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261.
The methylation of humic acids (HA) with dimethylsulfate in acetone and methanol followed by the iodometric determination of the methoxy groups (Zeisel reaction) were applied to determine the contents of –OH groups in solid samples of HA of different origins. For the coal- and peat-derived HA samples, the contents of –OH groups determined after methylation in acetone ranged from 6.6 to 8.7 mmol/g, whereas the contents of –OH groups determined after methylation in methanol ranged from 4.0 to 5.0 mmol/g. These differences may be related to the content of carboxylic groups in the HA molecule that were not methylated in methanol, as confirmed by a comparison with results of conventional titrimetric determinations. Observed differences were interpreted as results of different polarity of both solvents and alkalinity of the reaction mixture during the methylation. The contents of alcoholic groups as well as some other minor –OH groups can be estimated using the –OH group contents obtained after methylation in both solvents together with the results of the conventional determinations of acidic functional groups. A repeatability of the –OH groups determination as estimated from a series of triplicate analyses of different HA samples (n = 7) was in range of 0.15–0.73 mmol/g and 0.08–1.06 mmol/g (standard deviations) for methylation in acetone and methanol, respectively. Thus, the average repeatability of the –OH groups determination was estimated to be 0.38 and 0.50 mmol/g for methylation in acetone and methanol, respectively. 相似文献
262.
Jozsef Bako Marta Szepesi Adrienn J. Veres Csaba Cserhati Zsuzsa M. Borbely Csaba Hegedus Janos Borbely 《Colloid and polymer science》2008,286(3):357-363
Nanocomposite biocompatible hydrogels (NCHG) were synthesised as model systems for in situ cured potentially local drug delivery
devices for curing periodontal infections. The composite consists of the following components: nanoparticles (NPs), matrix
gel, and chlorhexidine (CHX) as antibacterial drug. The NPs were obtained by free radical initiated copolymerization of the
monomers, 2-hydroxyethyl methacrylate (HEMA) and polyethyleneglycol dimethacrylate (PEGDMA), in aqueous solution. The same
monomers were used to prepare crosslinked matrices by photopolymerization. NCHGs were obtained by mixing NPs, monomers, and
drug in an aqueous solution then crosslinked by photopolymerization. Mechanical properties, swelling behavior, and the kinetics
of drug release have been investigated. It was found that compression strength values increased with increasing ratio of the
crosslinker PEGDMA. Incorporation of NPs into the matrix resulted similar compression strength as the matrix hydrogel. The
hydrated NCHGs swelled more slowly but admitted more water. The drug was incorporated in NPs by swelling in CHX aqueous solution
or added to the solution of monomer mixture followed by photopolymerization. Studies of release kinetics revealed that on
average 60% of the loaded drug was released. The most rapid release was observed over a 24 h period for matrix gels with low
crosslinking density. For NCHGs, the release period exceeded 48 h. An unexpected result was observed for NCHGs without drug
in the NPs. In this case, increasing release was observed for the first 24 h. Thereafter, however, the apparent quantity of
detectable drug decreased dramatically. 相似文献
263.
Marie R Beech JP Vörös J Tegenfeldt JO Höök F 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10103-10108
By utilizing flow-controlled PLL-g-PEG and PLL-g-PEGbiotin modification of predefined regions of a poly(dimethylsiloxane) (PDMS) micro-fluidic device, with an intentionally chosen large (approximately 1 cm2) internal surface area, we report rapid (10 min), highly localized (6 x 10(-6) cm2), and specific surface-based protein capture from a sample volume (100 microL) containing a low amount of protein (160 attomol in pure buffer and 400 attomol in serum). The design criteria for this surface modification were achieved using QCM-D (quartz crystal microbalance with energy dissipation monitoring) of serum protein adsorption onto PLL-g-PEG-modified oxidized PDMS. Equally good, or almost as good, results were obtained for oxidized SU-8, Topas, and poly(methyl metacrylate) (PMMA), demonstrating the generic potential of PLL-g-PEG for surface modification in various micro-fluidic applications. 相似文献
264.
Kim do H Szanyi J Kwak JH Szailer T Hanson J Wang CM Peden CH 《The journal of physical chemistry. B》2006,110(21):10441-10448
Desulfation processes were investigated over sulfated Pt-BaO/Al2O3 with different barium loading (8 and 20 wt %) by using H2 temperature programmed reaction (TPRX), transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), sulfur K-edge X-ray absorption near-edge spectroscopy (XANES), and in situ time-resolved X-ray diffraction (TR-XRD) techniques. Both sulfated samples (8 and 20 wt %) form sulfate species (primarily BaSO4) as evidenced by S K-edge XANES and in situ TR-XRD. However, the desulfation behavior is strongly dependent on the barium loading. Sulfated Pt-BaO8/Al2O3, consisting predominantly of surface BaO/BaCO3 species, displays more facile desulfation by H2 at lower temperatures than sulfated Pt-BaO20/Al2O3, a material containing primarily bulk BaO/BaCO3 species. Therefore, after desulfation with H2 up to 1073 K, the amount of the remaining sulfur species on the former, mostly as BaS, is much less than that on the latter. This suggests that the initial morphology differences between the two samples play a crucial role in determining the extent of desulfation and the temperature at which it occurs. It is concluded that the removal of sulfur is significantly easier at lower barium loading. This finding can potentially be important in developing more sulfur resistant LNT catalyst systems. 相似文献
265.
266.
Péter Angyal Kristóf Hegedüs Bence Balázs Mészáros Dr. János Daru Ádám Dudás Anna Rita Galambos Nariman Essmat Dr. Mahmoud Al-Khrasani Dr. Szilárd Varga Dr. Tibor Soós 《Angewandte Chemie (International ed. in English)》2023,62(35):e202303700
Mitragynine pseudoindoxyl, a kratom metabolite, has attracted increasing attention due to its favorable side effect profile as compared to conventional opioids. Herein, we describe the first enantioselective and scalable total synthesis of this natural product and its epimeric congener, speciogynine pseudoindoxyl. The characteristic spiro-5-5-6-tricyclic system of these alkaloids was formed through a protecting-group-free cascade relay process in which oxidized tryptamine and secologanin analogues were used. Furthermore, we discovered that mitragynine pseudoindoxyl acts not as a single molecular entity but as a dynamic ensemble of stereoisomers in protic environments; thus, it exhibits structural plasticity in biological systems. Accordingly, these synthetic, structural, and biological studies provide a basis for the planned design of mitragynine pseudoindoxyl analogues, which can guide the development of next-generation analgesics. 相似文献
267.
Farideh Jalilehvand Mikhail Maliarik Janos Mink Magnus Sandstroem Andrey Ilyukhin Julius Glaser 《ChemInform》2002,33(27):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献