Journal of the Iranian Chemical Society
Volume:8 Issue: 3, Sept 2011

In continuation of our previous brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes by Aghabozorg et al. [1], we briefly surveyed the current research in the field of proton transfer compounds supramolecular synthons and their self-assembled metallic complexes from the points of view of Crystal Engineering and Density Functional Theory (DFT) since 2008. Our research groups have recently focused on the proton delivery from acids, which are considered to be suitable proton donors, to amines as proton acceptors. The results were the production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metal centers in the preparation of metal-organic compounds. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Our review and investigation of compounds revealed that they mainly focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron, mainly on the various interactions involved, including van der Waals, ion pairing, hydrogen bondings, face to face π-π stackings and edge to face C-H···π, C-O···π, N-H···π and S···S. These interactions were the most commonly used strategies in the extension of supramolecular structures.

A highly sulfonated carbon as an efficient, recyclable, nontoxic and green solid acid catalyst was synthesized readily by simultaneous sulfonation, dehydration and carbonization of sucrose C12H22O11 in sulfuric acid and was characterized with Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric and differential thermal gravimetric analysis (TG-DTG), X-ray diffraction (XRD), carbon-hydrogen-nitrogen-sulfur analysis (CHNS), neutralization potentiometric titration and scanning electron microscopy (SEM). This new catalyst was used in one pot three-component condensation reaction of various aromatic aldehydes with β-ketoester and urea under solvent-free conditions to afford the corresponding dihydropyrimidinones (DHPMs). This catalyst can be reused several times without loss of its activity.

Cyanuric chloride is shown to be an extremely efficient catalyst for the synthesis of β-enaminoesters from β-ketoesters under solvent-free conditions by grinding in a mortar with pestle at 25 °C. A short reaction time, an inexpensive and easily available catalyst, mild reaction conditions and excellent yields of the products are attractive features of this methodology.

The kinetic and mechanistic studies of homogeneously Rh(III)-catalysed oxidation of D-xylose and L-sorbose by N-bromoacetamide (NBA) in perchloric acid medium were carried out at 40 °C. The reactions were first-order with respect to each of [NBA], [Rh(III)] and [H+] and zero-order in [sugar]. Variation of [Cl-] showed positive effect while variation of [Hg(OAc)2] showed negative effect on the rate of the reactions. Addition of acetamide (NHA) had a negative effect on the rate of the reaction. The rate of the reaction was unaffected by the change in ionic strength (m) of the medium. Various activation parameters were calculated with the help of pseudo-first-order rate constant, k1, obtained at four different temperatures. The mechanisms involving RhCl4(H2O)2-, as reactive species of rhodium(III), and H2OBr+, as reactive species of NBA, are proposed which find support from the spectrophotometric evidence and activation parameters, especially the entropy of activation.

N-Protected α-amino acids, prepared from benzoyl chlorides, KSCN and α-amino acids, were used as the acid component in the Passerini reaction, in an ionic liquid, to produce functionalized α-acyloxythioamides in 59-95% yields. The work-up procedure was fairly simple and the products did not require further purification.

Multicenter multielectron integrals appearing in the study of multielectron properties of atomic and molecular systems are evaluated using one-range addition theorems in terms of complete orthonormal sets of ψα-exponential type orbitals (ψα-ETO, α = 1, 0, -1, -2, …) for ψα-ETO and Coulomb-Yukawa like correlated interaction potentials (CIP) introduced by the author. The final results are especially useful for the computation of arbitrary multicenter multielectron integrals that arise in the Hartree-Fock-Roothaan (HFR) approximation and also in the explicitly correlated methods based upon the use of ψα-ETO as basis functions.

In a one-pot four-component reaction, an aldehyde, an amine, benzil and ammonium acetate were condensed for the synthesis of 1,2,4,5-tetrasubstituted imidazoles in the presence of silica supported antimony pentachloride (SbCl5.SiO2) in improved yields. The catalyst is recoverable by simple filtration and can be used in the subsequent reactions.

