Link 6-DHI-melanin 


Key words: melanins, fullerenes, cosmids, MALDI, conducting polymers, X-ray diffraction, DHI-melanin, black particles, tensegrity.

Melanins ( 1 ) constitute an insoluble and infusible material difficult to purify

Black material could have origin from different molecules called melanogens. These are on earth, generally, hydroxylated aromatic compounds (orto.diphenols) of aromatic systems like benzene, indole, pyrrole, pyridine, quinoline. Substances of biological interest having the property generating black particles are DOPA, Cyclodopa, DHI (5,6-dihydroxindole), DHICA (5,6-dihydroxindole-2-carboxylic acid), dopamine, adrenaline, serotonin, 5,6-hydroxytryptamine [2], 6,7-dihydroxy-1-metil-tetrahydroisoquinoline (salsolinol) [3]. All the substances could, in different conditions, generate black materials. The chemical study of sepiomelanin indicate cyclodopa (leucodopachrome) as precursor. It is generally believed that DHI and DHICA are the precursors of pigment cell.  The particles (in biology granules) present themselves generally under ovate or globular shape (rugby or soccer ball) and are built up from the precursor’s oligomers. It is possible that these materials constitute cage systems of giant fullerene type or graphite - like stacking spacing of 3.45 A, 4-5 layers thick.The first phase consists of the formation of policonjugated chains the so called Little's spine [4]. It must be observed that the spine alone can result dielectric. But if opportunely substituted from quaternary lateral groups in which the charge could interact with the electrons moving in the spine the superconductive state is produced, i.e. a distinctive organic macromolecule with superconductive properties in agreement with the BCS theory [5] is formed. It is curious that in Little's model the spine was acetyleneblack and the lateral chains were constituted by diethylcyanine iodide, a well known light-sensitive compound.The structures formed from 16 (magic number ?) DHI units is reported. The structures, among those possible, differ for the presence of furane rings. These structures are theoretically semiconductors [7] or superconductors [5].The second phase of oligomerization is characterized by self-assembling of the different units up to achieve a particle.The first phase could be verified examining the reaction products by MALDI and MALDI-TOF mass spectrometry .It was suggested that indole oligomers could be formed until 11 units by oxidizing dopamine with peroxidase/H2O2 and until 8 by oxidizing tyrosine with tyrosinase [2a], [6]. From a chemical point of view must be said that the particle should be represented, according to polyindolequinone theory [1], with the formula C8H3O2N, instead we found a formula having the atomic proportions C8H5O3N. (1b) Other discrepancy may be explained with the binding property and the presence of  groups –OH, –COOH and cationic centers.


DHI-melanin ( autoxidation or enzymatic ) :

Found                                      C %  55.2, H% 3.3 N% 8.5

Calculated for C8 H3 O2 N          C% 66.2 H% 2.0 N% 9.6


Many  melanins are insoluble salts. For example, Sepia officinalis ink melanin is a Ca and Mg salt. The corresponding melanic acids loose CO2 by bland heating, . Melanins are sensitive to light, pressure, oxygen and peroxides.Interpretation of these propreties is difficult because the material is a mixture of of organelles like  premelanosome,melanosome and granules.

 Melanins and DHI-melanin react with Cl2, CH2N2, diazonium salt, show affinity for H2O, drugs, ions and gases as do active coal  or charcoal. The melanin cage explodes under the action of laser [8] recalling the behavior of giant fullerenes or grafite. The MALDI laser causes fragmentation of the black particle with formation of white  products ( depigmentation, depilation in Dermatology ) and show that the particle is formed by relative low weight oligomers. (2b,2c ).To be noted that Mass spectra are depending :

1.      method of extraction and purification adopted

2.      centrifuge speed

3.      time of storage

4.      presence of ions like Ca and Mg

5.      acid treatment of the sample

And naturally for LASER energy and matrix used. 


