Slobodan Gadžurić

Thermochromic complex compounds in phase change materials: Possible application in an agricultural greenhouse

The possibility to combine two physico-chemical phenomena is studied in this work in order to attain simultaneous control of temperature and light intensity in a greenhouse: (a) isothermal heat storage in phase change materials and (b) thermochromic behavior of complex compounds dissolved in the phase change materials. Two binary mixtures melting near the ambient temperature were studied: (a) 0.925 Ca(NO3)2·4.06 H20+0.075 CaCl2·6.11 H2O melting at 35.6°C and (b) 0.9 CH3CONH2+0.1 Ca(NO3)2·4 H2O, melting at 27.7°C. The melting temperature, the enthalpy of fusion and the heat capacity of both mixtures were determined from DSC measurements. Both mixtures showed to be suitable solvents for the formation of consecutive cobalt(II) chloride complexes. The compositions of the complex compounds were adjusted in each mixture so that the absorption spectra in visible spectral range exhibited low absorbance at the melting temperature and a pronounced increase of the absorbance and/or change of color with the increase of temperature in the range relevant for passive solar energy receivers. The combined latent heat storage and the outstanding reversible change of the optical properties of the dissolved complex compounds with temperature is proposed to be applied in solar heated agricultural greenhouses in areas with fluctuating climate conditions. The increase of absorbance with temperature acts as an auto-regulated shading protection from overheating.

DFT study of 1-butyl-3-methylimidazolium salicylate: a third-generation ionic liquid

A detailed theoretical investigation of the third-generation ionic liquid (IL) 1-butyl-3-methylimidazolium salicylate ([BMIM][Sal]), performed within the framework of density functional theory (DFT), is presented in this paper. The B3LYP-D3, M06-2X, and M06-2X-D3 functionals were used to obtain the equilibrium geometries of the two ions [BMIM]+ and [Sal]–. It is shown that the equilibrium ion geometries obtained with the dispersion-corrected B3LYP functional are very close to the ion geometries obtained with the M06-2X and M06-2X-D3 functionals. Global reactivity was assessed using molecular orbital theory and quantum molecular descriptors. Molecular electrostatic potential (MEP) surfaces and average local ionization energy (ALIE) surfaces were created in order to elucidate the charge distribution and reactivity of the investigated IL. Ion-pair binding energies were calculated with all three functionals, and the results confirmed the presence of a strong electrostatic interaction between the ions, while further insight into the interactions between the two ions was obtained by analyzing noncovalent interactions based on the reduced density gradient (RDG) surface, which revealed a total of nine interactions between the ions. Finally, the aromaticity of each ion was investigated by calculating the nucleus-independent chemical shift (NICS) parameter, which indicated that significant changes in the charge delocalization on each ion occur when the two ions interact.

Investigation of 1,2,3-trialkylimidazolium ionic liquids: experiment and density functional theory calculations

Physico-chemical properties, thermal stability and bonding in 1,2,3-trialkylimidazolium based ionic liquids (ILs) were investigated by viscosity and density measurements together with thermogravimetric analysis (TGA) and IR spectroscopy. The obtained results were compared to those obtained for the corresponding 1,3-dialkylimidazolium based ILs. To obtain more insight into the influence of the methylation at position C-2 of the imidazolium ion, IR spectra were calculated with the help of density functional theory (DFT) calculations. The reduction in bonding intensity between ions was confirmed as a consequence of chain reduction and methylation. In this regard, DFT calculations indicated a much higher influence of methylation and these results were explained through the analysis of inter-molecular non-covalent interactions (NCIs). Intra-molecular NCIs together with quantum molecular descriptors were also applied for the explanation of thermal stability of the investigated ILs.

Competition between Cation-Solvent and Cation-Anion Interactions in Imidazolium Ionic Liquids with Polar Aprotic Solvents.

