The determination of phosphonate base scale inhibitors in brines by plasma spectrometry

The determination of phosphonate base scale inhibitors in brines by direct current plasma (DCP) and inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The first method is based on a direct nebulization of the brine samples and plasma using the phosphorus line at 213.618 nm. The second method involves extraction of phosphorus as phospho-antimonyl molybdate complex into methylisobutyl ketone (MIBK) phase and analysis of the extract for molybdenum using the Mo 313.260 nm line. Comparison between the proposed methods and an established recommended method [1] shows excellent agreement between the results in addition to the sensitivity and ease of automation provided by AES.     

Computational evidence for methyl-donated hydrogen bonds and hydrogen-bond networking in 1,2-ethanediol-dimethyl sulfoxide

The 1:1 complex of 1,2-ethanediol with dimethyl sulfoxide was studied using density functional theory. A network of three hydrogen bonds holds the complex together, including two in which each methyl group donates to the same hydroxyl oxygen. Four lines of evidence support the existence of methyl-donated hydrogen bonds. The interaction energy is 36 +/- 5 kJ/mol using Becke's three parameter hybrid theory with the 1991 nonlocal correlation functional of Perdew and Wang, and a moderately large basis set (B3PW91/6-311++G**//B3PW91/6-31+G**). To determine the energy of each hydrogen bond, a relaxed potential energy scan was performed in a smaller basis set to break the weaker hydrogen bonds by forced systematic rotation of the methyl groups. Two cross-checking analyses show cooperative effects that cause individual hydrogen bond energies in the network to be nonadditive. When one methyl hydrogen bond is broken, the remaining interactions stabilize the complex by storing an additional 2-3 kJ/mol. With all hydrogen bonds intact, the O[bond]H...O[bond]S hydrogen bond contributes 26 +/- 2 kJ/mol stability, and each weak methyl bond stores 5 +/- 2 kJ/mol.     

Uncatalyzed asymmetric diels-alder addition of cyclopentadiene to (E)- and (Z) - (R) -4,5-di-O-isopropylidene-pent-2-enonates

The uncatalyzed Diels-Alder addition of cyclopentadiene to the acrylic ester derivatives {=1} proceeds with high diastereo- and enantioface selectitivity.     

Synthesis and structure of 6- and 7-(acylmethyl)pteridines

6-(Acylmethyl)-7-hydroxypteridines 7-14 as well as the isomeric 7-(acylmethyl)-6-hydroxypteridines 15-22 were prepared by condensation of 5,6-diaminouracils 1 and 2 with ethyl aroylpyruvates 3-6 in pyridine and hydrochloric acid, respectively. The structures of the newly synthesized compounds were confirmed by their hydrolysis into the 7-hydroxy-6-methyl- 23 , 24 and 6-hydroxy-7-methylpteridines 25 and 26 . The synthesis of the 2-(methylthio) derivative 28 is also described.     

Reactivity of 3-amino-, 3-halogeno-, and 3-nitro-2-pyrones and thiopyrones

Substituted pyrrole and furan-2-carboxylic acids were obtained from 3-amino- and 3-halogeno-2-pyrones. The reactions of several substituted 2-pyrones and thiopyrones with different amines and carbonyl reagents were studied.     

Computerized GC/MS detection of monoaromatic and triaromatic steroid hydrocarbons in Alamein crude oil

Series of C-ring monoaromatic steroid hydrocarbons (C₂₁, C₂₂, C₂₇ ? C₂₉) and triaromatic steroid hydrocarbons (C₂₀, C₂₁, C₂₆ ? C₂₈) have been recognized in the aromatic hydrocarbon fraction of Alamein crude oil from the western desert, Egypt. Detection of these compounds were based on mass fragmentography of the key ions m/z 253 and m/z 231 and comparison of the mass spectra and relative retention times with literature data. The predominance of the C₂₉ monoaromatic steroids and C₂₈ triaromatic steroids provide further evidence for a land plant origin of Alamein oil. The results substantiate previous evidence of the occurrence of an aromatization process with increasing maturation and indicate a moderate maturity level for Alamein oil.     

