共查询到20条相似文献,搜索用时 15 毫秒
1.
The effects of β-cyclodextrin (β-CD) on the spectral properties and electrochemical behaviour of barbitone sodium were studied using electrochemical and optical techniques. The apparent changes in the UV-visible absorption spectrum and fluorescence quenching of the barbiturate upon addition of β-CD afford clear evidence of the inclusion complex formation of β-CD in aqueous solutions. The redox acitivity of barbitone sodium in both the absence and presence of β-CD was assessed by an electrochemical method in 0.05 M potassium nitrate-nitric acid (pH 1.8) solution. While the complexation reaction remains is equilibrium, the apparent formation constant of the inclusion complex could be obtained by either spectral or electrochemical methods. Quantitative evaluation of the data gave 326 l mol−1 under equilibrium conditions at 20°C. Possible conclusions are discussed on the basis of environmental changes around the barbiturate molecules on inclusion. 相似文献
2.
Ezzat T. M. Selim 《Journal of Chemical Sciences》1982,91(4):359-369
Using mass spectrometric technique, the effect of geometrical isomerism on the first and higher appearance energy values for
C4H3
+, C4H7
+ and C3H,3
+ ions obtained from cis-2-butene andtrans-2-butene is reported. The structure in the ionization efficiency curves (studied for 9 eV above threshold) for the same ions
obtained from the two isomers is reported and compared. It is believed that at threshold C4H7
+ fragment is formed from the two isomers as methallyl ion. For C3H3
+ fragment formed from the cw-isomer at threshold the proposed structure is the propargyl ion with ΔHf equal to 279-4 kcal/mole while for that ion obtained fromtransisomer the proposed structure is the allenyl ion with ΔHf equal to 296.6 kcal/mole. 相似文献
3.
Alaize de P. Martins A. A. Craveiro M. I. L. Machado Fernanda N. Raffin T. F. Moura Cs. Novák Zsuzsanna éhen 《Journal of Thermal Analysis and Calorimetry》2007,88(2):363-371
Inclusion complex between the essential oil
of Mentha x villosa Hudson and β-cyclodextrin,
with a 1:9 mass/mass oil–β-cyclodextrin ratio was prepared by co-precipitation
and kneading methods in a hydroethanolic medium. The GC/MS analysis showed
a total volatile content of 99.5% in the Mentha x
villosa oil. The characterization of the complex involved the analysis
of the original essential oil, the surface and the total extracted oils. Among
28 detected compounds in the original essential oil, 13 are monoterpenes and
10 sesquiterpenes, furthermore, piperitenone-oxide is the major component
(35.4%). 12 compounds were totally and 11 partially complexed, 3 have been
adsorbed only on the surface of the β-CD and 2 have not been detected
neither in the surface oil nor in the complexed oil. A 13.6% encapsulation
efficiency was observed, while the total oil and volatiles retention was 15
and 77%, respectively. Non-parametric statistic analysis of the data showed
that the profile of the volatiles were not significantly different comparing
the original oil and the complexed oil (p>0.04).
The results of thermogravimetry-mass spectrometry and XRD analysis have proven
the inclusion complex formation between the essential oil and cyclodextrin. 相似文献
4.
Joshua E. Sussman Tara S. Morey Susie M. Miller Monte L. Helm 《Journal of organometallic chemistry》2009,694(21):3506-3510
We wish to report the synthesis and characterization of Group 9 metal complexes with the novel P,P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc) ligand. The complexes are readily prepared by direct ligand substitution reactions from the dichloro-bridged binuclear complexes, [{η5-Cp*M(Cl)2}2]. The complexes include: [η5-Cp*Rh(Cl)2]2(μ-dpdpc) (1), [η5-Cp*Ir(Cl)2]2(μ-dpdpc) (2), and [η5-Cp*Rh(Cl)(dpdpc)]PF6 (3). The structures for all three complexes are supported by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy as well as elemental analysis. The molecular structures of 1 and 3 have also been established by single-crystal X-ray analysis. 相似文献
5.
Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and α- and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between α-CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of nC=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and α-CD for the chain length nC>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3. 相似文献
6.
