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Search Results: 1 - 10 of 192852 matches for " Marinkovi? Aleksandar D. "
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Processing and nanomechanical properties of chitosan/polyethylene oxide blend films
?oki? Jelena D.,Kojovi? Aleksandar,Stojanovi? Du?ica,MarinkoviAleksandar
Journal of the Serbian Chemical Society , 2012, DOI: 10.2298/jsc121121139d
Abstract: Chitosan based films have found an increasing implementation in variety of topics among which as drug delivery carriers, in packaging industry and as water puritication filters. Therefore, in order to achieve mechanical integrity of such films while preserving processability and biocompatibility, chitosan based films are fabricated in forms of blends with polyethylene oxide (PEO). Nanoindentation study is undertaken in order to investigate nanomechanical properties and surface morphology of chitosan films in blends with various content of PEO. Results of differential scanning calorimetry, water uptake and nanoindentation revealed that films with 80/20 blend ratio of chitosan/PEO showed the optimal values of reduced modulus and hardness. It appears that the incorporation of synthetic PEO in chitosan films could lower the manufacturing cost while preserving the mechanical integrity of the films. [Projekat Ministarstva nauke Republike Srbije, br. EUREKA E!5851]
New method for synthesis of N-alkyl and N,N-dialkyl-O-ethyl and O-isopropylthiocarbamates by oxidation of ammonium salt of xhantogenic acid
Milisavljevi? Smiljka S.,MarinkoviAleksandar D.,Milosavljevi? Milutin M.
Hemijska Industrija , 2010, DOI: 10.2298/hemind100527049m
Abstract: A synthesis of N-alkyl and N,N-dialkyl-O-ethyl and O-isopropyl thiocarbamates by oxidation of ammonium salt of ethyl and isopropylxanthogenic acid in a presence of sodium hypochlorite and hydrogen peroxide were performed. Ammonium salt of ethyl and isopropylxanthogenic acid was obtained by the reaction of alkylammonium sulfate and sodium ethyl and isopropyl xanthate. Studies on a dependence of N-ethyl-O-isopropylthiocarbamate yield and purity with respect to reaction parameters (reaction time, molar ratio of oxidant and ethylamonium salt of isopropylxanthogenic acid) were performed. Optimal reaction conditions for synthesis of N-alkyl and N,N-dialkyl-O-ethyl and O-isopropyl thiocarbamates were established. Synthesized compounds have been fully characterized by FTIR, 1H NMR and MS data, while purity has been determined by GC method. A plausible pathway for the N-alkyl and N,N-dialkyl-O-ethyl and O-isopropyl thiocarbamates synthesis, in the presence of the oxidative agents sodium hypochlorite and hydrogen peroxide, was proposed. The presented synthetic methods has been developed at laboratory and applied at semi-industrial level. The developed optimal method provides a powerful and versatile method for the preparation of N-alkyl and N,N-dialkyl-O-ethyl and O-isopropyl thiocarbamates. This new optimized method offer several benefits, namely, simple operation, mild reaction conditions, bypass of hazardous organic solvents, moderately toxic and inexpensive reagents, and also short reaction times and high product yields.
Synthesis of N-and N,N-dialkyl-S-alkylthiolcarbamates by the rearrangement of N-and N,N-dialkyl-O-thioncarbamates
Milosavljevi? Milutin M.,MarinkoviAleksandar D.,?or?evi? Sini?a
Hemijska Industrija , 2006, DOI: 10.2298/hemind0602027m
Abstract: A series of N- and N,N-dialkyl-S-alkylthiolcarbamates were synthesized by the rearrangement of N- and N,N-dialkyl-O-alkylthioncarbamates in the presence of diethyl sulfate. The synthesis of some compounds without catalyst was also performed. The compounds were identified by IR, 1H NMR and MS spectroscopic methods. The starting thioncabamates were obtained from the corresponding xanthogenacetates and amines and their structures were also confirmed by IR, 1H NMR and MS data. Some of the thiolcarbamates were characterized for the first time in the literature.
