Showing papers by "Bulgarian Academy of Sciences published in 2002"

Screening of Plant Extracts for Antioxidant Activity: a Comparative Study on Three Testing Methods

Abstract: Three methods widely employed in the evaluation of antioxidant activity, namely 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method, static headspace gas chromatography (HS-GC) and β-carotene bleaching test (BCBT), have been compared with regard to their application in the screening of plant extracts. The strengths and limitations of each method have been illustrated by testing a number of extracts, of differing polarity, from plants of the genus Sideritis, and two known antioxidants (butylated hydroxytoluene and rosmarinic acid). The sample polarity was important for the exhibited activity in the BCBT and HS-GC methods but not for the DPPH method. The complex composition of the extracts and partition phenomena affected their activity in each assay. The value of the BCBT method appears to be limited to less polar samples. Although slow, the HS-GC method is preferable for assessing the antioxidant inhibitory properties on the formation of unwanted secondary volatile products. Being rapid, simple and independent of sample polarity, the DPPH method is very convenient for the quick screening of many samples for radical scavenging activity. Copyright © 2001 John Wiley & Sons, Ltd.

Gram-scale synthesis of monodisperse gold colloids by the solvated metal atom dispersion method and digestive ripening and their organization into two- and three-dimensional structures.

Abstract: We describe a synthetic procedure for preparation of large quantities of monodisperse thiol-stabilized gold colloids in toluene solution. The method is based on the solvated metal atom dispersion technique (SMAD), which is very suitable for preparation of large amounts of metal colloidal solutions, as well as of metal sulfide, metal oxide, and other types of dispersed compounds in different solvents. A combination of two different solvents like acetone and toluene is used for the preparation of the gold colloids. The necessity of initially carrying out the SMAD reaction in acetone comes from its high degree of solvation of gold particles. Acetone acts as a preliminary stabilizing agent. After its removal from the system, the particles are stabilized by dodecanethiol molecules, which enable their very good dispersion in toluene solution. A digestive ripening procedure is carried out with the gold−toluene colloid, and for this purpose pure toluene as solvent is necessary. This has a dramatic effect on the n...

Characterization of ceria-coated alumina carrier

Abstract: CeO2–Al2O3 mixed oxides with different CeO2 loading (in the range of 0.5–12 wt.%) were prepared by wetness impregnation of alumina with aqueous solution of di-ammonium hexanitrate cerate (NH4)2[Ce(NO3)6]. The samples after calcination at 773 and 1073 K were characterized by different techniques, using X-ray diffraction (XRD), UV–VIS diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). It is shown that different types of cerium oxide species are formed on the surface depending on the amount of CeO2 and temperature of calcination of the samples. XRD showed the formation of nanocrystallites of ceria on alumina surface when the amount of CeO2 is higher than 6 wt.%; at lower concentrations ceria was found to be amorphous. The ceria loading lower than 6 wt.% stabilizes the textural properties of alumina. At loading of 1 wt.% of CeO2 XPS spectra reveals the presence of a strong interaction between ceria and alumina leading to a formation of superficial CeAlO3-like phase. TPR results show that well dispersed CeO2 particles present on the surface of alumina form CeAlO3 at temperature of reduction in the range of 873–993 K, while for the reduction of CeO2 crystallites, a higher temperature of reduction of 1190 K is needed.

Lactic acid bacteria and yeasts in kefir grains and kefir made from them.

Abstract: In an investigation of the changes in the microflora along the pathway: kefir grains (A)→kefir made from kefir grains (B)→kefir made from kefir as inoculum (C), the following species of lactic acid bacteria (83–90%) of the microbial count in the grains) were identified: Lactococcus lactis subsp lactis, Streptococcus thermophilus, Lactobacillus delbrueckii subsp bulgaricus, Lactobacillus helveticus, Lactobacillus casei subsp pseudoplantarum and Lactobacillus brevis Yeasts (10–17%) identified were Kluyveromyces marxianus var lactis, Saccharomyces cerevisiae, Candida inconspicua and Candida maris In the microbial population of kefir grains and kefir made from them the homofermentative lactic streptococci (52–65% and 79–86%, respectively) predominated Within the group of lactobacilli, the homofermentative thermophilic species L delbrueckii subsp bulgaricus and L helveticus (70–87% of the isolated bacilli) predominated Along the pathway A→B→C, the streptococcal proportion in the total kefir microflora increased by 26–30% whereas the lactobacilli decreased by 13–23% K marxianus var lactis was permanently present in kefir grains and kefirs, whereas the dominant lactose-negative yeast in the total yeast flora of the kefir grains dramatically decreased in kefir C Journal of Industrial Microbiology & Biotechnology (2002) 28, 1–6 DOI: 101038/sj/jim/7000186

Locus of control and well-being at work: how generalizable are western findings

Abstract: Managers from 24 geopolitical entities provided data on work locus of control, job satisfaction, psychological strain, physical strain, and individualism/collectivism. The hypothesis that the salut...

