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The integrative response of a PFAS-specific passive sampler was evaluated in water streams where the concentration varied with time. An integrative response regime over 90 days was observed for most PFAS analytes.

High-resolution mass spectrometry was used to screen for emerging per- and polyfluorinated alkyl substances (PFAS) in precipitation samples collected in summer 2019 at seven sites in the United States. We previously quantified the concentration of ten PFAS in the rainwater samples using the method of isotopic dilution (Pike

Contaminants of emerging concern (CECs) are ubiquitous in aquatic environments across all continents and are relatively well known in the developed world. However, few studies have investigated their presence and biological effects in low- and middle-income countries. We provide a survey of CEC presence in the Volta River, Ghana, and examine the microbial consequences of anthropogenic activities along this economically and ecologically important African river. Water and sediment samples were taken by boat or from shore at 14 sites spanning 118 km of river course from the Volta estuary to the Akosombo dam. Sample extracts were prepared for targeted analysis of antimicrobial CECs, N,N-diethyl-meta-toluamide, and per- and polyfluoroalkyl substances (PFAS; water only). Concurrent samples were extracted to characterize the microbial community and antibiotic-resistant genes (ARGs). Antibiotics and PFAS (PFAS, 2-20 ng/L) were found in all water samples; however, their concentrations were usually in the low nanograms per liter range and lower than reported for other African, European, and North American studies. N,N-Diethyl-meta-toluamide was present in all samples. The number of different genes detected (between one and 10) and total ARG concentrations varied in both water (9.1 × 10

The widespread utilization and commercialization of hydrodechlorination (HDC) over Pd-based catalysts as a remediation technique has been impeded because of catalyst deactivation problems such as formation of carbonaceous deposits under the reductive environment of HDC. In this study, we investigated the use of a novel animated material, swellable organically-modified silica (SOMS), as a catalyst scaffold for HDC of trichloroethylene (TCE) to develop a catalytic system resistant to carbon formation. The state of aggregation of adsorbed TCE on Pd/SOMS was characterized. It was found that the unique nature of SOMS scaffold caused condensation of adsorbents in the SOMS matrix. This is of particular importance considering the fact that the increase of local concentration of reactants due to condensation may enhance the kinetics of catalytic reactions. To determine the resistance to the formation of carbonaceous materials under reaction conditions, in-situ vibrational spectroscopy experiments (diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and laser Raman spectroscopy) were undertaken over Pd-incorporated SOMS in the absence and presence of water vapor in the reactant stream. The commonly used HDC catalyst Pd/Al2O3 was also studied for comparison purposes. Formation of carbonaceous deposits of different nature were observed over Pd/Al2O3 whereas no detectable carbon formation was observed over Pd/SOMS. It was confirmed that surface hydroxyl groups which are in basic character act as coking agents. The carbon formation resistant behavior of Pd/SOMS is closely related to the nature and low concentration of surface hydroxyl groups.

Herein, the dual role of trichloroethylene (TCE) in liquid-phase hydrodechlorination with Pd catalysts supported on swellable organically modified silica (SOMS), is investigated. Batch experiments with TCE-soaked Pd/SOMS showed 45% higher conversion after 4 h than dry Pd/SOMS, suggesting that TCE acts as a reactant and as a swelling-agent. Flow experiments performed with and without ethanol (external swelling-agent) exhibited similar steady-state activities, confirming that TCE itself can cause swelling. Moreover, flow experiments, regardless of whether the SOMS-supported Pd catalysts were pre-reduced or not, yielded similar steady-state conversions, suggesting that Pd(2+) is rapidly reduced by H2 dissolved in water during approach to steady-state. In-situ characterization performed under reaction conditions using time-resolved X-ray absorption spectroscopy confirmed the reduction of Pd(2+) species to Pd(0) by dissolved H2. Overall, this study shows economic viability of hydrodechlorination of TCE using Pd/SOMS by eliminating the need for an external swelling-agent as well as a catalyst pre-reduction step.