Density functional theory (DFT) method at the level of B3LYP with 6-311G(d) basis set was used to investigate the effects of a variety of substituents (H, NH2, NMe2, OCH3, CH3, Cl, Br, CN, NO2) on the electronic and structural properties of 2,4-diamino-5-p-substituted-phenyl-6-ethyl-pyrimidines. The investigation showed that the atomization energy was affected by substitution. Likewise, the molecular orbitals HOMO and LUMO and energy gap DE were affected by the substituent. Dipole moment was also affected by the introduction of the substituent. On the other hand, the Mulliken charges at only C1', C2 and N7, were correlated with both MSP and DSP models.

Simple reverse flow injection analysis (rFIA) manifold with spectrophotometric detection was developed for an indirect determination of ascorbic acid. Parameters such as stability, accuracy and precision were established for the method and evaluated statistically to assess the applications of the method. Ascorbic acid in this procedure accelerates dediazoniation reaction of formed diazonium ions; hence its quantity can be determined by monitoring the derivatization product from coupling unreacted diazonium ion with phenol to give an azo dye (coupling reaction). The rFIA design was based on the injection of sodium nitrite into an acidic p-aminoacetophenon carrier stream in which diazonium ion was formed. This ion was inhibited by ascorbic acid stream before coupling with the phenol-Na2CO3 stream. Under optimum conditions, ascorbic acid acts in accordance with the Beer’s law at two concentration ranges 0.4-6.5 μg ml-1 (R = 0.9995) and 7.0-20.0 μg ml-1 (R = 0.9949), with detection limits of 0.25 μg ml-1. The developed method was applied to the determination of vitamin C in pharmaceutical formulations which produced satisfactory results compared with the standard methods reported in the British Pharmacopoeia.

The (E)-2-ethoxy-6-[(4-fluorophenylimino)methyl]phenol compound was synthesized and characterized by X-ray Diffraction, IR and Electronic spectroscopy. X-Ray and IR results showed that the title compound preferred the enol form in solid state. UV-Vis absorption spectra of the title compound were recorded in different solvents. The results showed that the molecule existed only in enol form even in the solvent media. Electronic structure and spectroscopic properties of the title compound were investigated from calculative point of view. The gas phase geometry optimization was obtained based on X-ray geometry by DFT method with B3LYP applying 6-311G(d,p) basis set. Geometry optimizations in the solvent media were obtained with the same level of theory by the polarizable continuum model (PCM). TD-DFT calculations starting from the optimized geometry were made in both gas and solution phase to measure the excitation energies of enol and keto tautomers. Vibrational frequency and natural bond orbital analysis (NBO) were performed and the thermodynamic properties of the title compound were obtained at the optimized geometry with the same level of theory.

A novel PVC membrane-selective electrode based on loratadine-tetraphenyl borate ion-pair was prepared for the determination of loratadine potentiometrically. This electrode exhibits a Nernstian slope of 59.1 ± 0.3 mV decade-1 for loratadine in a concentration range of 5.0 × 10-6-1.0 × 10-2 M at pH 2.2 with a detection limit of 2.9 × 10-6 M. The potential of the electrode is very stable and exhibits good reproducibility with very fast response time (~3 s). The selectivity of the proposed electrode towards some cations and organic compounds was tested and the selectivity coefficients were calculated. The electrode was successfully applied to the determination of loratadine in tablets and blood samples.

In this work, the antiradical activity of fresh and aged skins of two Iranian varieties of pomegranate husk and pistachio hull was measured in order to assess their concentration in antioxidant potential usable in various fields. The radical scavenging capacity (RSC) of pomegranate husks and pistachio hulls samples were studied using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) assay. To determine the RSC and stoichiometric factor of the samplers, the second-order rate constants (k2) and total H-atom-donating capacities (n) for the oxidation of polyphenol extracts by DPPH˙ were evaluated. The resulting k2 values were also compared with those of the natural and synthetic antioxidants. The order of relative second-order rate constants in methanol at 25 °C found to be pomegranate husk > gallic acid > tannic acid > pistachio hull. Furthermore, the RSCs based on the calculation of area under kinetic curve (AUC), total stoichiometric factor of natural phenolics and commercial antioxidants were also compared.

