The Influence of Carbonized Polymer Dots on Mechanical Properties of Polyurethane Foil

Nanocomposites of carbonized polymer dots (CPD) and polyurethane (PU) are promising materials. In order to use a material in a wide range of applications, it is necessary to know its mechanical properties. In this study, two CPD/PU nanocomposites, with different CPD, from citric acid/urea (CAUR) and from phloroglucinol (PHL), as well as the reference PU foil, were mechanically characterized. CAUR-CPD was synthesized by 2.1 g of citric acid and 1.8 g of urea, dissolved in 50 mL of acetone. PHL-CPD was synthesized by 500 mg of PHL mixed in 50 mL of acetone. Both solutions were transferred to a Teflon-lined autoclave for heating. After the condensation reactions, the products of CAUR-CPD and PHL-CPD were filtered and centrifuged to remove the unreacted precursors. The CAUR-CPD/PU and PHL-CPD/PU nanocomposites were prepared by dipping PU foil (0.2 mm thick) in CAUR-CPD or PHL-CPD solution in acetone. The swelling-shrink-encapsulation method was used to encapsulate the CAUR-CPD and PHL- CPD in PU. The samples were dried in a vacuum furnace to eliminate acetone from the composites. The mechanical properties were determined on universal testing machine Shimadzu, AG-X plus 10 kN. The samples were prepared in the form of plates with a width of 8 mm. The distance between the grips was 50 mm. The strain rate was set to 1 mm/min for determination of E modulus and to 50 mm/min until the end. Each sample was measured 5 times and the average values were taken. The reference PU sample showed the highest elastic modulus (33.3 MPa) and tensile strength (25.8 MPa). The nanocomposites, CAUR-CPD/PU and PHL-CPD/PU, showed similar mechanical properties: a lower elastic modulus (18.8 and 18.6 MPa, respectively) and tensile strength (14.6 and 16.9 MPa) but much higher strain at break (650 and 608 %) than the reference PU foil (434 %).29th International Symposium on Analytical and Environmental Problems : Proceedings; November 13-14, 2023; Szeged, Hungary

Employing Gamma-Ray-Modified Carbon Quantum Dots to Combat a Wide Range of Bacteria

Nowadays, it is a great challenge to develop new medicines for treating various infectious diseases. The treatment of these diseases is of utmost interest to further prevent the development of multi-drug resistance in different pathogens. Carbon quantum dots, as a new member of the carbon nanomaterials family, can potentially be used as a highly promising visible-light-triggered antibacterial agent. In this work, the results of antibacterial and cytotoxic activities of gamma-ray-irradiated carbon quantum dots are presented. Carbon quantum dots (CQDs) were synthesized from citric acid by a pyrolysis procedure and irradiated by gamma rays at different doses (25, 50, 100 and 200 kGy). Structure, chemical composition and optical properties were investigated by atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, UV-Vis spectrometry and photoluminescence. Structural analysis showed that CQDs have a spherical-like shape and dose-dependent average diameters and heights. Antibacterial tests showed that all irradiated dots had antibacterial activity but CQDs irradiated with dose of 100 kGy had antibacterial activity against all seven pathogen-reference bacterial strains. Gamma-ray-modified CQDs did not show any cytotoxicity toward human fetal-originated MRC-5 cells. Moreover, fluorescence microscopy showed excellent cellular uptake of CQDs irradiated with doses of 25 and 200 kGy into MRC-5 cells

A study of functioning of thylakoid membranes in inbred lines of maize (Zea mays L.)

Thermal processes of delayed chlorophyll fluorescence (DF) within an intact leaf segment of inbred lines of maize (Zea mays L.) within the temperature range of 24-60°C were studied. The method for chlorophyll DF measurements is non-invasive and was developed in order to study the connection between bioluminescence and photosynthesis. Two maize inbreeds (ZPPL 52 and ZPLK 132), that are considered to have a scientific and professional value in breeding, were observed. Obtained results on the temperature dependence of chlorophyll DF indicated that the inbred ZPPL 52 is more resistant to temperatures. The first temperature effect in this inbred was observed at 34°C, while the maximum chlorophyll DF intensity is registered at 60°C. The corresponding estimates in the inbred ZPLK 132 were detected at 31.5°C and 52.0°C, respectively. The air drought treatments of the inbred ZPLK 132 lowered the stated temperatures to 30.5°C, i.e. 47.5°C, respectively. Conformational changes were observed in thylakoid membranes of studied maize inbred lines. The obtained changes were determined by the number and the grade of critical temperatures. There were four critical temperatures in each of the studied inbreeds, while there were five critical temperatures in the inbred ZPLK 132 under air drought treatment. Different levels of activation energy (Ea, kJ mol-1) for chlorophyll DF thermal processes varied from -21,7 and -22.00 to 241.44 kJ mol-1. The values of Ea obtained in observed maize inbred lines differ over the number, sign and magnitude. Negative Ea values were detected in all cases of chlorophyll DF intensity increases with the temperature increase, which was established for the first time. Such values of Ea are explained by conformational changes in chlorophyll molecules and by their reactivity. Results and discussion of presented parameters of total thermal processes of chlorophyll DF (temperature dependence, critical temperatures and activation energy), can be an important factor for a more exact characterisation of maize inbred lines in relation to their resistance and adaptation to temperature and drought, contributing to a more rapid and rational development of the selection process