7.
The inclusion behavior between styrene (α-methyl styrene) and cyclodextrins (CDs) was studied by using 1H NMR titration in solution. The results indicate that 1:1 inclusion complexes were formed. The association constants of the inclusion complexes were determined by nonlinear least-square method. The inclusion process was also studied by using PM3 quantum-mechanical semi-empirical method. The calculated results are in agreed with the experimental data. 相似文献
8.
Starting with Biller-Biemann's work [J.E. Biller, K. Biemann, Anal. Lett. 7 (1974) 515], various kinds of approaches have been proposed to extract GC/MS data to obtain pure components responses. In this paper, an integrated chemometric approach is proposed, which combine four sequential steps, data pretreatment, component perception, resolution and component identification, and then the proposed approach is manipulated to analyze the essential oils of a herbal medicine named Houttuynia cordata (HC). On the basis of the selective information obtained from both chromatograms and mass spectra, the proposed integrated chemometric approach can resolve the two-way GC/MS responses matrix into pure chromatograms and mass spectra without any model assumption on the peak shape. The resolution results obtained from HC samples demonstrate the performance of the proposed approach and indicate that it may be a promising one for analyzing complex chromatograms. 相似文献
9.
Stanisaw Pasynkiewicz Antoni Pietrzykowski Lidia Trojanowska Piotr Sobota Lucjan Jerzykiewicz 《Journal of organometallic chemistry》1998,550(1-2)
The reaction of nickelocene with BrMgR, where R=CH2CH(CH3)C6H5, C2H5, (CH2)7CH3 and CH2CH2CH3, have been studied. It was found that the presence of β-hydrogen in R did not cause the total splitting of the carbon–nickel bond but alkylidynetrinickel clusters were formed. It is the first example of the synthesis of alkylidynetrinickel clusters (NiCp)3CR′ from the organonickel species possessing β-hydrogen. Besides trinickel clusters, the following compounds were always formed in all the studied reactions: (NiCp)4H2, (NiCp)6, CpNi(η3-C5H7) and (NiCp)2(μ-C5H6). The structure of (NiCp)3CCH(CH3)Ph has been determined by a single-crystal X-ray diffraction study. 相似文献
10.
An analytical method based on online combination of polymer monolith microextraction (PMME) technique with hydrophilic interaction LC (HILIC)/MS is presented. The extraction was performed with a poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) monolithic column while the subsequent separation was carried out on a Luna silica column by HILIC. After 1:1 v/v dilution with 20 mM phosphate solution at pH 7.0 and centrifugation, urine sample was directly used for extraction. After optimization, 85% ACN (containing 0.3% formic acid v/v) was used for rapid online elution, which was also the mobile phase in HILIC to avoid band broadening during separation or carry‐over that was usually observed in PMME‐RP LC system. Online automation of extraction and separation procedures was realized under the control of a program in this study. The developed method was applied to rapid and sensitive monitoring of three β2‐agonist traces in human urine. The LODs (S/N = 3) of the method were found to be 0.05–0.09 ng/mL of β2‐agonists in urine. The recoveries of three β2‐agonists spiked in five different urine samples ranged from 79.8 to 119.8%, with RSDs less than 18.0%. 相似文献
11.
G. Van Vyncht S. Preece P. Gaspar G. Maghuin-Rogister E. DePauw 《Journal of chromatography. A》1996,750(1-2):43-49
β-Agonists are substances used in veterinary and human medicine for the treatment of pulmonary disorders. They have found a use as growth promoters to improve meat-to-fat ratios in cattle but they are not authorized for use in the European Union. Due to their presence in trace levels (usually less than 1 μg/kg), to the diversity of the illegally used compounds and to the complexity of the biological matrices analysed, the detection of these residues requires a very sensitive and specific method of determination. This work describes the strategy of analysis we developed for five β-agonists in urine and liver. The combination of improved solid- or liquid-phase extraction methods and LC or GC-MS-MS (in the multiple reaction monitoring mode) has shown to provide a system suitable for the control of these substances. The efficiency of extraction and the sensitivity and selectivity allow this multiresidue detection down to, and below, the UK regulatory level of 0.5 μg/kg. Moreover, the use of LC removes the need for the derivatisation step (cyclic methylboronate derivatives) which is required prior to GC-MS-MS analysis. 相似文献
12.