A familiarity with denaturation process is highly significant in understanding the DNA replication, manipulation, and interactions involving DNA double helix stability. We have performed molecular dynamics simulation on B-DNA duplex (CGCGAATTGCGC) at different temperatures. At each temperature, configurational entropy was estimated using the covariance matrix of atom-positional fluctuations. By plotting the configuration entropy versus temperature, we calculated the melting temperature which was found to be 329.7 K. We also calculated the hydrogen bonding energy and heat capacity for the atoms participating in the hydrogen bonding between two strands of DNA. Moreover, their temperature dependencies were investigated to obtain the melting temperature which was found to be 330.9 K. Finally, by comparing the melting temperature and the shape of the transition curve obtained from different methods, it is concluded that the stacking interactions affect the shape of transition curve, while the hydrogen bonding and columbic interactions determine the position of the melting point temperature.

In this work, some phosphoramidothioates (PATs) with the general formula of (CH3O)2P(S)X and (CH3O)(CH3S)P(O)X, where, X = NH2 (1 & 6), NH(CH3) (2 & 7), N(CH3)2 (3 & 8), N(Et)2 (4 & 9), (CH3CH2O)2P(S)NH(CH3) (5) and (CH3CH2O)(CH3CH2S)P(O)NH(CH3) (10), were synthesized and characterized by 31P, 31P{1H}, 13C and 1H NMR spectroscopy. The ability of the compounds to inhibit AChE was predicted by PASS software (version 1.193). They were also experimentally evaluated by a modified Ellman's assay. The structure-activity relationship (SAR) between IC50and some physico-chemical properties such as lipophilicity (logP), electronic and steric effects of the compounds was studied. The logP values were experimentally determined by the shake-flask (gas chromatography) method. Inhibitory potency for the compounds 1-10 was 1 (3.38 mM) > 2 (3.97 mM) > 3 (4.75 mM) > 4 (6.00 mM) > 5 (5.51 mM) > 6 (0.07 mM) > 7 (0.23 mM) > 8 (0.39 mM) > and 9 (0.55 mM) > 10 (0.51 mM), respectively. IC50 and logP parameters of the P=O moiety were more than the P=S moiety in PAT analogues.

The synthesis, structural analysis and antibacterial reactivity of two octahedral complexes, namely [Fe(PLSC)2](NO3)2.H2O, 1 (PLSC is pyridoxal semicarbazone), and [Co(PLITSC-2H)(PLITSC-H)].CH3OH, 2 (PLITSC is pyridoxal S-methylisothio-semicarbazone) are reported.

The aqueous reactions of zinc(II) and cadmium(II) nitrate and pyridine-2,6-dicarboxylic acid, (pydcH2), with 9-aminoacridine, (AAcr), resulted in the formation of two new proton transfer compounds, (AAcrH)2[Zn(pydc)2].3H2O (1) and (AAcrH)2[Cd(pydc)2].4H2O(2). The compounds were characterized using IR spectroscopy and single crystal X-ray diffraction. Both compounds crystallized in the triclinic crystal system, space group P, with two molecules per unit cell. The anions were six-coordinate complexes with distorted octahedral geometries around the Zn(II) and Cd(II) centers. The dihedral angles indicated that the two (pydc)2- ligands were almost perpendicular to each other. The complex anions of [M(pydc)2]2- were neutralized with (AAcrH)+ cations. These cations formed extended stacks throughout the structures. The water molecules clustered around cyclic tetramers, bridging the anions and forming a link to the aminoacridiunium stacks. A potentiometric pH titration method was used to investigate the protonation constants of AAcr and pydc, the pydc-AAcr proton transfer equilibrium constants, and the stoichiometries and stabilities of complex formation with Zn2+ and Cd2+ ions in 50% dioxane-50% water.