Effects of solvent and structure on the reactivity of 6-substituted nicotinic acids with diazodiphenylmethane in aprotic solvents
Journal of the Serbian Chemical Society , 2009,
Abstract: The rate constants for the reactions of diazodiphenylmethane (DDM) with 6-substituted nicotinic acids in aprotic solvents at 30 °C were determined. The obtained second order rate constants in aprotic solvents, together with literature data for benzoic and nicotinic acids in protic solvents, were used for the calculation of solvent effects, employing the Kamlet-Taft solvatochromic equation (linear solvation energy relationship – LSER) in the form: log k = log k0 + s * + a + b . The correlations of the kinetic data were performed by means of multiple linear regression analysis taking appropriate solvent parameters. The sign of the equation coefficients (s, a and b) were in agreement with the postulated reaction mechanism, and the mode of the solvent influences on the reaction rate is discussed based on the correlation results. A similar contribution of the non-specific solvent effect and electrophilic solvation was observed for all acids, while the highest contribution of nucleophilic solvation was influenced by their high acidity. Correlation analysis of the rate data with substituent p parameters in an appropriate solvent using the Hammett equation was also performed. The substituent effect on the acid reactivity was higher in aprotic solvents of higher dipolarity/polarizability. The mode of the transmission of the substituent effect is discussed in light of the contribution of solute–solvent interaction on the acid reactivity.
Separation and determination of dimethylarsenate in natural waters
Ben Issa Nureddin,MarinkoviAleksandar D.,Rajakovi? Ljubinka V.
Journal of the Serbian Chemical Society , 2012, DOI: 10.2298/jsc110510010b
Abstract: A simple and efficient method for separation and determination of dimethylarsenate DMAs(V) was developed in this work. Two resins, a strong base anion exchange (SBAE) resin and iron-oxide coated hybrid (HY) resin were tested. By simple adjusting pH value of water at 7.00, DMAs(V) passed through the HY column without any changes, while all other arsenic species [inorganic arsenic and monomethylarsonate, MMAs(V)] were quantitatively bonded on HY resin. The resin capacity was calculated according to the breakthrough points in a fixed bed flow system. At pH 7.00 the HY resins bonded more than 4150 μg g-1 of As(III), 3500 μg g-1 of As(V) and 1500 μg g1 of MMAs(V). Arsenic adsorption behavior in the presence of impurities showed tolerance with the respect to potential interference of anions commonly found in natural water. DMAs(V) was determined in the effluent by ICP-MS. The detection limit was 0.03 μg L?1 and relative standard deviation (RSD) was between 1.1?7.5 %. Proposed method was established performing standard procedures: with external standard, certified reference material and the standard addition method.
Aleksandar D. Marinkovi,Jelena Nedeljkovi?,Du?an ?. Mijin,Nata?a Ili?
Chemical Industry and Chemical Engineering Quarterly , 2011,
Abstract: Linear free energy relationships (LFER) were applied to the IR, 1H- and 13C--NMR spectral data in N-alkyl and N-cycloalkyl cyanoacetamides. N-alkyl and N-cycloalkyl cyanocetamides were synthesized from corresponding amine and ethyl cyanoacetate. A number of substituents were employed for alkyl substitution, and fairly good correlations were obtained, using simple Hammett equation. In N-alkyl and N-cycloalkyl cyanoacetamides substituent cause SCS of N-H hydrogen primarily by steric interaction, polar subtituent effect influences SCS shift of C=O carbon, while steric effect of N-alkyl substituent causes IR stretching frequencies of N-H, C=O and CN group. The conformations of investigated compounds have been studied by the use of semiempirical PM6 method, and together with LFER analysis, give a better insight into the influence of such a structure on the transmission of electronic substituent effects. Negative ρ values for several correlations (reverse substituent effect) were found.
Substituent effect on IR, 1H and 13C NMR spectral data in n-(substituted phenyl)-2-cyanoacetamides: A correlation study
MarinkoviAleksandar D.,Brki? Dominik,Martinovi? Jelena S.,Mijin Du?an ?.
Chemical Industry and Chemical Engineering Quarterly , 2013, DOI: 10.2298/ciceq120109044m
Abstract: Linear free energy relationships (LFER) were applied to the IR, 1H and 13C NMR spectral data of N-(substituted phenyl)-2-cyanoacetamides. A variety of substituents were employed for phenyl substitution and fairly good correlations were obtained using the simple Hammett and the Hammett-Taft dual substituent parameter equations. The correlation results of the substituent induced 13C NMR chemical shifts (SCS) of the C1, C=O and N-H atom indicated different sensitivity with respect to electronic substituent effects. A better correlation of the SCSC=O with a combination of electrophilic and nucleophilic substituent constants indicated a significant contribution of extended resonance interaction (π-delocalization) within the π1-unit. The conformations of the investigated compounds were studied using the DFT B3LYP/6-311G method and, together with the results of 13C NMR and IR spectroscopic studies, a better insight into the influence of such a structure on the transmission of electronic substituent effects was obtained.
