Ditopic

Hexaammonium macrocycles [32]aneN6 and [38]aneN6 were designed as selective ditopic receptor molecules for dicarboxylates -02C—R—C02- such as succinate, glutarate, or adipate 51). Highest stability of the complex corresponds to the best fit between the substrate R length and the site separation of the receptor II. 

When the metalloporphyrin bears a donor group on its periphery, it can behave as a self-complementary ditopic unit capable of metal-ligand induced dimerization. Many systems have been synthesized using different metals, ligands, and spacers. The length and geometry of the spacer groups determine the stoichiometry of the assembly process. 

Other coordination modes of trans-diammac have been identified where one (154) or both (155) primary amines are free from the metal.721 725 An extension of this concept involves attachment of active functional groups such as crown ethers selectively at one primary amine to generate ditopic ligands capable of electrochemically sensing alkali metal ions through their inductive effect on the Co11111 redox potential. One example is provided by (156) further, the 15-crown-5 and 18-crown-6 analogs were also prepared.726... 

The hydrolysis of p-nitrophenyl acetate and bis(p-nitrophenyl phosphate) are frequently used to probe hydrolytic activity. A problem with some other dinuclear systems is that the Zn units are held together by bridging ligands which can be cleaved on reaction with the substrate.440 This is not the case in a ditopic ligand such as those designed by Lippard and co-workers based on Kemp s triacid imide with a xylyl spacer.441,442 Both zinc dimers and mixed metal dimers were formed and a structure characterized with a bridging phosphodiester (Figure 6). 

Koskela SJM, Fyles TM, James TD (2005) A ditopic fluorescent sensor for potassium fluoride. Chem Commun 7 945-947... 

Chrisstoffels, L. A. J. de Jong, F. Reinhoudt, D. N. Sivelli, S. Gazzola, L. Casnati, A. Ungaro, R. Facilitated transport of hydrophilic salts by mixtures of anion and cation carriers and by ditopic carriers. J. Am. Chem. Soc. 

Polytopic macrocyclic receptors 1, 2 (Figure 10.1) are able to complex the zwitterionic form of the amino acids by a double non-covalent charge interaction [28,29]. The unsymmetrical benzocrown sulfonamide derivative, 2 which contains benzo-18-crown-6 and benzo-15-crown-5 moieties was used as a ditopic receptor for multiple molecular recognition of the amino acids, by combining two non-covalent interactions ammonium-crown hydrogen bonding and carboxylate- complexed Na+-benzo-15-crown-5 charge interactions [28,33]. 

Interesting results were reported with dithiocarbamates derived from diamines. Thus, a series of dinuclear zinc(II), cobalt(II), and nickel(II) dithiocarbamate ditopic macrocyclic receptors containing various spacer groups of different sizes has been reported.412,413,414 Spectroscopic investigations and... 

In particular, for a ditopic receptor that can bind successively two cations (see previous section), the criterion for cooperativity is Kn/Ku > 1/4, i.e. complexation of a second cation is made easier by the presence of a bound cation. For instance, a cooperative effect was observed with fluoroionophore E-l (see Section 10.3.4). 

In an effort to impart selectivity and enhance complex stability for this class of anion receptor novel ditopic biscobaltocenium receptor molecules (Fig. 42) have been synthesized and their coordination and electrochemical properties have been studied (Beer et al., 1993f, 1995h). The two positively charged metallocene centres linked by various alkyl, aryl and calix[4]arene spacers... 

Figure 2.4. Ditopic receptors for the recognition of a,co-alkane diammonium ions.

F. Fages, J.-P. Desvergne, H. Bouas-Laurent, J.-M. Lehn, J. P. Konopelski, P. Marsau, and Y. Barrans, Synthesis and fluorescence emission properties of a bis-anthracenyl macrotricyclic ditopic receptor. Crystal structure ofits dinuclear rubidium cryptate, J. Chem. Soc., Chem. Commun. 655(1990). 

The property of the [Fe (Por)Cl] complex to act as a ditopic receptor towards diatomic anions is very attractive for studying its reaction... 

Bunyapaiboonsri, T Ramstrom, H. Ramstrom, O. Haiech, J. Lehn, J.-M. Generation of bis-cationic heterocyclic inhibitors of Bacillus subtilis HPr kinase/phosphatase from a ditopic dynamic combinatorial library. J. Med. Chem. 2003,46, 5803-5811. 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

In the case of ditopic molecules with two hydrogen bonding groups, linear noncovalent polymers can form in either solution or the solid state (Fig. 4.1). In this case, the degree of noncovalent polymerization (DP) depends directly on the association constant (ATJ in the medium and the concentration of the molecule (c) as shown in Eq. (4.3) (Xu et al. 2004) ... 

Figure 7.4 (a) MSPs composed of ditopic phenanthroline ligands (la and lb) complexed to... 

Figure 7.5 Water-soluble MSPs, based on a 2,6-pyridine dicarboxylate end-capped oligo(ethylene oxide) ditopic monomer (2a and 2b) and Zn ions prepared by Vermonden and coworkers (2003).

---