Publications

Abstract A novel, straightforward, and environmentally friendly direct coupling procedure to immobilize carbohydrates on solid supports is presented. A characterization study showed that all amino groups on solid supports participated in the linkage with a carbohydrate unit, implicating that the surface load can be easily adjusted by tuning the amination coverage of the surface. Most importantly, the integrity of the cyclic conformation of the linked sugar unit was demonstrated, a feature that is critical for most of the possible applications of carbohydrate-functionalized surfaces. Furthermore, carbohydrate-immobilized submicron particles synthesized by the direct coupling method, on which lectin profiling experiments were conducted, validated the successfulness of our simplistic approach.

Abstract The multifunctional alkoxysilane precursor, 2,6-bis(propyl-trimethoxysilylurelene)pyridine (DPS) was designed and synthesized, envisaging a multiple hydrogen-bond interaction in the molecular imprinting of the drug aminoglutethimide (AGT). Imprinted xerogels were obtained in bulk and spherical formats. The spherical format was achieved by pore-filling onto spherical mesoporous silica, as a straightforward technique to generate the spherical format. The bulk gels presented better selectivity for the template against its glutarimide (GLU) analogue (selectivity factor: bulk 13.4; spherical 4.6), and good capacity (bulk 5521 mu mol/L; spherical 2679 mu mol/L) and imprinting factor parameters (bulk 11.3; spherical 1.4). On the other hand, the microspherical format exhibited better dynamic properties associated to chromatographic efficiency (theoretical plates: bulk 6.8; spherical 75) and mass transfer, due mainly to the existence of a mesoporous network, lacking in the bulk material. The performance of the imprinted xerogels was not as remarkable as that of their acrylic counterparts, previously described. Overall it was demonstrated that the use of designed new "breeds" of organo-alkoxysilanes may be a strategy to achieve satisfactory imprints by the sol-gel processes. DPS may in principle be applied even more effectively to other templates bearing better-matching spatially compatible acceptor-donor-acceptor arrays.

Abstract A different approach to the preparation of microspheric particles of molecularly imprinted xerogels (MIX) is presented here. The technique consisted of filling up the pores of spherical, mesoporous, bare silica particles with a pregelification mixture by applying pressure. Upon gelification and drying, thin layers of MIX were deposited on the mesopores. Spherical composites of S-naproxen (S-NAP) imprints were produced by following this simple strategy. The performance of the imprints was quite satisfactory in terms of recognition ability (ascertained by selectivity against ibuprofen, alpha = 4.9, and an imprinting factor of 13) whereas an outstanding improvement on dynamic features (expressed as column efficiency), as compared to the corresponding bulk format MIX (9 vs. 1.2 theoretical plates/cm), was reached.

Abstract Straightforward crushing and sieving bulk polymeric R-aminoglutethimide-imprinted materials were prepared by classical free radical polymerization, whereas nano thin walled grafted imprinted materials were prepared using RAFT mediated control polymerization technique. A stoichiometric non-covalent approach based on a triply hydrogen bonding functional monomer-template 1:1 complex (K = 599 mol(-1) L-1) led to chiral selectors far outperforming previously used selectors for resolving this racemate. The recognitive materials produced here (enantioselectivity factors, alpha similar to 10) also have no match within the previously reported enantioselective imprinted polymers (alpha 1.2-4.5). We here demonstrate a potentially generic solution to produce good quality grafted MIPs for templates interacting by hydrogen bonding alone, relying on solvent polarity tuning, significantly extending the range of templates compatible with this format.

Abstract Imidazolium-based monomers were, for the first time, employed in a comprehensive investigation of the molecular imprinting process of naproxen in both acrylic and sal-gel tridimensional networks. To this end, molecularly imprinted polymer (MIP) and xerogel (MIX) were both optimized for performance, by testing different porogen, template speciation and component ratios. The developed imprints were characterized for their pore properties (nitrogen adsorption analysis), site heterogeneity, binding properties and other performance parameters such as the imprinting factor, selectivity (HPLC column tests), column efficiency and mass transfer kinetics (frontal analysis study). MIP exhibited mesoporosity (D-p 29 nm), whereas MIX did not, which was reflected in both the lower number of accessible imprinted sites (4.9 mu mol/g versus 3.7 mu mol/g) and the slower binding/dissociation in MIX. The naproxen/ibuprofen selectivity ratio was estimated as 6.2 for the MIX and 2.5 for the MIP. Given the high importance of capacity and fast mass transfer in typical applications of imprinted materials, and the satisfactory selectivity of MIP, it can be concluded that the acrylic approach was globally the most advantageous. Still, the remarkably high selectivity of MIX and its reasonable capacity demonstrate that future work devoted to further optimization of both formats is worthwhile.

