Chain growth promotion

The readsorption and incorporation of reaction products such as 1-alkenes, alcohols, and aldehydes followed by subsequent chain growth is a remarkable property of Fischer-Tropsch (FT) synthesis. Therefore, a large number of co-feeding experiments are discussed in detail in order to contribute to the elucidation of the reaction mechanism. Great interest was focused on co-feeding CH2N2, which on the catalyst surface dissociates to CH2 and dinitrogen. Furthermore, interest was focused on the selectivity of branched hydrocarbons and on the promoter effect of alkali on product distribution. All these effects are discussed in detail on the basis... 

The carbon number distribution of Fischer-Tropsch products on both cobalt and iron catalysts can be clearly represented by superposition of two Anderson-Schulz-Flory (ASF) distributions characterized by two chain growth probabilities and the mass or molar fraction of products assigned to one of these distributions.7 10 In particular, this bimodal-type distribution is pronounced for iron catalysts promoted with alkali (e.g., K2C03). Comparing product distributions obtained on alkali-promoted and -unpromoted iron catalysts has shown that the distribution characterized by the lower growth probability a, is not affected by the promoter, while the growth probability a2 and the mass fraction f2 are considerably increased by addition of alkali.9 This is... 

Chain-growth can be initiated with high operating temperatures and pressures, in the presence of alkaHnized zinc-chromium mixed oxides (1 2) possibly modified with other metals (3)- Such promoted catalysts allowed industrial scale production of alcohol mixtures containing up to 30 wt of C alcohols. 

The PI3 kinase (PI3-K) is translocated to the membrane by interaction of the SH2 domain of its p85 subunit with phosphotyrosine residues of the activated receptor. There it converts PtdIns(3,4)P2.into PtdIns(3,4,5)P3 which binds to PH domains of various effector molecules and recruits them into the signaling chain. The effector molecules can stimulate cell division or can induce the programmed cell death. The tumor suppressor PTEN hydrolyses phosphates from PtdIns(3,4,5)P3 and thus inhibits the growth promoting effect of the PI3 kinase signaling. An important effector of PI3 kinase is the protein kinase Akt which is also termed protein kinase B (PKB). GF growth factor GFR growth factor receptor. 

The observation of glycerol triacetate as a trace product of CO hydrogenation by this ruthenium system in acetic acid solvent (179) suggests that glycolaldehyde (ester) can undergo further chain growth by the process outlined in (26) for the cobalt system. As with formaldehyde, however, a carboxylic acid is apparently necessary to promote formation of the metal-carbon bonded intermediate which can produce the longer-chain product. 

A mechanism possibly involving intermolecular hydride transfer in this promoted ruthenium system is thus very different from the reaction pathways presented for the cobalt and unpromoted ruthenium catalysts, where the evidence supports an intramolecular hydrogen atom transfer in the formyl-producing step. Nevertheless, reactions following this step could be similar in all of these systems, since the observed products are essentially the same. Thus, a chain growth process through aldehyde intermediates, as outlined earlier, may apply to this ruthenium system also. 

Olaquindox is an antibacterial also used as a growth promoter for swine at an incorporation rate in feeds of 25-100 ppm. In swine, olaquindox is metabolized either by oxidation of the alcohol group on the side chain or removal of one or both of the A-oxide groups at the positions 1 and 4 on the quinoxaline ring. 

Relaxin is another peptide that can be extracted from the ovary. The three-dimensional structure of relaxin is related to that of growth-promoting peptides and is similar to that of insulin. Although the amino acid sequence differs from that of insulin, this hormone, like insulin, consists of two chains linked by disulfide bonds, cleaved from a prohormone. It is found in the ovary, placenta, uterus, and blood. Relaxin synthesis has been demonstrated in luteinized granulosa cells of the corpus luteum. 

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