Crown ethers pyridine-based

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

Pyridine-based crown ethers such as 3.107 have also been extensively studied. R,R 3.107 binds the R enantiomer of [a-(l-naphthyl) ethyl] ammonium some 12 kj mol-1 more strongly than the 5 enantiomer. The reason is evident from the stereoviews shown in Figure 3.74. The napthyl substituent on the R enantiomer avoids the bulky phenyl group of the receptor on the same face as the bound cation, while there is a steric clash in the 5enantiomer.49... 

The second method can be used to synthesize Vogtle-type podands [9,10] in two high-yielding steps from polyethylene glycol ditosylates. The ditosylate derivatives, which are also precursors of cyclic crown ethers, azacrown ethers and lariat ethers, can be prepared with pyridine as the base [11], However, they are synthesized more effectively in higher yields using aqueous sodium hydroxide and tetrahydrofuran (Figure 1.4) [12], These conditions also remove the necessity to... 

Calcium complexes amino acids, 33 arsine oxides, 9 bipyridyl, 13 crown ethers, 39 dimethylphthalate, 16 hydrates, 7, ionophores, 66 peptides, 33 phosphines, 9 pyridine oxide, 9 Schiff bases, 29 urea,9 Calixarenes... 

The most prominent cellulose ester produced on the industrial scale is cellulose acetate. The reaction is usually performed with acetic anhydride and with sulfuric acid as a catalyst. To minimize heterogeneities, acetylation is allowed to run nearly to completion, and subsequently partial ester hydrolysis is initiated by the addition of water until a desirable solubility is achieved that corresponds to a DS of about 2.5. Such higher acyl homologues as propanoyl or butanoyl exhibit more thermoplastic properties. Many specialized esters such as chiral (-)-menthyloxyacetates, furan-2-carboxylates, or crown-ether-containing acylates have been prepared on the laboratory scale and characterized by NMR spectroscopy. Various procedures have been applied, using anhydrides and acyl chlorides as acylating agents in combination with such bases as pyridine, 4-dimethylaminopyridine (DMAP), or iV,iV -carbonyldi-imidazole. The substitution pattern of cellulose acetates has also been modified by postchemical enzymatic deacetylation. Cellulose 6-tosylates have been used as activated intermediates for nucleophihc substitution to afford 6-amino-6-deoxy, 6-deoxy, or 6-deoxy-6-halo-celluloses. ... 

A variety of other chiral crown ethers were studied, although selectivities usually peaked at 10 1 or less. " Pyridine-based systems, typified by 9/ were subject to especially detailed investigations. The incorporation of phenolic units allows the crowns to bind amines, as opposed to ammonium ions, and may also be used to introduce a spectroscopic response to binding. For example, the calixarene-crown 10 acts as a colorimetric chiral sensor for amino alcohols, changing from red to blue on exposure to i -phenylglycinol 11 in ethanol (iCa=66 M ) but unresponsive to the enantiomeric substrate. ... 

The internal cavity of a cyclophane is endobasic if functional groups are present that are basic or electron donating the most obvious groups include the ethers, pyridines, amines, and phosphorus-based donors. Cyclophanes in this category would be expected to bind metal ions and also promote H-bonding interactions within the cavity. Hence, in this section, crown ethers and azamacrocycles could easily be included. Under this heading, we can also... 

In the optical sensors based on crown ethers, chromophores or tiuorophores are usually employed to generate output signals. For example, the chromophoric dinitrophenyla-zophenyl group was introduced to the crown ether, as shown in Figure 3(a). In the presence of Li+, the chloroform-pyridine solution produced a color change from... 

The selectivity of the formation of dimer [3,3]metacyclophanes lb and 8 versus trimer 18-membered macrocycles 2b and 9 which were perceived as crown ether analogues, was discussed by Vogtle in 1983 [6]. Both 1,3-bis(bromomethyl)benzene and 2,6-bis(bromomethyl)pyridine building blocks were used, with thioacetamide as the source of sulfur. Increasing the size of the counterion of the carbonate base raises the amount of trimers. Apparently, no higher oligomers were formed (Scheme 16.2). 

There is continuing interest in the synthesis and complexing properties of crown ethers " and cryptands " based on pyridine units. For example, cryptand (78) is an especially strong ligand for binding alkali-metal cations, and it forms stable crystalline complexes with lithium and sodium perchlorate. " Pyridino-phane cryptands, e.g. (79), also form stable Na" and complexes. ... 

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