Magarelli, Mario (2011) Purification, Characterization and Photodegradation studies of modified sepia melanin (Sepia officinalis). Determination of Eumelanin content in fibers from Alpaca (Vicugna pacos). PhD thesis, SCHOOL OF ADVANCED STUDIES - Doctorate course in Chemical sciences (XXIII cycle).
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Currently melanins are still enigmatic bio-pigments bearing a structure as well as methods of determination not clearly fixed by the international scientific community. In many respects melanins are unique among biopolymers. The other essential biopolymers, that is proteins, nucleic acids and carbohydrates are chemically well characterized and can be determined using well established methodologies. On the other hand, we still do not have a method of accurately determination of melanin. Basically, the classes of mammalian melanins exist in two chemically distinct forms: the brown to black Eumelanin (Eu) and the yellow to reddish-brown Pheomelanin (Pheo). It is believed that melanin has a photoprotective role in animals. Although melanin has been postulated to act as a cellular antioxidant, little is known about the molecular mechanism of melanin photo-protection. An oxidative insult can produce modifications in the physiochemical characteristics of melanin and compromise its photo protective function. Sepia melanin (Sepia officcinalis)represents 98 % of Eumelanin pigment, and is thus used as standard material for the analysis of melanic black. Commercial sepia melanin (very expensive) is purified according to an unknown procedure. In our research, we carried out studies on the extraction and purification of sepia melanin by acid treatment using different concentrations of hydrochloric acid, under mechanic or ultrasonic agitation. This proved effective in producing a high degree purity sepia melanin then fully characterized by Elemental Analysis (EA), Ultraviolet-Visible (UV-VIS) and Infrared (IR) spectroscopy, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for metal ion analysis and quantitative studies of Eu polymers for chemical degradation to PTCA and PDCA by High Performance Liquid Chromatography (HPLC). A first modification of sepia melanin using hydrochloric acid afforded the hydrolysis of the sepia melanin while a second modification, obtained adding different salts, resulted in melanin in the salt form. Sepia melanin stability was studied by photodegradation measurements, UV-Vis absorbance spectra of different melanin solutions were measured before and after ultraviolet exposure. The difference spectra reveal that following ultraviolet exposure, a photo-bleaching effect can be observed in this range. The irradiation with ultraviolet radiation induced significant photochemical alterations in the sepia melanin. The obtained results can be used to extrapolate melanin degradation rates in vivo conditions, including the potential limits of its protective effect in humans.
|Item Type:||Tesi (PhD)|
|Informazioni aggiuntive:||Tutor: Dott. Paolo Passamonti|
|Parole chiave:||Sepia melanin; Purification; Determination; Photodegradation|
|Settori scientifico-disciplinari:||SCIENZE CHIMICHE > CHIM/01 Chimica analitica|
|Depositato da:||Dr. Cristina Soave|
|Depositato su:||31 May 2011 10:56|
|Last Modified:||16 Jan 2012 10:16|
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