Bacteriochlorin spectrum

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. 

Reduction of the porphyrin 7t-system results in a bathochromic shift and an enhancement of the extinction coefficient of the Q-band. There are characteristic differences between bacteriochlorins and isobacteriochlorins. An ultraviolet spectrum of a pyrrocorphin (15) has been described, proving earlier reports on a synthesis of this compound to be erroneous (85CC1604). 

The Metallochlorin Spectrum and its n Anions . The spectrum of the chlorins and bacteriochlorins, where one pyrrole ring or two opposite rings of the porphyrin ring are hydrogenated, consists of four visible bands with a very intense a-band and a sharp Soret band of relatively low intensity. The n anions produce a similar spectrum with bathochromic shifts of the long-wavelength band of about 100 nm [.Fajer (55a)]. 

Hydroporphyrins. H. are derived from completely unsaturated porphyrins by reduction of the double bonds in the porphine skeleton. The spectrum of naturally occurring H. ranges from the dihydro derivatives chlorin and phlorin(s) through the tetrahydro derivatives bacteriochlorin and isobacteriochlorins, the hexahydro derivatives porphyrinogens and precor-rins to the more highly reduced corphins and factor F430. 

Although the formation of a bacteriochlorin resulted in further red shift in the electronic absorption spectrum, with long-wavelength absorption near 750 nm, these molecules were generally found to be air sensitive. Among various chlorin analogs, m-THPC (Foscan ) 7 (Scheme 1) appears to be quite effective and is currently under Phase III human clinical trials (see Chapter 147). 

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