The electrochemical behavior and characterization of the anodic oxide film formed on titanium in NaOH solutions

Titanium dissolution and passivation were studied in NaOH aqueous solution using open-circuit potential, potentiodynamic and potentiostatic techniques. Potentiodynamic data showed that the active-passive transition involves active metal dissolution followed by formation of a poorly conducting passive oxide film that passivates the electrode. The critical current density varied with pH as d log<I> j</I><SUB>m</SUB>/d pH=-0.098 in the pH range 11.00–14.00, while the passivation potential is changed according to the following two features: at pH 10.55–13.00, d<I>E</I><SUB>m</SUB>/d pH=-0.06 V; and at pH 13.50–14.00, d<I>E</I><SUB>m</SUB>/d pH=-0.40 V. The apparent activation energy, E*, was calculated from the slope of the Arrhenius plot and was found to be 12.6 kJ mol^–1. Current-time transients showed that the growth of titanium oxide passive film is a diffusion-controlled process. XPS measurements indicated that the passive oxide film consists mainly of TiO₂ and a mixture of suboxides of Ti₂O₃ and TiO. Electronic Publication     

Cathodic adsorptive stripping voltammetric determination of nalidixic acid in pharmaceuticals, human urine and serum

The quinolone antibacterial agent nalidixic acid (NAL) was studied by cyclic voltammetry (CV) and cathodic adsorptive stripping voltammetry (CASV). A sensitive method is described for the determination of NAL in its pure form, dosage forms and biological fluids. Controlled adsorptive accumulation of NAL on a hanging mercury drop electrode provides the basis for the direct stripping measurement of that compound in the nanomolar concentration level. Different variables were studied and optimized. The proposed method depends upon the voltammetric activity of NAL in Britton-Robinson buffer, whereby a well-defined cathodic peak is produced at pH 5.0 in presence of NO(3)(-). The calibration graph to determine NAL was linear in the range 7.4x10(-8)-2.5x10(-5) M by CASV. CAS voltammetry has been proved to be advantageous over a liquid chromatographic (LC) technique, allowing to detection limit signal to noise ratio, (s/n=3) of 0.766 ng ml(-1) (3.3x10(-9) M) NAL to be reached. The relative standard deviation (n=5) was 5.2% at concentration level of 1.0x10(-7) M NAL. The degree of interference from coexisting metal ions on the CASV signal for NAL was evaluated. The method was applied to two different commercial pharmaceutical products (Negram tablets and suspension) with very good recoveries. It was also shown that the method was successfully applied to the determination of NAL in human urine and blood serum. Mean recoveries were 98.8+/-0.3 and 98.9+/-0.41%, respectively.     

The Stabilities of the o-Carboxyphenylhydrazo-Ethylacetoacetate OF Cu,Ni, Co,Zn, Mn and Cd Chelate Compounds in Different Solvents

The dissociation constants for o-carboxyphenylhydrazoethylacetoacetate (o-CPHEA) ligand, as well as the stability constants for the divalent metal complexes of Cu, (II), Ni (II), Co (II), Zn (II)and Cd (II) ions, have been calculated pH-meterically in different solvents. The dissociation constans pK₁=4.10 and pK₂=10.55 of the insoluble organic ligand are calculated in aqueous medium. The effect of solvents, the relation between stabilities and both electronegativities and ionization potential are studied.     

Ternary complexes of N-(2-acetamido)iminodiacetic acid and some aromatic acids. Isolation and stability constants in solution

Summary Ternary 1:1:1 complexes of Y^III, Co^II, Ni^II, Cu^II, La^III, Ce^III and UO ₂ ²⁺ with N-(2-acetamido)iminodiacetic acid (H₂ADA) as primary ligand and salicylic, anthranilic or phthalic acid as secondary ligand are described. The complexes of Co^II and Cu^II were isolated and characterized by microanalysis, molar conductance measurements, thermal analysis, i.r. and u.v.-vis. spectra. The formation constants of the 111 ternary complexes were determined potentiometrically in 20% (w/w) EtOH-H₂O at 24 °C. The stabilities of the 111 M ⁿ⁺ :ADA^2–:aromatic acid ternary complexes are higher than those of the corresponding 11 M ⁿ⁺ :aromatic acid binary complexes.