Abstract
Abstract Six palmitic acids labeled at different methylene positions by paramagnetic doxyl moiety were used as guests in order to examine molecular discrimination using γ-cyclodextrin (γ-CD). The DPA inclusion complexes using γ-CD in an aqueous solution were characterized according to stability, conformation, and dynamics at 25 °C, mainly based on ESR spectral analyses and supported by force-field calculations. The stability was equal among all DPA complexes, as represented by the formation constant Ks = 8.0(±0.5) × 102 M−1 (M = mol dm−3), corresponding to the conformation constant when the palmitate chain penetrates a CD cavity and the doxyl ring locates inside the cavity. Both overall molecular motion and chain segmental motion of DPA, represented by the parallel (Rzz) and perpendicular components (Rxx = Ryy) of the rotational diffusion tensor, respectively, were significantly restricted in inclusion state. The magnitude of restriction of segmental motion increased towards the chain terminals from the center, indicating that faster segmental motion was restricted at a higher rate. Thus, a series of DPAs were discriminated by γ-CD in terms of chain segmental motion but not in terms of stability, to present a typical example of dynamic molecular discrimination.
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