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排序方式: 共有124条查询结果,搜索用时 15 毫秒
81.
Maha A. Aboul Ela Abdalla M. El‐Lakany Maged S. Abdel‐Kader Saleh I. Alqasoumi Safa M. Shams‐El‐Din Hala M. Hammoda 《Helvetica chimica acta》2012,95(1):61-66
Fractionation directed by hepatoprotective activity of Inula crithmoides L. root resulted in the isolation of two new quinic acid derivatives, 3,5‐di‐O‐caffeoylquinic acid 1‐methyl ether ( I ; caffeoyl=(E)‐3‐(3,4‐dihydroxyphenyl)prop‐2‐enoyl; quinic acid=1,3,4,5‐tetrahydroxycyclohexanecarboxylic acid) and 4,5‐di‐O‐caffeoylquinic acid 1‐methyl ether ( II ), in addition to the well‐known hepatoprotective compound, 1,5‐di‐O‐caffeoylquinic acid ( III ). The hepatoprotective effect was indicated by the significant decrease in the level of four measured serum biochemical parameters (SGOT, SGPT, ALP, and bilirubin) in experimental rats. The structures of the isolated compounds were determined by analyses of 1D‐ and 2D‐NMR spectroscopic data. 相似文献
82.
Deferiprone and other 3-hydroxy-4-pyridinones are used in metal chelation therapy of iron overload. To investigate the structure and stability of these compounds in the natural aqueous environment, ferric complexes of deferiprone and amino acid maltol conjugates were synthesized and studied by computational and optical spectroscopic methods. The complexation caused characteristic intensity changes, a 300× overall enhancement of the Raman spectrum, and minor changes in UV-vis absorption. The spectra were interpreted on the basis of density functional theory (DFT) calculations. The CAM-B3LYP and ωB97XD functionals with CPCM solvent model were found to be the most suitable for simulations of the UV-vis spectra, whereas B3LYP, B3LYPD, B3PW91, M05-2X, M06, LC-BLYP, ωB97XD, and CAM-B3LYP functionals were all useful for simulation of the Raman scattering. Characteristic Raman band frequencies for 3-hydroxy-4-pyridinones were assigned to molecular vibrations. The computed conformer energies consistently suggest the presence of another isomer of the deferiprone-ferric complex in solution, in addition to that found previously by X-ray crystallography. However, the UV-vis and Raman spectra of the two species are similar and could not be resolved. In comparison to UV-vis, the Raman spectra and their combination with calculations appear more promising for future studies of iron sequestrating drugs and artificial metalloproteins as they are more sensitive to structural details. 相似文献
83.
Cyril Koughia Go Okada Dancho Tonchev Safa Kasap Andy Edgar Christopher R. Varoy Heinz von Seggern 《Journal of Non》2011,357(11-13):2272-2277
Photoluminescence (PL) and conventional and modulated temperature differential scanning calorimetry (DSC and MDSC) experiments have been carried out on a typical fluorochlorozirconate glass and glass-ceramics doped with Sm3+ and Sm2+ introduced by the addition of SmF3 and a reducing agent, NaBH4, into the initial mixture of constituents. The nominal FCZ composition was 53% ZrF4, 20% NaF, 3% AlF3, 3% LaF3, 1% SmF3, 1% BaF2, 19% BaCl2 (molar percentages). Prior to DSC and PL measurements, some of the glasses have been heat treated (annealed at an elevated temperature) under different conditions, which has resulted in glass-ceramics containing BaCl2 nanocrystals with a hexagonal and/or orthorhombic crystal structure, depending on the heat treatment conditions. Hexagonal nanocrystals may be obtained by a simple one step annealing process while the formation of orthorhombic crystallites requires sequential multistep annealing treatments. Long duration, low temperature annealing, required for the formation of orthorhombic BaCl2 nanocrystals, leads to the appearance of an endothermic enthalpy peak at around 250 °C on the conventional DSC thermogram. Temperature modulated DSC experiments identify a clear glass transformation in this regions; and the endothermic peak has been attributed to the structural relaxation enthalpy in the host glass which is usually obscured by the thermal effects associated with the formation of BaCl2 nanocrystals. The observed thermodynamic effects correlate with the suppression of the broad PL band around 900 nm, which is most likely due to Sm2+ ions near or in the “shell-region” of the glass surrounding the nanocrystals. 相似文献
84.