The subtle interplay between ion solvation and association was analyzed in mixtures of imidazolium-based ionic liquids (ILs) with polar aprotic solvents. A site-specific pattern of cation-solvent and cation-anion interactions was disclosed by a careful analysis of the 1 H and 13 C NMR chemical shift dependence of the mixture composition. It was established that the less polar but more donating γ-butyrolactone is more prone to establish H-bonds with the imidazolium-ring hydrogen atoms of the IL cations than propylene carbonate, particularly at the H2 site and at high dilutions xIL <0.1. The H2 site was found to be more sensitive to intermolecular interactions compared to H4, 5 in the case of ILs with asymmetric anions like trifluoromethanesulfonate (TfO- ) or bis(trifluoromethylsulfonyl)amide (TFSA- ).

Advanced oxidation processes for the removal of [bmim][Sal] third generation ionic liquids: effect of water matrices and intermediates identification

Unique properties of ionic liquids make them green alternatives for conventional volatile organic compounds. Due to increased production and the high stability of these substances, they could be classified as persistent pollutants and could break through classical treatment systems into natural waters. A preliminary ionic liquid hydrolysis study demonstrated a pH dependent degradation profile with a significant decrease in hydrolysis efficiency as pH lowered from 10.0 to 2.8. In order to examine future prospects for ionic liquid removal, different advanced oxidation processes (TiO2 Degussa P25/H2O2, TiO2 Degussa P25, 7.2Fe/TiO2/H2O2, and H2O2) were studied for their applicability in the degradation of imidazolium-based ionic liquids in aqueous solution. These processes were conducted in the dark as well as in the presence of UVA and simulated sunlight (SS) radiation. Among the investigated dark processes, the 7.2Fe/TiO2/H2O2 system showed the highest efficiency, which can be attributed to a dark heterogeneous Fenton process. Otherwise, the most efficient among all the studied degradation processes was the UVA/TiO2 Degussa P25/H2O2 process. In order to make degradation processes more similar to that of the practical process SS radiation was used. Among studied processes, the 7.2Fe/TiO2/H2O2 system showed the greatest potential for the removal of ionic liquids. Also, it was observed that the impact of anions on the cation degradation efficiency was much more pronounced. Due to the possible fate of ionic liquids in the environment, for five different waters (pond, rain, tap, river, and condensate) degradations in the dark and under simulated sunlight were studied. For all processes, and all water types in the presence of SS radiation a remarkable positive effect of naturally dissolved organic matter on the degradation efficiency was observed. Also, in all experiments, the anion was less stable than the cation. The major photodegradation products identified using liquid chromatography-mass spectrometry (HPLC-MS/MS) techniques were hydroxylated compounds.

Toxicity reduction of imidazolium-based ionic liquids by the oxygenation of the alkyl substituent

In this work, five different salicylate based ionic liquids were prepared in order to study their toxicity: 1-butyl-3-methylimidazolium salicylate, [bmim][Sal], 1-(4-hydroxy-2-oxybutyl)-3-methylimidazolium salicylate, [OHC2OC2mim][Sal], 1-(3-hydroxypropyl)-3-methylimidazolium salicylate, [OHC3mim][Sal], 1-ethoxyethyl-3-methylimidazolium salicylate, [C2OC2mim][Sal] and imidazolium salicylate [Im][Sal]; aquatic organisms (Artemia salina) and a human non-tumor cell line (normal fetal lung fibroblasts, MRC-5) were also used in the investigation. The introduction of polar groups (in the form of hydroxide and/or ether group) into the alkyl side chain of the imidazolium cation, and their influence on the reduction of the ionic liquids toxicity, were also demonstrated. The results indicate that the toxicity against A. salina and cytotoxicity against the healthy cell line of lipophobic ionic liquids were significantly lower than for the non-functionalized analogues, and are the same order of magnitude as the reference standard sodium salicylate. These facts open up the possibility of designing new non-toxic ionic liquids that can be used as active pharmaceutical ingredients in liquid form, adjusting only the lipophilicity of the cations by introducing polar oxygen groups into the side alkyl chain of the cation.

