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排序方式: 共有106条查询结果,搜索用时 497 毫秒
11.
New hyperbranched hydrophobic cross‐linkers with peripheral azide groups were synthesized as follows: First, star‐shaped polycaprolactones (sPCL) were synthesized by ring‐opening polymerization of caprolactone in the presence of pentaerythritol and tin (II) octoate. In the next step, sequential acrylation, Micheal addition, tosylation, and azidation by acryloyl chloride, diethanol amine, tosyl chloride, and sodium azide were respectively exploited to synthesize azide‐functionalized hyperbranched star‐shaped polycaprolactones which were named sPCL‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐N3) and sPCL‐acrylate‐diethanolamine‐acrylate‐diethanolamine‐azide (sPCL‐AC‐DEA‐AC‐N3). All steps were thoroughly characterized by FT‐IR and 1H NMR spectroscopy. The GPC analysis showed that the molecular weight of sPCL increased after two azide functionalizations. Amphiphilic hydrogels based on sPCL‐AC‐DEA‐N3 (Mn = 8130 g/mol) and sPCL‐AC‐DEA‐AC‐N3 (Mn = 10112 g/mol) with linear alkyne‐terminated polyethylene glycols (PEG) (Mn = 2000, 4000, and 6000 g/mol) were synthesized through click coupling between azide and alkyne groups. In both hydrogels, the swelling ratio increased by increasing the molecular weight of PEG. The obtained results showed that the branching of the cross‐linker, significantly affected the swelling ratio of hydrogels. For instance, the swelling ratio of sPCL‐AC‐DEA‐AC‐N3 and PEG‐6000 (Q = 900) was higher than sPCL‐AC‐DEA‐N3 and PEG‐6000 (Q = 600). Despite the high cross‐linking density of sPCL‐AC‐DEA‐AC‐DEA‐N3–based hydrogels, the amount of released theophylline was higher than sPCL‐AC‐DEA‐N3–based hydrogels, due to the high content of PEG in these hydrogels. 相似文献
12.
Sohrab Kheradmandan Katja Heinze Helmut W. Schmalle Heinz Berke 《Angewandte Chemie (International ed. in English)》1999,38(15):2270-2273
Building blocks for conducting polymers or NLO materials are the linear, unsaturated carbon chain bridged manganese complexes 1 n+ (n=0–2). All oxidation states were investigated spectroscopically and by X-ray structure determinations. The analytical data confirm a communication of the electrons over the C4 chain—a prerequisite for electrical conductivity and NLO properties of oligo- or polymeric materials. 相似文献
13.
M. Sadegh Movahed Marzieh Farhang Sohrab Rahvar 《International Journal of Theoretical Physics》2009,48(4):1203-1230
We study one of the simplest covariant modified-gravity models based on the Dvali-Gabadadze-Porrati (DGP) brane cosmology,
a self-accelerating universe. In this model gravitational leakage into extra dimensions is responsible of late-time acceleration.
We mainly focus on the effects of the model parameters on the geometry and the age of universe. Also we investigate the evolution
of matter density perturbations in the modified gravity model, and obtain an analytical expression for the growth index, f. We show that increasing
leads to less growth of the density contrast δ, and also decreases the growth index. We give a fitting formula for the growth index at the present time and indicate that
dominant term in this expression verifies the well-known approximation relation f≃Ω
m
γ
. As the observational test, the new Supernova Type Ia (SNIa) Gold sample and Supernova Legacy Survey (SNLS) data, size of
baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), the position of the acoustic peak from the CMB observations and
the Cluster Baryon Gas Mass Fraction (gas) are used to constrain the parameters of the DGP model. We also combine previous
results with large scale structure formation (LSS) from the 2dFGRS survey. Finally to check the consistency of the DGP model,
we compare the age of old cosmological objects with age of universe in this model. 相似文献
14.
Ghasem Karim‐Nezhad Mohammad Hasanzadeh Lotfali Saghatforoush Sohrab Ershad Nasrin Shadjou 《中国化学会会志》2009,56(3):554-560
Electrocatalytic oxidation of acetaldehyde was investigated on a copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry and chronoamperometry techniques as well as steady state polarization measurements. It has been found that in the course of an anodic potential sweep the electro‐oxidation of acetaldehyde follows the formation of Cu(III) and is catalysed by this species through a mediated electron transfer mechanism. A mechanism based on the electrochemical generation of Cu(III) active sites and their subsequent consumption by the acetaldehyde in question was also investigated. 相似文献
15.
