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Eumelanin – Black/Brown Photoprotective Pigment
- Broadband UV absorption with non-radiative heat dissipation.
- Polymerized from IQ/DHICA units via oxidative polymerization.
- Mitigates UV-induced DNA photodamage (e.g., CPDs).
- Acts as a free-radical scavenger and redox buffer.
- Featureless broadband absorbance (visible → near-IR).
- Chelates Fe³⁺/Cu²⁺ ions, modulating redox chemistry.
- Hydration-dependent protonic/electronic conductivity.
- Major determinant of dark hair/skin and brown-black irides.
Pheomelanin – Sulfur-Containing Red/Yellow Pigment
- Forms via L-cysteine addition to dopaquinone (sulfur incorporation).
- Contains benzothiazine/benzothiazole structural units.
- Generates ROS under UV; weaker photoprotection vs eumelanin.
- Linked to MC1R variants (red hair, fair skin phenotypes).
- Accumulates in ephelides (freckles) and warm undertones.
- Associated with higher UV sensitivity/oxidative stress.
- Cysteine/thiol pool biases melanogenesis toward pheo-.
- Pheo:eume ratio helps set red-yellow to brown-black pigmentation.
Allomelanin / Phytomelanin – Nitrogen-Free Plant & Fungal Melanins
- Nitrogen-free melanins (contrast with eumelanin/pheomelanin).
- Fungal allomelanin often produced via the DHN pathway.
- Plant phytomelanin from catechols/phenolic precursors.
- Forms dark seed coats (sunflower, black sesame hulls).
- Shields against UV, desiccation, and pathogens.
- In fungi, melanin contributes to virulence and drug resistance.
- Heterogeneous polymers characterized via NMR/Raman.
- Explored for eco-dyes, protective coatings, bio-materials.