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81.
In this study ground and excited states acidic dissociation constants of a recently synthesized Schiff base was obtained in a DMF:water mixture of 30:70 (v/v) using absorption and fluorescent spectra of the Schiff base in different pH values with the aid of chemometric methods. In addition, the fluorescent of the two kinds of tautomers of this Schiff base was investigated and the rate of tautomerization was obtained using rank annihilation factor analysis (RAFA). The effect of different kinds of surfactants such as sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 on fluorescence spectrum of the Schiff base in a DMF:water mixture of 2:98 (v/v) was investigated. CTAB increased the fluorescence intensity of the Schiff base while SDS and Triton X-100 had no significant effect on it. β-Cyclodextrin increased the fluorescence intensity of the Schiff base. Also the sensing behavior of this Schiff base toward metal ions was studied in DMF and ethanol by fluorescence spectroscopy. The Schiff base showed prominent fluorescent signal in the presence of Zn2+, whereas other metal ions failed to induce response and ground-state dissociation constant of the complex was determined by direct fluorimetric titration as a function of Zn2+ concentration. 相似文献
82.
Hasan budak Ahmet Bulut Naziye etin Canan Kazak 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(1):m1-m3
The crystal structure of the first acesulfame–metal complex, namely tetraaquabis[6‐methyl‐1,2,3‐oxathiazin‐4(3H)‐onato 2,2‐dioxide‐κN]cobalt(II), [Co(C4H4NO4S)2(H2O)4], is reported. The CoII ion resides on a twofold axis and is coordinated by four aqua ligands defining the basal plane and by two monodentate acesulfamate ligands, via their ring N atoms, in the axial positions. Two intra‐ and three intermolecular hydrogen‐bonding interactions stabilize the crystal structure and form an infinite three‐dimensional lattice. 相似文献
83.
Yousef Alavi Gary Chartrand F. R. K. Chung Paul Erds R. L. Graham Ortrud R. Oellermann 《Journal of Graph Theory》1987,11(2):235-249
A connected graph is highly irregular if each of its vertices is adjacent only to vertices with distinct degrees. In this paper we investigate several problems concerning the existence and enumeration of highly irregular graphs as well as their independence numbers, with particular focus on the corresponding problems for highly irregular trees. 相似文献
84.
Yousef Hashem Zahran 《国际流体数值方法杂志》2008,57(6):745-760
We describe a hybrid method for the solution of hyperbolic conservation laws. A third‐order total variation diminishing (TVD) finite difference scheme is conjugated with a random choice method (RCM) in a grid‐based adaptive way. An efficient multi‐resolution technique is used to detect the high gradient regions of the numerical solution in order to capture the shock with RCM while the smooth regions are computed with the more efficient TVD scheme. The hybrid scheme captures correctly the discontinuities of the solution and saves CPU time. Numerical experiments with one‐ and two‐dimensional problems are presented. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
85.
86.
We have investigated the interaction of obliquely propagating ion acoustic solitary waves in a magnetoplasma with relativistically degenerate electrons. Using the quantum hydrodynamics model and by employing the extended Poincaré–Lighthill–Kuo technique, we have derived a set of Korteweg de Vries equations for two solitons. We have observed that the system under consideration allows the formation of only compressive solitons and their velocities remain in the sub-acoustic limit. Furthermore, phase shifts of solitons as a result of their interaction have been calculated. The phase shifts have been observed to be dependent on the obliqueness and the physical parameters of plasma. It has also been noticed that phase shifts remain negative for the whole range of parameters generally found in white dwarf stars. We have observed that the phase shifts enhance with the enhancement in number density, however, the converse happens when the magnetic field is enhanced. It has also been observed that the phase shift is slightly greater for the solitons that are less oblique as compared to their more oblique counterparts. Furthermore, we have estimated the spatial scales of interaction of solitons using the parameters found in white dwarf stars. 相似文献
87.
Hasan Guleryuz Ingeborg Kaus Claudine Filiàtre Tor Grande Mari-Ann Einarsrud 《Journal of Sol-Gel Science and Technology》2010,54(2):249-257
Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured
for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica
sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied
that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing
the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration
of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6
decreased the deposition rate due to aggregation of the primary silica particles. 相似文献
88.
Pijanka JK Kumar D Dale T Yousef I Parkes G Untereiner V Yang Y Dumas P Collins D Manfait M Sockalingum GD Forsyth NR Sulé-Suso J 《The Analyst》2010,135(12):3126-3132
Over the last few years, there has been an increased interest in the study of stem cells in biomedicine for therapeutic use and as a source for healing diseased or injured organs/tissues. More recently, vibrational spectroscopy has been applied to study stem cell differentiation. In this study, we have used both synchrotron based FTIR and Raman microspectroscopies to assess possible differences between human pluripotent (embryonic) and multipotent (adult mesenchymal) stem cells, and how O(2) concentration in cell culture could affect the spectral signatures of these cells. Our work shows that infrared spectroscopy of embryonic (pluripotent) and adult mesenchymal (multipotent) stem cells have different spectral signatures based on the amount of lipids in their cytoplasm (confirmed with cytological staining). Furthermore, O(2) concentration in cell culture causes changes in both the FTIR and Raman spectra of embryonic stem cells. These results show that embryonic stem cells might be more sensitive to O(2) concentration when compared to mesenchymal stem cells. While vibrational spectroscopy could therefore be of potential use in identifying different populations of stem cells further work is required to better understand these differences. 相似文献
89.
Joanna Wiśniewska Hasan Marai Andrzej Karocki Konrad Szaciłowski Ewa Kita Zofia Stasicka 《Journal of photochemistry and photobiology. A, Chemistry》2010,209(2-3):121-127
Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O2 and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C2O4? radicals. The species undergo fast redox reactions dependent on the presence of O2 and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to CrIII. Then geminate recombination regenerates substrate, whereas competitive release of the C2O4? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C2O4? and pda3?; the intermediate releases also eaq?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda. 相似文献
90.
Obaid-Ur-Rahman Abid Muhammad Nawaz Nasim Hasan Rama Peter Langer 《Tetrahedron letters》2010,51(4):657-7025
The [4+2] cycloaddition of 1-ethoxy-2-chloro-1,3-bis(trimethylsilyloxy)-1,3-diene with dimethyl acetylenedicarboxylate (DMAD) afforded dimethyl 4-chloro-3,5-dihydroxyphthalate. Site-selective Suzuki-Miyaura reactions of its bis(triflate) provide a convenient approach to 3,5-diaryl-4-chlorophthalates containing two different aryl groups. 相似文献