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A simple pyrrole-based Schiff base ligand, 2-[(2-pyrrolylmethylene)amino]phenol was used to synthesize a unique tetra palladium(II) complex by treating it with PdCl₂ in CH₃OH/CH₃CN for 1 h at room temperature. X-ray structure showed that each Pd(II) ion adopted a distorted square pyramidal structure and bonded to pyrrole “N”, imine “N”, two phenolate “O”s, and one Pd(II) ion with direct Pd(II)-Pd(II) bond. Three ligands are involved in completing the square pyramidal geometry of each Pd(II) ion and the structure appeared as a hashtag symbol and four Pd(II) ions formed a plus symbol within the hashtag structure. The tetra palladium (II) complex showed a very simple NMR spectrum and absorbs strongly in the UV-visible region.

The study of the corrosion inhibition of mild steel in acid medium 1 M HCl by the Schiff base compounds named {4,4′-Bis(pyrrole-2-carboxaldehyde) diphenyl diimino sulfide (L1) and 4,4′-Bis(thiophene-2-carboxaldehyde) diphenyl diimino sulfide (L2)} was carried out using various techniques: weight loss measurements, polarization curves, electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The influence of the concentration, immersion time and temperature was examined and the mode of adsorption of these inhibitors on the surface of the metal was highlighted by assigning the appropriate isotherm. The experimental results indicate that these compounds are effective corrosion inhibitors and the inhibitory competence rises with increasing inhibitor concentration. The adsorption of these compounds on the mild steel surface obeys the isotherm of Langmuir. The correlation between the molecular structures and the inhibitory properties of the compounds studied was performed using the Density Functional Theory (DFT) method. Furthermore, molecular dynamics (MD) simulation has been taken into account. The results indicate that the adsorption energy of L1 was less than L2, which is in accordance with the experimentally determined inhibition effect.

The cyano and nitro groups were chosen as acceptor groups, and the substituent amino or ether groups as donor groups to the matrix. Polyurethane (PU) was modified by glycerol to increase the content of chromophore and to improve the stability of the nonlinearity. T_g and T_m were raised and solubility, film-forming ability and other physical properties were improved. The average functional groups of the reactant can be adjusted to ≥ 2 with polygroups and monogroups mixture. These poled polymers show high second-order optical nonlinearity and would have potential application in frequency-doubling or electro-optical controlling devices.

A simple glass capillary-microreactor for studying the epoxidation of cyclohexene is described in this paper. Reaction conditions were optimized to achieve high reaction yield. The microreactor is easy to fabricate, fast and easy way for reliable catalyst screening in studying homogeneous oxidation reactions. Four different catalysts (i.e. manganese(II) and copper(II) metal complexes of Schiff and reduced Schiff base ligands) were synthesized and used. The reaction products were monitored by gas chromatography/mass spectrometry. The reaction performance was compared with conventional (batch scale) reaction. In both cases, catalytic activities and the product yields were found to be relatively higher for the copper(II) complexes when compared with the conventional route.

This work presents a computational study on the tautomeric forms of (E)-4-Methoxy-2-[(4-nitrophenyl)iminomethyl]phenol, an ortho-hydroxy Schiff base compound. The electronic structure of title compound has been characterized at the B3LYP/6-311G(d,p) level of density functional theory. The first hyperpolarizability values have been obtained from the molecular polarizabilities for both tautomers. The second-order non-linear optical properties have been investigated based on their relationships with the natural bond orbitals and frontier molecular orbitals. The changes of thermodynamic properties with temperature going from 100 K to 300 K have been investigated for the reactants and the reaction products tautomers. Tautomeric equilibrium constant derived from the difference between the Gibbs free energies of tautomers has been obtained at different temperatures. The relationship between formation enthalpy and entropy changes has been investigated with the enthalpy-entropy compensation.

Quantum chemical calculations of the structure, molecular electrostatic potential and thermodynamic functions have been performed using the density functional (DFT/B3LYP) method with the 6-311++G(d,p) basis set for the title compound 1-[N-(2-pyridyl)aminomethylidene}-2(1H)-Naphtalenone. The energetic behavior of the title compound in solvent media has been examined by applying the Onsager and the polarizable continuum model. To investigate second order nonlinear optical properties of the title compound, the electric dipole μ, the polarizability α and the first hyperpolarizability β were computed using the density functional B3LYP and CAM-B3LYP methods with the 6-311++G(d,p) basis set. According to our calculations, the title compound exhibits nonzero β value revealing second order NLO behavior. The changes of thermodynamic properties for the formation of the title compound with the temperature ranging from 200 K to 500 K have been obtained using the statistical thermodynamic method. The relationship between formation enthalpy and entropy changes has been investigated with the entropy–enthalpy compensation. Besides, natural bond orbital and frontier molecular orbital analysis of the title compound were investigated by theoretical calculations.

