Interplay between Hydrogen-Bond Formation and Multicenter pi-Electron Delocalization: Intramolecular Hydrogen Bonds

The specific case of intramolecular hydrogen bonds assisted by π-electron delocalization is thoroughly investigated using multicenter delocalization analysis. The effect of the π-electron delocalization on the intramolecular hydrogen-bond strength is determined by means of the relative molecular energies of “open” and “closed” structures, calculated at the B3LYP/6-311++G(d,p) level of theory. These relative energies are compared to variations in the multicenter electron delocalization indices and covalent hydrogen-bond indices, which are shown to correlate very well with the relative strength of the intramolecular hydrogen bonds studied. The multicenter electron delocalization indices and covalent bond indices have been computed using the quantum theory of atoms in molecules approach. The hydrogen bonds are formed with oxygen, nitrogen, or sulfur as acceptor atom, which are also the atoms considered to be bonded to the donor hydrogen. Malonaldehyde is taken as reference; the substitution of oxygen by other atoms at the acceptor and donor positions and the effect of the aromaticity have been studied. The results shown here match perfectly with the qualitative expectations derived from the resonance models. In addition, they provide a quantitative picture of the role played by the π-electron delocalization on the relative strength of intramolecular hydrogen bonds

Interplay between hydrogen bond formation and multicenter pi-electron delocalization: Intermolecular hydrogen bonds

The interplay between aromatic electron delocalization and intermolecular hydrogen bonding is thoroughly investigated using multicenter delocalization analysis. The effect on the hydrogen bond strength of aromatic electron delocalization within the acceptor and donor molecules is determined by means of the interaction energies between monomers, calculated at the B3LYP/6-311++G(d,p) level of theory. This magnitude is compared to variations of multicenter electron delocalization indices and covalent hydrogen bond indices, which are shown to correlate perfectly with the relative values of the interaction energies for the different complexes studied. The multicenter electron delocalization indices and covalent bond indices have been computed using the quantum theory of atoms in molecules approach. All the hydrogen bonds are formed with oxygen as the acceptor atom; however, the atom bonded to the donor hydrogen has been either oxygen or nitrogen. The water-water complex is taken as reference, where the donor and acceptor molecular environments are modified by substituting the hydrogens and the hydroxyl group by phenol, furan, and pyrrole aromatic rings. The results here shown match perfectly with the qualitative expectations derived from the resonance model

MIP loaded porous scaffolds for multi-mycotoxin analysis

Mycotoxins are important and naturally occurring contaminants in food and feed. These secondary metabolites produced by various fungal species are only present in very low concentrations (ppb-ppt range). However, they can cause toxic effects in humans and animals, and the economic consequences of contaminations should not be underestimated. Reducing the mycotoxin contamination risk by controlling through rapid, sensitive and accurate analysis is highly needed. Mycotoxin analysis includes rapid screening and confirmatory methods. In the past ten years, interest moved towards a multi-analyte approach. Therefore, selective recognition elements that bind with different target analytes are required. Antibodies represent the most commonly used recognition elements in mycotoxin analysis, but alternatives such as molecularly imprinted polymers (MIP) are being developed since antibodies suffer from some disadvantages. The aim of this research is to use MIP as alternative recognition elements for multi-mycotoxin analysis. MIP of different sizes (nm-µm) against ergot alkaloids were produced by using precipitation polymerization. In addition, the BioplotterTM technology was used to produce poly-e-caprolactone (PCL) scaffolds which are characterized by micrometer sized interconnective pores. MIP particles with sizes in the nanometer range will be immobilized into those scaffolds by means of Pluronic® F127 bismethacrylate (Pluronic® F127-BMA) hydrogel building blocks. In this way, MIP for different mycotoxins can finally be combined to develop multi-mycotoxin screening tests and new sample preparation methods by using solid phase extraction (SPE) columns. Very interestingly, the proposed strategy may result in more efficient multi-mycotoxin analysis

Development and Characterization of artificial receptors for boar taint by means of molecular imprinting

