Characterization of the Imprint Effect and the Influence of Imprinting Conditions on Affinity, Capacity, and Heterogeneity in Molecularly Imprinted Polymers Using the Freundlich Isotherm-Affinity Distribution Analysis

Abstract

Molecularly imprinted polymers (MIPs) have been used in a wide range of analytical applications in particular in chromatography and sensing. However, the binding properties in MIPs are typically measured only in a narrow concentration range, which corresponds to only a subset of the sites in MIPs. This limited analytical window and binding site heterogeneity of MIPs leads to inaccuracies and inconsistencies in the estimation of their binding properties. This has hampered the characterization and optimization of MIPs for analytical applications. In this study, the origins of the molecular imprinting effect were studied using the newly developed Freundlich isotherm-affinity distribution (FIAD) analysis. The analysis is able to readily calculate an affinity distribution for MIPs from the limited analytical window. The FIAD analysis also yields an estimate of number, affinity, and heterogeneity for this subset of binding sites. Consistent with previous studies, MIPs were found to have higher capacities than the corresponding nonimprinted polymers (NIPs). Interestingly, MIPs were also found to be more heterogeneous than NIPs. Examination of variables in the imprinting process including temperature, template concentration, and cross-linking percentages further confirmed these trends. Based on these observations, a model for the imprinting effect was developed. The larger population of high-affinity sites in MIPs appears to arise from a broadening of the heterogeneous distribution. This suggests that noncovalent MIPs may be ill-suited for chromatographic applications and other applications that are detrimentally affected by binding site heterogeneity and better suited to applications that are less affected by heterogeneity such as sensing.

Tailor-made molecularly imprinted polymers for dimethoate and deltamethrin recognition: synthesis, characterization and chromatographic evaluation

“…In order to evaluate the nature of the binding sites and cognizant of the fact that under non-covalent imprinting conditions, the resulting MIPs contain a heterogeneous mixture of cavities of varying affinity for the guest molecules, we have estimated the sorption capacity and equilibrium isotherm for the MIPs in this study, using Freundlich's isotherm (Eq. 1) as it is an empirical power function for non-ideal sorption on heterogeneous surfaces [4,[39][40][41]. where B is the amount of template bound to the polymer, C is the amount of free template in solution after equilibrium, a is a Freundlich adsorption coefficient related with the binding affinity and m is a Freundlich constant which represents the heterogeneity index and varies from 0 to 1 (values approaching 0 indicate increasingly heterogeneity and 1 is homogeneous).…”

Synthesis and binding site characteristics of 2,4,6-trichlorophenol-imprinted polymers

“…The broad applicability of MAA as a functional monomer is related to the fact that the carboxylic acid group serves well as a hydrogen bond and proton donor as well as a hydrogen bond acceptor. In aprotic solvents such as acetonitrile and chloroform, ethyl adenine-9-acetate and N-Z-L-Glu MIPs were prepared successively with MAA as functional monomer [1,30]. Often, a large excess of MAA in the synthesis step is required for recognition to be observed and then only in solvents of low to medium polarity and hydrogen bond capacity [31].…”

“…This is accomplished by synthesizing a network polymer in the presence of a template molecule. Removal of the template from the polymeric matrix leaves cavities of complementary size, shape, and chemical functionality to the template [1,2]. MIPs offer some advantages, for example, they are stable to a wide range of pressures, organic solvents, and pHs.…”

A Kinetic Consideration on the Selective Adsorption and Molecular Recognition by Molecularly Imprinted Polymer

“…It is also actually rough to deem the rate constant as a fixed-value in the presence of inter-or intra-molecular interactions. 16,17 Regarding the complexity of MIP adsorption, it appears to be necessary to discuss the mechanism with kinetic opinion since it can present not only the general information in dynamic process but also insight into the probable essence of these interactions. In literature, as noted, some endeavors have been tentatively made on this topic.…”