Per- and polyfluoroalkyl substances (PFAS) are transported in the atmosphere, leading to both wet and dry deposition to the surface. The concentrations of 15 PFAS were measured at six locations in the Ohio-Indiana region of the U.S. during the summer of 2019 and compared to samples collected at a distant site in NW Wyoming. ΣPFAS concentrations ranged from 50-850 ng L-1, with trifluoroacetic acid (TFA) being the dominant compound (~90%). Concentrations of perfluorooctanoic acid (PFOA) and perfluorosulfonic acid (PFOS) were similar to amounts observed over the past 20 years, indicating persistence in the atmosphere despite regulatory action, and the newer species HFPO-DA (GenX) was also widely detected in rainwater. ANOVA modeling and correlation matrices were used to determine association of PFAS concentrations, location, and functional group and chain length. Statistically significant differences (p < 0.05) in PFAS profiles across sites separated by 10-100 km indicate that local point sources strongly contribute to wet deposition. This work introduces correlation plots for PFAS that allow rapid visual comparison of multi-analyte and multi-site data sets.

Organosilica synthesis chemistry via the sol–gel method was used to create porous organosilica adsorbents designed to remove PFAS compounds from water. A set of adsorbents was created by incorporating a fluorophilic amide or fluoroalkyl function group along with quaternary groups for ion exchange within a continuous porous matrix. A distinguishing aspect of the adsorbents was the ability to volumetrically swell 2.5× (>6 mL g−1) in the presence of organic liquids. Swelling results from a flexible pore architecture and was used to create expanded mesopores which were hypothesized to yield greater adsorption capacity for PFAS compounds. Adsorption isotherms and adsorption kinetics experiments were conducted for a set of 12 PFAS analytes in deionized water and 50 mM NaCl in order to understand the effect of adsorbate characteristics and ionic strength on adsorption. PFAS of all chain lengths ranging from C4–C10 were bound to adsorbents possessing both fluorophilic and cationic groups. In comparison, only long-chain PFAS >C6 are bound when the adsorbents are exclusively hydrophobic or fluorophilic. An adsorbent was created where a cationic imidazolium containing polymer was entrapped within the swellable pores. The polymer-infused organosilica demonstrated the highest capacity across the suite of 12 short-chain and long-chain PFAS. In column experiments, the polymer organosilica yielded 47 mg g−1 capacity for perfluorooctanoic acid (PFOA) prior to breakthrough with an influent concentration of 200 μg L−1, approximately an order a magnitude greater than GAC. The high adsorption capacity is attributed to expandable pores which can accommodate polymer and PFAS adsorbates while maintaining sufficient access for mass transport.

Swellable-organically modified silica (SOMS) has been demonstrated to be an efficient catalyst scaffold for catalytic treatment of water contaminated with trichloroethylene (TCE). In this study, deactivation characteristics of Pd-incorporated SOMS for aqueous-phase hydrodechlorination (HDC) of TCE were investigated. Pd/SOMS catalysts were exposed to highly-concentrated chloride solutions (up to 1 M NaCl or 0.01 M HCl) to examine the deactivation resistant behavior of Pd/SOMS. The commonly used HDC catalyst Pd/Al2O3 was also studied for comparison purposes. Pd/SOMS and Pd/Al2O3 in their pristine and treated states were tested for aqueous-phase HDC of TCE and characterized by several techniques including N2 physisorption, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy, extended X-ray absorption fine structure spectroscopy (EXAFS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO. The aqueous-phase treatments had a pronounced adverse effect on the textural properties of Pd/Al2O3, although the effect was independent of the type of the chloride precursor, NaCl or HCl. Treating Pd/Al2O3 with chloride-containing solutions lowered the catalytic activity due to formation of Pd-Cl complexes and active metal leaching. The leached Pd obtained from the treatment solution was shown to be inactive for aqueous-phase HDC of TCE. While Pd/Al2O3 underwent severe deactivation due to the chloride treatments, Pd/SOMS exhibited resistance to chloride deactivation and metal leaching. The chloride treatments did not impact the textural properties of Pd/SOMS. The achieved deactivation resistance was attributed to the novel characteristics of the SOMS support.

