Conformational flexibility porphyrins

These data form part of an increasing body of evidence that demonstrates the significant conformational flexibility of the porphyrin skeleton in the solid and in solution. Since a wide spectrum of photosynthetic and enzymatic reactions proceed via tt radicals of porphyrin derivatives, the consequences of the macrocyles flexibility are considered for distances and orientations between donors and acceptors, interactions with ligands, nearby charges or polar groups, electronic profiles and the gaps between the aj and a u highest occupied orbitals. 

In the present work, we used a conformationally flexible covalently-linked porphyrin dimer (5,5-[1,3-Propenediyl bis(oxy-2,l-phenylene)]bis[10,15,20-tris(4-methylphenyl)-21H,23H-porphin](0,0 -C (TTPH2)2) The dimer is mainly in two different conformations. 

Chls and all tetrapyrroles are heteroaromatic compounds and the aromatic character of the underlying tetrapyrrole moiety and the reactivity of the functional groups in the side chains govern their chemistry. Three different classes of tetrapyrroles, differentiated by their oxidation level, occur in nature porphyrins (11, e.g. hemes), chlorins (12, e.g. chls) and bacteriochlorins (13, e.g. bchls). As a cyclic tetrapyrrole with a fused five-membered ring, the overall reactivity of chi is that of a standard phytochlorin 7. Such compounds are capable of coordinating almost any known metal with the core nitrogen atoms. Together with the conformational flexibility of the macrocycle and the variability of its side chains, this accounts for their unique role in photosynthesis and applications ... 

Bode, B. E., Plackmeyer, J., Prisner, T. F., and Schiemann, O. (2008). PELDOR measurements on a nitroxide labeled Cu(II) porphyrin Orientation selection, spin-density distribution and conformational flexibility. J. Phys. Chem. A 112, 5064—5073. 

Meso-porphyrinogens formally represent the structural transition between pyrroles and porphyrins. Stimulated by the work of Floriani et al. [251], porphyrinogens were considered as alternative ligand sets in lanthanide chemistry by Jubb and Teuben [68,252]. The tetraamide ligand offers a coordination environment which is obviously sterically and electronically more flexible than that provided by the standard Cp2Ln- fragment. The conformational flexibility... 

It is well known that the conformational flexibility of the porphyrin framework allows for the relevant functional properties to be effectively regulated. Several interesting investigations have been performed on ligand coordination [37-39]. To develop a precise understanding of the interplay mechanism between the structural distortions of the porphyrin framework and the ligation of small adducts, the carbon monoxide (CO) axial ligand was clearly identified in the saddle-type CoTPP and FeTPP arrays formed on Ag(lll) under UHV [39]. 

It is noteworthy that triplet energy transfer in acetylene-bridged porphyrin dimers has been interpreted in terms of the conformational flexibility of the system [215]. Thus, rapid relaxation between triplet levels occurs in a series of meso-... 

Bisporphyrin cleft molecule 25, which has dendritic wedges attached to the [60] fullerene molecules, forms an artificial peapod (Figure 9.26) [104]. [60]Fullerene is encapsulated within the cleft space provided by the two porphyrin components. As a result, the bisporphyrin cleft loses its conformational flexibility, and the two porphyrin units adopt a parallel arrangement, as in encapsulating [60]fullerene. This pre-organized structure assembles to produce a parallel array of the fullerene peapods. A fibrous morphology with a uniform diameter of 15nm is confirmed by TEM. 

The porphyrin ligand is sufficiently flexible to adopt nonplanar conformations in response to steric or electronic effects induced by the central metal, the axial ligands, or substitution at the porphyrin periphery. Coordination of the small, nonmetallic Si(IV), Ge(IV), P(V), and As(V) ions to porphyrins offer an ideal opportunity to study not only the direct effect on this phenomenon of... 

The high conformational mobility of porphyrin-quinone compounds with flexible bonding makes it difficult to elucidate in sufficient detail the mechanism of electron transfer between porphyrin and quinone fragments. Far greater possibilities for determining the role of mutual orientation of P and Q and the distance between them are offered by P-Q compounds in which the P and Q fragments are linked by several bridges. A P-Q compound of this... 

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