Chromatography molecular recognition

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

Jinno, K., Molecular planarity recognition for polycychc aromatic hydrocarbons in liquid chromatography, in Jinno, K. (Ed.), Chromatographic Separations Based on Molecular Recognition, Wiley-VCH, Inc., New York, 1997, p. 65. 

Nakagawa, T., Shibukawa, A., Kaihara, A., Itamochi,T., Tananka, H. (1986) Liquid Chromatography with Crown Ether-containing Mobile Phases VI. Molecular Recognition of Amino Acids and Peptides. 

There are numerous variations on free solution CE (FSCE), such as micellar electrokinetic capillary chromatography (MECC or MEKC), where a moving, pseudostationary phase is added to the CE buffer, and secondary chemical equilibria or interactions ensue that effect separations of even neutral compounds, as well as ionic analytes. However, in general, CE utilizes truly homogeneous, solution phase separation approaches, without a stationary (permanent, fixed) phase, making it perhaps ideally suited for molecular recognition in searching combinatorial libraries. 

Lipkowitz, K.B.,Theoretical studies in molecular recognition enantioselectivity in chiral chromatography, /. Comput. Chem.l9S9, 10(5), 718-732. 

C. Jones, A. Patel, S. Griffin, J. Martin, et al, Current trends in molecular recognition and bioseparation. Journal of Chromatography A 707, 3 (1995). 

Keywords Molecular recognition Imprinting Polymer Chromatography Catalysis... 

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