Carbon dioxide activation assisted

C.l. Carbon monoxide and carbon dioxide activation assisted by... 

Using solvents at the non-polar end of the spectrum offers a means of selectively extracting specific actives. An example from the nutraceutical sector is the selective extraction of ginkgo biloba with a high level of acetone in an ace-tone/water solvent mixture, which produces a 50 1 extract (50 kg of dried herb produces 1 kg of dried extract) standardised on 24% flavone glycosides and 6% terpenes. Sub- and supercritical forms of carbon dioxide produce very-fine quality extracts, and here again there is the possibility of using the difference in polarity between the sub- and supercritical states to assist in selective extraction. 

One role that metal ions play in the active site of enzymes is to stabilize the charges that may be present. For example, the enzyme carbonic an-hydrase, which plays the vital role of assisting the transport of carbon dioxide in the blood, is a metalloenzyme that includes zinc ions, Zn. This enzyme catalyzes the reaction of carbon dioxide with water to form hydrogen carbonate ions... 

Iwasawa et al. [21] also reported chelation-assisted reactions in an article entitled Rhodium(I)-Catalyzed Direct Carboxylation of Arenes with CO2 via Chelation-Assisted C-H Bond Activation, in which the cyclometalation reactions proceed easily and form cyclometalation intermediates. The metal atoms are active centers in their intermediates. Hence, the active metal atom reacts easily with inert carbon dioxide to give carboxylic acid derivatives. Examples include the cyclometalation of 2-phenylpyridine as a substrate in the presence of a rhodium intermediate. Carbon dioxide can be inserted into the rhodium-phenyl carbon bond, and a methyl ester is formed with TMSCH2N2 from a rhodium carboxylate, as shown in Eq. (6.5). The reaction mechanism is proposed as shown in Scheme 6.2 [21]. 

Colloidal osmium readily undergoes oxidation it catalvtieally assists the oxidation of unsaturated compounds by gaseous hydrogen. In this respect it is stated to be even more effective than the finely divided metal, but less active than either platinum or iridium. Carbon monoxide combines with oxygen, yielding the dioxide, when shaken at ordinary temperatures with the hydrosol of osmium.7... 

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