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Porphyrin Isomers (porphyrin + isomer)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

DFT study of core-modified porphyrin isomers

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2007
Y. Soujanya
Abstract B3LYP/6-311+G** calculations were performed systematically on 1,2 (syn) and 1,3 (anti) tautomeric forms of oxa- and thia- core-modified porphyrin isomers, which resulted in a total of 86 structures. The structural and energetic variation in all the isomers were analyzed. In corrphycene, hemiporphycene and porphycene the Z forms are more stable compared to the corresponding E forms in both the anti and syn oxa- and thiaporphyrin isomers. In contrast, in the syn isomeric forms of [3.0.1.0], [3.1.0.0] and [4.0.0.0] oxaporphyrins and in both syn and anti forms of thiaporphyrin isomers, Z forms are less stable. The HOMO and LUMO values are both negative and varied in a narrow zone, indicating no dramatic effect on the position of heteroatom substitution on the redox properties. The effect of geometric constraints due to the alteration of meso-bridge length and the hetero atom disposition in the porphyrin core on the relative stabilities of the isomers is analyzed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]

Novel Controlling Mechanism of the Oxygen Affinity in Myoglobin With Isomeric Porphyrins

ARTIFICIAL ORGANS, Issue 2 2009
Saburo Neya
Abstract The biological function of the core modified porphyrin isomers such as porphycene, corrphycene, and hemiporphycene was examined. The iron complexes stoichiometrically coupled with apomyoglobin to afford stable holoproteins. The oxygen affinity of the reconstituted myoglobins (Mbs) changed over a 60 000-fold range depending on the molecular structure of the prosthetic groups. For instance, a corrphycene with electronegative substituents to the bipyrrole part reduced the oxygen affinity of Mb to P50 = 300 mm Hg while the porphycene-substituted Mb exhibited a P50 = 0.005 mm Hg. A notable increase in the oxygen delivery capacity of the corrphycene-substituted Mb was explained on the basis of the trapezoidal corrphycene shape that stabilizes the iron displacement from the macrocycle plane toward the proximal histidine. The above observations demonstrate that the core modified heme isomers serve as novel molecular tools to regulate the oxygen affinity of Mb. [source]

Modification of Supramolecular Binding Motifs Induced By Substrate Registry: Formation of Self-Assembled Macrocycles and Chain-Like Patterns

CHEMISTRY - A EUROPEAN JOURNAL, Issue 42 2009
Leslie-Anne Fendt
Abstract The self-assembly properties of two ZnII porphyrin isomers on Cu(111) are studied at different coverage by means of scanning tunneling microscopy (STM). Both isomers are substituted in their meso -positions by two voluminous 3,5-di(tert -butyl)phenyl and two rod-like 4,-cyanobiphenyl groups, respectively. In the trans -isomer, the two 4,-cyanobiphenyl groups are opposite to each other, whereas they are located at right angle in the cis -isomer. For coverage up to one monolayer, the cis- substituted porphyrins self-assemble to form oligomeric macrocycles held together by antiparallel CN,,,CN dipolar interactions and CN,,,H-C(sp2) hydrogen bonding. Cyclic trimers and tetramers occur most frequently but everything from cyclic dimers to hexamers can be observed. Upon annealing of the samples at temperatures >150,°C, dimeric macrocyclic structures are observed, in which the two porphyrins are bridged by Cu atoms, originating from the surface, under formation of two CN,,,Cu,,,NC coordination bonds. The trans -isomer builds up linear chains on Cu(111) at low coverage, whereas for higher coverage the molecules assemble in a periodic, densely packed structure. Both cis - and trans -bis(4,-cyanobiphenyl)-substituted ZnII porphyrins behave very differently on Cu(111) compared to similar porphyrins in literature on less reactive surfaces such as Au(111) and Ag(111). On the latter surfaces, there is no signal visible between molecular orientation and the crystal directions of the substrate, whereas on Cu(111), very strong adsorbate,substrate interactions have a dominating influence on all observed structures. This strong porphyrin,substrate interaction enables a much broader variety of structures, including also less favorable intermolecular bonding motifs and geometries. [source]