Synthesis, spectroscopic characterization, antimicrobial activity, molecular docking and DFT studies of proton transfer (H-bonded) complex of 8-aminoquinoline (donor) with chloranilic acid (acceptor)

Abstract

The proton transfer complex has been synthesized by mixing 1:1 ratio of 8-aminoquinoline (donor) and chloranilic acid (acceptor) in methanol. FTIR, ¹³C NMR, ¹H NMR, Powder XRD and UV-visible studies confirmed the formation of the newly synthesized compound. These methods ascertain that cations and anions combine to form weak hydrogen bonds as N⁺–H----O^–. The physical properties such as energy of interaction (E_CT), resonating energy (R_N), Ionization potential (I_D), and oscillator strength (f), transition dipole strength (D) and free energy ($\Delta$ G) were estimated through UV-visible spectroscopy. The thermal stability of this complex and extensive erosion was analyzed by TGA/DTA study. Benesi-Hildebrand equation was used to determine 1:1 stoichiometry of this complex and to calculate the molar extinction coefficient (ε_CT), the formation constant (K_CT) and other physical parameters. The nature of transfer of charge relations plays a vital role in chemistry and in biological systems. The synthesized proton transfer complex has been screened for antibacterial activities against different bacteria and antifungal activities against different fungi. The proton transfer complex also displays outstanding interaction with the human protein (globulin) protein. The DFT calculations by B3LYP/6-311G** basis set gave theoretical establishment and HOMO (−5.468 eV) to LUMO (−3.328 eV) electronic energy gap ($\Delta E)$ as 2.140 eV. Theoretical analysis proves the biological characteristics as well. Molecular docking displays that CT complex is fully bound to the protein and determines the free binding energy value of −290.18 kcal/mol (FEB).

A new organic charge transfer complex has been prepared, characterized and explored for antibacterial, antifungal and protein binding properties. The experimental results are supported by theoretical analysis.

Communicated by Ramaswamy H. Sarma

Highlights

• Charge transfer complex was synthesized and characterized by various techniques.

• Spectrophotometric studies were made in different polar solvents. K_CT, ε_CT and E_CT of were determined using Benesi-Hildebrand equation.

• Structure and hydrogen-bonding network were also investigated by FT-IR and NMR (¹H & ¹³C).

• Thermal analysis (TGA–DTA) was also used to confirm the thermal fragmentation and the stability of the CT-complex.

• Synthesized CT-complex was screened for its antimicrobial activity and protein (globulin) binding.

Keywords:

• ¹³C/¹H NMR
• PXRD
• DFT
• antimicrobial activity
• protein binding

Acknowledgements

Special thanks to Chairman, Department of Chemistry, AMU, Aligarh for providing research facilities at Physical Chemistry lab. Also thank to my Supervisor, Dr. Ishaat M. Khan, for the guidance. New Delhi for financial assistance in the form of the UGC-BSR Start Up Grant No. F.-3-46/2014(BSR).

Disclosure statement

No potential conflict of interest was reported by the authors.