Aromatic carboxylate anions

Li and Wong reported a Tb + complex Tb-26 with pendant aza-15-crown-5 (Figure 13.12) that showed recognition of two important bio-active anions, lactate and salicylate, in aqueous solution [48]. The luminescence lifetime of Tb-26 in H2O was dependent on the nature of the ratio in solution. Upon addition of S.Oequiv of lactate, the luminescence lifetime of Tb-26 increased from 1.45 ms to its maximum of 2.15 ms. Moreover, Tb-26 shows a high selectivity of lactate over other anions such as HCOJ, H2PO4, AcO , and Cl . In addition, two coordi-natively unsaturated terbium complexes Tb-27 and Tb-28 (Figure 13.12) could be displaced upon metal chelation to aromatic carboxylic anions, such as salicylate, in water [49]. 

The carboxylic acid coupling partner is initially deprotonated by triethylamine typically, forming the carboxylate ion which then reacts with the acid chloride to give a mixed anhydride. This forms the first part of the two-step procedure. The acylating agent dimethyiaminopyridine (DMAP) is then added, which reacts with the mixed anhydride to form an acyl pyridinium salt with the elimination of an aromatic carboxylate anion. The second coupling partner, the alcohol, then reacts with the acyl pyridinium salt to give the desired ester. 

Rakitin, A. R., and Pack, G. R., Necessity of aromatic carboxylate anions to be planar to induce growth of cationic micelles, Langmuir, 21, 837-840 (2005). 

Echavarren. A. Galan. A. Lehn. J.-M. de Mendoza. J. Chiral recognition of aromatic carboxylate anions by an optically active abiotic receptor containing a rigid guanidinium binding subunit. J. Am. Chem. Soc. 1989. Ill (13). 4994-4995. 

Dimsyl anion 88 reacts with esters of aromatic carboxylic acids and aliphatic acids which do not have a readily transferable proton, to give /5-ketosulfoxides114,133,138-141. There are not many cases in which acyl chlorides were used142,143. However, the reaction... 

LDHs are also promising materials as sorbents for anionic organic contaminants via both ion-exchange and reconstruction reactions. There have been a large number of reports of the use of LDHs for removal of species such as aromatic carboxylic acids, phenols, pesticides, and humic or fulvic acids. Recently, Cardoso et al. [152] found that the sorption process of terephthalate anions from aqueous solutions by calcined Mg/Al - CO3 LDHs takes place by reconstruction of the LDHs and involves the intercalation and adsorption of terephthalate anions. Calcined Mg/Al - CO3 LDHs were found to be capable of removing 40 to 85 % of the benzoate from solutions in the concentration... 

The differences in aromaticity follow the results of theoretical analyses on the acidity of the NH proton of the pyrrole fragment of furo[ ]pyrroles <2000PJC207> and are nicely reflected in the observed stability of both systems. The total energy difference between methyl 4f/-furo[3,2- ]pyrrole-5-carboxylate 8a and methyl 6f/-furo[2,3- ]pyr-role-5-carboxylate 31a is rather small (—7.2 kj mol ) indicating the higher stability of the former system. However, if the increase of energy of the appropriate anions is compared (relative to the parent molecules), then it indicates that formation of 67/-furo[2,3-7]pyrrole-5-carboxylate anion is much easier (by —22.5 kJ mol ) than formation of 4//-furo[3,2- ]pyrrole-5-carboxylate anion. 

We also have looked at a large number of other anions, particularly aromatic carboxylates, including many containing heteroatoms. On that basis, we generally have concluded that the site is very hydrophobic and relatively long and narrow such that the decanoate ion, e.g., probably binds in a more or less extended conformation. 

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