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排序方式: 共有206条查询结果,搜索用时 421 毫秒
61.
Kalenius E Moiani D Dalcanale E Vainiotalo P 《Chemical communications (Cambridge, England)》2007,(37):3865-3867
H/D and guest-exchange ion-molecule reactions have been used as a new tool to elucidate the operation of multiple hydrogen bonding in gas-phase complexes formed between phosphonate cavitands and ethyl-substituted ammonium ions. 相似文献
62.
Contieri Abad F Winck PR Benvenutti EV do Carmo Ruaro Peralba M Bastos Caramão E Alcaraz Zini C 《Journal of separation science》2007,30(13):2109-2116
A new material for matrix solid phase dispersion (MSPD) was synthesized -- p-nitro-N-propylaniline/silica (pNNPASi) by grafting reactions, characterized by elemental analysis and N(2)-adsorption-desorption isotherms, and tested for multiclass multiresidue analysis of pesticides in wet and freeze-dried carrots. Results obtained applying this new solid phase sorbent to MSPD extraction of ten pesticides (trichlorphon, trifluralin, dicloran, chlorothalonil, prometryn, linuron, captan, procymidone, prochloraz, and deltametrin) in wet carrots showed better results than the ones obtained for freeze-dried samples. Recoveries were in the range of 48-106% and precisions varied from 6 to 20% when wet samples were employed. Comparison between pNNPASi sorbent and C(18) showed better performance of pNNPASi for eight out of ten pesticides tested. The LOQs show that the developed method can be used to detect the pesticides investigated in carrots at concentrations below the maximum residue levels (MRL) established by EU, USEPA, and National Sanitary Surveillance Agency (ANVISA). Linuron, captan, prochloraz, and deltamethrin were found in at least one of the two commercial samples studied in concentrations above the LOQ of this method. Concentrations of the last three pesticides were above the European MRL in one of the commercial samples. 相似文献
63.
One‐Pot Three‐Component Synthesis of Hantzsch 1,4‐Dihydropyridines Promoted by Dimethyl Phosphate Ionic Liquids
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A one‐pot three‐component reaction of ethyl acetoacetate, AcONH4, and different aldehydes has been successfully performed in the presence of ionic liquids (ILs) possessing a (MeO)2PO$\rm{{_{2}^{-}}}$ counterion. The impact of electronic and steric effects of the substituents of aromatic aldehydes, as well as the influence of different anions of ILs on the product yield, have been investigated. The application of dimethyl phosphate ILs in the synthesis of Hantzsch 1,4‐dihydropyridines presents a simple method for obtaining structurally diverse products in moderate to high yields without using any additional catalyst. 相似文献
64.
Superchiral Pd3L6 Coordination Complex and Its Reversible Structural Conversion into Pd3L3Cl6 Metallocycles
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Dr. Ondřej Jurček Pia Bonakdarzadeh Dr. Elina Kalenius Dr. Juha Matti Linnanto Dr. Michael Groessl Dr. Richard Knochenmuss Prof. Janne A. Ihalainen Prof. Kari Rissanen 《Angewandte Chemie (International ed. in English)》2015,54(51):15462-15467
Large, non‐symmetrical, inherently chiral bispyridyl ligand L derived from natural ursodeoxycholic bile acid was used for square–planar coordination of tetravalent PdII, yielding the cationic single enantiomer of superchiral coordination complex 1 Pd3 L 6 containing 60 well‐defined chiral centers in its flower‐like structure. Complex 1 can readily be transformed by addition of chloride into a smaller enantiomerically pure cyclic trimer 2 Pd3 L 3Cl6 containing 30 chiral centers. This transformation is reversible and can be restored by the addition of silver cations. Furthermore, a mixture of two constitutional isomers of trimer, 2 and 2′ , and dimer, 3 and 3′ , can be obtained directly from L by its coordination to trans‐ or cis‐N‐pyridyl‐coordinating PdII. These intriguing, water‐resistant, stable supramolecular assemblies have been thoroughly described by 1H DOSY NMR, mass spectrometry, circular dichroism, molecular modelling, and drift tube ion‐mobility mass spectrometry. 相似文献
65.
Chatelet B Payet E Perraud O Dimitrov-Raytchev P Chapellet LL Dufaud V Martinez A Dutasta JP 《Organic letters》2011,13(14):3706-3709
Hemicryptophanes are host molecules with many applications as supramolecular catalysts or in ion selective recognition. A very convenient and efficient modular approach for the synthesis of hemicryptophane-tren (tren, tris(2-aminoethyl)-amine) derivatives has been developed. For instance, hemicryptophane 1 was synthesized at the gram scale in four steps from vanillyl alcohol compared to the previous seven-step procedure. The size, shape, and functionalities of the molecular cavity were also easily modified. 相似文献
66.
Machado ME Fontanive FC de Oliveira JV Caramão EB Zini CA 《Analytical and bioanalytical chemistry》2011,401(8):2433-2444
The determination of organic sulfur compounds (OSC) in coal is of great interest. Technically and operationally these compounds
are not easily removed and promote corrosion of equipment. Environmentally, the burning of sulfur compounds leads to the emission
of SO
x
gases, which are major contributors to acid rain. Health-wise, it is well known that these compounds have mutagenic and carcinogenic
properties. Bitumen can be extracted from coal by different techniques, and use of gas chromatography coupled to mass spectrometric
detection enables identification of compounds present in coal extracts. The OSC from three different bitumens were tentatively
identified by use of three different extraction techniques: accelerated solvent extraction (ASE), ultrasonic extraction (UE),
and supercritical-fluid extraction (SFE). Results obtained from one-dimensional gas chromatography (1D GC) coupled to quadrupole
mass spectrometric detection (GC–qMS) and from two-dimensional gas chromatography with time-of-flight mass spectrometric detection
(GC × GC–TOFMS) were compared. By use of 2D GC, a greater number of OSC were found in ASE bitumen than in SFE and UE bitumens.