Freight transportation is a major component of logistical operations. Due to the increase in global trade, fierce competition among shippers and raising concerns about energy, companies are putting more emphasis on effective management and usage of transportation services. This paper studies the transportation pricing problem of a truckload carrier in a setting that consists of a retailer, a truckload carrier and a less than truckload carrier. In this setting, the truckload carrier makes his/her pricing decision based on previous knowledge on the less than truckload carrier’s price schedule and the retailer’s ordering behavior. The retailer then makes a determination of his/her order quantity through an integrated model that explicitly considers the transportation alternatives, and the related costs (i.e., bimodal transportation costs) and capacities. In the paper, the retailer’s replenishment problem and the truckload carrier’s pricing problem are modeled and solved based on a detailed analysis. Numerical evidence shows that the truckload carrier may increase his/her gainings significantly through better pricing and there is further opportunity of savings if the truckload carrier and the retailer coordinate their decisions. 相似文献
85.
86.
In this work, ab initio density functional theory (DFT) calculations have been performed on the 3,3-sigmatropic rearrangements of hexa-1,5-diene (Cope) and N-vinylprop-2-en-1-amine (3-aza-Cope) in the gas phase. The barrier heights and heats of reactions calculated at the B3LYP/6-311G** level of theory were in good agreement with experimental data. Transition states optimized with B3LYP/6-311G** theory were used for calculating the nucleus independent chemical shift (NICS) and, a natural bond orbital (NBO) analysis was also performed at the same level of theory. Our results indicate that the aromaticities of the transition states are controlled by the out-of-plane component and that the chair-like transition state of the Cope rearrangement exhibits the strongest aromatic character. Analysis of donor-acceptor (bonding and anti-bonding) interactions of σ3–4 → π*1–2 suggests that the TS structure in the hexa-1,5-diene reaction (the Cope rearrangement) has more aromatic character than the N-vinylprop-2-en-1-amine reaction (the 3-aza-Cope rearrangement). The NBO results show that in the hexa-1,5-diene and N-vinylprop-2-en-1-amine rearrangements, activation energies are controlled by σ3–4 → π*1–2 and σ3–4 → π*1–2 resonance energies. 相似文献
87.
Structural Chemistry - Today, the emission of poisonous gases in the atmosphere has caused many serious health and environmental problems. So, the finding of efficient methods for reducing or... 相似文献
88.
Hamideh Jalali Seyed Javad Hosseini Safa Ali-Asgari Jafar Izadi Nia 《Journal of heterocyclic chemistry》2020,57(1):419-427
The highly trans-stereoselective reaction of ammonium salt ( AS 2 ) toward (E)-N-benzylidene-4-methylbenzenesulfonamide ( IM 4 ) in the presence of Na2CO3 leading to an aziridine derivative, trans -Az 6 , was theoretically studied using Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G(d) computational level to probe energy transformation, selectivities, and molecular mechanism. The reaction starts by a nucleophilic substitution reaction between 1,4-diazabicyclo [2.2.2]octane ( DABCO ) and phenacyl bromide ( PB ) to form AS 2 which undergoes a proton abstraction by Na2CO3 to produce Ammonium Ylide ( AY 3) . Subsequently, nucleophilic addition of AY 3 to the double bond in IM 4 leads to form a betaine-like intermediate, namely, IN-Ta which named IN-Ta . Finally, trans -Az 6 is produced as a result of the nucleophilic attack of the negatively charged nitrogen atom on the carbon atom bearing DABCO in IN-Ta . Analysis of the relative Gibbs free energies shows that the ring closure step is the rate-determining step (RDS). By an investigation of the conceptual density functional theory, CDFT reactivity indices AY 3 and IM 4 are classified as a strong nucleophilic molecular system and as a strong electrophilic molecular system, respectively, which implies that the addition step of AY 3 to IM 4 has a high polar character. An analysis of the calculated electrophilic and nucleophilic Parr functions at the reactive sites of reagents clarifies the regioselectivity observed experimentally within the C1–C2 bond creation process. 相似文献
89.
Reactions between a series of nonenolisable aldehydes and tris(dimethylsilyl)methyllithium, (HMe2Si)3CLi, are described. The Peterson reaction takes place readily to give vinylbis(silanes). Moreover, styrene and butyl acrylate 1:1 copolymer (P), prepared by use of α,α′-azobis(isobutyronitrile) (AIBN) as an initiator in toluene at 70 ± 1°C, was formylated via direct electophilic substitution by methyl dichloromethyl ether (Cl2CHOMe) in the presence of tin(IV) chloride (SnCl4) in nitrobenzene (PhNO2) as solvent. The reaction of (HMe2Si)3CLi with formyl groups on the side chains of the copolymer led to new macromolecules bearing vinylbis(silane) functional groups. 相似文献
90.
JPC – Journal of Planar Chromatography – Modern TLC - A specific, precise, and accurate thin-layer chromatographic method for the simultaneous estimation of sulphadiazine sodium (SDZ)... 相似文献