Synthesis, spectroscopic characterization and structural investigation of a new charge transfer complex of 2,6-diaminopyridine with 4-nitrophenylacetic acid: Antimicrobial, DNA binding/cleavage and antioxidant studies

Enhancement of Haloperidol Binding Affinity to Dopamine Receptor Via Forming a Charge-Transfer Complex with Picric Acid and 7,7,8,8-Tetracyanoquinodimethane for Improvement of the Antipsychotic Efficacy

Haloperidol (HPL) is a typical antipsychotic drug used to treat acute psychotic conditions, delirium, and schizophrenia. Solid charge transfer (CT) products of HPL with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and picric acid (PA) have not been reported till date. Therefore, we conducted this study to investigate the donor–acceptor CT interactions between HPL (donor) and TCNQ and PA (π-acceptors) in liquid and solid states. The complete spectroscopic and analytical analyses deduced that the stoichiometry of these synthesized complexes was 1:1 molar ratio. Molecular docking calculations were performed for HPL as a donor and the resulting CT complexes with TCNQ and PA as acceptors with two protein receptors, serotonin and dopamine, to study the comparative interactions among them, as they are important neurotransmitters that play a large role in mental health. A molecular dynamics simulation was ran for 100 ns with the output from AutoDock Vina to refine docking results and better examine the molecular processes of receptor–ligand interactions. When compared to the reactant donor, the CT complex [(HPL)(TCNQ)] interacted with serotonin and dopamine more efficiently than HPL only. CT complex [(HPL)(TCNQ)] with dopamine (CTtD) showed the greatest binding energy value among all. Additionally, CTtD complex established more a stable interaction with dopamine than HPL–dopamine.

New Charge Transfer Complex between 4-Dimethylaminopyridine and DDQ: Synthesis, Spectroscopic Characterization, DNA Binding Analysis, and Density Functional Theory (DFT)/Time-Dependent DFT/Natural Transition Orbital Studies

A combined experimental and theoretical study of the electron donor 4-dimethylaminopyridine (4-DMAP) with the electron acceptor 2, 3-dichloro-5, 6-dicyano-p-benzoquinone (DDQ) has been made in acetonitrile (ACN) and methanol (MeOH) media at room temperature. The stoichiometry proportion of the charge transfer (CT) complex was determined using Job's and photometric titration methods and found to be 1:1. The association constant (K _CT), molar absorptivity (ε), and spectroscopic physical parameters were used to know the stability of the CT complex. The CT complex shows maximum stability in a high-polar solvent (ACN) compared to a less-polar solvent (MeOH). The prepared complex was characterized by Fourier transform infrared, NMR, powder X-ray diffraction, and scanning electron microscopy-energy-dispersive X-ray analysis. The nature of DNA binding ability of the complex was probed using UV-visible spectroscopy, and the binding mode of the CT complex is intercalative. The intrinsic binding constant (K _b) value is 1.8 × 10⁶ M^-1. It reveals a primary indication for developing a pharmaceutical drug in the future due to its high binding affinity with the CT complex. The theoretical study was carried out by density functional theory (DFT), and the basis set is wB97XD/6-31G(d,p), with gas-phase and PCM analysis, which supports experimental results. Natural atomic charges, state dipole moments, electron density difference maps, reactivity parameters, and FMO surfaces were also evaluated. The MEP maps indicate the electrophilic nature of DDQ and the nucleophilic nature of 4-DMAP. The electronic spectrum computed using time-dependent DFT (TD-DFT) via a polarizable continuum salvation approach, PCM/TD-DFT, along with natural transition orbital analysis is fully correlated with the experimental outcomes.

Charge transfer complexes: Emerging and promising colorimetric real-time chemosensors for hazardous materials

After introducing the concept of charge transfer (CT) complex formation by Mulliken and the discovery of crystalline picrate (association of picric acid and aromatic hydrocarbons) by Fritzsches, a large interest has been drawn in this field. CT complexes have been explored and exploited for different applications for several decades. The research has been aimed mostly for discovering and characterizing new CT materials and exploring applications mainly in the field of optoelectronic properties, antimicrobial activities and DNA/protein binding properties for the last six years. However, nowadays, CT complexes are exploited for their photocatalytic activities and designing chemosensors for the colorimetric real-time detection of hazardous materials like nitro explosives, anions and toxic heavy metal ions in an aqueous medium. This review sheds light on updates on CT complexes, their types, synthesis and applications. The brief discussion on the emergence of CT complexes as highly potential chemosensors along with the explanation of sensing mechanism through article summarization is the centerpiece of this review. The final outcomes are discussed and concluded.

Charge Transfer Complex of Neostigmine with 2,3-Dichloro-5,6-Dicyano-1,4-Benzoquinone: Synthesis, Spectroscopic Characterization, Antimicrobial Activity, and Theoretical Study

BACKGROUND

Electron donor-acceptor interactions are important molecular reactions for the activity of pharmacological compounds. The aim of the study is to develop a charge transfer (CT) complex: synthesis, characterization, antimicrobial activity, and theoretical study.

