Effect of Stacking and Redox State on Optical Absorption Spectra of Melanins−Comparison of Theoretical and Experimental Results

Stark, K.; Gallas, James M.; Zając, G.; Golab, Joseph T.; Gidanian, Shirley; McIntire, Theresa M.; Farmer, Patrick J.

doi:10.1021/jp046710z

Cited by 97 publications

(128 citation statements)

References 37 publications

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“…Certainly the covalent and noncovalent assembly of oxidized Bt by melanogenesis would be more facile for aggregated samples. This melanogenesis could be associated with the formation of a red-absorbing species in the SEC data for darker films, in agreement with calculations presented in ref 60, which attribute increased absorption in the red to noncovalent aggregation of melanin polymers. Whereas longterm storage of Bt-sensitized TiO 2 films does lead to a brown coloration, neither the SEC data nor the transient absorption data show evidence of quantitative formation of melanin, which is characterized by a spectrum in which absorption increases monotonically with decreasing wavelength.…”

Section: ■ Discussionsupporting

confidence: 91%

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection

et al. 2015

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We report spectroelectrochemical and transient absorption spectroscopic studies of electron injection from the plant pigment betanin (Bt) to nanocrystalline TiO 2 . Spectroelectrochemical experiments and density functional theory (DFT) calculations are used to interpret transient absorption data in terms of excited state absorption of Bt and ground state absorption of oxidation intermediates and products. Comparison of the amplitudes of transient signals of Bt on TiO 2 and on ZrO 2 , for which no electron injection takes place, reveals the signature of two-electron injection from electronically excited Bt to TiO 2 . Transient signals observed for Bt on TiO 2 (in contrast to ZrO 2 ) on the nanosecond time scale reveal the spectral signatures of photo-oxidation products of Bt absorbing in the red and the blue. These are assigned to a oneelectron oxidation product formed by recombination of injected electrons with the two-electron oxidation product. We conclude that whereas electron injection is a simultaneous two-electron process, recombination is a one-electron process. The formation of a semiquinone radical through recombination limits the efficiency and long-term stability of the Bt-based dye-sensitized solar cell. Strategies are suggested for enhancing photocurrents of dye-sensitized solar cells by harnessing the two-electron oxidation of organic dye sensitizers.

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Section: ■ Discussionsupporting

confidence: 91%

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection

et al. 2015

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“…(It should be noted that the similar dependence was observed by us also for some albumin and melanin, in [4]. )…”

Section: Uv Absorbance Of Aqueous Dnasupporting

confidence: 85%

UV Absorbance of Aqueous DNA

Vadimovich¹

2015

EJB

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Abstract:The UV absorption spectra of water with different electric charge (potential) were obtained. It was shown that UV absorption spectra of water with negative electric charge (potential) have the sharp peaks with maximum in the range 190 -200 nm and UV absorption spectra of water with positive electric charge (potential) have the wide peaks with maximum in the range 200 -220 nm. It was asked to explain this absorption. It was also established that UV absorption spectra of water solutions of surface inactive substances have sharp peaks with a maximum in the range 190 -200 nm and UV absorption spectra of solutions of surface active substances have the wide peaks with a maximum in the range 200 -220 nm. The UV absorption spectra of DNA solutions, which were prepared on the water with different electric charge (potential), were obtained. It was shown that these spectra are dependent on the electric charge (potential) of water used. It was proposed that UV absorption spectra of aqueous DNA reflect mostly the spectral properties of charged water or charged cuvette.

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“…Accordingly, eumelanin consists of many chemically distinct species and its broadband absorption spectrum is a result of averaging over the spectra of these species. The sharp peaks due to 5,6-dihydroxyindole (DHI) and its oligomers could be eliminated after this process 3,[11][12][13][14][15][16] . Even though the chemical disorder model combined with the superposition principle are able to reproduce broadband absorption spectra, they are, however, still insufficient to provide a full explanation of the optical properties of eumelanin.…”

mentioning

confidence: 99%

“…It is expected that when molecules are brought close to this extent, the electron density and spectrum will change. Studies have shown that the interactions among eumelanin protomolecules are strong enough to affect the spectrum significantly, where the superposition principle clearly does not hold 14 . Second, the molecular structures of eumelanin are still poorly understood, and so are the ratios of distinct species.…”

mentioning

confidence: 99%

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Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin

et al. 2014

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Eumelanin is a ubiquitous biological pigment, and the origin of its broadband absorption spectrum has long been a topic of scientific debate. Here, we report a first-principles computational investigation to explain its broadband absorption feature. These computations are complemented by experimental results showing a broadening of the absorption spectra of dopamine solutions upon their oxidation. We consider a variety of eumelanin molecular structures supported by experiments or theoretical studies, and calculate the absorption spectra with proper account of the excitonic couplings based on the Frenkel exciton model. The interplay of geometric order and disorder of eumelanin aggregate structures broadens the absorption spectrum and gives rise to a relative enhancement of absorption intensity at the higher-energy end, proportional to the cube of absorption energy. These findings show that the geometric disorder model is as able as the chemical disorder model, and complements this model, to describe the optical properties of eumelanin.

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Effect of Stacking and Redox State on Optical Absorption Spectra of Melanins−Comparison of Theoretical and Experimental Results

Cited by 97 publications

References 37 publications

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection

UV Absorbance of Aqueous DNA

Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin

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Effect of Stacking and Redox State on Optical Absorption Spectra of Melanins−Comparison of Theoretical and Experimental Results

Cited by 97 publications

References 37 publications

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO2: The Pursuit of Two-Electron Injection

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO2: The Pursuit of Two-Electron Injection

UV Absorbance of Aqueous DNA

Excitonic effects from geometric order and disorder explain broadband optical absorption in eumelanin

Contact Info

Product

Resources

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Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection

Dynamics of Interfacial Electron Transfer from Betanin to Nanocrystalline TiO₂: The Pursuit of Two-Electron Injection