Porphyrin electronic structure

The discussed experimental results provide a basic insight into the physical mechanism of the porphyrin electronic structure alternation by protein in a pigment-protein complexes. ... 

Tliey also described an interesting case of a porphyrin displaying simultaneously annular and functional tautomerism, very common in the azole series but very rare in porphyrins (88JOC1132). Tire only tautomers observed, 77a-77c, have an 18-atom 18-7r-electron structure similar to that of [18]diazaannulene.Tlie relative amounts of tautomers 77a-77c are solvent dependent for instance, in toluene-dg and in CD2CI2 they are 77a (53 and 78%), 77b (29 and 13%), and 77c (18 and 9%). 

The electronic absorption spectra of the products of one-electron electrochemical reduction of the iron(III) phenyl porphyrin complexes have characteristics of both iron(II) porphyrin and iron(III) porphyrin radical anion species, and an electronic structure involving both re.sonance forms Fe"(Por)Ph] and tFe "(Por—)Ph has been propo.sed. Chemical reduction of Fe(TPP)R to the iron(II) anion Fe(TPP)R) (R = Et or /7-Pr) was achieved using Li BHEt3 or K(BH(i-Bu)3 as the reductant in benzene/THF solution at room temperature in the dark. The resonances of the -propyl group in the F NMR spectrum of Fe(TPP)(rt-Pr) appear in the upfield positions (—0.5 to —6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, 5 = 2 spin state observed... 

Porphyrin is a multi-detectable molecule, that is, a number of its properties are detectable by many physical methods. Not only the most popular nuclear magnetic resonance and light absorption and emission spectroscopic methods, but also the electron spin resonance method for paramagnetic metallopor-phyrins and Mossbauer spectroscopy for iron and tin porphyrins are frequently used to estimate the electronic structure of porphyrins. By using these multi-detectable properties of the porphyrins of CPOs, a novel physical phenomenon is expected to be found. In particular, the topology of the cyclic shape is an ideal one-dimensional state of the materials used in quantum physics [ 16]. The concept of aromaticity found in fuUerenes, spherical aromaticity, will be revised using TT-conjugated CPOs [17]. 

We shall return to the discussion of the orientation and electronic structure of the dioxygen ligand during the next section which is primarily concerned with recent advances in the synthesis and physical characterization (particularly X-ray analysis) of oxygencarrying metal porphyrin model compounds. 

The indicated formal potential E° n of the corresponding monomer (-1.17V) in solution is very near that of the surface film (-1.13V vs. SSCE). That formal potentials of surface films on chemically modified electrodes are near those of their corresponding dissolved monomers (13,18) is actually a common, and quite useful, observation. In the present case, it demonstrates that the electronic structures of the porphyrin rings embedded in the polymer film are not seriously perturbed from that of the monomer. 

Lamoen, D., and M. Parrinello. 1996. Geometry and electronic-structure of porphyrins and porhyrazines. Chem. Phys. Lett. 248, 309. 

For a review of absorption and emission spectroscopy of porphyrins and metalloporphyrins, see Gouterman, M. Optical spectra and electronic structure of porphyrins and related rings. In The Porphyrins Dolphin, D., Ed., Academic Press New York 1978, Vol. Ill, pp 1-165. 

Porphyrin-Metal and Similar Complexes, Properties of (Braterman, Davies, Williams). Power Electrodes and their Application (Tomassi). Pressure, Effect on Electronic Structure (Drickamer ... 

As a consequence of the smaller covalence of Cu(TPP), the pyrrole proton tensors are nearly axially symmetric and the Cu-H distances calculated with the entire unpaired electron at the Cu(II) ion are in excellent agreement with X-ray data. The difference in covalency of Ag(TPP) and Cu(TPP) is also reflected by the s-spin densities on the pyrrole protons which amount to PH(Ag) = 0.15% and pH(Cu) = 0.093%, respectively. A comparison with the corresponding data of an Xa calculation on Cu(II)-porphine1725 (oh(Cu) = 0.071%) indicates that the state-of-the-art electronic structure calculation underestimates the amount of unpaired spin density on the porphyrin ring. 

To get a deeper insight into the factors which affect the electronic structure of hemopro-teins, systematic studies on heme model compounds have been undertaken by Scholes and coworkers79 247 255. The model systems used by these authors are protohemin, deuterohemin and ferric tetraphenylporphyrin with a series of axial ligands. All the published ENDOR data on high-spin heme model compounds were obtained in frozen solutions with B0 along gi = 2 which is oriented normal to the porphyrin plane. A 1 1... 

It is well known that crystal and electronic structures are interdependent and define the reactivity of chemical substances. In Section 1.4.2, it was noted that copper-porphyrin complex gives cation-radicals with significant reactivity at the molecular periphery. This reactivity appears to be that of nucleophilic attack on this cation-radical, which belongs to n-type. The literature sources note, however, some differences in the reactivity of individual positions. A frequently observed feature in these n-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of porphyrin consistent with a localized structure rather than the delocalized structure usually ascribed to cation-radical. A pseudo Jahn-Teller distortion has been named as a possible cause of this alternation, and it was revealed by X-ray diffraction method (Scheidt 2001). 

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