European Journal of Chemistry

The CaCO₃-oversaturated weakly basic water at around pH=8 was proved by the novel simple equations (e.g. log [Ca²⁺] = -2pH -logP_CO2 + 9.94) derived from material energetics and proton-controlled mechanism for coupling among proton/hydroxide production/consumption reactions (e.g. CaCO₃ + H⁺↔HCO₃^- + Ca²⁺) in equilibrium with atmospheric carbon dioxide. The cyclic/oscillating variation between pH=8.3 and 8.0 for marine calcifying organism-inhabited paleo and preindustrial seawaters was elucidated by applying the improved proton-controlled mechanismto biochemical reactions in cytoplasts or host tissues of marine calcifying phytoplanktons and phytosymbiont-bearing corals/zooplanktons. It was revealed that photosynthesis enhances biogenic calcificationand vice versa, as the thicker growth of CaCO₃-made outer casings causes proton production and photosynthesis continuously needs protons to produce CO₂(aq) from major HCO₃^-. The correlation between calcification and photosynthesis creates a number of stationary states with respect to oscillating pH variation. Marine biogenic calcification reaction releases no CO₂ to atmosphere and is no positive feedback to rising atmospheric P_CO2 levels.

Depending on their nature, nitrile activated methylene compounds add readily to β-enaminones in presence of chitosan to yield dienamides, pyridones or pyridine thiones. The dienamides, formed in this manner, can be readily converted to pyridones by stirring in refluxing acetic acid. Reaction of pyridazinones with a mixture containing benzaldehyde, malononitrile and chitosan affords phthalazines that are also produced by reaction of pyridazinone with benzylidene-malononitrile.

Transparent sol-gel glassy monoliths doped with coumarin molecules [ethyl 2-(7-hydroxy-2-oxo-2H-chromen-4-yl) acetate] displaying a strong blue luminescence are characterized by optical spectroscopy, X-Ray diffraction, SEM and TG/FT-IR spectroscopy. The UV/Vis, luminescence and excitation spectra of the doped sol-gel materials and of ethanol solutions of coumarin are discussed. The coumarin optical spectra are used as a probe for incorporation in the gel structure.

Voglibose is a potent glucosidase inhibitor used for type II diabetes mellitus. A simple and rapid high performance liquid chromatographic method with refractive index detection was developed for the determination of voglibose in pharmaceutical formulations. Development was performed on a C18 (250 x 4.6 mm, 5 µ) column using a mobile phase mixture of acetonitrile and water in the ratio of 50:50 which was fixed at a flow rate of 0.5 mL/min. Polarity of voglibose was found to be positive and elution time was found to be less than 5 min. The method was also validated as per ICH guidelines for its linearity, precision, accuracy and robustness. The limit of detection and quantification (LOD and LOQ) were found to be 2.91 and 9.7 µg/mL. The method could be successfully applied for the quantification of voglibose in pharmaceutical formulations.

A quantitative structure-property relationship (QSPR) study was performed to develop models that relate the structures of 133 polychlorinated biphenyls to their n-octanol-water partition coefficients (log K_ow). Molecular descriptors were derived solely from 3D structures of the molecules. The genetic algorithm-partial least squares (GA-PLS) method was applied as a variable selection tool.  The partial least square (PLS) method was used to select the best descriptors and the selected descriptors were used as input neurons in neural network model. These descriptors are: Balabane index (J), XY Shadow (SXY), Kier shape index (order 3) (3к), Wiener index (W) and Maximum valency of C atom (VmaxC). The use of descriptors calculated only from molecular structure eliminates the need for experimental determination of properties for use in the correlation and allows for the estimation of log Kow for molecules not yet synthesized. The root mean square errors for ANN predicted partition coefficients of training, test and external validation sets were 0.063, 0.112 and 0.126, respectively, while these values are 0.230, 0.164 and 0.297 for the PLS model, respectively. Comparison between these values and other statistical parameters for these two models revealed the superiority of the ANN over the PLS model.

Insight into chemistry conceptual foundations shows that a powerful, autonomous chemical methodology exists which is based on visualization and association of chemical "building blocks". Such methodology has been expanded by the use of incommensurable theories resulting from the interplay of quantum mechanics and heuristic chemical concepts, resulting in models of great utility as predictive tools in guiding the creation of new and useful substances. Understanding such historical development has real benefits to chemistry practitioners, be they researchers, analysts or chemical educators.

