ABSTRACT: Semisynthetic zinc chlorins are shown for the first time to self-assemble in the absence of an intrinsic hydroxy group, which is always present in the chlorosomal bacteriochlorophylls (BChl's) c, d and e. Instead, the presently studied compounds have carbonyl groups. These cannot function as hydrogen bond donating groups. However due to interspacing water molecules bound to the zinc ion, double hydrogen bonding can occur to adjacent tetrapyrrolic macrocycles equipped with carbonyl recognition groups. Solution studies comprising UV-Vis absorption, electronic circular dichroism (ECD) and FT-IR show that different aggregates are formed in hydrated solvents in comparison to dry nonpolar solvents. Single crystal X-ray studies show variable supramolecular interactions either with interspacing water molecules coordinating the Zn ion within a porphyrin or with the 17(2) carbonyl group of a chlorin ligating the Zn ion. Our findings have implications for a minimalistic design of self-assembling chromophores, which can act as efficient light-harvesting units.
Photochemical and Photobiological Sciences 04/2012; 11(6):1069-80. · 2.58 Impact Factor
ABSTRACT: The supramolecular chemistry of chlorins which are the most abundant photosynthetic pigments
is reviewed. In chlorophyll-protein complexes, ligation of the central magnesium atom can occur in
two diastereomeric configurations. Light-harvesting complexes of purple bacteria are formed by the
self-assembly of short polypeptides which bind bacteriochlorophylls into circular structures. The
light-harvesting organelle of green photosynthetic bacteria, the so-called “chlorosome”,
is the most efficient natural antenna system and is formed by self-assembly of bacteriochlorophylls
c, d or e
without the help of a protein scaffold. Semisynthetic and fully synthetic mimics of these self-assembling
bacteriochlorophylls have been prepared and their self-assemblies have been studied in detail in view
of artificial light-harvesting systems. From a single crystal X-ray diffraction analysis, one could
put into evidence hierarchic supramolecular interactions within such self-assembling systems. Interestingly,
hydrogen bonding which all present models of bacteriochlorophyll self-assemblies contain as one of
the important supramolecular interactions is absent in the fully synthetic mimics.
08/2005: pages 585-585;
Chemical Physics Letters, v.447, 284-288 (2007).
European Journal of Organic Chemistry, 414-422 (2006).