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71.
A GC–MS/MS method with EI ionization was developed and validated to detect and quantify N-nitrosodimethylamine (NDMA) and seven other nitrosamines in 105 samples of metformin tablets from 13 different manufactures. Good linearity for each compound was demonstrated over the calibration range of 0.5–9.5 ng/mL. The assay for all substances was accurate and precise. NDMA was not detected in the acquired active pharmaceutical ingredient (API); however, NDMA was detected in 64 (85.3%) and 22 (91.7%) of the finished product and prolonged finished product samples, respectively. European Medicines Agency recommends the maximum allowed limit of 0.032 ppm in the metformin products. Hence, 28 finished products and 7 pronged dosage products were found to exceed the acceptable limit of daily intake of NDMA contamination. The implications of our findings for the testing of pharmaceutical products are discussed. 相似文献
72.
Grzegorz Litak Arkadiusz Syta Marian Wiercigroch 《Chaos, solitons, and fractals》2009,40(5):2095-2101
We have examined the cutting process by using a two degrees of freedom non-smooth model with a friction component. Instead of the standard Lyapunov exponent treatment a statistical ‘0–1’ test based on the asymptotic properties of a non-harmonic Brownian motion chain has been successively applied to reveal the nature of the cutting process. In this test we calculated the control parameter K which is approaching asymptotically to 0 or 1 for regular and chaotic motions, respectively. The presented approach is independent on the integration procedure as we defined a characteristic distance between the points forming the time series used in the test separately. 相似文献
73.
Arkadiusz Jadczyk 《Advances in Applied Clifford Algebras》2011,21(4):721-756
Using the standard Cayley transform and elementary tools it is reiterated that the conformal compactification of the Minkowski
space involves not only the “cone at infinity” but also the 2-sphere that is at the base of this cone. We represent this 2-sphere
by two additionally marked points on the Penrose diagram for the compactified Minkowski space. Lacks and omissions in the
existing literature are described, Penrose diagrams are derived for both, simple compactification and its double covering
space, which is discussed in some detail using both the U(2) approach and the exterior and Clifford algebra methods. Using the Hodge *{\star} operator twistors (i.e. vectors of the pseudo-Hermitian space H
2,2) are realized as spinors (i.e., vectors of a faithful irreducible representation of the even Clifford algebra) for the conformal
group SO(4, 2)/Z
2. Killing vector fields corresponding to the left action of U(2) on itself are explicitly calculated. Isotropic cones and corresponding projective quadrics in H
p,q
are also discussed. Applications to flat conformal structures, including the normal Cartan connection and conformal development
has been discussed in some detail. 相似文献
74.
75.
Dr. Hubert Gojzewski Dr. Michael Kappl Gunnar Kircher Dr. Wojciech Koczorowski Prof. Dr. Hans‐Jürgen Butt Dr. Arkadiusz Ptak 《Chemphyschem》2013,14(3):543-549
Nanoadhesion on a self‐assembled monolayer of 4‐methyl‐4′‐mercaptobiphenyl is measured using a modified atomic force microscope. The dependence of the adhesion force on the loading rate is analyzed with the Dudko–Hummer–Szabo model, and the kinetic and interaction potential parameters for a single terminal group are extracted. The energy and location of the activation barrier suggest that the adhesion is dominated by van der Waals dispersion forces. The humidity effect on the nanoadhesion is also studied. The results are compared with previously measured values for methyl‐terminated alkane thiols and the influence of the thiol rigidity on the adhesion force is discussed. 相似文献
76.
Dr. Tomasz Kaczorowski Dr. Iwona Justyniak Daniel Prochowicz Dr. Karolina Zelga Arkadiusz Kornowicz Prof. Dr. Janusz Lewiński 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(42):13460-13465
Previous studies have demonstrated that [(CN)2AlCl] and [R2Al(μ‐CN)]2 (CN=deprotonated cinchonine) complexes can effectively act as chiral, semirigid, N,N‐ditopic metalloligands for Zn‐containing nodes, and provide viable means for constructing new, homochiral, heterometallic, coordination polymers of zigzag and helical topologies. These findings have prompted further investigations on the organometallic analogues of the formula [(CN)2AlR], anticipating their utility as N,N‐metalloligands for ZnR2 units. Surprisingly, reactions of [(CN)2AlMe]‐type metalloligands with ZnR2 compounds (R=Me or Et) revealed unprecedented ligand‐exchange processes, including zinc‐to‐aluminium and aluminium‐to‐zinc transmetalations of alkyl groups. The molecular and crystal structure of the resulting compounds was determined by X‐ray diffraction analysis. From the reaction of [(CN)2AlMe] with ZnMe2 a new pseudopolymorphic form of a noncovalent porous material based on [Me2Al(μ‐CN)]2 molecules was isolated. Strikingly, the analogous reaction involving ZnEt2 led to the generation of a new chiral 4N‐tetratopic heterometalloligand [(CN)EtAl(μ‐CN)2ZnEt]. The latter unit was successfully connected by alkyl‐exchanged ZnMe2 nodes to give an original homochiral heterometallic {[(CN)EtAl(μ‐CN)2ZnEt]ZnMe2}n coordination polymer adopting a snake 1D motif. The outcome of the revealed reactions indicates the complicated multistep reaction route that involves redistribution of cinchonine and alkyl ligands among the Al and Zn centers, and a general reaction scheme is proposed. The results are in strong contrast with the previously studied inorganic–organic [(CN)2AlCl/ZnCl2] system, which exclusively affords a helical coordination polymer based on ZnCl2 nodes and (CN)2AlCl metalloligands and lacks the exchange of CN ligands. 相似文献
77.
