Diaza-crown ethers

Photoresponsive systems incorporating an azobenzene moiety. The capped crown ether (196), shown as the (E) isomer, was synthesized initially by a high-dilution condensation between diaza-18-crown-6 and 3,3 -bis(chlorocarbonyl)azobenzene (Shinkai et al., 1980). Extraction patterns for the alkali metals differed between the (E) and (Z) isomers giving a clear example of photochemical control of the complexation behaviour. Subsequently, the analogue (197) was synthesized in which 2,2 -azopyridine was used for the cap (Shinkai Manabe, 1984). Photo-... 

Rate constants for reaction of Ca2+aq with macrocycles and with cryptands (281,282,291) reflect the need for conformational changes, considerably more difficult for cryptands than for crown ethers, which may be considerably slower than formation of the first Ca2+-ligand bond. Ca2+aq reacts with crown ethers such as 18-crown-6 with rate constants of the order of 5 x 107M 1 s, with diaza crown ethers more slowly (286,326). The more demanding cryptands complex Ca2+ more slowly than crown ethers (kfslow reaction for cryptands with benzene rings fused to the macrocycle. The dominance of kA over kt in determining stability constants is well illustrated by the cryptates included in Table X. Whereas for formation of the [2,1,1], [2,2,1], and [2,2,2] cryptates kf values increase in order smoothly and gently, the k( sequence Ca[2,l,l]2+ Ca[2,2,l]2+ Ca[2,2,2]2+ determines the very marked preference of Ca2+ for the cryptand [2,2,1] (290). 

Free energies of activation (AG in kcal mol-1 atTc) for exchange of RNH3X in diaza-crown ether complexes in CD2C12... 

Bourson J, Pouget J, Valeur B (1993) Ion-responsive fluorescent compounds. 4. Effect of cation binding on the photochemical properties of a coumarin linked to monoaza- and diaza-crown ethers. J Phys Chem 97 4552-4557... 

Fig. 13 Diaza and triaza crown ether species containing multiple ferrocene...

Figure 1. Dependence of butyl acrylate percent conversion to polymer on the stability constants for potassium ion complexation in methanol of the various crown ethers. Line calculated by regression analysis o, experimental values 1, 18-crown-6 2, dicyclohexyl-18-crown-6 3, 21-crown-7 4, dibenzo-18-crown-6 5, 15-crown-5 6, cyclohexyl-1 5-crown-5 8, 1,10-diaza-18-crown-6. Reproduced from Ref. 2. Copyright 1981, American Chemical Society.

Conductivity monitoring is most valuable for studying reactions which have very small spectral changes but which are accompanied by pH changes. The interaction of group 1 and 2 metal ions with cryptands and diaza-crown ethers has been studied by flow/conductivity methods. Conductivity monitoring has been linked to reactions which may follow pulse radiolysis, for example, in examining the... 

Pillared polyethers and polyimines have been also described, which present sorbent and ion exchange properties [7, 56]. Immobilization of crown ethers and diaza crown ethers has been carried out with the bisphosphonate pillars strategy by using the co-precipitation synthesis [44, 58]. Exchange re-... 

A novel diaza crown ether capped j3-cyclodextrin has been prepared (172) as outlined in Scheme 9. It should be noted that the cap is attached to the face of... 

Chirality derived from the readily accessible a-amino acids has been incorporated into the side chains of aza and diaza macrocyclic polyethers. A number of procedures suitable for peptide synthesis have proved (178) to be unsuitable for acylating the relatively unreactive secondary amine groups of aza crown ethers. Eventually, it was discovered that mixed anhydrides of diphenylphos-phinic acid and alkoxycarbonyl-L-alanine derivatives do yield amides, which can be reduced to the corresponding amines, e.g., l-172. By contrast, the corresponding bisamides of diaza-15-crown-S derivatives could not be reduced and so an alternative approach, involving the use of chiral A-chloroacetamido alcohols derived from a-amino acids, has been employed (178) in the synthesis of chiral receptors, such as ll-173 to ll-175, based on this constitution. 

