Porphyrin etio-type

Figure 5 Schematic representation of absorbance of porphyrin compounds in relation to tissue transmittance at various wavelengths (see text). The lowest energy band (Band I) is shown in each case, apart from the porphyrin spectrum (etio type shown) on the left. The transmittance curve refers to a fold of human scrotal sac 0.7 cm thick (Wan, S. Parrish, J. A. Anderson, R. R. Madden, M. Photochem. Photobiol. 1981, 34, 679-681). The broad feature at ca. 500-600 nm is ascribed to haemoglobin (reproduced by permission of the Royal Society of Chemistry from Chem. Soc. Rev. 1995, 24, 19-33).

Figure 2 Electronic absorption spectra (Soret band omitted) in chloroform a, etio type porphyrin b, rhodo type porphyrin c, oxorhodo type porphyrin d, phyllo type porphyrin...

Table 1. Important porphyrins of the ETIO-type (/ -pyrrolic alkyl substituents,...

The ms-tetraphenyl derivatives behave differently here the formation of a dication does not only lead to a reduction of the four-band neutral base spectrum, but also to a 50-nm bathochromic shift and a broadening of these bands, which are not found in any of the porphyrins with only partly substituted or nonsubstituted methine bridges. Even an ms-diphenyl porphyrin does not produce this effect [Treibs (77(5)]. The explanation is simple and straigthforward in the neutral form the phenyl rings lie almost perpendicular to the porphyrin plane, whereas in the highly distorted structure of the dication (arising from van der Waals and Coulomb repulsions) they rotate towards a more parallel position, which allows the overlap of n orbitals from the porphyrin and phenyl rings. This has also been shown by X-ray analysis of the dications [Fleischer ((55)]. Already the monocation is probably far from planarity, as is indicated by the immediate further protonation of this species. This extreme flexibility of the porphyrin plane has so far been demonstrated for TPP derivatives but not for ETIO-type porphyrins. 

Fig. 2. Esr spectrum of an ETIO-type magnesium porphyrin cation radical. The hyperfine couplings are from the methine protons...

The most stable manganese oxidation state in porphyrins is +3, and Mn111 complexes of ETIO-type porphyrins are the most prominent example of metalloporphyrins with a split Soret band. Instead of the usual intense band at 400 nm, these chelates possess two bands at 350 and 460 nm with an intensity ratio of 2 1. This change was related to a strong porphyrin-metal n-d(XZjyZ) interaction in addition to the usual a interaction between the four pyrrole nitrogens and the metal [Boucher (11)]. Theoretical calculations do indeed predict dxz,yg-n interactions because the metal d orbitals in the first transition series roughly match... 

Figure 1,2. The DPEP type and etio type porphyrins. Substituents on bridge and on pyrrole ring are possible. The alkyl groups may vary.

A number of research groups have reported the synthesis of simple strapped porphyrins. Ogoshi et al. condensed long-chain diamines with a difunctional etio-type porphy-... 

We shall not deal with the detailed statistical analysis of petroporphyrin mass spectra, the interested reader being referred to more authoritative texts. It is enough to say that the ratio of DPEP-type to etio-type porphyrins in a sediment is a good indicator of the amount of thermal stress that the sediment has been subjected to the higher the ratio of etiopor-phyrins, the greater the degree of thermal stress. 

Table 18. Electronic absorption data for several Mn and Fe porphyrins of the type M(P)X (for abbreviations, see Table 2 solvents used CHCI3 for Mn(Etio)X, CgHg for Fe(Deut-DME)X, CHjClj for Fe(OEP)X X in nm)...

Table 1 provides a fairly comprehensive listing of trivial names still in regular use in the porphyrin and chlorophyll area. The uro-, copro- and etio-porphyrins are examples of primary type isomer systems, while proto-, meso-, deutero- and hemato-porphyrins derive from the situation where 15 isomers exist. Phyllo-, pyrro- and rhodo-porphyrins, all being chlorophyll degradation products, are examples of the situation where there are four different kinds of porphyrin substituent. It transpires that, in biologically important porphyrin derivatives, the isomer chosen by Nature is Type-Ill (for the primary system), Type-IX (with three types of substituent) and Type-XV (with four). As can be seen in Schemes 1 and 2, primary type-III is related to type-IX in Scheme 2, and type-IX is in turn related to type-XV in the yet more complicated four-substituent system. 

Most structural information is gained from the less intense (e 2000-20 000) satellite peaks which appear, for metal-free, neutral porphyrins, between 500 and 700 nm. Visual inspection of the intensity ratios of these minor peaks enables four types of peripheral or methine substituent patterns to be identified, and these are shown in Figure 2. The etio ... 

With drastic variations in sediments, composition as well as types of vanadium complexes vary. Even within a series of samples there is a noticeable variation of the vanadium complexes. For example, as the age or the depth of the fossil remains increases, a transformation of the porphyrin types from philo to etio takes place. This is merely one example of the large variety of reactions and transformations occurring in petroleum as well as other bituminous substances. The study of such effects would reveal much knowledge concerning the migration, maturation, and transformation of a diversity of fossil remains. 

The greater lability toward vanadium removal and porphyrin destruction for the vanadyl petroporphyrins over the synthetic vanadyl porphyrins is a fortunate circumstance. This difference can be rationalized based upon structural differences of the porphyrins involved. Phyllo-type petroporphyrins all contain a cyclopentane ring, fused to one of the pyrrole rings with the methine carbon one of the units of the carbo-cyclic structure. Etio- and rhodo-type petroporphyrins appear to have alkyl substitution at one or more methine positions, as based upon nmr spectral data. Should all petroporphyrins have a carbon substituent on one or more methine carbons, the carbonium ion formed by the reaction would tend to have more charge localization on those methine carbons. These ions are a more stable species by an order of magnitude over those porphyrins without methine substitution. 

---