Ligand enhancement

The Table 7 shows Cu2+ ion effects. In a CTAB micelle, the Cu2+ ion itself without ligand enhances the rate 1900 fold as compared to 14 fold of the Zn2+ ion (Table 4). 

The strong o-donor property of NHC ligands enhances the catalytic activity in [3+2] cycloaddition by promoting the activation of internal alkynes (i.e. 26), which proceeds by the formation of a ti-alkyne complex 25 (Scheme 5.7). 

Allylic silanes show a pronounced tendency to react at the a-carbon in the presence of bidentate ligands.148 This regiochemistry is attributed to the preferential stabilization of cationic character by the silyl substituent. The bidentate ligands enhance the electrophilic character of the TS, and the cation stabilization of the silyl group becomes the controlling factor. 

The polymerization of ethylene was carried out in an identical way with these heterogeneous catalysts as with the homogeneous systems. Typical results are given in Table XII and show that the Si-0 ligand enhances the activity of the transition metal site for polymerization. Some of the higher activities are minimum values since the concentration of ethylene in the diluent is well below equilibrium concentrations and with these conditions the process is diffusion controlled. 

The catalyst system employed was the cationic rhodium solvent complex [Rh(P-P)S2]+ (P-P = BINAP, CHIRAPHOS, S = solvent). The BINAP ligand enhances the activity of the complex (Table 10), although additional studies have revealed that both the solvent and the substituents on Si influence the levels of enantioselectivity (Scheme 29).131,132... 

High bonding density is preferable for the majority of separations. The number of silanol groups not covered by the ligand is lower, exerting less influence on the separation, moreover, the hydrophobic ligand enhances the stability of the stationary phase at alkaline pH. 

Adorini L, Penna G, Giarratana N, Uskokovic M Tolerogenic dendritic cells induced by vitamin D receptor ligands enhance regulatory T cells inhibiting allograft rejection and autoimmune diseases. J Cell Biochem 2003 88 227-233. 

The electron-deficient aryl ligands enhance the electrophilicity of the bismuth (V) center and, as a result, accelerate the first step. 

In the one-phase reaction, complete conversion and ee values of about 72% were reached. In the biphasic system, the rhodium complex of the surfactant ligand 12 showed considerably higher activity than in the one-phase system, while retaining enantioselectivity (96). These results agree with results of earlier work that micelle-forming ligands enhance the solubility of lipophilic reactants in water. 

Fig. 1 Targeting and reversible shielding. Incorporation of targeting ligands enhances cellular uptake due to receptor-mediated endocytosis. Reversibly attached shielding moieties protect the polyplex during blood passage the pH-sensitive bonds are cleaved in the endosome upon acidification, setting free the positively charged polymer for further activity...

Kent, D.B. et al., Ligand-Enhanced Transport of Strongly Adsorbing Metal Ions in the Ground-water Environment, in Proceedings of the 7th International Symposium on Water-Rock Interaction, WRI-7, Kharaka, Y.K. and Maest, A.S., Eds., Park City, Utah, 13-18 July, 1992, 805. 

Such a proposal is further supported by another interesting trend in the dipicolinate system the degree of ligand enhancement is lanthanide dependent. We found a discrepancy in... 

It should be noted that it is only possible to correctly determine the rate constant for oxidation if the reaction is not affected by the kinetics of dissolution of the oxidized product. If the oxidized product on the solid surface is not rapidly dissolved, the surface accessible to the solute oxidants will decrease with time. This will slow down the surface reaction. For the U02-system, HCOg" and other potential ligands enhance the dissolution due to the formation of strong water soluble complexes with UO. The effect of HCOg" on the kinetics of UO2 oxidation has also been studied quantitatively enabling a more correct determination of the rate constant for UO, oxidation. ... 

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