Synthesis of a New Heteropolytopic Cryptand Through Schiff Base Condensation in the Presence of Ba(II) Ion

A new Schiff base cryptand (L) has been prepared via [2 + 2] condensation of 1,3,5-tris(2-formylphenoxymethyl)benzene (1) with 1,3,5-tris(aminomethyl)benzene trishydrochloride (2) in the presence of Ba(II) ion. The analytical data show that the Ba(II) cation is not retained by the product. Thus it seems that the role of the Ba(II) ion is to organize the transition state preceding the formation of the cryptand.     

Prediction of microscopic protonation constants of polybasic molecules via computational methods: A complete microequilibrium analysis of spermine

For the first time, a simple methodology is reported for theoretical calculation of microscopic protonation constants of polybasic molecules in solution. Density functional theory study was used for complete microequilibrium analysis of spermine, H₂N(CH₂)₃NH(CH₂)₄NH(CH₂)₃NH₂, a linear tetraamine with 16 known microspecies. A general thermodynamic cycle is proposed to calculate protonation microconstants of polybasic molecules using calculated micro‐ΔG values in aqueous solution. The microscopic protonation constants were determined with considering both the most abundant and most stable conformers for all microspecies. The results show that the microscopic protonation constants derived from the most abundant conformers (i.e., linear conformers in which the intramolecular hydrogen bonding does not exist) are in good agreement with the corresponding available experimental data. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electrochemical Derivatization of Acetaminophen for Indirect Determination of Eflornithine Using β‐CD Modified Glassy Carbon Electrode

In the present work, the oxidation of acetaminophen in the absence and presence of eflornithine was electrochemically investigated by means of cyclic voltammetry at a glassy carbon electrode (GCE). Our results indicate that N‐acetyl‐p‐benzoquinone imine (NAPQI) produced from two‐electron electrochemical oxidation of acetaminophen participates in a Michael addition reaction with eflornithine via an ECE mechanism. This fact was used for the determination of eflornithine using differential pulse voltammetry (DPV) technique on the surface of β‐Cyclodextrin modified glassy carbon (β‐CD/GC) electrode. β‐CD/GC electrode was prepared through an electrodeposition procedure and characterized by Fourier‐transform infrared spectroscopy (FT‐IR), Cyclic Voltammetry (CV), Field Emission Scanning Electron Microscopy (FESEM) and Energy‐dispersive X‐ray spectroscopy (EDS) techniques. Under optimum conditions, the β‐CD/GC electrode showed a good linearity as a function of the eflornithine concentration over the range from 5 to 100 μM with detection limit and quantification limit of 1.94 and 5.8 μM, respectively. Finally, the proposed protocol was confirmed to be successful in determination of eflornithine in human urine samples with good recovery, ranging from 97.2 % to 104.8 %.     

Structural,theoretical and multinuclear NMR study of mercury(II) complexes of phosphorus ylides: Mono and binuclear complexes

Reaction of phosphorus ylide Ph₃PCHC(O)C₆H₄Cl (Y₁) with HgX₂ (X = Cl, Br and I) and ylide (p-tolyl)₃PCHC(O)CH₃ (Y₂) with HgI₂ in equimolar ratios using methanol as solvent leads to binuclear products. The bridge-splitting reaction of binuclear complex [(Y₁) · HgCl₂]₂ by DMSO yields a mononuclear complex containing DMSO as ligand. O-coordination of DMSO is revealed by single crystal X-ray analysis in mononuclear complex of [(Y₁) · HgCl₂ · DMSO]. C-coordination of ylides is confirmed by X-ray structure of binuclear complex [(Y₂) · HgI₂]₂. Characterization of the obtained compounds was also performed by elemental analysis, IR, ¹H, ³¹P, and ¹³C NMR. Theoretical studies on mercury(II) complexes of Y₁ show that formation of mononuclear complexes in DMSO solution in which DMSO acts as a ligand, energetically is more favorable than that of binuclear complexes.     

Synthesis and crystal structure determination of some asymmetrical and symmetrical CR-type macrocyclic Schiff base complexes, with a single pendant coordinating 2-aminoethyl arm

A novel, totally asymmetrical tripodal 2,3',4"-tetraamine ligand, N((CH2)2NH2)((CH2)3NH2)((CH2)4NH2), epb, has been synthesized. In the presence of copper(II) and nickel(II) ions it condenses with 2,6-diacetylpyridine in 1:1 ethanol-water solution, producing some new CR-type complexes with a pendant primary amino group. The X-ray crystal structure of the resulting copper(II) complex, [Cu(3,4(2)-CR)](PF6)2 (1), and two other related complexes, [Cu(2,4(2)-CR)](ClO4)2 (2) and [Cu(3,3(2)-CR)](ClO4)2 (3), are reported. Crystal data: complex 1, monoclinic, P2(1)/n, a = 8.366(3) A, b = 15.549(3) A, c = 20.283(2) A, beta = 98.73(2) degrees, V = 2607.8(11) A3, Z = 4, R1 = 0.0621, wR2 = 0.1615; complex 2, monoclinic, P2(1)/c, a = 7.981(10) A, b = 18.882(3) A, c = 15.185(3) A, beta = 96.40(2) degrees, V = 2275.7(6) A3, Z = 4, R1 = 0.0773, wR2 = 0.1635; complex 3, monoclinic, P2(1)/n, a = 7.8764(10) A, b = 15.361(2) A, c = 19.370(2) A, beta = 100.330(10) degrees, V = 2305.7(5) A3, Z = 4, R1 = 0.0537, wR2 = 0.1397. In all of these, copper atoms are bonded to four nitrogens of a macrocyclic ring and a nitrogen of the pendant arm. The arrangements are slightly distorted square-pyramidal in which the primary amino groups occupy apical positions and have the longest Cu-N distances. For all isomers, copper(II) ions are somewhat above the plane of the imino-pyridine system of the macrocylic ring in the direction of the pendant coordinated primary amino group.     

