Margareta Vrtačnik

Students' understanding of molecular structure representations

The purpose of the investigation was to determine the meanings attached by students to the different kinds of molecular structure representations used in chemistry teaching. The students (n = 124) were from primary (aged 13-14 years) and secondary (aged 17-18 years) schools and a university (aged 21-25 years). A computerised Chemical Visualisation Test was developed and applied. The research indicates that students appreciation of three-dimensional molecular structures differs according to the kind of representation used. The best results were achieved with the use of concrete, and pseudo-concrete types of representations (e.g. three-dimensional models, their photographs, computer-generated models). However, the use of more abstract types (e.g. schematic representations, stereochemical formula) was less effective. A correlation between students results on the Chemical Visualisation Test and their educational level, spatial visualisation, and spatial relations skills was shown statistically, but no statistically significant gender differences were observed.

Effect of the antifungal activity of oxygenated aromatic essential oil compounds on the white-rot Trametes versicolor and the brown-rot Coniophora puteana

Abstract Essential oils and their constituents have a long history of applications as antimicrobial agents, but their use as wood preservatives has not yet been reported. In this study, 22 essential oil phenols, phenol ethers, and aromatic aldehydes have been tested for their antifungal activity against the wood-decaying fungi Trametes versicolor and Coniophora puteana . Minimal inhibitory concentrations of the selected compounds added to potato dextrose agar (PDA) in defined concentrations were determined by a screening test with the agar dilution method. A significant difference in the tolerance of the tested fungi towards the selected compounds was discovered and attributed to the differences in their metabolic characteristics. The influence of the chemical structure of the tested essential oil compounds on their antifungal activity is also discussed.

Evaluating the Educational Value of Molecular Structure Representations

An investigation examined the value of various representations (e.g. concrete three-dimensional models, virtual computer models, static two-dimensional computer models, stereo-chemical formulas) in supporting the achievement by students of an effective perception of molecular structures. Additionally, the usefulness was studied of concrete three-dimensional models, virtual computer molecular models, and their combination, as help tools for students in solving spatial chemistry tasks involving three-dimensional perception, rotation and reflection. Altogether 477 students from secondary schools (age: 18–19 years) took part in the investigation. For purpose of the inquiry a set of four Molecular Visualization Tests was developed. Information about students` manner of thinking while solving spatial tasks was initially gained with a questionnaire and then examined in depth with a structured interview. The data was processed by methods suitable for the respective quantitative and qualitative approaches taken. The results suggest that the information sources which serve as a foundation for students’ perception of molecular structure decrease in value from concrete models, to virtual models, to static computer models. Students’ perception of three-dimensional structure was better when a stereo-chemical formula was used in comparison to that supported by a computer image. The results indicate that both molecular models types used as help-tools can ease the solving of chemistry tasks that require three-dimensional thinking. Virtual computer models seem to be as effective as concrete models, but the combined usage of both can cause splits in students’ attention and therefore seems to be less appropriate.

HQSAR and CoMFA approaches in predicting reactivity of halogenated compounds with hydroxyl radicals

Two quantitative structure-activity relationship (QSAR) methods: hologram QSAR (HQSAR) and comparative molecular field analysis (CoMFa) were evaluated for predicting half-lives of the hydroxyl radicals reaction with substituted aromatic compounds. The HQSAR approach, which is topological in nature, results in a mathematical model which was more stable and has a greater predictive ability than the model derived on the 3-D CoMFA approach. Interpretations of the colour coded results of both methods are in good agreement with the proposed mechanism of the hydroxyl radical oxidation of halogenated aromatic compounds in the atmosphere.

Heterogeneous photocatalytic decomposition of halosubstituted benzyl alcohols on semiconductor particles in aqueous media

The photodegradation of 2-, 3- and 4-halosubstituted benzyl alcohols (HBAs) on semiconductive oxides (TiO2, ZnO) was studied. It was found out that the photodegradation rate increases from the fluoro to bromo derivates in the case of 2- and 4-HBAs, whereas in the case of 3-HBAs the reverse trend was observed.