The Dirac equation in the presence of the Dirac magnetic monopole potential, the Aharonov-Bohm potential, a Coulomb potential and a pseudo-scalar potential, is solved by separation of variables using the spinweighted spherical harmonics. The energy spectrum and the form of the spinor functions are obtained. It is shown that the number j in spin-weighted spherical harmonics must be greater than $\left| q \right| - \tfrac{1} {2}$ . 相似文献
16.
Sohrab Sohrabi Laleh Mir Yousef Sadeghi Mahdi Hanifi Mostaghim 《Czechoslovak Mathematical Journal》2012,62(1):105-110
Let R be a commutative Noetherian ring, a an ideal of R, M an R-module and t a non-negative integer. In this paper we show that the class of minimax modules includes the class of AF modules. The main result is that if the R-module Ext
R
t
(R/a,M) is finite (finitely generated), H
a
i
(M) is a-cofinite for all i < t and H
a
t
(M) is minimax then H
a
t
(M) is a-cofinite. As a consequence we show that if M and N are finite R-modules and H
a
i
(N) is minimax for all i < t then the set of associated prime ideals of the generalized local cohomology module H
a
t
(M,N) is finite. 相似文献
17.
Multicomponent (two, three, and four component) amphiphilic conetworks (APCNs) with tunable swelling behaviors were fabricated through the ring opening polymerization and click chemistry utilizing various combinations of azide and alkyne functionalized poly (ethylene glycol) (PEG) and poly (caprolactone) (PCL) precursors. Prepare azido‐terminated star‐shaped PCL, azido‐terminated PEG, alkyne‐terminated PEG, and propargylated pentaerythritol were characterized by hydrogen‐1 proton nuclear magnetic resonance (1H NMR) and Fourier‐transform infrared (FT‐IR) spectroscopy. The morphology and thermal behavior of the APCNs were studied by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The swelling behavior of APCNs could be manipulated through an establishment of a balance between hydrophilic segments, hydrophobic segments, and cross‐linking density. The 2,4‐dichlorophenoxyacetic acid (2,4‐D) herbicide was entrapped in APCNs as a model agrochemical to study the release profile from APCNs. The obtained results showed that the release of 2,4‐D could be controlled by the swelling degree of APCNs. Finally, the biodegradability rates of APCNs were investigated in agricultural soil. The results exhibited that the decrease in the swelling degree led to decreased degradation rate of APCNs. According to obtained results, these APCNs could be used as biomaterials for the controlled release of agrochemicals. 相似文献
18.
Seyedeh Mahboobeh Yousefi Farzaneh Shemirani Sohrab Ali Ghorbanian 《Chromatographia》2018,81(8):1201-1211
In this work, we evaluated the applicability of hydrophobic carboxylic acid-based deep eutectic solvents (DESs) as environmentally friendly alternatives to common organic solvents in microextraction methods based on solidification of floating drop (SFD). Due to the limited number of solvents that can be used in SFD, the introduction of new solvents can help in the development of these attractive methods. Deep eutectic solvents consisting of tetra-n-butyl ammonium bromide (TBAB) and carboxylic acids were prepared and used as extraction solvent. They had the desirable characteristics such as low density, suitable freezing point and proper hydrophobicity which make them suitable alternatives to conventional organic solvents for SFD. With the help of the synthesized hydrophobic DESs, a simple, fast, efficient and environmentally friendly microextraction method was developed based on solidification of deep eutectic solvent (SFDES) without using any organic solvent. The proposed organic solvent-less microextraction method based on SFDES was applied in the analysis of polycyclic aromatic hydrocarbons (PAHs) as model compounds in environmental water samples. By coupling this method with high-performance liquid chromatography–fluorescence detection, we achieved low LOD values which is a necessity in the ultra-trace analysis of PAHs in environmental water samples. Under the optimized conditions, good linearity and low limits of detection of 0.7–6.6 ng L?1 were obtained. The analysis of six PAHs in real water samples gave acceptable relative recoveries ranging from 83 to 117% with 5.4–10.5% intra-day relative standard deviations (RSD) and 4–7.1% interday RSD. 相似文献
Graphical Abstract
19.
20.
Mahmoud Mirmehrabi Sohrab Rohani Michael C. Jennings 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(12):o695-o698
The crystal structure of the title compound (systematic name: 2′,3′‐didehydro‐2′,3′‐deoxythymidine), C10H12N2O4, consists of two molecules in the asymmetric unit bound together by hydrogen bonds. The conformational geometry differentiates this form of stavudine from its two previously published polymorphs. In addition, a different hydrogen‐bonding scheme is observed compared with the previous two structures. This polymorph is the thermodynamically most stable form of the antiviral drug, as evidenced by differential scanning calorimetry (DSC) and IR data. 相似文献