Molecular Shape Recognition
through Self-Assembled
Molecular Ordering: Evaluation with Determining Architecture and Dynamics
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Abstract
The relationship between molecular gel-forming compound-based
double-alkylated l-glutamide-derived functional group-integrated
organic phase
(Sil-FIP) structure and chromatographic performance is investigated
and compared with widely used alkyl phases (C<sub>30</sub>, polymeric
and monomeric C<sub>18</sub>) as references. The functional group-integrated
molecular gel on silica is chemically designed newly in a way that
the weak interaction sites are integrated with high orientation and
high selectivity can be realized by multiple interactions with the
solutes. Its functions can be emphasized by being immobilizable with
a terminal carboxyl group and the fact that five amide bonds including
β-alanine subunit are integrated per molecule. Furthermore,
its self-assembling function can be detected by monitoring of the
chiroptical property. Temperature-dependent circular dichroism (CD)
intensity was determined as an indicator of chirality for the gel
forming compounds. <sup>13</sup>C cross-polarization magic angle spinning
(CP/MAS) NMR spectra of the Sil-FIP phase indicate that predominance
of gauche conformations exists at higher temperature (above 30 °C). <sup>29</sup>Si CP/MAS NMR were carried out to investigate the degree
of cross-linking of the silane and silane functionality of the modified
silica. Temperature-dependent <sup>13</sup>C CP/MAS NMR and suspended-state <sup>1</sup>H NMR measurements of the Sil-FIP phase exhibit the dynamic
behavior of the alkyl chains. To correlate the NMR and CD results
with temperature-dependent chromatographic studies, standard reference
materials (SRM 869b and SRM 1647e), column selectivity test mixture
for liquid chromatography was employed. Additional shape selectivity
text mixtures were also used to clarify the mechanism of shape selectivity
performance of Sil-FIP compared with commercially available columns.
The evaluation with the spectroscopic and chromatographic analyses
presents very important information on the surface morphology of the
new organic phase and the molecular recognition process. Integrated
and ordered functional groups were investigated to be the main driving
force for very high molecular shape selectivity of the Sil-FIP phase