Oxyanionic groups

DNA cleavage by, 43 158-159 reactions, copper proteins, 39 25 Oxo-trichloroselenates(IV), 35 270-271 Oxo-type molybdenum enzyme, see Molybdenum enzymes, pterin-containing Oxovandium (IV), solvent exchange and ligand substitution, 42 47-49 Oxyanions, Groups VIB and VIIB, redox reactions, kinetics and mechanism, 40 269-274... 

In order to overcome the limitations of the methacrylate-based MIPs for selective recognition in aqueous samples, Urraca et al. have prepared PenG-imprinted polymers using an urea-based functional monomer to target the single oxyanionic groups in the template molecule [34]. This polymer has shown excellent recognition in aqueous samples [90] and has been applied to the development of the first... 

The 65 35 product distribution of 6 and 7 in the rearrangement of substrate 5 with an anti relationship indicates that the usual preference of the oxyanionic group for a pseudoequatorial position is overruled by the steric demand of the axial methyl group966,967. 

The presence of a rvn-methyl group in the camphenyl derivatives 7 redirects electrophilic capture to the endo Jt-bond face. As a consequence, in combination with the preferred orientation of the oxyanion group, the rearrangement of 7 b now leads to a 99 1 ratio of products 9 and 8, whereas the rearrangement of 7 a results in the formation of a virtually 1 1 mixture. 

Again, the high chirality transfer is a consequence of the strong preference of the oxyanionic group for an equatorial position, which is probably due to stereoelectronic (the equatorial oxyanionic bond lies almost in plane with the vinyl group) as well as steric effects (large size of the oxyanionic group by ion-pair formation and/or solvation) 30. 

The hydrolysis of phosphoester bond can be accelerated by several catalytic factors, including enhancement of the nucleophilicity of the 2 -oxygen (Scheme 4.3-9), stabilization of the leaving 5 oxyanion group (Scheme 4.3-8), stabilization of the pentavalent intermediate (Scheme 4.3-8), and the presence of buffers (e.g., imidazole, morpholine, and carboxylates) and divalent or trivalent metal ions (e.g., Mg +, Zn ", Ca"", Cu"+, and Fe"+) [44]. 

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