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111.
In this paper 1,3-dipolar cycloaddition reaction has been studied. An efficient synthesis of 4′-[3-methyl-5-thioxo-1H-1,2,4-triazol-4(5H)-yl]-2′,5′-diphenyl-2′,4′-dihydro spiro(indolin-3,3′[1,2,4]triazol)-2-one derivatives using triethylamine in MeCN at room temperature is reported. The structures of the obtained compounds were confirmed by means of elemental analysis, MS and spectral (IR, 1H, and 13C NMR) methods. 相似文献
112.
INTRODUCTION: Image contrast between tissue types can be generated based on their T1/T2 ratio using spin-lock MRI techniques. An interesting application of such a concept would be to generate contrast in tissue with tissue relaxation times modified using exogenous contrast agents. An amplitude-modulated adiabatic waveform has been shown in the past to perform spin-lock MRI. However, implementation of this waveform may not prove to be efficient and practical in research or a clinical setup due to high radiofrequency power deposition. Recent advancement in software and hardware MR technology allows implementation of amplitude- and phase-modulated adiabatic waveforms on MR systems. The aim of this work was to explore role of adiabatic waveforms in performing rho imaging and demonstrate that amplitude- and phase-modulated waveforms [e.g., hyperbolic secant, B1 independent rotation-4 (BIR-4) waveforms] can be used to distinguish materials that differ in T1/T2 ratio. METHODS AND RESULTS: MR simulation was performed using computer routines implemented in MATLAB environment (Mathworks, Natick, MA). Modified Bloch equations with trapezoidal, hyperbolic secant and BIR-4 waveforms were used to perform MR simulation. Trapezoidal waveforms were only used for comparison to other waveforms. Gadolinium DTPA (Gad-DTPA) (T1/T2 approximately 1) and manganese chloride (MnCl(2)) (T1/T2 approximately 10) were used as examples of contrast agents due to their routine use in clinical and research setups and more importantly because they provide good examples of materials differing in T1/T2 ratios. Results of spin locking using trapezoidal waveform agree very well with the previously published results, thereby validating the computer routines used in this MR simulation. Plots of M(rho) (magnetization vector in rho domain) vs. offset frequency show distinct curves for these materials differing in T1/T2 for the three waveforms. BIR-4 waveform demonstrated a 40% difference in M(rho) ( approximately 150 Hz) for the materials. Rate of spin lock with hyperbolic secant waveform was rapid compared to other waveforms. DISCUSSION: MR simulation using contrast agents Gad-DTPA and MnCl(2) provided a useful way to demonstrate that amplitude- and phase-modulated adiabatic waveforms can be used to perform spin-lock imaging. Future work involves implementation of these waveforms on MR scanners and performing in vivo imaging to generate tissue contrast based on relaxation times ratio. 相似文献
113.
Johansson PG Rowley JG Taheri A Meyer GJ Singh SP Islam A Han L 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14522-14531
The role of low-lying π* orbitals in dye-sensitized solar cells based on mesoporous thin films of anatase TiO(2) nanocrystallites remains unknown. Herein we report three ruthenium compounds, cis-Ru(dcbq)(2)(NCS)(2), cis-Ru(dcbq)(bpy)(NCS)(2), and cis-Ru(dcb)(bq)(NCS)(2), where bpy is 2,2'-bipyridine, dcb is 4,4'-(CO(2)H)(2)-2,2'-bipyridine, bq is 2,2'-biquinoline, and dcbq is 4,4'-(CO(2)H)(2)-2,2'-biquinoline, that were synthesized, characterized, and contrasted with the well-known N3 compound (i.e., cis-Ru(dcb)(2)(NCS)(2)) in dye-sensitized solar cells. These compounds maintain the same cis-Ru(NCS)(2) core with a systematic variation in the energy of the π* orbitals of the diimine ligand: bpy > dcb > bq > dcbq. The lowered π* orbitals resulted in enhanced red absorption relative to N3. With HCl pretreated TiO(2) in regenerative solar cells, sensitization from 400 to 900 nm was realized with cis-Ru(dcb)(bq)(NCS)(2) and global power conversion efficiencies as high as 6.5% were achieved under 1 sun of AM 1.5 irradiation. The energy conversion efficiency was found to be acutely sensitive to the presence of p-tert-butylpyridine (TBP) in a 0.5 M LiI/0.05 M I(2) acetonitrile electrolyte. Nanosecond transient absorption studies revealed that the addition of TBP decreased the excited-state injection yield for the compounds with biquinoline ligands. Spectro-electrochemical studies showed that the HCl pretreatment lowered the effective density of TiO(2) acceptor states and confirmed that the presence of TBP raised them toward the vacuum level. There was no spectroscopic data to support the hypothesis that the π* levels of the diimine ligand mediate back-electron transfer to the oxidized dye or the redox mediator was found. 相似文献
114.
M. Ansari Fard G. H. Rounaghi M. Chamsaz K. Taheri 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(1-2):49-56
The complexation reaction between UO2 2+ cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile–methanol (AN–MeOH), nitromethane–methanol (NM–MeOH) and propylencarbonate–ethanol (PC–EtOH) binary mixed systems at 25 °C. In addition, the complexation process between UO2 2+ cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), acetonitrile–ethylacetate (AN–EtOAc), methanol–water (MeOH–H2O), ethanol–water (EtOH–H2O), acetonitrile–water (AN–H2O), dimethylformamide–methanol (DMF–MeOH), dimethylformamide–ethanol (DMF–EtOH), and dimethylformamide–ethylacetate (DMF–EtOAc) binary solutions at 25 °C using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between (18C6) and (DA18C6) with UO2 2+ cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L2] complex is formed in solutions. The values of stability constants (log Kf) of (18C6 · UO2 2+) and (DA18C6 · UO2 2+) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions. In all cases, a non-linear relationship is observed for the changes of stability constants (log Kf) of the (18C6 · UO2 2+) and (DA18C6 · UO2 2+) complexes versus the composition of the binary mixed solvents. The stability order of (18C6 · UO2 2+) complex in pure studied solvents was found to be: EtOH > AN ≈ NM > PC ≈ MeOH, but in the case of (DA18C6 · UO2 2+) complex it was : H2O > MeOH > EtOH. 相似文献
115.
