ChemInform Abstract: Low‐Frequency Vibrational Spectra of Chlorophylls a and b in Solution: Effects of Axial Coordination

Abstract

ChemInform Abstract (far-IR and polarized Raman spectra (100-500 cm-1) in solvent mixtures of benzene containing Py, THF or acetone; change of the state of coordination).

FAR‐INFRARED SPECTRA OF LANGMUIR‐BLODGETT FILMS OF CHLOROPHYLL a, CHLOROPHYLL b, PHEOPHYTIN a and THEIR ADDUCTS WITH WATER and DIOXANE*

“…These structural modifications are reflected in the spectral changes associated with vibrational frequencies in the 300-200 cm-l region. Similar behavior was observed in the far-IR spectra of Chl a in the solid state and in different non-aqueous solutions, where the coordination number of the Mg(I1) ion was changed from four to five and to six (Boucher et al, 1966;Fujiwara et al, 1988). These observations strongly support our tentative assignments of the vibrational frequencies (300-200 cm-l) to modes containing major contributions from Mg-N and Mg-0 stretching and bending modes.…”

“…Chl interaction (binding of the magnesium ion of the one Chl to C=O carbonyl group of the other Chl), will break down to the five-coordination metal ion with H 2 0 molecule as the fifth ligand in Chl b.H20 adduct, and alters to a six-coordinated metal cation in the Chl bdioxane complex (with two oxygen atoms from two bridging dioxane ligands). The spectral changes observed in the far-IR region of the spectra of Chl a and b for both monolayer and multilayer, as well as their water and dioxane complexes, are consistent with changes observed for the corresponding species in the mid-I R region (Ballschmiter and Katz, 1972;Chapados and Leblanc, 1983;Fujiwara et al, 1988;Fujiwara and Tasumi, 1986).…”

“…The main spectral features of Chl a monolayers were observed as several strong and medium intensity absorption bands at: 457, 434, 399, 378, 303, 278, 254, 202, 185, 164 cm-l. For the Chl a multilayer, corresponding IR bands were observed at 459, 434, 378, 304, 275, 244, 208 and 190cm-' (Table 1). These absorption bands are related mainly to skeletal deformations of the macrocycle, with strong contributions from N-Mg-N and Mg-0 stretching and bending modes (Boucher et al, 1966;Fujiwara et al, 1988). The main spectral difference observed between monolayer and multilayer of Chl a in this region can be related to the different states of aggregation in both monolayer and multilayer films.…”

“…The spectral analysis for Chl a, Chl b and Pheo a will be discussed separately. Our far-IR frequencies have been compared with those of the solid and solutions (Boucher et al, 1966;Fujiwara et al, 1988) and the results are shown in Table 1.…”

“…These modes include Mg-N stretching and bending for the non-aggregated form, as well as Mg-0 stretching observed in the aggregated state. Although the mid-IR spectra of Chl have been studied extensively, the far-IR investigation of Chl has been limited to solid or non-aqueous solutions (Boucher et al, 1966;Fujiwara et al, 1988). No report has appeared in the literature on the far-IR spectra of Chl LB monolayer and multilayer films.…”