Journal of the Iranian Chemical Society
Volume:4 Issue: 1, Mar 2007

This review presents a general overview about the development of ion-selective electrodes in Iran during the past decade (1996-2006). All of the reported ion-selective sensors (for cations, anions and organic species) are cited in this review. Sensors for 39 cations, 12 anions, and 23 organic compounds and drugs have been reported in this reivew. Some of the main group cations (e.g. beryllium) as well as most of the lanthanide ion (i.e., presidium, erbium, lutetium, cerium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, ytterbium, and thulium) sensors have been reported for the first time. It is noticable that the best reported sensors for HPO42-, SO2-, Cl-, ClO4-, Br-, and I3- have been designed and constructed by the Iranian researchers.

The new analogues of nifedipine, in which 2-nitrophenyl group at position 4 is replaced by phenylisoxazolyl substituent, were synthesized. The symmetrical dialkyl 1,4-dihydro-2,6-dimethyl-4-(5-phenylisoxazol-3-yl)pyridine-3,5-dicarboxylates were prepared by classical Hantzsch condensation, and the asymmetrical analogues were synthesized using a procedure reported by Dagnino that involved the condensation of alkyl acetoacetate with alkyl 3-aminocrotonate and 5-phenylisoxazole-3-carboxaldehyde. The structure of all compounds was confirmed by IR, 1H NMR and Mass spectra. In vitro calcium channel antagonist activities were evaluated as calcium channel antagonists using the high K+ concentration of guinea-pig ileum longitudinal smooth muscle (GPILSM) assay. These compounds exhibited moderate calcium antagonist activity (IC50 = 10-7 to 10-5 M range) relative to the reference drug nifedipine (IC50 = 1.10 ± 0.40 × 10-8 M).

Photoinduced electron transfer ring opening of α-epoxyketones using 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) in methanol and acetic acid solutions resulted in the formation of diastereomeric products, hydroxy ethers and hydroxy esters, respectively. However, the formation of cis-1,3-dioxolanes and cis-spirodioxolanes has been observed on reaction in acetone and cyclohexanone solutions, respectively. The effect of the electron donating character of the substituent influenced the rate of the ring opening. Quantum computational studies explain the mechanism of the addition.

Cyanuration of 2-naphthaldehyde (1) and 5-methyl-2-furaldehyde (2) yielded the racemic 2-hydroxy-2-(b-naphthyl)ethanenitrile (R,S)-3 and 2-hydroxy-2-(5-methyl-2-furyl)ethanenitrile (R,S)-5, respectively. The same reaction can be completed by using acetone cyanohydrin (4) as a transcyanating agent. The optically active (R)-3 and (S)-5 could be respectively obtained by hydrocyanation of 1 and 2 using (R)-hydroxynitrile lyase (R)-PaHNL [EC 4.1.2.10] from almonds (Prunus amygdalus) as a chiral catalyst. Cyanohydrins 3 and 5 in their racemic and optically active forms undergo a number of transformations which involve either the hydroxyl group or the cyanide function. Moreover, derivatization of 3 and 5 with (S)-NaproxenÒchloride (S)-14 gave the respective diastereoisomers. The optical activity of (R)-3 and (S)-5 as well as their derivatives were recorded. The postulated structures for the new products were supported with compatible elementary and spectroscopic (IR, 1H NMR, 13C NMR, MS, and single crystal X-Ray crystallography) analyses. The antimicrobial activity of some selected racemic new products and their respective optically active analogues were also undertaken.

Liquid membranes incorporating thioctic acid as a carrier to mimic an active transport system for alkaline earth metals has been described. A transport cell, operating on the same principle as the Schulman Bridge was used. It has been demonstrated that such a system is capable of transporting alkaline earth metals against a proton gradient, as driving force. The potential of thioctic acid to complex and transport these metal ions particularly Mg2+, Ca2+, and Ba2+ was verified. Furthermore, this transport phenomenon was extended to some different barium salts (Cl-, Br-, NO3-, and SCN-) to determine the effect of nature of anion on the transport of the Ba2+ ions. The order of the transport rate was found to be Ba2+ > Ca2+ > Mg2+ which is inconsistent with the stability of coordination to the carboxyl group. The rate of transport of Ba2+ ions were found to decrease with the anion type in the order SCN- > Br- > NO3- > Cl- which is related to the extent of hydration of the anions.

The kinetics and mechanism of interaction of periodate ion with [CoIIL(H2O)]2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N′,N′-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at lmax = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [CoIIL(H2O)]2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [CoIIL(H2O)]3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k2 [IO4-] + k3 [IO4-] 2) [CoIIL(H2O)]2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k2 is independent of pH over the entire pH range which suggest that unprotonated form of [CoIIL(H2O)]2-n is the only predominant species. The value of k2 is invariant to ionic strength variation in both the systems. The value of k3 is also found to be almost invariant to ionic strength in case of [CoIITMDTA(H2O)]2--[IO4]- system but it decreases considerably in case of [CoIIEGTA(H2O)]2--[IO4]- system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme.

