A new calix[4]pyrrole derivative and its anion (fluoride)/cation (mercury and silver) recognition

A new calix[4]pyrrole-based macrocycle, meso-tetramethyl-tetrakis{4-[2-(ethylthio)ethoxy]phenyl}calix[4]pyrrole, 7, has been synthesized and fully characterized. Unlike other calixpyrrole derivatives that show selective interaction with anions, calixpyrrole 7 described in the present work forms stable complexes with both metal cations and anions. The thermodynamics of complexation of this ditopic calixpyrrole derivative with metal cations (Hg2+ and Ag+) and the fluoride anion in nonaqueous solutions have been determined by titration calorimetry, and the host-guest composition has been investigated by using conductance measurements at 298.15 K. 1H NMR studies provide clear evidence about the sites of complexation of 7 with the ionic species, which show that the NH groups are taking part in the complexation of this ligand with the fluoride anion while the sulfur donor atoms are responsible for the interaction with metal cations. Using the present data on 7 and structurally related analogues (1-6), the complexation behavior is discussed comparatively from the thermodynamic point of view. Possessing four sulfur-containing pendent arms, 7 displays an enhanced hosting ability for Hg2+ in acetonitrile. As compared with 1, the calixpyrrole derivative, 7, shows a unique interaction with fluoride among the anions investigated in acetonitrile and dimethyl sulfoxide. As far as the fluoride complex is concerned, the medium effect is assessed in terms of the thermodynamics of the transfer of reactants and product from acetonitrile (reference solvent) to dimethyl sulfoxide.     

Preparation and antibacterial activity of copper and cobalt complexes of 4-chloro-3-nitrobenzoate with a nitrogen donor ligand

Copper and cobalt complexes with 4-chloro-3-nitrobenzoate (ClNBz) and the nitrogen ligands 1,3-diaminopropane (1,3-DAP) or o-phenylenediamine (o-PDA), were prepared and characterized. The complexes [Cu(ClNBz)2(1,3-DAP)] (1), [Cu(ClNBz)(o-PDA)]Cl (2), [Co(ClNBz)2(1,3-DAP)] (3) and [Co(ClNBz)2(o-PDA)2] (4) were characterized by FTIR, UV-Visible absorption, elemental analysis and thermal analysis. Complex [Cu(ClNBz)(o-PDA)]Cl (2) shows high antibacterial activity as indicated by its ability to inhibit the growth of Staphylococcus aureus, Enterococcus faecalis.     

Corrosion Inhibition Using Harmal Leaf Extract as an Eco-Friendly Corrosion Inhibitor

Extract of natural plants is one of the most important metallic corrosion inhibitors. They are readily available, nontoxic, environmentally friendly, biodegradable, highly efficient, and renewable. The present project focuses on the corrosion inhibition effects of Peganum Harmala leaf extract. The equivalent circuit with two time constants with film and charge transfer components gave the best fitting of impedance data. Extraction of active species by sonication proved to be an effective new method to extract the inhibitors. High percent inhibition efficacy IE% of 98% for 283.4 ppm solutions was attained using impedance spectroscopy EIS measurements. The values of charge transfer R_ct increases while the double layer capacitance C_dl values decrease with increasing Harmal extract concentration. This indicates the formation of protective film. The polarization curves show that the Harmal extract acts as a cathodic-type inhibitor. It is found that the adsorption of Harmal molecules onto the steel surface followed Langmuir isotherm. Fourier-transform infrared spectroscopy FTIR was used to determine the electron-rich functional groups in Harmal extract, which contribute to corrosion inhibition effect. Scanning electron microscopy SEM measurement of a steel surface clearly proves the anticorrosion effect of Harmal leaves.     

Spectral regression and correlation coefficients of some benzaldimines and salicylaldimines in different solvents

Sixteen Schiff bases obtained from the condensation of benzaldehyde or salicylaldehyde with various amines (aniline, 4-carboxyaniline, phenylhydrazine, 2,4-dinitrophenylhydrazine, ethylenediamine, hydrazine, o-phenylenediamine and 2,6-pyridinediamine) are studied with UV-vis spectroscopy to observe the effect of solvents, substituents and other structural factors on the spectra. The bands involving different electronic transitions are interpreted. Computerized analysis and multiple regression techniques were applied to calculate the regression and correlation coefficients based on the equation that relates peak position lambda(max) to the solvent parameters that depend on the H-bonding ability, refractive index and dielectric constant of solvents.     

Anion complexation by calix[3]thieno[1]pyrrole: the medium effect

The interaction of calix[3]thieno[1]pyrrole, 1, and halide and dihydrogen phosphate anions in a variety of solvents (acetonitrile, propylene carbonate, N,N-dimethylformamide, and dimethyl sulfoxide) has been investigated through 1H NMR, conductance measurements, and titration calorimetry. 1H NMR measurements reveal the sites of interaction of the ligand with the anions in CD3CN while the composition of the complex was determined through conductance measurements. A quantitative assessment of anion-ligand interactions is provided. Thus the thermodynamics of complexation of 1 with halide and dihydrogen phosphate anions in dipolar aprotic media at 298.15 K is reported. These data are interpreted in terms of the thermodynamics of transfer of reactants and product from a reference solvent (acetonitrile) to other solvents. The crucial role played by the solvent on the ability of the ligand to interact with anions and on the composition of the complex is demonstrated.     

