Measurement of thermophysical properties of polyvinyl alcohol complexed with some metal ions

Polyvinyl alcohol (PVA)-Cu(II) and PVA-Cr(III) complexes were prepared with different concentrations of CuC1₂ and Cr(NO₃)₃ salts. The structures of the obtained complexes were investigated using UV spectroscopy and x-ray analysis. The thermal properties (volumetric heat capacity, thermal diffusivity, and thermal conductivity) of aqueous solutions of PVA-metal complexes have been measured using the hot-wire (and strip) technique as a function of temperature (20°-80°C). The results show that the values of the thermal properties depend on the type and the concentration of metal ions bound to the polymeric chains of PVA and the temperatures. However, a considerable increase in the values of the thermal properties was observed for PVA-Cu(II) complex. The type of metal salt under investigation affects the structure of PVA. The complex of PVA-Cr(III) is more thermally stable than the complex of PVA with Cum. However, both polymer-metal complexes showed good properties which may make them acceptable for some practical uses.     

Kinetic studies of the oxidation of chromium(III) by N-bromosuccinimide

Summary A kinetic study of the oxidation of chromium(III) by N-bromosuccinimide (NBS) in aqueous solutions and H₂O-MeOH solvent mixtures were performed. The kinetics in aqueous solutions obeyed the rate law: d[Cr^VI]/dt = {k ₄ K _h K ₂[NBS][Cr^III]_T}/[₊]{1 + K _h/[H⁺] + (K ₁ + K _h K ₂/[H⁺][NBS])} where K _h, K ₁ and K ₂ are the hydrolysis constant of [Cr^III(H₂O)₆]³⁺, and pre-equilibrium formation constants for the protonated and deprotonated precursor complexes, respectively. An innersphere mechanism is proposed. An argument based on isokinetic correlations among activation parameters for the oxidation of a series of cobalt(II) and chromium(III) complexes including [Cr(H₂O)₆]³⁺ is presented in support of a common mechanism for these reactions. Abstracted from the Ph.D. Thesis (Ain Shams University) of A. E.-D. M. Abdel-Hady.     

Spectrofluorimetric determination of warfarin sodium by using N1-methylnicotinamide chloride as a fluorigenic agent

A spectrofluorimetric method is described for the determination of drugs containing active methylene groups adjacent to carbonyl groups. The method was applied successfully to the determination of warfarin sodium in laboratory-prepared mixtures, in commercial tablets, and in spiked human plasma samples. Finally, the method was applied to the determination of the steady-state concentration of warfarin sodium in the blood of a hospitalized patient. The method involves the reaction of warfarin sodium with 0.2 ml (0.4 x 10(-3)M) N1-methylnicotinamide chloride reagent in the presence of 3 mL 1.0N NaOH and cooling in ice for 8 min, followed by adjustment of the pH to 2.0, using formic acid and heating for 4 min, whereby a highly fluorescent reaction product is produced. The optimal wavelengths of excitation and emission were determined by using a synchronous wavelength search and found to be 284 and 354 nm, respectively. The standard curves were linear over a concentration range of 50-1500 ng/mL in both aqueous solutions and spiked human plasma samples. The mean recoveries (+/- standard deviation) were 101.157 (+/-1.33) and 95.73 (+/-1.88%) for aqueous solutions and spiked human plasma samples, respectively. The method showed good specificity and precision. The proposed method is simple and economical because of its minimal instrumentation and chemicals requirements. Nevertheless, it is highly sensitive, specific, and reproducible. Accordingly, it is suitable for quality-control applications, drug monitoring, and bioavailability and bioequivalency studies.     

Activated nitriles in heterocyclic synthesis: Synthesis of 6-thiophen-2-yl and 6-furan-2-ylthiazolo[2,3—a]pyridine derivatives

A variety of new 6-thiophen-2-yl and 6-furan-2-ylthiazolo[2,3—a]pyridine derivatives could be prepared via the reaction of 2-functionally substituted methyl-2-thiazolin-4-one with cyanomethylenethiophen-2-yl and cyanomethylenefuran-2-yl derivatives. The structure of the reaction products was established based on spectral data.

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Aktivierte Nitrile in der Heterocyclen-Synthese: Die Synthese von 6-Thiophen-2-yl-und 6-Furan-2-yl-thiazolo[2,3—a]pyridin-Derivaten

Zusammenfassung Es konnte eine Reihe neuer 6-Thiophen-2-yl- und 6-Furan-2-yl-thiazolo-[2,3—a]pyridine über die Reaktion von 2-funktionell-substituierten Methyl-2-thiazolin-4-onen mit Cyanomethylenthiphen-2-yl bzw. Cyanomethylenfuran-2-yl-Derivaten hergestellt werden. Die Struktur der Reaktionsprodukte wurde mit spektroskopischen Methoden ermittelt.

     

Synthesis and structure of 6- and 7-(2-arylvinyl)pteridines

7-Hydroxy-6-styrylpteridine 9 and 7-(2-arylvinyl)-6-hydroxypteridines 10–12 were synthesized via the condensation of 5,6-diaminouracil 1 with benzylidenepyruvic acids 2–4 . The synthesis of the 2-methylthio analogue 15 is also described.     

