Surface ester groups: hydrolysis

Mineral surfaces may accelerate the rate of ester hydrolysis (Stone, 1989 Hoffmann, 1990 Torrents and Stone, 1991). One plausible scheme for this heterogeneous catalysis assumes a nucleophilic addition of the ester to the surface functional group, e.g., in case of a carboxylic acid ester... 

The most facile entry into surface complexation involved hydrolysis of ester-terminated dendrimers (derived from Michael additions of surface NH2 groups to methyl acrylate) with stoichiometric amounts of alkali-metal hydroxides. In this manner, salts of Na+, K +, Cs+, or Rb+ were readily obtained (Scheme 31) as white hygroscopic powders. Dilute solutions of the sodium salts allowed direct observation of the individual dendrimer molecules by scanning transmission electron microscopy without the use of staining techniques [79-81]. Elemental analyses showed that essentially stoichiometric exchanges with divalent cations such as Ca2+ could be performed [164],... 

Scheme 2 Procedure used to anchor SMMs on a Si(lOO) siu-face (1) reaction of the terminal double bond with the Si(100)-H surface (2) hydrolysis of the ester groups (3) reaction of the grafted carboxylic acid layer with Mnn-acetate (adapted from [93])...

Alternatively, hyperbranched polymers can be prepared in situ on the monolayer surface. Treatment of the acid-terminated layer with chloroformate and amine-terminated poly(f-butyl acrylate) produces ester groups on the surface. Hydrolysis of the ester functions with tosic acid gives carboxyl groups. The whole procedure is then repeated several times... 

Mixed monolayers of the isonicotinate ester and nonanethiol which have ca 25% of the surface isonicotinate groups are, however, susceptible to hydroxide-mediated hydrolysis (equation 19). The kinetic plots of this reaction showed clean first-order behaviour, implying that the access of hydroxide ion to the reaction centre in disordered layers is not hindered. Attachment of the Ru(II) complex to the pendant isonicotinate at the surface of the monolayer increases the rate of reaction, probably because of the high positive charge of the Ru(II) moiety. 

In the case of polybutylcyanoacrylate microbubbles a httle caustic soda solution is needed to perform a hydrolysis of the ester groups just on the particle surface and the free carboxy groups can be used for the coupling of targeting ligands [15, 26]. To be more flexible in animal experiments we have preferred the coupling of streptavidin to the microcapsules. Biotinylation of antibodies is well established and the affinity of biotin to streptavidin is outstanding. To... 

Fig. 12 Schematic of base-catalyzed hydrolysis reaction in a SAMs of NHS-CIO and b ultrathin films of PNHSMA on oxidized silicon together with the definitions of surface and surface-near regions of the polymer film. The approximate depths in this tentative model were assigned based on the information depths of the techniques (CA 1 nm [148], IR the entire film, in other words 40 nm), the fact that only 25% of the NHS ester groups can be hydrolyzed, and that the reaction can be expected to start at the film-solution interface and to proceed homogeneously into the amorphous film. (Reprinted with permission from [128], copyright (2003), American Chemical Society)...

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