Abstract Macromolecules, such as polyethylene glycol (PEG), have been frequently used in the preparation of xerogels, mainly with the purpose of tuning the meso- or macroporosity. However, PEG has never been applied in the context of the preparation of molecularly imprinted xerogels for small molecules. Thus, we decided to conduct a computational and experimental study of the incorporation of PEG into formerly studied sol-gel mixtures for the preparation of damascenone-imprinted xerogels. Computationally, two types of pregelification models were studied, one representing the initial mixture (SI3/SIPA:S:3 models) and the other representing the same mixtures after considerable solvent loss (SI3/SIPA:40:1 models). The latter ones were particularly prolific in providing clear effects of the PEG. In the SI3:40:1 model (containing SI3 units of Si3O3(OH)(6) mimicking the final xerogels backbone), a prohibitive instead of a promoting effect of PEG on the template-SI3 association was observed. PEG was found to interpose the SI3 aggregates, turning them smaller and more disperse. In agreement with that, a much higher porosity and surface area were found for the corresponding xerogel prepared with PEG, while no appreciable improvement of the imprinting efficiency could be observed. In the SIPA:40:1 model (containing both SI3 and SIPA units; SIPA, Si3O3(OH)(5)C3H6NHC6H5, representing the introduction of the organic functional group into the xerogel network), the interactions related to the network structuring were not significantly affected. This was due to the fact that the SIPA units themselves had a dispersive effect on the silica network; the PEG molecules were "pushed" into the aqueous/methanolic continuum, and their presence was somewhat redundant. Accordingly, both prepared SIPA-xerogels (with PEG or not) exhibited higher porosity compared to SI3-xerogels. Although the simulation results were not conclusive about the effect of PEG on the template-functional group association, experimentally it was clear that the imprinting effect was not improved with PEG.

Abstract A series of molecular dynamics (MD) simulations of different pregelification mixtures representing intermediate stages of the sol gel process were set up to gain insight into the molecular imprinting process in xerogels, namely, to assess the template gel affinity and template self-aggregation. The physical plausibility of the parametrization was checked, confirming the reliability of the simulations. The simulated mixtures differed in the water/methanol ratio (1:3, 5:3, and 5:1) and in the absence/presence of an organic functional group (phenylaminopropyl-) in the silicate species. The simulation results, expressed mainly by the radial distribution functions and respective coordination numbers, showed that the affinity of the template molecule, damascenone (a hydrophobic species), for the gel backbone would not be attained without the tested functional group, phenylaminopropyl-. The affinity, related to the capability to trap the template within the gel network, was derived mostly from the hydrophobic interaction. It was also inferred from MD simulations that lower water contents (methanol-richer mixtures) would facilitate a better dispersion of both the functional group and the template within the final gel, therefore favoring the imprinting process. From the experimental counterparts of the simulated mixtures, a series of imprinted and nonimprinted xerogels were obtained. There was only one xerogel exhibiting the imprinting effect, namely, the one containing the organic group obtained at the lower water/methanol ratio (1:3), in agreement with predictions from the MD simulations. Such congruence demonstrates the ability of MD simulations to provide information regarding the fine aspects of molecular interactions in pregelification mixtures for imprinting.

Abstract The present manuscript reports the first application of molecular modelling to the design of molecularly imprinted polymers (MIPs) prepared by alkoxysilane sol-gel polymerization. The major goal was to determine the requisite level of theory for the selection of suitable alkoxysilane functional monomers. A comparative study, applied to the design of a MIP for beta-damascenone, involving different levels of theory, basis set superposition error (BSSE) correct ion and basis set augmentation and also semi-empirical methods, was performed. The computations results suggest that the use of the 3-21G basis set concomitantly with a method for BSSE correction represents a good compromise between theory level and computation time for the successful screening of functional monomers. Additionally, a few selected MIPs and their corresponding non-imprinted congeners (NIPs) were prepared and tested in the role of solid-phase extraction (SPE) sorbents. The confrontation of the computational results with the observed performance and morphological characteristics of the prepared MIPs suggest that besides the strength and type of interactions existing between template and functional monomers other concomitant features, related with the sol-gel process, must also be accounted for so that effective molecular imprinting is achieved in an alkoxysilane xerogel. Nevertheless, since an optimal ternplate-functional monomer interaction is a necessary condition for successful imprinting, the choice of the best monomers is still of the greatest importance and the proposed computational method may constitute an expeditious and reliable screening tool.