Figure 1.
Partial MALDI-TOF MS [M+H]+ and [M+Na]+ spectrum of the dark brown compound(s) obtained from the bacterium Azotobacter chroococcum.
Figure 2.
FTIR absorption spectrum (in KBr pellet under complete dry conditions in a nitrogen atmosphere) of the dark brown compound(s) obtained from Azotobacter chroococcum.
Figure 3.
Natural abundance CPMAS solid-state 13C-NMR 1D-spectrum of the dark brown compound(s) obtained from bacterium Azotobacter chroococcum.
Figure 4.
m/z values of the compound(s) obtained from the bacterium Azotobacter chroococcum in MALDI-TOF MS spectrum representing molecular ions corresponding to two sets of [M+H]+ and [M+Na]+ having difference of 191amu (one unit 5,6-dihydroxyindole-2-carboxylic acid).
Table 1.
Comparison of the 13C resonances of the compound(s) (melanin) extracted from bacterium Azotobacter chroococcum with other type of melanins obtained from different sources [a Magn. Reson Chem. (2008) 46, 471; b Magn. Reson Chem. (2003) 41, 466].
Figure 5.
Proposed putative structure(s) of the protomolecules of melanin hetero-polymers, obtained from the nitrogen-fixing soil bacterium Azotobacter chroococcum.