The coordination behaviour of the quinoxaline ligand with N and O donation sites, derived from 3-(2-oxo-2-p-tolylethyl)quinoxalin-2(1H)-one (HL), towards some transition metal ions namely Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) are reported. The metal complexes are characterized based on elemental analyses, IR, ¹H NMR, solid reflectance, magnetic moment, molar conductance and thermal analyses (TG, DTG and DTA). The ionization constants of the quinoxaline ligand as well as the stability constants of its metal chelates are calculated spectrophotometrically at 25 ^oC and ionic strength = 0.1 M (1M NaCl). The chelates are found to have octahedral structure. The ligand and its chelates are subjected to thermal analyses and the different activation thermodynamic parameters are calculated from their corresponding DTG curves to throw more light on the nature of changes accompanying the thermal decomposition process of these compounds. The biological activity of the synthesized ligand and its metal complexes also are screened against the desert locust Schistocerca gregaria (Forsk) (Orthoptera-Acrididae) and its adult longevities. They showed remarkable biological activity.

The title compound was efficiently synthesized in two steps starting from esterification of 4-aminobenzoic acid followed by amidation with 3-chlorobenzoyl chloride in dry tetrahydrofuran. The structure was confirmed by spectroscopic data and elemental analysis. The molecular structure was determined from single crystal X-ray diffraction data. It crystallizes in the triclinic space group P-1 with Z = 2 and unit cell dimensions a = 5.2941(15) Å, b = 8.157(2) Å, c = 16.238(4) Å, α = 82.682(6)°, β = 84.481(6)°, γ = 80.100(6)° and V = 683.2(3) ų.

Octahydroquinazolinone derivatives were synthesized in moderate to high yields via one-pot three component Biginelli reaction of dimedone, urea or thiourea and corresponding aromatic aldehydes in the presence of silica sulfuric acid as an efficient catalyst, in ethanol under reflux conditions. This protocol offers several advantages including good yields of products and easy experimental work-up procedure.

One new cucurbitane triterpenoid commonly named neokuguaglucoside, together with three known compounds momordicoside M, momordicoside N, and momordicoside A were isolated from the fresh fruits of Momordica charantia. The new one's structure with an interesting sugar-like groups attached to the side chain was elucidated by spectroscopic analysis and semiepirical (AM1) quantum chemical method.

Novel phosphorylated derivatives of stavudine were synthesized by the reaction of bis(2-chloroethyl)phosphoramidic dichloride/4-nitrophenyl phosphorodichloridate with various cyclic amines and amino acid esters in the presence of triethylamine in dry tetrahydrofuran through the corresponding monochloride intermediates 2a-l. Further reaction of the intermediates 2a-l with stavudine in tetrahydrofuran and pyridine in the presence of triethylamine formed the title compounds 4a-l. Their structures were characterized by IR,   ¹H-, ¹³C-, ³¹P-NMR and mass spectral data analyses. They exhibited good antibacterial and antioxidant activities. Their bioactivity was greatly influenced by the different groups present at the phosphorus.

A convenient method for synthesis of new sym-triazine ester and hydroxamate derivatives has been developed. Various reaction conditions were studied and optimized, and a series of new 1,3,5-triazine based esters and N-hydroxyamides were obtained with good yields (38-80%). The reaction between oxo-derivatives of 4,6-disubstituted-1,3,5-triazines and halogenated carboxylic esters derivatives using  Cs₂CO₃ as a catalyst was found to be the most convenient method for 4,6-disubstituted-1,3,5-triazine-2-yloxy esters  synthesis. These 1,3,5-triazin based esters served as precursors for the synthesis of 4,6-disubstituted-1,3,5-triazin-2-yloxy-N-hydroxybutanamides using solution of hydroxylamine hydrochloride in dry methanol and KOH at room temperature.  Structures of the newly synthesized compounds were obtained by ¹H NMR, ¹³C NMR, MS, IR spectral data and elemental analysis.

The equilibrium binding of a new water-soluble tetra-cationic porphyrin, 5-(1-(4-carboxybutyl)‎pyridinium-4-yl)10,15,20-tris(1-methylpyridinium-4-yl)‎porphyrin (5-CBPyP) with calf thymus DNA in comparison with meso-tetrakis(4-N-methyl‎pyridinium)porphyrin (TMPyP) has been studied in 7.5 mM phosphate buffer, pH=7.2; and at various temperatures by UV-Vis absorption, fluorescence spectroscopies and viscosity measurement. The thermodynamic parameters were calculated by van't Hoff equation at various temperatures. The values of -137.13±1.22 kJ/mol and -337.21±4.75 J/mol.K for 5-CBPyP and -159.12±1.22 kJ/mol and -406.11±4.45 J/mol.K for TMPyP, were estimated for enthalpy and entropy changes of interaction, respectively. The data indicate that the process is exothermic and enthalpy driven suggesting that electrostatic forces play a considerable role in the interaction process. The results of spectroscopic techniques and viscosity measurement represent the intercalation mode of binding for both porphyrins and higher binding affinity of TMPyP respect to 5-CBPyP.