 Chemistry and physics of giant fullerenes (for example C540) is interesting for melanin studies. In fact a giant fullerene is essentially a monostrate of hexagons with sp2 carbons that bend over among 12 pentagonal cusps necessary for the closing. As the fullerenes are formed of the pentagonal rings (pyrrole) and hexagonal rings (benzene), the symmetric giant fullerenes are not of round shape. If the fullerenes are formed of pentagonal, hexagonal, and heptagonal (octagonal) rings, there is a fair chance for forming the round-shaped melanosomes. These structures have furnished the key to understand carbon's microparticles inside [9]. Interstitial compounds could be formed in the proposed structures also with gases  [10].  Melanin affinity for O2 and H2O could suggest new mechanism and biological functions.  It is interesting to note that melanins hydration and dehydration could be imputable to an addition reaction of H2O to a carbonylic system (quinone) not known in literature  which explain the analytical results.


Hydration of quinone groups


Black material is able to link gases, liquid, organic and inorganic products,solvents and reagents.The granules of melanin (DHI-melanin) are able to bind different chemical substances which can be accumulated over time [12], [13].

Apart for numerous organic substances, notable is the affinity for inorganic ions too [14], [15] and the role played in the cell. (16).  At level of particle it is possible that morphology is affected by the purification and extraction procedure. Take care to the methods of purification and extraction adopted.  

The black material is able to catalyze, to start and influence numerous chemical reactions including those at the origin of the first autoassembling of molecules. Electrically conducting material like melanins (7) are novel in that their surface properties, including charge density and wettability, can be reversibly changed with an applied electrical potential.The Proctor-McGinness effect ( )

 could played an important role to control the shape and function of adherent cells, independent of any medium alteration. The black semiconductor can noninvasively control the shape and growth of mammalian cells (16) It could be hypothysized that biological evolution initiated on a melanin film rather than from the so-called biological soup.



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     b. R.J.S.Beer, T.Broadhurst, A.Robertson,  ‘’ The chemistry of melanins. Part V .The       autoxidation of 5,6-dihydroxyindoles  ‘’  J.Chem.Soc.  1947-1953, 1954

[2] a.  A. Bertazzo, C. Costa, G. Allegri, M. Schiavolin, D.Favretto P. Traldi, Enzymatic oligomerization of tyrosine by tyrosinase and peroxidase studied by matrix-assisted laser desorption / ionizationmass spectrometry  Rapid Comm. In Mass Spectrom. 13, 3947 (1999)

b. A.Napolitano, A.Pezzella, G.Prota, R.Seraglia,P.Traldi    Structural analysis of synthetic melanins from 5,6-dihydroxyindole by Matrix-assisted Laser desorption/ionization  Mass Spectrometry    Rapid Comm. Mass Spectrom., 10, 468-472, 1996

c.  A.Pezzella, A.Napolitano, M.D’Ischia, G.Prota, R.Seraglia,P.Traldi  Identification of partially degraded oligomers of 5,6-dihydroxyindle-2-carboxylic acid in Sepia melanin by Matrix-assisted Laser Desorption/ionization  Mass  Spectrometry   Rapid Comm. Mass Spectrom. , 11, 368-372,  1997

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[12] B.S. Larson, Interaction between chemicals and melanin, Pigment Cell Res. 6, 127 (1993)

[13] N.G. Lindquist, Accumulation of drugs on melanin, Acta Radiol. Suppl. 325, 1-92 (1973)

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[15] H. Rorsman, Binding of simple chemicals in melanin producing cells, Research Progress in Organic Biological and Medicinal Chemistry Vol. 3 part II eds. U. Gallo, L. Santamaria pag. 655-670, North Holland Publ.Co, Amsterdam (1972)

[16] J. Y. Wong, R. Langer, D.E. Ingber, Electrically conducting polymers can noninvasively control the shape and growth of mammalian cells, Proc. Natl. Acad.Sci, USA, 91, 3201 (1994)

[17] D.E. Ingber, Tensegrity: the architectural basis of cellular mechanotransduction, Ann. Rev. Physiol. 59 (1997)

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[21] H. Fischer, H. Orth, Die chemie des pyrrols, II Band 1.Hälfte, AVG, Leipsig (1937) pag 175- 618


Naples March 1998

Revised October 2003