Recently, powder metallurgy methods have been used widely for industrial purposes. In this work, powder-metallurgically produced samples were selected for zinc phosphate coating. Zinc phosphate coating was performed at 50 and 70 °C for 20 min in a bath containing 10 g l-1 ZnO, 25.5 g l-1 H3PO4, 5.88 g l-1 HNO3, and 2 g l-1 NaNO3. The effect of temperature on the phosphating process has been studied. The structure and corrosion resistance of coats have been investigated using scanning electron microscopy (SEM) and electrochemical methods (polarization and EIS). Results show that an increase in temperature affects the crystalline structure of the coats. The formation of the zinc phosphate coat on the powder metallurgical samples significantly decreases the corrosion rate of the samples.

Four new methods are described for the determination of ranitidine hydrochloride (RNH) in bulk drug and in formulations employing titrimetric and spectrophotometric techniques and using potassium dichromate as the oxidimetric reagent. In titrimetry (method A), RNH is treated with a measured excess of dichromate in acid medium, and the unreacted oxidant is back titrated with iron(II) ammonium sulfate. The three spectrophotometric methods are also based on the oxidation of RNH by a known excess of dichromate under acidic conditions followed by the determination of surplus oxidant by three different reaction schemes. In one procedure (method B), the residual dichromate is treated with diphenylcarbazide and the absorbance measured at 540 nm. Calculated amount of iron(II) is added to residual dichromate and the resulting iron(III) is complexed with thiocyanate and measured at 470 nm (method C). Method D involves reduction of unreacted dichromate by a calculated amount of iron(II) and estimation of residual iron(II) as its orthophenanthroline complex after raising the pH, and measuring the absorbance at 510 nm. In all the methods, the amount of dichromate reacted corresponds to the drug content. The experimental conditions are optimized. The titrimetric procedure is applicable over 5-10 mg range. In spectrophotometric methods, Beer''s law is obeyed in the ranges 5-50, 5-80, and 10-100 µg ml-1 for method B, method C, and method D, respectively. The methods were validated for accuracy, precision and recovery. The proposed methods were applied to the analysis of RNH in the tablet and the injection forms, and the results were in agreement with those obtained by the reference method.

The doped perovskite oxides such as La0.65Sr0.30MnO3-δ (LSM), La0.70Sr0.30CoO3-δ (LSC), La0.65Sr0.30FeO3-δ (LSF), La0.65Sr0.30NiO3-δ (LSN) and La0.60Sr0.40Co0.20Fe0.80O3-δ (LSCF) are proposed as alternate cathode materials for solid oxide fuel cells working at reduced temperature (< 1073 K). The critical requirement for their applicability is their chemical compatibility in conjunction with an alternate solid electrolyte, La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) without any new phase formation. To understand the chemical reactivity between these two components, thoroughly mixed different cathode and LSGM electrolyte (1:1 by wt.) powders were pressed as circular components and subjected to annealing at 1573 K for 3 h in air. XRD and SEM were used for the characterization of the annealed samples. XRD measurements revealed that no new secondary phases were formed in LSM, LSC, and LSF with LSGM mixtures whereas LSN and LSCF with LSGM resulted in the formation of new secondary phases after high temperature treatment. The sintering shrinkage for all the components (cathode + electrolyte mixture) was also estimated. For comparison of data, the individual powders (cathode/electrolyte) were also compacted and studied in the same manner. The obtained results are discussed keeping in view the requirements that the candidate cathode material must meet out with respect to its chemical compatibility to qualify for the LSGM based ITSOFC systems at 1073 K.

Amino acid germanate compounds are synthesized by the chemical reaction of germanium dioxide with a selected amino acid in the presence of an alkali medium at a suitable elevated temperature. Amino acids included in the novel synthesis include histidine, methionine and glutathione. The study evaluated their effects on induction of interleukin-12 and interferon-γ in Swiss albino Webster rats. The new germanium compounds, especially bis-methionino germanate, are considered as good interferon inducer that significantly enhance the immunologic function.

In present studies a new series of twenty four complexes of seven and ten coordinated compounds derived from 4[N-cinnamalidene)amino]antipyrine semicarbazone (CAAPS) as primary ligand and diphenyl sulfoxide (DPSO) as secondary ligand has been reported. All the complexes have the general composition LnX3.n(CAAPS).DPSO (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy or Ho, X = NCS or ClO4, n = 2, X = NO3, n = 1). The compounds have been characterized by elemental analysis, molar conductance, magnetic susceptibility, infrared and electronic spectra. Thermal characteristics were also reported. Based on the data appropriate structures are assigned for these complexes.