title: Ring-opening and meso substitution from the reaction of cyanide ion with zinc verdohemes.
abstract: The reactivity of zinc verdoheme, [Zn(II)(OEOP)](O(2)CCH(3)) where OEOP is the monoanion of octaethyl-5-oxaporphyrin, with cyanide ion has been shown to be a complex process that involves not only the expected ring-opening of the macrocycle, as occurs with other nucleophiles (methoxide, methanethiolate, dimethylamide), but also substitution at one or two of the meso positions. The ring-opened products have been subjected to crystallographic study. The structures of mu-H(2)O-[Zn(II)(OEB-10,19-(CN)(2))](2) and mu-H(2)O-[(Zn(II)(OEB-10,15,19-(CN)(3))](2) both consist of two helical tetrapyrrole subunits that are coordinated to a zinc ion through four Zn-N bonds. The two zinc ions are coordinated to a bridging water molecule that is also hydrogen bonded to a lactam oxygen atom at one end of each tetrapyrrole subunit. Thus the chiral sense of one helical Zn(II)(OEB-10,19-(CN)(2)) portion is transmitted to the other Zn(II)(OEB-10,19-(CN)(2)) unit and the resulting binuclear unit is chiral. In contrast Co(II)(OEB-15,19-(CN)(2)), which was obtained by the insertion of Co(II) into the free ligand, is monomeric with a four-coordinate cobalt ion. A series of DFT geometry optimization calculations were performed on zinc complexes of 5-oxaporphyrins (verdoheme), verdins (bilindione), 4-cyano-5-oxaporphyrins, and 19-cyanoverdins in an effort to gain insights to the features of these complexes and the reactions that lead to meso-cyano-substituted cyanoverdins.
authors.affiliation: Department of Chemistry, University of California, Davis, California 95616, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Johnson
authors.forename: M M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: A M
authors.initials: AM
authors.lastname: Stolzenberg
authors.forename: A L
authors.initials: AL
authors.lastname: Balch
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry*; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D015032:Zinc / Q000737:chemistry*
chemical_list: D003486:Cyanides; C099547:verdoheme; D006418:Heme; D015032:Zinc; D001205:Ascorbic Acid