Self quenching of chlorosome chlorophylls in water and hexanol-saturated water

Yinwen Zhu, Su Lin, B. L. Ramakrishna, Paula I. Van Noort, Robert E. Blankenship

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

The optical properties of a methyl ester homolog of bacteriochlorophyll d (BChl dM) and bacteriochlorophyll c (BChl c) in H2O, hexanol-saturated H2O and methanol were studied by absorption, fluorescence emission, and circular dichroism (CD). In H2O, BChl dM spontaneously forms an aggregate similar to that formed in hexane, with absorption maximum at 730 nm and fluorescence emission at 748 nm. For the pigment sample in hexanol-saturated H2O, while the absorption peaks at 661 nm, only slightly red-shifted compared to the monomer, the fluorescence emission is highly quenched. When diluted 2-3 fold with H2O, the absorption returns to around 720 nm, characteristic of an aggregate. The CD spectrum of the H2O aggregate exhibits a derivative-shaped feature with positive and negative peaks, while the amplitude is lower than that of chlorosomes. The Fourier transform infrared spectra of BChl dM aggregates in H2O and hexane were measured. A 1644 cm-1 band, indicative of a bonded 131-keto group, is detected for both samples. A marker band for 5-coordinated Mg was observed at 1611 cm-1 for the two samples as well. To study the kinetic behavior of the samples, both single-photon counting (SPC) fluorescence and transient absorption difference spectroscopic measurements were performed. For BChl dM in hexanol-saturated H2O, a fast decay component with a lifetime of 10 to 14 ps was detected using the two different techniques. The fast decay could be explained by the concentration quenching phenomenon due to a high local pigment concentration. For the pigment sample in H2O, SPC gave a 16 ps component, whereas global analysis of transient absorption data generated two fast components: 3.5 and 26 ps. The difference may arise from the different excitation intensities. With a much higher excitation in the latter measurements, other quenching processes, e.g. annihilation, might be introduced, giving the 3.5 ps component. Finally, atomic force microscopy was used to examine the ultrastructure of BChl dM in H2O and hexanol-saturated H2O. Pigment clusters with diameters ranging from 15 to 45 nm were observed in both samples.

Original languageEnglish (US)
Pages (from-to)207-218
Number of pages12
JournalPhotosynthesis research
Volume47
Issue number3
DOIs
StatePublished - Jan 1 1996

Keywords

  • Aggregate
  • Antenna
  • Atomic force microscopy
  • Bacteriochlorophyll c
  • Chlorosome
  • Concentration quenching
  • Energy transfer
  • Green bacteria
  • Photosynthesis

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology

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  • Cite this

    Zhu, Y., Lin, S., Ramakrishna, B. L., Van Noort, P. I., & Blankenship, R. E. (1996). Self quenching of chlorosome chlorophylls in water and hexanol-saturated water. Photosynthesis research, 47(3), 207-218. https://doi.org/10.1007/BF02184282