The properties of a swellable organically modified silica (SOMS) scaffold allowed us to synthesize “smart” catalysts with tunable accessibility of the active sites induced by organic swelling agents. Pd nanoparticles (NPs) deposited inside the swollen matrix of SOMS were shown to be selectively located on the interior surface, a surface which is only available through swelling. Techniques such as near ambient-pressure X-ray photoelectron spectroscopy (NAP–XPS) and cryogenic scanning electron microscopy (SEM) were employed to characterize Pd/SOMS in its swollen as well as unswollen state because their conventional counterparts do not preserve the swollen state of Pd/SOMS during spectral acquisition. The results obtained depicted significant differences between the unswollen and swollen state of Pd/SOMS. The most important difference is that Pd NPs became accessible on the surface after exposure to an organic compound. This indicates that the accessibility of the active sites can be controlled by changing t...

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.

Freshwater streams on oceanic islands serve critical ecological and economic functions. However, these are underrepresented in assessments of pollution from contaminants of emerging concern (CEC). Furthermore, freshwater streams and their endemic fauna often have characteristics that are distinct from those of continental streams and model species, calling extrapolations from studies of such systems into question for island streams. In the current study, we assessed the presence of CEC across three sampling events and five freshwater streams on the Island of Hawai’i. We also exposed juveniles of the native fish species Sicyopterus stimpsoni to a mixture of commonly co-occurring CEC for 96 h in static renewal experiments, testing for impacts of CEC in two ecologically relevant assays of functional performance. CEC from multiple sources were ubiquitous in Hawaiian streams, including human-use pharmaceuticals, agricultural herbicides, and industrial runoff. Concentrations of CEC were comparable to published studies from continental streams, exceeding total concentrations of 1000 ng/L for the eight quantified CEC in four samples, and approaching 2500 ng/L in one sample. Effects on exposed fish were subtle and limited to treatments with higher CEC concentrations but indicated potential impacts of CEC on locomotor performance. These results indicate that Hawaiian streams follow a global trend of widespread freshwater pollution by CEC that are accompanied by subtle effects on native fish species and highlight the need for the inclusion of endemic species and ecologically relevant assays when assessing the effects of contaminants in island habitats.

The adsorption of C2–C6 short chain carboxylic acids was measured for swellable organically modified silicas (SOMS), hydrophobic polysilsesquioxane based materials prepared via the sol–gel process. Adsorption was measured for SOMS materials that were either hydrophobic or incorporated variable amounts of quaternary amine groups to serve as ion exchange sites. Batch equilibrium experiments were performed for carboxylic acids and alcohols to standard hydrophobic SOMS. Results show that SOMS has partition coefficients for short chain alcohols that are approximately 3× greater than liquid–liquid extraction into octanol, and 10× greater for the extraction of short chain carboxylic acids. Affinity for valeric acid was similar to commercially available Amberlite XAD-4 resins, however the organosilica derived sorbent had a 3× higher total adsorption capacity which was attributed to the ability of the pores to expand. Column experiments using SOMS were used to measure breakthrough curves for valeric acid across a wide range of concentrations. The isotherm for dynamic adsorption was linear indicating that capacity to adsorb valeric acid was controlled by equilibrium and not limited by set pore volume capacity. Addition of quaternary amine sites to SOMS improved adsorption affinity of valeric acid at low concentrations, but those modifications reduced the swelling of the matrix and lowered capacity at higher concentrations. Overall, SOMS was found to be poorly suited to extract organic acids at concentrations

