Monotopic

In this way hosts 141-145 with both a cr-bonded Lewis acidic boron atom for complexation of anions and a conventional multidentate ligand for cations are generated. Complexation experiments of the 21-membered crown [6] boronate 142 with different potassium salts KX (X = F, Cl, Br, I, SCN, CN, OMe) indicate that there is a high specificity for the incorporation of KF, whereby F is bound covalently to the boron atom and is complexed by the crown ether (146, Fig. 39). An X-ray study has shown that the complexation of KF is heterotopic, i.e., both ions are complexed inside the same host. Some of the salts can only be bound in a monotopic way (KI and KSCN) [237]. 

Binda C, Hubalek F, Li M, Edmondson DE, Mattevi A. Crystal structure of human monoamine oxidase B, a drug target enzyme monotopically inserted into the mitochondrial outer membrane. FEBS Lett 2004 564 225-8. 

The substrate specificity of these enzymes is not stringent for example, CCD1 from tomato was also shown to cleave at the 9,10- and 9, 10 -positions of (1-carotene, zeaxanthin, lutein, violaxan-thin and neoxanthin all of which have different ionone ring modifications. Unlike NCEDs, CCD1 enzymes have no plastid-targeting sequences and are localized in the cytosol. It is postulated that they access the carotenoids in the plastids through a monotopic membrane association (Kloer et al. 

Integral membrane proteins with one transmembrane domain may have soluble domains at either or both surfaces. An example of a monotopic protein, cytochrome b5 has a single hydrophobic segment that forms a hairpin loop, acting as an anchor to the cytoplasmic surface but probably not totally penetrating the bilayer. 

Synapsins la, lb, Ha and lib Monotopic membrane proteins with common N-terminal domains, with phosphorylation sites for CaMKI and... 

In the present chapter, however, because the problem is considered from a retrosynthetic point of view, we will distinguish only between heterolytic and homolytic disconnections -to which we will refer to as "retro-annulations"- and concerted or "pericyclic (or cheletropic) cycloreversions". In the same way that Woodward-Hoffmann rules [2] apply to pericyclic reactions, the Baldwin rules [3] may be said to apply to heterolytic as well as to homolytic "monotopic" annulations (see Table 6.1). Although in the preceding Chapter (see 5.5) we have already described some radical "monotopic" annulations, later on in this Chapter (see 6.1.3) and mainly in Chapter 7 we will refer to some new methods, syntheses and strategies which have been developed recently. 

Monotopic refers to receptors which possess only one binding subunit. 

Columnar mesophases of rectangular section have been obtained by combining the monotopic components of 173 with the TP2 and TU2 units their occurrence may be attributed to the formation of mixed 2/1 supermolecules 175 [9.153],... 

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>. 

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