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排序方式: 共有307条查询结果,搜索用时 15 毫秒
21.
Ioana Sisu Valentina Udrescu Corina Flangea Sorin Tudor Nicolae Dinca Lucian Rusnac Alina D. Zamfir Eugen Sisu 《Central European Journal of Chemistry》2009,7(1):66-73
A variety of carbohydrates, in particular polysaccharides can be subjected to chemical modification to obtain derivatives
with amphiphilic properties, which enable biochemical or biological reactions at the polymer surface. In the present work,
a polydisperse maltodextrin mixture of average molecular weight 3000 was coupled with 1,6-hexamethylenediamine (HMD) via reductive amination reaction. Resulting products were characterized by thermal analysis and positive nanoelectrospray quadrupole
time-of-flight (Q-TOF) mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Both thermal analysis and MS screening
confirmed the formation of the HMD-polysaccharide coupling products. Moreover, HMD-linked polysaccharide chains containing
2 to 26 glucose building blocks were identified by nanoESI Q-TOF MS. MS/MS fragmentation using collision-induced dissociation
(CID) at low ion acceleration energies provided strong evidence for HMD-maltodextrin linkage formation and the set of sequence
ions diagnostic for the composition and structure of a HMD-linked chain containing 18 glucose residues.
相似文献
22.
A. Ungureanu H. V. Thang D. Trong On E. Dumitriu S. Kaliaguine 《Journal of Thermal Analysis and Calorimetry》2007,87(2):417-422
UL-ZSM-5 materials have been prepared by templated solid-state crystallization of zeolites starting from the amorphous mesostructured aluminosilicate Al-Meso. Microcalorimetry and FTIR have been employed to characterize their surface acidity. In good agreement with 27Al MAS NMR data, UL-ZSM-5 displayed an improved density and strength of Brönsted acid sites, as compared to Al-Meso, owing to the incorporation of aluminium in a tetrahedral environment similar to that of zeolite ZSM-5. Moreover, they showed an enhanced Brönsted/Lewis relative acid ratio. However, Al-Meso showed the highest concentration of strong Lewis acid sites due to its largest amount of aluminium in extraframework positions. 相似文献
23.
Distribution of some major and trace elements in Danube Delta lacustrine sediments and soil 总被引:2,自引:0,他引:2
L. C. Dinescu E. Steinnes O. G. Duliu C. Ciortea T. E. Sjobakk D. E. Dumitriu M. M. Gugiu M. Haralambie 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):345-354
Sediment cores collected from lakes Mesteru and Furtuna (eastern part), Sontea channel and soil samples collected from Caraorman
bar, all located in the Danube Delta, were analyzed for 42 elements (Ag, Al, As, Be, Na, Mg, P, S, K, Ca, Sc, Ti, V, Cr, Mn,
Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Mo, Ag, Cd, In, Sn, Sb, Cs, Ce, Hf, Hg, Tl. Pb, Bi, Th. U) by instrumental
neutron activation analysis (INAA), thick target proton induced X-ray emission (TT-PIXE) and inductively coupled plasma-mass
spectrometry (ICP-MS). The INAA and TTPIXE yielded total concentrations whereas the ICP-MS data reflected the fractions soluble
in 14M HNO3. The ICP-MS data exhibited surface enrichment relative to the lower part of the sediment core of Cu, Zn, As, Ag, Cd, In,
Sn, Sb, Hg, Tl, Pb, and Bi, most prominently by Cd and Hg. Their vertical distribution in the investigated cores generally
reflected the pollution history of recent sediments in Danube delta, showing a steady increase until the end of the 1980s
followed by a slow decrease after 1990. The vertical profiles of most remaining elements were characterized by a relatively
uniform distribution along the cores. In some cases, the concentrations of As, Cd, Cu, Cr, Mn, Ni and Pb exceeded minimum
thresholds of safety, as defined by the Romanian regulations. The elemental composition of the sediment below 20 cm depth
(total concentrations) was similar to that of the upper continental crust (UCC) for most elements. Values distinctly higher
than UCC were observed for As, Sb (factor ~5) and Cr, Ni, Cu (factor 2 to 3). The nitric acid soluble element concentrations
in the soil samples in some cases showed increased values at the surface as compared to 30 cm depth, either due to air pollution
or to the action of plants. In no case a large contribution to the topsoil from atmospheric deposition was evident, indicating
that the surface contamination of the sediments was mainly by riverine transport.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
24.
25.
