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Spectroscopic analysis of chlorophyll model complexes: methyl ester ClFe(III)pheophorbides
L A Andersson1, T M Loehr, T M Cotton
1Department of Chemical and Biological Sciences, Oregon Graduate Center, Beaverton 97006-1999.
Biochimica Et Biophysica Acta
|May 8, 1989
Summary
This study used FTIR and Raman spectroscopy to analyze chlorophyll a models. Five-coordinate iron(III) pheophorbides are better chlorophyll models than four-coordinate nickel(II) pheophorbides, revealing insights into chlorophyll structure and function.
Area of Science:
- Biophysical Chemistry
- Spectroscopy
- Photochemistry
Background:
- Chlorophyll a (Chl a) is crucial for photosynthesis.
- Understanding Chl a structure-function relationships requires accurate molecular models.
- Pheophorbides serve as valuable Chl a analogs for spectroscopic studies.
Purpose of the Study:
- To evaluate methyl ester ClFe(III)pheophorbides as models for Chl a using FTIR and RR spectroscopy.
- To investigate the influence of metal coordination and macrocycle structure on spectral properties.
- To elucidate the vibrational interactions between the C-9 keto and C-10 carbomethoxy groups in phorbins.
Main Methods:
- Fourier Transform Infrared (FTIR) absorption spectroscopy.
- Resonance Raman (RR) spectroscopy, including Surface-Enhanced Resonance Raman Scattering (SERRS).
- Comparative analysis of spectral data from Chl a, ClFe(III)pheophorbides, and Ni(II)pyropheophorbide a.
Main Results:
- The metal-sensitive IR chlorin band (above 1600 cm-1) is diagnostic for macrocycle type and responsive to metal spin state and coordination.
- Five-coordinate ClFe(III)pheophorbides exhibit spectral characteristics superior to ruffled four-coordinate Ni(II)pheophorbides as Chl a models.
- Vibrational coupling between C-9 keto and C-10 carbomethoxy groups was identified, suggesting potential conjugation of the C-10 ester in phorbins.
Conclusions:
- Five-coordinate ClFe(III)pheophorbides are superior spectroscopic models for Chl a compared to Ni(II)pheophorbides.
- The C-9 keto and C-10 carbomethoxy groups exhibit significant vibrational interactions.
- The conjugation of the C-10 ester group in phorbins may play a role in biological functions, particularly in the E ring of chlorophylls.