Diazacrown ethers

Calcium-selective electrodes have long been in use for the estimation of calcium concentrations - early applications included their use in complexometric titrations, especially of calcium in the presence of magnesium (42). Subsequently they have found use in a variety of systems, particularly for determining stability constants. Examples include determinations for ligands such as chloride, nitrate, acetate, and malonate (mal) (43), several diazacrown ethers (44,45), and methyl aldofuranosides (46). Other applications have included the estimation of Ca2+ levels in blood plasma (47) and in human hair (where the results compared satisfactorily with those from neutron activation analysis) (48). Ion-selective electrodes based on carboxylic polyether ionophores are mentioned in Section IV.B below. Though calcium-selective electrodes are convenient they are not particularly sensitive, and have slow response times. 

PET-19 (Figure 10.16) consists of a diazacrown ether with two pendant pyrene groups. As expected, cation binding results in a large change in the monomer/... 

J. Bourson, J. Pouget, and B. Valeur, Ion-responsive fluorescent compounds. 4. Effect of cation binding on the photophysical properties of a coumarin linked to monoaza- and diazacrown ethers,... 

Akabori et al. employed an interesting tethering system by linking cinnamyl groups onto the amine of a diazacrown ether [22]. Since the... 

Alkali cations have also been involved in two interesting photophysical studies concerned with PET processes. In the first of these, sodium ion com-plexation to a diazacrown ether spacer between a PET donor-acceptor pair causes an acceleration of the electron transfer supporting a superexchange interaction [129]. The second case relies on sodium ion induced conformational changes in a calix[4]arene tetraester diagonally substituted with a PET donor-acceptor pair [130]. This results in a good fluorescent sensory action. 

Stability constants for complexes between Ln(CF3SC>3)3 and various diazacrown ethers and cryptates in... 

Molecular boxes , capable of binding a decanediyldiammonium or dodecanediyl-diammonium ion in their cavities, have been constructed from diazacrown ethers and pendant nucleotide bases. ° For example, structure 25 is based on hydrogen-bonded adenine-diazacrown-adenine and thymine-diazacrown-thiamine monomer units. The bis(ammonium) salt interacts with the oxygen atoms of two azacrown rings contained in each half of the cyclic 1 1 host-guest box . Characterisation of this product was largely performed using H-NMR spectroscopy and vapour... 

Mannich reaction of A, A -bis(methoxymethyl)diaza-18-crown-6 with 4-chloro-2-(l/f-pyrazol-3-yl)phenol gave the N-linked bis(3-(5-chloro-2-hydroxy)pyrazol-l-ylmethyl)-substituted diazacrown ether, which interacted with various metal ions and was evaluated by calorimetric titration <1999JOC8855>. Intramolecular nitrilimine cycloadditions were exploited in the preparation of a number of azacrown ethers having a medium or large ring annulated to pyrazole units <1997T3005>. 

The regioselectivity of analogous cycloadditions in 4-(alkenyloxy)-quinolin-2-(1H)-ones is determined by the chain length irradiation of quinolone (92 n=1), for example, gave the adduct (93), whereas the related quinolone (92 n=3) was converted photochemically into the adduct (94). Intramolecular [ 2 + 2] photocycloaddition has also been employed in the preparation of photoresponsive cyclobutane-1,2-dicarbonyl-capped[2.n]diazacrown ethers. 

Kise and coworkers found an efficient intramolecular hydrodimerization of aromatic diimines using a lead cathode providing 1,4-diazacrown ethers, as in Eq. (24) [186,187]. The stereoselectivity greatly depended on the ring size of the products and solvents used. 

In general, intermolecular [2 -I- 2] photocycloaddition of simple alkenes does not show satisfactory regioselective control. An approach to improve the reaction selectivity is use of a tether to constrain the reactive alkene functional groups proximate to each other and therefore allow the photocycloaddition to proceed. Tethers which have been employed include sugar alcohols such as d-maimitol and L-erythritol [101], diazacrown ethers [102], cyclophane [103], and silanes [104]. In all cases, the tether preorganized alkenes yield head-to-head adducts. The silane-tethered method can bind different alkene groups as well as alkynes, as shown in Scheme 27 [105]. Photoreactions of polyacetylenes and alkenes have also been investigated [106]. 

Gatto, V.J. Gokel. G.W. Syntheses of ealeium-selective, substituted diazacrown ethers A novel, one-step formation of bibracchial lariat ethers (BiBLES). J. Am. Chem. Soc. 1984, 106, 8240-8244. 

Figure 8 Di- and triazacrown ethers (a) diazacrown ether synthesis by a 2 + 2 reaction " (b) diazacrown ether synthesis via the diester (c) triazacrown ether synthesis via the diester.

Buschmann H-J, MutihacL, Jensen K, SchollmeyerE.Cucurbit[6]urilasligandforthe complexation of diamines, diazacrown ethers and cryptands in aqueous formic add solution. J Indus Phenom Macro Chem 2005 53 281. ... 

The diazacrown ethers LI428 and LI429 are obtained from the corresponding ligsons on an Na+ matrix in an analogous way (Eq, 6.50) [156]. 

Nitrogen-substituted diazacrown ethers derived from 15-crown-5, L1500-L1508, and from 18-crown-6, L1509-L1517, have been prepared according to Scheme 6-10 [174]. 

Sodium, potassium and caesium have been used as the metal cation templates for the preparation of the bis(2-hydroxyethyl)diazacrown ethers L1518-L1520 and the macrobicyclic polyethers L1521-L1532 [175, 176], following the transformations depicted in Scheme 6-11. 

---