Addition charge-directed

Conjugate addition. Charge-directed addition to a-silylated a,/3-unsaturated amidate anions is observed. "-1,2-Addition is suppressed in such substrates. 

IEC is very sensitive to additives that directly alter the charge of sample components. Several classes of additives provide a range of opportunities to exploit this approach. All involve complexants that bind to the proteins in a sample. 

A screening of possible redox couples has led to the choice of Fe3+/Fe2+ as a very suitable catholyte, while Cr2+/Cr3+ and Ti3+/Ti02+ have been suggested for the anolyte. The latter shows problems connected with hydrolysis effects unless very low pH is maintained, and in addition has a low exchange current density. Cr /Cr3+ is also kinetically slow, especially in the charging direction. In cells tested so far, voltages and current densities have been low and considerable improvements are needed in... 

In contrast, chemoselectivity can be attained by a charge directed conjugate addition strategy in which 1,2-additions are suppressed, not by steric constraints, but by the presence of an adjacent negative... 

In the case of porphyrin systems, there is an agreement that electron injection occurs from the lowest singlet excited state (438, 439). In the tetraruthenated porphyrins, the mechanisms involved in ET are more complex, since both components are responsible for photocurrent generation. As already discussed, from the HOMO and LUMO compositions, the peripheral ruthenium complexes can effectively transfer electronic charge to the porphyrin center via Ru( Jtt) porphyrin MLCT transitions. In addition, the direct interaction between the ZnTPyP core and Ti02 plays an important role in the photoresponse efficiency. 

The low-T form of UHj can be prepared by cathodic charging of U metal in a solution of HCIO or NaOH below 20°C, in addition to direct reaction with Hj gas at -40°C. 

Another route to substituted ylides via ylide anions involves charge-directed addition of a wide range of carbon nucleophiles to 7,8-unsaturated acylphosphoranes yielding intermediate anions which further react with electrophiles, mostly alkyl halides (equation 94).>6i,i84,i92... 

---