Water selective binding

Each of these goals requires the synthesis of a compound with sufficiently selective binding and concomitant fluorescent signal transduction in water. However, the scientific base on which to start the rational design process does not, at present, exist. We have set as our research agenda the evaluation of new ways in which an ion or molecule recognition event can be transduced into a fluorescence event. 

Tomeiro M, Still WC. Sequence-selective binding of peptides in water by a synthetic receptor molecule. J Am Chem Soc 1995 117 5887-5888. 

Some authors based their approach to selective binding of the more lipophilic a-amino acids in water on hydrophobic effects using water-soluble, cavity-containing cyclophanes for the inclusion of only the apolar tail under renouncement of any attractive interaction of the hosts with the zwitterionic head . Kaifer and coworkers made use of the strong affinity of Stoddart s cyclobis(paraquat-p-phenylene) tetracation 33 for electron-rich aromatic substrates to achieve exclusive binding of some aromatic a-amino acids (Trp, Tyr) in acidic aqueous solution [48]. Aoyama et al. reported on selectivities of the calix[4]pyrogallolarene 34 with respect to chain length and t-basicity of aliphatic and aromatic amino acids, respectively [49]. Cyclodextrins are likewise water-soluble and provide a lipophilic interior. Tabushi modified )S-cyclodextrin with a 1-pyrrolidinyl and a carboxyphenyl substituent to counterbalance the... 

These features make the design of suitable ligands that can displace water and bind both strongly and selectively to these freely diffusing cations a difficult task. The only basis for selectivity between alkali metal... 

Schmuck, C., Schwegmann, M., A Molecular flytrap for the selective binding of citrate and other tricarboxylates in water. J. Am. Chem. Soc. 2005,127, 3373-3379. 

In one approach, the free energies of binding, out of water into the enzyme active site, of the reactant(s) and transition structure are computed, in order to see if rate acceleration can be explained by selective binding of the transition structure. However, there are several caveats associated with such an approach. First, it must be decided whether to use the same reactant and transition state structures in solution and in the enzyme. If the same structures are used, then the potential for catalysis specifically by selective transition state binding can be quantified. Of course, the actual enzyme-bound structures may be different than those in aqueous solution, and... 

The non-toxic 3-hydroxypyrones (Structure 12) bind iron(III) forming water-soluble complexes [44], In the pH range 4-7, they possess a lower affinity for iron(III) than EDTA, and by virtue of the kinetic lability of such complexes, are able to donate iron to high-affinity binding sites, while minimizing non-selective binding to foodstuffs. Thus, iron presented as a maltol complex is relatively well absorbed [103,104], In contrast, the presence of EDTA reduces iron absorption by the intestine. Ferric maltol is the only simple iron(III) preparation which compares favourably with iron(II) sulphate [105], and in contrast to iron(II) sulphate, there are few, if any, side effects associated with the oral administration of ferric maltol. Consequently, patient compliance is likely to be superior with this iron preparation. 

The complexing of calcium by EDTA and also by polyphosphates is of importance, not only for removal of calcium ions from water, but also for the volumetric estimation of calcium. In Ca[CaEDTA]-7H20 the coordination of the Ca ion is 8. Calcium ions are involved in many natural processes such as bones (Ca5(P04)30H), blood clotting, transmission of nerve impulses, and so on as well as in selective binding to various proteins with a range of functions. 

As we have implied, the ability of these host molecules to bind guests is often very specific, often linked to the hydrogen-bonding ability of the host, enabling the host to pull just one molecule or ion out of a mixture. This is called molecular recognition In general, cryptands, with their well-defined 3D cavities, are better for this than monocyclic crown ethers or ether derivatives. An example is the host 30, which selectively binds the dication 31 ( = 5) rather than 31 ( = 4), and 31 n = 6) rather than 31 (n = 7). The host 32, which is water soluble, forms 1 1 complexes with neutral aromatic hydrocarbons, such as pyrene and fluoranthene. 

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