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161.
3,4-Dichloro-5-hydroxy-2(5H)-furanone treated with methyl chloroformate in the presence of diisopropylethylamine (Hünig's base) gave the corresponding carbonate. The labile methoxycarbonyloxy group smoothly undergoes substitution by amino alcohols. The obtained 5-(w-hydroxyalkylamino) mucochloric acid derivatives reacted with peracetylated glucals using triphenylphosphine hydrobromide as a catalyst to give the title muchloric acid glycoconjugates. 相似文献
162.
Jarosław Grolik Łukasz Dudek Julita Eilmes Andrzej Eilmes Marcin Górecki Jadwiga Frelek Benoît Heinrich Bertrand Donnio 《Tetrahedron》2012,68(20):3875-3884
Two optically pure derivatives of dibenzotetraaza[14]annulene, bearing four (S)- or (R)- 3,7-dimethyloctoxy peripheral chiral tails, respectively, and two hydroxybenzoyl meso substituents were synthesized using a convergent multi-step route. The structure of the products was determined by 1H and 13C NMR spectroscopy, ESI-MS, and elemental analysis. The mesomorphic behavior of the two chiral compounds, deciphered by differential scanning calorimetry (DSC), small-angle X-ray diffractometry (SA-XRD), and polarizing optical microscopy (POM) investigations, revealed the induction of two lamello-columnar phases, i.e., columnar stacks confined in smectic layers, whose columns may be arranged either according to the pg rectangular planar symmetry (for the low-temperature phase) or without registry between vicinal layers (for the high-temperature mesophase). Evidence of a helical organization of the molecules in the mesophases was obtained using a combination of electronic circular dichroism (ECD) and SA-XRD results, Molecular Dynamics simulations and quantum-chemical calculations. 相似文献
163.
Krzysztof Kozak Beata Koz?owskaTadeusz A. Przylibski Jadwiga MazurAnna Adamczyk-Lorenc Kalina Mamont-Cie?laOlga Stawarz Jerzy DordaBarbara K?os Miros?aw JanikEl?bieta Kochowska 《Radiation measurements》2012,47(1):89-95
The paper presents the results of intercalibration measurements of 222Rn concentration in water samples. The aim of the experiments was to evaluate the different measurement methods of radon determination in water samples performed by eleven laboratories in Poland and to test these methods in field work. In the years 2001-2003 three national intercomparison experiments were organized. The results allowed the participating laboratories to improve their measurement methodologies and to achieve better, i.e. more convergent results of determining radon concentration in water samples. The results show that the use of liquid-scintillation technique seems to be the best measurement method. It should be emphasized that comparative experiments are essential for all laboratories and they should be carried out as often as possible, based both on prepared samples with known concentration values of 222Rn and natural water samples, the most commonly used in laboratory practice. 相似文献
164.
Tomasz Gubica Andrzej Temeriusz Pawe? Paw?owski Jadwiga Stroka 《Journal of Physical Organic Chemistry》2010,23(9):853-858
The effect of the non‐electroactive groups on the redox potentials of the active centres of 26 nitrophenyl O‐glycosides possessing various substituents has been studied electrochemically using cyclic voltammetry. The potentials of both redox processes, a two‐electron quasi‐reversible R‐NHOH/R‐NO (Ef) and four‐electron irreversible R‐NO2/R‐NHOH (Epc(I)) systems, have been determined and compared for all the compounds under investigations. The nitrophenyl O‐glycosides were chosen as model compounds as they significantly vary in many aspects of their structure such as: (i) the isomeric substitution of nitro group in benzene ring to the sugar moiety (ortho, meta and para isomers); (ii) the size of sugar moieties (the derivatives of mono‐ and disaccharides); (iii) the presence and absence of additional groups in saccharidic fragments (e.g. pentose and hexose); (iv) functionalisation of hydroxyl groups (free or acetylated hydroxyl groups) and (v) absolute configurations of selected sugar carbon atoms (e.g. the pairs of anomers). Among other effects, a significant variation in the increasing order of the two‐electron quasi‐reversible (Ef, ortho > meta > para) and four‐electron irreversible (Epc(I), meta > ortho > para) redox processes has been found and explained taking into account the negative inductive effect (–I) caused by the glycosidic oxygen atom that facilitates the electroreduction of the nitro group, and the positive mesomeric effect (+M) which makes the electroreduction more difficult. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
165.
