The visible absorbance maximum of 2-hydroxy-1,4-naphthoquinone as a novel probe for the hydrogen bond donor abilities of solvents and solvent mixtures

Summary The electronic absorption spectra of 2-hydroxy-1,4-naphthoquinone (HNQ) in one- and two-component solvents are discussed. The visible absorption of this reagent has been shown to arise from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating solvent. The formation constant of the 1:1 hydrogen bonded complex with methanol, ethanol, andn-propanol has been determined at 25 °C from the spectral behaviour in mixed solvents. The tautomerization equilibrium ofHNQ in aqueous ethanol is demonstrated and characterized. The dependence of the absorbance maximum ofHNQ on the hydrogen bond donor ability of the solvent in the visible spectrum, as measured by theTaft-Kamlet parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation ofHNQ as a novel probe for hydrogen bond donor ability in pure solvents and in mixed aqueous solvents.

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Das Absorptionsmaximum von 2-Hydroxy-1,4-naphthochinon im sichtbaren Bereich als neues Maß für die Wasserstoffbrückenbindungsbildungsfähigkeit von Lösungsmitteln und Lösungsmittelgemischen

Zusammenfassung Die Absorptionsspektren von 2-Hydroxy-1,4-naphthochion (HNQ) in Ein- und Zweikomponentensystemen werden diskutiert. Die Absorption im sichtbaren Bereich stammt von einemcharge-transfer — Übergang des zwitterionischen Tautomers, das über Wasserstoffbrückenbindungen zum Lösungsmittel stabilisiert wird. Die Bildungskonstanten der binären Komplexe mit Methanol, Ethanol undn-Propanol wurden aus spektroskopischen Daten in Lösungsmittelgemischen bei 25 °C emittelt. Das Tautomeriegleichgewicht vonHNQ in wäßrigem Ethanol wird iskutiert. Die Abhängigkeit des Absorptionsmaximums vonHNQ vond der Wasserstoffbrückenbindungsbildungsfähigkeit des Lösungsmittels wird mittels desT aft-Kamlet — Parameters beschrieben. Experimentelle Ergebnisse ermutigen zur Verwendung vonHNQ als neue Testsubstanzfür die Wasserstoffbrückenbindungsbildungsfähigkeit von reinen und gemischten Lösungsmitteln.

     

Selective removal of heavy metal ions using sol-gel immobilized and SPE-coated thiacrown ethers

Sorbent materials based on three thiacrown ethers, 1,4,7,10-tetrathiacyclododecane (12S4), 1,4,7,10,13-pentathiacyclopentadecane (15S5) and 1,4,7,10.13,16-hexathiacyclooctadecane (18S6) were prepared either by immobilizing the ligands into sol-gel (SG) matrix or coating on commercial solid phase extraction (SPE) column. SG sorbents were characterized by FT-IR, energy dispersive X-ray microanalysis (EDX) and thermogravimetric analysis/derivative thermogravimetric analysis (TGA/DTG). A marked thermal stability of the ligands when immobilized in sol-gel matrix was noted. The competitive sorption characteristics of a mixture of eleven metal ions (Mg²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Ca²⁺, Cu²⁺, Ni²⁺, Ag⁺, V⁴⁺, Hg²⁺) using: (i) batch method with ligands trapped in SG matrices, and (ii) off-line SPE column containing coated ligands were studied using ICP-MS. The extraction of metals were optimized for key parameters such as pH, contact time/flow rate, particle size (for SG sorbents) and ligand concentration. Under the optimized conditions, all the immobilized thiacrown ethers exhibited highest selectivity toward Ag⁺, with lesser responses to Hg²⁺ while the extraction of other metal ions were negligible. Among the SG sorbents, 18S6-SG offer the highest capacity and the best selectivity over Hg²⁺. However, for practical applications such as for selective isolation and preconcentration of Ag⁺, the SPE type especially based on 18S6 is preferred as analysis time and recoveries are favorable. The sorbents can be repeatedly used three times as there was no significant deterioration in the metal uptake (%E > 90%) or interference from other metal ions. The optimized procedures were successfully applied for the separation and preconcentration of traces Ag⁺ in different water samples.     

Thermal phenomena during anodizing of aluminium in sulfuric acid

The heat developing at the oxide-aluminium interface during anodizing in sulfuric acid has been measured. The temperature of the aluminium anode increases rapidly to attain a steady value after a few minutes, and drops sharply upon current interruption. The rise in temperature increases linearly with the current density. The effects of the concentration and temperature of the electrolyte and the anodizing voltage on the heat developed in aluminium have been examined. The results are discussed with regard to the dispute concerning the conditions necessary at the base of the pores for the relatively high local dissolution.     

