Molecular Simulation of Enantiodifferentiating Photoisomerization of Cyclooctene by Chiral Sensitizers

Hiromitsu HASHIMOTO, Tetsuro SHIMO*, Mikito ATSUCHI, Masaru MITSUSHIO and Kenichi SOMEKAWA*

Department of Applied Chemistry and Chemical Engineering, Faculty of Engineering, Kagoshima University
1-21-40 Korimoto, Kagoshima 890-0065, Japan

(Received: June 9, 2008; Accepted for publication: September 16, 2008; Advance publication: October 24, 2008)

  For theoretical study on interesting enantiodifferenciating photoisomerization of (Z)-cyclooctene (1Z) to (E)-cyclooctene (1E) by chiral benzenepolycarboxylates (2a) in solution, the profiles of energy and stereochemical change of the sensitized photoisomerization were inferred by molecular simulation by use of MOPAC-PM5 method.
  The energy, stereochemical change and equilibrium of the ground states and excited singlet states of 1Z, 1E, tetramethyl 1,2,4,5-benzenetetracarboxylate (2b), dimethyl 3,5-bis(trifluoromethyl)benzoate (2c), and (R)- and (S)-dimenthyl 3,5-bis(trifluoromethyl)benzoate (2dr and 2ds) as a chiral model of 2a were first interpreted. 1Z has an asymmetric conformer and the isomerization to (R)- or (S)-1E may be dependent on preferential one-side rotation. Inferred exciplexes (Ex1) such as 1Z.2b* (2b*: excited singlet state of 2b) occur via energy transfers through some interactions to bring the next loose exciplexes (Ex2) such as 1E*.2b, which give 1E at the respective 1E/1Z ratio. The Ex1 and Ex2 structures were inferred to possess proper p*/p and C-H/p interactions, ester C=O/HC (olefin and allyl) and F/H hydrogen bondings, placed in parallel or alongside depending on the substituents. The photoisomerization may depend on the energy difference between the two exciplexes, and the transition state (TS) energy. The carbonyl groups and p components on the enantiomeric polycarboxylates make selective hydrogen bondings, p*/p and CH/p interactions with the olefin and allyl groups on asymmetric 1Z, and bring diastereomeric Ex1. Those interaction accumulations are inferred to bring enantiodifferentiating energy transfer by one-side rotation (asymmetric environment) of the two molecules for (R)-1E or (S)-1E like enzymes.

キーワード: Molecular simulation, PM5, Enantiodifferentiation, Photoisomerization, Cyclooctene, Chiral sensitizer, Benzenepolycarboxylate

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