Cobalt Picket Fence Porphyrins Research Articles

Observation in the gas phase of the ligation of 1-methylimidazole to hemoprotein mimics.

Hemoprotein mimics, cobalt picket fence porphyrins have been prepared in the gas phase as neutral molecules for the first time. Their ligation properties have been studied with 1-methylimidazole and compared with those of other cobalt porphyrins, tetraphenyl porphyrin, and cobalt protoporphyrin IX chloride, in view of studying the sterical properties of the ligation. It is shown that the cobalt picket fence porphyrin can only accept one 1-methylimidazole ligand in contrast to less sterically crowded porphyrins like cobalt tetraphenylporphyrin that present two accessible ligation sites. The femtosecond dynamics of these ligated systems have been studied after excitation at 400 nm, in comparison with the unligated ones. The observed transients are formed in much shorter times, 30 fs for the ligated species, as compared to free species (100 fs), supporting the porphyrin to metal charge transfer nature of these transients. The similar decays of the ligated transients <1 ps reveal the absence of photodissociation of the cobalt-1-methylimidazole bond at this step of evolution.

Variation of Oxo-Transfer Reactivity of (Nitro)Cobalt Picket Fence Porphyrin with Oxygen-Donating Ligands

Derivatives of (nitro)cobalt picket fence porphyrin with oxygen-donating ligands have been prepared in solution and in the solid state. Crystal structures of two of these derivatives, (H2O)CoTpivPP(NO2) and (CH3OH)CoTpivPP(NO2), have been determined. The ethanol complex (C2H5OH)Co(TPP)(NO2) has been obtained and spectrally characterized using sublimed layers methodology. The formation constant and the DeltaH degrees value of the association reaction with ethanol have been determined by FTIR measurements in CCl4 solution. Catalytic oxygen activation and oxo-transfer reactions of these derivatives have been assessed in solution. Correlations between the oxo-transfer reactivity, thermodynamics, and characteristics of the nitro ligand show that although calculated and observed ONO vibrational spectra and bond lengths suggest activation of the NO2 ligand and enhanced oxo-transfer reactions as seen in the analogous five-coordinate complexes, density functional theory calculations support that thermodynamics limits oxo-atom transfer reactions in these six-coordinate systems.

Oxygen-binding to simple cobaltporphyrins combined with polyvinylmidazole

Reversible oxygen-binding was observed at low temperature for the poly(vinylimidazole-co-octyl methacrylate) complexes of the simple or planar cobaltporphyrins (CoP) such as cobalt-tetraphenylporphyrin and cobalt-octaethylporphyrin. The oxygen-binding affinity and rate constants were compared with those for the cobalt-picketfence porphyrin, a typical oxygen-carrier. The low oxygen-binding affinity for the CoP complexes was attributed to the enormously large oxygen-releasing rate constant.

Molecular recognition of oxygen by protein mimics: dynamics on the femtosecond to microsecond time scale.

Molecular recognition by biological macromolecules involves many elementary steps, usually convoluted by diffusion processes. Here we report studies of the dynamics, from the femtosecond to the microsecond time scale, of the different elementary processes involved in the bimolecular recognition of a protein mimic, cobalt picket-fence porphyrin, with varying oxygen concentration at controlled temperatures. Electron transfer, bond breakage, and thermal "on" (recombination) and "off" (dissociation) reactions are the different processes involved. The reaction on-rate is 30 to 60 times smaller than that calculated from standard Smoluchowski theory. Introducing a two-step recognition model, with reversibility being part of both steps, removes the discrepancy and provides consistency for the reported thermodynamics, kinetics, and dynamics. The transient intermediates are configurations defined by the contact between oxygen (diatomic) and the picket-fence porphyrin (macromolecule). This intermediate is critical in the description of the potential energy landscape but, as shown here, both enthalpic and entropic contributions to the free energy are important. In the recognition process, the net entropy decrease is -33 cal mol(-1) K(-1); Delta H is -13.4 kcal mol(-1).

