AGGREGATION OF MONOVINYL‐ and DIVINYL‐PROTOCHLOROPHYLLIDE IN ORGANICSOLVENTS*

Abstract

Abstract— Two different protochlorophyllides (PChlide), PChlide 629/433 (absorption data in methanol) and PChlide 630/441 (the monovinyl (MV) and divinyl (DV) forms) were isolated from the pigment mutant C‐2A'of Scenedesmus obliquus. Their spectroscopic behaviour in several organic solvents and their aggregation in toluene was investigated. In polar solvents such as ether, acetonitril or acetone, absorption maxima similar to those in methanol were observed, while in solvents such as tetrahydrofuran and pyridine a bathochromic shift of the blue absorption band compared to the spectra in methanol occurred. The absorption maxima of MV‐PChlide shifted from 629 nm and 433 nm in methanol (monomeric form), to 631 nm and 443 nm in toluene (aggregated form). The absorption maxima of DV‐PChlide shifted from 630 nm and 441 nm in methanol to 655 nm and 483 nm in toluene (aggregated form). The fluorescence excitation and emission spectra of the two protochlorophyllides yielded the according results. The aggregation process was faster for DV‐PChlide than for MV‐PChlide and was reversible upon addition of small amounts of polar solvents. The similarity of the spectral characteristics of the aggregated forms of the different protochlorophyllides after toluene treatment with those reported for “active”‐PChlide in vivo are discussed.