Melanin is a class of biologic pigments widely distributing in most organisms. Despite of the significant biological importance, the chemical structure and formation mechanism of melanins are still not well-understood. Since natural melanins are not soluble in common solvents, the previous studies analyzing the structures of melanins are mostly based on the chemical degradation which will severely damage the original structures of the natural melanins. Therefore, in chapter 2 of this thesis work, the water-soluble synthetic DOPA-melanin has been studied in order to get information about the structure of natural melanins. UV-Vis absorption spectrophotometry and electrospray ionization mass spectrometry (ESI-MS) have been utilized to analyze the oligomers arising in the growing process of...[ Read more ]

Melanin is a class of biologic pigments widely distributing in most organisms. Despite of the significant biological importance, the chemical structure and formation mechanism of melanins are still not well-understood. Since natural melanins are not soluble in common solvents, the previous studies analyzing the structures of melanins are mostly based on the chemical degradation which will severely damage the original structures of the natural melanins. Therefore, in chapter 2 of this thesis work, the water-soluble synthetic DOPA-melanin has been studied in order to get information about the structure of natural melanins. UV-Vis absorption spectrophotometry and electrospray ionization mass spectrometry (ESI-MS) have been utilized to analyze the oligomers arising in the growing process of the DOAP-melanin formation. The results indicated that DOPA monomer would firstly form aggregates via noncovalent bonds before oxidation. It is speculated that the various reactions were more likely to occur in the aggregates and thus a small quantity of DOPA molecules would highly possibly be tapped in the final structure as the form of aggregates. By UPLC-QqQ MS analysis, the molecule of DOPA was found in the Sepia officinalis melanin which has been treated with 5% hydrogen peroxide. This is the first time to detect the DOPA in the natural melanin, which may provide a new direction to research the natural melanins as well as the synthetic melanins.

Despite the structure of melanin has not been fully understood, some distinct properties owned by melanins have been applied in chemistry. One mussels-inspired melanin-like material, polydopamine, has been widely used as a coating method since 2007. In the third chapter, a novel reversed phase sorbent, C8 functionalized polydopamine coated silica (C8PDASil), has been successfully synthesized based on the adhesive property of the polydopamine. Used as a stationary phase in HPLC, C8PDASil displays a mixed-mode retention mechanism: hydrophobicity, hydrophilicity and ionic exchange. Compared with traditional stationary phases normally possessing just one single retention mechanism, this new sorbent would reduce the column purchasing cost for the analyst, which would be the new developing direction for the commercial column.