Photophysical
Properties of the Excited States of
Bacteriochlorophyll <i>f</i> in Solvents and in Chlorosomes
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Abstract
Bacteriochlorophyll <i>f</i> (BChl <i>f</i>) is a photosynthetic pigment predicted
nearly 40 years ago as a
fourth potential member of the <i>Chlorobium</i> chlorophyll
family (BChl <i>c</i>, <i>d</i>, and <i>e</i>). However, this pigment still has not been found in a naturally
occurring organism. BChl <i>c</i>, <i>d</i>, and <i>e</i> are utilized by anoxygenic green photosynthetic bacteria
for assembly of chlorosomeslarge light-harvesting complexes
that allow those organisms to survive in habitats with extremely low
light intensities. Recently, using genetic methods on two different
strains of Chlorobaculum limnaeum that
naturally produce BChl <i>e</i>, two research groups produced
mutants that synthesize BChl <i>f</i> and assemble it into
chlorosomes. In this study, we present detailed investigations on
spectral and dynamic characteristics of singlet excited and triplet
states of BChl <i>f</i> with the application of ultrafast
time-resolved absorption and fluorescence spectroscopies. The studies
were performed on isolated BChl <i>f</i> in various solvents,
at different temperatures, and on BChl <i>f</i>-containing
chlorosomes in order to uncover any unusual or unfavorable properties
that stand behind the lack of appearance of this pigment in natural
environments