Publications

Abstract The paper presents geoecological evaluation of the city of Loznica for the purposes of sports and recreational tourism based on quantitative method of diversity, V-Wert Method. Using the GIS tool by the quantitative method, the criteria of natural components (relief, forest, water surface and climate) are evaluated for the analyzed area. In the proposed method, the climate factor was supplemented by the analysis of the bioclimatic index Universal Thermal Climate Index (UTCI). When the evaluation was completed, the final results were obtained based on which the degrees of convenience of different parts of the analyzed area have been presented. Out of the total analyzed surface, which amounts to 705 km(2), favorable surfaces comprise 21 km(2) (2.98%), and very favorable surfaces comprise 33 km(2), i.e. 4.68% of the territory. The largest area consists of conditionally favorable terrains - 33 km(2) (47.23%). Since one of the basic strategic priorities of the City of Loznica is improvement and development of sports and recreational tourism, the aim of this analysis is to emphasize the potential of the mentioned area in terms of general suitability of the terrain for the development of this type of tourism.

Abstract The effect of pH of precursor solution has studied on structural and up/downconversion emission properties of Ho3+/Yb3+ doped Gd2O3 host synthesized through hydrothermal route. Best sample morphology (rod-shaped) is found corresponding to the pH value of pH-9.1 of the precursor solution. Due to the low phonon frequency of Gd2O3 host, intense green upconversion emission around 539, 550nm wavelength is observed from the sample on 980nm diode laser excitation. In down conversion emission mode, bands around 539, 550nm and 653nm are found on 449nm arc lamp excitation. The prepared samples were further studied for cathodoluminescence and the effect of magnetic field on the upconversion emission. The sample has also shown optical bi-stability in upconversion emission when the magnetic field was increased from zero to 1.05x10(4) Oe and then decreased to zero.

Abstract Steady-state and time-resolved fluorescence techniques were employed to study a superphotoacid with a pK(a)* of similar to-7, the chlorobenzoate phenol cyanine picolinium salt (CBCyP) in acetonitrile-water mixtures. We found that the time-resolved fluorescence is bimodal. The amplitude of the short-time component depends on chi(water); the larger chi(water), the greater the amplitude. We found that the excited-state proton transfer (ESPT) rate constant, k(PT), is >= 5 X 10(12) s(-1) in mixtures of chi(water) >= 0.08, whereas in neat water, k(PT), = 6 X 10(12) s(-1). The long-time component has a lifetime of 50 ps at chi(water) = 0.75. We attribute this time component to the CBCyP molecules that are not hydrogen-bonded to H2O clusters. The results suggest that the ESPT rate constant to water in acetonitrile-water mixtures depends only slightly on the water cluster size and structure surrounding the CBCyP molecule. We attribute the independence of the ESPT rate on the average water-cluster size to the large photoacidity of CBCyP. QM TD-DFT calculations found that in the excited-state the RO-(S-1) species that is formed by the ESPT process is more stable than the ROH(S-1) species by -5 kcal/mol when four water molecules accept the proton, and when six water molecules accept the proton, the RO-(S-1) drops to -10 kcal/mol. The calculations show that energy stabilities are kept constant in implicit CH3CN-H2O solvent mixtures of dielectric constant of epsilon >= 45.

Abstract In the present work, we report the standard combustion energies of 2-mercapto-l-methylimidazole, 2-mercapto-5-aminobenzimidazole and 2-mercapto-5-methoxybenzimidazole, obtained experimentally from measurements with a rotatory-bomb combustion calorimeter. With these data, for each one of the three aforementioned compounds, the corresponding standard molar combustion enthalpies and the standard molar enthalpies of formation, in the crystalline phase, are calculated. The enthalpies of sublimation of each compound, obtained experimentally using a Calvet Setaram HT 1000 microcalorimeter, are also reported. Using the values of the enthalpies of formation in the crystalline phase and the enthalpies of sublimation, both at 298.15 K, for each compound, the corresponding standard molar enthalpies of formation in gas phase were calculated. Complementary, the enthalpies of formation in the gaseous phase were derived from theoretical calculations made with Gaussian-n composite methodology with n = 3 and 4. The experimental and computational studies suggest that in gaseous phase, the form more stable of each compound is the thione form. (C) 2018 Elsevier Ltd.

Abstract Nanotechnology has led to the development of new nanomaterials with unique properties and a wide variety of applications. In the present study, we focused on the cellular uptake of a group of nanoparticles with a single metal core by pancreatic cancer cells, which has been studied by Yap et al. (Rsc Advances, 2012, 2 (2):8489-8496) using classification models. In this work, the development of a further Quantitative Nanostructure Activity Relationship (QNAR) model was performed by linear multiple linear regression (MLR) and nonlinear artificial neural network (ANN) techniques to accurately predict the cellular uptake values of these compounds by dividing them into three groups. Judging from the attained statistical results, our derived QNAR models have an acceptable overall accuracy and robustness, as well as good predictivity on the external data sets. Moreover, the results of this study provide some insights on how engineered nanomaterial features influence cellular responses and thereby outline possible approaches for developing and applying predictive computational models for biological responses caused by exposure to nanomaterials.