When a single DNA molecule is stretched beyond its normal contour length, a force-induced melting transition is observed. Ethidium binding increases the DNA contour length, decreases the elongation upon melting, and increases the DNA melting force in a manner that is consistent with the ethidium-induced changes in duplex DNA stability known from thermal melting studies. The DNA stretching curves map out a phase diagram and critical point in the force-extension-ethidium concentration space. Intercalation occurs between alternate base pairs at low forces and between every base pair at high forces. 相似文献
26.
Ioana Cioranescu Valentin Keyantuo 《Proceedings of the American Mathematical Society》2000,128(12):3587-3593
Using entire regularizations of groups, we give a characterization of their analytic generators which we apply to the study of products of such generators.
27.
JPC – Journal of Planar Chromatography – Modern TLC - Given the large applicability in both pharmaceutical and cosmetic field, this work was aimed at analytical (high-performance... 相似文献
28.
S. Dumitriu M. I. Popa I. Hăulică A. Crîngu A. Stratone 《Colloid and polymer science》1989,267(7):595-599
Ampicillin and chloramphenicol were coupled on xanthan by activation by dicyclohexyl-carbodiimide. Drug release from the support was studied in vitro for ampicillin, and in vitro and in vivo conditions for chloramphenicol. 相似文献
29.
Niculina D. Bogdan Dr. Mihaela Matache Veronika M. Meier Dr. Cristian Dobrotă Dr. Ioana Dumitru Gheorghe D. Roiban Dr. Daniel P. Funeriu Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2170-2180
Herein we describe the design and synthesis of the first series of di‐functional ligands for the directed construction of inorganic‐protein frameworks. The synthesized ligands are composed of a metal‐ion binding moiety (terpyridine‐based) conjugated to an epoxysuccinyl peptide, known to covalently bind active cysteine proteases through the active‐site cysteine. We explore and optimize two different conjugation chemistries between the di‐functionalized metal‐ion ligand and the epoxysuccinyl‐containing peptide moiety: peptide‐bond formation (with limited success) and CuI‐catalysed click chemistry (with good results). Further, the complexation of the synthesized ligands with FeII and NiII ions is investigated: the di‐functional ligands are confirmed to behave similarly to the parent terpyridine. As designed, the peptidic moiety does not interfere with the complexation reaction, in spite of the presence of two triazole rings that result from the click reaction. ES‐MS together with NMR and UV/Vis studies establish the structure, the stoichiometry of the complexation reactions, as well as the conditions under which chemically sensitive peptide‐containing polypyridine ligands can undergo the self‐assembly process. These results establish the versatility of our approach and open the way to the synthesis of di‐functional ligands containing more elaborated polypyridine ligands as well as affinity labels for different enzyme families. As such, this paper is the first step towards the construction of robust supramolecular species that cover a size‐regime and organization level previously unexplored. 相似文献
30.
Traian Mazilu M?d?lina Dumitriu Cristina Tudorache 《Journal of sound and vibration》2011,330(15):3729-3743
The paper herein deals with the study of the dynamic behaviour generated by the instability of the vibration of a loaded mass, uniformly moving along an Euler-Bernoulli beam on a viscoelastic foundation, induced by the anomalous Doppler waves excited in the beam. This issue is relevant for the case of modern trains travelling along a track with soft soil when the trains speed exceeds the phase velocity of the waves induced in the track. The model corresponds to a railway vehicle reduced to a loaded wheel running along a (half) track. The beam takes account of the bending stiffness of the rail and the mass of the track, including the mass of the rail, semi-sleepers and half of the ballast layer, where the viscoelastic foundation represents the subgrade. The model includes the wheel/rail Hertzian contact and it allows the simulation of the possibility of contact loss. The nonlinear equations of motion are integrated using a numerical approach based on the Green’s function method. When the vibration becomes unstable, the system evolution is a limit cycle characterised by a succession of shocks, due to the action of two opposite factors: the anomalous Doppler waves that pump energy at the interface between the moving mass and the beam, thus forcing the mass to take off, and the static load that push the mass downwards. The frequency of the shocks increases at higher velocity and the magnitude of the impact force decreases; the most dangerous velocity is the critical one, which represents the stability limit of the linear approximation of the motion equations. The transient behaviour that precedes the limit cycle appearance is being analysed. The Hertzian contact influences the time history of the limit cycle and the magnitude of the impact force and, therefore, it is essential to be included in the model. To the authors’ knowledge, this problem has never been dealt with. 相似文献