Complexation and Chiral Recognition Thermodynamics of 6-Amino-6-deoxy-β-cyclodextrin with Anionic, Cationic, and Neutral Chiral Guests:  Counterbalance between van der Waals and Coulombic Interactions

Abstract

The stability constant (K), standard free energy (Delta G degrees), enthalpy (Delta H degrees), and entropy changes (T Delta S degrees) for the complexation of 6-amino-6-deoxy-beta-cyclodextrin with more than 50 negatively or positively charged as well as neutral guests, including 22 enantiomer pairs, have been determined in aqueous phosphate buffer (pH 6.9) at 298.15 K by titration microcalorimetry. The thermodynamic parameters obtained in this study and the relevant data for native beta-cyclodextrin indicate that the complexation and chiral discrimination behavior of the cationic host with charged guests are governed by the critical counterbalance between the electrostatic interactions of the charged groups in host and guest and the conventional intracavity interactions of the hydrophobic moiety of guest, such as hydrophobic, van der Waals, solvation/desolvation, and hydrogen-bonding interactions.

A spectrofluorimetric study of binary fluorophore–cyclodextrin complexes used as chiral selectors

“…Chiral recognition ability is not dependent on the effect (stabilization or destabilization) of ternary agent addition, as can be seen from data relative to Py/b-CD/Phe and Py/ am-b-CD/Met at pHZ8.0. Differently from that previously reported by Inoue et al 24 who observed a loss of chiral recognition with the enhancement in complex stability. In our opinion, the disagreement comes from the difference in substrate-CD interaction and substrate-binary complex interaction.…”

Molecular Modeling of Enantio-discrimination of α-Methoxy-α-trifluoromethylphenylacetic Acid (MTPA) by Cyclomaltoheptaose (β-Cyclodextrin) and 6-Amino-6-deoxy-cyclomaltoheptaose

“…In other words, the NH 3 + Î CO 2 − interaction is the decisive factor in stabilizing the complex for complexation of the MTPA with β-CD. 9 They also indicated that enantio-discrimination power of am-β-CD was stronger than β-CD about 2.1 fold, which would be well correlated with the experimental data where am-β-CD had 1.9 fold more stable than β-CD in the free energy of chiral interaction. 9 It should be emphasized that the β-CD cavity exhibits consistent enantio-discrimination toward a series of structurally related guests 29 and that the amino substitution does not alter but rather enhances the original enantiodifferentiation obtained with native β-CD.…”

“…9 In fact, it has been reported that cationic mono-and diaminoCDs exhibit higher/lower affinities toward negatively/positively charged guests than the corresponding native CDs. 6,[10][11][12][13] In this study, the chiral recognition of α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) by neutral or charged CD (Chart 1) was investigated.…”

Molecular and supramolecular chirality: R2PI spectroscopy as a tool for the gas‐phase recognition of chiral systems of biological interest

“…These methods include classical and quantum numerical simulations. Classical molecular dynamic and Monte-Carlo Docking calculations, [52][53][54][55][56] based on standard force fields, have been used especially to investigate conformational issues. Quantum approaches have generally been employed to carry out ab initio calculations of more or less higher accuracy, depending on the size of the basis set.…”