Isolation and characterization of polydopamine subunits to determine the dependence of aggregation on eumelanin photoreactivity
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Date
2022-05
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The Ohio State University
Abstract
Eumelanin is a naturally occurring, heterogeneous pigment that is known to have both photoprotective and photoreactive capabilities. It can serve as a barrier to harmful light rays, but it can also sensitize reactive oxygen species. However, the mechanism that changes eumelanin's properties from photoprotective to photoreactive is largely unknown. With polydopamine as a synthetic model, nanoparticles and their subunits were used to discern the changes in optical properties and photoreactive function of eumelanin due to changes in hierarchical structure. Synthesis, de-aggregation and spectroscopic analysis were used in this study to accomplish this discernment. It was found that polydopamine fractions are sensitive to oxidative degradation when introduced to highly alkaline environment in the presence of oxygen, which leads to an increase in emission intensity and likely associated photoreactivity. Further, it was found that lower molecular weight fractions of de-aggregated nanoparticles are more emissive and have higher quantum yield than high molecular weight fractions. This leads to postulation that de-aggregation reveals a greater number of reduced subunits that causes photoreactivity over photoprotection. When compared with melanin-like catechol and indolequinone model compounds, similarities in emission peaks and quantum yield were also observed in the lower molecular weight and high molecular weight fractions of de-aggregated polydopamine. This reaffirms the hypothesis that changes in the amount of reduced and oxidized subunits in each fraction leads to the observed changes in optical properties.
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Keywords
Melanin, Physical Chemistry