Chiral Recognition of Propranolol with β-Cyclodextrin in the Presence of 1- and 2-Butanol

Synchronous spectrofluorimetric study of the supramolecular host-guest interaction of β-cyclodextrin with propranolol: A comparative study

The objective of this work is to assess the use of constant-wavelength synchronous fluorescence spectroscopy (SFS) in comparison to conventional fluorescence spectroscopy (CFS) for the investigation of the supramolecular host-guest interaction of β-CD with propranolol (PPL) in aqueous solutions. Scanning for the optimal Δλ at which the SFS can be performed in the presence of β-CD was examined. The results obtained revealed three distinguishable shapes for PPL using SFS that can be represented by three different Δλ values, namely 10, 40, and 100 nm. However, the effect of the β-CD concentration on the fluorescence intensity of PPL was examined using CFS and SFS of PPL at a Δλ of 10 and 100 nm. The change in the fluorescence intensity was used to calculate the equilibrium constant (Keq) for the formation of the β-CD:PPL inclusion complex by applying the Benesi-Hildebrand method. Keq values of 108, 112, and 117 M(-1) were obtained using SFS with a Δλ of 10 and 100 nm, and CFS, respectively. Further, the SFS method was successfully employed to examine the iodide quenching effect on the fluorescence intensity of PPL, where the results obtained revealed a Stern-Volmer quenching constant of 42.8 M(-1), which is in good agreement with results obtained using CFS. All results obtained using the SFS method were compared with the results obtained using the CFS method.

Amylose's recognition of chirality in polylactides on formation of inclusion complexes in vine-twining polymerization

Amylose selectively includes poly(L-lactide) (PLLA) among the poly(lactide)s (PLAs) to produce an inclusion complex when the phosphorylase-catalyzed polymerization of α-D-glucose 1-phosphate is performed in the presence of PLLA, poly(D-lactide) (PDLA), or poly(DL-lactide) (PDLLA) (vine-twining polymerization). This result indicates that amylose recognizes the chirality in PLAs on the formation of an inclusion complex in vine-twining polymerization. Modeling calculations support the amylose's chiral recognition in favor of PLLA and the atomistic details of the inclusion complex which involved the preferred orientation of the constituent molecular chains with respect to their fiber axis is proposed.

Thermodynamics of inclusion complexes of natural and modified cyclodextrins with propranolol in aqueous solution at 298K

The association constant, standard Gibbs energy, enthalpy and entropy for formation of inclusion complexes of propranolol, a beta-blocker, with various natural and modified cyclodextrins have been determined by calorimetry at 298 K. Both natural and methyl-modified alpha-cyclodextrins do not form complexes, while beta- and gamma-cyclodextrins do. Complexing ability of 2-hydroxypropyl-beta-cyclodextrin depends on the average substitution degree. For gamma-cyclodextrin, hydrophobic interactions play the major role in binding the guest. The association of natural and modified beta-cyclodextrins is ruled by van der Waals interactions and hydrogen bonding because of the tighter fit of the guest into the cavity. Decreasing pH determines increasingly negative values of the association enthalpies.

Use of fluorescence shift and fluorescence anisotropy to evaluate the re-binding of template to (S)-propranolol imprinted polymers

The binding of (R)- and (S)-propranolol to an (S)-propranolol imprinted polymer in organic and aqueous solutions has been studied using fluorescence. The amount of propranolol that binds can be measured by separating non-bound propranolol from the polymer by centrifugation, and measuring the fluorescence intensity. However, this work demonstrates that other measurements can indicate how much propranolol has bound without the need to separate bound and non-bound analyte. In toluene + 0.5% AcOH, and in aqueous buffer (25 mM citrate pH 6 + 0.5% Triton X100) the fluorescence anisotropy increases as the fraction of analyte bound to the polymer increases. In aqueous buffer, binding to the polymer is also accompanied by a change in the relative intensities of fluorescence at 322 nm and at 352 nm. These non-separation techniques have been used to show that the imprinted polymer binds more (S)-propranolol than a non-imprinted polymer, and at least in organic solvent, shows selectivity for (S)- over (R)-propranolol.