Carboxylic arid derivatives

We have looked at a whole series of interconversions between carboxylic acid derivatives and, after this next section, we shall summarize what you should have learned. We said that it is always easy to move down the series of arid derivatives we listed early in the chapter and, so far, that is all we have... 

DKR strategies with reductive enzymes in most cases refer to substrates possessing a stereogenic center that has an addic proton, thus fadlitating racemization through the enol form (e.g., a-substituted carboxylic add derivatives and a-substi-tuted ketones) [9]. The introduction of an electron-withdrawing substituent E at the stereogenic center of 1 enhances the aridity and therefore the mobility of this proton, as shown in Scheme 12.2. 

Seki and Tirrell [436] studied the pH-dependent complexation of poly(acrylic acid) derivatives with phospholipid vesicle membranes. These authors found that polyfacrylic acid), poly(methacrylic arid) and poly(ethacrylic acid) modify the properties of a phospholipid vesicle membrane. At or below a critical pH the polymers complex with the membrane, resulting in broadening of the melting transition. The value of the critical pH depends on the chemical structure and tacticity of the polymer and increases with polymer hydro-phobicity from approximately 4.6 for poly(acrylic acid) to approximately 8 for poly(ethacrylic acid). Subsequent photophysical and calorimetric experiments [437] and kinetic studies [398] support the hypothesis that these transitions are caused by pH dependent adsorption of hydrophobic polymeric carboxylic acids... 

---