyanobilin are investigated with these methods. Results indicate that the most stable structure is all-syn, all-Z conformation. Other local minima are also obtained, such as ZZZass, EZZass and ZZZssa, which are stabilized by intramolecular hydrogen bonds and favorable geometric structures minimizing steric interactions. (C) 2008 Elsevier B.V. All rights reserved.