116.
In this work, the effect of cyclic pre-hardening (CPH) and monotonic pre-hardening (MPH), on the Cyclic Stress-Strain Curve (CSSC) and fatigue are considered. New tension-compression tests on two types of 304L alloys used in nuclear power plants are carried out under the following conditions: (i) strain or stress control near endurance limit; (ii) zero or positive mean stress; (iii) virgin, CPH or MPH specimens. Macroscopic results show a detrimental effect of pre-hardening in strain control and a beneficial one in stress control. Some macroscopic considerations are given to explain this result and the effects of an applied mean stress which differ under stress and strain control. Relations between macroscopic results and microstructures at failure are investigated using SEM and TEM. SEM is used for analysis of fatigue striation space.TEM analyses suggest that cyclic pre-hardening mainly promotes wavy slip during subsequent fatigue testing, while monotonous pre-loading favors planar slip. For CPH case it seems that primary cells which are preserved and refined for the most part during fatigue testing, constitute the hard stable structure. After MPH and subsequent fatigue testing, a hard structure is constituted by embedding of three kinds of microstructures, small twins, small cells, crossing twin systems. The formation of a hard structure creates an important internal stress. Observation shows that in pre-hardened specimens, softening arrays as veins and PSBs are frequent under strain control and rather scarce under stress control. It can be so deduced that the increase of fatigue life by pre-hardening in stress control is related to reduced mean free path of mobile dislocations due to internal stress.The obtained results may help to understand some aspects about linear versus non linear fatigue damage accumulation. 相似文献
117.
Elham Sadat Taheri Mohsen Jahanshahi Mohammad Taghi Hamed Mosavian 《Particle & Particle Systems Characterization》2012,29(3):211-222
Protein nanoparticles have been recognized as carriers to deliver low molecular‐weight drugs, anticancer drug, DNA, vaccines, oligonucleotides, peptides and etc. The purpose of this research was preparation of Egg Albumin (EA) nanoparticle with suitable size/size distribution and good surface properties for drug delivery application based on simple coacervation method along with optimization of the nanoparticles by employing Taguchi method. Several synthesis parameters were examined to characterize their impacts on nanoparticle size and topography. These variables were including temperature, EA concentration, desolvating agent volume, pH value and agitation speed. In addition, size and morphology of prepared nanoparticles were analyzed by photon correlation spectroscopy (PCS) as well as atomic force microscopy (AFM). As result of Taguchi analysis in this research, desolvating agent volume and pH were most influencing factors on particle size. The minimum size of nanoparticles (~51 nm) were obtained at Temperature 55 °C, 30 mg/ml EA concentration, desolvating agent volume 50 ml, agitation speed of 500 rpm and pH 4. The mechanistic of optimum conditions for preparing protein nanoparticles from Egg Albumin for the first time and their characterization as delivering nano system are discussed. 相似文献
118.
A. Vikas Aggarwal Dr. Stefan‐S. Jester Sara Mehdizadeh Taheri Prof. Dr. Stephan Förster Prof. Dr. Sigurd Höger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4480-4495
We present the efficient synthesis of a new molecular spoked‐wheel structure ( MSW‐3 ). Two derivatives with diameters of approximately 4 nm have been prepared. By highlighting the importance of pseudo‐high‐dilution conditions during cyclization, we were able to access the compounds on a several hundred milligram scale. In addition to the standard characterization (NMR spectroscopy, MS), we describe a detailed investigation of the optical properties of the fluorescent MSWs by comparison with appropriate model chromophores. Furthermore, a comprehensive study of the structure in solution by means of light‐ and X‐ray scattering experiments has been conducted. Scanning tunneling microscopy (STM) revealed the two‐dimensional organization of the molecules on highly oriented pyrolytic graphite and emphasized the spoked‐wheel structure. The diameter of these molecules measured by small‐angle X‐ray scattering is in very good agreement with that obtained from STM and matches the results of molecular modeling. This confirms the rigidifying effect of the spokes, which results in highly shape‐persistent nanometer‐sized oblate organic compounds. 相似文献
119.
Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography 下载免费PDF全文
Salman Taheri Fahimeh Jalali Nazir Fattahi Gholamreza Bahrami 《Journal of separation science》2015,38(2):309-315
A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r2 = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples. 相似文献
120.
Mehdi Ghandi Abuzar Taheri Abolfazl Hasani Bozcheloei Alireza Abbasi Reza Kia 《Tetrahedron》2012,68(18):3641-3648
The initially prepared 2-formylphenyl-(E)-2-phenylethenesulfonates from the condensation of (E)-2-phenylethenesulfonyl chloride with 2-hydroxybenzaldehyde derivatives underwent intramolecular [3+2] cycloaddition with methyl or phenylhydroxylamine, sarcosine, and l-proline, affording the corresponding novel isoxazolidine, pyrrolidine and pyrrolizidine-annulated γ,δ-benzo-δ-sultones, respectively, in good yields. Unambiguous assignment of the molecular structures was carried out by single-crystal X-ray diffraction. 相似文献