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. 2021 Dec 16;11(63):39994-40010.
doi: 10.1039/d1ra07658b. eCollection 2021 Dec 13.

Exploring the charge transfer dynamics of hydrogen bonded crystals of 2-methyl-8-quinolinol and chloranilic acid: synthesis, spectrophotometric, single-crystal, DFT/PCM analysis, antimicrobial, and DNA binding studies

Palnati Manojkumar  1 , Harilal  2 , Varukolu Mahipal  1 , Gangadhari Suresh  1 , Nampally Venkatesh  1 , Macha Ramesh  3 , Tigulla Parthasarathy  1
Affiliations

Exploring the charge transfer dynamics of hydrogen bonded crystals of 2-methyl-8-quinolinol and chloranilic acid: synthesis, spectrophotometric, single-crystal, DFT/PCM analysis, antimicrobial, and DNA binding studies

Palnati Manojkumar et al. RSC Adv. .

Abstract

The new chemistry of the hydrogen-bonded charge and proton transfer complex (HB CT) between electron-donor 2-methyl-8-quinolinol (2 MQ) and electron-acceptor chloranilic acid (CHLA) has been studied using electronic absorption spectroscopy in acetonitrile (ACN), methanol (MeOH), and ethanol (EtOH) polar media at room temperature. The stoichiometric proportion of the HB CT complex was observed to be 1 : 1 from the Job data and photometric titration process. The association constant (K CT) and molar absorptivity (ε CT) of the HB CT complex were determined by using the modified Benesi-Hildebrand equation in three polarities. Other spectroscopic physical parameters like the energy of interaction (E CT), ionization potential (I D), resonance energy (R N), standard free energy change (ΔG°), oscillator strength (f), and transition dipole moment (μ) were also evaluated. The HB CT complex structure was confirmed by different characterization techniques, such as FT-IR, NMR, TGA-DTA, and SEM-EDX analysis. Powder XRD and single-crystal XRD were used to determine the nature and structure of the synthesized HB CT complex. DNA binding studies for the HB CT complex produced a good binding constant value of 2.25 × 104 L mol-1 in UV-visible and 1.17 × 104 L mol-1 in fluorescence spectroscopy. The biological activity of the HB CT complex was also tested in vitro against the growth of bacteria and fungi, and the results indicated remarkable activity for the HB CT complex compared to the standard drugs, ampicillin and clindamycin. Hence, the abovementioned biological results of the synthesized HB CT complex show it could be used as a pharmaceutical drug in the future. Computational analysis was carried out by DFT studies using the B3LYP function with a basis set of 6-31G(d,p) in the gas phase and PCM analysis. The computational studies further supported the experimental results by confirming the charge and proton transfer complex.

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Conflict of interest statement

The authors state that they have no known competing financial interests or personal relationships that could have influenced the research presented in this study.

Figures

Fig. 1
Fig. 1. Electronic absorption spectra of 2 MQ (A), CHLA (B), and CTC (C) in acetonitrile, methanol, and ethanol, respectively, at room temperature.
Scheme 1
Scheme 1. Naked eye color of donor 2 MQ, acceptor CHLA, and HB CT complex in methanol solvent.
Scheme 2
Scheme 2. Probable mechanism of the HB CT complex.
Fig. 2
Fig. 2. Benesi–Hildebrand plot of 1 : 1 HB CT complex in different solvents.
Fig. 3
Fig. 3. FT-IR spectra of 2MQ, CHLA, and HBCT complex.
Fig. 4
Fig. 4. 1H NMR spectra of (A) 2 MQ and (B) HBCT complex in DMSO-d6.
Fig. 5
Fig. 5. SEM images and EDX spectrum for HB CT complex.
Fig. 6
Fig. 6. Powder XRD patterns show the crystalline nature of 2 MQ, CHLA, and HB CT complex.
Fig. 7
Fig. 7. (A) ORTEP view of the HB CT complex. (B) Hydrogen bonding interaction between donor and acceptor in the HB CT complex with anisotropic displacement ellipsoids drawn at the 50% probability level.
Fig. 8
Fig. 8. (A and B) Crystal packing of the HB CT complex. (Red, grey, blue, green, and white colors correspond to oxygen, carbon, nitrogen, chlorine, and hydrogen atoms, respectively.)
Fig. 9
Fig. 9. UV-visible absorption spectra of HB CT complex with increasing concentration of CT-DNA from 0 to 10 μM and static concentration of HB CT complex. The arrow (↓) displays changes in absorption intensity upon increasing DNA concentration. Inset: linear plot for the calculation of the intrinsic binding constant, Kb.
Fig. 10
Fig. 10. Fluorescence quenching curve of EB bound to CT-DNA by the HB CT complex. The arrow shows the intensity changes on increasing the concentration of the complex. Inset: plot of I0/I vs. [HB CT complex].
Fig. 11
Fig. 11. 1Optimized structures of donor 2 MQ, acceptor CHLA, and HB CT complex in the gas phase.
Fig. 12
Fig. 12. Electrostatic potential surface maps of 2 MQ, CHLA, and HB CT complex in the gas phase.
Fig. 13
Fig. 13. FMO surfaces of the HB CT complex in the PCM analysis.
See this image and copyright information in PMC

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