The co-crystal of iron(II) complex hydrate with hydroxybenzoic acid: [Fe(Phen)<Subscript>3</Subscript>]Cl(p-hydroxybenzoate).2(p-hydroxybenzoic acid).7H<Subscript>2</Subscript>O

Crystal of [Fe(Phen)₃]Cl(PHB).2(PHBH).7H₂O (1) is triclinic, space group P-1 with a = 12.0388(11) ?, b = 15.5286(14) ?, c = 15.7794(14) ?, α = 89.759(2)°, β = 75.818(2)°, γ = 71.900(2)° and Z = 2, (phen = phenanthroline, PHBH = p-hydroxybenzoic acid, PHB = p-hydroxybenzoate anion). The phen in adjacent Fe(phen)₃ ²⁺ cations are π–π interacted forming offset face to face (OFF) motifs. Juxtaposition of four phen ligands from two cations encapsulate an R₂ ²(8) dimeric unit of H-bonded PHBH molecules within a centrosymmetric box froming a filled aryl box motif (FAB). Alternation of OFF and FAB motifs form {OFF⋯FAB}∞ strands. The Fe(phen)₃ ²⁺ cation engages its phen ligands in π–π and/or CH–π interactions with two crystalographically different PHBH molecules and one PHB anion. Seven water molecules and a chloride anion per iron(II) trisphenanthroline cation fill empty spaces in the structure forming a hydrophilic cluster. Extensive intermolecular H-bond interactions occur between water molecules, chloride anions, PHBH molecules, and PHB anions. Thermal analysis of (1) was done under N_2(g). The TG, and dTG curves revealed the expected mass losses. All associated processes are endothermic as shown in the DSC curve.     

Supramolecular structure of tetrakis-μ-(4-chloro-3-nitrobenzoato)-bis(methanol)dicopper(II)

The title compound, [Cu₂(II)(4-Cl-3-NO₂–C₆H₃CO₂)₄(CH₃OH)₂] or [Cu₂(4-chloro-3-nitrobenzoate)₄(MeOH)₂] has been prepared and its structure determined using X-ray crystallography. The complex crystallizes in the triclinic space group P-1 with a = 9.6887(9)Å, b = 10.6448(9)Å, c = 11.4194(10)Å, = 108.094(2), = 110.682(2), = 105.055(2), V = 952.691(15)ų, and Z = 1. The structure consists of centrosymmetric dimers in which the Cu(II) atoms display a square pyramidal CuO₅ coordination, with four carboxylate O atoms in the basal plane [CuO 1.951(2)–1.968(2)Å] and the methanol O atoms in the apical position [CuO 2.170(2)Å]. The Cu atoms are 2.614(1)Å apart and are bridged by four benzoate groups. The discrete dimers are extended into 1D chains that result from hydrogen bonding between the coordinated methanol on one Cu(II) dimer and the nitro substituent on an adjacent Cu(II) dimer. The chains are interdigited and held by – stacking interactions forming 3D supramolecular array.     

An Integrated Experimental and Theoretical Studies on the Corrosion Inhibition of Carbon Steel by Harmal Extracts

The corrosion inhibition effect of the three extracts from Harmal roots (HRE), leaves (HLE), and flowers (HFE) were studied for carbon steel corrosion inhibition in 0.25 M H₂SO₄ solution. The electrochemical impedance study indicated that the three types of extracts decreased corrosion effectively through a charge transfer mechanism. Harmal roots and leaf extracts showed inhibition values of 94.1% and 94.2%, while it was 88.7% for Harmal flower extract at the inhibitor concentration of 82.6 ppm. Potentiodynamic polarization data revealed that Harmal extracts acted through predominant cathodic type inhibition. Both the corrosion current density and corrosion rate decreased significantly in the presence of Harmal extracts compared to blank solution. The corrosion rate (mpy) value was 63.3, 86.1, and 180.7 for HRE, HLE, and HFE, respectively. The adsorption-free energy change ΔG_ads (kJ·mol⁻¹) values calculated from the Langmuir adsorption isotherm plots were for HRE (−35.08), HLE (−33.17), and HFE (−33.12). Thus, corrosion inhibition occurred due to the adsorption of Harmal extract on the carbon steel surface via the chemisorption mechanism. Moreover, a computational investigation using B3LYP/6-311G++(d,p) basis set in both gaseous and aqueous phases was performed for the major alkaloids (1–8) present in the Harmal extract.     

Derivative-ratio spectrophotometric method for the determination of ternary mixture of aspirin, paracetamol and salicylic acid

A derivative spectrophotometric method was developed for the assay of a ternary mixture of aspirin (ASP), paracetamol (PAR) and salicylic acid (SAL). The method is based on the use of the first and second derivatives of the ratio spectra and measurement at zero-crossing wavelengths. The ratio spectra were obtained by dividing the absorption spectrum of the mixture by that of one of the components. The concentration of the other components are then determined from their respective calibration curves treated similarly. The described method was applied for the determination of these combinations in synthetic mixtures and dosage forms. The results obtained were accurate and precise.