Porphyrins linked to high acceptor strength cyano quinones as models for the photosynthetic reaction center

Szelinski, Helga; Niethammer, Dominique; Tian, P.; Kurreck, H.

doi:10.1016/0040-4020(96)00405-x

Cited by 5 publications

(7 citation statements)

References 40 publications

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“…Some studies, however, have probed the effect of scaffolding on controlling intramolecular electron transfer in complexes with the donor and acceptor connected via flexible linkers. Solution studies have utilized micelles, − cyclodextrins, ,− liquid crystals, − vesicles, − and lipid bilayers. , …”

Section: Introductionmentioning

confidence: 99%

Effect of DNA Scaffolding on Intramolecular Electron Transfer Quenching of a Photoexcited Ruthenium(II) Polypyridine Naphthalene Diimide

et al. 1999

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Intramolecular emission quenching of a photoexcited ruthenium(II) polypyridine by a covalently linked naphthalene diimide (NDI) has been measured in aqueous buffer both without and with calf thymus DNA. The complex consists of a Ru(2,2'-bipyridine)(2)(2,2'-bipyridine-5-carboxamide)(2+) electron donor covalently attached by way of a -CH(2)CH(2)CH(2)- linker to a 1,4,5,8-naphthalene diimide acceptor (Ru-NDI, 1). The NDI portion of the complex intercalates in calf thymus DNA, as indicated by the hypochromism of its optical absorbance bands and observation of an induced circular dichroism spectrum in the same region. Emission quenching in Ru-NDI has been measured relative to a Ru tris-bpy model lacking the NDI moiety by both lifetime and emission quantum yield techniques. Using lifetime averages, the relative emission quenching is, respectively, 99.1% and 97.9% in aqueous buffer solutions without and with DNA. The emission quenching is ascribed to intramolecular electron transfer within the Ru-NDI complex with an estimated driving force (-DeltaG degrees ) of 0.33 eV. In buffer, the emission decays of Ru-NDI alone are fit well with a triexponential model with lifetimes of 0.34 (0.88), 1.99 (0.11), and 12.6 (0.008) ns (relative amplitude). The emission decays of the DNA-intercalated Ru-NDI complex are also fit well with a triexponential model with lifetimes of 0.31 (0.79), 2.00 (0.13), and 11.8 (0.08) ns. Thus, the fractional amplitudes of the lifetimes change upon DNA intercalation of the complex, while the lifetimes themselves remain essentially the same. The average rates of electron transfer in aqueous buffer without and with DNA are, respectively, 1.6 x 10(9) and 6.8 x 10(8) s(-)(1). The striking result of this study is that the overall character of electron transfer quenching in Ru-NDI is very similar whether or not it is bound to DNA. Intercalation of the NDI in DNA apparently has negligible consequences for electron transfer, implying either that the activation energy and electronic coupling in Ru-NDI are largely unaffected by this, at first glance, seemingly significant environmental change or that changes in these parameters on DNA binding cancel fortuitously.

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Section: Introductionmentioning

confidence: 99%

Effect of DNA Scaffolding on Intramolecular Electron Transfer Quenching of a Photoexcited Ruthenium(II) Polypyridine Naphthalene Diimide

et al. 1999

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“…In particular, the different magnitudes of vicinal and geminal couplings 21 between two axial (9-13 Hz), an axial and an equatorial (3)(4)(5), two equatorial (2)(3)(4), and two geminally grouped protons (11-15 Hz), respectively, gave rise to characteristic coupling patterns that enabled us to discriminate unambiguously between the cis and trans diastereomers. The most characteristic coupling patterns were observed for the protons connected to the cyclohexane ring carbons bearing the substituents, i.e., to C-1 and C-4, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…13. 4 Hz, J1a2e ≈ J2e3a ≈ J2e3e ≈ 3.2 Hz, 2H, He-2, He-6), 1.58 (tt, 2 J3a3e ≈ J2a3a ≈ 13.8 Hz, J2e3a ≈ J3a4e ≈ 3.9 Hz, 2H, Ha-3, Ha-5), 1.86 (dq, 2 J3a3e ) 13.8 Hz, J2a3e ≈ J2e3e ≈ J3e4e ≈ 3.5 Hz, 2H, He-3, He-5), 1.92 (m, 1H, He-4), 2.34 (qd, 2 J2a2e ≈ J1a2a ≈ J2a3a ≈ 13.0 Hz, J2a3e ) 3.6 Hz, 2H, Ha-2, Ha-6), 3.06 (tt, J1a2a…”

