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Writing class


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Writing class

  1. 1. Metal Ion Effects on theRedox Properties ofPorphyrinsRachel GarciaAGEP Writing ClassApril 18,2007
  2. 2. Osaka, Japan
  3. 3. Electron Transfer in Porphyrins:Key Component in PhotosynthesisIt is important to study the electron transfer, or redox properties of porphyrins
  4. 4. Investigated PorphyrinsNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III) or Zn (II)How will the site of electron transfer be effected in thepresence of Sc3+?PQ
  5. 5. Cyclic Voltammetry:NNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-MM PP PP210 mV shiftNew processMM PPPPTitration with Sc(OTf)3
  6. 6. Site of electron transfer: SpectroscopyNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-300 400 500 600 700 800 900Wavelength,nm(PQ)AuPF6inCH2Cl2a)1streductionEapp=-0.70V436409549 587b)2ndreductionEapp=-1.20V439409422549 587Metal centeredOu et al., Inorg Chem. 2004,43,2078-2086Resulting spectra resembles2ndreduction of (PQ)AuPF6Porphyrin with reducing agent ( add electrons tocompound) and Sc3+
  7. 7. Absorbance plots for spectroscopic titrationsNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNNM = Au (III)+PF6-Indicates it is a 1electron reductionIndicates 2 Sc3+ions arecomplexed
  8. 8. ESR signal of PQAuPF6 in the presence of Sc3+In the presence of excess scandium, the complex is reduced by 1 electronwith the site of electron transfer to the quinoxaline group of theporphyrin.300 Gg = 2.003020472048Metal CenteredOu et al., Inorg Chem. 2004,43,2078-2086Radical anion
  9. 9. M =Zn (II)Electrochemistry of PQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN0.00.41.1Electrochemical titration of (PQ)Zn with Sc3+in PhCN, 0.1 MTBAPF6-1.27-1.27-0.17-0.17-1.27[Sc3+]/[PQM] when oneelectron is added
  10. 10. M =Zn (II)Site of electron transfer: SpectroscopyNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN500 600 700 8000. spectral titration of 1.62 x 10-5M (PQ)Zn with Me10Fc(6.58 x 10-4M) in the presence of 8.02 x 10-4M Sc3+437460640radical anion
  11. 11. M =Zn (II)Stoichiometric Plots for PQZnNNNNt BuBu tBu tt Bu Bu tt But BuBu tMNN00. 0.5 1 1.5 2 2.500. 1 2 3 4 5 6 7Plot of 451 nm absorbance of neutral PQZn vs. [Sc3+]/[(PQ)Zn]Plot of 437 nm absorbance of (PQ)Zn vs.[Me10Fc]/[(PQ)Zn] with excess Sc3+[Sc3+]/[(PQ)Zn][Me10Fc]/[(PQ)Zn]1 electron transfer2 Sc3+ions1 or 2 Sc3+ions? 1with excess Me10Fc[SC3+]/[(PQ)Zn]
  12. 12. ESR of PQZn + Sc3++ (BNA)2 in PhCN300 Gg = 2.003620472048Indicates a radical anion
  13. 13. DFT calculation of QPQAuPF6QuickTime™ and adecompressorare needed to see this picture.(QPQ)AuLUMO OrbitalsQuickTime™ and adecompressorare needed to see this picture.(QPQ)Au + H+Basis set: B3LYP/Lanl2dzPredicts the first electron will go to the quinoxaline group
  14. 14. Another Key Component in Photosynthesis:The Electron Donor-Acceptor Compounde-The time of the charge separated state of donor-acceptor compounds is a key factorin determining electron donor acceptors
  15. 15. -0.004-0.00200.0020.004400 500 600 700 800∆ΑβσΩαϖελενγτη, νµΝΝΝ ΝΑρΑρΑρ ΑρΖνΝΝΝΝΝΝΑρ ΑρΑρΑρΑυΝΝ[ΖνΠΘ−ΑυΠΘ+] = 1.0 ξ 10−5 Μ[Σχ(ΟΤφ)3] = 5.0 ξ 10–3 Μιν ΠηΧΝεξχιτατιον: 430 νµΖνΠΘ−ΑυΠΘ+00.0010.0020.0030.0040 1 2 3 4ΔAbs at 600-800 nmTime, μsC S Lifetime: 430 nsInthe absence ofSc3+: τcs = 250 psOhkubo, K. etal. C hem. Phys. 2006, 326, 3CS lifetime of 2 bound PQM:
  16. 16. SummaryZn and AuPF6 (PQ)-type compounds undergo 1-electronreduction at the quinoxaline in the presence of Sc3+2 Sc3+ions are complexed to one compoundThe redox properties of Zn and AuPF6 (PQ)-type compoundswere studied in the presence of Sc3+:In the presence of Sc3+, the charged-separated lifetime of theconguated Zn(PQ)-AuPF6(PQ) compound has increased,which is ideal for photosynthetic systems.
  17. 17. Acknowledgements• AGEP• My boss, Dr. Kadish• Dr. Fukuzumi, Osaka University