Crown Ethers and Their Derivatives

The formation of host-guest complexes between crown ethers and organic ammonium cations and the high solubility and functionality of crown ethers in organic solvents enable the synthesis of molecular machines such as molecular elevators and molecular shuttles. Complexation of metal cations into the cavity of crown ethers contributes to the solubilization of metal cations in organic solvents and enhances the reactivity of 

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It should be noted that selective carrier facilitated transport experiments involving the crown ethers and their derivatives have not been... 

The transport of alkali and alkaline earth metal cations by many crown ethers and their derivatives has been extensively studied. Much effort has been paid to increase their selectivity as well as their efficiency. Making highly Li selective ionophores is a primary concern in this field, because large quantities of lithium could be extracted from sea water for use to nuclear fusion generators... 

Attachment of crown ethers and their derivatives to silica gel via a hydrocarbon-type linkage was applied for selective and quantitative removal of cations from aqueous solutions. The modified phases were found to be of potential value in preconcentration of nanogram per milliliter levels of some cations. In addition, these phases were operated without loss of the macrocycle and maintained the same selectivity toward metal ions in aqueous solution by the particular macrocycle in the free state. ... 

Crown ethers and their derivatives also display a cooperative, multisite binding of molecular cations as well as metal ions. Here, H-bonding and electrostatic interactions play a role. The number of H bonds will also influence the affinities, as evidenced in the simple ammonium series, with NH4+ about equal to CH3NH3+ (log T =4.27 and 4.25,... 

Moreover, supra-molecular systems involving crown ethers, fullerene and k-extended systems have been achieved that can mimic the photosynthetic process [9-14]. The fullerene Qo has been used successfully as an electron acceptor in the construction of model photosynthetic systems [9], the r-extended systems, such as porphyrins [12], phthalocyanines [13], r-extended tetrathiafulvalene (w -exTTF) derivatives [9,10], which are utilized as electron donors, while the crown ethers act as a bridge between the electron donor and acceptor. In the absorption spectrum of the complexes, the absorption maxima are associated experimentally and theoretically with the formation of charge-transfer states [14-16]. Consequently, these supramolecular systems have potential for applications in photonic, photocatalytic, and molecular optoelectronic gates and devices [9-14]. As a result, the study of the conformations and the complexation behavior of crown ethers and their derivatives are motivated both by scientific curiosity regarding the specificity of their binding and by potential technological applications. 

Crown ethers and their derivatives have gained attention for their ability to form stable complexes with metal ions. The selective complexing properties of crown ethers towards metal ions have led recently to their incorporation into polymeric matrices. There are three main methods of crown ethers incorporation into polymer matrices. The first method is direct polymerization of the crown ether in a step-growth process, the second one is the polymerization through a chain-growth process, and the third one is post-functionalization of pre-formed polymers. 

Although some scattered examples of binding of alkali cations (AC) were known (see [2.13,2.14]) and earlier observations had suggested that polyethers interact with them [2.15], the coordination chemistry of alkali cations developed only in the last 30 years with the discovery of several types of more or less powerful and selective cyclic or acyclic ligands. Three main classes may be distinguished 1) natural macrocycles displaying antibiotic properties such as valinomycin or the enniatins [1.21-1.23] 2) synthetic macrocyclic polyethers, the crown ethers, and their numerous derivatives [1.24,1.25, 2.16, A.l, A.13, A.21], followed by the spherands [2.9, 2.10] 3) synthetic macropolycyclic ligands, the cryptands [1.26, 1.27, 2.17, A.l, A.13], followed by other types such as the cryptospherands [2.9, 2.10]. 

S. Jarosz and A. Listkowski, Sugar derived crown ethers and their analogues Synthesis and properties, Curr. Org. Chem., 10 (2006) 643-662. 

Incidentally, C. J. Pedersen s first report on crown ethers and their complexes was published in the same year as the mechanism of the biological activity of valinomycin was clarified [2], Crown ethers are cyclic derivatives of polyethylene glycol of varying ring size, an example of which is also depicted in Figure 2.2.1. The structural relationship with the ionophores is clearly visible. It is thus not surprising that crown ethers also bind metal cations by coordination with the oxygen atoms [1, 3]. 

