The 3,5-dimethylphenylcarbamates of cellulose and amylose bearing a small amount of 3-(triethoxysilyl)propyl residues were synthesized by a simple process and efficiently immobilized onto a silica gel support by intermolecular polycondensation of the triethoxysilyl groups. The obtained chiral packing materials (CPMs) were evaluated by high-performance liquid chromatography. The polysaccharide derivatives containing about 1-2% of the 3-(triethoxysilyl)propyl residue were efficiently immobilized with a high chiral recognition. The immobilized CPMs could be used with the eluents containing chloroform and tetrahydrofuran, which cannot be used with the conventional coated-type CPMs. By using these eluents, the chiral recognitions for many racemates could be improved. 相似文献
The adsorption and desorption of Au nanoparticles (AuNP) in colloidal D2O suspension on the (3-aminopropyl)triethoxysilane treated SiO2/Si surface was investigated by in situ attenuated total reflection surface enhanced infrared absorption (ATR-SEIRA) spectroscopy with a liquid flow cell. With increasing surface density of AuNP, the absorption of the vibrational modes of D2O and of the citrate molecules covering the AuNP increases due to SEIRA. Repulsive electrostatic Coulomb forces between the AuNP lead to the saturation of the AuNP surface density at submonolayer coverage. We show that the adsorption kinetics can be investigated by monitoring in situ the molecular vibrational modes of D2O and the citrate molecules. Furthermore, we clarify that the adsorption process can be described very well by a diffusion-limited first-order Langmuir kinetics model. When exposing a saturated AuNP submonolayer to 2-aminoethanethiol (AET)/D2O solution, the AuNP are removed from the surface and the IR absorption of the D2O vibrational modes become weaker again. Taking into account the time dependencies of the OD and the CH peaks, we propose a microscopic model where the AET molecules quickly adsorb on the AuNP by replacing most of the precovering citrate molecules exposed to the AET solution. As this takes place, the AuNP agglomerate-as we could detect with scanning electron microscopy-and are finally removed from the surface. 相似文献
Quaternary ammonium compounds containing at least one long alkyl chain act as cationic surfactants and are widely used as fabric softeners, disinfectants and human hair cosmetics. After usage, the surfactants are generally discharged via waste water treatment facilities to surface waters. Hence they can disturb the ecological balance due to their toxicity to aquatic organisms. In this context reliable analytical methods for determination of quaternary alkylammonium compounds are required in the analysis of environmental samples as well as in the quality control of manufactured products. 相似文献
Ab initio molecular orbital calculations (Hartree–Fock, HF and density functional theories, DFTs) have been carried out for SiO2 polymorphs coesite, low cristobalite, and α-quartz, in order to investigate the reliability of this method for predicting 29Si and 17O nuclear magnetic resonance (NMR) properties of silicates. Oxygen- and silicon-centered clusters consisting of one (1T) to three tetrahedral (3T) shells (one to four atomic shells), taken from real crystal structure, have been investigated. It is found that for reasonable predication of both the 29Si and 17O chemical shifts (δiSi and δiO), the minimum cluster is one that gives the correct second neighbors to the nucleus of interest. Both the δiSi and δiO have reached convergence with respect to cluster size at the OH-terminated two tetrahedral (2T) shell (three atomic shells around Si and four atomic shells around O) model. At convergence, the calculated δiSi values agree well (within ±1 ppm) with experimental data. The calculated 17O electric field gradient (EFG)-related parameters also agree with experimental data within experimental uncertainties. The calculation also reproduces small differences in δiO for O sites with similar tetrahedral connectivities, but shows deviations up to about 10 ppm in relative difference for O sites with different tetrahedral connectivities. The poor performance for the latter is mainly due to the approximations of the HF method. Our study thus suggests that the ab initio calculation method is a reliable mean for predicting 29Si and 17O NMR parameters for silicates. Such an approach should find application not only to well-ordered crystalline phases, but also to disordered materials, by combining with other techniques, such as the molecular dynamics simulation method. 相似文献
This paper discusses recent progress in transition‐metal‐catalyzed living radical polymerizations, partly focusing on the search of metal complex catalysts that play a critical role in controlling polymer molecular weights, then‐distributions, and architectures. Following a brief overview of the design of initiating systems (initiators and metal catalysts), half‐metallocene‐type complex catalysts are presented that induce living radical polymerizations of methacrylates, acrylates, and styrene to give markedly narrow molecular weight distributions and controlled molecular weights. Some of these halfmetallocenes also work in water where suspension living radical polymerization is feasible. 相似文献
As shown in the Scheme, 3-(1-nitro-2-oxocyclooctyl)propanal ( 1 ) prepared earlier from cyclooctanone was converted into the 14-membered lactones 6 and 7 . The aldehyde 1 was submitted to allylation to give 2 using allyltitnium or allylsilicon reagents. After lactonizatrion and transformation of the C,C-double bond to an alcohol, 4 was translactonized under acidic conditions to form 5 , from which 6 and 7 were prepared. 相似文献
Via a batch process in an autoclave, the foam processing of neat polylactide (PLA) and two different types of PLA/layered silicate nanocomposites has been conducted using supercritical carbon dioxide as a foaming agent. The morphological correlation between the dispersed silicate particles with nanometer dimensions in the bulk and the obtained closed‐cell structure of the foam is discussed. This is the first report that deals with the possibility of preparing biodegradable nanocellular polymeric foams via nanocomposite technology.
SEM image of the freeze‐fracture surface of a PLA/layered silicate foam, exhibiting closed‐cell structure. 相似文献