Carboxylic acids hydrogen-bond affinity

A broad range of functional monomers and cross-linkers has been used for the preparation of MIPs. The choice of the functional monomers depends on the nature and functionalities of the print molecule. The most widely used monomer is methacrylic acid, which has been shown to interact through ionic interactions and hydrogen bonds with amines, amides, carbamates and carboxylic acids [13-15]. The monomers and the print molecules self-assemble upon mixing and the strength of the complex is of importance for the selectivity of the polymer. For this reason, a considerable amount of research effort has focused on finding optimal monomers for various classes of print molecules and functionalities. For example, for some print molecules, polymers prepared with vinylpyridines [16,17], 2-(trifluoromethy-l)acrylic acid [18] or acrylamide [19] resulted in higher selectivities and affinities than polymers made from methacrylic acid. Mixtures of functional monomers... 

Similar intense bands at approximately the same frequencies are observed when other molecules of comparable proton affinity are adsorbed in HZSM-5 e.g.water [41],dimethylether [38,40,41], acetone and various carboxylic acids [41]. Pelmenschikov et al. [42,43] pointed out that these bands are very similar to the so-called A,B,C triplet of OH bands characteristic of strong molecular hydrogen bonded complexes in liquid or solid phases. The most widely accepted explanation for the A,B,C triplet in hydrogen bonded systems is that due to Claydon and Sheppard [44], who suggested that the A,B,C triplet are in fact pseudobands caused by the superposition onto a very broad single (OH) band of two so-called Evans transmission windows caused by Fermi resonance between the (OH) mode and the first overtones of in-plane ( 2 5(OH) = 2600 cm l) and out of plane ( 2 y(OH) = 1900 cm l) bending... 

X 10 if the enolate anion intermediate were not stabilized in the active site this value is 10 -fold less than the observed value for the kcat, 500 s. Recall that an enolate anion is necessarily on the reaction coordinate, so the value of AG° must be reduced for the enolate anion to be kinetically competent irrespective of whether AG int can be reduced. Thus, the active site of mandelate racemase must decrease AG° from the value predicted from the values of the substrate carbon acid and the active site base in solution. The obvious strategy to accomplish this reduction is preferential stabilization of the enolate anion intermediate relative to the carbon acid substrate, the increased negative charge on (or proton affinity of) the carbonyl/carboxylate oxygen of the enolate anion intermediate provides a convenient handle for enhanced electrostatic or hydrogen bonding interactions with the active site. 

---