Copper Schiff base complex immobilized on silica‐coated Fe3O4 nanoparticles: a recoverable and efficient catalyst for synthesis of polysubstituted pyrroles

In this work, a copper Schiff base complex immobilized on silica‐coated Fe₃O₄ nanoparticles is synthesized, and studied as a highly efficient, recyclable, green and heterogeneous catalyst for the preparation of polysubstituted pyrroles under solvent‐free and mild conditions. This new catalyst was characterized by different techniques, such as Fourier transform infrared (FT‐IR), X‐ray powder diffraction (XRD), field‐emission scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), inductively coupled plasma (ICP) and vibrating sample magnetometry (VSM). The simple and environmentally one‐pot multicomponent condensation of nitromethane, an aryl aldehyde, a 1,3‐dicarbonyl compound and an amine in the presence of above catalyst affords the title compounds at room temperature. At the end, we compared the results for the synthesis of polysubstituted pyrroles in the presence of our nanocatalyst with previously reported catalysts in the literature.     

Synthesis of New Phosphonium Ylides Containing Thiophene and Furan Rings and Study of Their Reaction with Mercury(II) Halides: Spectral and Structural Characterization

Reactions of phosphonium ylides (4‐MeC₆H₄)₃PCHC(?O)(2‐C₄H₃S) (tptpy), Ph₃PCHC(?O)(2‐C₄H₃O) (fppy), and (4‐MeC₆H₄)₃PCHC(?O)(4‐BrC₆H₄) (bbtppy) with HgX₂ (X=Cl, Br, and I) in equimolar ratios in MeOH as solvent leads to the binuclear products 1 – 3 (Scheme 1). The bridge‐splitting reaction of the binuclear complex [{HgI₂(bbtppy)}₂] ( 3c ) by DMSO yields the mononuclear complex [HgI₂?(bbtppy) (DMSO)] ( 3d ) (Scheme 2). This bridge‐splitting reaction can also be a method for the synthesis of mononuclear products. C‐Coordination of the ylide and O‐coordination of DMSO are demonstrated by a single‐crystal X‐ray‐analysis of the mononuclear complex 3d . Characterization of the obtained compounds was also performed by means of elemental analysis and IR and ¹H‐, ³¹P‐, and ¹³C‐NMR spectroscopy. A theoretical study of some Hg^II complexes with phosphonium ylides is also reported.     

A Comparison between the Experimental and Theoretical Investigations on Carbon‐13 Isotropic Shielding Constants of Some Tripodal Tetraamine Ligands

The direct implementation of GIAO and CSGT methods for calculation of ¹³C isotropic shielding constants of fully protonated forms of six tripodal tetraamine ligands tren, pee, ppe, tpt, epb and ppb at the Hartree‐Fock level of theory are presented. The shielding constants were determined using hybrid methods (including a mixture of Hartree‐Fock exchange and DFT exchange‐correlation) and are close to the experimental data. A splayed‐like conformation was considered for fully protonated forms of all ligands, and it was confirmed that this is the most stable conformation for the latter form of such ligands. A good linear correlation between the calculated chemical shielding at gas‐phase and experimental shift values in D₂O solution was obtained.     

New equation for calculating total interaction energy in one noncyclic ABC triad and new insights into cooperativity of noncovalent bonds

In this work, a new equation consist of A???B, B???C, A???BC, and AB???C interactions is proposed for calculating the total interaction energy of noncyclic ABC triads. New equations are also proposed for calculating the changes in values of A???B and B???C interactions on the formation of triad from the corresponding dyads. The advantages of equations proposed here in comparison with many‐body interaction energy approach are discussed. All proposed equations were tested in F₃MLi???NCH???HLH and F₃MLi???HLH???HCN (M = C, Si; L = Be, Mg) as well as H₃N???XY???HF (X, Y = F, Cl, Br) noncyclic A???B???C triads. The data show that the total cooperativity of triad correlates well with the sum of the changes in values of A???B and B???C interactions calculated through new equations proposed here. © 2016 Wiley Periodicals, Inc.     

Oxidative Diels-Alder reaction of 2, 5-dihydroxybenzoic acid with 1, 3-cyclopentadiene

The electrochemical oxidation of 2,5-dihydroxybenzoic acid (1) has been studied in the presence of 1,3-cyclopentadiene (2) as a diene in water/ethanol (40/60, v/v) mixture using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of 1 in the presence of 2 is presented. Compound 1 was converted into bis-adduct 5 via electrooxidation, Diels-Alder reaction of 2 to anodically generated 3,6-dioxocyclohexa-1,4-dienecarboxylic acid (1ox), decarboxylation reaction, electrooxidation and Diels-Alder reaction. The electrochemical synthesis of 5 was performed in a onepot reaction, without toxic reagents, at a carbon electrode in a simple cell using an environmentally friendly method.