The (E)-α-selenylvinylstannanes react with acyl halides in presence of a catalytic amount of Pd(PPh3)4 to give the corresponding (Z)-α-selenyl-α,β-unsaturated ketones in good yield. 相似文献
13.
Michael Block Matthias Linnert Santiago Gmez-Ruiz Dirk Steinborn 《Journal of organometallic chemistry》2009,694(20):3353-3361
Lithiation of O-functionalized alkyl phenyl sulfides PhSCH2CH2CH2OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh3, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH2CH2OR}(tmeda)] (α-2a–d) and [Li{o-C6H4SCH2CH2CH2OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu3SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu3SnCH(SPh)CH2CH2OR (α-3a–d) and n-Bu3Sn(o-C6H4SCH2CH2CH2OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH2CH2OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO2CH2CH2CH2OR (R = Me, 5a; i-Pr, 5b; CPh3, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO2Ph)CH2CH2OR] (6a–c) that were found to react with n-Bu3SnCl yielding the requisite α-stannylated compounds n-Bu3SnCH(SO2Ph)CH2CH2OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (1H, 13C, 119Sn). 相似文献
14.
Ian D. Fawcett Gabriel M. Veith Martha Greenblatt Mark Croft Israel Nowik 《Solid State Sciences》2000,2(8)
The SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe3+ and Fe4+. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn4+, Fe(4+δ)+ and Fe(3+)+. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-eg orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe(3+)+/Fe(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution. 相似文献
15.
The enantiomers of the perfluorodiether “compound B” [2-(fluoromethoxy)-3-methoxy-1,1,1,3,3-pentafluoropropane], a decomposition product of the inhalational anesthetic sevoflurane [2-(fluoromethoxy)-1,1,1,3,3,3-hexafluoropropane], were separated by gas chromatography on octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-γ-cyclodextrin (Lipodex E), dissolved in polysiloxane PS 255 (30% w/w), with an unexpectedly high separation factor of =10.6 at 26 °C. Using the concept of the retention increment R′, non-enantioselective and enantioselective contributions to retention were separated and thus reliable thermodynamic parameters of enantioselectivity, i.e. −ΔS,R(ΔG)=5.7 (0.05) kJ/mol at 303 K, −ΔS,R(ΔH)=20.1 (0.64) kJ/mol, ΔS,R(ΔS)=−47.4 (2.0) J/K mol and Tisoenant=424 (30) K or 150 °C, were determined by temperature-dependent measurements. The enantiomeric bias represents the largest values ever measured in enantioselective gas chromatography. An equation is presented which allows calculation of the non-enantioselective contributions to retention from measurements at two arbitrary concentrations of Lipodex E in polysiloxane. Surprisingly, the enantioselectivity is greatly reduced when employing the β-cyclodextrin analogue and breaks down completely with the -cyclodextrin analogue of Lipodex E. 相似文献
16.
Lu Wang 《Analytica chimica acta》2009,647(1):72-65
A novel method for analysis of essential oil in Cuminum cyminum L. using simultaneous ultrasonic nebulization extraction and headspace single drop microextraction (UNE-HS-SDME) followed by gas chromatography-mass spectrometry was developed. Experimental parameters, including the kind of suspended solvent, microdrop volume, sample amount, extraction time, enrichment time and salt concentration were examined and optimized. Compared with hydrodistillation (HD), UNE-HS-SDME provides the advantages of a small amount of sample (50 mg), time-saving (20 min), simplicity, cheapness and low toxicity. In addition, UNE-HS-SDME also provided higher enrichment efficiency and sensitivity compared with stirring extraction (SE)-HS-SDME, ultrasonic assistant extraction (UAE) and UNE. Some constituents in the essential oil, were identified and the detection limits for β-pinene, p-cymene and γ-terpinene range from 6.67 pL L−1 to 14.8 pL L−1. The results indicated that the UNE-HS-SDME is simple and highly efficient extraction and enrichment technique. 相似文献
17.