Polymerization of N-aryl maleimides

Overall rates of polymerization of ring-substituted-N-phenylmaleimides were measured, mainly in dioxane. Rate equations were deduced. The rate of polymerization increased on addition of ZnCl₂; the effect was attributed to the interaction of the Lewis acid and the π-cloud of the growing maleimide radical. The effect of solvent on the rate of polymerization was also investigated.     

Identification of an artifact peak co-eluting with formaldehyde-2,4-dinitrophenylhydrazone derivative by GC-MS and chemometrics

A chemometric approach was utilized to identify an artifact peak co-eluting with formaldehyde-2,4-dinitophenylhydrazone. Application of the methods of principal component analysis to the mass spectra of the formaldehyde-hydrazone peaks collected at 200-280 °C has revealed the presence of two factors contributing to these spectra. Moreover, the use of self-modeling curve resolution (SMCR) techniques has enabled the reconstruction of the spectra of the pure components. One of the identified components that contribute to the spectra of the mixture was formaldehyde-2,4-dintrophenylhydrazone, whereas the other component was 1-amino-2,4-dinitrobenzene, a degradation product of 2,4-dintrophenylhydrazine.     

Unimolecular reactivity of uracil-Cu(2+) complexes in the gas phase.

The gas-phase interaction of copper(II) ions with uracil are studied by means of mass spectrometry and B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d) calculations. Positive-ion electrospray spectra show that the reaction of uracil with copper(II) gives rise to singly charged species, whereby the [Cu(uracil--H)](+) complex is the most intense ion in the spectra at low concentration. Mass spectrometry/mass spectrometry (MS/MS) experiments show that the loss of HNCO and NCO are the dominant fragmentation processes, accompanied by a minor loss of CO. A systematic study of the spectra obtained with different labeled species, namely, 2-(13)C- (m/z 175), 2-(13)C,1,3-(15)N(2)- (m/z 177) and 3-(15)N-uracil (m/z 175), concludes unambiguously that both the loss of HNCO and NCO involve exclusively C2 and N3, whereas only C4 is involved in the loss of CO. Suitable mechanisms for these fragmentation processes are proposed through a theoretical survey of the corresponding potential energy surface. In these mechanisms, pi complexes, which lie high in energy with respect to the global minimum, play a significant role in the loss of NCO; this explains why both products, HNCO and NCO involve the same atoms of the ring.     

Determination of tin (IV) in alloys and in canned food by visible spectrophotometric technique using pyrimidine azo compounds in presence of mixed surfactants

The complex of tin (IV) with 5-(4'-nitro-2',6'-dichlorophenylazo) (I) and 5-(4'-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (II) in the presence of nonyl phenoxy polyethoxyethanol (NPE) and cetyltrimethylammonium bromide (CTAB) has a sensitive absorption band with lambda max 517 and 488 nm, respectively. Under the optimal conditions, Beer-Lambert law is obeyed over the range 0.05-1.50 and 0.05-1.30 micrograms ml-1 Sn(IV) with molar absorptivity being 9.50 x 10(4) and 1.05 x 10(5) L mol-1 using ligand I and II, respectively. As compared with the visible methods which uses bromopyrogallol red (BPR) as the chromogenic reagent (lambda max = 550 nm) and that using phenylfluorone (lambda max = 360 nm), our method is highly sensitive and selective because the complexes have a high and sharp absorption band. In addition, the present method is simple and rapid, no heating or standing time is needed. By means of the mixed surfactants, the precipitation caused by the ion association of cetyltrimethyl-ammonium cation and I3- anion is avoided if iodide is used for separating micro amounts of tin(IV) from a sample matrix. An application of the proposed method to the determination of tin(IV) in a variety of alloys and in a canned food was made with satisfactory results.     

Spectrophotometric methods for the determination of anti-emetic drugs in bulk and in pharmaceutical preparations.

Four rapid, simple, reproducible and sensitive methods (A-D) for assaying domperidone (I) and metoclopramide (II) in a bulk sample and in dosage forms were investigated. The first and second methods, A and B, are based on the oxidation of I and/or II by Fe3+ in the presence of o-phenanthroline (o-phen) or bipyridyl (bipy). The formation of tris-complex upon reactions with Fe3+-o-phen and/or Fe3+-bipy mixture in an acetate buffer solution of the optimum pH-values was demonstrated. Methods C and D involve the addition of excess Ce4+ and the determination of unreacted oxidant by a decrease of the red color of chromotrope 2R (C2R) at a suitable lambda(max) of 528 nm for method C, or a decrease in the orange pink color of Rhodamine 6G (Rh6G) at a suitable lambda(max) value of 525 nm for method D. A regression analysis of Beer-Lambert plots showed a good correlation in the concentration range of 0.2-5.8 microg ml(-1). The apparent molar absorptivity, Sandell sensitivity, detection and quantification limits were calculated. For a more accurate analysis, the Ringbom optimum concentration ranges are 0.35-5.6 microg ml(-1). The developed methods were successfully applied to the determination of domperidone and metoclopramide in bulk and pharmaceutical preparations without any interference from common excipients.