Synthesis, CMC determination, and intercalative binding interaction with nucleic acid of a surfactant–copper(II) complex with modified phenanthroline ligand (dpq)

Abstract

A surfactant–copper(II) complex, [Cu(dpq)₂DA](ClO₄)₂ (dpq = dipyrido[3,2-d:2′-3′-f]quinoxaline; DA-dodecylamine), was synthesized and characterized on the basis of elemental analyses, UV–vis, IR, and EPR spectra. The critical micelle concentration (CMC) value of this surfactant–copper(II) complex in aqueous solution was found out from conductance measurements. Specific conductivity data at different temperature served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (, , and ). In addition, the complex has been examined by its ability to bind to nucleic acids (DNA and RNA) in tris-HCl buffer by UV–vis absorption, emission spectroscopy techniques, and viscosity measurements. The complex has been found to bind strongly to nucleic acids with apparent binding constants at DNA and RNA is 4.3 × 10⁵, 9.0 × 10⁵ M⁻¹_, respectively. UV–vis studies of the interaction of the complex with DNA/RNA have revealed that the complex can bind to both DNA and RNA by the intercalative binding mode via ligand dpq into the base pairs of DNA and RNA which has been verified by viscosity measurements. The presence of long aliphatic chain in the surfactant complex increases this hydrophobic interaction. The binding constants have been calculated. The cytotoxic activity of this complex on human liver carcinoma cancer cells was determined by adopting 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyl tetrazolium bromide assay and specific staining techniques. The antimicrobial and antifungal screening tests of this complex have shown good results.

Keywords:

• Surfactant–copper(II) complex
• intercalation
• DNA
• RNA
• hydrophobicity
• antimicrobial
• antitumour

Acknowledgments

We are grateful to the UGC-COSIST and DST-FIST programs of the Department of Chemistry, Bharathidasan University, and UGC-RFSMS fellowship to one of the authors, K. Nagaraj, Bharathidasan University.

Funding

Financial assistance from the CSIR [grant number 01(2461)/11/EMR-II], DST [grant number SR/S1/IC-13/2009] and UGC [grant number 41-223/2012(SR)] sanctioned to S. Arunachalam are also gratefully acknowledged.