Porphin structure

Porphyrins—Pigments widely distributed throughout nature (e.g., heme, bile pigments, cytochromes) consisting of four pyrroles joined in a ring (porphin) structure. 

Figure 1.4. Porphin structure with two cycloalkano rings.

In the present definition, the nonporphyrins will also include the altered or modified porphin structure, such as hydroporphins (ab), arylporphins (ac), and porphin-degraded products (ad). All three classes have been included in the discussion of the above section since they are the secondary or tertiary derivatives or the precursors of the regular porphin structure (aa). In many cases they lose their porphyrin identity (properties) even when they exist in the same environment. 

Porphyrins are heteroaromatic compounds characterised by a tetrapyrrolic structure that consists of four pentagonal pyrroles linked by four methylene bridges, the porphine structure (Figure 1). 

Even if this porphine structure can be oxidised or reduced, it is usually considerably stable. It is characterised by an absorption spectrum having a specific band... 

HPD absorbs light between 350 and 630 nm. Its basic structure, represented in Figure 2, is made up of a porphine structure substituted by ... 

The iron porphyrin models discussed above all share a nearly planar porphine core, similar to the hone in Mb, whereas the heme in Cyt c is distorted from the planar structure by the covalent bonds and hydrogen bonds with surrounding protein residues. To address the effect of environmentally induced heme distortion on the mechanism of VER, rather than including the surrounding protein residues explicitly (too expensive for any reasonable high level of theory), we replaced the heme s central iron atom by nickel. Due to the smaller size of nickel relative to iron, the porphine structure is distorted in the Ni-substituted Ni-hane in a manner similar to the heme distortion observed in cytochrome c. Another nickel porphyrin model, nickel octa-ethylporphyrin (NiOEP), was also optimized to a structure with similar nonplanar porphine core geometry [90]. 

As an example for the soft ionization possibility of MUPI in contrast to electron impact, both the El and the MUPI mass spectra of a biological sample are displayed in figure 10. Here the mass spectra of native chlorophyll a, obtained by methanolic extraction of the cyano-bacterium Spirulina geitlerie without further purification, are shown. The soft ionization mass spectrum shows three different molecular ions, the chlorophyll a at mass 892, 10-hydroxy-chlorophyll a at mass 908 and phaeophytin a at mass 870. This mass spectrum again demonstrates the abilities of laser ionization, since by choosing the right wavelength only the porphin structures in the mixture are ionized. 

Polonovski reaction 622 Porphin, structure 568 Protecting groups—see also Amino group, protection and Amine derivatives... 

Fig. 4.14 Structures, energy diagrams, and excitations of poiphin, chlorin and bacteriochlorin. The horizontal bars are schematic representations of the energies of the highest two occupied molecular orbitals ( i and 2) and the first two unoccupied orbitals (V>3 and >4). relative to the energy of r/ij in each molecule. Arrows indicate excitations from one of the ocupied orbitals to an empty orbital, x and y correspond to the molecular axes shown as dotted lines with the porphin structure, and convey the symmetry of the product of the initial and final wavefunctions for each configuration, e.g., —> 4. Configurations with the same symmetry mix in the excited stales, and...

---