Chemical composition of European propolis: expected and unexpected results.

Abstract: Ten propolis samples from Bulgaria, Italy and Switzerland were analyzed by GC-MS. As expected, most samples displayed the typical chemical pattern of "poplar" propolis: they contained pinocembrin, pinobanksin and its 3-O-acetate, chrysin, galangin, prenyl esters of caffeic and ferulic acids. Two samples differed significantly: one from the Graubunden Alpine region, Switzerland, rich in phenolic glycerides, and one from Sicily which contained only a limited number of phenolics and was rich in diterpenic acids.

Deep-water contourite systems: modern drifts and ancient series, seismic and sedimentary characteristics

Abstract: Countourites are a widespread but poorly known group of sediments linked to the action of powerful bottom currents in deep water. Although we know they are especially common along continental margins and through oceanic gateways, they have been surrounded by contoversy since they were first recognized in the early 1960s. Where correctly recognized and decoded they can provide one of the keys to our better understanding of bottom water circulation and of the ocean–climate link. They are part of the spectrum of deposits that confronts the oil industry as exploration moves into progressively greater water depths. This memoir is an important outcome of the International Geological Correlation Project 432 on Bottom Currents, Contourites and Palaeocirculation . It includes 30 papers involving over 75 key scientists from around the world. Following an introductory state–of–the–art paper by the editors, there are 25 separate case studies on modern drifts and four on ancient contourite series. Each contribution highlights the specific geological and oceanographic setting, bathymetry, physiographic and stratigraphic context, seismic attributes and sedimentary characteristics of that drift. Case studies range from some of the well-documented North Atlantic drifts to those much less known from the Mediterrenean, from important syntheses of the Gulf of Cadiz and Vema Channel Gateway, to completely new data on South Atlantic, Pacific and Antartic margin systems. The four papers on ancient series from Japan, China and Cyprus serve to emphasise the complex nature and subtle characteristics of contourites, which make their identification a scientific challenge. This volume is dedicated to the memory of Charlie Hollister (1936–1999), one of the founding fathers and pioneers of countourite research.

Fast string correction with Levenshtein automata

Abstract: The Levenshtein distance between two words is the minimal number of insertions, deletions or substitutions that are needed to transform one word into the other. Levenshtein automata of degree n for a word W are defined as finite state automata that recognize the set of all words V where the Levenshtein distance between V and W does not exceed n. We show how to compute, for any fixed bound n and any input word W, a deterministic Levenshtein automaton of degree n for W in time linear to the length of W. Given an electronic dictionary that is implemented in the form of a trie or a finite state automaton, the Levenshtein automaton for W can be used to control search in the lexicon in such a way that exactly the lexical words V are generated where the Levenshtein distance between V and W does not exceed the given bound. This leads to a very fast method for correcting corrupted input words of unrestricted text using large electronic dictionaries. We then introduce a second method that avoids the explicit computation of Levenshtein automata and leads to even improved efficiency. Evaluation results are given that also address variants of both methods that are based on modified Levenshtein distances where further primitive edit operations (transpositions, merges and splits) are used.

Low temperature water gas shift over gold catalysts

Abstract: This review summarizes the results reported in the literature on the water gas shift (WGS) over goldcontaining catalysts. Attention is focused on the influence of the preparation method and the nature of the support on the gold dispersion and WGS activity. Special emphasis is paid to the enhanced reducibility of the metal oxide support in the presence of gold. Some aspects of the reaction mechanism of the WGS are discussed.