No OSC were identified with 1D GC–qMS, although some benzothiophenes and dibenzothiophenes were detected by use of EIM and
SIM modes. GC × GC–TOFMS applied to investigation of OSC in bitumens resulted in analytical improvement, as more OSC classes
and compounds were identified (thiols, sulfides, thiophenes, naphthothiophenes, benzothiophenes, and benzonaphthothiophenes).
The roof-tile effect was observed for OSC and PAH in all bitumens. Several co-elutions among analytes and with matrix interferents
were solved by use of GC×GC. 相似文献
67.
A GC-μECD and a GC×GC-μECD method were developed for the analysis of pesticides in sediments. For 1D-GC, instrumental LOD and LOQ were found in the range from 0.60 to 2.31μgL(-1) and 1.83 to 5.62μgL(-1), respectively. For GC×GC method development two sets of columns were tested (DB-5/DB-17ms, and HP-50+/DB-1ms), and the best results were obtained with the set of columns DB-5/DB-17ms. Instrumental LOD and LOQ were found in the range from 0.08 to 1.07μgL(-1) and 0.25 to 3.23μgL(-1), respectively. The LOD for the GC×GC was about 36% lower than those obtained for the 1D-GC. Concentrations of 21.18μgkg(-1) through 1D-GC method and 3.34μgkg(-1) for GC×GC for trifloxystrobin were found in a sediment sample which was collected close to an area of rice plantation. 相似文献
68.
Kong WM Chik Z Ramachandra M Subramaniam U Aziddin RE Mohamed Z 《Molecules (Basel, Switzerland)》2011,16(9):7344-7356
The extract from Mitragyna speciosa has been widely used as an opium substitute, mainly due to its morphine-like pharmacological effects. This study investigated the effects of M. speciosa alkaloid extract (MSE) on human recombinant cytochrome P450 (CYP) enzyme activities using a modified Crespi method. As compared with the liquid chromatography-mass spectrometry method, this method has shown to be a fast and cost-effective way to perform CYP inhibition studies. The results indicated that MSE has the most potent inhibitory effect on CYP3A4 and CYP2D6, with apparent half-maximal inhibitory concentration (IC(50)) values of 0.78 μg/mL and 0.636 μg/mL, respectively. In addition, moderate inhibition was observed for CYP1A2, with an IC(50) of 39 μg/mL, and weak inhibition was detected for CYP2C19. The IC(50) of CYP2C19 could not be determined, however, because inhibition was <50%. Competitive inhibition was found for the MSE-treated CYP2D6 inhibition assay, whereas non-competitive inhibition was shown in inhibition assays using CYP3A4, CYP1A2 and CYP2C19. Quinidine (CYP2D6), ketoconazole (CYP3A4), tranylcypromine (CYP2C19) and furafylline (CYP1A2) were ACCESSused as positive controls throughout the experiments. This study shows that MSE may contribute to an herb-drug interaction if administered concomitantly with drugs that are substrates for CYP3A4, CYP2D6 and CYP1A2. 相似文献
69.
Kalenius E Beyeh NK Jänis J Rissanen K 《Chemical communications (Cambridge, England)》2011,47(9):2649-2651
Pyrogallarene shows concentration-dependent instability in dilute solutions resulting in elimination of two ketene molecules and formation of pyrogallarene lactones. This unexpected phenomenon, which is not observed with resorcinarenes, highlights the significance of the four hydroxyl groups at 2-position for the molecular characteristics of pyrogallarenes. 相似文献
70.
Kirsi S. Mikkonen Leena Pitk?nen Ville Liljestr?m Elina Mabasa Bergstr?m Ritva Serimaa Lennart Salmén Maija Tenkanen 《Cellulose (London, England)》2012,19(2):467-480
The chemical structure of rye arabinoxylan (rAX) was systematically modified, exploiting selective enzymes to mimic different
naturally occurring xylans, i.e., its degree of substitution (DS) was decreased using α-l-arabinofuranosidase, and a controlled decrease in the degree of polymerization (DP) was performed using endo-1,4-β-d-xylanase. The arabinose to xylose ratio was decreased from 0.45 to 0.27 and the weight-average molar mass was decreased from
184,000 to 49,000 g/mol. The resulting samples were used to prepare films, as such, and with 15% (wt. − %) softwood-derived
microfibrillated cellulose (MFC) to obtain novel plant-derived biocomposite materials. The enzymatic tailoring of rAX increased
the crystallinity of films, evidenced by X-ray diffraction studies, and the addition of MFC to the debranched, low DS rAX
induced the formation of ordered structures visible with polarizing optical microscopy. MFC decreased the moisture uptake
of films and increased the relative humidity of softening of the films, detected with moisture scanning dynamic mechanical
analysis. For the first time, the chemical structure of xylan was proven to significantly affect the reinforcement potential
of nano-sized cellulose, as the tensile strength of films from high DP rAXs, but not that of low DP rAXs, clearly increased
with the addition of MFC. At the same time, MFC only increased the Young’s modulus of films from rAX with high arabinose content,
regardless of DP. 相似文献