METHOD AND RESULTS

A solid CT complex of neostigmine (NSG) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) was synthesized and characterized by infrared spectra, NMR, and UV-visible spectroscopy. The results confirm the formation of a CT complex. The stability of the CT complex between NSG and DDQ in acetonitrile was determined in solution via spectrophotometric measurement, ie, by calculating the formation constant, molar extinction coefficient, and different spectroscopic parameters. The stoichiometry of the formed NSG-DDQ complex was determined using Job's method. The absorption band of the NSG-DDQ complex can be used for the quantification of NSG.

CONCLUSION

The DFT geometry optimization of NSG, DDQ, and the CT complex and the UV comparative study of both theoretical and experimental structures are presented. The experimental results confirm the charge transfer structure. The bacterial study shows that the NSG-DDQ complex has good antibacterial activity against both Gram-positive and Gram-negative bacteria as well as antifungal activity against Candida albicans.

Synthesis, Characterization, and Biological Evaluation of a New Hydrogen-Bonded Charge-Transfer Complex of 2-Amino-4-methoxy-6-methylpyrimidine

A new hydrogen-bonded charge-transfer (HB-CT) complex formed between the donor 2-amino-4-methoxy-6-methylpyrimidine (AMMP) and the π-acceptor 2,5-dihydroxy-p-benzoquinone (DHBQ) was investigated in both solid and solution states. The investigation was conducted using UV-Vis, CHN, FTIR, 1H NMR, XRD, and TG-DTA analyses. The molecular composition of the CT complex in MeOH was found to be 1 : 1. The formation constant (KCT), molecular extinction coefficient (ε), and several other spectroscopic physical parameters were evaluated at different temperatures. The thermodynamic properties of the CT interaction in MeOH were studied by calculating the enthalpy (ΔH°), entropy (ΔS°), and free energy (ΔG°). The thermodynamic parameters indicated that van der Waals interactions and hydrogen bonding occur between AMMP and DHBQ in MeOH. The CHN, FTIR, and TG-DTA measurements confirmed that the solid HB-CT complex forms in a 2 : 1 ratio, i.e., [(AMMP)2(DHBQ)], and exhibits high stability. Moreover, XRD analysis was used to establish that the mean particle size of the complex is 23 nm. Finally, the solid HB-CT complex was screened for its antibacterial, antifungal, and antioxidant activities. It shows good activity against various bacterial and fungal species. Furthermore, the HB-CT complex exhibits good DPPH scavenging activity.

Hydrogen bonded charge transfer molecular salt (4-chloro anilinium-3-nitrophthalate) for photophysical and pharmacological applications

Radical scavenging activity against DPPH radical and binding properties of a hydrogen bonded charge transfer molecular salt 4-chloro anilinium-3-nitrophthalate(CANP) with calf thymus DNA has been studied by electronic absorption and emission spectroscopy. The molecular structure and crystallinity of the CANP salt have been established by carried out powder and single crystal X-ray diffraction analysis which indicated that cation and anion are linked through strong N⁺H^…O^- type of hydrogen bond. FTIR spectroscopic study was carried out to know the various functional groups present in the crystal. ¹H and ¹³C NMR spectra were recorded to further confirm the molecular structure of the salt crystal. The thermal stability of the title salt was established by TG/DTA analyses simultaneously on the powdered sample of the title crystal. Further, the CANP salt was examined against various bacteria and fungi strains which showed a remarkable antimicrobial activity compared to that of the standards Ciproflaxin and Clotrimazole. The results showed that the CANP salt could interact with CT-DNA through intercalation. Antioxidant studies of the substrates alone and synthesized CANP salt showed that the latter has been better radical scavenging activity than that of the former against DPPH radical. The third order nonlinear susceptibility of the CANP salt was established by the Z-scan study.

Indole-containing new types of dyes and their UV-vis and NMR spectra and electronic structures: Experimental and theoretical study

Indole containing dyes were synthesized via a simple method with high yield. These molecules have different colors and UV-vis spectra of them were recorded. Impact of solvents on absorbances was investigated and it was observed that basic solvent such as DMF and pyridine have blue shift. TD-DFT calculations were done and results were compared with experimental data. NMR data of molecules were analyzed and tautomeric forms of colorants and their ratio were determined. It was find out that two tautomers might be formed in solution, called indole and indolenine form. HOMO-LUMO and energy gaps were calculated and plotted. Furthermore, molecular electrostatic potentials were simulated to find out electrophilic and nucleophilic regions.

Charge transfer complexes of 4-isopropyl-2-benzyl-1,2,5-thiadiazolidin-3-one1,1-dioxide with DDQ and TCNE: experimental and DFT studies

We investigated the interaction between sulfahydantoin and two acceptors (DDQ and TCNE) in the liquid phase and in the solid state.

Growth, physicochemical and quantum chemical investigations on 2-amino 5-chloropyridinium 4-carboxybutanoate – an organic crystal for biological and optoelectronic device applications

Optically transparent organic single crystals of 2-amino 5-chloropyridinium 4-carboxybutanoate (2A5C4C) with sizes of 7 × 4 × 2 mm³ were grown by a slow evaporation solution growth technique at room temperature using methanol solvent.