Spectroscopic analysis of models for heme d1: isomeric copper(II) porphyrindiones

Mylrajan, M.; Andersson, Laura A.; Loehr, Thomas M.; Wu, Wenyuan; Chang, C. K.

doi:10.1021/ja00013a040

Cited by 10 publications

(7 citation statements)

References 4 publications

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“…The spectra for the two dyads are essentially identical to those we have previously reported for similar monomeric chlorins and oxochlorins . The scattering characteristics of all of these chlorins and oxochlorins are also generally similar to those that have been reported for other structurally similar macrocycles. , In general, the resonance Raman spectra of the chlorins and oxochlorins are much richer than those of porphyrins. This spectral richness arises because of the lower symmetry of the chlorins (and oxochlorins), which results primarily from saturation of one of the β-pyrrole bonds.…”

Section: Resultssupporting

confidence: 83%

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Comparison of Excited-State Energy Transfer in Arrays of Hydroporphyrins (Chlorins, Oxochlorins) versus Porphyrins: Rates, Mechanisms, and Design Criteria

Taniguchi

Kirmaier

et al. 2003

J. Am. Chem. Soc.

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A set of chlorin-chlorin and oxochlorin-oxochlorin dyads has been prepared with components in the same or different metalation states. In each case a 4,4'-diphenylethyne linker spans the respective 10-position of each macrocycle. The dyads have been studied using static and time-resolved absorption and emission spectroscopy, resonance Raman spectroscopy, and electrochemical techniques. Excited-state energy transfer from a zinc chlorin to a free-base (Fb) chlorin occurs with a rate constant of (110 ps)(-1) and an efficiency of 93%; similar values of (140 ps)(-1) and 83% are found for the corresponding oxochlorin dyad. Energy transfer in both dyads is slower and less efficient than found previously for the analogous porphyrin dyad, which displays a rate of (24 ps)(-1) and a yield of 99%. The slower rates and diminished efficiencies in the ZnFb chlorin and oxochlorin dyads versus the ZnFb porphyrin dyad are attributed to substantially weaker linker-mediated through-bond (TB) electron-exchange coupling (as indicated by resonance Raman data). Although the through-space (TS, i.e., dipole-dipole) coupling in the ZnFb-chlorin and -oxochlorin dyads is enhanced relative to the ZnFb porphyrin dyad (as indicated by Förster calculations), this enhancement is insufficient to compensate for the greatly diminished TB coupling. Taken together, the chlorin and oxochlorin dyads examined herein serve as benchmarks for elucidating the energy-transfer, electrochemical, and other properties of light-harvesting arrays containing multiple chlorins or oxochlorins.

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Section: Resultssupporting

confidence: 83%

“…A key spectral feature that distinguishes the oxochlorins from the chlorins is the band due to the stretching vibration of the keto group (ν C  O ) . The ν C  O mode is observed at ∼1722 cm -1 and is strongly resonance enhanced with Soret excitation (Figure , right panel, bottom trace).…”

Section: Resultsmentioning

confidence: 99%

Comparison of Excited-State Energy Transfer in Arrays of Hydroporphyrins (Chlorins, Oxochlorins) versus Porphyrins: Rates, Mechanisms, and Design Criteria

Taniguchi

Kirmaier

et al. 2003

J. Am. Chem. Soc.

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“…This fluorescence compromises the acquisition of Q y -excitation resonance Raman spectra of Zn, Mg, or Fb complexes in solution. The scattering characteristics for the chlorins and oxochlorins are generally similar to those that have been previously reported for these types of macrocycles. , In general, the resonance Raman spectra of the chlorins and oxochlorins are much richer than those of porphyrins. This spectral richness arises because of the lower symmetry of the chlorins (and oxochlorins), which results primarily from saturation of one of the β-pyrrole bonds.…”

Section: Resultssupporting

confidence: 82%

“…The ν C  O mode is much less strongly enhanced with Q y excitation. The relatively weak Q y enhancement is due to the fact that the keto group of the oxochlorin is at the 17-position, thus lying primarily along the x -axis of the macrocycle (Chart ). , In contrast, the ν C  O vibration of the keto group of chlorophyll is strongly enhanced with Q y excitation. , In the case of chlorophyll, the keto group is not appended to the saturated pyrrole ring of the macrocycle, but rather is attached to the 13-position as part of an exocyclic five-membered ring; the keto group thus lies along the y -axis of the chlorophyll chromophore. Finally, an additional vibrational feature that is observed for Cu4 and Oxo-Cu4 is the stretching vibration of the ethyne group (ν C ⋮ C ).…”

