Esters binding modes

Moss et al. (1979) examined the micelle-catalyzed hydrolysis of ll- and DL-N-carbobenzyloxyalanylproline p-nitrophenyl esters. They found that the kLL/kDL ratio changes from 0.62 to 4.33 depending upon the surfactant micelles, and the catalytic efficiency was rationalized in terms of difference in the binding mode. 

A consistent stereochemical structure-activity pattern may be built up on the basis of the 4-phenylpiperidine ligands associating with the opioid receptor in the form of equatorial 4-phenyl chair conformations. Other conformations (i.e., axial 4-phenyl chairs or flexible boat forms) could have been employed as the basic active species but greatest adherence to probable conformations is possible by the approach adopted furthermore, no need arises to assume a major difference in the binding modes of the few examples of esters in which axial 4-phenyl chair conformations may be favored. 

Asyimnetric hydrogenation of prochiral ketones is an important method for the preparation of chiral secondary alcohols. Until recently, however, such reactions were limited to substrates with pendent metal binding sites, like /3-keto esters. Many of the catalysts that efficiently hydrogenate C-C double bonds exhibit little or no reactivity with isolated ketones. This discrepancy may be ascribed to the different binding modes of alkenes and ketones, and the chemoselectivity of catalysts for these groups. While substrates with C-C double bonds can form metal... 

The stronger but less productive binding of 43 by 42 compared with that prepared by random functionalization suggests the binding mode of 44. Interaction of the metal-bound water molecule of the TC complex with the carbonyl group of the bound ester facilitates the complexation. On the other hand, the assembly of 44 may sterically protect the ester linkage from attack by nucleophiles. 

Several studies have addressed how car-boxylated Ru complexes interact with Ti02 surface [303, 378, 380-382, 385], In most vibrational studies, an asymmetric C—O stretch consistent with carboxylate binding modes (bidentate or bridging) has been reported [378, 380, 385]. Evidence for ester linkages and H-bonded network have also been reported [303, 376, 382]. Qu and Meyer [378] demonstrated that high surface proton concentrations favor carboxylic acid type linkage where low proton concentrations favor carboxylate type binding modes for complexes. Possible modes of coordination of the... 

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