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Granules of potato starch and amylopectin potato starch were methylated in aqueous alkaline suspension. Here, an overview is given of all structural aspects that have been studied with respect to the determination of the location of the substituents. Methods, which are generally applicable, were developed for the separation of different areas of derivatised starch granules, followed by determination of the substitution level. For methylated starch granules it was found that methyl groups are predominantly present in branched regions and amorphous domains, and that amylose is higher substituted than amylopectin. No differences were found between substitution levels of granules of various sizes, nor radially across the granules
In summary, a highly active Cr polymerization site can be created by dissociative chemisorption ofCH 2Cl2 to give a species that does not need initiation by ethylene. This work will stimulate the appearance ofa new class of highly active polymerization catalysts. The challenge in the near feature will be optimization ofthe experimental procedure (e.g., time, pressure, temperature ofCH 2Cl2 contact) to maximize the fraction of sites (b) in Scheme 1. This means that the order of magnitude that we have gained here in the activity per active site could be gained for the overall catalyst.[17] As a side remark, our study indicates that one should be aware of the potential other roles CH2Cl2 may play in catalysis. This is particularly relevant, as chlorinated hydrocarbons have found widespread use as solvents in a variety ofreactions , a fact...
Glycerol is considered a potential renewable building block for the synthesis of existing as well as new chemicals. A promising route is the telomerization of 1,3-butadiene with glycerol leading to C8 chain ethers of glycerol with applications in, for example, surfactant chemistry. Recently, we reported a new set of palladium-based homogeneous catalytic systems for the telomerization of 1,3-butadiene with glycerol and found that palladium complexes bearing methoxy-functionalized triphenylphosphine ligands are highly active catalysts capable of converting crude glycerol without any significant loss of activity. Herein, we present a detailed account of these investigations by reporting on the influence of the butadiene/glycerol ratio, temperature, and reaction time on product selectivity and activity allowing further optimization of cata...
Chlorinated hydrocarbons (CHCs) remain important industrial chemical intermediates and solvents, especially for the exploration of the potential of La-based materials for the conversion of chlorinated waste compounds.[1] The production of industrially important CHCs frequently occurs with concurrent formation of less desirable side-products. For example, mixtures of chlorinated C1 and C2 hydrocarbons are still formed as by-products in industrial processes such as the production of vinyl chloride monomer (VCM).[2, 3] Another example is carbon tetrachloride (CCl4) formation in the production of chloroform (CHCl3) and other chlorinated methanes. The United States Clean Air Act and the Montreal Protocol limit the production and sale of CCl4,[4,5] therefore methods to effectively recycle chlorinated side-products, in particular CCl4, would ...
In recent years a number of in situ microspectroscopic techniques have been explored to investigate catalytic reactions taking place in heterogeneous catalysts in a timeand space-resolved manner.[1–8] These spectroscopic methods have proven to be very successful in elucidating valuable structure–function relationships for acid–base catalytic reactions. In the work of Roeffaers et al. fluorescence microscopy has been applied to demonstrate the crystal-face-dependent catalysis on layered double hydroxide (LDH) materials.[1] By this elegant approach one can track interconversion processes of individual molecules in catalytic solids and obtain indirect data on the chemical nature of the reaction products formed, provided they display fluorescence. For example, the red shift of the emission bands of specific carbocations formed was used to ...
An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co2+ complexes inside Co/Al2O3 catalyst extrudates after impregnation with Co2+/citrate solutions of different pH and citrate concentrations. UV/Vis/NIR microspectroscopic measurements were carried out simultaneously to obtain complementary information on the nature of the Co2+ complexes. In this way, it could be confirmed that the actual distribution of Co2+ inside the extrudates could be derived from the MRI images. By combining these space- and time-resolved techniques, information was obtained on both the strength and the mode of interaction between [Co(H2O)6]2+ and different Co2+ citrate complexes with the Al2O3 support. Complexation of Co2+ by citrate was found to lead to a stronger interact...
Plants belonging to the genus Salsola (Family: Chenopodiaceae) are common in the arid and semiarid regions of our planet with no less than 69 different Salsola species found in Namibia and the Republic of South Africa. This genus is used as a traditional medicine and aqueous extracts of Salsola have been used by Bushmen women as an oral contraceptive. Ingestion of the Namibian shrub Salsola tuberculatiformis Botsch. by pregnant Karakul sheep leads to prolonged gestation and fetal post-maturity and, as a result, the pelts of the new-born karakul lambs are worthless. This initiated an investigation into the active agents in the plant, using the terminal enzyme in adrenal corticosteroidogenesis, cytochrome P450- dependent 11b-hydroxylase (P450c11), as a bioassay. Although the active fraction, S2, was extremely labile, partial structure de...
Racemic 2-{[1-(chloromethyl)-5-nitro-3-{5-[2-(dimethylamino)ethoxy]indol-2-carbonyl}-1,2-dihydro-3H-benzo[e]indol-7-yl]sulfonyl}aminoethyl dihydrogen phosphate, a synthetic nitro derivative of the duocarmycins, is a hypoxia-selective prodrug active against radiation-resistant tumour cells at nontoxic doses in mice. An intermediate in the synthesis of this prodrug was resolved by chiral HPLC and the absolute configuration assigned by X-ray crystallography. The intermediate was used to prepare the prodrug's enantiomers, and also the enantiomers of the active nitro and amino metabolites. In vitro analysis in the human cervical carcinoma cell line SiHa showed that both nitro enantiomers are hypoxia-selective cytotoxins, but the "natural" S enantiomer is at least 20-fold more potent. Examination of extracellular amino metabolite concentrati...
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