Сп. „Химия“, книжка 5/2018

Education: Theory & Practice

Immobolization of Fructosyltransferases on Composite Films of Polylactic Acid, Xanthan and Chitosan [In Bulgarian]

Absract. Fructosyltransferases catalyze the synthesis of Levan type polysaccharides in the presence of sucrose in the reaction medium. In the presence of acceptors (maltose, isomaltose, lactose, fructose) and fructose donor sucrose, they synthesize oligosaccharides with a degree of polymerization DP 3 – 5 monosaccharide residues that have prebiotic potential. In the present study, the fructosyltransferase from Leuconostoc mesenteroides Lm17 strain is immobilized on a multilayer polysaccharide structure composed of chitosan and xanthan. The layers were applied onto pre-loaded corn root cans of polylactic acid. The resulting composite films were investigated for the degree of immobilization of the enzyme and the ability to synthesize fructan on the surface of the film. The activity of immobilized enzyme film was found 0.73 U/mg in the resulting films. In carrying out an enzymatic reaction in the presence of over 10 % sucrose, a hydrolysis and transferase reaction was established by which a polysaccharide was synthesized in both the solution and the membrane. Surface morphology of multilayer films is investigated using the Nanosurf Flex AFM. The values of the average roughness were obtained. It is found that it increases with increasing number of layers, regardless of their sequence.
Keywords: polylactic acid, corona discharge, fructosyltrasnferase, levansucrase, immobilized enzymes

I. Iliev, T. Vasileva, V. Bivolarski, A. Viraneva, I. Bodurov, M. Marudova, T. Yovcheva

Education: Theory & Practice

Electrical Impedance Spectroscopy of Graphen-E4 Liquid-Crystal Nanocomposite

Absract. We have examined the electrical response of graphene-nanostructured liquid crystal E7. The nematic E7 was doped with graphene at concentration of 10-3 wt.%. Thin planar-oriented films with a thickness of 7 µm of this nanocomposite were studied by means of electrical impedance spectroscopy in the frequency range from 0.1 Hz to 1 MHz. Their electrical impedance at a room temperature was compared to that of identical films of pure liquid crystal E7 measured under the same experimental conditions. The doping with graphene leads to decrease in electrical conductivity of the studied nanostructured liquid-crystalline material and, thereby, to improvement of its electro-optical performance.
Keywords: electrical impedance spectroscopy, graphene-doped liquid crystals, nanocomposite materials

T. Vlakhov, Y. Marinov, G. Hadjichristov, A.G. Petrov

Education: Theory & Practice

Surface Photovoltage Spectroscopy Characterization of GaAsSbN Layers Grown by Liquid-Phase Epitaxy

Absract. We present an experimental study of GaAsSbN layers with thickness around 1μm, grown by liquid-phase epitaxy on n-type GaAs substrates. The samples are studied by surface photovoltage (SPV) spectroscopy at room temperature. The analysis of the SPV spectra has provided information about the optical absorption and the photocarrier transport in the samples. In particular, a red shift of the energy bandgap with respect to GaAs is found. Its values are larger as compared to our previous data obtained in InGaAsN layers, grown by the same technique.
Keywords: dilute nitrides, GaAsSbN, surface photovoltage, band gap shift

S. Georgiev, V. Donchev, M. Milanova

Education: Theory & Practice

On the Possibility to Analyze Ambient Noise Recrded by a Mobile Device Through the H/V Spectral Ratio Technique

Absract. The analysis of the spectral properties of ambient seismic noise has recently turned to be a promising approach in the study of site effects impact on seismic hazard. In the present paper we present some results from our investigation on the possibility to use mobile devices to record analyze seismic noise through the examination of the horizontal to vertical (H/V) spectral ratio. The results were compared to the ones, obtained by the application of professional seismological equipment, a velocimeter of type GBV-316 of the GEOSIG company. Some divergence of the results from the mobile device and those from GBV-316 were identified, revealing that the application of a mobile device in this case is questionable.
Keywords: H/V spectral ratio technique, ambient noise, fundamental frequency

D. Gospodinov, D. Zlatanski, B. Rangelov, A. Kandilarov

Education: Theory & Practice

Rheological Properties of Batter for Gluten Free Bread

Absract. Gluten free and not gluten free batters for bread were prepared from wheat, rice, chestnut, maize and sweet potato batters. The rheological parameters of different gluten free batters were analysed by texture analyser (relaxation and retardation test) and rotational viscometer (Herschel–Bulkleymodel). The traditional wheat bread batter was used in comparison like control. The aim of the study was to see the capability of texture analyser in the investigation of rheological properties of batter. The received parameters are useful in the description of the differences between the behaviours of the batters from different batters. Based on the parallel experiments the ingredients of gluten free batters can be optimized.