A theoretical study of the antioxidant behavior of N${}^{\prime }$-(2-hydroxy-3-methoxy-benzylidene)-4-tert-buty-lenzohydrazide (1), N${}^{\prime }$-(5-bromo-2-hydroxy-benzylidene)-4-tert-butyl benzohydrazide (2) and N${}^{\prime }$-(2-hydroxy-3-methoxybenzylidene)-4-methyl-benzene-sulfonohydrazide (3) and their tautomers 1${}^{\prime }$–3${}^{\prime }$ have been carried out at B3LYP/6-31$++$G(2d,2p). The numerical values of descriptors, namely, bond dissociation enthalpy, proton affinity (PA), electron transfer enthalpy (ETE), ionization potential, and proton dissociation enthalpy (PDE) have been calculated in gas phase and media solution (EtOH, DMSO and water). The obtained results show that the hydrogen atom transfer (HAT) mechanism is more favored thermodynamically in gas phase, whereas the sequential proton loss electron transfer (SPLET) mechanism is more preferred in solvents. Moreover, the couple (3,3${}^{\prime }$) is found to be the most potent antioxidant as expected experimentally. Furthermore, the BDE values of compound 3${}^{\prime }$ is much lower than that of ascorbic acid (AA), indicating that the tautomerization of compounds 1–3 has great influence on the antioxidant activity of these compounds. The antioxidant power of compounds (3.3${}^{\prime }$) was also rationalized by the calculation of the atomic spin density. In addition, the molecular docking study of compounds 1–3 and 1${}^{\prime }$–3${}^{\prime }$ on xanthine oxidase (XO) as the protein target revealed important interactions between active compounds and amino acids. Moreover, compound 3 is predicted to be a potential inhibitor with higher activity.

A new method to synthesize a degradable terminal amino group-containing copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL-NH₂), was developed in the following three steps: (1) the ring-opening polymerization (ROP) of ε-caprolactone from the Schiff base prepared from benzaldehyde and ethanolamine (Ph–CH=NCH₂CH₂OH) used as an initiator to obtain heterobifunctional poly(ε-caprolactone) with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH₂CH₂N=CH–Ph); (2) the coupling reaction of two reactive precursors, a hydroxy-terminated HO-PCL-CH₂CH₂N=CH–Ph and α-monocarboxy-ω-monomethoxy poly(ethylene glycol) (CMPEG) to synthesize MPEG-PCL-CH₂CH₂N=CH–Ph; (3) the conversion of the –N=CH–Ph end-group into NH₂ end-group by acidification of acetic acid to obtain MPEG-PCL-NH₂. The structures from the precursors to the terminal amino group-containing copolymer were confirmed by ¹H-NMR and their molecular weights were measured by gel permeation chromatography. The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell. The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.

We report here the synthesis and structural characterization of a novel expanded Schiff base oligopyrrolic macrocycle TxLH ($i.e.$ compound 2) along with its smaller congener hemi-TxLH ($i.e.$ compound 1). The solid-state structure of TxLH is reminiscent of the shape of a Texas Longhorn${}^{TM}$. It thus defines a new architectural form for porphyrin analogues. The present study thus underscores the potential of using functionalized oligopyrroles as readily accessible molecular building blocks for the construction of structurally non-trivial molecules.

A novel and cost-effective 2,4-dinitrophenyl hydrazine derived from Schiff base 1-benzylidine-2-(2,4-dinitrophenyl) hydrazine ( L) was designed and characterized using various spectroscopic techniques. The interaction between L and bovine serum albumin (BSA) has been carried out using UV–Vis and fluorescence spectroscopy, DSC, SEM, and molecular docking methods. The phosphate buffer ($\mathrm{\text{pH}}=7.4$) solution of BSA showed fluorescence emission maxima at 342nm. Upon addition of L to the BSA solution, it quenched the fluorescence emission at 342nm. The quenching of the fluorescence emission is due to the formation of a complex between L and BSA. The binding constant was calculated from the fluorescence titrations and found to be $6.745\times 10^6$M${}^{-1}$. Further, molecular docking analysis was carried out to establish the binding between L and BSA.