Boar taint is an off-odour resulting from the accumulation of androstenone (AEON), skatole (SK), and indole (IND) in adipose tissue of intact male porcines [1]. Since boar taint causes negative consumer reactions, it is crucial to prevent tainted pig carcasses to reach consumers. To this end, rapid screening methods are required in which molecularly imprinted polymers (MIPs) can serve as artificial recognition elements. In this study, different MIPs for AEON and SK were synthesized through precipitation polymerization. Afterwards, all MIPs were characterized by batch rebinding studies through binding isotherms and scatchard analysis. Synthesis of MIPs was executed using 3 functional monomers, 3 cross-linkers, 3 porogen solvents, and 2 initiators. The polymerization reaction was initiated thermally or by UV-radiation and the reaction time varied from 8 to 48 hours. Most of the MIPs showed a low specificity with mean imprinting factors (IF) ranging from 1.10 to 1.99 and 1.13 to 1.69 for AEON and SK, respectively. This low affinity could also be derived from the dissociation constants (Kd) and maximum binding sites (Bmax) of the MIPs with Kd values ranging from 48 to 319 µmol l-1 and 38 to 547 µmol l-1 and Bmax values ranging from 3.38 to 20.89 µmol g-1 and 1.59 to 10.89 µmol g-1 for AEON and SK, respectively. Despite the low specificity due to low functionality and small size of the templates, for SK two MIPs with a higher specificity could be synthesized with IF values of 2.64 and 5.61 for MIP S1 and MIP S9, respectively. MIP S1 was associated with a Bmax value of 2.73 µmol g-1 and Kd of 30 µmol l-1. MIP S9 presented a Bmax of 2.27 µmol g-1 and Kd of 15 µmol l-1. For AEON, a slightly higher specificity and affinity were observed for MIP A6, which was associated with an IF of 1.99, Kd of 1.85 µmol l-1 and Bmax of 23 µmol g-1. Because of the small size and limited functionality of SK and AEON, most MIPs presented too low specificity and affinity, which compromises their ability to serve as highly specific recognition elements in sensor technology. For this reason, future perspectives include increasing specificity and selectivity by applying a fingerprinting approach and controlling the imprinting process by surface grafting or colloidal crystal templating

Bioimprinting for multiplex luminescent detection of deoxynivalenol and zearalenone

A sensitive tool for simultaneous quantitative determination of two analytes in a single spot with the use of a bioimprinted protein is presented for the first time. BSA is chosen as a scaffold for generation of binding sites specific towards two compounds. A multiplex immunosorbent assay for screening of two cereal-born mycotoxins, deoxynivalenol and zearalenone, in wheat and maize is realized with the use of fluorescent silica coated quantum dots as labels. Water-soluble fluorescent nanostructures consist of core/shell Cd-QDs enrobed in silica shells to ensure their solubility. The mycotoxins are simultaneously detected by scanning the assay outcome at two different wavelengths, since two QD@SiO2 labelled conjugates fluorescent in different parts of the spectrum. The assay is combined with a rapid extraction technique. The limits of detection for the simultaneous determination were 100 and 700 mu g kg(-1) in both matrices for zearalenone and deoxynivalenol, respectively. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used to confirm the obtained results

Development of suspension polymerized molecularly imprinted beads with metergoline as template and application in a solid-phase extraction procedure toward ergot alkaloids

The first successfully developed molecularly imprinted polymer toward six ergot alkaloids and their respective epimers is described. A new imprinting molecule, metergoline, was used as template analogue in the production of suspension polymerized beads. These spherical particles functioned as selective sorbent in a solid-phase extraction column. The application of this column in the cleanup of barley samples prior to liquid chromafography coupled with tandem mass spectrometry allowed simple and cost-efficient sample preparation. The performance of the imprinted polymer and a non-imprinted control polymer was evaluated. This includes determination of the recovery values and the matrix effect of each of the 12 tested ergot alkaloids as well as a cross-reactivity study with 25 common mycotoxins. The binding isotherms were obtained for metergoline, thus allowing comparison with other (imprinted) sorbents. A comparison between bulk and suspension polymerization is provided to determine the appropriate production technique