INVESTIGATION OF THE ALLOMERIZATION REACTION OF CHLOROPHYLL a: USE OF DIODE ARRAY HPLC, MASS SPECTROMETRY AND CHEMOMETRIC FACTOR ANALYSIS FOR THE DETECTION OF EARLY PRODUCTS |
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| Authors: | Richard G Brereton Ali Rahmani Yi-zeng Liang Olav M Kvalheim |
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| Institution: | School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 ITS, UK;Department of Chemistry, University of Bergen, N-5007 Bergen, Norway |
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| Abstract: | Abstract –The products of chlorophyll allomerization in methanol were isolated and analyzed by open column sucrose chromatography, liquid chromatography mass spectrometry (LCMS) and DAD-HPLC (diode-array high-performance liquid chromatography). Four main bands were found with molecular ions of (a) 908, (b) 938, (c) 938 and (d) 938, consistent with the structures (a) 132-hydroxy-chlorophyll a (II), (b) and (c) Mg(II)-31,32-didehydro-151-hydroxy-151-methoxy-rhodochlorin-15 acetic acid δ-lactone 152-methyl 173-phytyl ester and its epimer (III) and (d) Mg(II)-31,32-didehydro-rhodochlorin-15-glyoxylic acid 131,152-dimethyl 173-phytyl ester (IV), evidence enhanced by UV/visible spectroscopy, chromatographic coelutions and chemometrics. Chlorophyll a was degraded both in the dark and light, under O2 and N2. DAD-HPLC of the resultant degradation mixtures were analyzed using the chemometric heuristic-evolving latent projection method for resolution. Ultraviolet/visible spectra of II and III are reproducibly extracted from the mixtures after a short degradation time, whereas III and IV are the dominant compounds after longer degradation times. Changes in relative elution order of IV using open column chromatography and reverse-phase HPLC are established. A possible allomerization pathway is proposed. |
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