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

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 (Δ 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 (ΔE) 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.

Mono- and Di-Quaternized 4,4'-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

Mono- and di-quaternized 4,4'-bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4'-bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium- and environment-responsive 4,4'-bipyridine derivatives. Two important classes of 4,4'-bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N'-disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4'-bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications.

Supramolecular inter-ionic charge-transfer complexes between derivatives of pyridinium-4-oxime cations and hexacyanoferrate(ii) anions

Mono- and bis-pyridinium-4-oxime compounds are introduced as new electron acceptors for the formation of colored, supramolecular, inter-ionic charge-transfer complexes with hexacyanoferrate(ii) as a donor.

Spectroscopic and theoretical studies of charge-transfer interaction of 1-(2-pyridylazo)-2-napthol with nitroaromatics

1-(2-Pyridylazo)-2-napthol (hereafter 1Q) is widely used as a chelating ligand applied in chelatometric, spectrophotometric analysis of metal ions. It appeared from the literature survey that no inclusion complex of 1Q was reported with nitroaromatics. The formation of charge-transfer complex gives an opportunity to improve the physico-chemical properties of different donors. So the complex of 1Q with 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), picric acid (PA), and 3,5-dinitrosalicylic acid (3,5-DNSA) was described in this work in methanol medium. The ground and excited state binding constants and other spectroscopic data have been determined using UV-vis and fluorescence spectroscopic studies. All the complexes have been synthesized and characterized using FT-IR, ¹H NMR, and elemental analysis. Spectroscopic data reveal that 1Q joins by a N⁺HO^- type hydrogen bond with nitroaromatics. Job's plot of the continuous variation of absorbance indicates that stoichiometry of CT-complex was 1:1. Thermal stability of the synthesized complex has determined by TGA-DTA analysis. Energy-minimization DFT calculation further supported the formation of the H-bonded charge-transfer adduct.

Preferential Solvation of a Highly Medium Responsive Pentacyanoferrate(II) Complex in Binary Solvent Mixtures: Understanding the Role of Dielectric Enrichment and the Specificity of Solute-Solvent Interactions

In this work, the preferential solvation of an intensely solvatochromic ferrocyanide(II) dye involving a 4,4'-bipyridine-based ligand was examined in various binary solvent mixtures. Its solvatochromic behavior was rationalized in terms of specific and nonspecific solute-solvent interactions. An exceptional case of solvatochromic inversion was observed when going from alcohol/water to amide/water mixtures. These effects were quantified using Onsager's solvent polarity function. Furthermore, the sensitivity of the solvatochromism of the dye was determined using various solvatochromic parameters such as π* expressing the dipolarity/polarizability of solvents and α expressing the hydrogen-bond-donor acidity of solvents. This analysis was useful for the rationalization of the selective solvation phenomena occurring in the three types of alcohol/water and amide/water mixtures studied. Furthermore, two preferential solvation models were employed for the interpretation of the experimental spectral results in binary solvent mixtures, namely, the model of Suppan on dielectric enrichment [J. Chem. Soc. Faraday Trans. 1 1987, 83, 495-509] and the model of Bosch, Rosés, and co-workers [J. Chem. Soc., Perkin Trans. 2, 1995, 8, 1607-1615]. The first model successfully predicted the charge transfer energies of the dye in formamide/water and N-methylformamide/water mixtures, but in the case of MeOH/water mixtures, the prediction was less accurate because of the significant contribution of specific solute-solvent interactions in that case. The second model gave more insights for both specific solute-solvent as well as solvent-solvent interactions in the cybotactic region. The role of dielectric enrichment and specific interactions was discussed based on the findings.