CIRCULAR AND LINEAR DICHROISM OF AGGREGATES OF CHLOROPHYLL-A AND CHLOROPHYLL-B IN 3-METHYLPENTANE AND PARAFFIN OIL

A circular (CD) and linear dichroism (LD) study of the water adducts o f the green plant chlorophylls a (Chl a) and b (Chl b) in hydrocarbon solvents 3-methylpentane and paraffin oil is presented, A strong red s hift of the Q(y)-absorption band from 663 to 746 nm (1678 cm(-1)) is o bserved as the water adduct of Chl a is formed, The Chl a-water adduct shows a strong, nonconservative CD signal, which is characterized by a positive peak at 748 nm and two negative peaks at 720 and 771 nm, Th e maximum CD (A(L) - A(R)) is only one order of magnitude smaller than the isotropic absorption maximum, We propose that this exceptionally strong signal is the so-called psi-type CD. The LD spectrum was measur ed in a flow of paraffin oil, The isotropic absorption maximum peaks a t 742 nm in paraffin oil, whereas the maximum of the LD signal is at 7 43 nm. The LD signal is positive over the whole water-adduct absorptio n band indicating that the transition dipole of the 742 nm transition is preferentially oriented along the long axis of the aggregate. The s tructure of the Chl b-water adduct is less well defined, The preparati ons of the Chl b-water adduct are unstable, The Chl b-water adduct abs orption band maximum is at 683 nm. The CD signal of the Chl a-water ad duct is about 200-fold the CD of the Chl b-water adduct, We could not orient the Chl b-water adducts by flow, which suggests that the adduct s are small or disordered.