Hydration effects on the electronic properties of eumelanin building blocks

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dc.creatorOliveira, Leonardo Bruno Assis
dc.creatorFonseca, Tertius Lima da
dc.creatorCabral, Benedito Jose Costa
dc.creatorCoutinho, Kaline Rabelo
dc.creatorCanuto, Sylvio Roberto Accioly
dc.date.accessioned2024-07-15T11:40:30Z
dc.date.available2024-07-15T11:40:30Z
dc.date.issued2016
dc.description.abstractTheoretical results for the electronic properties of eumelanin building blocks in the gas phase and water are presented. The building blocks presently investigated include the monomeric species DHI (5,6-dihydroxyindole) or hydroquinone (HQ), DHICA (5,6-dihydroxyindole-2-carboxylic acid), indolequinone (IQ), quinone methide (MQ), two covalently bonded dimers [HM ≡ HQ + MQ and IM ≡ IQ + MQ], and two tetramers [HMIM ≡ HQ + IM, IMIM ≡ IM + IM]. The electronic properties in water were determined by carrying out sequential Monte Carlo/time dependent density functional theory calculations. The results illustrate the role played by hydrogen bonding and electrostatic interactions in the electronic properties of eumelanin building blocks in a polar environment. In water, the dipole moments of monomeric species are significantly increased ([54–79]%) relative to their gas phase values. Recently, it has been proposed that the observed enhancement of the higher-energy absorption intensity in eumelanin can be explained by excitonic coupling among eumelanin protomolecules [C.-T. Chen et al., Nat. Commun. 5, 3859 (2014)]. Here, we are providing evidence that for DHICA, IQ, and HMIM, the electronic absorption toward the higher-energy end of the spectrum ([180–220] nm) is enhanced by long-range Coulombic interactions with the water environment. It was verified that by superposing the absorption spectra of different eumelanin building blocks corresponding to the monomers, dimers, and tetramers in liquid water, the behaviour of the experimental spectrum, which is characterised by a nearly monotonic decay from the ultraviolet to the infrared, is qualitatively reproduced. This result is in keeping with a “chemical disorder model,” where the broadband absorption of eumelanin pigments is determined by the superposition of the spectra associated with the monomeric and oligomeric building blocks. Topics
dc.identifier.citationOLIVEIRA, Leonardo Bruno Assis; FONSECA, Tertius L.; CABRAL, Benedito J. Costa; COUTINHO, Kaline; CANUTO, Sylvio. Hydration effects on the electronic properties of eumelanin building blocks. Journal of Chemical Physics, New York, v. 145, p. 084501, 2016. DOI: 10.1063/1.4961147. Disponível em: https://pubs.aip.org/aip/jcp/article/145/8/084501/561832/Hydration-effects-on-the-electronic-properties-of. Acesso em: 30 maio 2023.
dc.identifier.doi10.1063/1.4961147
dc.identifier.issne- 1089-7690
dc.identifier.issn0021-9606
dc.identifier.urihttps://pubs.aip.org/aip/jcp/article/145/8/084501/561832/Hydration-effects-on-the-electronic-properties-of
dc.language.isoeng
dc.publisher.countryEstados unidos
dc.publisher.departmentInstituto de Física - IF (RMG)
dc.rightsAcesso Restrito
dc.titleHydration effects on the electronic properties of eumelanin building blocks
dc.typeArtigo

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