Peripheral Metal Complexes: Chlorophyll “Isomers” with Magnesium Bound to the Ring E ß-Keto Ester System

Peripheral magnesium complexes of methyl pheophorbides a and b, bacteriomethyl pheophorbide a, bacteriopheophytin a, and protopheophytin a have been prepared and characterized by UV-vis, IR, ‘H NMR, and luminescence spectroscopy. In these compounds, Mg is bound to the peripheral p-keto ester system present in most chlorophylls rather than to the central tetrapyrrole cavity as in the chlorophyll proper. The ligand exchange reactions at Mg have been characterized, and the equilibrium between the peripheral complexes and their free ligands has been studied over the concentration range lo-’- M. AGO for complex formation has been determined by ’H NMR spectroscopy

Proton-Electron Hyperfine Coupling Constants of the Chlorophyll a Cation Radical by ENDOR Spectroscopy

In this paper we describe the assignment of the major coupling constants in monomer chlorophyll a cation free radical by ENDOR spectroscopy. To facilitate chemical manipulation methylpyrochlorophyllide a has been used as a stand-in, and a suite of six selectively deuterated derivatives have been subjected to ENDOR investigation. Details of the synthesis of these compounds are described. To study the effect of structural features on the spin distribution in the free radicals, six additional chlorophyll derivatives have been studied. Five coupling constants have been assigned, which account for about 80% of the observed electron spin resonance line width in the chlorophyll a monomer cation radical. The spin distribution appears to be highly asymmetric

Bacteriochlorophyll aggregates in positively charged micelles

Micellar complexes were prepared from bacteriochlorophyll a and bacteriopheophytin a with the cationic detergents, cetyltrimethyl ammonium bromide and cetylpyridinium chloride. These complexes have spectroscopic properties (absorption, circular dichroism) which are very different from the ones formed with non-ionic detergents like Triton X-100, and also with anionic detergents. Bacteriochlorophyll a forms two complexes: One is blue-shifted and has excitonically coupled Qy transitions. The second one is extremely red-shifted. The unusual properties are suggested to result from interactions of the positively charged head-group of the detergent with the tetrapyrrole