An all-electron scalar relativistic calculation of CunNCO (n = 1-13) clusters has been made using density functional theory with the generalized gradient approximation at BLYP level. In all CunNCO clusters, the NCO species prefered to occupy the single-fold coordination site and the small copper cluster tended to bond with the nitric. The Cun structures were only distorted slightly and the NCO species retained linear structure. The N-C bond-length contraction and C-O bond-length elongation were observed clearly. The reactivity enhancement of NCO species toward CO2 was obvious. But, no reactivity enhancement of NCO to form N2 related to the N-C bond strength could be observed. It seems that the NCO species is more favorably adsorbed by odd-numbered small copper clusters, relatively. Some discrepancies between our work and earlier works were found which may be explained in terms of the scalar relativistic effect. Further studies to focus on the reactivity enhancement of NCO to form N2 are clearly in order.

A novel coordination polymer of zinc(II) atom, [(pipzH2)[Zn(pyzdc)2].6H2O]n (1) (H2pyzdc and pipz are pyrazine-2,3-dicarboxylic acid and piperazine, respectively), was successfully synthesized under hydrothermal conditions and structurally characterized by means of elemental analysis, FTIR, TGA and SEM. Polymer 1 was further structurally characterized by single crystal X-ray diffraction consisting of 1D-polymeric units. The crystal structure of the title polymer consisted of polymeric Zn complex anions and discrete piperazindiium cations. The Zn cation, located on the inversion center, was N,O-chelated by two (pyzdc)2- anions in the basal plane, and was further coordinated by two carboxyl O atoms from the adjacent pyzdc anions in the axial directions with a longer Zn-O bond distance of 2.1746(15) Å, forming a distorted ZnN2O4 coordination geometry. The pyzdc anions bridged the Zn cations to the one-dimensional polymeric chains running along the crystalographic b axis. The (pipzH2)2+ linked with the complex chains via kinds of hydrogen bonds. The polymer 1 crystallized in the monoclinic space group P21/n with Z = 2. The cell parameters of the title polymer were a = 6.5318(16) Å, b = 17.492(4) Å, c = 10.688(3) Å and β = 100.841(4)°. The polymer 1 bears ion-pairing interactions, O-H…O, N-H…O, and C-H…O hydrogen bonds as main factors in the formation of its 1D supramolecular architecture. Obtained results from tga showed that the title polymer was thermally quite stable, and so its framework possessed remarkable thermal stability up to 700 °C. The SEM analysis verified that layers present in 1 were formed in Nano-sized particle. The protonation constants of acridine (Acr), H2pyzdc, and pipz as the building blocks of the proton transfer systems including pyzdc-Acr in mixed 20% dioxane-80% water (V/V) solvent and pyzdc-pipz in aqueous solvent, and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability of complexation of these systems with Zn2+ ion were investigated by potentiometric pH titration method. The stoichiometry of the most complex species in the solution was compared with the corresponding crystalline metal ion complexes.

Some recyclable SO3H-functionalized ionic liquids have been used as catalysts in water for the aza-Michael reactions of amines with α,β-unsaturated compounds to produce β-amino compounds. High yields of the products, short reaction times, mild reaction conditions, simple experimental procedure, reusable catalysts and no obvious loss of the catalytic activity make this protocol a contribution to organic chemistry.

This paper presents the synthesis and the thermal behavior of some symmetrical derivatives containing two ferrocenyl units. The influence of the following factors upon the thermal stability was estimated: the degradation atmosphere, the nature of the linking groups, the number of the benzene units and the flexible segment position.

