Receptor monotopic

Monotopic refers to receptors which possess only one binding subunit. 

Distances between the bridgehead amines vary according to the topicity of the receptors. For monotopic complexes, the bridgehead distances are between 6.5 and 7.9 A. In terms of incorporating multiple species, however, the azacryptands appear to be the most flexible, as seen additionally in the dinitrate structure with 5 [30]. When... 

A noteworthy finding emerging from these detailed studies was that the monotopic cyclopeptide 44 actually proved to be a more efficient receptor for sulfate anions than the ditopic system 45 (for 44, AH = 19.3kJ/mol and logKT = 6.48 in 50% D20/CH30H, where /< , = K n-K.l2 M 2 ). Furthermore, in contrast with the design expectations, microcalorimetric titrations (e.g., ITC analyses) revealed that sulfate is bound to receptor 45 with a 2 1 binding stoichiometry. 

The covalent anchoring of a benzo-15-crown-5 moiety to the meta or para phenolic oxygen of a zinc tetraphenyl porphyrin via ether formation has produced m-29 and p-29, respectively. These heteroditopic receptors can bind NaCN in a ditopic fashion with a visible color change, in contrast with other sodium salts (including F, CF, BF, I-, and SCN-), which are bound in a monotopic fashion without a color change <2002CC512>. 

Another recent example of circular helicate is the Cs-symmetrical pyramidal architecture with general formula [Ln4(L)9(/f3-OH)] (004)2 obtained from an enantiomerically pure monotopic pinene-bipyridine receptor (Lama et al., 2008). 

Exotic calix[4]arene monotopic (23) and ditopic (24) anion receptors containing one and two ruthenium(II) bipyridyl moieties have been prepared (Schemes 5 and 6) and shown by NMR and cyclic voltammetry to bind and electrochemically recognise halide, dihydrogen phosphate and hydrogen sulphate anions. 

Figure 29. This receptor contained an aza crown ring that was designed to include cations, whereas anions may be bound by hydrogen bonding to the amine group to maintain electrical neutrality. This receptor has similar selectivity to that of the monotopic receptor—dicyclohexano-18-crown-6 among alkali metal ions (K+ > Na" " > Li" ) however, the flux obtained with this ditopic receptor was up to 10 times higher than with the monotopic receptor.

In order to probe this concept the substrate specificities of two artificial ditopic receptors 1 and 2 have been studied, each of which is composed of two different and independent anchor groups interlinked by a freely rotatable p-xylene spacer unit. The monotopic receptor 3, a common building block of either di topic receptor 1 or 2 is known to bind hydrophobic preferentially anionic guest species whereas the other subsites of 1 and 2 have been shown to complex hydrophic anions and... 

The selectivity advantage of the ditopic design of 1 in relation to its monotopic parent compound 3 was investigated using the dimensional probes 4-8 each containing two anionic functions at a fixed distance. Analysis of the UV-absoption band shifts experienced by these solvato-chromic probes on inclusion into the molecular cavity of the larger tetrahedral receptor site 3 yielded the 1 1 association constants in water. 

The K values of the complexation of H5.15 with different -butylammo-nium cations (G5.71-G5.73) were approximately 10 -10 (Table 5.5, runs 85-87). Meanwhile, the K values between these guests and per-methylated pillar[5]arene without the urea moiety (H5.2) were very low (kT= 10-10 runs 88-90). Therefore, the hydrogen bonding between the urea moiety in H5.15 and the counter anion improved the recognition of the all lammonium guest by the heteroditopic receptor H5.15 when compared with the monotopic receptor H5.2. 

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