How to rank and discriminate artificial neural networks? Case study: prediction of anticancer activity of 17-picolyl and 17-picolinylidene androstane derivatives

Model discrimination is still not a resolved task. The classical statistical approaches lead to different results (for the same models) and at the same time a lot of models seem to be statistically equivalent. The authors deliberately select such conditions when their algorithm is superior. Hence, it is better to apply different approaches to compare and rank the models fairly. This paper presents the application of methodology called sum of ranking differences (SRD) to rank the artificial neural network models [quantitative structure–activity relationship (QSAR) models] designed for prediction of anticancer activity of 17-picolyl and 17-picolinylidene androstane derivatives toward androgen receptor negative prostate cancer cells (AR-, PC-3). The SRD method suggests the consistent models, in terms of compounds order and proximity to the golden standard, which should preferably be used in the prediction of anticancer activity of studied androstane derivatives.

The effect of imidazolium based ionic liquids on wheat and barley germination and growth: Influence of length and oxygen functionalization of alkyl side chain

In this work five different imidazolium based ionic liquids, namely: 1-(2-oxybutyl)-3-methylimidazolium chloride, [C2OC2mIm][Cl]; 1-(2-oxypropyl)-3-methylimidazolium chloride, [C1OC2mIm][Cl]; 1-(3-hydroxypropyl)-3-ethylimidazolium chloride, [OHC3eIm][Cl]; 1-(3-hydroxypropyl)-3-methylimidazolium chloride, [OHC3mIm][Cl]; 1-(2-hydroxyethyl)-3-methylimidazolium chloride, [OHC2mIm][Cl], together with commercial 1-butyl-3-methylimidazolium chloride, [bmim][Cl] and synthesized protic imidazolium chloride, [Im][Cl], were prepared and their toxicity examined towards wheat and barley germination and growth. Introduction of the polar groups (in the form of hydroxyde and/or ether group) in the alkyl side chain of the imidazolium cation and their influence on the reduction of the ionic liquids toxicity is demonstrated. The results indicate that toxicity of oxygen functionalized ILs is significantly lower against wheat comparing to non-functionalized analogues. In the case of barley, influence on germination follow the same trend as in the case of wheat, but for seedlings growth different trend is observed with more pronounced toxicity of ether functionalized ILs. From these results it was also shown that alkylation in the position N-3 atom of the imidazole significantly reduces toxicity of cation.

Determination of Carbendazim by an Ionic Liquid Modified Carbon Paste Electrode

ABSTRACT A new method for the electroanalytical determination of carbendazim is reported using a novel ionic liquid-based carbon paste electrode. 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide were used as additives in the paste for electrode fabrication. The electrodes were characterized by cyclic voltammetry of the couple and scanning electron microscopy. The carbon paste electrode containing 19% 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was selected for the electrochemical determination of carbendazim by differential pulse adsorptive stripping voltammetry. The influence of electrolyte pH, accumulation potential and time, and the presence of selected pesticides on electrochemical behavior of carbendazim were characterized. The optimal conditions for differential pulse adsorptive stripping voltammetry of carbendazim were determined to be a pH 5.0 Britton–Robinson buffer, an accumulation potential of −0.05 V, an accumulation time of 120 s, a start potential of −0.10 V vs. the reference; an end potential of +1.30 V, and a scan rate of 0.050 V s−1. The linear dynamic range of the method was from 0.010 to 0.247 mg L−1 with a correlation coefficient of 0.9995. The recovery was 104.1% in fortified tap water, demonstrating its suitability for the analysis of water.

Metal Complex Formation in Melts of Acetamide-Ammonium Nitrate-Water Mixtures, Part I. Cobalt(II) Chloride Complexes

The complex formation between cobalt(II) and chloride ions in molten NH4NO3・2.61H2O, NH4NO3・CH3CONH2・1.61H2O and NH4NO3・2.61CH3CONH2 has been investigated. Absorption spectra of cobalt(II) chloride containing variable amounts of ammonium chloride were recorded at 45 to 60 °C. In the absence of chloride, the solutions show spectra typical for octahedral co-ordination of cobalt(II). Addition of chloride caused a shift of the absorption maximum toward lower energies and an increase of the molar absorption coefficient with increasing chloride concentration. The position of the absorption maximum and the intensity of the absorption indicate tetrahedral or severely distorted octahedral co-ordination. The stability constants for [Co(NO3)4]2−, [Co(NO3)2Cl2]2− and [CoCl4]2− complex formation in NH4NO3・2.61CH3CONH2 are reported.