Pd catalysts supported on swellable organically-modified silica (SOMS) and high-temperature-treated swellable organically-modified silica (H-SOMS) were characterized and tested for gas-phase hydrodechlorination (HDC) of trichloroethylene (TCE) conditions. The high-temperature treatment on SOMS resulted in an increase in surface area and pore diameter as well as significant improvement of Pd dispersion on H-SOMS with smaller Pd particle sizes compared to the Pd/SOMS catalyst. Although the high-temperature treatment led to some alteration of the SOMS polysiloxane network, the hydrophobicity and organic vapor adsorption characteristics of SOMS were preserved. The reduction and oxidation characteristics of Pd on SOMS and HSOMS were investigated in situ using XANES technique. It was found that the Pd sites in the pores of SOMS was accessible to small molecules such as H2, facilitating the reduction of PdOx, whereas oxidation of metallic Pd was limited even at higher temperatures when O2 was used. This effect was only observed over Pd/SOMS catalyst. For Pd/H-SOMS, because the pores were more widely open than Pd/SOMS, both reduction and oxidation of Pd were observed. Finally, the catalytic activity of Pd/H-SOMS for gas-phase HDC of TCE was significantly better than Pd/SOMS. When water was added to the reactant stream (TCE + H2O), both Pd/SOMS and Pd/H-SOMS maintained its catalytic performances due to hydrophobic property of the supports.

The catalytic activity and resistance to poisoning of Pd catalysts supported on swellable organically-modified silica (SOMS) were investigated for hydrodechlorination (HDC) of trichloroethylene (TCE). The promising catalytic activity of 1% Pd/SOMS sample was attributed to the high affinity of SOMS for organics and its high hydrophobicity. While latter characteristic repels water, the adsorptive capacity for organics allows TCE dissolved in aqueous media to concentrate inside the pores, in the vicinity of the active sites, thus helping the kinetics. In the liquid phase, using a continuous flow reactor, higher TCE conversion was obtained over the 1% Pd/SOMS compared to the commercial 1% Pd/Al 2 O 3 catalyst. When the pores of 1% Pd/SOMS sample were fully opened by pre-treating it with ethanol prior to the reaction, HDC activity was seen to significantly increase. In the gas phase, the extent of adsorption was less, reducing the concentration of reactants near the active sites. As a result, 1% Pd/SOMS was less active than 1% Pd/Al 2 O 3 for HDC of TCE. To determine their resistance to poisoning, 1% Pd/SOMS and 1% Pd/Al 2 O 3 catalysts were poisoned ex-situ with Li 2 S. The ex-situ poisoned Pd/SOMS sample maintained its catalytic activity for HDC of TCE. However, a significant loss in catalytic activity of the Pd/Al 2 O 3 catalyst was observed after poisoning. Protection from aqueous phase sulfide poisoning was attributed to the hydrophobicity of the Pd/SOMS, which would exclude anionic species from the embedded Pd particles. The XPS, STEM and ICP-OES results indicated that when Pd/Al 2 O 3 and Pd/SOMS were treated with 1 M HCl, most of the Pd metal was leached from the Pd/Al 2 O 3 catalyst in contrast to Pd/SOMS, which had negligible leaching. Overall, due to hydrophobicity and high affinity for organics, SOMS has potential as a catalyst scaffold for different reactions in groundwater remediation applications.

One of the problems of catalytic water treatment systems is that sulfur-containing species present in contaminated water have a detrimental effect on the catalytic performance because of strong interactions of sulfur species with active metal sites. In order to address these problems, our research has focused on developing a poison-resistant catalytic system by using a novel material, namely, swellable organically modified silica (SOMS), as a catalyst scaffold. Our previous investigations demonstrated that the developed system was resistant to chloride poisoning, active metal leaching, and carbon deposition under reaction conditions. This study examines the sulfur tolerance of the developed catalytic system for hydrodechlorination (HDC) of trichloroethylene (TCE) by subjecting Pd-incorporated samples to different sulfur species, including sulfates (SO42–), bisulfides (HS–), and hydrogen sulfide (H2S). The pristine and sulfur-treated catalysts were then tested for aqueous- and gas-phase HDC of TCE and characterized by several techniques, including N2 physisorption, X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and temperature-programmed reaction (TPrxn) with H2. The investigations were also performed on Pd/Al2O3, a commercially used HDC catalyst, to have a basis for comparison. The activity and characterization results revealed that Pd/Al2O3 underwent deactivation due to exposure to sulfur-containing compounds. Pd/SOMS, however, exhibited better resistance to aqueous sulfates, bisulfides, and gas-phase H2S. In addition, the removal of sulfur species from completely poisoned catalysts was found to be more facile in Pd/SOMS than Pd/Al2O3. The tolerance of Pd/SOMS to sulfur poisoning was attributed to stem from the novel characteristics of SOMS, such as swelling ability and extreme hydrophobicity.

