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Microcystins are cyclic heptapeptide toxins produced by cyanobacteria that are frequently detected in surface waters during seasonal blooms. Chemisorption of microcystin through covalent bond formation to the acryloyl group common to all congeners was hypothesized to be a high affinity adsorption mechanism. Sol-gel derived organosilica materials were synthesized as sorbents that could potentially facilitate a Michael addition reaction between an immobilized thiol group on the adsorbent and the acryloyl group of microcystin. Amine groups were also added to the organosilica to catalyze the thiol addition reaction at neutral pH. Adsorption isotherms of microcystin-LR, -LA, and –RR were measured for sol–gel derived sorbents and compared to adsorption by wood-based powdered activated carbon, which has been demonstrated to be an effective adsorbent for microcystin. The amine/thiol containing organosilica demonstrated a broad specificity to remove all three congeners from water. Adsorption capacities for MC-LR from natural water were reduced compared to deionized water, especially for the thiol-amine organosilica media. Adsorption of Cu(II) ions by the amine/thiol organosilica was measured which indicated metal ions were bound, however, the degree of metal ion binding was insufficient to significantly decrease adsorption microcystin. Overall, the reaction of microcystin with a surface thiol appeared to be promoted by an initial physical adsorption event and thiol deprotonation by the amines to create a better nucleophile for the Michael addition reaction.

Gold surfaces modified with C3−C18-alkanethiols (CH3(CH2)X-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fr...

Molecularly imprinting sol-gel materials for DDT using both a noncovalent and a covalent approach was examined. A nonpolar porous sol-gel network was created through the use of the bridged polysilsesquioxane, bis-(trimethoxysilylethyl)benzene (BTEB), as the principal sol-gel component. Noncovalent molecular imprinting was deemed unsuccessful, presumably because of the lack of strong intermolecular interactions that can be established between the DDT and the sol-gel precursor. A covalent imprinting strategy was employed by generating a sacrificial spacer through the reaction of two 3-isocyanatopropyltriethoxysilanes with one of two different template molecules: 4,4'-ethylenedianiline (EDA) or 4,4'-ethylidenebisphenol (EBP). After formation of the sol-gel, the bonds linking the spacer template to the matrix were cleaved in a manner that generated a pocket of the appropriate size bordered by amine groups that could aid in the binding of DDT through weak hydrogen bonding interactions. Experiments indicated that DDT could be bound selectively by such an approch. To generate a sensor, an environmentally sensitive fluorescent probe, 7-nitrobenz-2-oxa-1,3-diazole, (NBD) located adjacent to the DDT binding site was used to transduce the binding of analyte. EDA-imprinted sol-gels, deposited as films on glass microscope slides, were shown to quantitatively detect DDT in water to a limit-of-detection of 50 ppt with a response time of60 s. Repeat measurements could be made with the same sensing films after rinsing with acetone between each measurement. The EDA sensing material was selective for DDT and other structurally similar molecules. However, the sensing film design was limited by the relatively minor changes in fluorescence intensity upon binding DDT. This situation may be remedied by an alternative methodology that can facilitate attachment of the NBD fluorophore in an optimal position proximal to the binding pocket.