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191.
Monika Kijewska Alicja Kluczyk Piotr Stefanowicz Zbigniew Szewczuk 《Rapid communications in mass spectrometry : RCM》2009,23(24):4038-4046
Hexose‐modified peptides, products of the enzymatic hydrolysis of glycated proteins, could be used as markers of diabetes mellitus, the aging process and other diseases. The main difficulty in this approach is the detection of glycated peptides in the complex mixtures of compounds. In this study we investigated the formation of borate complexes of the peptide‐derived Amadori products by high‐resolution mass spectrometry (HRMS) and tandem mass spectrometry (MS/MS) experiments. It was found that the formation of a complex with the borate ion stabilizes the sugar moiety, resulting in the simplification of the fragmentation patterns of peptide‐derived Amadori products. The level of dehydration, as well as the elimination of formaldehyde from the precursor ions of borate complexes, was lower as compared to the free peptide. On the other hand the intensity of the b‐ and y‐type ions for borate complexes is significantly higher in comparison to the free peptide‐derived Amadori product. Moreover, the elimination of a whole hexose moiety was not detected in the examined peptides. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
192.
Alicja Janik Andrzej Olech Anna Stasiewicz‐Urban Katarzyna Stadnicka 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(2):o70-o75
The room‐temperature crystal structures of four new thio derivatives of N‐methylphenobarbital [systematic name: 5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trione], C13H14N2O3, are compared with the structure of the parent compound. The sulfur substituents in N‐methyl‐2‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2‐thioxo‐1,2‐dihydropyrimidine‐4,6(3H,5H)‐dione], C13H14N2O2S, N‐methyl‐4‐thiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐4‐thioxo‐3,4‐dihydropyrimidine‐2,6(1H,5H)‐dione], C13H14N2O2S, and N‐methyl‐2,4,6‐trithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenylpyrimidine‐2,4,6(1H,3H,5H)‐trithione], C13H14N2S3, preserve the heterocyclic ring puckering observed for N‐methylphenobarbital (a half‐chair conformation), whereas in N‐methyl‐2,4‐dithiophenobarbital [5‐ethyl‐1‐methyl‐5‐phenyl‐2,4‐dithioxo‐1,2,3,4‐tetrahydropyrimidine‐6(5H)‐one], C13H14N2OS2, significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen‐bonding patterns of the derivatives. In the cases of the 2‐thio, 4‐thio and 2,4,6‐trithio derivatives, there is a preference for the formation of a ring motif of the R22(8) type, which is also a characteristic of N‐methylphenobarbital, whereas a C(6) chain forms in the 2,4‐dithio derivative. The preferences for hydrogen‐bond formation, which follow the sequence of acceptor position 4 > 2 > 6, confirm the differences in the nucleophilic properties of the C atoms of the heterocyclic ring and are consistent with the course of N‐methylphenobarbital thionation reactions. 相似文献
193.
Pawe? Foralewski Alicja Szymaszkiewicz 《Journal of Mathematical Analysis and Applications》2008,345(1):410-419
Some criteria for extreme points and strong U-points in Cesàro-Orlicz spaces are given. In consequence we find a Cesàro-Orlicz sequence space different from c0 which has no extreme points. Some examples show that in these spaces the notion of the strong U-point is essentially stronger than the notion of the extreme point. Various examples presented in this paper show that there are some differences between criteria for extreme points and strong U-points in Orlicz spaces and in Cesàro-Orlicz spaces. We also show that the uniqueness of the local best approximation needs the notion of SU-point, that is, the notion of the extreme point is not strong enough here. 相似文献
194.
Alicja Ustrzycka Natalia Piotrowska Alicja Bonk Janusz Filipiak Wojciech Tylmann 《Isotopes in environmental and health studies》2018,54(3):225-243
An isotopic monitoring was undertaken in 2012–2014 at Lake ?abińskie (Mazurian Lakeland, NE Poland). The aim was to identify the factors and processes controlling an isotopic composition of the lake water and to explore the mechanism responsible for recording the climatic signal in stable isotope composition of deposited carbonates. δ18O and δ2H in the precipitation, lake water column, inflows and outflow, δ18O and δ13C in the carbonate fraction of sediments trapped in the water column were recorded with monthly resolution. A relationship between δ18O and δ2H in local precipitation was used to estimate the local meteoric water line. The dataset obtained for the water enabled to identify the modification of the water’s isotopic composition due to evaporation, connected with seasonal lake water stratification and mixing patterns. Statistically significant correlation coefficients suggest that the δ18O of the carbonate fraction in the sediment traps depends on the δ18O of rainfall water and on air temperature. The fractionation coefficient α shows that in summer months the carbonate precipitation process is closest to equilibrium. As expected for an exorheic lake, no significant correlation was observed between δ18O and δ13C in precipitated carbonate. 相似文献
195.
