THEORETICAL CALCULATION OF CIRCULAR DICHROIC EXCITON-SPLIT SPECTRA INPRESENCE OF 3 INTERACTING 2-NAPHTHOATE CHROMOPHORES

Ample experimental evidence shows that the principle of pairwise addit ivity holds in exciton coupled CD systems consisting of three or more interacting chromophores. This principle is one of the most important from a practical viewpoint. However, the rule has so far not been prov en theoretically. In order to prove the additivity principle by calcul ation, three ouabagenin bisnaphthoates and 1,3,19-tris-naphthoates wer e chosen as models. Since this represents a challenging case where the 2-naphthoate chromophore can adopt s-cis or s-trans conformations and , moreover the C-19 side chain of ouabagenin is flexible, Monte Carlo conformational search was performed prior to the CD calculation. The p i-electron SCF-CI-DV MO calculation of CD was applied to all conformer s within 3 kcal/mol range from the lowest energy. Good agreement betwe en experimental and theoretical CD spectra was obtained for the ouabag enin bisnaphthoates and trisnaphthoate.