Biosurfactant Production by a New Pseudomonas putida Strain

Abstract: Observation of both tensio-active and emulsifying activities indicated that biosurfactants were produced by the newly isolated and promising strain Pseudomonas putida 21BN. The biosurfactants were identified as rhamnolipids, the amphiphilic surface-active glycolipids usually secreted by Pseudomonas spp. Their production was observed when the strain was grown on soluble substrates, such as glucose or on poorly soluble substrates, such as hexadecane, reaching values of 1.2 g l(-1). When grown on hexadecane as the sole carbon source the biosurfactant lowered the surface tension of the medium to 29 mN m(-1) and formed stable and compact emulsions with emulsifying activity of 69%.

Excitatory and Inhibitory Effects of A1 and A2A Adenosine Receptor Activation on the Electrically Evoked [3H]Acetylcholine Release from Different Areas of the Rat Hippocampus

Abstract: The modulation by adenosine analogues and endogenous adenosine of the electrically evoked release of [3H]acetylcholine ([3H]ACh) was compared in subslices of the three areas of the rat hippocampus (CA1, CA3, and dentate gyrus). The mixed A1/A2 agonist 2-chloroadenosine (CADO; 2-10 microM) inhibited, in a concentration-dependent manner, the release of [3H]ACh from the three hippocampal areas, being more potent in the CA1 and CA3 areas than in the dentate gyrus. The inhibitory effect of CADO (5 microM) on [3H]ACh release was prevented by the A1 antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 50 nM) in the three hippocampal areas and was converted in an excitatory effect in the CA3 and dentate gyrus areas. The A2A agonist CGS-21680 (30 nM) produced a greater increase of the evoked release of [3H]ACh in the CA3 than in the dentate gyrus areas, whereas no consistent effect was found in the CA1 area or in the whole hippocampal slice. The excitatory effect of CGS-21680 (30 nM) in the CA3 area was prevented by the adenosine receptor antagonist 3,7-dimethyl-1-propargylxanthine (10 microM). Both adenosine deaminase (2 U/ml) and DPCPX (250 nM) increased the evoked release of [3H]ACh in the CA1 and CA3 areas but not in the dentate gyrus. The amplitude of the effect of DPCPX and adenosine deaminase was similar in the CA1 area, but in the CA3 area DPCPX produced a greater effect than adenosine deaminase. It is concluded that the electrically evoked release of [3H]ACh in the three areas of the rat hippocampus can be differentially modulated by adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

The terminology of larval cestodes or metacestodes

Abstract: The terminology associated with the nomenclature of larval or metacestodes is reviewed as well as the various morphological and developmental characters used to define different types of larval cestodes. Based on a review of the literature, the key characters differentiating the types of larval cestodes are the presence of a primary lacuna and the invagination/retraction of the scolex. The presence of a cercomer and of a bladder-like enlargement of the larval cestode were considered to be useful secondary characteristics. Using these characters, six basic types of larval cestodes were identified: the procercoid, an alacunate form which cannot develop further until ingested by a second intermediate host; the plerocercus, an alacunate form with a retracted scolex; the plerocercoid, an alacunate form with an everted scolex; the merocercoid, an alacunate form with an invaginated scolex; the cysticercoid, a lacunate form with a retracted scolex; and the cysticercus, a lacunate form with an invaginated scolex. The diversity of larval types within the broad classifications of cysticercoid and cysticercus can be differentiated by the use of appropriate prefixes. Deficiencies in knowledge of specific types of larval cestodes are identified and further avenues of research are indicated.

Pharmacophore model of drugs involved in P-glycoprotein multidrug resistance: explanation of structural variety (hypothesis).

Abstract: A general pharmacophore model of P-glycoprotein (P-gp) drugs is proposed that is based on a highly diverse data set and relates to the verapamil binding site of the protein. It is derived from structurally different drugs using the program GASP. The pharmacophore model consists of two hydrophobic points, three hydrogen bond (HB) acceptor points, and one HB donor point. Pharmacophore patterns of various drugs are obtained, and different binding modes are presumed for some of them. It is concluded that the binding affinity of the drugs depends on the number of the pharmacophore points simultaneously involved in the interaction with P-gp. On the basis of the obtained results, a hypothesis is proposed to explain the broad structural variety of the P-gp substrates and inhibitors: (i) the verapamil binding site of P-gp has several points that can participate in hydrophobic and HB interactions; (ii) different drugs can interact with different receptor points in different binding modes.

Effects of propolis from Brazil and Bulgaria on fungicidal activity of macrophages against Paracoccidioides brasiliensis.

