Boronic acid ligands

Chemical sensors based on the competitive binding of sugars to the boronic add ligand have been reported. When 3-aminophenyl boronic acid was covalently linked to GSH-capped CdSe-ZnS QDs, the boronic acid ligand formed boronate esters with... 

In a further example, phenyl boronic add-functionalized CdSe/ZnS QDs were used to bind NADor NADH via the boronic acid ligand to form boronate esters. The quenching of the QDs luminescence by the NAD + cofactor, via an ET quenching route, was substantially more efficient than was the quenching of QDs by NADH. This difference in quenching between NAD and NADH enabled QDs to be used for the luminescence analysis of NAD -dependent enzymes and their substrates, such as the AlcDH/ethanol system [141] (Figure 6.31a). The biocatalytic reduction of the... 

The Willner group functionalized a SWCNT anode with Nile Blue and the cofactors NADP" and NAD" via a phenyl boronic acid ligand [23]. Connecting the anode to a BOD cathode, one ethanol biofuel ceU based on alcohol dehydrogenase delivered 23 pW cm and one glucose biofuel cell based on glucose dehydrogenase (GDH) delivered 58 pW cm . ... 

Thus, capture of czs-diol-containing biomolecules, especially glycoproteins, of very low concentration by conventional boronate affinity materials is rather difficult or impossible. Therefore, it is essential to develop novel boronic acids ligands or boronate affinity materials that can significantly improve the binding strength. 

In work that has been ongoing since the late 1960s, Pizer and co-workers extensively examined the physical properties of trigonal boron acid - ligand complexation. From initial studies it was observed that the overall reaction proceeded with a change in geometry at boron, from trigonal to tetrahedral, on complexation. 

Therefore, while the detailed mechanism by which trigonal boron acid-ligand complexation proceeds has not been fully elucidated, there is general agreement in the literature on a number of salient points. 

The influence of boron-bonded ligands on the kinetics and mechanistic pathways of hydrolysis of amine boranes has been examined (37,38). The stoichiometry of trimetbyl amine azidoborane [61652-29-7] hydrolysis in acidic solution is given in equation 10. It is suggested that protonation occurs at the azide ligand enabling its departure as the relatively labile HN species. 

Scheme 3.60 Thiazolidine ligand for arylations of aldehydes with aryl boronic acids.

Scheme 4.19 Arylations of ketones with boronic acids and HOCSAC ligand.

There are only a few examples of displacement of a fluorine atom in a cross-coupling reaction. With tricarbonylchromium complexes of fluoroarenes as substrates, cross-coupling with both boronic acids and vinylstannanes has been realized. Interestingly, only PMe3 is effective as ligand in this reaction (89).2" See Section 9.6.3.4.10 for an example of the involvement of unactivated fluoroarenes in cross-coupling reactions. 

The same ligand allowed the cross-coupling of various boronic acids (aryl, alkenyl, alkyl) with alkyl bromides in the system (Pd(OAc)2/PMe Bu2, BuOK. amyl alcohol, r.t.).411... 

The interaction of PBA derivatives with molecular species having the above functional groups occurs optimally in the pH range of 8-9, but it is typically reversible at acid pH or in the presence of a high concentration of competing ligand. However, the heterocyclic boronic acid complex is relatively stable under optimal conditions of formation. 

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