| 1. |
- Corani, Alice, et al.
(författare)
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Bottom-Up Approach to Eumelanin Photoprotection: Emission Dynamics in Parallel Sets of Water-Soluble 5,6-Dihydroxyindole-Based Model Systems.
- 2012
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 116:44, s. 13151-13158
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Tidskriftsartikel (refereegranskat)abstract
- The molecular mechanisms by which the black eumelanin biopolymers exert their photoprotective action on human skin and eyes are still poorly understood, owing to critical insolubility and structural heterogeneity issues hindering direct investigation of excitation and emission behavior. Recently, we set up strategies to obtain water-soluble 5,6-dihydroxyindole (DHI)-based polymers as useful models for disentangling intrinsic photophysical properties of eumelanin components from aggregation and scattering effects. Herein, we report the absorption properties and ultrafast emission dynamics of two separate sets of DHI-based monomer-dimer-polymer systems which were made water-soluble by means of poly(vinyl alcohol) or by galactosyl-thio substitution. Data showed that dimerization and polymerization of DHI result in long-lived excited states with profoundly altered properties relative to the monomer and that glycosylation of DHI imparts monomer-like behavior to oligomers and polymers, due to steric effects hindering planar conformations and efficient interunit electron communication. The potential of S-glycation as an effective tool to probe and control emission characteristics of eumelanin-like polymers is disclosed.
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| 2. |
- Corani, Alice, et al.
(författare)
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Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:9, s. 1383-1388
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Tidskriftsartikel (refereegranskat)abstract
- Excited-state proton transfer has been hypothesized as a mechanism for UV energy dissipation in eumelanin skin pigments. By using time resolved fluorescence spectroscopy, we show that the previously proposed, but unresolved, excited-state intramolecular proton transfer (ESIPT) of the eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA) occurs with a time constant of 300 fs in aqueous solution but completely stops in methanol. The previously disputed excited-state proton transfer involving the 5- or 6-OH groups of the DHICA anion is now found to occur from the 6-OH group to aqueous solvent with a rate constant of 4.0 x 10(8) s(-1).
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| 3. |
- Corani, Alice, et al.
(författare)
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Superior photoprotective motifs and mechanisms in eumelanins uncovered.
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:33, s. 11626-11635
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Tidskriftsartikel (refereegranskat)abstract
- Human pigmentation is a complex phenomenon commonly believed to serve a photoprotective function through the generation and strategic localization of black insoluble eumelanin biopolymers in sun exposed areas of the body. Despite compelling biomedical relevance to skin cancer and melanoma, eumelanin photoprotection is still an enigma: What makes this pigment so efficient in dissipating the excess energy brought by harmful UV-light as heat? Why has Nature selected 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as the major building block of the pigment instead of the decarboxylated derivative (DHI)? By using pico- and femtosecond fluorescence spectroscopy we demonstrate herein that the excited state deactivation in DHICA oligomers is 3 orders of magnitude faster compared to DHI oligomers. This drastic effect is attributed to their specific structural patterns enabling multiple pathways of intra- and interunit proton transfer. The discovery that DHICA-based scaffolds specifically confer uniquely robust photoprotective properties to natural eumelanins settles a fundamental gap in the biology of human pigmentation and opens the doorway to attractive advances and applications.
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| 4. |
- Huijser, Annemarie, et al.
(författare)
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Functionality of epidermal melanin pigments: current knowledge on UV-dissipative mechanisms and research perspectives.
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 13, s. 9119-9127
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Tidskriftsartikel (refereegranskat)abstract
- So far it is not known whether epidermal melanins are solely photoprotective or also phototoxic. Also largely unknown are underlying UV-induced mechanisms and impact of the chemical structure. This perspective will focus on the current insights into the UV-dissipative mechanisms in melanin model systems and the implications for the in vivo pigments. We will also identify future research perspectives towards a full understanding of the functionality of epidermal pigments.
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| 5. |
- Huijser, Annemarie, et al.
(författare)
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Photophysics of indole-2-carboxylic acid in an aqueous environment studied by fluorescence spectroscopy in combination with ab initio calculations.
- 2012
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 14:6, s. 2078-2086
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Tidskriftsartikel (refereegranskat)abstract
- The photo-physics and -chemistry of indoles are known to be highly complex and strongly dependent on their precise molecular structure and environment. Combination of spectroscopic analysis with quantum chemical calculations should be a powerful tool to unravel precise excited state deactivation mechanisms. At the same time, combined studies are seldom and likely far from trivial. In this work we explore the feasibility of combining spectroscopic and quantum-chemical data into one consistent model. The molecule of choice is indole-2-carboxylic acid (ICA) in aqueous media. Excited state dynamics are determined by time-resolved fluorescence experiments, while excited state reaction pathways of ICA-H(2)O clusters are explored by ab initio calculations.
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| 6. |
- Huijser, Annemarie, et al.
(författare)
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Shedding Light on the Nature of Photoinduced States Formed in a Hydrogen-Generating Supramolecular RuPt Photocatalyst by Ultrafast Spectroscopy
- 2018
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:31, s. 6396-6406
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced electronic and structural changes of a hydrogen-generating supramolecular RuPt photocatalyst are studied by a combination of time-resolved photoluminescence, optical transient absorption, and X-ray absorption spectroscopy. This work uses the element specificity of X-ray techniques to focus on the interplay between the photophysical and -chemical processes and the associated time scales at the catalytic Pt moiety. We observe very fast (<30 ps) photoreduction of the Pt catalytic site, followed by an ∼600 ps step into a strongly oxidized Pt center. The latter process is likely induced by oxidative addition of reactive iodine species. The oxidized Pt species is long-lived and fully recovers to the original ground state complex on a >10 μs time scale. However, the photosensitizing Ru moiety is fully restored on a much shorter ∼300 ns time scale. This reaction scheme implies that we may withdraw two electrons from a catalyst that is activated by a single photon.
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| 7. |
- Huijser, Annemarie, et al.
(författare)
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UV-Dissipation Mechanisms in the Eumelanin Building Block DHICA
- 2010
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 11:11, s. 2424-2431
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Tidskriftsartikel (refereegranskat)abstract
- The UV-dissipative mechanisms of the eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and the 4,7-dideutero derivative (DHICA-d(2)) in buffered H2O or D2O have been characterized by using ultrafast time-resolved fluorescence spectroscopy. Excitation of the carboxylate anion form, the dominating state at neutral pH, leads to dual fluorescence. The band peaking at lambda = 378 nm is caused by emission from the excited initial geometry. The second band around lambda = 450 nm is owed to a complex formed between the monoanion and specific buffer components. In the absence of complex formation, the mono-anion solely decays non-radiatively or by emission with a lifetime of about 2.1 ns. Excitation of the neutral carboxylic acid state, which dominates at acidic pH, leads to a weak emission around lambda = 427 nm with a short lifetime of 240 ps. This emission originates from the zwitterionic state, formed upon excitation of the neutral state by sub-ps excited-state intramolecular proton transfer (ESIPT) between the carboxylic acid group and the indole nitrogen. Future studies will unravel whether this also occurs in larger building blocks and ESIPT is a built-in photoprotective mechanism in epidermal eumelanin.
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