Maria Roulia

Biofunctional characteristics of lignite fly ash modified by humates: a new soil conditioner.

Fly ash superficially modified with humic substances from the Megalopolis lignitic power plant was prepared and evaluated for agricultural uses. UV-vis spectrophotometry and IR spectroscopy revealed that fly ash shows high sorption efficiency towards humic substances. Adsorption proceeds stepwise via strong Coulombic and hydrophophic forces of attraction between guest and host materials. Langmuir, Freundlich, BET, Harkins-Jura, and Dubinin-Radushkevich isotherm models were employed to evaluate the ongoing adsorption and shed light to the physicochemical properties of the sorbent-adsorbate system. Humic substances desorption and microbial cultivation experiments were also carried out to examine the regeneration of the humates under washing and explore the possibility of this material acclimatizing in real soil conditions, both useful for biofunctional agricultural applications.

THE USE OF THE ARRHENIUS EQUATION IN THE STUDY OF DETERIORATION AND OF COOKING OF FOODS SOME SCIENTIFIC AND PEDAGOGIC ASPECTS

Conservation and cooking of foods can be used by students and instructors to demonstrate a fundamental relation of chemical kinetics, the Arrhenius equation. By plotting the logarithms of available conservation and cooking times versus the corresponding inverse temperatures, apparent activation energies for both the deterioration and the cooking of foods of various compositions can be obtained. Such simple applications lead to meaningful results. Examples of deviation from the Arrhenius equation are given by plotting data (shelf-life of certain frozen food at various temperatures) given on the food package. A better fit is obtained by applying a second order polynomial regression to the data. Cooking time (lnt) vs. the inverse of temperature for five categories of foods is also examined and for each category there appears to be a common rate-determining step. Detailed results are presented for the meat category. The pedagogic aspects of the use of Arrhenius equation in the study of deterioration and of cooking of foods are also presented. [Chem. Educ. Res. Pract. Eur.: 2002, 3, 87-97]

Structurally Diverse Metal Coordination Compounds, Bearing Imidodiphosphinate and Diphosphinoamine Ligands, as Potential Inhibitors of the Platelet Activating Factor

Metal complexes bearing dichalcogenated imidodiphosphinate [R2P(E)NP(E)R2′]− ligands (E = O, S, Se, Te), which act as (E,E) chelates, exhibit a remarkable variety of three-dimensional structures. A series of such complexes, namely, square-planar [Cu{(OPPh2)(OPPh2)N-O, O}2], tetrahedral [Zn{(EPPh2)(EPPh2)N-E,E}2], E = O, S, and octahedral [Ga{(OPPh2)(OPPh2)N-O,O}3], were tested as potential inhibitors of either the platelet activating factor (PAF)- or thrombin-induced aggregation in both washed rabbit platelets and rabbit platelet rich plasma. For comparison, square-planar [Ni{(Ph2P)2N-S-CHMePh-P, P}X2], X = Cl, Br, the corresponding metal salts of all complexes and the (OPPh2)(OPPh2)NH ligand were also investigated. Ga(O,O)3 showed the highest anti-PAF activity but did not inhibit the thrombin-related pathway, whereas Zn(S,S)2, with also a significant PAF inhibitory effect, exhibited the highest thrombin-related inhibition. Zn(O,O)2 and Cu(O,O)2 inhibited moderately both PAF and thrombin, being more effective towards PAF. This work shows that the PAF-inhibitory action depends on the structure of the complexes studied, with the bulkier Ga(O,O)3 being the most efficient and selective inhibitor.

Preparation of bioinorganic fertilizing media by adsorption of humates on glassy aluminosilicates

Surface-modified expanded perlite was synthesized using humic substances from the Megalopolis peaty lignite. Adsorption is efficient and increases at higher temperatures and lower pHs. The preparation can be carried out under mild conditions leading to an eco-friendly, bioinorganic material useful as soil conditioner and biofertilizer. Six adsorption models were applied; the Klotz, Freundlich and Redlich-Peterson isotherms fit more successfully to the experimental data. The obeying of the theoretical models was correlated with the heterogeneity and non-uniform distribution of the adsorption sites, host-guest attraction forces as well as the formation of self-assembled aggregates and self-organized multilayers of humic substances onto the aluminosilicate adsorbent, consistent with changes in micromorphology. Thermodynamic quantities revealing distinct physicochemical characteristics of the adsorption phenomena, i.e., enthalpy, entropy and free energy change, were calculated. Desorption experiments and cultivation of microorganisms demonstrated that perlite may act successfully as host material for microbial populations upgrading the humic-loaded perlite for soil applications.

Innovative biocatalytic production of soil substrate from green waste compost as a sustainable peat substitute.

In the present work, a new simple and quick eco-friendly method is discussed to handle effectively the green wastes and produce a sustainable peat substitute of high quality on the large scale. Principal physicochemical parameters, i.e., temperature, moisture, specific weight, pH, electrical conductivity and, also, microorganisms, organic matter, humic substances, total Kjeldahl nitrogen and total organic carbon, C/N ratio, ash, metal content and phytotoxicity, were monitored systematically. Humic substances content values were interrelated to both C/N ratio and pH values and, similarly, bulk density, TOC, TKN, C/N, GI, ash and organic matter were found interconnected to each other. A novel biocatalyst, extremely rich in soil microorganisms, prepared from compost extracts and peaty lignite, accelerated the biotransformation. Zeolite was also employed. The compost does not demonstrate any phytotoxicity throughout the entire biotransformation process and has increased humic substances content. Both humic substances content and germination index can be employed as maturation indices of the compost. Addition of compost, processed for 60 days only, in cultivations of grass plants led to a significant increase in the stem mass and root size, annotating the significant contribution of the compost to both growth and germination. The product obtained is comparable to peat humus, useful as peat substitute and can be classified as a first class soil conditioner suitable for organic farming.

AN INTERDISCIPLINARY MODEL FOR TEACHING THE TOPIC “FOODS”: A CONTRIBUTION TO MODERN CHEMICAL EDUCATION

Modern chemical education aims at teaching based on critical thinking, problem solving and decision-making that may be developed through an interdisciplinary approach. An interdisciplinary model for teaching the topic “foods” is suggested. The goal of the suggested approach is for students to develop their evaluative thinking in order to adopt a responsible behaviour towards health. The proposed model consists of four main steps: i) programming/planning of the teaching strategy; ii) orientation/participation of the students in the procedure; iii) treatment of the subject and presentation of the work produced; and iv) evaluation (group and self-evaluation) of the work. The application of our project confirms that the main objective of our model, that is the promotion of HOCS learning, has been achieved since the students learned to distinguish and to decide about choosing foods which are not harmful for their health, to evaluate advertisements about foods and to distinguish/decide about the misleading ones, to express their ideas on health aspects and critically discuss them, to compare various dietary products and to evaluate them. Our project’s pedagogic value is reflected on the fact that during its application students participating in the teamwork developed skills and behavioral attitudes such as cooperation, communication, involvement, adjustability, action, mutual support and acceptance of the individuality of each member of the team that will be important for them as citizens. [Chem. Educ. Res. Pract.: 2004, 5, 143-155]