M. Sutkowski P. Garbat E. Nowinowski-Kruszelnicki A. Walczak J. Parka J. Wo?nicki 《Opto-Electronics Review》2009,17(1):53-58
Image analysis using polarizing methods allows removing the polarized light component from recorded images. This is known
as polarization difference imaging (PDI). The use of liquid crystals (LC) in PDI was proposed in 2002. Modified LC unit with
a properly oriented LC layer was proposed by the authors. The main parameters which characterize an imaging system, employing
a circular LC filter, were determined and presented in previous papers.
In this work, the basics of the circular LC filter construction and theory are presented. Two application configurations of
PDI imaging systems are shown. Experimental results of image processing based on object’s polarization properties are discussed. 相似文献
166.
Anna Hering Jadwiga Renata Ochocka Helena Baranska Krzysztof Cal Justyna Stefanowicz-Hajduk 《Molecules (Basel, Switzerland)》2021,26(21)
Polyphenolic compounds—mangiferin and hesperidin—are, among others, the most important secondary metabolites of African shrub Cyclopia sp. (honeybush). The aim of this study was to compare the percutaneous absorption of mangiferin and hesperidin from solutions (water, ethanol 50%, (v/v)) and extracts obtained from green and fermented honeybush (water, ethanol 50%, (v/v)). Research was performed with the Bronaugh cells, on human dorsal skin. The mangiferin and hesperidin distributions in skin layers (stratum corneum, epidermis, and dermis) and in acceptor fluid (in every 2, 4, 6, and 24 h) were evaluated by HPLC–Photodiode Array Coulometric and Coulometric Electrochemical Array Detection. The transdermal distribution of hesperidin was also demonstrated by fluorescence microscopy. Results indicated that mangiferin and hesperidin were able to cross the stratum corneum and penetrate into the epidermis and dermis. An advantage of hesperidin penetration into the skin from the water over ethanol solution was observed (451.02 ± 14.50 vs. 357.39 ± 4.51 ng/cm2), as well as in the mangiferin study (127.56 ± 9.49 vs. 97.23 ± 2.92 ng/cm2). Furthermore, mangiferin penetration was more evident from nonfermented honeybush ethanol extract (189.85 ± 4.11 ng/cm2) than from solutions. The permeation of mangiferin and hesperidin through the skin to the acceptor fluid was observed regardless of whether the solution or the honeybush extract was applied. The highest ability to permeate the skin was demonstrated for the water solution of hesperidin (250.92 ± 16.01 ng/cm2), while the hesperidin occurring in the extracts permeated in a very low capacity. Mangiferin from nonfermented honeybush ethanol extract had the highest ability to permeate to the acceptor fluid within 24 h (152.36 ± 8.57 ng/cm2). 相似文献
167.
On a class of Szász-Mirakyan type operators 总被引:1,自引:0,他引:1
Zbigniew Walczak 《Czechoslovak Mathematical Journal》2008,58(3):705-716
The actual construction of the Szász-Mirakyan operators and its various modifications require estimations of infinite series
which in a certain sense restrict their usefulness from the computational point of view. Thus the question arises whether
the Szász-Mirakyan operators and their generalizations cannot be replaced by a finite sum. In connection with this question
we propose a new family of linear positive operators. 相似文献
168.
Jie Guang Zachary A. Rumlow Lauren M. Wiles Sloane ONeill Maciej A. Walczak 《Tetrahedron letters》2017,58(52):4867-4871
Sulfated liposaccharides are known inhibitors of telomerase and here we describe the synthesis of a series of sulfated liposaccharides inspired by the natural product axinelloside A, reported to act as an inhibitor of human telomerase. We established a robust and scalable synthetic route to galactosyl liposaccharides capitalizing on a series of regioselective acylation reactions with 2-decenoic acid and imidazolium sulfate esters. 相似文献
169.
170.
Adam Bartoszek Paweł G. Walczak Szymon M. Walczak 《Bulletin of the Brazilian Mathematical Society》2014,45(1):179-195
We study the order of tangency of surfaces and Dupin cyclides. We show that generically the maximal tangency order equals 4 and provide a number of examples. 相似文献