Calixarenes amides

It was shown that narrow-rim CMPO derivatives form stronger 1 1 lanthanide complexes than their wide-rim counterparts. However, lanthanide extraction results display a stronger extracting ability. This discrepancy can be explained by the fact that, contrary to the wide-rim CMPO calixarenes that form polymeric species, a part of less lipophilic monomeric narrow-rim CMPO calixarene piles up at the interface instead of being extracted, as predicted by Wipff for the extraction of strontium by mixed amide calixarenes (see Section 4.4.1.1). This assumption is all the more... 

Chang and coworkers [10] have synthesized amide derivatives of calixarenes and examined their ion binding properties with Group I and Group II cations. They observed that although the amides are much less effective than the esters for the complexation of Group I cations they are more effective for Group II cations. 

Kimura and coworkers [17], Diamond [18], and Damien et al. [19] have described that the polymeric calix-[4]arenes have been used as ionophores in ion selective electrodes for Na (based on calixarene esters and amides) and for Na and Cs (based on p-alkylcalixarene acetates). The electrodes are stated to function as poten-tiometric sensors as well, having good selectivity for primary ion, virtually no response to divalent cations, and being stable over a wide pH range. 

Polymer supported xanthene derivatives have been used in the solid phase synthesis of 1-aminophosphinic acids, RCH(NH2)PH(0)0H, <%TL1647> and of C-terminal peptide amides <96JOC6326>. Xanthene units also feature in crown ethers <96JCS(P2)2091>, calixarenes <96JOC5670> and in a flexible template for a P-sheet nucleator <96JOC7408>. 

Some other cinchona alkaloid derivatives that have been synthesized and were evaluated as chiral selectors for liquid chromatographic enantiomer separation comprise CSPs based on cinchonan hydrazides [68], cinchonan ureas [42], cin-chonan amides [42], and urea-linked cinchonan-calixarene hybrid selectors [42]... 

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

Increasing the size of calixarenes favors the extraction of strontium and leads to a decrease of sodium extraction. For p-t-butyl calix[5]arene pcnta(di-/V-pcntyl)amide (CA3) (10-2 M in NPOE), DNa = 0.79, DSl = 1.5. For p-t-butyl calix[6]arene hexa (di-A-ethyl)amide (CA4) (5 x 10 3 M in NPOE), DNa = 0.05, DSl=3.8. Under the same conditions (HN031 M), this compound displays higher selectivity than DC18C6. 

Cavitands, prepared by the Twente group, differ from the wide-rim CMPO calixarene not only by the basic scaffold, but also by the distance to the rim and in the amido function (tertiary amide versus secondary amide). In comparison to CMPO calixarenes, compounds Cvl and Cv2 did not lead to improvements in terms of extracting ability or selectivity.17169... 

Under the same conditions, in contrast to what is observed for calix[4]arene-bearing CMPO moieties, with CPil2, distribution ratios of lanthanides increase from the lightest lanthanide, lanthanum, to europium. Americium can be easily separated from the lightest lanthanides (separation factor DAm/La > 20, DAm/Ce =15, /lAlll,Nd = 10, UAi /si = 7.5, DAm/Eu = 6), which are the most abundant lanthanides in fission-product solution. Cavitands bearing picolinamide (Cv5) or thiopicolin-amide (Cv6) residues seems much less selective than their calixarene counterparts, giving SAm/Eu < 2.18... 

Extraction by Wide-Rim Calixarenes Bearing Amide Residues... 

This review groups the information published on degradation of the main families of extractants studied in the frame of long-lived minor-actinide and fission-product recovery (1-4) (see Chapter 1) alkyl-phosphorus compounds (phosphates, phosphonic acids, bifunctional compounds like CMPO), amide compounds (dialkyl-amides, malonamides, and diglycolamides), N-donor compounds, and macrocycles like crown ethers and calixarenes (Table 8.1). The multicomponent systems based on the chlorinated cobalt dicarbollide process have not been considered. 

The extractant s stability can be improved if the selected diluent has a lower ionization potential than the extractant, like aromatic compounds (183). This protective effect has been observed for numerous extractants alkyl phosphates, alkyl phosphonates, amides, and calixarenes (25, 39, 68, 84,... 

Recently the separation of enantiomers by RIfS and SPR using calixarenes with chiral amide residues was demonstrated [19]. Chirasil-Calix (Fig. 7) is well known from capillary GC as a stationary-phase material because of its good thermal and long-term stability. The separation of amino acid derivatives and lactic esters was widely studied [23]. 

As with cation binding hosts, it is also possible to use calixarene frameworks (Section 3.14) to organise anion binding moieties. Addition of a cobaltocinium bis(amide) moiety to the upper rim of a calix[4]arene with p-toluenesulfonate functionalities to enhance solubility results in a rigid host 4.64... 

Crystallographic analysis of the 3 C1 complex (Fig. 3a,b) verified the proposed structure where chloride anion is held almost symmetrically by the amidic functions (Cl...HN=2.45 and 2.52 A). It is also evident that there are several close contacts with the aromatic hydrogens of calixarene (ArH...Cl= 3.05, 3.15 A) and metallocene (CH...C1=2.75, 2.95 A) moieties. As the whole structure creates a dimeric form of head-to-tail type, the chloride anion is held by additional HBs of the metallocene unit from the second molecule (CH... Cl= 2.77,2.93 A). 

Contrary to derivative 3, calixarene 5 was found to create a 1 2 complex with chloride anion in the solid state. Both amidic functions introduced into the upper rim of calixarene operated independently of each other and held one chloride anion with a Cl... HN distance of approx. 2.37 A and two CH... Cl con-... 

Another interesting and potentially very useful group of calixarene-based anion receptors is represented by systems with appended transition metal complexes of 2,2-bipyridine units. Technically, these systems utilise classical hydrogen bonding interactions of amidic/urea functions hence, from this point of view, they do not differ from many other receptors. On the other hand, the covalent attachment of bipyridine complexes of ruthenium(II) or rhe-... 

This type of receptor is represented by compounds 16a,b bearing ruthenium ) bipyridine moieties. Both calixarenes [18] exhibit 1 1 binding of chloride and bromide anions (DMSO-d6), and they are especially suitable for the complexation of H2POj (X16a=2.8-104 M-1 K16b=5.2 103 M"1). On the other hand, if we compare these results with those for similar non-calixarene receptors, where the bipyridine unit is substituted by alkyl, aryl or ethylene glycol substituents, the introduction of calixarene does not bring any substantially new features into the complexation abilities of these derivatives. As shown by X-ray analysis, the anion is encapsulated within the cavity formed by amidic functions with the contributions of CH...anion interactions from the bipyridine unit. 

To compare the complexation ability of amide versus urea groups, the calixarenes 29e and 29d bearing two functions on the upper rim were prepared [45]. 

Fig. 40. Ternary complex with an amide-acid calixarene and dbm (Hebbink et al., 2001a).

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