Bacteriochlorin Bacteriochlorophyll

Transformations which alter the bacteriochlorin chromophore are quite rare. An important reaction in the structural elucidation of the bacteriochlorophylls is the dehydrogenation to chlorophyll derivatives. Thus, bacteriopyromethylpheophorbide a (1) can be smoothly dehydrogenated with 3,4,5,6-tetrachloro-l,2-benzoquinone to the corresponding chlorin 3-acetyl-pyromethylpheophorbide a (2) in high yield.1 la,b... 

A study of the hyperfine splitting of the e.s.r. spectrum of the cation radical of oxidized zinc(n) bacteriochlorin, together with selective deuteriation, has allowed assignment of the electron density to the atoms of the system.279 There is high spin density on the protons of the saturated rings of the bacteriochlorin with or without the zinc. A similar situation may pertain in metal-free bacteriochlorophyll. 

Because of its long-wavelength absorption close to 800 nm, naturally occurring bacteriochlorophylls are ideal candidates for PDT. However, due to their unstable nature, synthesis of stable bacteriochlorins has been a challenge for porphyrin chemists worldwide. 

Most of the naturally occurring bacteriochlorins (e.g., 132) have absorptions between 760 and 780 nm and are extremely sensitive to oxidation, resulting in a rapid transformation into the chlorin state 133 which generally has an absorption maximum at or below 660 nm (Scheme 37). Furthermore, if a laser is used to excite the bacteriochlorin in vivo, oxidation may result in the formation of a new chromophore absorbing outside the laser window, reducing its photodynamic efficacy. Due to the desirable photophysical properties of bacteriochlorins, there has been increasing interest in the synthesis of stable bacteriochlorins from bacteriochlorophyll a or other similar tetrapyrrolic systems. 

The bacteriochlorin (7) (2,3,12,13-tetrahydroporphyrin) structural type named after the bacteriochlorophylls is formally derived from a porphyrin by saturation of two peripheral double bonds in opposite pyrrole rings. Again the 187r-electrons of the chromophore give rise to the aromatic character of the structure. 

Figure 13.67. Zinc bacteriochlorin aggregates within a lipid bilayer are spectroscopically similar to bacteriochlorophyll aggregates.

Figure 13.67. As with most of the approaches in this section, the design of the assembly very closely resembles the features of LHi and LH2 natural systems. Aggregates of zinc bacteriochlorins are trapped in a lecithin or Triton-X bilayer to generate chromophore assemblies with spectroscopic behavior that resembles that of the bacteriochlorophyll c aggregates in the antennae systems The aim of the work is indeed to mimic the function of chlorosomes. Chlorosomes are aggregates of BChl c, d, and e that are embedded in lipid monolayers.

The most important chromophores in biological systems are chlorophylls and bacteriochlorophylls. They derive from chlorine and bacteriochlorine. Porphyrins derive from porphine (Figure 14.3). The two protons on the nitrogen... 

Dependent Density Functional Theory for Long-Range Charge-Transfer Excited States The Zincbacteriochlorin-Bacteriochlorin and Bacteriochlorophyll-Spheroidene Complexes. 

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