Synthesis of ¹⁸O-labeled photosynthetically active chlorophylls at the 3- or 7-carbonyl group with high regioselectivity.
The 3- and 7-formyl groups of chlorophyll-d (Chl-d) and bacteriochlorophyll-e (BChl-e), respectively, were regioselectively labeled with an isotopically stable oxygen-18 (¹⁸O) atom to give 3¹-¹⁸O-labeled Chl-d and 7¹-¹⁸O-labeled BChl-e (ca. 90% ¹⁸O) by exchanging the carbonyl oxygen atoms in the presence of acidic H₂ ¹⁸O (ca. 95% ¹⁸O). Another photosynthetically active chlorophyll, BChl-a possessing the 3-acetyl group was treated under similar acidic conditions to afford a trace amount of 3¹-¹⁸O-labeled BChl-a and further demetallated compound, the corresponding 3¹-¹⁸O-labeled bacteriopheophytin-a as the major product with 55% ¹⁸O-degree. The FT-IR spectra of ¹⁸O-(un)labeled chlorophylls in the solution and the solid states showed that the 3- and 7-carbonyl stretching vibration modes moved to about a 30-cm⁻¹ lower wavenumber by ¹⁸O-labeling at the 3¹- and 7¹-oxo moieties. In artificial chlorosome-like self-aggregates of BChl-e, the ¹⁸O-labeled 7-carbonyl stretching mode was completely resolved from the specially hydrogen-bonded 13-C=O stretching mode, evidently indicating no interaction of the 7-CHO with other functional groups in the supramolecules.
Morishita
Hidetada
H
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
Mizoguchi
Tadashi
T
Tamiaki
Hitoshi
H
D001429:Bacteriochlorophylls / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D017550:Spectroscopy, Fourier Transform Infrared
D001429:Bacteriochlorophylls; C120930:bacteriochlorophyll e; D002734:Chlorophyll; C107509:chlorophyll d
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