Barbara Wozniak Iwona MatraszekZuchowska Alicja Klopot Andrzej Posyniak 《Journal of separation science》2019,42(21):3319-3329
For the detection of 19 steroid hormones in bovine muscle, a fast and sensitive liquid chromatography with electrospray ionization tandem mass spectrometry method was developed using both positive and negative ionization mode. Chromatographic separation on Poroshell 120‐EC C18 column was achieved in less than 10 min using isocratic elution of mobile phase of acetonitrile/methanol/water. The compounds were extracted from muscle tissue using ethyl acetate and quick, easy, cheap, effective, rugged, and safe technique. The purification of the obtained extract was performed by dispersive solid‐phase extraction with sorbents C18, primary secondary amine and magnesium sulphate. The method was validated in accordance with the Commission Decision 2002/657/EC. For all steroids tested good recoveries were obtained (from 51.2 to 121.4%) in the concentration range from decision limits until 5 µg/kg. The values of decision limits and the detection capabilities for individual compounds were in the range 0.10–0.48 and 0.17–0.95 µg/kg, respectively. The method was characterized by satisfactory linearity for most compounds (correlation coefficients > 0.99) and the reproducibility was lower than 35%. The elaborated procedure has met the criteria for confirmatory methods and is currently used in the official control of hormones. 相似文献
196.
An efficient synthesis of 17-epi-calcitriol 2, an epimer of natural hormone, via 17-epi-cholesterol 5a is described. Synthesis of 5a includes palladium-catalyzed cyclopropanation of the common androstane derivative 7 with an alkyl diazoacetate, reductive fission of the less shielded side of cyclopropane carboxylic acid esters 6, oxidation of the products into acid 11a, and alkylation of ester 11b. Photolysis of 7,8-dedydro-17-epi-25-hydroxycholesterol 19b and consecutive thermal rearrangement gave a mixture of several products that was subjected to ozonolysis to provide, after chromatography, hydroxy ketone 3a. The silyl derivative 3b was coupled with the respective ring A building block. 相似文献
197.
It is known that Goertzels algorithm is much less numerically accurate than the Fast Fourier Transform (FFT) (cf. [2]). In order to improve accuracy we propose modifications of both Goertzels and Horners algorithms based on the divide-and-conquer techniques. The proof of the numerical stability of these two modified algorithms is given. The numerical tests in Matlab demonstrate the computational advantages of the proposed modifications. The appendix contains the proof of numerical stability of Goertzels algorithm of polynomial evaluation.
AMS subject classification 65F35, 65G50 相似文献
198.
Andrzej Gobiowski Kazimierz Stoecki Urszula Prokop Alicja Kumierowska Tadeusz Borowiecki Andrzej Denis Czesawa Sikorska 《Reaction Kinetics and Catalysis Letters》2004,82(1):179-189
The influence of K2O on the amounts of chemisorbed hydrogen on a Ni catalyst, the catalyst activity and its resistance to coking were measured.
Introducing potassium into the commercial catalyst (not into the support) appeared to enhance its resistance to coking. The
best catalytic characteristics was noticed for a system containing ~0.5 wt. % K2O. The investigations show a good agreement between the resistance to coking obtained by the temperature-programmed reaction
(TPReaction) method and by the traditional thermogravimetric method.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
199.
Rümmeli MH Schäffel F Kramberger C Gemming T Bachmatiuk A Kalenczuk RJ Rellinghaus B Büchner B Pichler T 《Journal of the American Chemical Society》2007,129(51):15772-15773
Detailed HREM studies on carbon nanotubes (CNTs) synthesized via chemical vapor deposition (CVD) using nanoengineered Fe particles on oxide supports show capped tops and open-ended roots. We demonstrate that the pristine catalyst particle dictates the CNT diameter and number of walls at nucleation. The consecutive inward formation of concentric graphene caps during nucleation constricts and elongates the catalyst particle within the tube core. Continued growth stems from the oxide support. 相似文献
200.
Pilling S Duarte ES Domaracka A Rothard H Boduch P da Silveira EF 《Physical chemistry chemical physics : PCCP》2011,13(35):15755-15765
An experimental study of the interaction of highly charged, energetic ions (52 MeV (58)Ni(13+) and 15.7 MeV (16)O(5+)) with mixed H(2)O : C(18)O(2) astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H(2)O and CO(2) is about 3-4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C(18)O, CO (with oxygen from water), and H(2)O(2) increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies. 相似文献