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Effects of Nonpolar and Polar Solvents on the Q x and Q Y Energies of Bacteriochlorophyll a and Bacteriopheophytin a
Author(s) -
Limantara Leenawaty,
Sakamoto Shun,
Koyama Yasushi,
Nagae Hiroyoshi
Publication year - 1997
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1997.tb08566.x
Subject(s) - polar , chemistry , solvent , bacteriochlorophyll , absorption (acoustics) , analytical chemistry (journal) , crystallography , photochemistry , organic chemistry , physics , pigment , optics , astronomy
The effects of nonpolar and polar solvents on the Q x and Q y energies of bacteriochlorophyll (BChl) a and bacteriopheophytin (BPhe) a were examined by electronic absorption spectroscopy. All of the four different energies exhibited a linear dependence on R ( n ) = (n 2 ‐ l)/(n 2 + 2), where n is the refractive index of the solvent, in both nonpolar and polar solvents. The energy of each state of both pigments could be expressed as v = ‐dR ( n ) + e (in cm ‐1 ) where coefficient d was related to the dispersive interaction between the solute and the solvent molecules. A theory developed by Nagae showed that coefficient d originates from the quantum‐mechanical fluctuation of the multipole moments of the solute, in terms of which the following characteristics of the observed d values were explained: (1) In all of the four cases of the Q x , and Q y energies of both BChl a and BPhe a , the d values for the polar solvents were smaller than those for the non‐polar solvents. (2) In both nonpolar and polar solvents, the d value of BChl a was larger than that of BPhe a in the Q y energy, whereas the d value of BPhe a was larger than that of BChl a in the Q x energy. (3) The d value of the Q x energy was larger than that of the Q y , energy for either case of BChl a or BPhe a.