Synthesis and characterization of the "pocket" porphyrins

Collman, James P.; Brauman, John I.; Collins, Terrence J.; Iverson, Brent L.; Lang, Georgina; Pettman, Roger B.; Sessler, Jonathan L.; Walters, Mark

doi:10.1021/ja00348a018

Cited by 109 publications

(74 citation statements)

References 6 publications

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“…However, the 1 H-NMR spectrum of these species is not as well-defined as with CObound or O 2 -bound species (33,34) suggesting that multiple species with different spin states may be present. Upon drying the sample by azeotropic distillation with toluene the following observations were made: (i) paramagnetic signals develop first at 15 ppm then at 50-60 ppm corresponding to the signals of ␤-pyrrole protons (35)(36)(37)(38) and (ii) the 4 band of a high spin species develops (1,342 cm Ϫ1 ) to give a 3:7 ratio 4 band(HS)/4 band(LS). However, washing a dry sample with water resulted in the disappearance of both the 1 H-NMR paramagnetic signals and the resonance Raman 4 high spin marker band.…”

Section: Resultsmentioning

confidence: 99%

Water may inhibit oxygen binding in hemoprotein models

Collman

Decréau²,

Dey³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Three distal imidazole pickets in a cytochrome c oxidase (CcO) model form a pocket hosting a cluster of water molecules. The cluster makes the ferrous heme low spin, and consequently the O2 binding slow. The nature of the rigid proximal imidazole tail favors a high spin/low spin cross-over. The O2 binding rate is enhanced either by removing the water, increasing the hydrophobicity of the gas binding pocket, or inserting a metal ion that coordinates to the 3 distal imidazole pickets.spin cross-over ͉ tris-imidazole pocket ͉ water cluster H emoglobin (Hb), myoglobin (Mb) and cytochrome c oxidase (CcO) are hemoproteins that bind O 2, subsequently transporting or reducing it in a 4e-/4Hϩ process (1, 2). The kinetics of oxygen binding to the active sites of these biomolecules are tuned by stabilizing interactions between the oxygen complex and the immediate environment (3, 4). In monometallic proteins such as myoglobin or hemoglobin, a distal histidine stabilizes the oxygen complex by hydrogen bonding (5, 6). A distal copper tris-imidazole ligand in CcO also provides enthalpic stabilization (7). In addition to structural factors affecting oxygen adduct stability in Mb and Hb, it has been suggested that the molecules of water present in the binding pocket could contribute to the relative oxygen affinities (4, 8, 9) in a model dubbed the ''water displacement model.'' This proposed model could logically be extended to CcO where water is the product of the 4e-/4Hϩ reduction of O 2 . Water is expected to be present in larger quantities in CcO than in Hb or Mb, and it is removed from the binding site by water channels (10-13). Here, we describe well-defined biomimetic hemoprotein models 1-4 ( Fig. 1) that demonstrate the role of water in slowing the binding of O 2 . The rates of reaction correlate with the hydrophobicity of the distal pocket (tris-pivalamido-or picket fence in 2, tris-imidazole in 3) and the presence or absence of a distal bound metal [Cu(I) or Zn(II) in 4ab]. Results and DiscussionThe reaction of oxygen with ferrous porphyrins 1-4 was carried out by injecting an anaerobic solution of porphyrin into O 2 -saturated dichloromethane solution (10 mM) under 1 atm of O 2 . Under the initial conditions of the reaction it is assumed, based on earlier studies (15), that the ligand association rate k on (O 2 ) is several orders of magnitude faster than the ligand dissociation rate k off (O 2 ) and consequently the dissociation rate can be assumed negligeable. The O 2 binding rates were obtained by monitoring the change in of the Soret and Q bands in the UV/Vis spectrum (Fig. 2) that shifted from 426 nm to 421 nm, and from 535 nm to 550 nm, respectively. The oxygen complex was characterized at various stages of the reaction by 2 resonance Raman stretches: (i) an oxygen isotope sensitive band observed at 570/544 cm Ϫ1 that corresponds to the Fe-O stretch and (ii) a 4-band (a spin state and redox state marker band) at 1,370 cm Ϫ1 that is typical of a ferric-superoxo species (16)(17)(18)(19). Second order k on (O 2 ) ra...

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Section: Resultsmentioning

confidence: 99%

Water may inhibit oxygen binding in hemoprotein models

Collman

Decréau²,

Dey³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…1B) [2]. This type of atropisomerism in porphyrins has been utilised in the design of superstructured models of the active sites of hemoproteins [3][4][5][6][7].Porphyrins (see Fig. 3) are macrocycles consisting of four pyrroles linked by four methine bridges.…”

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“…1B) by visual comparison of the areas of the six types of methyl group resonances [11]. According to other studies on porphyrins (see references [3][4][5] and [12][13][14][15][16][17][18][19] for a representative list of examples), the existence of atropisomers is usually revealed in NMR spectroscopy by multiplets with rather broad peaks mainly due to extensive overlap of signals.To clearly illustrate atropisomerism, we discuss the wellresolved 250 MHz 1 H NMR spectrum of meso-tetrakis(3-sulfonatomesityl)porphyrin tetrasodium salt (Fig. 3), a porphyrin prepared (note 1) as a potential antiviral agent [20] Illustrating atropisomerism in the porphyrin series using NMR spectroscopy -the mesityl ring introduced in the meso positions of the porphyrin has methyl substituents in both ortho positions of the phenyl group, which greatly increases the activation energy of the rotation barrier around the C-C bond diminishing the possibility of thermal isomerization [12].…”