Young-hee Kim Paul A Cooke Robert Greatrex John D Kennedy Mark Thornton-Pett 《Journal of organometallic chemistry》1998,550(1-2)
[7,7-(PMe2Ph)2-9-(η6-isoPrC6H4Me)-7,9-PtRuB9H11] has a formal closo Wadian cluster-electron count, but a nido geometry, whereas [1-(η6-isoPrC6H4Me)-4,4-(PMe2Ph)2-1-4-RuPtB9H9], which does have a closo geometry, has a formal sub-closo cluster electron count; both compounds are formed in the reaction between [6-(η6-isoPrC6H4Me)-nido-6 RuB9H13], KH and [PtCl2(PMe2Ph)2]. 相似文献
18.
The chemical composition of Schizonepeta tenuifolia Briq. (Sch.t.Briq.) is mainly composed of several volatile substances that affect multiple pharmacological targets and provide clinical efficacy. In this work, a headspace/solid-phase microextraction gas chromatography/mass spectrometry (HS-SPME-GC/MS) method was developed to evaluate the profiles of volatile compounds in Sch.t.Briq. The optimization of SPME conditions was carried out using four kinds of fiber, extraction time and temperature, desorption temperature and time, and sample amount. The GC/MS analysis allowed the tentative identification of 21 compounds, with similarities higher than 85%, in accordance with the NIST/Wiley mass spectral library. Major components such as (+)-menthone (14.32%), (−)-pulegone (47.73%), 2-hydroxy-2-isopropenyl-5-methylcyclohexane (5.97%), cis-pulegone oxide (4.12%), and schizonal (5.36%) were identified by comparison of retention time and mass spectral data of standards isolated from Sch.t.Briq. The contents of these compounds were about above 78% against total amounts of volatile compounds extracted from Sch.t.Briq. Based on optimized SPME method, 19 different Sch.t.Briq. samples collected from markets in Korea and China were analyzed to obtain the profiling data of volatile compounds. In addition, principal component analysis (PCA) was performed on the profiling data in order to classify the samples collected from the different regions. PCA could possibly visualize the grouping tendencies of the studied varieties of herbal samples, as well as the identification of the volatiles responsible for discriminating the groups. 相似文献
19.
A simple, sensitive, and accurate method for determination of polybrominated diphenyl ethers (PBDEs) in soil has been developed based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). Permethylated-β-cyclodextrin/hydroxyl-termination silicone oil (PM-β-CD/OH-TSO) fiber was first prepared by sol–gel technology and employed in SPME procedure. By exploiting the superiorities of sol–gel coating technique and the advantages of the high hydrophobic doughnut-shaped cavity of PM-β-CD, the novel fiber showed desirable operational stability and extraction ability. After optimization on extraction conditions like water addition, extraction temperature, extraction time, salts effect, and solvents addition, the method was validated in soil samples, achieving good linearity (r > 0.999), precision (R.S.D. < 10%), accuracy (recovery > 78%), and detection limits (S/N = 3) raging from 13.0 to 78.3 pg/g. 相似文献
20.
Cody Timmons Dianjun Chen C. Elizabeth Barney Sameer Kirtane Guigen Li 《Tetrahedron》2004,60(52):12095-12099
A new nitrogen source combination was found for the regio- and stereoselective diamination of α,β-unsaturated ketones. This combination employs the readily available and inexpensive combination of NCS and 2-NsNH2 as the electrophilic nitrogen source, and acetonitrile as the nucleophilic nitrogen source, respectively. The reaction is easily performed by mixing olefin, 2-NsNH2, NCS and 4 Å molecular sieves in freshly distilled acetonitrile at room temperature. The reaction is chemoselective without the formation of any haloamine side products. A new aziridinium ion formed from enones and 2-NsNHCl is suggested to exist and to react with nitrile via a [2+3] cycloaddition mechanism, which is responsible for the excellent regio-, stereoselectivity of the resulting diamination products. 相似文献