Transformation of endocrine active compounds (EACs) by either chlorination (Cl-D) or UV disinfection (UV-D) was studied by field sampling and bench-scale validation studies. Field testing assessed concentration of 13 EACs in effluent at two Chicago area 250 MGD wastewater reclamation plants (WRP) over two years. One WRP uses chlorination/dechlorination while the other employs UV disinfection. Target compounds included bupropion, carbamazepine, citalopram, duloxetine, estradiol, estrone, fluoxetine, nonylphenol, norfluoxetine, norsertraline, paroxetine, sertraline, and venlafaxine. Concentrations of 9/13 target compounds were partially reduced after disinfection (5–65% reduction). None of the target compounds were fully transformed by either chlorination or UV treatment at the WRP scale. In bench-scale experiments each compound was spiked into deionized water or effluent and treated in a process mimicking plant-scale disinfection to validate transformations. Correlation was observed between compounds that were transformed in bench-testing and those that decreased in concentration in post-disinfection WRP effluent (10/13 compounds). A survey of potential reaction products was made. Chlorination of some amine containing compounds produced chloramine by-products that reverted to the initial form after dechlorination. Transformation products produced upon simulated UV disinfection were more diverse. Laboratory UV-induced transformation was generally more effective under stirred conditions, suggesting that indirect photo-induced reactions may predominate over direct photolysis.

In this study, effect of ethanol on the performance of Pd supported on swellable organically modified silica (SOMS) for hydrodechlorination (HDC) of trichloroethylene (TCE) is investigated. SOMS is a hydrophobic material that swells to 3–4 times its original volume when contacted with organic solvents. Catalytic HDC of TCE suffers from inhibition due to HCl which is worsened by the slow removal of HCl from the hydrophobic pores of SOMS. Addition of ethanol resulted in swelling of SOMS matrix causing expansion of pores, thereby facilitating the removal of HCl. The inhibitory effect of HCl was alleviated by ethanol, without altering the HDC reaction pathway. Characterization using near-ambient pressure X-ray photoelectron spectroscopy and extended X-ray absorption fine structure showed the effect of ethanol on swellability and HCl removal, respectively. Lastly, a mechanism has been proposed for the uninhibited reaction, which exhibited first order kinetics with respect to TCE.

Swellable organically modified silica (SOMS) is a sol–gel derived material that spontaneously expands >2.5× upon contact with organic liquids, absorbing 7.8 mL/g. Adsorption of gas-phase volatile organic compounds by SOMS was measured to examine how the capability to swell affects capacity and rate of organic vapor absorption. Static adsorption capacities of SOMS for organic vapors at saturated vapor pressure ranged from 0.7 to 1.05 g/g, which was higher than values for other sorbents (powdered activated carbon, Amberlite XAD-4, Tenax TA, OptiPore, and organophilic zeolite). Rates of adsorption by SOMS were similar to those of XAD-4, a porous polymer with similar surface chemistry, and slower than that of activated carbon. Sequential coadsorption of multiple compounds by SOMS was measured, yielding enhanced adsorption capacity attributed to adsorption-induced pore expansion. The sequential adsorption of phenol and acetone vapor (p = p0) led to a total capacity of 5.7 g/g. Adsorption of organic vapors was ...

