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排序方式: 共有473条查询结果,搜索用时 15 毫秒
91.
Kumari S Prabhakar S Vairamani M Devi CL Chaitanya GK Bhanuprakash K 《Journal of the American Society for Mass Spectrometry》2007,18(8):1516-1524
L-Tyrosine and iodinated L-tyrosines, i.e., 3-iodo-L-tyrosine and 3,5-diiodo-L-tyrosine, are successfully used as chiral references for the chiral discrimination of aliphatic, acidic, and aromatic amino acids. Chiral discrimination is achieved by investigating the collision-induced dissociation spectra of the trimeric complex [Cu(II)(ref)(2)(A) - H](+) ion generated by electro spraying the mixture of D- or L-analyte amino acid (A), chiral reference ligand (ref) and M(II)Cl(2) (M = Ni and Cu). The relative abundances of fragment ions resulted by the competitive loss of reference and analyte amino acids are considered for measuring the degree of chiral discrimination by applying the kinetic method. The chiral discrimination ability increases as the number of iodine atom increases on the aromatic ring of the reference and the discrimination is better with Cu when compared with Ni. A large chiral discrimination is obtained for aliphatic and aromatic amino acids using iodinated L-tyrosine as the reference. Computational studies on the different stabilities of the diastereomeric complexes also support the observed differences measured by the kinetic method. The suitability of the method in the measurement of enantiomeric excess over the range of 2% to 100% ee with relative error 0.28% to 1.6% is also demonstrated. 相似文献
92.
Based on a thermodynamic model, we investigate how the density variation influences the smectic (Sm A)–isotropic (I) phase transition. We find that the density variation shifts the smectic A–isotropic transition temperature, however, first-order nature of the transition remains the same. Here, we also examine the effect of high pressure on the thermodynamic quantities. The present analysis shows that the pressure strongly influences the enthalpy and density step at the clearing transition. The pressure dependence of the thermodynamic properties is incorporated through the pressure dependent second Landau coefficient and the coefficients which couple the nematic and smectic order parameters to the density. We find a close agreement between theoretical and experimental results. Furthermore, we discuss the implications of the results for achiral liquid crystals. 相似文献
93.
Latha Kumari S. V. Subramanyam 《Applied Physics A: Materials Science & Processing》2009,95(2):343-349
Amorphous carbon–sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in
the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature
of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content
and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural
disorder or increase in sp
2 or π-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp
3/sp
2 hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp
2 hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration
and the pyrolysis temperature. 相似文献
94.
Kumari Rinki Pradip K. Dutta Andy J. Hunt James H. Clark Duncan J. Macquarrie 《Macromolecular Symposia》2009,277(1):36-42
A novel chitosan-formaldehyde porous derivative (scaffolds) was prepared by reaction of 85% deacetylated chitosan with 37% aq. formaldehyde using supercritical carbon dioxide (sc. CO2). Prior to reaction, the chitosan hydrogel was prepared in 1% aq. acetic acid (AcOH) and formaldehyde. The prepared hydrogel was subjected to solvent exchange. The identity of the Schiff base was confirmed by Fourier transform infrared spectroscopy (FTIR). The chitosan-derivative was evaluated by thermal analysis, scanning electron microscopy, and porosimetry analysis. Overall, the sc. CO2 assisted chitosan derivative opens new perspectives as biomedical material. 相似文献
95.
Kamlesh Kumari K. K. Raina P. P. Kundu 《Journal of Thermal Analysis and Calorimetry》2009,98(2):469-476
The curing of chitosan–alanine with glutaraldehyde as curing agent in the presence of Chlorpheniramine Maleate (CPM) is carried out with the help of differential scanning calorimeter (DSC). The effect of concentration of chitosan and percentage of crosslinker on the curing is studied at a rate of 5 °C/min. Cure kinetics are measured from 30 to 200 °C at four different heating rates (3, 5, 7 and 10 °C/min). It is observed that the crosslinking of chitosan–alanine is an exothermic process which results in a positive peak in the curves. An increase in activation energy (E α) is observed with extent of conversion. 相似文献
96.
Colorimetric detection of anions (HSO4? and CN?) was achieved via analyte triggered colour changing of the dipodal and tripodal sensors in CH3CN–H2O (1:1). The sensors exhibited very sharp visual colour changes and fluorescence quenching–enhancing effect upon addition of the HSO4? and CN?. The large downfield shift of the NH proton signals in 1H-NMR complexation studies and quantum chemical DFT calculations proved the formation of hydrogen-bonded complexes where no proton transfer mechanism was found. 相似文献
97.
Raj Kumari Sumandeep Kaur 《中国物理快报》2014,(11):39-43
By using various proximity potentials, the fusion barrier heights and positions are calculated for proton and helium induced reactions with targets in the mass range 51≤ A ≤130 and 12≤ A ≤233, respectively. The calculated fusion barriers are parameterized by using the relations RB^Par = aX1 + b and VB^Par = cX2, where X1 and X2 are A2^1/3 and Z1Z2/RB^Par, respectively. The values of the constants a, b and c are different for different versions of proximity potentials. We find that the parameterized forms derived by using Proximity 1977 yield values closer to the empirical data in proton as well as helium induced reactions and can be used further to estimate directly the barrier parameters for the fusion reactions of proton and helium with any target. 相似文献
98.
Ionic liquid catalyzed synthesis of 7-phenyl-1,4,6,7-tetrahydro-thiazolo[5,4-d]pyrimidine-2,5-diones
Prashant Singh Kamlesh Kumari Monica Dubey Vijay K. Vishvakarma Gopal K. Mehrotra Narender D. Pandey Ramesh Chandra 《Comptes Rendus Chimie》2012,15(6):504-510
A simple, green and catalyst free one pot synthesis of 7-phenyl-1,4,6,7-tetrahydro-thiazolo[5,4-d]pyrimidine-2,5-diones via a multicomponent reaction between thiazolidine-2, 4-dione (TZD), aromatic aldehyde and urea analogues is described. The ionic liquid has been used as a solvent as well as catalyst for this reaction. This reaction proceeded smoothly in good to excellent yields and offered several other advantages including short reaction time, simple experimental workup procedure and no by-products. 相似文献
99.
A new bis‐indolyl‐based colorimetric probe has been synthesized. This allows a Michael‐type adduct formation for the detection of cyanide ions. The probe shows a remarkable color change from red to colorless upon addition of the cyanide ions in pure water. The cyanide ion reacts with the probe and removes the conjugation of the bis‐indolyl moiety of the probe with that of the 4‐substituted aromatic ring. This renders the probe colorless. The mechanism of the reaction of the probe with the cyanide ion was established by using 1H and 13C NMR spectroscopy, mass spectrometry, and kinetic studies. 相似文献
100.
Solution structure of insulin templated C-methyl resorcin[4]arene nanocapsules has been investigated using neutron scattering. The insulin biotemplate has enhanced the limits of encapsulation and enabled formation of a larger spherical molecular host. 相似文献