Keywords: texture, Herschel–Bulkleymodel, gluten free bread batter, relaxation and retardation characteristics

G. Zsivanovits, D. Iserliyska, M. Momchilova, M. Marudova

Education: Theory & Practice

The Effect of Hydrocolloids Concentration on the Physical Properties of Gluten Free Cake

Absract. In the present study the influence of hydrocolloids addition at different concentration (0.45, 0.9 and 1.5 %) to gluten-free cakes was studies and the quality of cakes was investigated. Based on investigation results it was found that, with the addition of xanthan – guar gum blend at concentrations 1.5 % (50:50 ratio) to the rice flour favorable results were achieved, represented by increased specific volume, lower loss of weight and decreased hardness of the products if compared to the control. The results from the sensory test indicated that all of the sample formulations produced high consumer acceptance rating (x6). Additionally the use of xanthan – guar gum blend (1.5 %) as well as xanthan gum (0.9 %) showed a trend to retard the staling of rice cakes in the interval between 24 and 96 hour of the storage. The enthalpy values of cakes with hydrocolloids added were lower than the control sample for the whole period of 140 h of storage.
Keywords: hydrocolloids, gluten-free cake, quality, staling, sensory analysis

D. Iserliyska, G. Zsivanovits, M. Marudova

Education: Theory & Practice

Polyelectrolyte Complex Formation of Chtosan and Casein [In Bulgarian]

Absract. In the recent decades, intensive studies have been performed on the interactions between polyelectrolytes and the possibilities for polyelectrolyte complex (PEC) formation. The main purpose of these studies is to investigate the properties of PECs and to extend their application in solving different technological and environmental problems. The interest in natural polyelectrolytes – polysaccharides, proteins, amino acids, DNA, etc., has been increased due to their role in living organisms, their bioavailability, biodegradability and uses in pharmacy and medicine. In the present study attractive, electrostatic interactions between oppositely charged polyelectrolytes have been used to prepare a novel complex between a polyampholyte casein and a natural polycation — chitosan. The complex casein/chitosan is formed during the mixing of acid chitosan solutions and basic casein solutions. The complex yield was investigated by viscometric, spectroscopic and gravimetric methods. The optimum stoichiometry of the complexes at different pH has been determined.
Keywords: polyelectrolyte complexes, chitosan, casein, pH

A. Marinova, T. Yovcheva, A. Viraneva, I. Bodurov, M. Marudova

Education: Theory & Practice

Distribution of Lamb Waves in AlScN Resonator Structures

Absract. In this paper we present the results of a simulated model of resonator device comprised of AlScN/6H-SiC piezo-layers for use in RF electronic circuits. The device uses the piezoelectric effect and Al electrode gratings to generate Lamb waves with great frequencies. The small mechanical impedance, micrometric size and good electromechanical characteristics make it especially suited for the manufacturing of RF band-pass filters. Moreover, because of the mechanics of the Lamb Wave Resonator (LWR) device, it can allow for multiple resonant frequencies to be used with the same configuration. Here we show the basic characteristics of one such system using Al0,91Sc0,09N piezo-active layer and base layer from hexagonal SiC.
Keywords: AlScN, Lamb wave, Lamb Wave Resonator (LWR), 6H-SiC, resonant frquency

B. Nedyalov, E. Valcheva

Education: Theory & Practice

Chemiluminescent and Photometric Determination of the Antioxidant Activity by Cocoon Extracts

Absract. The extract obtained during the silk production contains sericin, which exhibits good antimicrobial, anticoagulant, antioxidant and other properties that make it interesting for medical applications. In the present paper, we tested the antioxidant activity (AOA) of Bombyx mori cocoon extracts, obtained under soft extraction conditions – with ultrasound and incubation at 60 °C. For this purpose, we used tests for determination of total antioxidant activity (TAOA) – ABTS and DPPH assays, as well as chemiluminescent methods for registration of reactive oxygen species (ROS). The carried-out tests show that the cocoon extracts have AOA determined with the methods for TAOA and at the same time they can influence the quantity of ROS, which makes their activity biologically important. The extracts have stronger AO properties than the ones registered for sericin because of the extraction of additional substances with AO properties most likely with plant origin.
Keywords: silk cocoon, chemiluminescence, antioxidant activity

Y. Evtimova, V. Mihailova, L.A. Atanasova, N.G. Hristova-Avakumova, M.V. Panayotov, V.A. Hadjimitova

Education: Theory & Practice

Interdisciplinary Lectures – A Challenge for Students and Educators [In Bulgarian].

