4th EucheMs chemistry congress

Monday, 27-Aug 2012
s674
chem. Listy 106, s587–s1425 (2012)
food Chemistry food /Agriculture /Agrochemistry / Nanotechnology, food and processing
Microconstituents and analysis
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the free rAdiCAL invoLved in the oxidAtion
of fLAvonoidS By LACCASe. An ASSAy for
Pro-oxidAnt reACtivity
A. C. Mot 1 , G. dAMiAn 2 , C. SArBu 1 ,
r. SiLAGhi duMitreSCu 1
1 Babes-Bolyai University, Faculty of Chemistry and Chemical
Engineering, Cluj-Napoca, Romania
2 Babes-Bolyai University, Faculty of Physics, Cluj-Napoca,
Romania
Under certain conditions polyphenolics may display
prooxidant rather than antioxidant properties, and this may lead
to undesirable consequences such as inhibition of mitochondrial
respiration, direct DNA damage, lipid peroxidation and
mutagenicity - but also to benefic effects such as tumor cell
apoptosis, cytoprotective enzyme induction, or activation of
oxidative-stress-responsive transcription factors.
Here, we describe a transient species that may be detected
with UV-vis and EPR spectroscopy during turnover of a laccase
with a polyphenolic compound – quercetin. This transient species
is assigned as a quercetin-derived radical, based on EPR spectra as
well as based on UV-vis similarities with previously reported data
obtained via a non-enzymatic route. The formation and decay of
this species correlate well with the prooxidant reactivity manifested
by flavonoids in the presence of laccase. An assay for the
prooxidant reactivity of natural compounds is proposed based on
the results reported here and applied on several propolis extracts;
this assay has the advantages of using a biologically-relevant
process (hemoglobin oxidation), and of not needing added
oxidizing agents such as peroxide or superoxide. A series of
flavonoids are assayed with this method and their characteristics
are discussed. Correlations, or the lack thereof, between the
prooxidant parameters and the redox potentials, antioxidant
capacities and lipophilicities are analyzed.
The advantage of using a laccase instead of a peroxidase is
that it does not use H O as co-substrate but O ; indeed, H O 2 2 2 2 2
might have direct action on some compounds or it may generate
reactive oxygen species due to traces of transition metals.
Moreover, laccases are multicopper oxidases structurally and
functionally similar to ceruloplasmin. This proposed assay for
pro-oxidant activity would thus involve direct action of phenoxyl
radicals of flavonoids, with no other reactive species needed.
Acknowledgement: Financial support from
POSDRU/88/1.5/S/60185 – “Innovative doctoral studies in a
knowledge based society” is gratefully acknowledged by ACM.
Keywords: quercetin; flavonoid; radical; laccase; pro-oxidant;
Microconstituents and analysis
4 th EucheMs chemistry congress
o - 0 3 8
AntirAdiCAL CAPACity And redox PotentiAL
of PhenoLiC BetALAinS
L. GonCALveS 1 , e. BAStoS 2
1 Universidade Federal do ABC, Centro de Ciencias Naturais e
Humanas, Santo André, Brazil
2 Instituto de Química, Departamento de Química Fundamental,
Sao Paulo, Brazil
Betalains are natural pigments with high antioxidant
capacity, which have been used as therapeutic agents in several
conditions related to oxidative stress. In this work, we describe
the semi-synthesis of artificial phenolic betalains and the pH
dependence of antiradical capacity and redox potentials.
Betalamic acid was obtained by alkaline hydrolysis of betanin and
coupled with ortho-, meta- and para-aminophenol under acid
conditions resulting in BtPh-2-OH, BtPh-3-OH and BtPh-4-OH
(average yield = 50%). Products were purified by reversed-phase
column chromatography and characterized by LC/ESI(+)-MS and
NMR spectroscopy.
The antiradical capacity of the three regioisomers was
evaluated using the TEAC/ABTS method and reported as Trolox
equivalents. All betalains prepared have higher antiradical
capacity than ascorbic acid and the vitamin E analogue Trolox.
BtPh-3-OH has the highest TEAC (5.1 ± 0.3, pH = 7.4). The
TEAC of BtPh-2-OH and BtPh-4-OH in the same experimental
conditions was found to be 3.8 ± 0.3 and 3.0 ± 0.1, respectively.
The antiradical capacity increases with the pH for all isomers until
the hydrolysis limit (pH = 9.0). Square-wave voltammetry on
boron-doped diamond electrode was used to determine the redox
potentials of the phenolic betalains. Anodic potentials (E (mV, p
Ag vs. AgCl) 482 and 842 (BtPh-2-OH); 803 (BtPh-3-OH);
348 and 830 (BtPh-4-OH)) might indicate the oxidation of the
phenolic portion as well as the 1,7-diazaheptamethine moieties.
Control experiments with indicaxanthin (non-phenolic betalain of
L-Pro) were performed (TEAC = 1.6 ± 0.1; E = 1044 mV
p
(Ag vs. AgCl)). Results indicate that the phenol portion decreases
the oxidation potential as well as increases the antiradical capacity.
Keywords: betalain; antioxidant; natural pigment;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc