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101.
Summary The Bu4N[Cr2H(CO)10] species reacts with hydrogen chloride in methanol to produce Bu4N[Cr(CO)5Cl].Analogous reactions using the complex K(phen)3Cr2H(CO)10 and K(bpy)2Cr2H(CO)10 salts (phen = 1,10-phenanthroline, bpy = 2,2-bipyridine) give the new (phen)2H[Cr2H(CO)10], phenH[Cr2H(CO)10], (phenH)2(Cl)[Cr2H(CO)10], and bpyH[Cr2H(CO)10] derivatives respectively. 相似文献
102.
Summary The use of monofunctional organosilanes for the preparation of packings with chemically bonded phases guarantees to obtain
a defined monomeric structures of bonded alkylsilyl groups. The effect of hydrophobization of the surface of silica gel support
modified with methyloctadecylchlorosilane in the presence of an activator has been investigated. A dense coverage of the surface
(>4 μmoles/m2) with the C18 groups is obtained at pKa ≈ 8. By changing the nature and concentration of the activator packings with controlled surface density can be prepared,
when the structure of the starting silica gel support are properly selected. On the basis of a simplified cylindrical model
of the support’s pores and the geometrical structure of the C18 molecules the maximum value of surface coverage as well as the dimensions of the chains of chemically bonded phases could
be estimated. 相似文献
103.
104.
The dynamics of electrooxidation of adsorbed CO on Pt(111) microfacets was examined in CO-saturated 0.1 M HClO4 aqueous solutions by in situ time resolved second harmonic generation (SHG). Analysis of the temporal dependence of the intensity of the SHG signals recorded for experiments in which the potential was stepped to values high enough for adsorbed CO oxidation to ensue, was found to be consistent with the mean field theory model, yielding rate constants somewhat higher than those reported by Lebedeva et al. (N. P. Lebedeva, M. T. M. Koper, J. M. Feliu and R. A. v. Santen, J. Electroanal. Chem., 2002, 524-525, 242-251) in sulfuric acid solutions. The smaller rates observed by these authors may be ascribed to the presence of anions, ie. in all likelihood bisulfate, which are capable of competing effectively for Pt sites thereby blocking formation of oxygenated species on the surface. Also discussed in this work are the virtues and limitations of in situ SHG for monitoring fast surface processes. 相似文献
105.
Analysis of the modified nucleosides is particularly important in the medical area because of a possibility of cancerogenic processes studies. The aim of this work was to study the selectivity tuning of modified nucleosides through the investigations of interactions analyte (modified nucleoside) <==> stationary phase <==> mobile phase. A series of homemade stationary phases with different surface properties has been utilized. All of them contain various interaction sites such as: cholesterol (SG-CHOL); n-acylamide (SG-CHOL, SG-AP); aminopropyl (SG-CHOL, SG-AP, SG-NH2, SG-MIX); cyanopropyl, phenyl, octyl (SG-MIX), octadecyl (SG-MIX, SG-C18) and silanols localized on the silica gel surface of all packings. The attempt to predict the main interactions responsible for the retention between nucleosides and stationary phase ligands was done on the basis of the elemental analysis, and proportional part of an individual ligand bonded to silica surface results. In order to study the influence of different packing types on the analyzed nucleosides retention, the relationship between pH of the mobile phase buffer and the selectivity of a stationary phase was investigated. 相似文献
106.
If Q is a Steiner symmetric domain, symmetric about the y-axis,then it can be proved that for an analytic function F:D C (D= {zC: |z| < 1}), such that Im F(0) = 0, and for t> 0,the inequality
holds, where denotes the Lebesgue measure of a set A T and CQ is some constant dependent onlyon Q. The best constantCQ is found. Some weak-type inequalitiesfollow, which generalize results of Baernstein. 相似文献
107.
Jarmalaviciene R Kornysova O Bendokas V Westerlund D Buszewski B Maruska A 《Analytical and bioanalytical chemistry》2008,391(6):2323-2328
In analytical sciences the design of novel materials and stationary phases for the sample preparation and separation of analytes
from biological fluids is needed. In this work we present different strategies for modification of stationary phases to produce
tailored solutions for the analytical problem. In this context a novel shielded polymeric reversed-phase monolithic material
was prepared in the presence of different numbers of reactive groups and concentrations of the coating polymer. Chromatographic
experiments were performed using benzoic acid propyl ester in order to characterize the hydrophobicity and efficiency of the
different restricted-access continuous beds prepared. Inverse size-exclusion chromatography was used for investigation of
the pore structure properties of the beds. Capillary columns were applied for nanochromatography of biological fluids containing
a mixture of nitrazepamum and medazepamum.
Presented at the 11th International Conference on Chemistry and the Environment, 9–12 September 2007, Torun, Poland 相似文献
108.
Jarmalaviciene R Szumski M Kornysova O Kłodzińska E Westerlund D Krawczyk S Mickevicius D Buszewski B Maruska A 《Electrophoresis》2008,29(8):1753-1760
Hyperlink robust biocompatible solid-phase microextraction (SPME) devices were prepared using continuous bed (monolithic) restricted-access media (RAM) as the SPME capillary insert. The RAM-based SPME approach was able to simultaneously separate proteins from a biological sample, while directly extracting the active components of caffeine, paracetamol and acetylsalicylic acid from the drug NeoCitramonum. The devices were interfaced with a CZE system and fully automated analysis for sample preconcentration, desorption, separation and quantification of analytes was evaluated. Comparative study of in-line coupled SPME-CZE using RAM and RP capillary inserts was carried out. Using an SPME (RAM) insert, the calculated caffeine, paracetamol and acetylsalicylic acid LODs in a bovine plasma sample were 0.3, 0.8 and 1.9 ng/mL, respectively. 相似文献
109.
Asymmetrical flow field-flow fractionation (AF4) and hollow-fiber flow field-flow fractionation (HF5) are techniques widely used in analytical, industrial and biological analyses. The main problem in all AF4 and HF5 analyses is sample loss due to analyte–membrane interactions. In this work the impact of liquid carrier composition on latex nanoparticles (NPs) separation in water and two different concentrations of NH4NO3 was studied. In AF4, a constant trend of decreasing the size of 60 and 121.9 nm particles induced by the ionic strength of the carrier liquid has been observed. In contrast, an agglomeration effect of the biggest 356 nm particles was observed when increasing ionic strength, which induced a significant drop of recovery to 35%. H5F provides better resolution and intensified peaks of NPs, but careful optimisation of system parameters is mandatory to obtain good separation. 相似文献
110.
Isolation,Separation, and Preconcentration of Biologically Active Compounds from Plant Matrices by Extraction Techniques 总被引:1,自引:0,他引:1
Development of efficient methods for isolation and separation of biologically active compounds remains an important challenge for researchers. Designing systems such as organomineral composite materials that allow extraction of a wide range of biologically active compounds, acting as broad-utility solid-phase extraction agents, remains an important and necessary task. Selective sorbents can be easily used for highly selective and reliable extraction of specific components present in complex matrices. Herein, state-of-the-art approaches for selective isolation, preconcentration, and separation of biologically active compounds from a range of matrices are discussed. Primary focus is given to novel extraction methods for some biologically active compounds including cyclic polyols, flavonoids, and oligosaccharides from plants. In addition, application of silica-, carbon-, and polymer-based solid-phase extraction adsorbents and membrane extraction for selective separation of these compounds is discussed. Potential separation process interactions are recommended; their understanding is of utmost importance for the creation of optimal conditions to extract biologically active compounds including those with estrogenic properties. 相似文献