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A. Szczurowski, J. Dillon, E.R. Gaillard; Comparison of the Structural Patterns Between Different Kinds of Melanin by MALDI–TOF Mass Spectrometry . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1612.
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Purpose: The purpose of the study is to determine if the fragmentation pattern of different kinds of melanin obtained via MALDI–TOF–MS can be used to distinguish them structurally. Methods: Four samples of melanins were analyzed: synthetic melanin (soluble and insoluble fractions) from polymerized L–DOPA, sepiamelanin that was purchased from Sigma–Aldrich and ocular melanins, which were isolated from calf and human RPE. The optimal ionization conditions were established for each kind of melanin by varying the matrix (3–indoleacrylic acid [IAA], 1,8,9–anthracenetriol [Dithranol] or α–cyano–4–hydroxycinnamic acid [CHCA]), the solvents and solvent concentration (TFA, THF) and the laser power (from 60% to 80%). A series of analyses were carried out by MALDI–TOF–MS (Bruker Omniflex). Results: The spectra of the melanins exhibit regular peak distributions. Molecular weight differences between the peaks are very similar for each specific melanin but vary between different melanins. These data allow for monomer building block structures to be proposed for each type of melanin. The major proposed building blocks are dihydroxyindoleacetic acid (fragment m/z = 186, 191, 192) for synthetic melanin, pyrrhole tetracarboxylate (fragment m/z = 207, 208, 209, 210) for sepia melanin and sulfur containing quinoline analog (fragment m/z = 282) for mammalian ocular melanin. Conclusions: Different types of melanin can be distinguished based on their fragmentation pattern obtained via MALDI–TOF–MS thus providing a spectroscopic signature unique to the type of melanin.
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