Retention of the Structural Type

These evaluations suggest that Ceo and related fullerenes should be more reactive than benzene. However, it is difficult to directly compare the reactivities of these typical representatives of two- and three-dimensional aromatics. In contrast to benzene and other planar aromatics, the jt systems of the fullerenes have no boundaries. In other words, the fullerenes contain no hydrogens that can be replaced via substitution reactions. As a consequence, a chemical transformation of fullerenes is always accompanied with a change of the structure, whereas retention of the structural type is characteristic for reactions of benzene-like aromatics. Two main types of primaiy chemical transformations are possible addition reactions and redox reactions. 

The effect of the structure, type, and concentration of the polar mobile phase modifier (mpm) on retention (k ) and stereoselectivity (ot) has been studied by a number of investigators (28-30). In general, an increase in the steric bulk of the mpm results in an increase in the observed enantioselec-tivity. An example of these studies is the work reported by Zief et al. (28) in which the solute was 2-trifIuoro-l-(9-anthryl)ethanol and the mobile phases were composed of hexane and either ethanol, 2-propanol, or f-butanol as the mpm. Of the three alcohols tested, the use of t-butanol as... 

The effect of the structure, type, and ccarcentration of the polar mobile phase modifier (mpm) on retention (k ) and stereoselectivity ( ) has been studied (57,58). Wainer et al. (57) chromatographed a series of enantio-... 

By comparison, the direction of halogenation of monomethyl-substituted bicyclo[4.3.0] nona-3,7-dienes depends" considerably on the position of the methyl group. For a diene lacking a substituent at C(3), the reaction proceeds with retention of the initial structure (equation 83), whereas in the case of the 3-methyl substituted diene, it occurs through transannular cyclization giving a brexane type monoiodo derivative (equation 84). 

Proper protein folding is a concern in the production of a bioactive protein therapeutic, and it is of interest to verify that the conformation of a recombinant protein is the same as the wild-type molecule. Because retention in RPLC depends on the surface hydrophobic contact area, comparable chromatographic behavior of a recombinant protein with that of the wild-type molecule provides evidence of similar 3-D structure.17 38... 

The separation and identification of disaccharides is often an important step in the elucidation of the structure of a natural polysaccharide, and Percival484 has published useful data on the O-trimethyl-silyl derivatives of a variety of disaccharides and their reduction products. In some instances, the trimethylsilyl ethers of the disaccharide alditols have lower retention times than those of the disaccharide derivatives. The per-O-trimethylsilyl derivatives of gentiobi-itol and maltitol were encountered in studies on the structure of Pneumococcus Type II capsular polysaccharide.4843... 

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