Application of matrix-assisted laser desorption/ionization mass spectrometry to the detection of melanins formed from Dopa and dopamine

Bertazzo, Antonella; Costa, Carlo Virgilio Luigi; Allegri, Graziella; Favretto, Donata; Traldi, Pietro

doi:10.1002/(sici)1096-9888(199909)34:9<922::aid-jms851>3.0.co;2-f

Cited by 32 publications

(28 citation statements)

References 23 publications

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“…In the previous investigation, carried out in the absence of PEG, the formation of dihydroxyindole oligomers was observed, in agreement with Raper‐Mason melanogenesis mechanisms 14. As Fig.…”

Section: Resultssupporting

confidence: 86%

“…A previous investigation of melanogenesis arising from reaction of DOPA with tyrosinase had shown that the process takes places rapidly, with the formation of black precipitates 14. When the solution was ultrafiltered to separate the enzyme in order to obtain the solution to be analyzed by MALDI, the black precipitate was retained on the filter (XM 50).…”

Section: Resultsmentioning

confidence: 99%

“…In subsequent studies,12–14 using matrix‐assisted laser desorption ionisation (MALDI), we revealed the presence of oligomers in the early stages of melanogensis, when tyrosinase was added to solutions of tyrosine or DOPA. The MALDI spectra obtained in the case of DOPA showed simple oligomerization products of DHI, perfectly matching the results obtained in the tyrosine‐tyrosinase reaction 15.…”

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

New Mechanistic Insights into the Iridium–Phosphanooxazoline‐Catalyzed Hydrogenation of Unfunctionalized Olefins: A DFT and Kinetic Study

Brandt

Hedberg

Andersson

2002

Chemistry A European J

157

120

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The reaction mechanism of the iridium-phosphanooxazoline-catalyzed hydrogenation of unfunctionalized olefins has been studied by means of density functional theory calculations (B3LYP) and kinetic experiments. The calculations suggest that the reaction involves an unexpected Ir(III)-Ir(V) catalytic cycle facilitated by coordination of a second equivalent of dihydrogen. Thus, in the rate-determining migratory insertion of the substrate alkene into an iridium-hydride bond, simultaneous oxidative addition of the bound dihydrogen occurs. The kinetic data shows that the reaction is first order with respect to hydrogen pressure. This is interpreted in terms of an endergonic coordination of this second equivalent of dihydrogen, although a rate-determining step, in which coordinated solvent is replaced by dihydrogen, could not be ruled out. Furthermore, the reaction was found to be zeroth order with respect to the alkene concentration. This correlates well with the calculated exothermicity of substrate coordination, and the catalyst is thus believed to coordinate an alkene in the resting state. On the basis of the proposed catalytic cycle, calculations were performed on a full-sized system with 88 atoms to assess the appropriateness of the model calculations. These calculations were also used to explain the enantioselectivity exerted by the catalyst.

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Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

New Mechanistic Insights into the Iridium–Phosphanooxazoline‐Catalyzed Hydrogenation of Unfunctionalized Olefins: A DFT and Kinetic Study

Brandt

Hedberg

Andersson

2002

Chemistry A European J

157

120

View full text Add to dashboard Cite

show abstract

“…A variety of mass spectrometry and imaging studies on synthetic eumelanins argue that the pigment is an aggregated system of small oligomeric (∼4–6 monomers) molecules. Supporting mass spectrometry data have been reported for synthetic (61–63) and natural melanins, such as isolated from Sepia (64), human hair (65) and iris (19). Solubilization of natural pigment by detergent solution suggested the dominant forces holding the melanin granules together are not covalent in nature, but rather arise from hydrophobic interactions (54).…”

Section: Morphology Of Melanin Assemblies As Determined By Modern Imamentioning

confidence: 97%

Isolation and Biophysical Studies of Natural Eumelanins: Applications of Imaging Technologies and Ultrafast Spectroscopy

Liu

Simon

2003

Pigment Cell Research

174

154

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The major pigments found in the skin, hair, and eyes of humans and other animals are melanins. Despite significant research efforts, the current understanding of the molecular structure of melanins, the assembly of the pigment within its organelle, and the structural consequences of the association of melanins with protein and metal cations is limited. Likewise, a detailed understanding of the photochemical and photophysical properties of melanins has remained elusive. Many types of melanins have been studied to date, including natural and synthetic model pigments. Such studies are often contradictory and to some extent the diversity of systems studied may have detracted from the development of a basic understanding of the structure and function of the natural pigment. Advances in the understanding of the structure and function of melanins require careful characterization of the pigments examined so as to assure the data obtained may be relevant to the properties of the pigment in vivo. To address this issue, herein the influence of isolation procedures on the resulting structure of the pigment is examined. Sections describing the applications of new technologies to the study of melanins follow this. Advanced imaging technologies such as scanning probe microscopies are providing new insights into the morphology of the pigment assembly. Recent photochemical studies on photoreduction of cytochrome c by different mass fraction of sonicated natural melanins reveal that the photogeneration of reactive oxygen species (ROS) depends upon aggregation of melanin. Specifically, aggregation mitigates ROS photoproduction by UV-excitation, suggesting the integrity of melanosomes in tissue may play an important role in the balance between the photoprotective and photodamaging behaviors attributed to melanins. Ultrafast laser spectroscopy studies of melanins are providing insights into the time scales and mechanisms by which melanin dissipates absorbed light energy.

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“…These steps include the oxidation of DOPA to dopaquinone (Bertazzo et al, 1999), the oxidative polymerization of indolic melanin monomers to form eumelanin (d'Ischia et al, 1991), and the oxidation of phenothiazine type intermediates in the production of pheomelanins (Kasraee, 2002a). In melanoma cells, pigment deposition begins to appear when peroxidase exhibits its highest levels of activity, i.e., in stages II and III premelanosomes (Shibata et al, 1993).…”

Section: Methimazole Is An Inhibitor Of Melanin Synthesis In Culturedmentioning

confidence: 99%

Methimazole Is an Inhibitor of Melanin Synthesis in Cultured B16 Melanocytes

Kasraee

Hügin

Tran

et al. 2004

Journal of Investigative Dermatology

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Application of matrix-assisted laser desorption/ionization mass spectrometry to the detection of melanins formed from Dopa and dopamine

Cited by 32 publications

References 23 publications

New Mechanistic Insights into the Iridium–Phosphanooxazoline‐Catalyzed Hydrogenation of Unfunctionalized Olefins: A DFT and Kinetic Study

New Mechanistic Insights into the Iridium–Phosphanooxazoline‐Catalyzed Hydrogenation of Unfunctionalized Olefins: A DFT and Kinetic Study

Isolation and Biophysical Studies of Natural Eumelanins: Applications of Imaging Technologies and Ultrafast Spectroscopy

Methimazole Is an Inhibitor of Melanin Synthesis in Cultured B16 Melanocytes

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