Synthesis and characterization of "tailed picket fence" porphyrins

Collman, James P.; Brauman, John I.; Doxsee, Kenneth M.; Halbert, Thomas R.; Bunnenberg, E.; Linder, Robert E.; LAMAR, G. N.; Gaudio, John Del; Lang, Georgina; Spartalian, K.

doi:10.1021/ja00532a033

Cited by 177 publications

(105 citation statements)

References 9 publications

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“…As a result of being low spin, species 3-4ab displayed mostly diamagnetic NMR features (the off-rate of water being obviously slower than the NMR time scale). 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).…”

Section: Resultsmentioning

confidence: 93%

“…The fact that 1 still displays LS character strongly suggests that the proximal tail itself, possibly because of its rigid design with a 1.3 disubstituted phenyl linker between the imidazole ring and the porphyrin, has a strong coordinating effect that induces a spin equilibrium making the 5C ferrous complex 1 borderline high spin/low spin [a covalently attached tail can be considered as being equivalent to ca 40 equiv. of free imidazole (34)]. This tail is rigid, unlike previous ''floppy'' imidazole tails where the imidazole was linked to the porphyrin by several methylene linkages (15,32,34).…”

Section: Resultsmentioning

confidence: 98%

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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: 93%

Section: Resultsmentioning

confidence: 98%

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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“…Rotary evaporation yielded Pre-APEB* as an orange solid (201 mg, 98%). 1 49 with SnCl 2 ,49 followed by dicyclohexylcarbodiimide (DCC) coupling with propynoic acid led to 6. Iron(II) was inserted into 6 to give 3 with standard procedures.…”

Section: Preparation Of Pre-apebmentioning

confidence: 99%

“…The details of the preparation and characterization of new porphyrins 3 and 6 are provided below and follow standard procedures in porphyrin chemistry. 49,51 meso-5-Mono-o-propynamidophenyl-10,15,20-triphenylporphyrin (6)-5 (100 mg, 0.158 mmol), propynoic acid (500 mg, 7.30 mmol), and DCC (150 mg, 0.73 mmol) were mixed in ethyl acetate (20 mL) and the resulting mixture was stirred at room temperature for 24 h. After most of the starting material had been consumed (monitored by TLC), the volume of the solution was expanded (50 mL EtOAc) and the mixture was washed with NaHCO 3 solution (2 × 50 mL) and water (2 × 100 mL) and dried (Na 2 SO 4 ). After evaporation of the solvent, the residue was subjected to chromatography [SiO 2 , 63 μm Scheme depicting the formation of mixed monolayers on gold electrodes coupled to redox species via Cu(I)-catalyzed azide-acetylene cycloaddition.…”

Section: Preparation Of Pre-apebmentioning

confidence: 99%

Rate of Interfacial Electron Transfer through the 1,2,3-Triazole Linkage

et al. 2006

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The rate of electron transfer is measured to two ferrocene and one iron tetraphenylporphyrin redox species coupled through terminal acetylenes to azide-terminated thiol monolayers by the Cu(I)-catalyzed azide-alkyne cycloaddition (a Sharpless "click" reaction) to form the 1,2,3-triazole linkage. The high yield, chemoselectivity, convenience, and broad applicability of this triazole formation reaction make such a modular assembly strategy very attractive. Electron-transfer rate constants from greater than 60,000 to 1 s −1 are obtained by varying the length and conjugation of the electron-transfer bridge and by varying the surrounding diluent thiols in the monolayer. Triazole and the triazole carbonyl linkages provide similar electronic coupling for electron transfer as esters. The ability to vary the rate of electron transfer to many different redox species over many orders of magnitude by using modular coupling chemistry provides a convenient way to study and control the delivery of electrons to multielectron redox catalysts and similar interfacial systems that require controlled delivery of electrons.

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“…by their dimensions. The methods of porphyrin synthesis with a certain axial discrimination over the dimensions of coordinating molecules was designed by Collman et al (1975Collman et al ( , 1980.…”

Section: Electron Tunneling In Reactions Of Metalloporphyrin Moleculementioning

confidence: 99%

Long Range Electron Tunneling in Biological and Model Systems

Khairutdinov

Brickenstein

1986

Photochem & Photobiology

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Abstract-This review paper reports the data on the role of long range electron tunneling in photosynthetic and model systems. The main papers concerned with elucidation mechanisms and kinetical peculiarities of electron transfer in reaction centers of bacteria and green plants are considered. The paper reviews the articles on long range electron transfer in reactions of metalloporphyrinssynthetic analogs of the main natural pigment of photosynthesis, chlorophyll. Liquid and solid phase redox reactions of electronically excited porphyrin molecules, intramolecular and photosensitized electron transfer processes are considered.

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Synthesis and characterization of "tailed picket fence" porphyrins

Cited by 177 publications

References 9 publications

Water may inhibit oxygen binding in hemoprotein models

Water may inhibit oxygen binding in hemoprotein models

Rate of Interfacial Electron Transfer through the 1,2,3-Triazole Linkage

Long Range Electron Tunneling in Biological and Model Systems

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