A note on a generalized Douglas space

Periodica Mathematica Hungarica -     

Optical Spectroscopy and Theoretical Studies in Calixarene Chemistry

This review summarizes different applications of optical spectroscopic methods in calixarene chemistry including UV/Vis spectrometry, vibrational spectroscopic techniques (FTIR and Raman spectroscopy), luminescence spectroscopy (including fluorescence and phosphorescence), ellipsometry and various optical microscopic methods. Moreover, the results of theoretical studies (AM1, PM3, DFT, ab initio, etc.) are summarized based on selected papers in the field of conformational studies, thermodynamics and complexation features. About 300 references are processed systematically from the results reported mainly in the recent years with emphasis on the potential of practical application of these molecules.     

Complex formation reaction of the iron(III) hydroxo dimer with periodate ion

The kinetics and mechanism of the ligand substitution reaction between Fe(2)(OH)(2)(4+) and periodate ion has been studied. This process is unique among the reactions of the iron(iii) hydroxo dimer because the initial rate is second-order with respect to Fe(2)(OH)(2)(4+). The formation of a bi- and a tetranuclear complex, Fe(2)(OH)(2)(H(4)IO(6))(3+) and Fe(4)(OH)(4)(H(4)IO(6))(7+), is proposed. Comprehensive fitting of the kinetic data was used to show that the proposed model, which is very similar to earlier models used with other inorganic oxoanions, gives a reasonable interpretation of all observations. It is shown that the lifetime of Fe(2)(OH)(2)(H(4)IO(6))(3+) is relatively long and it can open a pathway to form oligomeric and less soluble products at higher initial concentrations. The speciation of aqueous periodate ion solution was also studied and it is proposed that the tetrahedral form, IO(4)(-), is less dominant over the octahedral form, H(4)IO(6)(-), than previously thought.     

A new approach for the sequential injection spectrophotometric determination of the total antioxidant activity

A sequential injection system based on the ABTS (2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic-acid) methodology was developed. The proposed method, incorporating a mixing chamber in the side port of the selection valve, was evaluated to measure the total antioxidant activity of several beverages and foods.The ABTS⁺ is generated by oxidation of ABTS with potassium persulfate and is reduced in presence of hydrogen-donating antioxidants converting into a colourless product. The applicability of the developed method was tested by measurement of the antioxidant activity of pure compounds as well as by analysing complex food and beverage samples. The antioxidant activity was presented as l(+) ascorbic acid equivalence. The values obtained by this methodology were not significantly different from the results obtained by the original spectrophotometric ABTS assay. For most of the studied antioxidants, antioxidant activity varied with pH and dilution. The proposed SIA system is suitable for screening direct or diluted total antioxidant activity of pure compounds or food samples.     

Synthesis and enantiomeric recognition studies of a novel 5,5-dioxophenothiazine-1,9 bis(thiourea) containing glucopyranosyl groups

A novel optically active 5,5-dioxophenothiazine-1,9 bis(thiourea) containing glucopyranosyl groups was synthesized and its enantiomeric recognition properties were examined towards the enantiomers of tetrabutylammonium salts of chiral α-hydroxy and N-protected α-amino acids using UV–vis spectroscopy.     

Rheological analysis of the structural properties effecting the percutaneous absorption and stability in pharmaceutical organogels

This study presents the organogels of glyceryl monostearate emulsifiers and coconut oil as an alternative for developing the traditional organogels. We investigated how the emulsifier type affects the semisolid consistency and the drug release. In these aspects we compared glyceryl monostearate organogels (GMSO) to commercially available references, while studying the effect of the individual constituents on the structural and functional properties.Rheology provided indirect information on the structure, relevant from an application point of view. We observed that glyceryl monostearate as an organogelator results in a network with elastic nature and moderate crosslink energy. The products had low viscosity and low yield value which means practically an easily spreadable pharmaceutical dosage form with soft consistency.Modelling the percutaneous absorption in vitro, we observed that the diffusion of the piroxicam incorporated was significantly affected by the thermodynamical potency of piroxicam, which was favoured by the emulsifier. The glyceryl monostearate enhanced the partition of the suspended drug, resulting in higher drug release.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Sequential Injection Kinetic Flow Assay for Monitoring Glycerol in a Sugar Fermentation Process by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

