Recognition linear

Fig. 10. Linear recognition diagrammatic representation of the recognition of linear dicationic (a) and dianionic (b) substrates (c, d) typical examples of...

Linear programming algorithms, for gasoline blending, 12 411 Linear recognition, 16 779, 781 Linear regression analysis, 6 27... 

Linear recognition is displayed by the hexaprotonated form of the ellipsoidal cryptand bis-tren 33, which binds various monoatomic and polyatomic anions and extends the recognition of anionic substrates beyond the spherical halides [3.11, 3.12]. The crystal structures of four such anion cryptates [3.11b] provide a unique series of anion coordination patterns (Fig. 4). The strong and selective binding of the linear, triatomic anion N3" results from its size, shape and site complementarity to the receptor 33-6H+. In the [N3 pyramidal arrays of +N-H "N- hydrogen bonds, each of which binds one of the two terminal nitrogens of N3-. 

Linear Recognition of Molecular Length by Ditopic Coreceptors... 

Thus, for both the terminal diammonium and dicarboxylate substrates, selective binding by the appropriate receptors describes a linear recognition process based on length complementarity in a ditopic binding mode. Important biological species, such as polyamines, amino acid and peptide diamines, and dicarboxylates [4.18] may also be bound selectively. Recognition is achieved by multiple coordination to metal ions in dinuclear bis-macrocyclic coreceptors that complex selectively complementary bis-imidazole substrates of compatible length [4.21]. 

The binding stability constant were determined by UV absorption spectrometry (Table 1) it appears that the most tightiy bound diammonium includes 7 methylene units and it does not correspond exactly with the best geometry for maximum fluorescence quantum yields but, using fluorescence spectroscopy, the selectivity is in favor of n = 6 whereas the linear recognition is in favor of longer chain n 12 for the related 2,6-disubstituted maaotricyclic receptot (Fig. 10-Table 1). 

As a consequence of die above investigations, the tonnelet could be used for the selective critical detection of a,oHliainmonium salts (linear recognition) and Rb (spherical recognition). 

C(CH2)mC02 substrate. Selectivity peaks are found with m = 2,3 for (118), m = 5,6 for (119) as a result of structural complementarity (linear recognition) between the receptor and the dicarboxylate substrates (120) (Figure 2.47). 

When two binding subunits are located at the poles of a coreceptor molecule, the complexation of a difunctional substrate will depend on the complementarity between the distance of the two binding sites in the receptor and the distance of the two corresponding functional groups of the substrate. Such linear recognition by ditopic coreceptors has been achieved for both dicationic and dianionic substrates, diammonium and dicarboxylate ions respectively, and corresponds to the binding modes schematically represented by (17) and (18). 

As in the above case of the binding of diammonium substrates to the macrotricyclic coreceptors, the present chain length selection also describes a linear recognition process based on structural complementarity between the dianionic substrates and the coreceptors in a ditopic binding mode (see (28)). In both cases, the receptor molecule acts as a discriminating sensor of molecular length. 

---