Photochromism of Dihydroindolizines. Part III [1]. Synthesis and Photochromic Behavior of Novel Photochromic Dihydroindolizines Incorporating a Cholesteryl Moiety

Summary. Ten novel photochromic dihydroindolizines (DHIs) based on 1,5-electrocyclization and bearing a cholesteryl moiety at 7-position of the DHI skeleton were synthesized. 1D, 2D, NOESY ¹H NMR spectra, mass spectrometry, and elemental analysis were used for their characterization. Irradiation of the DHIs in CH₂Cl₂ solution with polychromatic light leads to the formation of red to red-violet colored betaines. Most colored betaine forms are notable in CH₂Cl₂ solution at room temperature because of their slow 1,5-electrocyclization except in one case, where the colored betaine could be observed only after cooling with liquid nitrogen due to the fast electrocyclization back reaction. The kinetics of the reverse 1,5-electrocyclization of the colored betaines into the corresponding DHIs were detected using both UV/VIS and flash photolysis measurements.The presence of three isosbestic points in the fading spectrum of the betaines proved that the thermal back reaction to the DHIs follows a first order mechanism. Tuning of the photophysical properties of DHIs and their colored betaines was achieved by change of substituents in the ester and fluorene regions. A notable increase of the t₃₀-value of some betaines by a factor ranging between 1.01 and 1.57 compared with the betaine form of dicyanopridazine DHI standard (t₃₀=243min) was observed. The high photo-fatigue resistance of these betaines will help to find their applications.Present address: Special Division for Human Life Technology, National Research Institute of Advanced Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan     

Colorimetric method for the quantitative determination of the antibilharzial drug praziquantel and its application to pharmaceutical preparations.

A method for the colorimetric assay of praziquantel has been developed. For the colorimetric assay, it was necessary to hydrolyse praziquantel with 3 mol dm-3 NaOH, 6 mol dm-3 HCl and 85% phosphoric acid separately. 4-Chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) reacts with the basic hydrolysis product in methanolic aqueous phosphate buffer (pH 7.4), resulting in the formation of an orange product with a characteristic absorption maximum at 478 nm. The red-orange product of the interaction between the hydrochloric acid hydrolysis product and NBD-Cl showed an absorption maximum at 486 nm. The colours obtained were stable for 24 h. The colour system obeyed Beer's law in the concentration range 2-15 and 2-18 micrograms ml-1 for the basic hydrolysis product and the acid hydrolysis product, respectively. The results obtained showed good recoveries with relative standard deviations of 0.378 and 0.47% for the basic and the acid hydrolysis product, respectively. The determination limit was found to be 0.124 and 0.150 micrograms ml-1 for the praziquantel basic hydrolysis product and the acid hydrolysis product, respectively. The coloured reaction products obtained with the proposed method were synthesized. The structures of these products were studied and the compounds identified.     

Selective extraction of salbutamol from human plasma with the use of phenylboronic acid

An investigation was conducted on the usage of a single-step extraction procedure involving the retention of a phenylboronate-salbutamol complex on an end-capped C18 solid-phase sorbent to determine the level of salbutamol in human plasma samples. Propranolol, a beta-blocker, was chosen as the internal standard for this assay. In this solid-phase clean-up method, 50 mM sodium carbonate buffer, pH 9.60, was used for conditioning the column as well as washing the endogenous interference. Under the optimal conditions, the recovery of salbutamol from spiked plasma samples was found to be high and reproducible with mean recoveries (n = 3) of more than 90% after elution by using 50% 1 M trifluoroacetic acid in methanol. This sample clean-up step was effectively analyzed under reversed-phase high-performance liquid chromatography with fluorimetric detection. The method was successfully applied to the routine measurement of salbutamol in human plasma from the bioequivalence study on the different administration route of salbutamol. Quantification of salbutamol was convincingly reported with the correlation of coefficient of 0.9980 for the concentration range from 0 to 1000 ng ml(-1). An adequate precision was achieved with both between- and within-day precisions of less than 10% (n = 6) for 100 and 1000 ng ml(-1) and less than 15% (n = 6) for 10 ng ml(-1).     

Proton-induced x-ray emission analysis of tea leaves

Proton-induced X-ray emission (PIXE) spectroscopy has been used for the determination of the concentration of 12 elements in tea leaves of four different brands. The elements are: Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Br, Rb and Sr. The transference ratio of the elements into solution, when tea is leached by percolation is reported. It was found that some elements are totally transferred into solution and some are partially retained by the leaves. The significance of some of the elements found in the samples is discussed.     

Hydrodeoxygenation of benzofuran over sulfided and reduced Ni–Mo/γ-Al2O3 catalysts: Effect of H2S

Effect of H₂S on the catalytic performance of the reduced and sulfided Ni–Mo/Al₂O₃ catalysts in hydrodeoxygenation of benzofuran is studied. The steady-state reaction experiments showed a decrease in activity for both reduced and sulfided catalysts when H₂S was introduced into the feed. The reaction conversion of benzofuran over the reduced catalyst still remained superior to that of the sulfided catalyst in the presence of H₂S, however, at high reaction temperatures, the product distribution over the pre-reduced catalyst is similar to the sulfided catalyst. The studies with temperature-programmed desorption (TPD), temperature-programmed reaction (TPRxn) and X-ray photoelectron spectroscopy (XPS) techniques showed a partial sulfidation of the reduced catalysts when exposed to H₂S under reaction conditions, however, the catalyst does not go through a complete conversion to a molybdenum sulfide phase. Instead oxygen–sulfur exchange on the surface leaves behind oxisulfide species, with catalytic activity closely resembling that of the reduced catalysts. The effect of H₂S on the reaction performance is mainly coming from the competitive adsorption between H₂S and benzofuran and the formation of SH groups with decomposition of H₂S at high temperatures.     

Mössbauer spectroscopic study of FeAl1−x Co x

We report the results of a Mössbauer study of the alloy sytem FeAl_1?x Co _x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN₂ temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases.