Thermal and mass spectroscopic characterization of a sulphur-containing bacterial melanin from Bacillus subtilis

Novel insights on the physicochemical properties of eumelanins and their DMSO derivatives

“…The temperature at which the first minimum of the derivative (water loss) takes place is slightly higher than for Sigma melanin, 171 ± 5 °C, in good agreement with the literature . The second maximum could tentatively be ascribed to the loss of strongly bound water; however, in the literature it has been reported at higher temperatures . The second decomposition step can be tentatively ascribed to the decarboxylation of DHICA building blocks as well as to the rupture of the supramolecular structure and substructure of natural melanin and to the non‐covalent bonds between layers in oligomer planes .…”

“…44 The second maximum could tentatively be ascribed to the loss of strongly bound water; however, in the literature it has been reported at higher temperatures. 47,48 The second decomposition step can be tentatively ascribed to the decarboxylation of DHICA building blocks 41 as well as to the rupture of the supramolecular structure and substructure of natural melanin and to the non-covalent bonds between layers in oligomer planes. 47 The further three steps are associated with breaking of the bonds between the indole units and to the opening of pyrrole and indole rings.…”

“…47,48 The second decomposition step can be tentatively ascribed to the decarboxylation of DHICA building blocks 41 as well as to the rupture of the supramolecular structure and substructure of natural melanin and to the non-covalent bonds between layers in oligomer planes. 47 The further three steps are associated with breaking of the bonds between the indole units and to the opening of pyrrole and indole rings. 47 The presence of a higher number of decomposition steps for Sepia than for Sigma melanin can be explained considering that the supramolecular structure of Sepia melanin is more complex than Sigma melanin, conferring the ability to 'store' both weakly and hardly bound water 49 as well as implying multiple degradation steps during its heating.…”

Physicochemical characteristics and antioxidant activity of arginine-modified melanin from Lachnum YM-346

“…Melanins are produced by animals, plants, and microbes (Gómez-Marín & Sánchez, 2010;Tu, Sun, Tian, Xie, & Chen, 2009;Wang, Pan, Tang, & Huang, 2006), and can be used as light protectant, anti-radiation agent, chelating agent, immunostimulating agent, liver-protecting agent, natural antioxidant and biological semiconductor material (Bettinger, Bruggeman, Misra, Borenstein, & Langer, 2009;Sava, Galkin, Hong, Yang, & Huang, 2001;Sava, Hung, Blagodarsky, Hong, & Huang, 2003;Szpoganicz, Gidanian, Kong, & Farmer, 2002;Tu et al, 2009).…”

“…Using microbial fermentation to produce melanin has the advantages of not being restricted by seasons, being low cost, being easy to operate, and requiring mild reaction conditions. Bacillus subtilis, Laetiporus sulphureus, Hypoxylon archeri and Lachnum can produce melanin (Gómez-Marín & Sánchez, 2010;Olennikov, Agafonova, Stolbikova, & Rokhin, 2011;Wu, Shan, Yang, & Ma, 2008;Ye, Xu, Chen, Yang, & Lin, 2010), but they are only soluble in alkaline solution, and insoluble in water generally, which has substantially limited their application in industry, agriculture and medicine. However, it was reported that methylation of tyrosine melanin (non-water-soluble) could be used to make it soluble in water (Wilczok, Bilinska, Buszman, & Kopera, 1984) and Monascus pigment modified by amino acids could also soluble in water (Gan, Jian, Guan, Liu, & Yang, 2008).…”