Artificial host-guest binding

One important reason for the mediocre performance of many artificial hosts may originate from the ambiguity of the binding modes. If we take host-guest binding of anions in water as an example, the blueprint of host design almost always relies on the creation of polar interactions which should attract the guest... 

Even though the fundamentals of host-guest binding at least in their crude outlines appear well understood, it remains a formidable task to translate these insights into the concrete covalent structure of a compound that in the end displays the anticipated molecular properties. Looking back on a history of 35 years of striving to accomplish selective anion binding by artificial host... 

Free energy perturbation calculations use Monte Carlo or molecular-dynamics approaches to calculate relative free energies (e.g., of solvation or host-guest binding) on the basis of thermodynamic cycles involving the binding processes of two related systems and the artificial mutation of one system into the other. 

Provided the stoichiometry n is secured by supplementary noncalorrmetric evidence and, furthermore, is unperturbed by high concentrations of the interaction partners, an analysis of the statistical error allows some recommendations to be made for parameter adjustment to optimize the precision [24], Hence, under these prerequisites (which admittedly seldom apply in artificial host-guest systems) the enthalpy AH and association constant Kassoc can be determined to less than 1% relative error in a broad range (10 < Kassoc < 10 valid for AH, too, when Kassoc > 30 just following a simple recipe [23] (i) Use no more than 10 injections of the titrant solution (ii) set the final molar ratio in accord with the empirically determined Eq. (3.8), but not smaller than 1.1 where c is as defined in Eq. (3.7) this requires a crude estimate of the binding constant Kassoc- Table 3.1 lists the digest of... 

In other case of assembly with a linker, the biological recognized molecules, such as biotin-streptavidin [64,65] or DNA compensatory binding formation [11,57-59] to bind tightly and selectively, have been often used instead of the artificial host-guest molecules. As an interestingly case with the interaction, Murphy et al. 

Table 1. Binding constants (K) for host-guest complexes of artificial receptors with 11, and microenvironmental polarity parameters ( ) and steady-state fluorescence polarization values (P) for the guest bound to hosts in aqueous solution at 30.0 °C ...

As mentioned above, some naturally occurring cyclic hosts that possess molecular recognition capabilities were known before crown ethers (the first artificial host molecules) were discovered. For example, the cyclic oligopeptide valinomycin and the cyclic oligosaccharide cyclodextrin were found to bind to specific guest molecules. The chemical modification of cyclodextrin was particularly well-researched, and artificially modified cyclodextrins became one of the most important compoimds used in host-guest chemistry. 

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