Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Coupling constant & Catalysis. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

β-Galactosyl Yariv reagent binds to the β-1,3-galactan of arabinogalactan-proteins

Abstract: Yariv phenylglycosides [1,3,5-tri(p-glycosyloxyphenylazo)-2,4,6-trihydroxybenzene] are a group of chemical compounds that selectively bind to arabinogalactan proteins (AGPs), a type of plant proteoglycan. Yariv phenylglycosides are widely used as cytochemical reagents to perturb the molecular functions of AGPs as well as for the detection, quantification, purification, and staining of AGPs. However, the target structure in AGPs to which Yariv phenylglycosides bind has not been determined. Here, we identify the structural element of AGPs required for the interaction with Yariv phenylglycosides by stepwise trimming of the arabinogalactan moieties using combinations of specific glycoside hydrolases. Whereas the precipitation with Yariv phenylglycosides (Yariv reactivity) of radish (Raphanus sativus) root AGP was not reduced after enzyme treatment to remove α-l-arabinofuranosyl and β-glucuronosyl residues and β-1,6-galactan side chains, it was completely lost after degradation of the β-1,3-galactan main chains. In addition, Yariv reactivity of gum arabic, a commercial product of acacia (Acacia senegal) AGPs, increased rather than decreased during the repeated degradation of β-1,6-galactan side chains by Smith degradation. Among various oligosaccharides corresponding to partial structures of AGPs, β-1,3-galactooligosaccharides longer than β-1,3-galactoheptaose exhibited significant precipitation with Yariv in a radial diffusion assay on agar. A pull-down assay using oligosaccharides cross linked to hydrazine beads detected an interaction of β-1,3-galactooligosaccharides longer than β-1,3-galactopentaose with Yariv phenylglycoside. To the contrary, no interaction with Yariv was detected for β-1,6-galactooligosaccharides of any length. Therefore, we conclude that Yariv phenylglycosides should be considered specific binding reagents for β-1,3-galactan chains longer than five residues, and seven residues are sufficient for cross linking, leading to precipitation of the Yariv phenylglycosides.

The effect of ceria content on the properties of Pd/CeO2/Al2O3 catalysts for steam reforming of methane

Abstract: The effect of CeO 2 loading on the surface properties and catalytic behaviors of CeO 2 –Al 2 O 3 -supported Pd catalysts was studied in the process of steam reforming of methane. The catalysts were characterized by S BET , X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). The XRD measurements indicated that palladium particles on the surface of fresh and reduced catalysts are well dispersed. TPR experiments revealed a heterogeneous distribution of PdO species over CeO 2 –Al 2 O 3 supports; one fraction of large particles, reducible at room temperature, another fraction interacting with CeO 2 and Al 2 O 3 , reducible at higher temperatures of 347 and 423 K, respectively. The PdO species reducible at room temperature showed lower CO adsorption relative to the PdO species reducible at high temperature. In contrast to Pd/Al 2 O 3 , the FTIR results revealed that CeO 2 -containing catalyst with CeO 2 loading ≥12 wt.% show lower ratio (LF/HF) between the intensity of the CO bands in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). This ratio was constant with increasing the temperature of reduction. The FTIR spectra and the measurement of Pd dispersion suggested that Pd surface becomes partially covered with ceria at all temperature of reduction and with increasing ceria loading in Pd/CeO 2 –Al 2 O 3 catalysts. Although the PdO/Al 2 O 3 showed higher Pd dispersion compared to that of CeO 2 -containing catalysts, the addition of ceria resulted in an increase of the turnover rate and specific rate to steam reforming of methane. The CH 4 turnover rate of Pd/CeO 2 –Al 2 O 3 catalysts with ceria loading ≥12 wt.% was around four orders of magnitude higher compared to that of Pd/Al 2 O 3 catalyst. The increase of the activity of the catalysts was attributed to various effects of CeO 2 such as: (i) change of superficial Pd structure with blocking of Pd sites; (ii) the jumping of oxygen (O * ) from ceria to Pd surface, which can decrease the carbon formation on Pd surface. Considering that these effects of CeO 2 are opposite to changes of the reaction rate, the increase of specific reaction rate with enhancing the ceria loading suggests that net effect results in the increase of the accessibility of CH 4 to metal active sites.

Determination of polarized parton densities from a QCD analysis of inclusive and semi-inclusive deep inelastic scattering data

Abstract: A new combined next to leading order QCD analysis of the polarized inclusive and semi-inclusive deep inelastic lepton-hadron scattering (DIS) data is presented. In contrast to previous combined analyses, the 1/Q 2 terms (kinematic - target mass corrections, and dynamic - higher twist corrections) in the expression for the nucleon spin structure function g1 are taken into account. The new COMPASS data are included in the analysis. The impact of the semi-inclusive data on the polarized parton densities (PDFs) and on the higher twist corrections is discussed. The new results for the PDFs are compared to our (Leader, Sidorov, Stamenov) LSS’06 PDFs, obtained from the fit to the inclusive DIS data alone, and to those obtained from the de Florian, Sassot, Stratmann, and Vogelsang global analysis.

Muscle fatigue during dynamic contractions assessed by new spectral indices.

Abstract: Purpose: The aim of the present study was to test the applicability and sensitivity of new electromyography (EMG) spectral indices in assessing peripheral muscle fatigue during dynamic knee-extension exercise. Methods: Seven subjects completed 10 sets of 15 repetitions of right knee-extension exercise lifting 50% of their one-repetition maximum. Torque (T), knee-joint angle, and the interference EMG of rectus femoris muscle were recorded simultaneously. Maximal voluntary isometric contraction (MVC) was tested before and after exercise. Median spectral frequency (Fmed) and new spectral indices of muscle fatigue (FInsmk) were calculated for each repetition. Results: The rate and range of FInsmk- and Fmed-relative changes against the first repetition of the corresponding set increased gradually across successive repetitions within the set, reflecting accumulation of peripheral muscle fatigue. The maximal change of FInsmk observed in the present experiment was approximately eightfold, whereas that of Fmed was only 32%. Significant between-subject variability in the range of FInsmk changes (P 400%), medium (N = 4, 200% < FInsmk change < 400%), and low (N = 2, FInsmk change < 200%) muscle fatigability. The changes in muscle performance during (last vs first repetition peak T, P = 0.03) and after (post- vs preexercise MVC, P = 0.012) exercise were significantly different between clusters (one-way ANOVA). The rate of fatigue development was also significantly different between clusters (linear regression analysis of Fmed and FInsmk changes). Conclusions: The new spectral indices are a valid and reliable tool for assessment of muscle fatigability irrespective of EMG signal variability caused by dynamic muscle contractions, and these indices are more sensitive than those traditionally used.