The literature on crown ethers and their complexes is vast, with approximately 5000 papers citing the term as a key word, and the best introduction to their chemistry is through review articles and books [4-7]. Suffice to say that applications run the range from simple cation detection by piezoelectric sensors [8] to the detection of metals in blood [9] and the more complicated problems of neurotransmitter [10] and biologically relevant sugar derivatives [11]. 

Interestingly the highest selectivity toward Li cations among paracrowno-phanes is obtained by 34c (s. Scheme 1) with five ethereal oxygen atoms, whose structure differs from the so-called lithiophilic crown compounds with four ethereal oxygen atoms such as 12-crown-4 (37), 14-crown-4, and their derivatives (38) (Structure 20). These results clearly suggest that the combination of number of oxyethylene units and the shape of the ether cavity leads to this suitable Li" selective ionophore. 

Another type of phase-transfer catalysts is synthetic macro-cyclic polyethers, so-called cro m ethers, and poly(ethylene glycol) derivatives. Since the discovery of crown ethers and their complex-ing capabilities toward metal and ammonium ions in 1967 by Pedersen, crown ethers and modified compounds such as cryptates > have been attracting ever increasing interest among scientists having different applications in their mind. Complexes formed between these compounds and cations correspond to Q" " shown in Fig. 1 and possess phase-thransfer capacity for anions. The nature of cations is known to greatly influence the complexation with a given crown either or cryptate. ... 

M -Dialkyldiazacrown ethers and their precursors fcis(alkylamino) derivatives of tri- and tetraethylene glycols were prepared <96CCCC622>. New hydroxy-bearing dibenzo-azocrown ethers have been conveniently prepared utilizing l,3-Ws(2-formylphenoxy)-2-propanol and a diamine, followed by reduction of the intermediate diimine <96P1197>. Fluorescent photoinduced electron transfer sensor 5 with monoaza-18-crown-6 and guanidinium receptor units demonstrated a fluorescence with T -aminobutyric acid in a mixed... 

Various types of research are carried out on ITIESs nowadays. These studies are modeled on electrochemical techniques, theories, and systems. Studies of ion transfer across ITIESs are especially interesting and important because these are the only studies on ITIESs. Many complex ion transfers assisted by some chemical reactions have been studied, to say nothing of single ion transfers. In the world of nature, many types of ion transfer play important roles such as selective ion transfer through biological membranes. Therefore, there are quite a few studies that get ideas from those systems, while many interests from analytical applications motivate those too. Since the ion transfer at an ITIES is closely related with the fields of solvent extraction and ion-selective electrodes, these studies mainly deal with facilitated ion transfer by various kinds of ionophores. Since crown ethers as ionophores show interesting selectivity, a lot of derivatives are synthesized and their selectivities are evaluated in solvent extraction, ion-selective systems, etc. Of course electrochemical studies on ITIESs are also suitable for the systems of ion transfer facilitated by crown ethers and have thrown new light on the mechanisms of selectivity exhibited by crown ethers. 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

The chemistry of a-haloketones, a-haloaldehydes and a-haloimines Nitrones, nitronates and nitroxides Crown ethers and analogs Cyclopropane derived reactive intermediates Synthesis of carboxylic acids, esters and their derivatives The silicon-heteroatom bond Syntheses of lactones and lactams The syntheses of sulphones, sulphoxides and cyclic sulphides... 

In this study, we report synthesis of a new thiourea derivative (2) which contain crown ether and phenanthroline ring by the reaction of 5-amino-1,10-phenanthro-line with 15-isothiocyanatobenzo[15-crown-5] (1) (Fig. 43.1) and its complex with Cu(I) is obtained. The structures of the ligand and the complex were determined by their elemental analysis, UV-vis, FTIR, H NMR (DMSO-d ), C NMR (DMSO-dg) and Mass spectra (LC-MS). 

Crown ethers and cryptands show much of the same functional group chemistry as simple ether- or amine-containing molecules. The remarkable reactivity of these macropolycyclic species is primarily derived not from the composition of functional groups but from their three-dimensional arrangement. The important property of strong cation complexation is determined by the topology of the cavity defined by the ether and amine groups in the molecular superstructure. 

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