45 Electrochemical investigation of the interaction between G-quadruplex and some ligands using MWCNT modified carbon paste electrode

Abstract

The G-quadruplex is an unusual DNA secondary structure based on the Hoogesteen G–G base pairing, which stabilizes in the presence of certain metal cations, mainly alkali ions such as K+ (Elahi, Bathaie, Mousavi, Hoshyar, & Ghasemi, 2012). In continuation of our previous studies on the interaction between DNA and small molecules (Ghanbari, Bathaie, Mousavi, 2008; Heli, Bathaie, & Mousavi, 2004), more recently, interaction of G-DNA with polyamines and ethidium bromide was studied (Elahi et al., 2012). In the present study, we investigated the interaction of carotenoids (crocin and crocetin) and monoterpene aldehydes (safranal) of saffron with G-DNA. The MWCNT was ultrasonically treated in 35% solution of nitric acid for 6 h to be functionalized with carboxylic acid groups. The carbon paste electrode was prepared by mixing graphite powder with paraffin at the ratio 65:35. The resulting paste was packed into Teflon tube. The outer layer of the electrode was made of carbon paste modified by the addition of modified MWCNT at the concentration of 10% (w/w). G-DNA was covalently immobilized onto the CPE modified with MWCNT (MWCNT/CPE) in the presence of EDC/NHS. Interaction of G-DNA with the named ligands was investigated by cyclic voltammetry and differential pulse voltammetry using the electroactive complex [Ru(NH3)6]3+ (RuHex). The results showed that crocetin has more affinity than crocin and safranal for binding to G-DNA. Binding constants for these interactions are 4.4 × 104, 1.4 × 104, and 1.6 × 104 M−1 for crocetin, crocin and safranal, respectively.