A sequential injection system to monitor glycerol in a Saccharomyces cerevisiae fermentation process was developed. The method relies on the rate of formation of nicotinamide adenine dinucleotide in its reduced form (NADH, measured spectrophotometrically at 340 nm) from the reaction of glycerol with NAD⁺ cofactor, catalysed by the enzyme glycerol dehydrogenase present in solution. This procedure enables the determination of glycerol between 0.046 and 0.46 g/l, (corresponding to yeast fermentation samples with concentrations up to 50 g/l) with good repeatability (relative standard deviation for n = 10 lower than 2.2% for three different samples) at a sampling frequency of 25/h. The detection and quantification limits using a miniaturised spectrophotometer were 0.13 and 0.44 mM, respectively. Reagent consumption was of 0.45 μmol NAD⁺ and 1.8 μg enzyme per assay, and the waste production was 2.8 ml per determination. Results obtained for samples were in agreement with those obtained with a high-performance liquid chromatography method.     

Exploiting the bead injection LOV approach to carry out spectrophotometric assays in wine: application to the determination of iron

A sequential injection lab-on-valve (SI-LOV) system was used to develop a new methodology for the determination of iron in wine samples exploiting the bead injection (BI) concept for solid phase extraction and spectrophotometric measurement. Nitrilotriacetic Acid (NTA) Superflow resin was used to build the bead column of the flow through sensor. The iron (III) ions were retained by the bead column and react with SCN⁻ producing an intense red colour. The change in absorbance was monitored spectrophotometrically on the optosensor at 480 nm. It was possible to achieve a linear range of 0.09-5.0 mg L⁻¹ of iron, with low sample and reagent consumption; 500 μL of sample, 15 μmol of SCN⁻, and 9 μmol of H₂O₂, per assay. The proposed method was successfully applied to the determination of iron in wine, with no previous treatment other than dilution, and to other food samples.     

Effect of iron restriction on outer membrane protein composition of Pseudomonas strains studied by conventional and microchip electrophoresis

In this study the outer membrane protein (OMP) composition of six Pseudomonas aeruginosa strains had been analyzed by conventional CE and microchip electrophoresis. Bacterial OMPs are important virulence factors and play a significant role in the pathogenesis of infectious diseases. Changes in their composition might refer to the altered pathogenic properties and antibiotic sensitivity of a certain strain. Pathogenic bacteria invading the human host have to multiplicate under iron-restricted conditions that induce changes in the OMP composition. High-molecular-weight OMPs have to be expressed, which serve as receptors for the iron-siderophore complexes. OMP patterns of bacteria obtained by the two different methods in this study were similar, all major proteins could be detected by both techniques, and the molecular weights showed good correlations, although direct comparison of the peak areas is not straightforward due to the different detection methods (UV and LIF). Changes in OMP composition under iron restriction could be detected, and appearance of a 92 kDa protein in all six P. aeruginosa strains and a 94 kDa protein in the KT 2 strain could be demonstrated. Besides that up- and downregulation of certain proteins could be also detected. The increased separation speed, picoliters of sample consumption, baseline separation achieved more frequently by this method--especially in the high-molecular-weight region--showed the advantages of microchip electrophoresis in the analysis of clinical samples.     

In vitro study of antibiotic effect on bacterial adherence to acrylic intraocular lenses

Implantation of artificial intraocular lenses into the eye during ophthalmic surgical procedures ensures an unliving surface on which bacterial pathogens may attach and form biofilms. Despite antibiotic treatment bacteria growing in biofilms might cause inflammation and serious complications. In this study the adhesive ability of 7 Staphylococcus aureus and 11 coagulase-negative Staphylococcus (CNS) strains to the surface of acrylic intraocular lenses had been examined by the ultrasonic method. In untreated cases adhesion of the S. aureus and CNS strains did not differ significantly. We could not demonstrate significant differences between the adhesive ability of the standard strains and the clinical isolates. In this study a single – 60 min long – antibiotic (ciprofloxacin and tobramycin) treatment had been applied, that correlate well with the single or intermittant antibiotic prophylaxis of patients. Ciprofloxacin administration was able to reduce significantly the number of attached cells on the surface of acrylic lenses both in the case of S. aureus and CNS strains. Dependence of the effect from concentration could also be demonstrated. Tobramycin treatment was able to inhibit significantly the attachment of S. aureus cells. Despite the debate on antibiotic prophylaxis we presented in our experiments that a single antibiotic administration can decrease the attachment of bacterial cells to the surface of acrylic intraocular lenses, and might be effective in the prevention of postoperative endophthalmitis, that is a rare but serious complication of ophthalmic surgery.