Ditopic compound

The recognition of different re-donating arene guests with a common re-accepting host has been subjected to control by metal ion crown ether recognition in the next case history to be described. The 18-crown-6 derivative 18, which bears a DNP ring system [12], is a ditopic compound that can act (Figure 11) as a host for alkali metal (e.g., K+) cations as well as as a... 

In principle, there are a number of ways that supramolecular chemistry can be utilized to influence/access LC polymeric systems. One way is to access different polymeric architectures, such as main-chain, side-chain, or network structures (Fig. 3). For example, main-chain SLCPs can be formed through the aggregation of low(er) molecular weight ditopic compounds whose chain ends interact with each other through specific non-covalent interactions. Conceptually, this can occur in a number of different ways. The simplest conceptual... 

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. ... 

Yount et al. (2005) reported the formation of organogels using poly(vinylpyridine) (PVP) and ditopic metallopincer cross-linkers. This study provided particularly pertinent information on the dynamic elements of MSPs and elegantly demonstrated how they control the material s properties. PVP dissolved in dimethylsulfoxide (DMSO) is cross-linked with either bis-Pd - (18a) or Pt -pincer compounds (18b, Fig. 7.13 Yount et al. 2005). Addition of 5% 18a -Pd to a PVP solution results in a viscous material (77 = 6.7 Pa s), whereas the corresponding PVP 18b Pd is a gel (77 = 550 Pa s). Changing R from methyl to ethyl does not affect the thermodynamics of the pyridine/Pd interaction however, the rate of exchange decreases by approximately 2 orders of magnitude. Further studies on these materials and their... 

Subsequent to the preparation of 8, a number of other sapphyrin-nucleobase conjugated carriers were synthesized in the authors laboratories. These include compound 9 that has two cytosine moieties appended to the sapphyrin macrocycle, as well as two guanine-bearing sapphyrins, 10 and 11. Here, as expected, the ditopic sapphyrin-guanine receptor 10 served to enhance the transport of cytosine-5 -monophosphate (but not GMP or AMP). By contrast, the two tritopic receptors, namely 9 and 11, were designed with the intention of allowing for the formation of the complexation-derived triple-helix-like C-G-C and G-C-G motifs in addition to phosphate chelation by sapphyrin. In other words, it was expected that a centrally... 

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],... 

The dinuclear Sr complex of the ditopic ligand 17 increases the rate of basic ethanolysis ofthe malonate derivative 19 by a surprising 5700-fold, but increases by only 9.5-fold the rate of cleavage of 14 [28]. It is remarkable that such a huge rate-enhancement occurs under extremely dilute conditions, namely 15 pM 19 and 30 pM 17-Sr2. A slightly lower rate enhancement is observed in the presence of 17-Ba2. It seems likely that under the dilute conditions of the catalytic experiments several crown-complexed metal species occur simultaneously (Scheme 5.4). Given the plethora of species involved in such a complicated system of multiple equilibria, quantitative kinetic treatment is out of reach. Nevertheless, a comparison with the reactivity of model compounds, particularly that of the malonate derivative 20, provides insight into the composition of the reactive intermediate (Table 5.8),... 

Dithiocarbamates, in Ru and Os half-sandwiches, 6, 493 Dithiocarbenes, Pt complexes, 8, 439 Dithiocarboxy ligands, in molybdenum carbonyls, 5, 447 Dithiolate-bridged compounds in dinuclear iron compounds with Fe-Fe bonds, 6, 238 as iron-only hydrogenase biomimetic models, 6, 239 Dithiolate diamides, with Zr(IV), 4, 784 Dithiolene—uranium complexes, synthesis and characterization, 4, 212 Ditopic receptors, characteristics, 12, 489 Ditungsten complexes, associated reactions, 5, 748 Divinyllead diacetates... 

The ditopic receptors 66-68 containing crown ether and urea/thiourea functional groups have been synthesised. Compound 66 immobilised in the 1,3-al-... 

In this section, we discuss macrocyclic receptors prepared specifically with the aim of producing molecules with different binding motifs. Such systems, which will be considered mostly in the context of binding anions with multiple protonation sites (e.g., phosphates or sulfates) in solution, can be considered as a subset of the large class of compounds known as ditopic receptors. 

The performance of ditopic receptors will suffer if the spacer is not long and/or flexible enough to allow simultaneous full contact at all binding centers. In some cases one observes only weakening of affinities [41], while in other cases one of the possible intermolecular forces cannot materiahze at all. Thus, additive ion pairing as well as dispersive interactions with positively charged polyaromatic host compounds are present, e.g., in complexes of AMP with tetrapyridinium porphy-... 

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