Fahimeh Eivazi

π–π Aggregation in metalloporphyrins: causative factors

The strength of aggregation in PdII, NiII, ZnII, and CdII metalloporphyrins is shown by n.m.r. spectroscopy to depend upon interaction of the metal ion with the porphyrin π-system; within a selected series of 2,4-disbustituted deuteroporphyrin-IX dimethyl esters complexed with a constant metal ion the aggregation is further enhanced by the presence of electron-withdrawing substituents on the porphyrin periphery.

New syntheses of deuterated protoporphyrin-IX derivatives for heme protein nmr studies

Abstract An efficient total synthesis of 1,5-di(trideuteromethyl)protoporphyrin-IX ( 3 ) dimethyl ester from monopyrrole precursors is described, the synthesis proceeding through crystalline tripyrrene and a,c-biladiene salt intermediates. The 2- and 4-vinyl groups in ( 3 ) are formed from the corresponding (2-chloroethyl) substituents by way of base-promoted dehydrochlorination. In protio solvents, this synthetic step is shown to exchange out preferentially deuterons in the 1-methyl group, and this observation is exploited in an efficient synthesis of the 1,3-di(trideuteromethyl)protoporphyrin-IX ( 22 ) dimethyl ester from 2,4-diacetyldeuteroporphyrin-IX ( 20 ) dimethyl ester (which is in turn accessible from commercially available protoporphyrin-IX ( 5 )). Thus, basic exchange in deuterated solvent of ( 20 ) gives the deuterated analog, which after reduction and dehydration gives the 1,3-di(trideuteromethyl)protoporphyrin-IX analog ( 22 ), in which the vinyl H 2 and propionic C H 2 ·CO functions have also become deuterated.

The NMR spectra of porphyrins—12: 13C and proton NMR spectra of the zinc(ii)coproporphyrin isomers2

Abstract The 13 C and proton NMR spectra of the zinc(II) complexes of the tetramethyl esters of the four coproporphyrin type isomers are reported and assigned. Effects of aggregation phenomena on these shifts are discussed and a method involving addition of a slight excess of pyrrolidine is proposed for measurement of the spectra of the “monomeric” species; spectra obtained under these conditions are capable of simple, straight-forward interpretation and assignment in terms of molecular symmetry. Thus, a facile distinction between the type isomers is obtained. The “monomer” chemical shifts so derived allow consistent SCS parameters to be derived. The C β -Me SCS are shown to be related to the bond order of the C β -C β bond in the porphyrin ring, and are thus quite different from the corresponding SCS in pyrroles. Aggregation shifts in the 13 C and proton spectra are shown to be consistent with the presence of “stacked” aggregates with the ring current of one molecule affecting the other, together with an additional effect on the chemical shifts of the meso carbons, which is probably steric in origin.

Mechanisms of aggregation in metalloporphyrins: demonstration of a mechanistic dichotomy

N.m.r. spectroscopy is used to demonstrate that the predominant interaction in aggregations of magnesium(II) porphyrins [e.g.(1)] involves the metal atom in one molecule and the propionate carbonyl group in another; in contradistinction, the similarly strong aggregation observed for the first time in zinc(II) porphyrins [e.g.(2)] is shown to be independent of a metal to side-chain interaction.

Bile pigment studies—III: Controlled oxidative degradation of 1,19(21,24h)-bilindiones (bilitrienes)

Treatment of the model 1,19(21,24H)-bilindione (1) with thallium(III) acetate in methanol gives the thallium(III) complex (11) which is unstable and in the presence of air and methanol is transformed into the 15,16-dimethoxy complex (12), characterised as the metal free derivative (13). When exposed to light, solutions of (12) are oxidised to afford, after work-up, the 14-formyl-1(15H)-tripyrrinone (4) and ethylmethylmaleimide (17). A general discussion of mechanistic implications is presented.

Crystal and molecular structure of a 4,5-dimethyoxbilindione derived from etiobiliverdin-IVγ: a possible model compound for the phytochrome chromophore

The structure of a synthetic bile pigment, 3,8,12,17-tetraethyl-4,5-dimethoxy-2,7,13,18-tetramethyl-4,5-dihydrobilin-1,19(21H,24H)-dione, C33H44N4O4, has been determined using three-dimensional diffractometer data. It crystallizes in the triclinic space group P with a= 12,755 (2), b= 12.944(s), c= 12.615(2)A, α= 112.27°(2), β= 113.76°(2), γ= 75.45°(2), Z= 2. There is one-half of an n-hexane molecule of crystallization present per formula unit. The structure was solved by direct methods and refined by full-matrix least squares to yield a final R factor of 0.105. The compound, which could be considered as a model for the far-red form (Pfr) of the phytochrome chromphore, belongs to the class of bile pigments known trivially as bilipurpurins. Three of the four pyrrole rings form a conjugated system which is not strictly planar, but is quasi-helical in nature. The fourth ring which is joined to the others by an sp3 carbon atom, is considerably out of the plane of the other three. Bond lengths and angles show a large degree of bond fixation. There is intermolecular hydrogen bonding so that the molecules form hydrogen-bonded dimers.

Bile pigment studies. Part 5. Some fragmentation reactions of bilindiones (bilitrienes)

Anodic oxidation of the model bilindione (1) at platinum electrodes in the presence of methanol gives a good yield of the 15,16-dimethoxybilindione (3). With nickel(II) acetate, this compound gives the chelate (6) which fragments upon treatment with acid toafford the tripyrrinone aldehyde (2)via the vinyl ether (8). When the metal-free 15,16-dimethoxybilindione (3) is treated with aqueous acid the same tripyrrinone aldehyde (2) to gether with the parent bilindione (1) are obtained.

Crystal and molecular structure of 3,8,12-triethyl-14-formyl-2,7,13-trimethyl-1(15H)-tripyrrinone, a tripyrrolic aldehyde derived from aetiobiliverdin-IVγ

The structure of the title compound, a tripyrrolic compound derived from aetiobiliverdin-IVγ has been determined from three-dimensional X-ray diffractometer data. The tripyrrolic skeleton shows only small deviations from planarity. Adjacent rings assume the Z-configuration with the nitrogen atoms syn. Bond lengths in the three rings are quite different. No intra- or inter-molecular hydrogen bonding is observed. The compound crystallizes in the orthorhombic space group Pna21 with cell dimensions a= 9.773(2), b= 11.468(2), c= 19.402(3)A, Z= 4. The structure was solved by direct methods and refined by least-squares techniques to R 0.063 for 1 037 observed reflections.