Chlorophylls. VI. Epimerization and Enolization of Chlorophyll a and Its Magnesium-free Derivatives.
- 1 January 1979
- journal article
- research article
- Published by Danish Chemical Society in Acta Chemica Scandinavica
- Vol. 33b (9) , 637-648
- https://doi.org/10.3891/acta.chem.scand.33b-0637
Abstract
The properties of chlorophyll a'' (Chl a'') were investigated in detail by visible, IR and 1H NMR spectroscopy. A new method for the preparation of Chl a'' was developed which permits the isolation of this pigment in a yield of 40% and a high degree of purity. The visible and IR spectra of Chl a'' were virtually identical with those of Chl a. The whole 1H NMR spectrum of Chl a'' was measured in acetone-d6, THF-ds [tetrahydrofuran] and benzene-d6 and compared with that of Chl a. The NMR spectra of these 2 compounds were found slightly different in the positions of the methine, C10, C10b methyl and C5a methyl proton resonances. The t1/2 of the interconversion between Chl a'' and Chl a is at room temperature approximately 1 h, 24 h and several days in acetone, THR and benzene, respectively. Experimental evidence for the aggregation of Chl a'' in benzene-d6 at a concentration .gtoreq. 10-2 M was obtained by NMR spectroscopy. Careful survey of the NMR spectra at low field did not reveal any resonance peak attributable to an enolic proton, in spite of the fact that the underlying mechanism for the interconversion between Chl a and Chl a'' is keto-enol tautomerism. These observations confirm the earlier results supporting the epimer nature of Chl a''. The higher solubility of Chl a'' in nonpolar solvents, its greater tendency to pheophytinize and slight spectroscopic difference in comparison to Chl a were interpreted on the basis of the conformational alterations resulting from the stereochemical change at C10 of ring V. More definitive evidence for these conclusions was obtained by trapping the enols of Chl a, pheophytin a and methylpheophorbide a as trimethylsilyl ethers. The electronic absorption spectrum of the silylated enol of Chl a was found essentially different in the Soret band region but quite similar in the red band region to that of Chl a.This publication has 10 references indexed in Scilit:
- Reduction of chlorophyll a, a′ and b by sodium borohydride: separation of diastereoisomeric desoxo-chlorophyll alcohols on a sucrose columnJournal of Chromatography A, 1979
- Application of elution analysis to the study of chlorophyll transformations by column chromatography on sucroseJournal of Chromatography A, 1979
- Thin-layer chromatography of chlorophylls and their derivatives on cellulose layersJournal of Chromatography A, 1977
- Chlorophylls. V. Isolation of Chlorophylls a and b Using an Improved Two-phase Extraction Method Followed by a Precipitation and a Separation on a Sucrose Column.Acta Chemica Scandinavica, 1977
- Extraction, Separation, Estimation, and Isolation of the Chlorophylls**Based on work carried out under the auspices of the U. S. Atomic Energy Commission.Published by Elsevier ,1966
- Hydrogen Exchange in Chlorophyll and Related Compounds, and Correlation with Molecular Orbital Calculations1Journal of the American Chemical Society, 1965
- Partial purification and determination of oxidation reduction potential of the photosynthetic chlorophyll complex absorbing at 700 mμBiochimica et Biophysica Acta, 1961
- Reduction of Chlorophyllides, Chlorophylls and Chlorophyll Derivatives by Sodium Borohydride.Plant Physiology, 1959
- THE PHASE TEST INTERMEDIATE AND THE ALLOMERIZATION OF CHLOROPHYLL aCanadian Journal of Biochemistry and Physiology, 1958
- STUDIES IN THE CHLOROPHYLL SERIES. III. PRODUCTS OF THE PHASE TESTJournal of the American Chemical Society, 1930