Intra-group separations

There is also evidence that non-cyclic polyethers can function as synergists in lanthanide/actinide separation. Ensor and Shah (1983,1984) report that 1,13-bis(8-quinolyl)-l,4,7,10,13-pentaoxatridecane (Kryptofix-5, or K-5) enhances the extraction of Ce(III), Eu(III), Tm(III), Am(III), Cm(III), Bk(III) into chloroform solutions of TTA. The extracted complex has the stoichiometry R(TTA)3-K-5, and the synergistic enhancement is comparable to that of TBP under the conditions studied. Intra-group separation factors for lanthanides and actinides are approximately two while the usual synergistic leveling effect is observed for Am/Eu separation (i.e., they are worse than those for TT A alone). 

Both the (organic) diluent (in solvent extraction systems) and the composition of the aqueous solution can have a profound effect on extraction efficiency, group separation, and intra-group separation. An example of this effect has already been seen above in the reported enhancement of trivalent metal ion extraction by amines or neutral or-ganophosphorus extractants from nitrate salts versus nitric acid (a salting-out effect). 

Choppin et al. 1954, 1956, Smith and Hoffman 1956). This system proved useful for intra-group separation of both the lanthanides and actinides (table 9). There are numerous examples of more recent applications of both the specific system and adaptations of it in lanthanide and actinide processing (Elesin et al. 1986, Vobecky 1989, Billion 1979, Aly and Latimer 1970b, 1967, Guseva and Tikhomirova 1979). 

Of the separation methods discussed in this chapter, several are useful primarily for intra-group separations. Comparison of data from different authors is usually not... 

N-heterocyclic ligands have particularly complex behavior. In addition to coordinating to the metal, N-heterocycles can be protonated and act as counterions to anionic metal complexes. The polar, aromatic ring systems of these ligands can also give rise to a number of noncovalent interactions. As extractants, N-heterocycles such as bis(triazine) pincer ligands are an important class of extractants in actinide-lanthanide separations [57]. 1- and 2-methylimidazole have also been studied as extractants for lanthanides into ILs and show promise for intra-group separations [58]. 

Table 2 summarizes the numerical results on average intermolecular/interi-onic 0---0 and intramolecular/intra-ionic C-0 structural parameters for the [COOH]n---[COOH]n, [COOH]a---[COOH]a and [COOH]A---[COO]A inter-molecular interactions, together with those obtained for the [COOH] A- [COO ]A sample in the case of the hydrogen oxalate anion. Data were retrieved from the CSD with a cut-off distance on 0-"0 separations of 3.0 A. A visual prospect of the data listed in column III is provided in Fig. 6, where histograms of intramolecular C-0 distances within the protonated and deprotonated COOH/COO groups are presented. 

Taylor and colleagues [98] at the Mayo Clinic published a method for the simultaneous analysis of urinary cortisol and cortisone. They used 2H4 cortisol as an internal standard and took a 0.5-ml urine sample. An API 2000 with Turboion-spray source was used in the positive-ion mode. Chromatography was conducted on a standard-bore C18 column with Q8 precolumn filter. MRM was conducted in the positive-ion mode monitoring m/z 363—>121 for cortisol, 367—>121 for 2TL, cortisol, and 361— -121 for cortisone. Cortisol and cortisone were separated and both were eluted within 2 min. Inter- and intra-assay variation for both compounds was < 9% for amounts above 2 pig/dl. The values obtained agree well with those of other studies, such as ours (Table 5.3.2) [62]. They found a range for cortisol for adult males of 4.2-60 pg/24 h and for adult females 3.0-43 pg/24 h. In summary, the 3-min run time of their method has allowed the Mayo group to completely transfer their cortisol and cortisone workload from RIA and HPLC to MS/MS. 

The intramolecular photodimerization and [2 + 2]-photocycloaddition in DNA involves thymine or cytosine as the chromophore. This chemistry has been intensively investigated with regards to DNA damage and repair [131]. Despite the fact that the area is of continuous interest [132], the synthetic applications are limited and are not covered here in detail. However, some preparative aspects of 4-pyrimidinone photocycloaddition chemistry will be addressed. Aitken et al. have prepared a plethora of constrained cyclobutane P-amino acids by intra- or intermolecular [2 + 2]-photocycloaddition to uracil and its derivatives [133, 134]. In a chiral adaptation of this method, the uracil-derived enone 140 was employed to prepare the diastereomeric cyclobutanes 141 in very good yield (Scheme 6.49). The compounds are easily separated and were - despite the relatively low auxiliary-induced diastereoselectivity - well suited to prepare the as-2-aminocyclobutanecarboxylic acids 142 in enantiomerically pure form. Enantioselective access to the corresponding trans-products was feasible by epimerization in a-position to the carboxyl group [135],... 

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