The kinetics and mechanism of the adduct formation of diorganotin(IV)dichlorides (R2SnCl2), where R = Ph, Me, Bu, with Co(II) tetraaza Schiff base complexes such as: [Co(appn)]{[N,N'-1,2-propylenebis(o-amino-α-phenylbenzylideneiminato) cobalt(ΙΙ)]} and [Co(cappn)]{[N,N'-1,2-proylenebis(5-chloro-o-amino-α-phenylbenzylideneiminato)cobalt(II)]}, were studied spectrophotometrically. The kinetic parameters and the rate constant values show the acceptor tendency trend for the diorganotin(IV)dichlorides as follows: Ph2SnCl2 > Me2SnCl2 > Bu2SnCl2. Adducts were separately synthesized and fully characterized by 119Sn NMR, IR, UV-Vis spectra and elemental microanalysis (C.H.N) methods. The trend of the rate constants for the adduct formation of the cobalt complexes with a given tin acceptor decreased as follows: Co(appn) > Co(cappn). The linear plots of kobs vs. the molar concentration of the diorganotin(IV)dichlorides, the high span of the second order rate costant k2 values and the large negative values of ΔS‡ suggest an associative (A) mechanism for the acceptor-donor adduct formation. Moreover, [Co(aptn)]{[N,N'-1,3-propylenebis-(o-amino-α-phenylbenzylideneiminato)cobalt(ΙΙ)] and [Co(captn)]{[N,N'-1,3-proylenebis-(5-chloro-o-amino-αphenylbenzylideneiminato)cobalt(II)]} were synthesized and characterized but, their kinetics with R2SnCl2 were so fast that it was impossible to follow them using the conventional methods.

The electrochemical oxidation of 4-nitrocatechol in aqueous media was studied using cyclic voltammetry. The results indicate that the stability of electrochemically generated o-nitrobenzoquinone is low and decreases with increasing pH. Also, our voltammetric data show that the species produced from the conversion of o-nitrobenzoquinone are electro-inactive in the studied potential range. In addition, the results reveal that the rate of conversion of o-nitrobenzoquinone is dependent on the nature of the solvent. According to EC mechanism, the observed homogeneous rate constant of the conversion of o-nitrobenzoquinone was estimated by comparing the experimental cyclic voltammograms with the digitally simulated results. Finally, a possible mechanism is proposed for the electrode process, on the basis of the present and previous investigations.

Chitosan was grafted with polyvinylsulfonic acid (CHI-graft-PVS) through either chemical activation (CA) or ultrasound radiation (US) methods and the percentages of grafting (%G), grafting efficiency (%E) and the average degree of polymerization (R) were determined. The effect of CHI-graft-PVS as templates for in vitro crystallization of CaCO3 was evaluated by using gas diffusion method at different pH. It was found that CHI-graft-PVS act as an efficient modifier of crystal morphology or inhibit the crystallization depending on the experimental media and the method of grafting used. SEM analysis revealed that CHI-graft-PVS obtained through US method act as an inhibitor for CaCO3 crystallization. When CHI-graft-PVS from CA method was used, SEM analysis showed different CaCO3 morphologies such as spherical, prismatic, biconcave and needle-like crystals. Additionally, EDS confirmed the presence of S atoms from CHI-graft-PVS adsorbed on the surface of CaCO3 crystals. Results indicated that CHI-graft-PVS controls the nucleation, polymorphs and morphology of CaCO3 crystals. The composition of this new template and the control of pH of the mineralization solution seem to be crucial during CaCO3 crystallization. CHI-graft-PVS template represents an alternative approach for understanding the biomineralization process and offers a wide range of possibility for polymer controlled crystallization.

