Link
6-DHI-melanin
www.tightrope.it/nicolaus/index.htm
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 ( www.organicsemiconductors.com
)
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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‘’ The chemistry of melanins. Part V .The autoxidation of
5,6-dihydroxyindoles ‘’
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Naples March
1998
Revised
October 2003