The synthesis of unsymmetrical, cylindrical cryptands necessitates a stepwise construction of the tricycle. This is best achieved by initially mono-protecting the diaza crown ether (41) as its monobenzyloxycarbonyl derivative (77NJC77). 

Most of the liquid crystals discussed in this section bear a diaza[18]crown-6 40, a 4,4 -diaminodibenzo[18]crown-6 41, or a thia crown ether 42 in their center (Scheme 23). Substitution in 40 and 41 is conveniently feasible on the nitrogen atoms by formation of a Schiff base or an aza compound (in the case of 41) or by N-alkylation or -acylation (in the case of 41). O-Alkylation and -acylation of 42, which are difficult to obtain, open a path to thia crown centered liquid crystals. 

Goodby presented a series of substituted diaza crown ethers 51-53 (Scheme 29, Table 2) containing three aromatic rings on each attached arm and studied the effects of different central ring sizes (6-, 12- and 18-membered rings), different... 

Scheme 29 Diaza crown ethers 51-53 of different sizes and with different terminal substituents...

A study of the selectivity of lariat aza[15] crown-5 (3.133) and BiBLE (bi-brachial lariat ether) diaza[18] crown-6 derived ligands (3.134) containing variously substituted arene rings showed that the Ag+ complex stability decreased as a function of the electron-withdrawing ability of the substituents, R, as measured by the substituents Taft o° inductive constant (a parameter measuring the electron-withdrawing... 

Another significant deviation from known rules has been observed in the rather low affinity of K+ with the 1,10-diaza crown 18-C-6 with only AG=10 kJ/mol (in methanol). It has been shown that the free energy of binding AG in crown ether and ciyptand complexes usually is an additive function of number and electron donicity of the host donor atoms which are in contact with the metal ion.[17] Molecular mechanics calculations suggest the reduced affinity with the diazacrown to be due to the N-lone pairs in pseudoaxial position, pointing away from the metal ion (Figure 4). This has led to experiments with the N-methyl substituted crown here the N-alkyl substituents would clash which each other inside the macrocycle, therefore a pseudoequatorial lone pair orientation towards the cation is enforced, and the stability of the complex indeed returns to the normal scale with an increase to 29.5 kJ/mol.[ 18]... 

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

The only reported example of this type of behavior comes from the work of Bal-zani and Stoddart and their teams. It is based upon the threading/unthreading processes of a pseudorotaxane (see Chapters 7 and 8),[701 with concomitant fluorescence output changes. The constituent components of the pseudorotaxane are a naphtho-crown ether, 25, and a diazapyrenium dication, 26. On accommodation of the diaza-pyrenium thread, a nonfluorescent complex is formed, abolishing the fluorescent properties of the individual components. This corresponds to the first row of the truth table as no inputs are present and no fluorescence output is observed. The introduction of protons (in the form of CF3S03H) causes an unthreading of the... 

Reaction of [l,r-ferrocenediyl6/s(methylene)]bi s[pyridinium] salt with diaza-12-crown-4 afforded the ferrocene crown ether l,l r,r -6(. s(ferrocenediyl)b/s[4,10-Ws(methylene)-1,7-dioxa-4,10-diazacyclododecane [95IC3964],... 

Shinkai et al/73,74 have reported the construction of crowned arborols that incorporated diaza crown ethers as spacers, and three-directional, aromatic branching centers (Scheme 5.24). In this case, the convergent construction was found to be more effective than the divergent approach. Tetraoxadiazacrown monomer 93 was prepared from N-benzyloxycarbonyldiazacrown ether (94) and a monoacyl chloride 95, affording the diprotected intermediate 96, which was catalytically debenzylated (Pd/C, H2) to give diester 93 or hydrolyzed (aq.base) to afford diacid 97. Monomer 97 was then transformed to tetraester 98, by means of the mixed anhydride method, with two equivalents of the... 

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