Experimental and Theoretical Study of the Adsorption Behavior and Mass Transfer Kinetics of Propranolol Enantiomers on Cellulase Protein as the Selector

Abstract

The thermodynamics and mass transfer kinetics of the retention of the R and S enantiomers of propranolol were investigated on a system comprising an acetic acid buffer solution as the mobile phase and the protein cellobiohydrolase I immobilized on silica as the stationary phase. The bi-Langmuir isotherm model fitted best to each set of single-component isotherm data. The monolayer capacity of the nonchiral type of adsorption sites was 22.9 mM. For the chiral type of sites, it was 0.24 mM for the R enantiomer and 0.64 mM for the S enantiomer. Peak tailing was observed, even at very low concentrations allowing operation of the low-capacity chiral sites under linear conditions. This tailing can be explained on the basis of heterogeneous mass transfer kinetics. At higher concentrations, which are often used in analytical applications, the isotherms on the chiral sites no longer have a linear behavior, and peak tailing is consequently more pronounced. Under those conditions, peak tailing originates from the combined effect of heterogeneous thermodynamics and heterogeneous mass transfer kinetics. These complex phenomena are explained and modeled using the transport-dispersive model with a solid film linear driving force model modified to account for heterogeneous mass transfer kinetics. The rate coefficient of the mass transfer kinetics was found to be concentration dependent.

Peer Reviewed: Nonlinear Effects in LC and Chiral LC

“…Black, 278 K; green, 288 K; red, 298 K; blue, 308 K; and yellow, 318 K. Adapted from Ref. 22. slower on the enantioselective type II sites than on type I sites (11). This agrees with the qualitative observation of very broad and tailing peaks, especially for the most retained enantiomer.…”

“…Also, the calculation program (assuming fast mass transfer) gave band profiles in poor agreement with the experimental bands, in spite of the excellent agreement on the modeling of the experimental isotherms. Experimental band profiles were then compared with profiles calculated using a program implementing the simple kinetic model previously described to account for slow mass transfer kinetics, with two assumptions-a single rate constant and a rate constant for each type of site (11). The latter gave by far the best fits.…”

A closer study of chiral retention mechanisms

“…Because of the high interaction energy and of the severe steric requirements, mass transfer on type-II sites tend to be slower than on type-I sites. 24 We must also keep in mind that, in the case of proteinbonded silica, several kinds of type-II sites may coexist on the surface. It could happen, in some cases, that the two enantiomers interact differently with these different kinds of sites or even that one enantiomer interacts with one kind of site, not with another.…”

“…29 Using this procedure, we studied the separation of several pairs of enantiomers: N-benzoyl derivatives of several amino acids and methyl mandelate on immobilized BSA, 6,30,31 ketoprofen and methyl mandelate on an immobilized cellulose derivative; 7,32 Tröger's base on microcrystalline cellulose triacetate; [33][34][35][36] and propranolol on cellobiohydrolase I (CBH I), a protein bonded to silica. 9,24 Only in the case of Tröger's base was it not possible to resolve the two contributions, because the more retained S-isomer has an S-shaped isotherm while the R-isomer follows Langmuir adsorption behavior. 35 In all the other cases, the equilibrium isotherm data fit well the bilangmuir isotherm model.…”

“…Note that the reliability of the isotherm is verified by the excellent agreement between measured and calculated band profiles. [7][8][9]24,26,[30][31][32][33][34][35][36] The two Langmuir contributions correspond, respectively, to the enantioselective and the nonselective interactions. If the data are fitted to the set of Eqs.…”