Tetrahedral receptors

Fig. 13 Computer-aided design of a self-assembled tetrahedral receptor for sulfate encapsulation...

SS Yoon, WC Still. Cyclooligomeric receptors for the sequence selective binding of peptides. A tetrahedral receptor from trimesic acid and 1,2-diamines. Tetrahedron Lett 35 8557-8560, 1994. 

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. 

Molybdate is also known as an inhibitor of the important enzyme ATP sulfurylase where ATP is adenosine triphosphate, which activates sulfate for participation in biosynthetic pathways (56). The tetrahedral molybdate dianion, MoO , substitutes for the tetrahedral sulfate dianion, SO , and leads to futile cycling of the enzyme and total inhibition of sulfate activation. Molybdate is also a co-effector in the receptor for steroids (qv) in mammalian systems, a biochemical finding that may also have physiological implications (57). 

Lehn has also reported the hydrogen-bonding templated assembly of receptors based on bipyridine copper and palladium complexes [102]. A mixture of substituted bipyridines (76, 77) (see Scheme 39) with copper(I) triflate generates a mixture of tetrahedral complexes and uncoordinated ligands. 

AU the synthesized compounds, regarchess of their probe s size or charge, display microbial activity in P. putida similar to that of the biomimetic analogs lacking the probe. These results provide an indication that the epical site in the tetrahedral carbon-based templates is available for attachment of chemical moieties without hampering iron(in) coordination and receptor recognition. 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

Spherical cryptand (13) contains four nitrogen atoms in a tetrahedral arrangement this is the topologically ideal receptor for the ammonium ion (NH4+) which has a tetrahedral... 

Development of ditopic receptors 58 for both an anion and a cation is a logical extension [19b]. It should be stressed that the recognition by cyclodextrins, calixarenes, hemicarcerands, and many other systems does not involve specific recognition sites, whereas tetrahedral recognition by 53 and 54, the adenine 56 selective binding, and multiple recognition like the one shown in formula 59 [20] require the presence of specific sites in receptor capable of directional interactions. 

Tetrahedral tetraazonium compounds 5a and 5b, developed by Schmidt-chen, bind carboxylates, such as formiate, acetate, and benzoate, among a variety of other anions [8]. Although these receptors do not display hydrogen bond interactions, they are endowed with well localized polycationic centers, which are independent on the acidity of the medium. A ditopic receptor build up of both a 5a and a 5b subunits bridged by a p-xylylene spacer showed selectivity towards the largest members of a series of dianionic probes [9],... 

Recognition of a tetrahedral substrate geometry requires the construction of a receptor molecule with a tetrahedral recognition site. This may be realized by positioning four suitable binding sites at the corners of a tetrahedron and incorporating them into a bridged molecular framework. 

The non-complementarity between the ellipsoidal 33-6H+ and the spherical halides results in much weaker binding and appreciable distortions of the ligand, as seen in the crystal structures of the cryptates 35 where the bound ion is F , Cl-, or Br-. In these complexes, F- is bound by a tetrahedral array of hydrogen bonds whereas Cl- and Br- display octahedral coordination (Fig. 4). Thus, 33-6H+ is a molecular receptor for the recognition of linear triatomic species of a size compatible with the size of the molecular cavity [3.11]. 

Fig. 15. Schematic representation of a planar, tetrahedral, octahedral and double-helical arrangement of external interaction sites (arrows) on ligands organized around metal ions of given coordination geometry in metallo-exo receptors a linear strand is also shown.

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