We present a theoretical framework that describes the force generated by the expansion of swellable organically modified silica (SOMS) upon exposure to organic solvent. The total swelling force, produced from the differential contributions of localized swelling domains, is related logarithmically to the amount of material confined to a rigid space. The model is further parameterized according to the physical dimensions of that space and the intrinsic swellability of SOMS. This mathematical representation is validated experimentally using a piston force sensor apparatus, which shows that the solvent-induced force and pressure exerted by SOMS increase logarithmically with the amount of material that is present. Comparison with theory implies that the commercially available varieties of SOMS CyclaSorbTM and OsorbTM have Young’s expansion moduli YC ∼ 0.8 MPa and YO ∼ 0.7 MPa, respectively, which succinctly quantifies their relative behavior. The theoretical model and experimental technique should be widely applicable to other swellable and stimuli-responsive materials.

Swellable organically modified silica (SOMS) is a mesoporous sol-gel derived material that spontaneously swells >6 mL/g upon addition organic liquids. Adsorption of 8 different proteins to swollen-state SOMS was studied as a function of adsorbate molecular size and solution pH. Adsorption capacity was dependent on molecular size with the highest capacity of 690 mg/g measured for wheat germ acid phosphatase (58 kDa), a mid-size protein. Adsorption capacities were generally independent of pH suggesting protein-protein interactions do not play a major role in the adsorption mechanism. Rate of adsorption was measured at different protein loadings and fit to a pseudo second-order rate equation. Adsorption rates were independent of loading state when the pH was near a protein's isoelectric point (pI), but varied when the pH differed from the pI of adsorbate. Adsorption was found to irreversible for all proteins when rinsed with buffer solution or ethanol. Infrared spectroscopy of adsorbed cytochrome c and myoglobin indicated that both proteins maintain a native folded state that is stabilized to thermal denaturation. Adsorbed streptavidin was found to bind FITC-biotin (63% binding site saturation) suggesting that adsorbed proteins are accessible to small molecules in bulk solution. Acid phosphatase showed catalytic activity when adsorbed to swollen SOMS, however, specific activity of the bound enzyme was 10-fold lower compared to free enzyme in solution. Adsorption to SOMS appears to be a one-step, reagent-free method to irreversibly immobilize small to mid-sized proteins. Data supports an adsorption mechanism where protein molecules become sterically entrapped in the flexible mesoporous material.

Iron-Osorb® is a solid composite material of swellable organosilica with embedded nanoscale zero-valent iron that was formulated to extract and dechlorinate solvents in groundwater. The unique feature of the highly porous organosilica is its strong affinity for chlorinated solvents, such as trichloroethylene (TCE), while being impervious to dissolved solids. The swellable matrix is able to release ethane after dechlorination and return to the initial state. Iron-Osorb® was determined to be highly effective in reducing TCE concentrations in bench-scale experiments. The material was tested in a series of three pilot scale tests for in situ remediation of TCE in conjunction with the Ohio Environmental Protection Agency at a site in central Ohio. Results of these tests indicate that TCE levels were reduced for a period of time after injection, then leveled out or bounced back, presumably due to depletion of zero-valent iron. Use of tracer materials and soil corings indicate that Iron-Osorb® traveled distances of at least 20 feet from the injection point during soil augmentation. The material appears to remain in place once the injection fluid is diluted into the surrounding groundwater. Overall, the technology is promising as a remediation method to treat dilute plumes or create diffuse permeable reactive barriers. Keys to future implementation include developing injection mechanisms that optimize soil distribution of the material and making the system long-lasting to allow for continual treatment of contaminants emanating from the soil matrix. © 2011 Wiley Periodicals, Inc.