Section: Resultsmentioning

confidence: 99%

Synthesis and Electronic Properties of Regioisomerically Pure Oxochlorins

et al. 2002

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We describe a two-step conversion of C-alkylated zinc chlorins to zinc oxochlorins wherein the keto group is located in the reduced ring (17-position) of the macrocycle. The transformation proceeds by hydroxylation upon exposure to alumina followed by dehydrogenation with DDQ. The reactions are compatible with ethyne, iodo, ester, trimethylsilyl, and pentafluorophenyl groups. A route to a spirohexyl-substituted chlorin/oxochlorin has also been developed. Representative chlorins and oxochlorins were characterized by static and time-resolved absorption spectroscopy and fluorescence spectroscopy, resonance Raman spectroscopy, and electrochemistry. The fluorescence quantum yields of the zinc oxochlorins (Phi(f) = 0.030-0.047) or free base (Fb) oxochlorins (Phi(f) = 0.13-0.16) are comparable to those of zinc tetraphenylporphyrin (ZnTPP) or free base tetraphenylporphyrin (FbTPP), respectively. The excited-state lifetimes of the zinc oxochlorins (tau = 0.5-0.7 ns) are on average 4-fold lower than that of ZnTPP, and the lifetimes of the Fb oxochlorins (tau = 7.4-8.9 ns) are approximately 40% shorter than that of FbTPP. Time-resolved absorption spectroscopy of a zinc oxochlorin indicates the yield of intersystem crossing is >70%. Resonance Raman spectroscopy of copper oxochlorins show strong resonance enhancement of the keto group upon Soret excitation but not with Q(y)()-band excitation, which is attributed to the location of the keto group in the reduced ring (rather than in the isocyclic ring as occurs in chlorophylls). The one-electron oxidation potential of the zinc oxochlorins is shifted to more positive potentials by approximately 240 mV compared with that of the zinc chlorin. Collectively, the fluorescence yields, excited-state lifetimes, oxidation potentials, and various spectral characteristics of the chlorin and oxochlorin building blocks provide the foundation for studies of photochemical processes in larger architectures based on these chromophores.

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“…(3) ν CdO Mode. The ν CdO mode of 2-OMH is expected in the 1680-1750-cm -1 region (Ching et al, 1982;Andersson et al, 1990;Mylrajan et al, 1991). The exact frequency of this mode is expected to be sensitive to a variety of factors such as the oxidation-state of the iron ion, the hydrogen bonding, and the dielectric properties of the host medium (Babcock, 1988;Lutz & Robert, 1988;Krawczyk, 1989;Palaniappan & Bocian, 1995).…”

Section: Properties Of the Hemes In Synthetic Cytochromesmentioning

confidence: 99%

Structural and Electronic Properties of the Heme Cofactors in a Multi-Heme Synthetic Cytochrome

et al. 1996

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Resonance Raman, absorption, and electron paramagnetic resonance spectra are reported for a water soluble, synthetic cytochrome. The protein is a variant of the cytochrome beta maquette described by Robertson et al. [Robertson, D. E., et al. (1995) Nature 368, 425-432] and is composed of 62 amino acid residues arranged in a di-alpha-helical unit which dimerizes in solution to form a four-helix bundle. Each di-alpha-helical unit contains histidine residues at the 10,10' positions which serve as ligands to the hemes. When protoheme IX is incorporated, both hemes in the dimer are bis-ligated and low spin. The two hemes are inequivalent with respect to both binding affinity and redox properties. To investigate the properties of the heme cofactors, spectroscopic studies were conducted on peptides reconstituted with protoheme IX (PHa) and several related variants. These hemes include 2-vinyldeuteroheme (2-VDH), 4-vinyldeuteroheme (4-VDH), protoheme III (PHs), and 1-methyl-2-oxomesoheme XIII (2-OMH). Collectively, the spectroscopic studies reveal the following: (1) 2-VDH, 4-VDH, and 2-OMH bind to the protein and form bis-ligated low-spin complexes similar to PHa. The structures of the two hemes in the dimers are identical as are the immediate protein environments around the bound cofactors. These results indicate that the redox inequivalence of the two hemes is due to heme-heme electronic interactions rather than structural and/or environmental differences between the two cofactors. (2) The two hemes in the dimer are arranged in a edge-to-edge arrangement wherein the oxo group (2-OMH) or the vinyl group(s) are in the hydrophobic interface between the two units which comprise the dimer. The propionic acid tails point outward toward the hydrophilic region and extend into the solvent. (3) The PHs protein differs from the other synthetic proteins in that it contains one pentacoordinate, high-spin and one hexacoordinate, low-spin heme rather than two hexacoordinate low-spin cofactors. The open coordination site on the high-spin heme is inaccessible to exogenous imidazole but readily bind cyanide, suggesting that the alpha-helix containing the unbound histidine is nearby and partially shields the coordination site. The high-spin heme converts to low-spin at low-temperature, presumably via binding of the histidine residue on this nearby alpha-helix. It is suggested that the different behavior observed for the PHs protein is due to the fact that this heme is symmetric with respect to rotation about the alpha,gamma-axis of the macrocycle which bisects the meso-carbons between the vinyl groups and propionic acid residues. This symmetry precludes rotational isomerism about the alpha,gamma-axis to establish an unhindered fit. In contrast, all the other hemes examined contain at least one substituent smaller than a vinyl group which together with the fact that two different alpha,gamma-rotational isomers are possible for each heme in the dimer could allow these hemes to avoid the like-substituent--like-substituent heme--heme interac...

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Spectroscopic analysis of models for heme d1: isomeric copper(II) porphyrindiones

Cited by 10 publications

References 4 publications

Comparison of Excited-State Energy Transfer in Arrays of Hydroporphyrins (Chlorins, Oxochlorins) versus Porphyrins: Rates, Mechanisms, and Design Criteria

Comparison of Excited-State Energy Transfer in Arrays of Hydroporphyrins (Chlorins, Oxochlorins) versus Porphyrins: Rates, Mechanisms, and Design Criteria

Synthesis and Electronic Properties of Regioisomerically Pure Oxochlorins

Structural and Electronic Properties of the Heme Cofactors in a Multi-Heme Synthetic Cytochrome

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