Aleksandar D. Marinkovi,Milutin Milosavljevi?,Dragan Milenkovi?,Goran Ivanovi?
Chemical Industry and Chemical Engineering Quarterly , 2008,
Abstract: A two-step optimized laboratory synthetic method of zinc dialkyldithiocarbamates is presented. In the course of the first phase, a sodium salt of dialkyldithiocarbamic acid has been synthesized from the dialkylamines, carbon disulfide and sodium hydroxide. The synthesis of zinc dialkyldithiocarbamates was achieved by the precipitation from sodium dialkyldithiocarbamic acid by zinc sulfate under the optimized conditions. The synthesized products have been characterized by FTIR, 1H and 13C NMR, AAS spectroscopic methods, as well as by elemental analysis and melting points. Kinetic studies of the motor oil oxidation inhibited by synthesized compounds have been tested using a standard method.
Synthesis and characterization of phencyclidine and his derivatives
Ili? Nata?a C.,MarinkoviAleksandar D.,Brki? Danijela V.,Petrovi? Slobodan D.
Hemijska Industrija , 2010, DOI: 10.2298/hemind100523050i
Abstract: Phencyclidine (PCP) or 1-phenyl-cyclohexylpiperidine is the best known representative drug from the compound class of arylcyclohexylamines. On an account of pharmacological activities it belongs to the family of drugs known as a dissociative anesthetics. In recent years, great attention has been paid to the investigation of the substances that have been abused, including PCP. PCP is the synthetic drug with stimulant and hallucinogens effects (street name “angel dust”) and it's situated on the Schedule Substances List, in Serbia and worldwide. In the beginning, PCP has been sold in pharmacies as local anesthetic, but very quickly it was pulled from sale because of the unwanted effects on consumer′s health causing psychoactive addiction. Taking into the account that today a great attention has been given to the substances that are subject of abuse, in this paper, biological and pharmacological effect of PCP and it's derivative is described. It is shown that PCP is antagonist of N-methyl-D-aspartate (NMDA) and that it causes antiglutamateric hallucinations. Unlike BTCP which agonist is NMDA receptor and is obtained by modifying the structure of PCP. This paper presents a PCP metabolism and provides an overview of the methods for their identification and quantification in the biological samples. Immunological tests of PCP in the biological samples can provide a quick but wrong result because of the possible interference with the other substances of abuse as opposed to instrumental methods. Based on the presented method and the results it was concluded that the method of choice for the examinations of biological samples for the presence of PCP is gas chromatography in combination with mass spectroscopy.
Immobilization of enzymes onto carbon nanotubes
Prlainovi? Nevena ?.,Bezbradica Dejan I.,Kne?evi?-Jugovi? Zorica D.,MarinkoviAleksandar D.
Hemijska Industrija , 2011, DOI: 10.2298/hemind110330028p
Abstract: The discovery of carbon nanotubes (CNTs) has opened a new door in nanotechnology. With their high surface area, unique electronic, thermal and mechanical properties, CNTs have been widely used as carriers for protein immobilization. In fact, carbon nanotubes present ideal support system without diffusional limitations, and also have the possibility of surface covalent functionalization. It is usually the oxidation process that introduces carboxylic acid groups. Enzymes and other proteins could be adsorbed or covalently attached onto carbon nanotubes. Adsorption of enzyme is a very simple and inexpensive immobilization method and there are no chemical changes of the protein. It has also been found that this technique does not alter structure and unique properties of nanotubes. However, a major problem in process designing is relatively low stability of immobilized protein and desorption from the carrier. On the other hand, while covalent immobilization provides durable attachment the oxidation process can reduce mechanical and electronic properties of carbon nanotubes. It can also affect the active site of enzyme and cause the loss of enzyme activity. Bioimmobilization studies have showed that there are strong interactions between carbon nanotubes surface and protein. The retention of enzyme structure and activity is critical for their application and it is of fundamental interest to understand the nature of these interactions. Atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and circular dichroism (CD) spectroscopy provide an insight into the structural changes that occur during the immobilization. The aim of this paper is to summarize progress of protein immobilization onto carbon nanotubes.
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