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Karolina Pecková Tomáš Navrátil Bogdan Yosypchuk Josino Costa Moreira Katia Christina Leandro Jiří Barek 《Electroanalysis》2009,21(15):1750-1757
A new simple and direct electroanalytical method was developed for the determination of azidothymidine in commercial pharmaceutical preparations. It is based on differential pulse voltammetry at silver solid amalgam electrode with polished surface (p‐AgSAE) or surface modified by mercury meniscus (m‐AgSAE). The electroreduction of azidothymidine in basic media at these electrodes gives rise to one irreversible cathodic peak. Its potential in 0.05 mol L?1 borate buffer, pH 9.3 at ca. ?1050 mV is comparable to that using hanging mercury drop electrode (HMDE). Achieved limits of quantitation are in the 10?7 mol L?1 concentration range for both amalgam electrodes. According to the procedure based on the standard addition technique, the recoveries of known amounts of azidothymidine contained in pharmaceutical preparations available in capsules were 101.4±1.8% (m‐AgSAE), 100.3±3.5% (p‐AgSAE) and 102.0±1.0% (HMDE) (n=10). There was no significant difference between the values gained by proposed voltammetric methods and the HPLC‐UV recommended by the United States Pharmacopoeia regarding the mean values and standard deviations. 相似文献
394.
An inexpensive cationic ruthenium(II) catalyst enabled the expedient synthesis of isocoumarins through oxidative annulations of alkynes by benzoic acids. This C-H/O-H bond functionalization process also proved applicable to the preparation of α-pyrones and was shown to proceed by rate-limiting C-H bond ruthenation. 相似文献
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Detlef Schröder Dr. Jana Roithová Dr. Esmail Alikhani Prof. Karolina Kwapien Joachim Sauer Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):4110-4119
The C? H bond activation of small alkanes by the gaseous MgO+. cation is probed by mass spectrometric means. In addition to H‐atom abstraction from methane, the MgO+. cation reacts with ethane, propane, n‐ and iso‐butane through several pathways, which can all be assigned to the occurrence of initial C? H bond activations. Specifically, the formal C? C bond cleavages observed are assigned to C? H bond activation as the first step, followed by cleavage of a β‐C? C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO+. for the attack of primary C? H bonds. This feature represents a notable distinction of the main‐group metal oxide MgO+. from various transition‐metal oxide cations, which show a clear preference for the attack of secondary C? H bonds. The results of complementary theoretical calculations indicate that the C? H bond activation of larger alkanes by the MgO+. cation is subject to pronounced kinetic control. 相似文献
397.
M. E. Kazmierczak R. E. Fornes D. R. Buchanan R. D. Gilbert 《Journal of Polymer Science.Polymer Physics》1989,27(11):2173-2187
The morphology of a series of segmented polyurethane block copolymers is characterized by x-ray scattering, differential scanning calorimetry (DSC), density measurements, and tensile studies. The materials contain hard segments formed from paraphenylene diisocyanate (PPDI) and flexible segments formed from poly(oxytetramethylene) (POTM) ranging in molecular weight from 650 to 2000. Four different molecular weight compositions were investigated, with the weight fraction of the hard segment (wh) ranging from 0.14 to 0.33. The microphase structure has been examined using small-angle x-ray scattering, and the microphase transition zone thickness is estimated to be on the order of 1 nm. Oriented samples have been characterized with wide-angle x-ray scattering, and the flexible segment is shown to undergo stress-induced crystallization. DSC thermograms show flexible segment melting in the compositions containing the highest two molecular weights of the flexible segments. The hard segment thermal transitions were complex with a broad melting peak that varied with weight fraction and with a high temperature transition attributed to regions with hard segment lengths longer than the bulk of the hard segment component. There is an increase in tensile strength and initial modulus and decrease in elongation with increasing wh. Density data suggest the existence of a multiphase system. 相似文献
398.
Borowiak-Resterna A Frański R Klonowska K Olszanowski A 《Rapid communications in mass spectrometry : RCM》2005,19(2):283-286
Mass spectrometric decompositions of complexes of nicotinic acid esters and amides with copper are discussed. Liquid secondary ion mass spectrometry (LSIMS) was used as an ionisation technique and metastable ion spectra were recorded by using B/E linked scans. The fragmentation pathways consist mainly of the loss of one ligand molecule and also the cleavage of amide or ester bonds. It may be possible, on the basis of cleaved neutral fragments, to determine the site of coordination in the gas phase. It was also found that the presence of a chlorine atom affects the fragmentation pathways of complexes. 相似文献
399.
Ilona Turowska-Tyrk Karolina Grze?niak El?bieta Trzop Tomasz Zych 《Journal of solid state chemistry》2003,174(2):459-465
We studied the [2+2]-photodimerization in crystals of pyridine analogs and hydroxy derivatives of chalcone using the X-ray structure analysis. The mutual orientation of adjacent molecules in the crystals was analyzed in a quantitative way and the results were compared with data for known photoactive crystals undergoing the [2+2]-photodimerization. In the case of one pyridine analog, we processed the single-crystal-to-single-crystal photodimerization and determined the structure for the mixed crystal containing both the substrate and the product. We also explained a role of hydrogen bonds in the [2+2]-photodimerization in the case of the hydroxy derivatives of chalcone. C5H4N-CO-CHCH-C6H5: , , , β=91.318(10)°, monoclinic, . The irradiated crystal of the above analog: , , , β=91.870(10)°, monoclinic, . C6H5-CO-CHCH-C5H4N: , , , β=110.01(3)°, monoclinic, C2/c,Z=8. C6H5-CO-CHCH-C6H4(o-OH): , , , β=109.73(5)°, monoclinic, . C6H5-CO-CHCH-C6H4(p-OH): , , , orthorhombic, . 相似文献
400.