Ligand movement

Receptor-mediated endocytosis is the process of ligand movement from the extracellular space to the inside of the cell by the interaction of the ligand with a specific cell-surface receptor. Receptors bind the ligand at the surface, internalize it by means of coated pits and vesicles, and ultimately release it into an acidic endosomal compartment (Figure 1.4). 

Although the complexity of the dynamic stereochemistry of 3a-3e does not allow a conclusive elucidation of the mechanism of the hindered ligand movement on the basis of the NMR data, a rotation of the diene ligands... 

According to their temperature-dependent NMR spectra, the [M(CO)3L-( j4-diene)] complexes 15a-15f (21), 17b, 17d (22), 19a-19f (21,23), and 22a-22i (24) show hindered ligand movements. With very few exceptions, a preference for the a isomers is found. For compounds 15b, 15d, 19b, 19d, and 22g / isomers can be detected in addition to a isomers. The bulky tricyclo[6.3.0.02,7]undeca-3,5-triene ligand in 22i causes the / isomer to be preferred, in agreement with its molecular structure. 

All the [M(CO)3L( /4-diene)] complexes exhibit a second ligand movement with a higher barrier of activation. At low temperatures, complexes with unsymmetrically substituted diene ligands show three different carbonyl signals in their, 3C-NMR spectra, according to the different [M(CO)2(13CO)L-( j4-diene)] isotopomers d, e, and /. At higher temperatures, the coalescence... 

In the [M(CO)2L2b -diene)] complexes, the monodentate donor ligands are found almost exclusively at the a and / positions. There is evidence for the ad and ae stereoisomers only for [Cr(CO)2 P(CH3)3 P(OCH3)3 -(i/ -butadiene)] (36a) (29). A hindered ligand movement, which causes temperature-dependent NMR signals for the donor ligands, is explained by a... 

By D-NMR spectroscopy, up to three hindered ligand movements were detected in [Cr(CO)2L(tj4 CH-diene)] complexes, a situation comparable to [Mn(CO)3(t/3 CH-cyclohexenyl)] complexes (46-51). Only small activation barriers are found for exchange processes of the C—H—Cr bridge. Higher barriers are observed for the site exchange of the three monodentate ligands. Similar energies are necessary to activate 1,5-H shifts (Table VI). 

Activation Parameters for Hindered Ligand Movements in [M(CO)2L( 4 CH-diene)] Complexes"... 

A local induced fit motion is sampled by ADAM docking in combination with an energy minimization. ADAM utilizes a vdW-offset 3D grid. To enlarge the pocket uniformly, the potential curve is shifted that allows the atoms to get closer. The stmcture optimization covers side chains and ligand movements. The energy minimization is performed with the L-BFGS method [74]. 

There have been two reports of CO migrations in binuclear metal complexes. In both cases carbonyl motions are coupled with other ligand movements. Whilst simple W—W bond rotation is responsible for the isomerization in solution of [W2(CO)gCp2], the P and NMR spectra of [WRh(/i-CO)2(CO)(PPhj)2Cp] establish a pseudorotational process that interchanges the inequivalent PPhj groups and all CO ligands. The carbonyl fluxionality of [CH2 (f/ -C5H4)M(CO) 2(At-CO)] (M = Rh, Ir)... 

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