Photosynthetic properties of elite erect leaf maize inbred lines and their contribution to seed production improvement

A hypothesis that elite erect leaf maize inbred lines are characterized by properties of an efficient photo-model and that as such are very desirable in increasing the number of plants per unit area (plant density) in the process of seed production has been confirmed in the present study. The properties of the observed elite erect leaf maize inbred lines were based on the effects and characteristics of thermal processes of delayed chlorophyll fluorescence occurring in their thylakoid membranes. The temperature dependence of the delayed chlorophyll fluorescence intensity, the Arrhenius plot for the determination of phase transitions (critical temperatures) and activation energy are the principal parameters of the thermal processes. Based on the obtained results on photosynthetic properties it was also possible to estimate the tolerance and adaptation of elite erect leaf maize inbred lines to high temperatures and drought

Problems in weed control in Serbian maize seed production

Weed control in the seed maize production is facing some specific problems. Maize inbred lines are known to be susceptible to many stress factors, including actively growing weeds and some herbicides. The slower growth of maize inbreds, as well as, the open space between rows provide favourable conditions for emergence and growth of weeds during the whole growing season. Herbicide combinations applied in the seed maize production are the same as those applied in the commercial maize production, but, their efficiency is differently expressed in these crops. Environmental factors significantly affect weeds and maize development, as well as, herbicides affect maize inbred lines. The introduction of sulfonylurea herbicides, controlling grass weeds, has resulted in susceptibility of a greater number of maize inbred lines. Therefore, it was found that reaction of maize inbred lines gives a wide variability to sulfonilurea herbicides. Considering specificity of maize inbred lines, this study presents some problems in weed control in maize seed production

Sixty years of ZP maize hybrid breeding

The modern ZP maize hybrids breeding at the Maize Research Institute, Zemun Polje, begun during the fifties of the 20(th) century. Collecting of the initial material was the first step in conducting maize breeding programs. The maize inbred line-developing programs from three local populations has initiated in 1953. That was beginning of breeding first cycles ZP maize hybrids. From that period up to present time, we have had five generations of ZP maize hybrids. Each generation has characterized by introduction of the new potentially higher yielding hybrids and with better other agronomics characteristics. According to results from different studies, the genetic yield potential of ZP maize hybrids over the last 40 years amounted to 100 kg.ha(-1) per year. ZP 755 was the first registered maize hybrid in the country in 1964. Total 499 ZP maize hybrids have released by the State Government Commission's since 1964 and 99 ZP maize hybrids have registered in 15 countries. Since the seventies biotechnology methods have been applied in the breeding programs. The main part of biotechnology work is based on the molecular marker application for determining genetic diversity, QTL mapping for drought tolerance and identification of chromosome regions harbouring QTLs for economically important traits (yield, kernel oil content)

Facile synthesis of L-cysteine functionalized graphene quantum dots as a bioimaging and photosensitive agent

Nowadays, a larger number of aggressive and corrosive chemical reagents as well as toxic solvents are used to achieve structural modification and cleaning of the final products. These lead to the production of residual, waste chemicals, which are often reactive, cancerogenic, and toxic to the environment. This study shows a new approach to the modification of graphene quantum dots (GQDs) using gamma irradiation where the usage of reagents was avoided. We achieved the incorporation of S and N atoms in the GQD structure by selecting an aqueous solution of L-cysteine as an irradiation medium. GQDs were exposed to gamma-irradiation at doses of 25, 50 and 200 kGy. After irradiation, the optical, structural, and morphological properties, as well as the possibility of their use as an agent in bioimaging and photodynamic therapy, were studied. We measured an enhanced quantum yield of photoluminescence with the highest dose of 25 kGy (21.60%). Both S- and N-functional groups were detected in all gamma-irradiated GQDs: amino, amide, thiol, and thione. Spin trap electron paramagnetic resonance showed that GQDs irradiated with 25 kGy can generate singlet oxygen upon illumination. Bioimaging on HeLa cells showed the best visibility for cells treated with GQDs irradiated with 25 kGy, while cytotoxicity was not detected after treatment of HeLa cells with gamma-irradiated GQDs