The interplay of students' motivational orientations, their chemistry achievements and their perception of learning within the hands-on approach to visible spectrometry

The purpose of the study was to determine the relationship between students motivational orientations and their chemistry achievements and perception of learning within the original case of the hands-on approach to visible spectrometry. A total of 295 students from Polish and Slovenian vocational and technical high schools participated in the study. By applying the k-mean clustering procedure, two distinct clusters of students motivational orientations were identified based on the SDT theory about autonomous and controlled motivation. Students classified as the good quality motivation group (Cluster II) outperformed students in the low quantity motivation group (Cluster I) in their knowledge gained through the hands-on approach and assessed the hands-on approach more positively with regard to their active participation in learning selected concepts from visible spectrometry. Altogether, the results of the present study confirm previous research findings about the importance of the quality of students’ motivation for learning; the results show that hands-on laboratory work with autonomy-supportive teachers could create a motivating learning environment for students to learn with understanding and to cooperate with each other in academic tasks at a higher level of cognitive complexity. The main implication for teachers in chemistry classes is, therefore, to plan their teaching more systematically and creatively in order to provide students with individualised cognitively and motivationally challenging learning situations (both in terms of content and didactical methods) and to foster learning with understanding even within very abstract and cognitively complex learning tasks.

Biodegradation of PAHs by Ligninolytic Fungi Hypoxylon Fragiforme and Coniophora Puteana

ABSTRACT White-rot and brown-rot fungi degrade structural components of wood. The possibility of PAHs degradation by these fungi is based on their structural similarity with lignin (primary degraded by white-rot fungus) and hemi-cellulose and cellulose (degraded by brown-rot fungus). This study compares biodegradation level of polycyclic aromatic hydrocarbons (PAHs) using the two ligninolytic fungi Hypoxylon fragiforme (HF) and Coniophora puteana (CP). The biodegradation of ten PAHs was performed in liquid media (2% w/v in water, of malt extract and 0.5% w/v in water, solution of glucose). After 3 weeks of incubation, non-degraded pollutants were extracted by benzene and determined using the GC/MS technique. Both fungi completely degraded 1-methylnaphthalene and 2-methynaphthalene. 1-methylfluorene was also completely degraded by HF while about 62.7% of it was degraded by CP. The remaining PAHs were degraded by HF and CP fungi, respectively, in the following percentages: 82.0 and 79.0 for acenaphthene; 90.3 and 80.0 for acenaphthylene; 17.8 and 41.3 for anthracene; 5.8 and 53.8 for 1,2-benzanthracene; 0.0 and 20.3 for benzo(k)fluoranthene; 50.5 and 15.8 for byphenil; 85.8 and 74.8 for fluorene; 65.5 and 47.5 for phenanthrene; 42.5 and 50.5 for pyrene.

Biodegradation and Photooxidation Studies of Model Organic Pollutants

In the paper we present the results of biodegradation and photooxidation studies of halosubstituted benzyl alcohols. The basic goal of our research was to examine the effect of the type and position of the halogen atom in the aromatic ring on the degradation rate and to use the experimental data for the development of HQSAR models for predicting degradation rates. Biodegradation results of 2-halosubstituted benzyl alcohols correlate with the size of the halogen atom, while for 4-halosubstituted benzyl alcohols, a good correlation with the energy of C—X bond was observed. In the photooxidation process, the impact of position of the halogen on the rate of reaction is smaller. The HQSAR model was derived only for photooxidation data sets, while for the biodegradation it was not possible to obtain a model with satisfactory statistical characteristics.

Students’ Achievement in Learning Chemistry Through the Design and Construction Approach to Laboratory Activity and the Relation with their Prior Achievements and Motivation to Learn

Students’ achievement in learning chemistry through the design and construction approach to laboratory activity and the relation with their prior achievements and motivation to learn is discussed in this chapter by Vrtacnik, Sodja, and Jurisevic. Authors claim that the design and construction approach to activities in chemistry lessons for middle school students is regarded as an authentic science activity, and that this approach to learn chemistry is quite rarely practised in science classes. In this approach, students were asked to design their own experiments and control variables. The results suggest that students’ success in the design and construction approach depended upon the complexity of a particular task. A significant drop off in achievements and motivation scores was found with tasks based on more abstract thinking, e.g., analyzing data and setting up hypotheses. In evaluating the design and construction approach, students expressed the highest appreciation for a positive classroom atmosphere and their active participation in the laboratory activity. The research findings revealed that students with higher achievement in chemistry are also highly extrinsically and intrinsically motivated for learning chemistry and have a higher academic self-concept.

The impact of the type and position of the halogen atom on the biodegradation of halosubstituted benzyl alcohols

The biodegradation of 2‐halosubstituted and 4‐halosubstituted benzyl alcohols was studied using two sources of biodegrative micro‐organisms: mixed culture from the STUDA waste water treatment plant, Domžale, and the white rot fungus Phanerochaete chrysosporium strain MZKI B‐223 (ATCC 24725). The results obtained by this study indicate the interrelationship between the types of micro‐organism used in the experiments and the type and position of the halogen element on the aromatic ring.