Spectroscopic characterization of charge transfer complexes of 2,3-diaminopyridine with chloranilic acid and dihydroxy-p-benzoquinone in polar solvent

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.

Spectrophotometric study on the proton transfer reaction between 2-amino-4-methylpyridine with 2,6-dichloro-4-nitrophenol in methanol, acetonitrile and the binary mixture 50% methanol+50% acetonitrile

Proton transfer reaction between 2-amino-4-methylpyridine (2AMP) as the proton acceptor with 2,6-dichloro-4-nitrophenol (DCNP) as the proton donor has been investigated spectrophotometrically in methanol (MeOH), acetonitrile (AN) and a binary mixture composed of 50% MeOH and 50% AN (AN-Me). The composition of the complex has been investigated utilizing Job(')s and photometric titration methods to be 1:1. Minimum-maximum absorbance equation has been applied to estimate the formation constant of the proton transfer reaction (K(PT)) where it reached high values in the investigated solvent confirming its high stability. The formation constant recorded higher value in AN compared with MeOH and mixture of AN-Me. Based on the formation of stable proton transfer complex, a sensitive spectrophotometric method was suggested for quantitative determination of 2AMP. The Lambert-Beer(')s law was obeyed in the concentration range 0.5-8 μg mL(-1) with small values of limits of detection and quantification. The solid complex between 2AMP with DCNP has been synthesized and characterized by elemental analysis to be 1:1 in concordant with the molecular stoichiometry in solution. Further analysis of the solid complex was carried out using infrared and (1)H NMR spectroscopy.

Synthesis, characterization and biological studies of a charge transfer complex: 2-aminopyridinium-4-methylbenzenesulfonate

A single crystal charge transfer (CT) complex, 2-aminopyridinium-4-methylbenzenesulfonate (APTS) was synthesized and recrystallized by slow solvent evaporation solution growth method at room temperature. The complex has been characterized with the elemental analysis, UV-visible, infrared (IR), (1)H and (13)C nuclear magnetic resonance (NMR) spectra. Thermogravimetric (TG) and differential thermal analysis (DTA) were reported the thermal behaviour of the complex. Single crystal XRD studies showed that the orthorhombic nature of the crystal with space group Pbca. The biological activities of CT complex, such as DNA binding and antioxidant activity has been carried out. The results indicated that the compound could interact with DNA through intercalation and show significant capacity of scavenging with 2,2-diphenyl-2-picryl-hydrazyl (DPPH).