Effect of antioxidant plant pigments on the viability of cells subjected to oxidat...
Floral betalamic pigments: fluorescence and antiradical capacity
Comparison of the antiradical capacity of flavonoids obtained with different methods
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Author(s): |
Karina Kinuyo Nakashima
Total Authors: 1
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Document type: | Master's Dissertation |
Press: | São Paulo. |
Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
Defense date: | 2015-12-21 |
Examining board members: |
Erick Leite Bastos;
Wendel Andrade Alves;
Josef Wilhelm Baader
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Advisor: | Erick Leite Bastos |
Abstract | |
A series of four artificial betalains was prepared in order to determine the effect of imine nitrogen methylation and phenyl hydroxylation (position 3) over stability and antiradical, photophysical and redox properties of this class of natural pigments. The study of m-betalainophenol, N-methyl-m-betalainophenol, phenylbetalain and N-methylbetalain, revealed that the methylated compounds present a small hypsochromic shift of both absorption and fluorescence maxima when compared to the others. The Stokes shifts are around 4 kJ mol-1 higher for methylated betalains, whereas the quantum yields are approximately three times lower. Their hydrolysis was investigated between pH 3 and 7. All compounds are more persistent in pH = 6, and imine methylation increases the overall stability in aqueous medium. The presence of a phenol group, in comparison with a phenyl substituent, has a minor effect on the photophysical properties of betalains and has a less pronounced effect over stability than that of methylation. The electrochemical behavior was studied by cyclic voltammetry, in the same pH range, and is also more significantly affected by methylation, rather than by hydroxylation. Methylation increases anodic peak potential up to 200 mV, and the potential is also much higher in more acidic media for all compounds. The number of protons involved in the electrochemical oxidation is the same as the number of electrons for most peaks The antiradical capacity was quantified using the TEAC assay, and ABTS•+ as radical. The methylated betalains presented, in average, the same TEAC value, although only one of them is phenolic. Among the non methylated, which are 2 to 3 units more efficient than the others, the phenolic one has a greater TEAC. These results suggest a participation of the 1,2,3,4-tetraidropiridinic ring electrons in the oxidation by ABTS•+, coupled to the imine nitrogen proton. (AU) | |
FAPESP's process: | 13/24964-9 - Study of the antiradical mechanism of betalains |
Grantee: | Karina Kinuyo Nakashima |
Support Opportunities: | Scholarships in Brazil - Master |