Melanin is soluble only on alkaline solutions.Then why it is soluble in DMSO ? What is the chemical process behind its solubility?
Hello,
DMSO is a polar aprotic solvent.
The structure of melanin contains several polar functional groups (carboxylic acids, aminos, alcool) that can forms hydrogen bonding interactions with DMSO. But Melanin also contains apolar groups that can forms weak hydrophobic interaction with DMSO
All of these intermolecular forces improve the solvatation of melanin in DMSO
Water is a polar protic solvent so in order to solubilise melanin in water you need to make melanin "more polar" (-> you deprotonate carboxilic acids in alkaline solution).
Best regards,
Laurent
Not sure of the chemical process, but the absorption spectrum of melanin in DMSO is similar to that of an alkaline solution of melanin. This might be a clue to suggest that chemical process of melanin solubility in DMSO is same as that of it solubility in an alkaline solution.
If melanin is kept for long in water, it oxidizes slowly and starts dissolving, however not completely. But if you add a little H2O2 and HRP, it dissolves instantly. same happens with peroxynitrite. So basically it is the oxidative breakdown of melanin polymer, and based on the oxidizing agent, the oligomers, monomers released from breakdown will vary which should lead to variability in the absorption spectrum.
Not a direct answer, but hope it helps.
Absolutly Sir..It may be the same process occur in alkali and DMSO.As it is soluble in DMSO.It is advantageous to use in various studies including in vitro studies.Thanks to the magic solvent :)
Sir I had also read that thioalkylation of phenolic units in melanins by DMSO is the reaction responsible for the solubility.Anyway it helps melanin research a lot.
I had never gone into the absorption spectrum of both solutions.Thanks a lot for giving some new information.
Hello,
DMSO is a polar aprotic solvent.
The structure of melanin contains several polar functional groups (carboxylic acids, aminos, alcool) that can forms hydrogen bonding interactions with DMSO. But Melanin also contains apolar groups that can forms weak hydrophobic interaction with DMSO
All of these intermolecular forces improve the solvatation of melanin in DMSO
Water is a polar protic solvent so in order to solubilise melanin in water you need to make melanin "more polar" (-> you deprotonate carboxilic acids in alkaline solution).
Best regards,
Laurent
Hello Laurent,
Thank you for the insight. it is really useful. Do you happen to know why oxidizers like peroxynitrite, or hydrogen peroxide with HRP also dissolve synthetic DOPA melanin? What I have observed is that DOPA melanin from SIGMA breaks down in to a dark solution with the oxidizers mentioned above. However, the sepia melanin, which is grey-ish not dark, does not dissolve. Thanks.
Hi Laurent
Will you please give some references which I can cite about what you have said.I would like to add this to my thesis.
Usually you find these kind of information in chemical organic textbook like the Clayden or the Klein.
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