Biology Reference
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of Cu(I) with purine bases forming sparingly soluble compounds
that are accumulated on the surface of mercury electrodes. Using
cathodic stripping voltammetry (CSV), the Cu(I) in Cu(I)-purine
complex is reduced to Cu(0), and this very sensitive reaction
is monitored. Under optimal conditions (accumulation potential,
accumulation time, scan rate, copper concentration, and pH), the
ultra-trace CSV determination of adenine and guanine was done
by Farias [56-58]. DosSantos
et al.
[59] showed that the Cu(I)-
purinecomplexonHMDEcanalsobeoxidizedtoCu(II)usinganodic
stripping voltammetry (ASV). There are other examples where a
combination of Cu(II) and purine derivatives was used for sensitive
AdSV determination, for example, xanthine and its derivatives [60],
guanine[61], ormethylated guanines[62].
In the case of ODN, the formation of the corresponding Cu(I)-
purinecomplexissuppressedanditsdeterminationispossibleafter
the release of nucleobases from its chain by acid hydrolysis. Purine
nucleobases from an oligonucleotide chain can be released under
acid hydrolysis, for example, 0.5 M perchloric acid, at a temperature
of 75
◦
C for 30 min. Under these conditions, only purine bases
are released from the oligonucleotide chain. Then the sample is
cooledandneutralized,andaliquotsaremixedwiththebackground
electrolyte for voltammetric measurements.
In our recent experiments, we have studied the determination
of adenine (A), adenosine (Ado), and hydrolyzed adenosine (hAdo)
in the presence of Cu(II) ions using LSV and EVLS in connection
with the adsorptive stripping technique [63]. The differences in
the electrochemical behavior of A and Ado were found to be
dependent not only on the presence of copper ions, scan rate,
adenine concentration, and pH, but also on the accumulation
time and potential where a Cu(I)-adenine complex is formed. A
deeper evaluation of voltammetric responses was carried out by
EVLS using function E4, eliminating charging and kinetic current
components and conserving the diffusion current component. This
function was capable of enhancing the current sensitivity of LSV
peaks and of detecting electron transfer in adsorbed state. The
irreversible electrode process of a totally adsorbed electroactive
species is indicated by means of a peak-counterpeak signal
(Fig. 11.6).