Section: -[4(e)-(hydroxymethyl)cyclohex-(e)-yl]-56-dimethoxy-3-methyl...unclassified

“…The aliphatic cyclohexylene spacer, linking porphyrin and quinone either in 1,4- cis or - trans conformation, respectively, has proved useful in this context. − In the present paper we take advantage of this system and report on synthesis and characterization of a variety of P−Q's which have in common the donor 10,15,20-tris(4-methylphenylene)porphyrin-5-yl residue, abbreviated as P and the cyclohexylene spacer, whereas the quinone acceptors (Q) are different (Figure ). The underlying idea was to essentially keep the basic molecular frame constant and to modify only one parameter (the driving force Δ G ° of PET).…”

Section: Introductionmentioning

confidence: 99%

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Cyclohexylene-Bridged Porphyrin Quinones with Variable Acceptor Strength as Biomimetic Models for Photosynthesis: Evidence for Twist-Boat Conformation

et al. 1997

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Rigidly and covalently linked porphyrin quinones are well-suited as biomimetic model compounds for studying the photoinduced electron transfer (PET) reaction occurring in primary processes of photosynthesis. In this context, the synthesis of new porphyrin quinones with a cis- or trans-1,4-disubstituted cyclohexylene bridge linking the electron donor and the electron acceptor is reported. To study the dependence of the PET rate of the difference of the free enthalpy of the PET reaction, four quinones with different structures and therefore redox potentials were used as electron acceptor components. As a whole, two series of each four new cis- and trans-1,4-cyclohexylene-bridged porphyrin quinones with variable acceptor strength were synthesized. The most important synthetic steps comprised the free radical addition of the ester functionalized cyclohexylene bridge to the quinone, reduction of the ester to the alcohol group with lithium borohydride or DIBALH, oxidation of the alcohol to the corresponding aldehyde with PCC or TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)/NaOCl, and condensation of these aldehydes with pyrrole and 4-methylbenzaldehyde under equilibrium conditions. Analysis of the 1H NMR spectra unambiguously indicated the chair conformation for the cyclohexane ring of all porphyrin precursors and trans-cyclohexane-bridged porphyrin quinones, whereas the cis-cyclohexane-bridged porphyrin quinones had the cyclohexane ring in the unusual twist-boat conformation. This was additionally confirmed by an X-ray crystal structure of one of the cis-porphyrin quinones and the corresponding trans-porphyrin quinone. NOE experiments gave information about the spatial arrangement of the diastereomeric target compounds in solution.

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“…13 As the model compounds employed here have the acceptor connected to the donor at a position of small spin density and basic data for porphyrin cation radicals are available. 14 We have concentrated on functional studies. Of special interest was the question of how the large substituent (porphyrin) might influence the spin density distribution in a semiquinone anion radical, and whether the spin density distribution can be varied by chelating the quinone oxygen atoms.…”

Section: Epr Spectroscopymentioning

confidence: 99%

Isomeric porphyrin phenanthrenequinones: synthesis, NMR spectroscopy, electrochemical properties, and in situ EPR/ENDOR studies of the o-semiquinone anion radicalsElectronic supplementary information (ESI) available: 1H and 13C NMR data for various phenanthrene derivatives. See http://www.rsc.org./suppdata/p2/b1/b110273g/

Speck¹,

Niethammer²,

Senge³

2002

J. Chem. Soc., Perkin Trans. 2

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Porphyrins linked to high acceptor strength cyano quinones as models for the photosynthetic reaction center

Cited by 5 publications

References 40 publications

Effect of DNA Scaffolding on Intramolecular Electron Transfer Quenching of a Photoexcited Ruthenium(II) Polypyridine Naphthalene Diimide

Effect of DNA Scaffolding on Intramolecular Electron Transfer Quenching of a Photoexcited Ruthenium(II) Polypyridine Naphthalene Diimide

Cyclohexylene-Bridged Porphyrin Quinones with Variable Acceptor Strength as Biomimetic Models for Photosynthesis: Evidence for Twist-Boat Conformation

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