High Oxygen-Binding Affinity of Poly(4-Vinylimidazole-co-octylmethacrylate)-Cobaltporphyrin Complex: Effect of Hydrogen-Bond at the Imidazole Residue

The oxygen-binding affinity of the cobalt-picketfence-porphyrin (CoP) ligated with imidazole was enhanced in the presence of an additive which forms a hydrogen-bond with the ligated imidazole. The CoP complex with poly(4(5)-vinylimidazole-co-octylmethacrylate) rapidly and reversibly bound oxygen and showed very high oxygen-binding affinity: The oxygen transport in the CoP-polymer membrane was efficiently facilitated.

ChemInform Abstract: Resonance Raman Spectra of Dioxygen Adducts of Cobalt Picket Fence Porphyrins.

AbstractThe resonance Raman spectra (406.7 nm, ca. ‐90 °C) of (I) (α4‐, α3‐, cis‐α2‐ and trans‐α2‐atropisomers) are measured in toluene.

Resonance Raman spectra of dioxygen adducts of cobalt picket fence porphyrins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTResonance Raman spectra of dioxygen adducts of cobalt picket fence porphyrinsJ. Odo, H. Imai, E. Kyuno, and Kazuo. NakamotoCite this: J. Am. Chem. Soc. 1988, 110, 3, 742–748Publication Date (Print):February 3, 1988Publication History Published online1 May 2002Published inissue 3 February 1988https://doi.org/10.1021/ja00211a014RIGHTS & PERMISSIONSArticle Views147Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

Oxygen binding to cobalt porphyrins

The thermodynamic constants of oxygen binding to cobalt picket fence porphyrin complexes, meso-tetra(a,o,a,o- o-pivalamidophenyl)porphyrinatocobalt(II)- 1 -methylimidazole and 1,2-dimethylimidazole, are reported. In contrast to pre- viously studied cobalt porphyrins, these complexes bind oxygen with the same affinity as cobalt substituted myoglobin and he- moglobin. Solvation effects are discussed as the source of this difference. The use of sterically hindered axial bases as models of T state hemoglobin is discussed. In studies of myoglobin (Mb) and hemoglobin (Hb), the replacement of the neutral iron porphyrin prosthetic group with different metalloporphyrins has proved to be a useful tech- nique.2 Artificial hemoglobins containing ~inc,~.~ manga- ne~e,~-* ~opper,~ and nickel9 have been reconstituted, and their properties compared with those of the native iron proteins. These artificial systems, however, are incapable of reversible oxygenation. In contrast, cobalt substituted hemoglobin and myoglobin (CoHb and CoMb)l0 are functional,I1-l3 although their oxygen affinities are 10-100 times less than those of native Hb and Mb. CoHb exhibits cooperativity in oxygen binding, though to a lesser degree than Hb. The extent of this cooperativity is conveniently expressed as AG;, , the free energy difference between the intrinsic binding of the first and the fourth 02 to Hb.13b,c For CoHb, AG:l is roughly one-third that of Hb under comparable condition^.'^^ Because of the different stereo- chemical and electronic factors involved in binding oxygen to a cobalt porphyrin, the observation of cooperativity in CoHb has been variously used either to que~tion~9~~J~ or s~pport'~~,'~ the elegant proposal of Perutz concerning the molecular mechanism of cooperativity in natural Hb.16 At the heart of this proposal is the assumption, based on earlier ideas of Hoard and Williams,18 that the high-spin iron in the unli- gated, low 02 affinity form of Hb (T state) lies out of the porphyrin plane, and that on binding 02, the iron becomes low spin and moves into the plane. The resulting motion of the proximal imidazole (0.6 A) then causes conformational changes in the protein which produce a higher 02 affinity quaternary form of the protein (R state). In the deoxy form of coboglobin, cobalt is low spin rather than high spin and the best estimates from simple cobalt model systems indicate that the proximal imidazole in CoHb moves -0.4 A upon oxygen- ation'4,'9,20 as opposed to the 0.6 8, for Hb. The resulting motion of the proximal histidine upon binding 02 will therefore only be two-thirds as great. This seems to be qualitatively consistent with the lowered AGil of CoHb.