UV/Vis spectroscopic behaviour of some new hydroxy azocoumarin derivatives

Summary The UV/Vis spectroscopic behaviour of six new hydroxy azocoumarin compounds in solution has been investigated. The observed bands are assigned to electronic transitions. Azocoumarin compounds exist mainly in the azo form, whereas 6-(2-hydroxy-6-aminonaphthyl-1-azo)-coumarin exhibits an azo-hydrazone tautomeric equilibrium. The solvatochromic behaviour of the azo compounds is investigated by studying their spectra in pure and mixed organic solvents of different characteristics. The longer wavelength band of the azocoumarins inDMF solution is assigned to an intermolecular CT transition.

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UV/Vis-spektroskopisches Verhalten einiger neuer Hydroxyazocumarinderivate

Zusammenfassung Das UV/Vis-spektroskopische Verhalten von sechs neuen Hydroxyazocumarinen in Lösung wurde untersucht. Die beobachteten Banden werden elektronischen Übergängen zugeordnet. Azocumarine liegen hauptsächlich in der Azoform vor, während 6-(2-Hydroxy-6-aminonaphthyl-1-azo)-cumarin eine Azo-Hydrazon-Tautomerie zeigt. Das solvatochrome Verhalten der Azoverbindungen wird durch Messung ihrer Spektren in reinen und gemischten organischen Lösungsmitteln mit unterschiedlichen Eigenschaften studiert. Die bei inDMF gelösten Azocumarinen auftretende langwellige Bande wird einem intermolekularen CT-Übergang zugeordnet.

     

Evaluation of radiostability of some steroid derivatives

The effect of ionising radiation (15-100 kGy) on the physico-chemical properties of 6 steroid derivatives in solid state (Hydrocortisone, Hydrocortisone acetate, Prednisolone, Prednisolone acetate, Dexamethasone and Fludrocortisone acetate) was studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), UV spectrophotometry, high-performance liquid chromatography (HPLC), X-ray powder diffraction and polarimetry. DSC and DTA results revealed that the irradiated compounds undergo phase transitions at lower temperatures, show lower melting points and lower enthalpy of the melting process their non-irradiated analogues. The results of HPLC measurements proved a loss in the active substance content after irradiation ranging from 0.5 to 2.88%. No significant effect of irradiation was detected by the UV spectrophotometry or polarimetry in the course of the UV spectrum, absorbancy or optical rotation, as well as in the SEM photographs and X-ray patterns. For some compounds studied a correlation was found between the irradiation dose and the shifts in DSC curves and the loss of content determined by the HPLC method. Similar, but not so much pronounced relations were established in or earlier studies of the derivatives of nitroimidazole and 1,4-dihydropyridine. In general the results have shown relatively high radiochemical stability of the compounds studied and have proved that the DSC method is a sensitive detector of irradiation-caused changes in drugs in solid phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of acidic chlorinated pesticides in water: Comparison of official EPA method 515.1 and liquid-solid extraction HPLC/UV and HPLC/PBMS analyses

Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.Deceased July 31, 1996     

A photo-oxidation procedure using UV radiation/H2O2 for decomposition of wine samples — Determination of iron and manganese content by flame atomic absorption spectrometry

This paper proposes the use of photo-oxidation with UV radiation/H₂O₂ as sample pretreatment for the determination of iron and manganese in wines by flame atomic absorption spectrometry (FAAS). The optimization involved the study of the following variables: pH and concentration of buffer solution, concentrated hydrogen peroxide volume and irradiation time. The evaluation of sample degradation was monitored by measuring the absorbance at the maximum wavelength of red wine (530 nm). Using the experimental conditions established during the optimization (irradiation time of 30 min, oxidant volume of 2.5 mL, pH 10, and a buffer concentration of 0.15 mol L^− 1), this procedure allows the determination of iron and manganese with limits of detection of 30 and 22 μg L^− 1, respectively, for a 5 mL volume of digested sample. The precision levels, expressed as relative standard deviation (RSD), were 2.8% and 0.65% for iron and 2.7% and 0.54% for manganese for concentrations of 0.5 and 2.0 mg L^− 1, respectively. Addition/recovery tests for evaluation of the accuracy were in the ranges of 90%–111% and 95%–107% for iron and manganese, respectively. This digestion procedure has been applied for the determination of iron and manganese in six wine samples. The concentrations varied from 1.58 to 2.77 mg L^− 1 for iron and from 1.30 to 1.91 mg L^− 1 for manganese. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level).     

Preparation and characterization of pentaerythritol/butane tetracarboxylic acid/polyethylene glycol crosslinking copolymers as solid-solid phase change materials

Pentaerythritol/butane tetracarboxylic acid/polyethylene glycol (PBPEG) crosslinking copolymers as a novel solid-solid phase change material (SSPCM) were successfully synthesized through the reaction mechanism and conditions of hydroxyl-carboxyl condensation reaction. The composition and chemical structure, crystalline properties, phase change behaviors, thermal reliability and chemical stability of PBPEG crosslinking copolymers were investigated by Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD), polarization optical microscopy (POM), differential scanning calorimetry (DSC), and thermogravimetry (TGA), respectively. The results show that PBPEG crosslinking copolymers have typical solid-solid phase transition temperatures in the range of 10.31～53.27°C and high latent heat enthalpy in the range of 89.6～102.8 J/g, the synthesized SSPCMs have good thermal reliability and chemical stability after 300 thermal cycles, and PBPEG crosslinking copolymers have good thermal stability before 364°C. In summary, the synthesized PBPEG crosslinking copolymers could be potentially used for thermal energy storage.     

Investigation of antioxidants and UV stabilizers from plastics. Part I: Comparison of HPLC and SFC; preliminary SFC/MS study

Synthetic mixtures of additives (antioxidants, UV stabilizers) used in the manufacture of food packaging materials were separated by normal phase HPLC under isocratic or gradient elution, and by capillary SFC using CO₂ as mobile phase. SFC proved to be more efficient for the separation and determination of additives with a wide range of boiling points and for substances lacking a UV chromophoric moiety. Combined SFC/MS, using a direct coupling interface, produced clear charge transfer spectra resembling EI spectra and proton exchange CI spectra when ammonia was added to the ion source.     

On the influence of some strong electrolytes on the partitioning of acetic acid to aqueous/organic two-phase systems in the presence of tri-n-octylamine: Part II: Toluene as organic solvent

Water-insoluble amines (dissolved in an organic solvent/organic solvent mixture) are often used for the extractive recovery of carboxylic acids from aqueous phases. The basic design of the extraction process requires a thermodynamic framework that should be able to describe the liquid–liquid phase equilibrium not only in the phase forming systems (water + carboxylic acid + organic solvent + reactive extractant), but also when the aqueous feed phase contains additionally small amounts of strong electrolytes. Even small amounts of strong electrolytes might considerably reduce the recovery rate. In part I of this series such a model was presented and discussed for methyl isobutyl ketone as organic solvent and tri-n-octylamine (TnOA) as the chemical extractant. The present part II is to demonstrate that the procedures/methods described for methyl isobutyl ketone as organic solvent can be applied also for other organic solvents. By way of example, here toluene is that organic solvent. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium acetate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + toluene + tri-n-octylamine) at 25 °C. An extension/adaptation of the previously published thermodynamic framework is successfully applied to describe/predict the new experimental liquid–liquid phase equilibrium data.