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Illustrating atropisomerism in the porphyrin series using NMR spectroscopy

et al. 1999

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Atropisomers are stereoisomers resulting from restricted rotation around single bonds such that the rotational barrier is high enough to permit observation of the isomeric species. Atropisomers are numerous in number and type: among atropisomers of the sp 2 -sp 2 single bond type, a classical example is constituted by the biphenyls (or biaryls in general) as shown in figure 1A. When X ≠ Y and U ≠ V and if the steric interaction of X-U, X-V, and/or Y-V, Y-U is large enough, two nonplanar, axially chiral enantiomers exist [1]. Another example of atropisomerism, related to the biphenyltype, was first reported by Gottwald and Ullman in the porphyrin series (Fig. 1B) [2]. This type of atropisomerism in porphyrins has been utilised in the design of superstructured models of the active sites of hemoproteins [3][4][5][6][7].Porphyrins (see Fig. 3) are macrocycles consisting of four pyrroles linked by four methine bridges. Carbons 5,10, 15 and 20 are designated meso and carbons 2,3,7,8,12,13, 17 and 18 are the β pyrrole positions (Fisher's convention [8]). Porphyrins with four identical aryl groups in the meso position are derivatives with restricted rotation about the aryl-porphyrin bond due to interactions of the β-CH groups with the ortho-substituents of the meso-aryl groups (R or R' ≠ H, R and R' magnetically nonequivalent, Fig. 1B). At room temperature, the conformational rigidity is frequently sufficient to observe and also to isolate the corresponding atropisomers. These isomers may be described in terms of whether the ortho substituents are above (β) or below (α) the plane of the porphyrin ring [9]. When the porphyrin ring is formed by random linkages of pyrroles and mono-o-substituted benzaldehydes, the statistical ratio for the four possible isomers β 4 , αβ 3 , α 2 β 2 and αβαβ is 1:4:2:1, respectively (Fig. 2). Gottwald and Ullman [2] separated these isomers by chromatography in their study on meso-tetrakis (o-hydroxyphenyl)porphyrin. Recently, the structure of two atropisomers was assigned based on X-ray analysis [10]. The distribution of the four atropisomers was estimated in the case of the nickel complex of meso-tetra-o-tolylporphyrin (R = Me, R' = H, Fig. 1B) by visual comparison of the areas of the six types of methyl group resonances [11]. According to other studies on porphyrins (see references [3][4][5] and [12][13][14][15][16][17][18][19] for a representative list of examples), the existence of atropisomers is usually revealed in NMR spectroscopy by multiplets with rather broad peaks mainly due to extensive overlap of signals.To clearly illustrate atropisomerism, we discuss the wellresolved 250 MHz 1 H NMR spectrum of meso-tetrakis(3-sulfonatomesityl)porphyrin tetrasodium salt (Fig. 3), a porphyrin prepared (note 1) as a potential antiviral agent [20] Illustrating atropisomerism in the porphyrin series using NMR spectroscopy -the mesityl ring introduced in the meso positions of the porphyrin has methyl substituents in both ortho positions of the phenyl group, which greatly increases the activatio...

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“…The first is an extension of single-step coupling of benzaldehyde and pyrrole to produce meso-tetraphenylporphyrin (1 2). Aromatic aldehydes with potential amino groups as ortho-substituents are condensed with pyrrole and the protective structures are linked to the amino groups via amide linkages using appropriate acyl chlorides (5,6). In a modification of this method, the protective structures are linked to the aromatic aldehydes at their ortho positions via ester or ether functions, prior to the coupling with pyrrole (7, 9, 10).…”

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Synthesis and characterization of durene-capped porphyrins and the crystal structure of a hemin derivative

David¹,

Dolphin²,

James³

et al. 1986

Can. J. Chem.

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, 208 (1986). Sterically hindered porphyrins having a fully hydrophobic cavity have been prepared. The cavity is capped with a 2,3,5,6-tetramethylbenzene moiety containing at the 1,4-positions methylene -(CH2),,-chains ( n = 4, 5, 7) bonded at trans pyrrole rings of a porphyrin that is alkylated with methyl or ethyl groups at the other P-pyrrolic positions. The iron(II1) chloride derivative of the 4,4-durene-capped base has been obtained as single crystals, and subjected to X-ray structural analysis. The typical high spin, square pyramidal geometry of five-coordinate hemin chlorides is maintained; the porphyrin core is strongly distorted and there is no interaction between the phenyl group of the strap and the iron.

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Synthesis and characterization of the "pocket" porphyrins

Cited by 109 publications

References 6 publications

Water may inhibit oxygen binding in hemoprotein models

Water may inhibit oxygen binding in hemoprotein models

Illustrating atropisomerism in the porphyrin series using NMR spectroscopy

Synthesis and characterization of durene-capped porphyrins and the crystal structure of a hemin derivative

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