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41.
An improved procedure for intramolecular cyclization of some Δ5-alkenols, using PhSeX (X = Cl, Br) has been developed. We found that cyclization can be facilitated in the presence of pyridine, Ag2O, and some Lewis acids as catalysts. Thus catalytic amount of additives (pyridine and Ag2O) influences higher yields but equimolar amount achieves almost quantitative yield under extremely mild experimental conditions. In the presence of Lewis acids (ZnCl2 and FeCl3) high yields of cyclic ether products are obtained with catalytic amounts. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:146–149, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10227 相似文献
42.
Ezddin Ali Farag Hutli Milos S. Nedeljkovic Nenad A. Radovic 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(5):329-341
Experimental setup with a submerged cavitating jet has been used for the study of influences of material, exposure time and
working fluid temperature on the erosion process. Each of the parameters has been varied separately, and the results of erosion
are analyzed in detail. Additionally, comparison of experiments with nitrated and non-nitrated material has been made in order
to study the enhancement (mostly reflected as the prolonged incubation time) of erosion resistance achieved by nitrating the
specimen surface. 相似文献
43.
Biljana Cosic Arthur Fontijn Paul Marshall 《Proceedings of the Combustion Institute》2007,31(1):349-356
The high-temperature photochemistry (HTP) technique, previously used for reactions of neutral species, has been adapted to the study of atomic metal ion-molecule reactions. Ca+ ions were generated by 193 nm multi-photon photolysis of calcium acetyl acetonate and its pyrolysis fragments. The relative ion concentrations were monitored by laser-induced fluorescence at 393.4 nm. Ar was used as the bath gas. The data for the Ca+ + O2 + M → CaO2+ + M association reaction (1) are fitted by k1(907-1425 K) = 3.5 × 10−32 exp(+3161 K/T) cm6 molecule−2 s−1. Combining with an approximate k1(296 K) value in the literature leads to k1(296-1425 K) = 5.8 × 10−22 (T/K)−2.9 exp(−601 K/T) cm6 molecule−2 s−1. Over much of the observed temperature range reaction (1) has much smaller rate coefficients than the corresponding neutral Ca association reaction. Reaction (1) is shown to behave very similarly to the O2 association reaction with neutral K atoms, with which Ca+ is iso-electronic. This suggests that the initial step is ion-pair complex formation of the superoxide Ca2+(O2)−, which is also consistent with results from density functional calculations. The k1 values are rationalized via Troe’s unimolecular formalism, which leads to good accord with the experiments. 相似文献
44.
Friedrich?HammerschmidtEmail author Biljana?Peric Simov Susanne?Schmidt Sabine?Schneider Ilse?Zolle 《Monatshefte für Chemie / Chemical Monthly》2005,136(2):229-239
Summary. Metomidate (ee 99%) substituted with iodine in the phenyl ring was prepared from (S)-1-(4-iodophenyl)ethanol (ee >98%) obtained by lipase-catalysed resolution and methyl 1H-imidazole- 5-carboxylate. The two fragments were joined highly regioselectively (alkylation only at N-1 of substituted imidazole) with inversion of configuration using the Mitsunobu reaction. Finally, p-iodometomidate was transformed into the p-trimethylstannyl derivative. 相似文献
45.
Zorica M. Bugarčić Biljana Mojsilović Ljiljana Marjanović Stanimir Konstantinović 《Monatshefte für Chemie / Chemical Monthly》2000,131(10):1091-1096
Summary. The reaction of some alkenols with tetrachloromethane in the presence of a radical initiator was investigated. Regarding
the effects of structural features of the starting alkenol (number and position of methyl substituents at the double bond
and at the carbinol carbon atom, constitutional relationship between the double bond and the hydroxyl group) there are two
possible competing reactions: addition and cyclization. In the case of the simplest alkenols (without substituents and with
a more remote double bond) addition occurs; mono- and disubstituted secondary and tertiary Δ4- and Δ5-alkenols cyclize in high yields to give the corresponding cyclic ethers.
Received March 17, 2000. Accepted (revised) May 31, 2000 相似文献
46.
Nađa Kostić Yannis Dotsikas Anđelija Malenović Biljana Jančić Stojanović Tijana Rakić Darko Ivanović Mirjana Medenica 《Journal of mass spectrometry : JMS》2013,48(7):875-884
In this article, a step‐by‐step optimization procedure for improving analyte response with implementation of experimental design is described. Zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, were chosen as model compounds to undergo chloroformate‐mediated derivatization followed by liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS) analysis. Application of a planned stepwise optimization procedure allowed responses of analytes, expressed as areas and signal‐to‐noise ratios, to be improved, enabling achievement of lower limit of detection values. Results from the current study demonstrate that optimization of parameters such as scan time, geometry of ion source, sheath and auxiliary gas pressure, capillary temperature, collision pressure and mobile phase composition can have a positive impact on sensitivity of LC‐MS/MS methods. Optimization of LC and MS parameters led to a total increment of 53.9%, 83.3% and 95.7% in areas of derivatized vigabatrin, pregabalin and gabapentin, respectively, while for signal‐to‐noise values, an improvement of 140.0%, 93.6% and 124.0% was achieved, compared to autotune settings. After defining the final optimal conditions, a time‐segmented method was validated for the determination of mentioned drugs in plasma. The method proved to be accurate and precise with excellent linearity for the tested concentration range (40.0 ng ml?1–10.0 × 103 ng ml?1). Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
47.
