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Molecular Structures of Linear Polypyrrolic Pigments
Author(s) -
Sheldrick W. S.
Publication year - 1983
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198300023
Subject(s) - chemistry , biliverdin , intramolecular force , protonation , bile pigments , hydrogen bond , stereochemistry , tetrapyrrole , crystallography , pigment , molecule , heme , organic chemistry , ion , heme oxygenase , enzyme
The results of X‐ray structural analyses of open‐chain polypyrrolic compounds are reviewed. Particular emphasis is placed on bilirubin and biliverdin derivatives and on the relevance of their observed conformations to the biological function and properties of natural bile pigments. Typical for bilirubin derivatives is a ridge‐tile conformation stabilised by six intramolecular hydrogen bonds, in which the individual pyrromethenone units are Z‐syn periplanar. Macrocyclic helical conformations are adopted by biliverdin derivatives and model bilatrienes‐ abc . The bonding pattern and degree of bond delocalisation within the tetrapyrrole skeleton are discussed in comparison to the molecular geometries of model bi‐ and tripyrrolic compounds. The results indicate that the methine bridge at C5 may demonstrate considerable conformational flexibility in bilatrienes‐ abc , whereas a marked degree of bond delocalisation is observed for the B, C and D rings. Protonation or metal complexation leads to pronounced changes in the degrees of stretch and widening of the helix and to corresponding changes in the electronic spectrum.