5-phenylazo-2-thioxo-thiazolidin-4-one and four of its derivatives have been investigated as corrosion inhibitors for C-steel in 1 M sulphuric acid solution using weight-loss and galvanostatic polarization techniques. The efficiency of the inhibitors increases with increase in inhibitor concentration but decreases with a rise in temperature. The conjoint effect of the thiazole derivatives and KBr, KSCN and KI has also been studied. The apparent activation energy (E_a*) and other thermodynamic parameters (ΔS*, ΔH* and ΔG*_ads) for the corrosion process have also been calculated. The galvanostatic polarization data indicated that, the inhibitors were of mixed-type, but the cathode is more polarized than the anode. The slopes of the cathodic and anodic Tafel lines (ß_c and ß_a) are approximately constant and independent of the inhibitor concentration. The adsorption of these compounds on C-steel surface has been found to obey the Temkin's adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.

Two amino acids, leucine and valine, were studied by X-ray powder diffraction (XRPD). The linear correlations between intensity of racemate (decrease) or enantiomer (increase) and enantiomeric excesses were observed in each case.

New 1,2,4-triazoles (4a-c), 1,3,4-thiadiazoles (5a-c) and 1,3,4-oxadiazoles (6a-c) containing isomeric pyridyl and cyclohexyl were synthesized by intramolecular cyclization of 1,4-disubstituted thiosemicarbazides (3a-c) in alkaline media, acid and neutral condition respectively. The chemical structures of newly synthesized compounds were established with help of FT-IR, ¹H-NMR and mass spectral data.

The EP₁ receptor inhibitory activity of 1,2-diarylcyclopentene derivatives have been quantitatively analyzed in terms of Dragon descriptors. The derived QSAR models have provided rationales to explain the EP₁ receptor inhibitory activity of 1,2-diarylcyclopentene derivatives. The 2D-autocorrelation descriptors (MATS4e, MATS5e, MATS7v, GATS5e and GATS7v) have highlighted the role of atomic properties in respective lags of autocorrelations to explain the biological actions of 1,2-diarylcyclopentene analogues. Presence of fluorine atom (nF) and smaller distance between N and O atoms (T(N..O)) in molecular structures, in addition to Kier-Hall electrotopological states (Ss) have also shown prevalence to optimize the EP₁ receptor inhibitory activity. Partial least square analysis has confirmed the dominance of information content of the combinatorial protocol in multiple linear regression identified descriptors. Applicability domain analysis revealed that the suggested model matches the high quality parameters with good fitting power and capability of assessing external data. All the compounds are within the applicability domain of the proposed model and were evaluated correctly.

Decatungstodivanadogermanic acid (H₆GeW₁₀V₂O₄₀.22H₂O) was used as a novel and green heterogeneous catalyst for the acetylation of hydroxy compounds under solvent-free conditions at room temperature. Efficient and selective acetylation of various alcohols and phenols was conducted with acetic anhydride as an acetylating agent over H₆GeW₁₀V₂O₄₀.22H₂O under solvent-free conditions. All acetylated products were selectively obtained in excellent yields with very short reaction times. The reaction times were longer for the acetylation of phenols than for alcohols, so that an alcoholic OH group could be selectively acetylated in the presence of a phenolic OH group by the appropriate choice of reaction time. The catalyst can be recycled several times without observable loss of activity and selectivity.

Fluorescence behavior of intramolecular charge transfer probe trans-ethyl-p-(dimethylamino) cinnamate (EDAC) is extremely sensitive to the local environment. This study explores the interaction of EDAC with several Igepal, Brij and Tween series of non-ionic surfactants by steady state and picoseconds time-resolved fluorescence spectroscopy. The physico-chemical properties, like critical micelle concentration and micropolarity of the micellar media surrounding the probe were determined. In most of the cases, the observed values were in good agreement with the data reported in the literature. Results obtained from time-resolved fluorescence experiments show a substantial reduction in total non-radiative decay rate of the probe in micellar medium compared to that in aqueous phase. This indicates preferential association of the probe inside the micellar core. The association constant of the probe-micelle interaction was also evaluated in different cases.