A novel series of complexes of lanthanides(III) with 4[N-(furfuralamino]antipyrine semicarbazone (FFAAPS) as the primary ligand and diphenyl sulfoxide (DPSO) as the secondary ligand with the general composition LnX3(FFAAPS)nDPSO (X = NO3-, n = 1; X = NCS- or ClO4-, n = 2; Ln = La3+, Pr3+, Nd3+, Sm3+, Gd3+, Tb3+, Dy3+ or Ho3+), is reported. All the synthesized complexes were characterized through various physico-chemical techniques i.e.elemental analysis, conductance measurements and magnetic susceptibilities, spectroscopic and thermal studies. The coordinated FFAAPS behaved as tridentate N,N,O-donor, while DPSO acted as unidentate oxygen donor. Nitrates were bicovalently bonded, while the thiocyanate was coordinated through N-atom. Perchlorate ions did not participate in the coordination sphere. The absorption bands of the representative Pr(III), Nd(III) and Sm(III) complexes in the visible and near infrared region appeared due to transitions from the ground levels to the excited J-levels of 4f-configuration. From the hypersensitive bands, the nephelauxetic effect (β) was calculated. And from the β-values, the covalence factor (b1/2), Sinha parameter (σ%) and the covalency angular overlap (η) were calculated. The ligand and the corresponding lanthanide(III) complexes were simultaneously screened for their antibacterial and antifungal activities. Thermal stabilities of these complexes were studied by thermogravimetric analysis. Depending on the nature of the anionic ligands, the coordination number of the lanthanide(III) in the case of nitrate or thiocyanate complexes was ten, while it was seven in the case of perchlorate complexes.

An efficient and eco-friendly synthesis of triarylmethanes by the reaction of arenes with aldehydes in the presence of silica sulfuric acid as a heterogeneous and reusable catalyst under ultrasonic irradiation is reported. The advantages of this protocol are the use of green solvents, inexpensive catalyst, commercially available precursors, reusability of SSA, simple work-up, high yields and short reaction times.

Heteropoly acid supported on silica gel (H3PW12O40/SiO2) is easily used as a heterogonous, reusable and efficient catalyst for the synthesis of N-substituted, 2- and 3-unsubstituted pyrroles in solution or under solvent-free microwave irradiation. The catalyst can be easily recovered and reused for several times without loss of activity.

1-Butyl-3-methylimidazolium nitrite, [bmim]NO2 was used as a new effective reagent for the preparation of N-nitrosamines from the corresponding secondary amines at 0 °C to room temperature, under mild conditions in good to excellent yields.

Task-specific phosphinite ionic liquid (IL-OPPh2) was used as a reagent for the efficient synthesis of 4-substituted coumarins via the reaction of di(methyl or ethyl) acetylenedicarboxylate with phenolic compounds under microwave irradiation conditions. The effects of parameters such as the amount of the phosphinite ionic liquid, reaction temperature and reaction time on this procedure were investigated. Products were obtained in good yields using this mild and one-pot methodology under solvent-free conditions. In addition, the ionic liquid recycling test showed that it could be reused for three times without loss of its activity.

The combinatorial factor method (CFM) was used to find the critical points of the 2-D square lattice Ising model with the nearest neighbor (with the coupling constant Jnn) and the next nearest neighbor (with the coupling constant Jnnn) interactions. In the absence of the magnetic field, for the various values of coupling ratio, α = Jnnn/Jnn (0 ≤ α < 1), the exact values of jc (= Jnn/kTc) were obtained. Finally, based on such values, an analytical expression for the jc as a function of α has been proposed

Calix[4]crown-6 (L) was synthesized and the stoichiometry and stability of its complexes with alkali, alkaline earth, Ag+, Tl+ and NH4+ ions were studied conductometrically in acetonitrile solution. The resulting 1:1 Ba2+-L complex was found to be the most stable one among all cation complexes studied. The optimized structures of the ligand and its Ba2+ complex are also reported. Based on the findings, L was used as a suitable ionophore to prepare a PVC-membrane selective electrode for Ba2+ ion. The electrode revealed a Nernstian behavior over wide barium ion concentration 1.0 × 10-6 to 1.0 × 10-3 M with only little trace of 7.1 × 10-7 M. The potentiometric responses were found to be independent of the pH of test solutions in the range of 4.0-10.0. The proposed electrode response time of about 10 s proved to be highly selective for Ba2+ ion over a wide variety of cations including alkali, alkaline earth, transition and heavy metal ions. The sensor could be used for at least three months without any noticeable deviation. The practical utility of the proposed electrode was also examined.