Theory for electronic Raman activity of chlorophyll dimers

Haley, L. V.; Koningstein, J. A.

doi:10.1139/v83-003

Cited by 10 publications

(7 citation statements)

References 8 publications

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“…It is pertinent to note the decrease in absorbance due to Ru(bpy)32+ at 455 and 290 nm and the concommitant increase in absorbance at 370 and 540 nm. 15 The increase in absorbance at these wavelengths is attributed to the (12) Steven Kelder and Joseph Rabani, J. Phys. Chem., 85, 1637 (1981).…”

Section: Resultsmentioning

confidence: 99%

“…Recently, initial investigations have been made with the recording of vibrational Raman scattering of modes in electronic excited states.5"9 Relaxed triplet states of ßcarotene have been generated with pulsed radiolysis techniques and the Raman spectrum was obtained with a pulsed laser.8"13 On the other hand, vibrational Raman scattering from a 265-fs singlet excited state was recorded by using the radiation of a single-pulsed laser. 15 Part of this radiation served as an optical pump while the other part was utilized to excite the Raman process (monobeam pumping and scattering technique).6 Time-resolved methods were employed to assist the assignment of vibrational scattering in the singlet and triplet excited states of aZZ-trans-3-carotene. Although the absorption spectrum of this molecule in solvents in well-known, little information is available on the position of its electronic states.3,16…”

Section: Introductionmentioning

confidence: 99%

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Photochemistry of compounds adsorbed into cellulose. 1. Decay of excited tris(2,2'-bipyridine)ruthenium(II)

Milosavljevic¹,

Thomas²

1983

J. Phys. Chem.

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for transfer of even as much as 0.1 electron, large shifts in frequency should not occur. Quite a bit of charge clearly can be added, or removed, or redistributed in the porphyrin without large accompanying changes in vibrational frequencies. Therefore, the energetics of ligand binding and oxidation and reduction may be influenced significantly by charge-transfer interactions without producing frequency shifts in the Raman spectra that are detectable with conventional Raman equipment.Additional evidence for small frequency shifts comes from Raman excitation-profile studies of metalloporphyrins.22'26 These studies show that the vibrational motion is virtually uncoupled from the electrons in the visible (Q band) and near-UV (Soret band) electronic states. This means that large changes in the electronic structure of the frontier orbitals will be reflected only weakly in vibrational frequency shifts in the ground state of the metalloporphyrin.Acknowledgment. I thank D. L. Rousseau for reading the manuscript and helpful discussions. I also thank C. Jenkins and M. Dobry for their technical assistance, and S. Neuhauser for editorial assistance. This work was performed at Sandia National Laboratories supported by the U. S. Department of Energy under Contract No. DE-AC04-76DP00789.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photochemistry of compounds adsorbed into cellulose. 1. Decay of excited tris(2,2'-bipyridine)ruthenium(II)

Milosavljevic¹,

Thomas²

1983

J. Phys. Chem.

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“…Among several molecular orbital models developed to describe properties of the primary donor dimer (18)(19)(20)(40)(41)(42), the effects of the H-bond on the P O /P •+ redox midpoint potential have recently been examined by Artz et al (17) and may be qualitatively understood in terms of a simple dimer Hu ¨ckel-type molecular orbital (MO) model ( 40) of the primary donor, as proposed by Plato (18) and by Parson (19,20) and their co-workers. Figure 6 schematically shows the asymmetric dimer molecular orbital model of the primary electron donor of Rb.…”

Section: Discussionmentioning

confidence: 99%

Effects of Hydrogen Bonds on the Redox Potential and Electronic Structure of the Bacterial Primary Electron Donor

et al. 1998

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The primary donor, P, of photosynthetic bacterial reaction centers (RCs) is a dimer of excitonically interacting bacteriochlorophyll (BChl) molecules. The two constituents are named PL and PM to designate their close association with the L- and M-subunits, respectively, of the RC protein. A series of site-directed mutants of RCs from Rhodobacter sphaeroides has been constructed in order to model the effects of hydrogen bonding on the redox midpoint potential and electronic structure of P. The leucine residue at position M160 was genetically replaced with eight other amino acid residues capable of donating a hydrogen bond to the C9 keto carbonyl group of the PM BChl a molecule of P. Fourier transform (FT) (pre)resonance Raman spectroscopy with 1064 nm excitation was used to (i) determine the formation and strengths of hydrogen bonds on this latter keto carbonyl group in the reduced, neutral state (PO), and (ii) determine the degree of localization of the positive charge on one of the two constituent BChl molecules of P in its oxidized, radical cation state (P*+). A correlation was observed between the strength of the hydrogen bond and the increase in PO/P*+ redox midpoint potential. This correlation is less pronounced than that observed for another series of RC mutants where hydrogen bonds to the four pi-conjugated carbonyl groups of P were broken or formed uniquely involving histidinyl residues [Mattioli, T. A., Lin, X., Allen, J. P. and Williams, J. C. (1995) Biochemistry 34, 6142-6152], indicating that histidinyl residues are more effective in raising the PO/P*+ redox midpoint potential via hydrogen bond formation than are other hydrogen bond-forming residues. In addition, an increase in positive charge localization is correlated with the strength of the hydrogen bond and with the PO/P*+ redox midpoint potential. This latter correlation was analyzed using an asymmetric bacteriochlorophyll dimer model based on Hückel-type molecular orbitals in order to obtain estimates of certain energetic parameters of the primary donor. Based on this model, the correlation is extrapolated to the case of complete localization of the positive charge on PL and gives a predicted value for the P/P+ redox midpoint potential similar to that experimentally determined for the Rb. sphaeroides HL(M202) heterodimer. The model yields parameters for the highest occupied molecular orbital energies of the two BChl a constituents of P which are typical for the oxidation potential of isolated BChl a in vitro, suggesting that the protein, as compared to many solvents, does not impart atypical redox properties to the BChl a constituents of P.

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“…Lifetime determinations (see ref 15) yield (8[™) =¿ 2.5 ps and TfS,11,4™ =¿1.2 ps. The latter estimated value of r has to be compared with ^4™) =¿ 300 fs from lifetime-broadening measurements of Raman bands in S,1™5 in CS2 (ref 13).…”

Section: Raman and Fluorescence And Monochromatic Transmissionmentioning

confidence: 99%

“…This mode has the same shift in both isomers in the two solvents used in this work, carbon disulfide (CS2) and hexane. The second area of published data, obtained with pulsed lasers, includes Raman spectral data from electronic excited states.6 *" 13 Information on the position of in Chem. Phys.…”

Section: Introductionmentioning

confidence: 99%

Photoisomerization and time-resolved Raman studies of 15-15'-cis-.beta.-carotene and 15-15'-trans-.beta.-carotene

Wylie¹,

Koningstein²

1984

J. Phys. Chem.

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Theory for electronic Raman activity of chlorophyll dimers

Cited by 10 publications

References 8 publications

Photochemistry of compounds adsorbed into cellulose. 1. Decay of excited tris(2,2'-bipyridine)ruthenium(II)

Photochemistry of compounds adsorbed into cellulose. 1. Decay of excited tris(2,2'-bipyridine)ruthenium(II)

Effects of Hydrogen Bonds on the Redox Potential and Electronic Structure of the Bacterial Primary Electron Donor

Photoisomerization and time-resolved Raman studies of 15-15'-cis-.beta.-carotene and 15-15'-trans-.beta.-carotene

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