The introduced study portrays the development and validation of an effortless, speedy and selective first order derivative zero-crossing spectrophotometric method to estimate ezetimibe and simvastatin simultaneously in combined drug products over and above in the presence of ezetimibe alkaline degradation products. Ezetimibe and its alkaline degradates spectra showed zero-crossing point at 249 nm, so the amplitude at 249 nm could be used for calculating the concentration of simvastatin. While simvastatin and ezetimibe alkaline degradates spectra showed a zero-reading value at 261 nm, so ezetimibe could be determined by measuring the amplitude at 261 nm. Regression plots revealed good linear relationships in the concentration range 1-16 µg/mL with accuracy checked by conducting recovery studies; average recovery was 99.61 ± 1.183 and 100.47 ± 1.310 for ezetimibe and simvastatin, respectively. The suggested first derivative spectrophotometric method was successfully applied for the determination of the cited drugs in "Inegy 10/10, 10/20 and 10/40 tablets". Satisfactory results were obtained for the recovery of both drugs and were in good agreement with the labeled amounts.  Method validation was estimated according to USP guidelines.

Thieno[2,3-b]pyridine-2-carboxylate was utilized to construct a variety of new heterocyclic systems such as thienopyrimidinone, thienopyridine and pyridothienoxazinone derivatives. Treatment of pyridothienoxazinone derivative with some other nitrogen nucleophiles afforded 3-substituted-pyridothienopyramidinone derivatives. Secondary amines such as morpholine, piperidine and N-methylaniline reacted smoothly with the oxazinone derivative. When the oxazinone derivative was allowed to react with ethanol containing few drops of pyridine or formamide as a basic catalyst and heated to reflux, afforded thienopyridine ester. All the compounds were fully characterized by means of IR, MS, ¹H NMR spectra and elemental analyses.

Aerobic oxidative coupling of 2-naphthol to 1,1'-binaphthyl-2,2'-diol has been achieved using chiral/achiral copper salen complexes as catalyst. Moderate enantioselectivity was obtained for the reaction of 2-napthol with a coordinating substituent with a chiral salen complex. Unsubstituted 2-naphthol resulted in racemic 1,1'-binaphthyl-2,2'-diol only with all chiral complexes. Electron paramagnetic resonance spectroscopy has been used to understand the factors influencing the asymmetric induction.

2-[1-(Furan- or thiophen-2-yl)ethylidene)malononitriles (1a,b) undergo dimerization reactions in ethanol catalyzed by sodium ethoxide to afford 2-[4,6-di(furan- or thiophen-2-yl)-3-cyano-6-methyl-5,6-dihydropyridin-2(1H)-ylidene]malononitrile derivatives (2a,b), respectively. Compounds 2a and 2b couple with arene diazonium salts (3a-c) to afford the hydrazo derivatives (4a-f). They react also with hydrazines (5a,b) to afford the pyrazolo[3,4-H][1,6]naphthyridine derivatives (6a-d) and with urea derivatives (7a-c) to afford the pyrimido[4,5-H][1,6]naphthyridine derivatives (8a-f), respectively.

It is known that 5-aminolevulinic acid (5-ALA) is not stable in an aqueous solution because of the auto-condensation reaction between two 5-ALA molecules; however, in this study, 5-ALA was stabilized by the zinc(II) ion in an aqueous solution of neutral pH. This stabilization effect was ascertained by UV-Vis Spectroscopy and ¹H and ¹³C NMR Spectroscopy.

An efficient protocol has been developed for the preparation of a series of 2-arylbenzothiazoles derivatives from condensation of 2-aminothiophenol with aromatic aldehydes using ammonium chloride, which is a very inexpensive, metal-free and readily available reagent. The target compounds were obtained in good to excellent yields (58-92%) under fairly mild reaction conditions at room temperature.

An analytic perturbation theory has been developed for screened Coulomb radial wave functions by interpolating the screened Coulomb potential of McEnnan for elements lanthanum to uranium and was used to calculate alignment of vacancies in L3 sub shell. To check the authenticity of the present method of calculation, the intermediate steps are compared with our earlier formulation of point Coulomb potential for the calculations. A close agreement has been obtained among the values of intermediate steps involved in both the formulations that proved the reliability of present calculations and prompted us to extend the calculations for the elements lanthanum to uranium in the energy region threshold to 60 keV.

A trace amount of zinc dust is able to promote instantaneous quantitative acylation of a large variety of functionalized phenols, thiophenol, amines and alcohols with acyl chlorides under solvent-free condition at 25 °C. The catalyst can be recovered and recycled making the procedure potentially useful for industrial applications.

This review represents the methods developed for the synthesis of phosphorus containing 1,2,4-triazine moieties. These methods depends on the phosphorylation of side functional groups of 1,2,4-triazines and cyclization of side functional groups of 1,2,4-triazines with phosphorus reagents to give isolated and fused phosphorus heterocyclic systems.