Abstract The authors have synthesized water-dispersible NaYF4: Er3+/Yb3+ upconversion particles via a thermal decomposition route and optimized the green upconversion emission through a concentration variation of the Yb3+ sensitizer. The prepared particles were found to be ellipsoid in shape having an average particle dimension of 600 x 150 nm. It is observed that the sample with 18 mmol% Yb3+ ion concentration and 2 mmol% Er3+ ion gives optimum upconversion intensity in the green region under 980 nm excitation. Colloidal dispersibility of the sample in different solvents was checked and hexane was found to be the best medium for the prepared particles. The particle size of the sample was found to be suitable for the preparation of colloidal ink and security writing on a plain sheet of paper. This was demonstrated successfully using ink prepared in polyvinyl chloride gold medium.

Abstract Experimental and computational studies were performed in this work with the aim of evaluating and understanding the energetic effect inherent to the substitution of the hydrogen of the morpholine amino group by aminoalkyl substituents: N-(2-aminoethyl)morpholine and N-(3-aminopropyl)morpholine. The standard enthalpies of vaporization and the standard energies of combustion of the two morpholine derivatives obtained, respectively, from Calvet microcalorimetry and combustion calorimetry measurements, are reported. These data were used to derive the standard enthalpies of formation of the morpholine derivatives, in the liquid and gaseous phases, at T=298.15 K. The computational study involved the energetic analysis of the most stable conformers on the potential energy surfaces and the determination of their gas-phase standard enthalpies of formation at the reference temperature of 298.15 K. All the computational calculations were performed using the G3(MP2)//B3LYP composite method. The combination of experimental and computational data determined in this work for morpholine derivatives, together with other available in the literature for related molecules, enabled the analyses of the energetic effects associated with the substitution of the hydrogen of the morpholine amino group by substituents aminoalkyl and alkyl, as well as the establishment of incremental schemes for the determination of the gas-phase enthalpies of formation. (C) 2018 Elsevier Ltd.

Abstract The energetic study of 6-methyl-1-indanone, 6-methoxy-1-indanone and 5,6-dimethoxy-1-indanone has been developed using calorimetric techniques and a computational methodology. The enthalpies of combustion and of sublimation of these compounds were determined from, respectively, static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry. From these experimental data, the gas-phase standard molar enthalpies of formation were derived. Also, the temperature and the enthalpy of fusion of each compound were obtained by differential scanning calorimetry. Additionally, the gas-phase standard molar enthalpies of formation of these compounds were obtained from high-level ab initio calculations, at the G3(MP2)//B3LYP level of theory. The computational approach of these three indanone derivatives allowed us to establish their molecular structures, the co-existence of two and four stable conformations for 6-methoxy-1-indanone and 5,6-dimethoxy-1-indanone, respectively. Furthermore, the energetic effects associated with the presence of one methyl group and one or two methoxy groups in the indanone structure were evaluated. These enthalpic increments were compared with the homologous substitutions in the benzene and naphthalene molecules.

Abstract Coelenterazine is a common substrate used by marine species in enzyme-catalyzed bioluminescent reactions, in which thermal energy is converted into excitation energy. Coelenterazine is also known to emit chemiluminescence, in the absence of enzymes. Moreover, the scaffold of this molecule is present in organisms of eight phyla, making it a prototypical system for marine chemi-/bioluminescence. The characterization of the chemiexcitation step responsible for light emission is essential for future applications in bioimaging, bioanalysis and biomedicine. We have found evidence to support the identification of a neutral dioxetanone intermediate as the responsible for efficient chemiexcitation. This is explained by attractive electrostatic interactions between the CO2 and Coelenteramide moieties, which allow the reacting dioxetanone to spend time in a PES region of degeneracy between singlet ground and excited states. Contrary to expected, there is no relationship between electron (ET)/charge (CT) transfer, from an electron-rich moiety to the peroxide, and efficient chemiexcitation. Thus, neither Chemically Induced Electron-Exchange Luminescence (CIEEL) nor Charge Transfer-Initiated Luminescence (CTIL) can be used to explain imidazopyrazinone-based chemi-/bioluminescence. We have also found a concentration-dependent quenching effect, more prevalent at acidic pH.

Abstract Coelenterazine is a common substrate used by marine species in enzyme-catalyzed bioluminescent reactions, in which thermal energy is converted into light-emission. Besides bioluminescence, Coelenterazine is also known to emit chemiluminescence in aprotic solvents. We report here the study of Coelenterazine chemiluminescence in aqueous solution. Water inhibits light-emission even in mixtures with water content as low as 20%. Moreover, we provide convincing spectroscopic evidence that the presence of water affects the ground state (S-0) chemical reaction, and not the excited state processes (as chemiexcitation and the fluorescent quantum yield). However, the energetics of the S-0 chemical reaction is not affect by addition of water, which points to the inhibition being caused by the reduced lifetime of superoxide anion in water, which is an intermediate in the luminescent reactions of Coelenterazine. This finding indicates that one of the catalytic roles of bioluminescent enzymes is to extend the lifetime of this radical.