Abstract: Paracoccidioidomycosis is the most important systemic mycosis in Latin America. Its etiological agent, Paracoccidoides brasiliensis, affects individuals living in endemic areas through inhalation of airborne conidia or mycelial fragments. The disease may affect different organs and systems, with multiple clinical features, with cell-mediated immunity playing a significant role in host defence. Peritoneal macrophages from BALB/c mice were stimulated with Brazilian or Bulgarian propolis and subsequently challenged with P. brasiliensis. Data suggest an increase in the fungicidal activity of macrophages by propolis stimulation, independently from its geographic origin.

On the massive star contents of Cygnus OB2

Abstract: We present a near-infrared spectroscopic survey of a large area centered on the Cygnus OB2 association aimed at constraining its massive star contents. Our goal is to establish a nearly complete list of O-type members of the association, both to examine recent claims based on starcounts that suggest a richer content than previously thought, and to provide a suitable database for further studies of the entire high-mass end of one of the richest associations of the Galaxy. The target selection is based on the JHK photometry published in the 2MASS all-sky survey. We identify 46 new early-type candidates, most of them expected to be O-type stars, plus 16 new stars with emission in Br and often in other lines as well, characteristic of evolved massive stars undergoing intense mass loss. We also present spectra of three luminous stars with CO overtone emission, one of them having also intense H2 emission and being associated with compact nebulosity. By considering our ndings, those of other authors, and plausible completeness corrections, we estimate the number of O-type stars or stars having evolved from a O-type progenitor to be 90{100, slightly below, but compatible with, most recent starcounts estimates by Knodlseder (2000, A&A, 360, 539). These results support the notion that Cygnus OB2 may be considered as a young globular cluster. The lists of new members that we provide, in particular those with emission lines, should be a useful resource for future investigations of Cygnus OB2 itself, as well as of very massive stellar evolution by providing a nearby, abundant sample of stars sharing a common environment.

Surface species formed after NO adsorption and NO + O2 coadsorption on ZrO2 and sulfated ZrO2: An FTIR spectroscopic study

Abstract: Adsorption of NO and its coadsorption with oxygen on ZrO2 and sulfated ZrO2 have been studied by FTIR spectroscopy. It has been found that NO adsorption on ZrO2 results in formation of N2O (2282, 2244, and 1233 cm-1) and small amounts of nitro species (1443 and 1423 cm-1), nitrates (1558, 1189, and 1057 cm-1), and nitric acid (1621 and 1142 cm-1). With time, the nitrate bands (1640−1560, 1290−1220, and 1042−1004 cm-1) develop and enhance the Lewis acidity of nearby Zr4+ cations. As a result, coordinated NO (1906 cm-1) is formed. On sulfated zirconia, nitrosyls (1908 cm-1) are produced immediately after NO adsorption evidencing an increased acidity of the Zr4+ cations as a result of the sulfate inductive effect. In addition, nitrates and nitric acid are produced similarly to the case of the sulfate-free sample. Addition of oxygen to the NO−ZrO2 system results in formation of nitrites (1180 cm-1, disappearing in excess oxygen) and in a strong increase in concentration of the nitrates. Besides, NO+ (2206 cm-...

Finite element modeling of the morphology of β to α phase transformation in Ti-6Al-4V alloy

Abstract: In the present work, a mathematical model and computer programs were developed for numerical simulation of the processes of nucleation and growth of the α-phase Widmanstatten plates during the course of the β ⇒ α phase transformation in a Ti-6Al-4V alloy. The α-phase appearance at the grain boundary of β phase is described by a numerical procedure for random nucleation as a function of the vanadium concentration and the temperature. The rate at which an interface moves depends both on the intrinsic mobility and on the rate at which diffusion can remove the excess of vanadium atoms ahead of the interface. The finite-element method (FEM) was used for solving the diffusion equation on the domain occupied by β phase. The elements chosen have dimensions in both space and time. A computer code based on the finite-element modeling and the volume of fluids method was developed to trace the movement of the α/β interface. The influences of the cooling rate and the temperature of isothermal exposure on the Widmanstatten morphology were simulated and analyzed. The developed models and program packages are capable of one-dimensional (1-D) and two-dimensional (2-D) simulations of the morphology of the β ⇒ α phase transformation in Ti-6Al-4V alloy for continuous cooling with any cooling path and for an arbitrary combination between continuous cooling and isothermal exposure.