Urea recognition

Fig. 13. Hydrogen bond dominated substrate recognition of (a), (c) dicarboxylic acids (b) 2-anainopyrknidine and (d) urea.

Etter, M. C., Z. Urbanczyk-Lipowska, M. Zia-Ebrahimi, and T. W. Pananto. 1990. Hydrogen Bond Directed Cocrystallization and Molecular Recognition Properties of Diaryl Ureas. J. Am Chem. Soc. 112, 8415. 

Recognition and activation by ureas and thioureas stereoselective reactions using ureas and thioureas as hydrogen-bonding donors (Y. Takemoto, 2005) [2]. 

Wilcox[102-104] A/,A/ -disubstitued (thio)urea derivatives studies on substituent effects in anion recognition and supramolecular chemistry... 

Series of various mono,- bi-, and poly-(thio)urea-functionalized (poly)saccha-rides have already been synthesized and studied for molecular recognition of, e.g., dimethyl and phenylphosphate as model compounds for monoanionic and polyanionic phosphate esters, respechvely [111]. Thiourea derivatives such as 195-197 were analyhcally identified to provide double hydrogen bonding mediated host-guest complexes of well-defined dimension and orientations and were also reported to serve as phosphate binders even in the hydrogen bonding environment of water (Figure 6.57) [111]. 

Depending on the functionality of the stopper (amine 52 or phenol 71), the reaction affords rotaxanes with urea bonding pattern 72-74 or with carbamate units 75. In each instance the temperature had to be raised to 40°C to ensure rotaxane formation and, interestingly, the free axle 76 was the only one to be isolated. This indicates that the low solubility of the reactants and the dumbbells can be the limiting factor in rotaxane synthesis when diisocyanates are incorporated. Molecular recognition is still effective, and again the decisive pattern for molecular aggregation seems to be the initial amide bond. Furthermore the macrocycle confers solubility on the thread. 

Similarly, a series of urea-based vinyl monomers were synthesized for stoichiometric oxy anion recognition [22], One of these urea-based monomers,... 

In order to overcome the limitations of the methacrylate-based MIPs for selective recognition in aqueous samples, Urraca et al. have prepared PenG-imprinted polymers using an urea-based functional monomer to target the single oxyanionic groups in the template molecule [34]. This polymer has shown excellent recognition in aqueous samples [90] and has been applied to the development of the first... 

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