Crown binding properties

A number of bridged crown ethers have been prepared. Although the Simmons-Park in-out bicyclic amines (see Sect. 1.3.3) are the prototype, Lehn s cryptands (see Chap. 8) are probably better known. Intermediates between the cryptands (which Pedersen referred to as lanterns ) and the simple monoazacrowns are monoazacrowns bridged by a single hydrocarbon strand. Pedersen reports the synthesis of such a structure (see 7, below) which he referred to as a clam compound for the obvious reason . Although Pedersen appears not to have explored the binding properties of his clam in any detail, he did attempt to complex Na and Cs ions. A 0.0001 molar solution of the clam compound is prepared in ethanol. The metal ions Na and Cs are added to the clam-ethanol solutions as salts. Ultraviolet spectra of these solutions indicate that a small amount of the Na is complexed by the clam compound but none of the Cs . 

Although the first all-sulfur macrocycles were prepared many years ago " the first systematic study of such compounds was initiated by Busch and his coworkers , who were interested in the cation binding properties of such ligands. A sequential synthesis was utilized to produce 1,4,8,11-tetrathiacyclotetradecane [tetrathia-14-crown-4 (70)] . In the first step, 1,3-propanedithiol is metallated using sodium and alkylated with 2-chloroethanol. The diol was then treated with thiourea to form the dimercapto-dithioether compound 9. The latter was once again metallated with sodium and allowed to react with 1,3-dibromopropane. The yield of 70 in the ring closure step, conducted at high dilution in absolute ethanol, was 7.5% after recrystallization. The entire sequence is illustrated in Eq. (6.8) . ... 

A good deal of work has been done on polymeric crown ethers during the last decade. Hogen Esch and Smid have been major contributors from the point of view of cation binding properties, and Blasius and coworkers have been especially interested in the cation selectivity of such species. Montanari and coworkers have developed a number of polymer-anchored crowns for use as phase transfer catalysts. Manecke and Storck have recently published a review titled Polymeric Catalysts , which may be useful to the reader in gaining additional perspective. 

Anionic units have not only been attached to macrocyclic polyethers via flexible arms but have also been incorporated into the cycle itself. Alberts and Cram (1976, 1977) have studied the ion-binding properties of crown ethers containing / -diketone units, such as [72] and [73]. 

The electrochemical properties of ferrocene have been utilized by many workers in the field of electrochemical molecular recognition. Saji (1986) showed that the previously synthesized (Biernat and Wilczewski, 1980) ferrocene crown ether molecule (Fig. 3 [1]), whose binding properties had previously been studied only by nmr and UV/Vis techniques (Akabori et al., 1983), could be used as an electrochemical sensor for alkali metal cations involving a combination of through-space and through-bond interactions. 

Cation-Binding Properties of Crown Ethers, Lariat Ethers, Bibracchial Lariat Ethers, and Poly(ethylene glycols) as Potential Phase-Transfer Catalysts... 

Cyclic dilactones can be prepared in high yields from the corresponding diadd chloride and diol, and have interesting cation binding properties (81JA1821). A useful method for their reduction to crown ethers using lithium aluminum hydride has recently been reported (82CC248). 

The selective cation binding properties ol crown ethers and cryptands have obvious commercial applications in the separation of metal ions and these have recently been reviewed (B-78MI52103.79MI52102, B-81MI52103). Many liquid-liquid extraction systems have been developed for alkali and alkaline earth metal separations. Since the hardness of the counterion is inversely proportional to the extraction coefficient, large, soft anions, such as picrate, are usually used. 

The enantioselective binding properties of certain chiral crown ethers have been employed in the resolution of amino add racemates. The racemic amino ester is adsorbed onto silica gel as its ammonium salt and eluted by a chloroform solution of the chiral crown ether. An excellent separation of the two enantiomers is achieved by this method (74JA7100). 

The question of carrier design was first addressed for the transport of inorganic cations. In fact, selective alkali cation transport was one of the initial objectives of our work on cryptates [1.26a, 6.4]. Natural acyclic and macrocyclic ligands (such as monensin, valinomycin, enniatin, nonactin, etc.) were found early on to act as selective ion carriers, ionophores and have been extensively studied, in particular in view of their antibiotic properties [1.21, 6.5]. The discovery of the cation binding properties of crown ethers and of cryptates led to active investigations of the ionophoretic properties of these synthetic compounds [2.3c, 6.1,6.2,6.4-6.13], The first step resides in the ability of these substances to lipophilize cations by complexation and to extract them into an organic or membrane phase [6.14, 6.15]. 

ArnaudNeu, F., Asfari, Z., Souley, B., Vicens, J., Binding properties of calix [4 ]-bis-crowns towards alkali cations. New J. 

Lariat ethers, which were designed to add dimensionality to the essentially flat crown ether, have been used as synthetic ionophores for decades. The binding properties of crown ethers are now well documented and generally well understood. Most such studies have been conducted with metal ions, although complexation of ammonium species and some neutral species (Gokel, 1973 Kyba, 1977) have also been reported. 

Synthesis, metal-binding properties and polypeptide solubilization of Crowned arbo-rols. [T. Nagasaki, O. Kimura, M. Ukon, S. Arimori, I. Hamachi, S. Shinkai, J. Chem. Soc., Perkin Trans. 1 1994, 75-81] [ 315],... 

The binding of an alkali metal cation to a crown ether is another reaction involving a supramolecular concept181-183. It allows a comparison of the binding property of a crown ether either in solution or when included in a hydrid xerogel. Therefore, with precursor... 

Recently, efforts have been initiated to examine intrinsic host-guest chemistry in the solvent-free environment of a mass spectrometer. Of present interest are preliminary reports on perfluorinated hosts, crown ethers and cryptands, which are physiologically compatible and may possess important biological properties, such as the ability to carry oxygen and transport ions through membranes. Specifically, the oxygen-binding properties of... 

Majerski, K.M. Kragol, G., Design, synthesis and cation-binding properties of novel adaman-tane and 2-oxaadamantane-containing crown ethers, Tetrahedron. 2001, 57, 449 157... 

New photoresponsive crown ethers incorporating an azobenzene moiety have been prepared. The binding properties of the crown ether (3) containing an intraannular 4-methoxyphenylazo substituent... 

More recently, an elegant access to a pentaoxa[5]peristylane 123 has been reported by Wu et al. (Scheme 22) [85]. The Diels-Alder reaction of 5-(bismeth-oxy)methylcyclopentadiene 119 and czs-enediones 120 furnished the anti-endo adduct 121. After cleavage of the dimethyl acetal moiety and ozonolysis of the double bond in 122, the pentaoxa[5]peristylanes 123 (R=Me, n-Bu, n-Oct) were obtained in high yields. Compounds 123 resemble an interesting novel type of crown ether, the cation binding properties of which are being studied [85]. 

---