Marko Jovanović Biljana Jančić Stojanović Tijana Rakić Anđelija Malenović Darko Ivanović Mirjana Medenica 《Central European Journal of Chemistry》2013,11(7):1150-1162
Five different columns (two silica, two cyanopropyl and one diol) were investigated in hydrophilic interaction liquid chromatography (HILIC). For the assessment of columns behavior in HILIC mode, six basic drugs (lamotrigine, thioridazine, clozapine, chlorpheniramine, pheniramine and sulpiride) were chosen. The assessment of the influence of the concentration of organic modifier on analytes’ retention on each column was provided by fitting the retention data into theoretical models. Utilizing the statistical analysis, the selection of the model that provides better prediction of the retention behavior was enabled. Dual RP-HILIC mechanism was suggested on cyanopropyl and diol columns, therefore the transition points between the two mechanisms on these columns were calculated. Furthermore, in order to investigate the impact of three factors simultaneously on the retention behavior of the analyzed substances on Betasil Silica column, chemometrically-aided empirical models were built. The experiments were conducted according to the matrix of Box-Behnken design and on the basis of the retention data, six quadratic models were obtained and their adequacy was confirmed using ANOVA test. The obtained coefficients of quadratic models enabled the elucidation of both single factor and factor interactions influence. This was also graphically presented in 3D response surface plots. 相似文献
48.
Marko Petković Zita Šereš Biljana Pajin Vojislav Banjac 《Journal of Thermal Analysis and Calorimetry》2014,117(1):277-284
The purpose of this study is to research the thermal properties of spreads with maltitol. Thermal characteristics of spreads depend on process parameters (temperature, mixer speed rotation). Spreads are produced at different temperatures (30, 35, and 40 °C) and mixer speed rotation (1, 1.33, and 1.67 Hz). The thermogravimetric method shows the peak position and determinate the spread composition. The temperature decomposition of sucrose and maltitol is two stages (two peaks), and palm fat has a single stage decomposition (one peak). Maltitol peak is dominant for spreads containing 100 and 70 % maltitol as a sweetener. This peak is sharper than sucrose peak and the inflection point is more expressed. Shape and the position of these peaks in spreads are modified. Peaks of maltitol, palm fat, and sucrose in spreads are lower and wider because of the grinding process and the interaction between spread ingredients. Increasing the process parameters (temperature, mixer speed rotation), temperatures of these peaks are higher (closer to temperature peak of pure ingredients). The dominant parameter is mixer speed rotation. The most thermally stable spreads with any amount of maltitol are produced at a temperature of 40 °C and high mixer speed rotation (1.33 and 1.67 Hz), while the least stable maltitol spreads are produced at minimum process parameters (30 °C, 1 Hz). 相似文献
49.
Biljana Šmit Biljana Petrović Sofija Sovilj Dragan Čanović Živadin D. Bugarčić 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1197-1202
The reactions of cisplatin with nizatidine and ranitidine were studied in D2O at pD 7.4 and 298 K by means of 1H NMR spectroscopy. The second order rate constants, k
2, for the reaction of cisplatin with nizatidine is (2.71 ± 0.11) × 10−4 M
−1 s−1, and for the reaction with ranitidine (6.72 ± 0.17) × 10−4 M
−1 s−1. The reactions of nizatidine and ranitidine were also studied with other Pd(II) and Pt(II) complexes. The set of the complexes
was selected because of their difference in reactivity, steric hindrance, and binding properties.
Correspondence: Prof. Dr. Živadin D. Bugarčić, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac,
Serbia. 相似文献
50.
Mimica-Dukic N Simin N Cvejic J Jovin E Orcic D Bozin B 《Molecules (Basel, Switzerland)》2008,13(7):1455-1464
In this paper, the study of antioxidant activity and phenolic composition of three different extracts (EtOAc, n-BuOH and H(2)O) of field horsetail (Equisetum arvense L.) is presented. The antioxidant activity has been evaluated measuring the total reducing power (expressed by Ascorbate Equivalent Antioxidant Capacity - AEAC), inhibition of lipid peroxidation, and free radical scavenging capacity (RSC) towards 2,2-diphenyl-1-picrylhydrazyl (DPPH radical) and nitric oxide (NO), respectively. In addition, the total flavonoid content (TFC) and phenolic constituents of each extract have been determined. The results obtained show that the highest RSC regarding both DPPH and NO radicals is expressed by EtOAc extract (EC(50)=2.37 microg/mL and EC(50)=90.07 microg/mL, respectively), and the lowest by H(2)O extract (EC(50)=37.2 microg/mL and EC(50)>333.33 microg/mL, respectively). n-BuOH extract showed the highest total reducing power (AEAC=13.40 microg/mL). Differences in the phenolic composition of examined extracts are found comparing the HPLC chemical profiles. Although, isoquercitrin is the main flavonoid in both EtOAc and n-BuOH extracts, a considerable amount of di-E-caffeoyl-meso-tartaric acid was presented in the n-BuOH extract. In H(2)O extract high content of phenolic acids and low percentage of flavonoids were detected. 相似文献