Absract. In this article we share our experience in conducting lessons of collaboration with subjects as: Physics and Astronomy, Biology and Health Education, Chemistry and Environmental Protection, Geography and Economics, History and Civilization, Fine Art: „Medicine through the eyes of three sciences, three teachers and one class“, „Ionizing rays through the eyes of one class, three sciences and three teachers“, „Electrolysis and its applications“, „The world is small – science and technology everywhere“, „Living Conditions on Earth“, „Light and Colors“.
Keywords: experience, lessons, collaboration, geography, fine art

Y. Belcheva, R. Zaharieva

Education: Theory & Practice

Research-Like Student Lab [In Bulgarian]

Absract. The work presents an approach in which an experimental assignment is carried out similarly to a scientific study in the frames of a student lab course. The approach aims to meet the students with the basic stages in experimental studies and to instill in them the excitement of shared “discoveries”. It was first tested in the frames of a General physics lab course with 76 freshman students majoring in Molecular biology. In contrast to classical labs, the proposed approach involved: application of the scientific method, selecting an applicable experimental method, out-of-class teamwork, drawing conclusions from the obtained results and presenting the results in public. The selected assignments can be completed with common materials, simple equipment and smartphone applications. The current work summarizes the observation of the involved faculty and the results from a survey among the students. The stages that the students had most difficulty with were identified as the following: setting up a hypothesis, modeling the physical processes, processing the results and drawing conclusions from them, and cooperating with team members. It was concluded that the proposed educational approach can be inspiring and useful for the development of the students’ critical thinking and creativity. Furthermore, it is widely applicable to students at different levels of competence.
Keywords: physical laboratory, research-like approach

I. Dimitrova, G. Goev, S. Georgieva, T. Tsanova, L. Ivanova, B. Georgiev

Curriculum Matters

Historical Development of the Conceptions of Reversibility and Chemical Equilibrium – A Base for Their Teaching and Learning [In Bulgarian]

Absract. Chemical equilibrium is a key conception in chemistry education both at high school and university. The teaching and learning of chemical equilibrium are associated with difficulties which can be related to the introduction of specific historical views. In the present research a review of the historical development of key conceptions, related to chemical equilibrium, is conducted, namely – incomplete reactions, reversibility, equilibrium constant and dynamics. The possibilities of applying that part of the history of chemistry in teaching context are discussed for better understanding of the contents and nature of science; for using teaching methods, which develop students’ thinking and improving the understanding of teachers of students’ difficulties and misconceptions.
Keywords: history of chemistry, chemistry education, reversibility, chemical equilibrium

K. Atanassov, A. Gendjova

Teaching Efficiency

Instruments for Using the Chemical Experiment and Self-Assessment in the Strategies for Axtive Teachimg in Man and Nature Subject [In Bulgarian]

Absract. In this paper the author shares her own teaching experience and suggests instruments for realisation of a laboratory work of “Chemical properties of substances” 6th grade and for self-assessment of students’ individual work and assessment of students’ group work. The laboratory work aims at developing skills for self-planning, skills for describing work and observations, and interpreting the results. The laboratory work was conducted with 98 pupils from „Jane Sandanski“ Primary School in Plovdiv in the year 2017/2018. Self-assessment cards show high self-assessment and excellent student motivation.
Keywords: chemical experiment, self-assessment, active learning, Man and Nature

K. Ivanova

Advanced Science

Methul, The Smallest Alkyl Group with Stunning Effects

Absract. In several instances, methyl group was found to play a pivotal role when present in a molecule. Its hydrophobic character has been the key success factor for specific performances when lipophilicity is the basic requirement for a phenomenon to occur. In some cases, chemical reactivity and physical phenomena are specifically linked to the effects of methyl group.
Keywords: caffeine, chemiluminescence, chocolate, fragrance, methyl, NLAP, SOA

S. Moulay

Advanced Science

The Fourth State of Matter

Absract. It is shown that quantum entanglement is the only force able to maintain the fourth state of matter, possessing fixed shape at an arbitrary volume. Accordingly, a new relativistic Schrödinger equation is derived and transformed further to the relativistic Bohmian mechanics via the Madelung transformation. Three dissipative models are proposed as extensions of the quantum relativistic Hamilton-Jacobi equation. The corresponding dispersion relations are obtained.
Keywords: Fourth state of matter; quantum entanglement; quantum potential.

R. Tsekov

Reviews

New Dimensions of Learning: Synthesis of Innovations and Traditions (Kostova, 2108) [In Bulgarian]

A. S. Georgiev

Свързани статии:

Сп. „Химия“, книжка 1/2018 Сп. „Химия“, книжка 2/2018 Сп. „Химия“, книжка 3/2018 Сп. „Химия“, книжка 4/2018