Biological
sciences / 9. Biochemistry and biophysics
Bezrukaviy D.V., Rossikhin V.V.
ASSESSMENT OF THE ANTIOXIDIC ACTIVITY LEVEL OF
BIOLOGICAL ACTIVE COMPOUNDS APPLYING ELECTROCHEMICAL METHODS
There
exists a method that relates to the field of pharmaceutical chemistry and
concerns the methods for quantitative determination of biologically active
substances, in particular the total content of flavonoids
–the substances with apparent antioxidant properties. The essence is: the
transfer of substances from a sample (plant material) into a solution having
the following voltammetric value, which is carried
out using an indicator glass-carbon electrode with a saturated chloride silver
electrode on the background of 0.1 mol/l of the phosphate buffer (pH 6.86) with
the following recording of the anode peaks at a direct current form of the scan
potential at the speed of 0.04 V/s. The concentration of the total content of flavonoids in the plant material is determined by the
volume of the anode peak of the oxidation of substances at the range of
potentials from +0.1 to +0.5V in a relatively saturated chlorine silver
electrode. The area of the determined content of the total amount
of flavonoids ranges from 1õ10-5g/ml to
1õ10-4 g/ml.
Also
there exists a well-known method that can be used in the food, cosmetic,
pharmaceutical industries, as well as in medicine and forensic science. The
proposed method allows measuring of the activity of antioxidants in relation to
the most hazardous OH-radicals for the organism. In the process of recovering
the substance on the electrode in the solution of the background electrolyte, a
model reaction generating OH radicals is used, and the registration of the
cathode waves of the recovery of the substance leads at the range of potentials
-1.2 +- 1.9 V in a relatively saturated chlorine silver electrode comparison.
In the indicated interval a peak appears, presumably, of OH-radicals, which
decreases in proportion to the amount of added antioxidant. The activity of
antioxidants is determined by the relative reduction of this peak.
The
effect of the determination of the oxidant/antioxidant activity of the
substances uses a method comprising the preparation of an initial solution with
a mediator system containing both an oxidized and renovated form of a reagent
and an evaluation of the oxidant/antioxidant activity on the grounds of the
electrochemical parameters of the extract of the analyzed substance injected
into the initial solution, and is characterized by the fact that the initial
solution is divided into two volumes interconnected through a semipermeable membrane, and the extract of the test
substance is injected into one of the volumes of the initial solution and constant electromotive force is
used as the electrochemical evaluation parameters of oxidant/antioxidant value
in the measuring system.
Using
this method allows increasing the accuracy and reliability of the information
received.
There
is an amperîmetric method that relates to the field of
pharmacology and pharmacy, and can be used to evaluate the antioxidant activity
(AOA) of various multicomponent mixtures without
prior separation. The method involves the preparation of samples of the
analyzed and standard substances, their electrochemical oxidation in the amperometric detector cell, the amplification of electrical
signals for their registration, and the calculation of AOA from the proposed
mathematical dependence. The method allows estimating the total antioxidant
activity with high accuracy and reproductive performance and using simple and
available equipment.
There
is a new approach to the estimation of integral antioxidant capacity with the
help of electrogenerated titrants.
The antioxidant effect of 78 kinds of plants was investigated. For the
quantitative assessment of antioxidant capacity, the proposed characteristic
was implemented which was bromine antioxidant capacity (AOC), expressed in
units of amount of electricity (coils), spent on titration of 100g (100 ml) of
the preparation electro-generated by bromine. The relationship between the
integral antioxidant capacity of food products, medicinal plant material and
the content of individual groups of biologically active compounds was
established: the sum of flavonoids, tocopherols and substances of a restorative nature.
It
should be noted that not only one method for assessing the antioxidant activity
of compounds exists, moreover it is quite complicated to compare the results
obtained by different methods. In view of this it may be explained by the
variety of radical processes occurring in nature.
However,
in our opinion, the most appropriate method should be considered, in which the
wave of electrolytic reduction O2 is used as a standard.
Implementing the model reaction of the electrolytic reduction process O2,
which follows the mechanism, similar to the restoration of oxygen in cells of
the human body and animal, plant tissues and is the main oxidation process on
all objects of artificial and natural origin, which makes this method more
appealing.
In
order to determine the total amount of antioxidants in the investigated object,
a scalar is constructed which is relative to the change of the electrolytic reduction
current O: from the concentration of ascorbic acid in the solution. Further out
of this dependence on the value the relative change in the current in the
presence of the object under study the total amount of antioxidants converted to the concentration of ascorbic acid is determined.
This unified method also solves a number of problems associated with the
absence of standard antioxidant samples and a standardized total antioxidant
activity.