De novo synthesis and properties of analogues of the self-assembling chlorosomal bacteriochlorophylls
- North Carolina State Univ., Raleigh, NC (United States)
- Washington Univ., St. Louis, MO (United States)
- Univ. Of California, Riverside, CA (United States)
Natural photosynthetic pigments bacteriochlorophyllsc, d and e in green bacteria undergo self-assembly to create an organized antenna system known as the chlorosome, which collects photons and funnels the resulting excitation energy toward the reaction centers. Mimicry of chlorosome function is a central problem in supramolecular chemistry and artificial photosynthesis, and may have relevance for the design of photosynthesis-inspired solar cells. The main challenge in preparing artificial chlorosomes remains the synthesis of the appropriate pigment (chlorin) equipped with a set of functional groups suitable to direct the assembly and assure efficient energy transfer. Prior approaches have entailed derivatization of porphyrins or semisynthesis beginning with chlorophylls. This paper reports a third approach, the de novo synthesis of macrocycles that contain the same hydrocarbon skeleton as chlorosomal bacteriochlorophylls. The synthesis here of Zn(II) 3-(1-hydroxyethyl)-10-aryl-13¹-oxophorbines (the aryl group consists of phenyl, mesityl, or pentafluorophenyl) entails selective bromination of a 3,13-diacetyl-10-arylchlorin, palladium-catalyzed 13¹-oxophorbine formation, and selective reduction of the 3-acetyl group using BH₃·tBuNH₂. Each macrocycle contains a geminal dimethyl group in the pyrroline ring to provide stability toward adventitious dehydrogenation. A Zn(II) 7-(1-hydroxyethyl)-10-phenyl-17-oxochlorin also has been prepared. Altogether, 30 new hydroporphyrins were synthesized. The UV-Vis absorption spectra of the new chlorosomal bacteriochlorophyll mimics reveal a bathochromic shift of [similar]1800 cm-1 of the Qy band in nonpolar solvent, indicating extensive assembly in solution. The Zn(II) 3-(1-hydroxyethyl)-10-aryl-13¹-oxophorbines differ in the propensity to form assemblies based on the 10-substituent in the following order: mesityl
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Photosynthetic Antenna Research Center (PARC)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- SC0001035
- OSTI ID:
- 1065623
- Journal Information:
- New Journal of Chemistry (Online), Vol. 35, Issue 11; Related Information: PARC partners with Washington University in St. Louis (lead); University of California, Riverside; University of Glasgow, UK; Los Alamos National Laboratory; University of New Mexico; New Mexico Corsortium; North Carolina State University; Northwestern University; Oak Ridge National Laboratory; University of Pennsylvania; Sandia National Laboratories; University of Sheffield, UK; ISSN 1369-9261
- Publisher:
- Royal Society of Chemistry
- Country of Publication:
- United States
- Language:
- English
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