Zelga K Leszczyński M Justyniak I Kornowicz A Cabaj M Wheatley AE Lewiński J 《Dalton transactions (Cambridge, England : 2003)》2012,41(19):5934-5938
An equimolar reaction between ZnEt(2) and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) results in the formation of EtZn(hpp) (1) which crystallizes as a trinuclear agglomerate with the guanidinate ligands spanning 4-coordinate Zn centers. Exposure of a pre-formed THF solution of 1 to undried air leads to a ZnO-incorporating derivative 1(4)·ZnO, while an analogous experiment with CH(2)Cl(2) as solvent leads to a novel tetranuclear mixed aggregate formulated as [EtOZn(hpp)](2)[ClZn(hpp)](2) (2). The composition of 2 indicates that its formation proceeds via a complex multi-step reaction route that involves not only the oxygenation of ZnEt moieties, but also the activation of CH(2)Cl(2), causing the transfer of a chloride anion to the Zn center. Compounds were characterized by (1)H NMR spectroscopy and single-crystal X-ray diffraction analysis. 相似文献
78.
A novel method to determine of azaarenes in refined and cold‐pressed vegetable oils and animal fats is reported. The method may be used to determine eight most important acridine derivatives (benz[a]acridine, dibenz[a,i]acridine, benz[c]acridine, dibenz[a,j]acridine, 7,9‐dimethylbenz[c]acridine, dibenz[a,h]acridine, dibenz[a,c]acridine, dibenz[c,h]acridine) at a high sensitivity (LOQ in the 2–25 ng kg?1 range), high analyte recovery rates (70.7–98.7%), sufficient linearity within the studied concentration range (r > 0.97). The method is fast, simple, and needs no expensive clean‐up procedures to successfully determine the analytes. Azaarene concentration in the studied oil samples ranged from 2 to 250 ng kg?1. Benz[a]acridine and dibenz[a,j]acridine were the compounds found most commonly and at the highest concentrations. The observed concentrations most probably reflected levels of environmental contamination of raw materials used to produce the analyzed oil/fat samples. 相似文献
79.
Tomasz ?ojewski Katarzyna Zi?ba Arkadiusz Knapik Jacek Bagniuk Anna Lubańska Joanna ?ojewska 《Applied Physics A: Materials Science & Processing》2010,100(3):809-821
The study presents an overview of the chromatographic (SEC), spectroscopic (FTIR, UV/VIS), viscometric (DP) and chemical methods
(titration, pH) used for the evaluation of the degradation progress of various kinds of paper under various conditions. The
methods were chosen to follow different routes of paper degradation. Model paper samples represented boundary paper types
from pure cellulose cotton paper, through softwood to low quality acidic, sized groundwood paper The accelerated ageing conditions
were adjusted to achieve maximum effect (climatic chamber RH 59%, 90oC) and also to mimic the environment inside books (closed vials). The results were settled on the literature data on the degradation
mechanisms and compared in terms of the paper types and ageing conditions. The estimators of coupled de-polymerisation and
oxidation have been proposed based on the correlation between SEC, UV/VIS and titrative coppper number determination. The
overall oxidation index derived from FTIR results was shown to correlate with the summary –CHO and –COOH concentration determined
by titrative methods. 相似文献
80.
Dr. Iwona Olejniczak Arkadiusz Frąckowiak Prof. Roman Świetlik Dr. Tatiana G. Prokhorova Prof. Eduard B. Yagubskii 《Chemphyschem》2013,14(17):3925-3935
The polarized infrared reflectance and Raman spectra of the three quasi‐two‐dimensional β′′‐(BEDT‐TTF)4[(H3O)Fe(C2O4)3]?Y bifunctional charge‐transfer salts, where BEDT‐TTF=bis(ethylenedithio)tetrathiafulvalene and Y=C6H5Br, (C6H5CN)0.17(C6H5Br)0.83, (C6H5CN)0.4(C6H5F)0.6, have been measured as a function of the temperature. Signatures of charge inhomogenity have been found in both Raman and infrared spectra of the β′′‐(BEDT‐TTF)4[(H3O)Fe(C2O4)3]?Y superconductors. A 100 K transition to a mixed insulating/metallic state is clearly seen for the first time in the temperature dependence of the electronic spectra of superconducting β′′‐(BEDT‐TTF)4[(H3O)Fe(C2O4)3]?C6H5Br. We suggest that this phase transition is due to subtle changes in the ethylene groups ordering, which are related to a structural phase transition in the anionic layer. The infrared and Raman spectra of quasi‐two‐dimensional metal α‐′pseudo‐κ′‐(BEDT‐TTF)4[(H3O)Fe(C2O4)3]C6H4Br2 are also investigated. 相似文献