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41.
Kragulj Isakovski Marijana Molnar Jazić Jelena Maletić Snežana Tubić Aleksandra Agbaba Jasmina Tričković Jelena Dalmacija Božo 《Accreditation and quality assurance》2018,23(4):243-250
Accreditation and Quality Assurance - This study investigates measurement procedure validation for the determination of hexachlorobenzene, pentachlorobenzene and trifluralin as priority hazardous... 相似文献
42.
Doping boron clusters with Be and its heavier alkaline-earth congener, Mg, usually leads to complexes of different geometry and electronic structure. In this work we show that both neutral BeB8 and MgB8 exhibit a singlet ground state umbrella-like form. In addition, the stability, electronic structure, and aromaticity of the target molecules are compared. The magnetically induced current densities show that BeB8 and MgB8 are double aromatic systems: π and σ electrons induce strong diatropic currents. The current densities induced in the studied complexes are of very similar intensity, but with a different spatial distribution. The differences in the current density patterns observed for BeB8 and MgB8 arise from the very nature of the bonding interactions between the M atom and B8 fragment, as demonstrated through the energy decomposition analysis. 相似文献
43.
The reactions of platinum(II) complexes, [PtCl2(dach)] (dach = (1R,2R)‐1,2‐diaminocyclohexane) and [PtCl2(en)] (en = ethylenediamine) with biologically relevant ligands such as 5′‐GMP (guanosine‐5′‐monophosphate) and l ‐His (l ‐histidine) were studied by UV–vis spectrophotometry, 1H NMR spectroscopy, and high‐performance liquid chromatography (HPLC). Spectrophotometrically, these reactions were investigated under pseudo‐first‐order conditions at 310 K in 25 mM Hepes buffer (pH 7.2) and 10 mM NaCl to prevent the hydrolysis of the complexes. The [PtCl2(en)] complex reacts faster than [PtCl2(dach)] in the reaction with studied nucleophiles. This confirms the fact that the reactivity of studied Pt(II) complexes depends on the structure of the inert bidentate ligand. Also, the substitution reactions with l ‐His are always faster than the reactions with nucleotide 5′‐GMP. The reactions of [PtCl2(dach)] and [PtCl2(en)] complexes with l ‐histidine are studied by 1H NMR spectroscopy. The obtained rate constants are in agreement with those obtained by UV–vis. The same reactions were studied by HPLC comparing the obtained chromatograms during the reaction. The changes in intensity of signals of the free and coordinated ligand show that after a few days there is only one dominant product in the system. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 99–106, 2011 相似文献
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45.
Pérez-Prieto J Morant-Miñana MC Galian RE Miranda MA 《Photochemistry and photobiology》2006,82(1):231-236
Drug-induced photoallergy requires as the first step formation of covalent drug-protein photoadducts. One of the key amino acids involved in this process is tryptophan (Trp). In this context, several diaryl ketones, including 2-benzoylthiophene (BT), [2-(5-benzoyl-5-thienyl)]-2-methylpropanoic methyl ester (TPA methyl ester) and 4-(2-thienylcarbonyl)phenyl]-2-methylpropanoic methyl ester (SUP methyl ester) have been irradiated in the presence of N-BOC-(L)-tryptophan methyl ester. Laser flash photolysis has allowed to detect three neutral radicals (ketyl, indolyl and skatolyl radicals) resulting from formal hydrogen-atom abstraction. This correlates well with the isolation of homodimers, as well as with cross-coupling products, in the preparative irradiation. The main cross-coupling products were in all cases lactones arising from the reaction of the Trp-derived skatolyl radicals with the corresponding ketyl radicals. These lactones were obtained as the (4R) stereoisomers with remarkable diasteroselectivity. No coupling products through the phenyl p-position of BT or TPA methyl ester were found. By contrast, ketone homodimers and cross-coupling products arising from reaction through the thienyl 5-position were obtained when using BT and SUP methyl ester; this is very interesting, because stable LAT-derived products are difficult to isolate. 相似文献
46.
Stankov-Jovanović VP Nikolić-Mandić SD Mandić LM Mitić VD 《Analytical and bioanalytical chemistry》2006,385(8):1462-1469
Pancuronium bromide (PCBr) inhibition effect on enzyme cholinesterase from pooled human serum (Che, EC 3.1.1.8 acylcholine
acylhydrolase) was used for development of a spectrophotometric kinetic method for PCBr determination in human serum and urine.
Optimal conditions for the basic and inhibitor reactions were established: pH=7.7 and substrate concentration c(benzoylcholine
chloride)=1.33 mmol/L. Kinetic parameters were also determined: Michaelis-Menten’s constant KM=0.40 mmol/L, maximal reaction rate Vmax=52.2 μmol/L min, inhibition constant Ki=0,56 μmol/L and IC50=1.31 μmol/L. Linear dependence between the reaction rate and inhibitor concentration exists in PCBr concentration range 8.20–68.25 nmol/L,
which corresponds to the real sample concentrations from 0.328 to 2.730 μmol/L. The method detection and quantification limits
were 2.01 nmol/L and 6.67 nmol/L, respectively. Precision of the method was tested for three pancuronium concentrations (10.70,
29.35 and 51.25 nmol/L). Relative standard deviation (RSD) was in the range 0.15–7.45%. Accuracy was examined by standard
addition method. Influence of the substances usually present in serum and urine on the reaction rate was tested. The developed
method was applied for PCBr content determination in serum model samples, urine model samples and in urine taken during surgery.
The method has good sensitivity, accuracy, precision and it is suitable for clinical practice.
相似文献
47.
48.
Snežana S. Mitić Gordana Ž. Miletić Aleksandra N. Pavlović Snežana B. Tošić Dragan S. Velimirović 《中国化学会会志》2007,54(1):47-54
A kinetic method for the determination of micro quantities of amino acid arginine (Arg) is described in this paper. The catalytic activity of cobalt in the reaction of oxidation of purpurin (1,2,4‐trihydroxy‐antraquinone, PP) by hydrogen peroxide in alkaline buffer solution decreases in the presence of micro quantities of arginine, because of the formation of the complex. Operating conditions for the successful determination of arginine were optimized. The optimized conditions yielded a theoretical detection limit of 1.45 μg mL?1. Kinetic equations are proposed for the investigated process. The interference effects of certain foreign ions and amino acids upon the reaction rate were studied and removed in order to assess the selectivity of the method. The developed procedure was successfully applied to the determination of arginine in various pharmaceutical samples. The typical feature of this procedure is that determination can be carried out at room temperature and in a short analysis time. The newly developed method is simple, inexpensive and efficient for use in the analysis of a large number of samples. 相似文献
49.
50.
Pérez-Prieto J Galian RE Burgos PO Morant Miñana Mdel C Miranda MA López-Ortiz F 《Organic letters》2005,7(18):3869-3872
Efficient benzylic radical formation from benzo[d]-1,2-oxaphospholes has demonstrated their suitability as precursors of stabilized C-centered radicals, a property associated with antioxidant potential. A remarkable stereodifferentiation is observed for alkyl- and aryl-substituted derivatives. [reaction: see text] 相似文献