Tea is a very important source of the terepenoid $\alpha$-ionone, which is much appreciated as a medicinal beverage. Schiff bases are a very important class of organic compounds usually formed by the condensation of carbonyl compounds with amines. $\alpha$-ionone is a carbonyl terpenoid obtained from Schiff bases on condensation with nucleobases like adenine and cytosine and the amino acid $l$-leucine. We synthesized these three Schiff bases and characterized them using UV, FTIR, and H1 and C13-NMR spectra. The molecules were optimized using B3LYP/6-311+G(2d,p) level followed by the simulation of FT-IR spectra, of which the simulated and experimental spectra showed complete agreement. The UV spectra were simulated using TD-DFT, and the electronic excitations were carefully analyzed. Natural bond orbitals provided an analysis of the stability of the compound, which is supplemented by the data from frontier molecular orbital analysis. Detailed wavefunction analysis is reported which predicts the active centers, reactivity profile, and the extent of non-covalent interactions. PASS indicated that compounds show antieczemic properties and antiarthritic properties, which is confirmed with the help of molecular docking results.

A new Schiff base compound and its derivative, 3-cyclopropyl-4-(4-nitrofuran-1-yl)methyleneamino-4,5-dihydro-1$H$-1,2,4-triazol-5-one (3-CNM) and 1-acetly-3-cyclopropyl-4-(4-nitrofuran-1-yl)methyleneamino-4,5-dihydro-1$H$-1,2,4-triazol-5-one (1-ACNM), were synthesized. The structures of compounds were characterized by ${}^{13}$C-NMR, ¹H-NMR and FT-IR spectroscopy techniques. The antioxidant capacities of the molecules were investigated by different methods (metal chelation, DPPH and reducing power). Some quantum chemical calculations are performed on the B3LYP, B3PW91, MPW1PW91 functionals with the 6-311++G(d,p) level basis set of the density functional theory (DFT). Using the optimized structures of Schiff bases, the frontier molecular orbital, the theoretical spectroscopic and the nonlinear optic (NLO) analysis, the molecular electrostatic potential (MEP) surface, the thermodynamic parameters, the dipole moment, the molecular geometric properties and the total energy were calculated. The calculation results showed that the 3-CNM compound can be used as a suitable and good nonlinear optical compound. In addition, electronegative and electropositive atoms were determined from the MEP surface map. The difference between ($\mathrm{\Delta }E$) the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) energies was calculated as 3.3eV and 3.4eV for 3-CNM and 1-ACNM, respectively, and these values express the chemical stability of the molecule and the orbital interactions. This work is important because it includes the synthesis of two new molecules and theoretical calculations that support their experimental properties. It can also provide significant benefits in terms of synthesis of similar Schiff base compounds and their calculated electronic, geometric and thermodynamic properties.

Schiff bases possess a range of unique physical, chemical and medicinal properties, which contribute to their potency as biological agents. A Schiff base was synthesized, which consisted of 4-chloro aniline and vanillin. The successful formation of the compound was confirmed by their comparable FTIR, UV–Vis, ¹HNMR and ${}^{13}$CNMR spectra. The compound was analyzed using X-ray crystallography, which revealed that it crystallizes in the monoclinic system with the space group P21/c. The Hirshfeld surface analysis revealed valuable information about the intermolecular interactions present in the crystal lattice. The most common contacts observed were between hydrogen and hydrogen, as well as carbon and hydrogen. The obtained fluorescence values of 375 nm and 412 nm at excitation wavelength 322 nm strongly indicated the luminescent nature of the compound. The thermal stability of the compound was assessed through thermogravimetric analysis (TGA). DFT was used to optimize the geometry using the B3LYP/cc-pVDZ basis set. The compound exhibited an energy gap of 2.35 electron volts (eV). According to the analysis of molecular electrostatic potential, C and O atoms were found to be electrophilic. According to Mulliken charge analysis, C atoms possess both positive and negative charges, hydrogen atoms exclusively carry positive charges, and Cl, O and N atoms exclusively carry negative charges. Upon analysis of the molecule, the electron localization function discovered that the atoms of carbon, nitrogen and chlorine exhibited delocalized electron density. Also, the localized orbital locator identified the localized orbital positions in the hydrogen atoms. The reduced density gradient (RDG) maps exhibit a wide range of noncovalent interactions. In comparison to the standard amoxicillin, the synthesized compound demonstrated moderate antimicrobial efficacy against the gram-positive bacteria Klebsiella pneumoniae and the fungi Candida albicans. The compound’s concentration-dependent antioxidant and anti-inflammatory properties were demonstrated through in vitro biological evaluation using 2,2-diphenyl-1-picrylhydrazyl and human red blood cell (HRBC) methods. The compound was docked using the proteins 7BYE and 4LEB were chosen from both organisms. The lowest binding attractions obtained were −3.40 kcal/mol for 7BYE and −4.51 kcal/mol for 4LEB. To investigate the stability of the protein–ligand complex, molecular dynamic simulation was employed. The ligands in silico toxicity potentialities were analyzed using seven toxicity models and the results indicated that the ligand is biocompatible.