Experimental

CV behaviour

CV experiment was conducted to understand voltammetric behaviour of Aza redox reactions on Au disc electrode. CV images of 5.0 x 10^-6 M Aza on Au electrode at SR of 360 mV/s in a BRB with pH 4 are shown in Fig. 1.

Figure 1: CV of 5.0 x 10^-6 M Aza on Au electrode at a SR of 360 mV/s in a BRB with pH 4 

Aza revealed to be an electroactive drug during the initial scan. It was oxidised at Au electrode between 0.0 and 1.1 V, yielding one distinct, irreversible oxidation peak that could be seen at 0.544 V on the anodic scan. The absence of a reductive peak in the reverse scan established an irreversible electrochemical process paired with a quick chemical reaction immediately after electron transfer process.

Effect of SR

Fig. 2 shows that when SR rose, anodic i _p location shifted towards more positive potentials, and i _p height rose, which could be due to the somewhat quick electron transfer rate of the oxidative process at Au electrode. To understand the behaviour and reversibility of electrode reactions, the influence of SR potential on the electrochemical process was examined.

Figure 2: CV of 5.0 x 10^-6 M Aza on an Au electrode at various SR in a BRB solution with pH 4. 

A representation of anodic i_p obtained from a CV of 5 x 10^-6 M Aza with pH 4.0 at the Au electrode using SR square root “(v)1/2” and SR “(v)” is shown in Fig. 3.

Figure 3: Plot of i _p vs. (a) SR and (b) square root of SR for Aza at an Au electrode. 

Oxidation i _p height was observed to grow with SR, as “(v)^1/2’’ and “(v)” of Aza had a good linear relationship. This behaviour was consistent with the notion that Aza species are transported in large quantities on Au electrode by a process that is mostly controlled by diffusion, with some adsorption ¹⁸.

According to the slope of i _p vs. v ^1/2, Table 1 shows values of D.

Table 1: Values of electrochemical parameters obtained from ordinary Au electrodes. 

^a CV data; ^b deconvolutive data

It was found that faster SR (v) increased current and shifted E _p to more positive values. E _p and i _p were highly correlated, although there have been few quantitative studies on this connection. E _1/2 should be approximately equal to the extrapolation to zero current potential for each straight line ¹⁹.

Oxidative transfer coefficients were determined using Eq. (1) ²⁰.

(1)

Additionally, D values were calculated using i _p equation and ’v ^1/2’ ²⁰ (Table 1). Heterogeneous rate constant k _s values were determined from 'E _p-E _p/2' vs. dimensionless parameter ‘’ψ’’, as established in literature ²¹.

E _p-E _p/2 values were in the range from 68 to 103 mV, for the chosen SR. They increased with higher SR, as seen in Fig. 4, which led to Aza’s redox reaction having a quasi-reversible system for k _s rate.

Figure 4: Plot of i _{p vs}. E _p - E _p/2 of Aza. 

Plotting i _pa against E _p, as seen in Fig. 5, is one method for assessing potential shift.

Figure 5: ip vs. E _p of Aza. 

ConvV

CV examination was followed by convolutional mathematical transformation. The method is relatively insensitive to iR decrease and yields quantities that are directly connected to the concentration of electroactive species at the electrode surface (as opposed to the flux of a compound, as in original approaches).

In the event of a straightforward electron transfer mechanism for electroactive species A, it was discovered that Fick's Second Law might be expressed as ²⁰:

(2)

This equation may be solved at the electrode to provide

(3)

where I ₁ signifies current semi-integration, which is defined as in ²²:

(4)

Under pure diffusion-controlled situations [i.e., when C _{(0,t) = 0}], I ₁(t) gives its limiting value, I _lim:

(5)

Semi-integration changes the shape of the cyclic curve (i-E) into an S-shaped plot of I(t)-E curve, which results in a steady-state curve and, in some situations, is more adaptable for data processing ²⁰. To accurately assess I ₁(t), Eq. (6) was employed ²⁰:

(6)

The current at equal intervals of time is represented by i(jΔt), while gamma function of x is represented by Γ(x). Aza’s I ₁ convolution curve at the Au electrode is shown in Fig. 6a, which clearly distinguishes forward and backward sweeps, when driven in the opposite direction ^21,22. The slow electron transport rate may explain these phenomena. Furthermore, the inclusion of a chemical step in the redox pathway of Aza molecule at the Au electrode surface was confirmed by the fact that the backward scan of I ₁ convolution could not return to zero.

Figure 6: ConvV (a) and DeconvV (b) of Aza at ordinary Au electrode in pH 4.0. 

DeconvV was defined as by ^23,24:

(7)

The symbols a and ζ are defined as follows:

(8)

(9)

DeconvV curve at an ordinary Au electrode with v = 320 mV/s^-1 is displayed in Fig. 6b. The half-width of the deconvoluted peak should be ¹⁹:

(10)

Experimental measurements showed that half-width of the deconvoluted peak at half of its own height (w _p) was 95 mV, indicating that the electron transport of Aza at the Au electrode surface appeared to be moderate. Table 1 contains the values of symmetry factor (α), as determined by Eq. (10). Additionally, the absence of a deconvolutive peak in the reverse direction indicates and validates the conclusion of a quick chemical reaction that followed Aza’s electro oxidation.

The DeconvV peak height was used for calculating D via Eq. (11) ²⁴ (Table 1).

(11)

The remaining parameters have their recognized meanings, while the symbol e _p stands for E _p (in amperes). Table 1 lists D values that were established using Eq. (11). The number of electrons engaged in the mechanistic pathway was also determined using Eq. (12).

(12)

For the electrode reaction of Aza, the calculated number of electrons, n, involved in the electrode reaction via Eq. (12), was found to be 2.01. As demonstrated, the aforementioned equation offers an effective and straightforward technique for figuring out how many electrons were spent in the electrode reaction without knowing its surface area. I ₁ vs. E and (dI ₁/dt) vs. E curves were found to be easier to understand and establish the electrode reaction’s nature based on the aforementioned data.

DSM

DSM is a crucial and effective tool for understanding the type of mechanistic pathway of electrode reactions and for theoretic calculation of kinetic parameters ^25,26. For anodic electrode reactions, the transfer coefficient, E _1/2, D and heterogeneous rate constants were experimentally calculated and verified by DSM ^21,23,26. Electrochemical parameters that showed the least amount of variation between the numerically simulated curves and the experimental plots were compared between experimental and theoretical curves. Wave parameters shown in Table 2 support the proposed mechanism and the reliability of Aza compounds’ determined electrochemical properties.

Table 2: simulated and experimental wave parameters. 

^aSimulated wave parameters; ^bExperimental wave parameters.

Theoretical and recorded experimental CV, as shown in Fig. 7, support the validity of EC mechanistic route of the electrode reaction and the precision of electrochemical parameters experimentally derived.

Figure 7: CV of (a) simulated and (b) experimental Aza at an ordinary Au electrode at a SR of 0.8 V/s.