Ligand degradation

The use of substitution at the 3-position to modify the steric environment about the metal center has been described in Section II,D,1. In a similar vein, substitution at the remote 5-position has been used with the specific goal of providing steric protection for the B-H moiety in attempts to inhibit ligand degradation. Indeed, as will be described, the steric protection that is provided by the methyl groups of the... 

If a solvent is used as part of the catalyst solution, then it also must be separated from the product. Finally, the buildup of various byproducts from ligand degradation, from raw material side reactions and from subsequent reaction of the desired product must be addressed so that the catalyst solution remains fully functional to achieve an economic catalyst life. 

Loss of metal by ligand degradation. The oxidation of phosphorus ligands by peroxide impurities in the feed is an example. Purification of the feed is an obvious remedy. It is much more difficult to find a solution when ligand degradation is inherent to the catalytic reaction mechanism (e.g., phosphonium salt formation). 

The remainder of the procedure is carried out under air and is executed relatively quickly to minimize ligand degradation. To precipitate the [Li(TME-DA)][PhB(CH2PPh2)3l product, the reaction mixture is cooled to — 78°C and... 

B. L. Clarke and P. H. Weigel, Differential effects of leupeptin, monensin and colchicine on ligand degradation mediated by the two asialoglycoprotein receptor pathways in isolated rat hepatocytes, Biochem. J. 262 277-284 (1989). 

Ru-porphyrin complexes covalently bound to MCM-41 were used as catalysts for the oxidation of alkenes, giving turnover numbers 20-40 times higher than the free complex [190]. Porphyrin complexes have also been attached to Nb dopants in the MCM-41 matrix, and behaved as cyclohexene epoxidation catalysts and were stable towards ligand degradation [44b]. Grafting of ethylenediamine ligands on... 

In contrast, receptor-mediated endocytosis is very specific. Embedded in the membrane are proteins with specific receptor sites exposed to the extracellular fluid. The receptor proteins are usually clustered in regions of the membrane called coated pits, which are lined on their cytoplasmic side by a fuzzy layer consisting of a protein called clathrin. When ligands bind to the receptor sites, they are carried into the cell by the inward budding of a coated pit to form a coated vesicle. Clathrin-coated vesicles become uncoated and fuse to form an endosome. Ligand and receptor dissociate within the endosome, and the receptor shuttles back to the cell surface. The endosome fuses with the lysosome on which ligand degradation occurs. 

To fine-tune the metal complex sterics, electronics, and geometries, as well as the stability of the resulting cationic catalysts with respect to ligand degradation due to C-H activation, a series of Zr(iv) and Hf(iv) diamide, dichloride, and dialkyl complexes incorporating tridentate bis(arylamido)amines 145134 135 and a bis(arylamido)pyridine 146136 137 has been synthesized using a combination of standard salt metathesis, amine elimination, and alkylation... 

Ligand degradation and receptor reutilization (e.g., low-density lipoproteins. Chapter 20 asialoglycoproteins. Chapter 10 transcobalamin II, Chapter 38 some peptide hormones ... 

Both receptor and ligand degradation (e.g., epidermal growth factor, immune complexes) ... 

Receptor recycles, ligand degraded Receptor recycles. Receptor transported, Re( ligand recycles ligand transported liga eptor recycles, nd released... 

In the presence of O2, nonbiological copper(I) [and iron(II)] complexes are often susceptible to ligand degradation, which may give the illusion of O2 binding 102 jjjg mechanisms by which this reaction occurs remain essentially unknown. Iron-porphyrin systems are rather more robust. Nonetheless, there are now several well-characterized copper(I) systems that reversibly bind dioxy-at least at low temperature. One that has been structurally character-... 

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