Waveguide interferometry was employed as a transduction scheme to create a highly sensitive detector for vapor phase TNT in air. Selectivity for TNT was accomplished by using molecularly imprinted sol–gel derived organic/inorganic films deposited on the surface of the waveguide sensing channel. Response varied greatly as a function of the sensing film composition and required the presence of a bridging structure possessing an aromatic group linking silicon centers. The most sensitive film was composed of bis(triethoxysilyl)benzene with binding sites for TNT prepared by the chemical removal of a covalently bound TNT template which was co-polymerized into the matrix. A continuous unidirectional phase shift was observed upon exposure to TNT which was only partially reversible. As a result, the limit-of-detection is a function of both vapor phase concentration and exposure time. Only 2.4 parts-per-trillion (volume) of TNT is required to reach a 0.5 degree phase angle change for 2 min exposure time using the optimized film composition. The sensor responds with much reduced sensitivity (

Organically modified silica that rapidly and reversibly swells to >3 times their dry volume have been recently described. Here, these organosilica materials were demonstrated to have the ability absorb trichloroethylene (TCE), perchloroethylene (PCE), methyl t -butyl ether (MTBE), toluene, naphthalene, acetone, 1,4-dioxane, and 1-butanol from water. Direct experimental comparisons indicated that swellable organically modified silica (SOMS) has in many instances greater capacity than activated carbon and molecular sieves and possesses the ability to capture a wide range of dissolved polar and non-polar organic contaminants. The absorption of organic species to SOMS is enhanced by matrix expansion leading to non-selective capture of organics beyond what could only be attributed to physisorption. This process appears to be facilitated by initial adsorption events unlatching the collapsed matrix leading to the opening of nanometer-scale pores within the tensioned SOMS material, thus providing volume for absorption. Partition coefficients for the absorption of organic species from water by SOMS ranged from 2.8 × 10 5 to 1.0 × 10 2 , and vary depending on polarity of the contaminant, concentration, and the total mass of contaminant absorbed. Maximum capacity exceed three times the dry weight of the absorbent under conditions of high contaminant concentration. SOMS was repeatedly regenerated with mild thermal treatment (60–110 °C) in air to evaporate absorbates from the matrix which could be subsequently collected. Only a slight decrease in effectiveness is observed after regeneration. Absorption is equally effective from salt water. Minimal loss of capacity and affinity is lost when extracting environmentally relevant concentrations of TCE from a topsoil/water mixture, presumably due to a molecular sieving effect.

A novel type of sol–gel derived zerogels that instantaneously swell greater than three times their dried volume in nonpolar solvents were investigated. Hybrid organic–inorganic materials that swell were only produced from a narrow set of precursors that possess an organic bridging group that contains an aromatic segment that is flexibly linked to the alkoxysilane polymerizable ends. Careful control over the processing conditions (catalyst, solvent, aging time) was necessary to yield animated zerogels. Various materials were studied by electron microscopy, infrared spectroscopy, nitrogen adsorption, and fluorescence spectroscopy using a covalently linked pyrene reporter. Collectively, the data support a model where swelling is derived from a morphology of interconnected organosilicate nanoparticles that are cross-linked to a particular extent during the gel state. Upon drying to the zerogel form, tensile forces generated by capillary-induced collapse of the polymeric matrix are released when interparticle ...

A chemical sensor was developed to detect the explosive 2,4,6-trinitrotoluene (TNT) utilizing planar integrated optical waveguide (IOW) attenuated total reflection spectrometry. Submicron thick films of organically modified sol–gel polymers were deposited on the waveguide surface as the sensing layer. Sol–gels were molecularly imprinted for TNT using covalently bound template molecules linked to the matrix through 1 or 2 carbamate linkages. Upon chemical cleavage of the template and displacement of the TNT-like pendant groups from the matrix, shape-selective binding sites were created that possess a primary amine group. The amine was used to deprotonate bound TNT yielding an anionic form that absorbs visible light. Binding of TNT and subsequent conversion to the anion results in the attenuation of light propagating through the waveguide, thus creating a spectrophotometric device. Sensitivity can be achieved by taking advantage of the substantial pathlength provided by the use of single mode IOWs. The limit-of-detection to gas-phase TNT was found to be five parts-per-billion (ppbV) in ambient air at a flow rate of 40 mL min −1 given a 60 s sampling time. The sensor is highly selective for TNT due to the selectivity of binding site recognition of TNT and the subsequent generation of the TNT anion. Response to TNT is not reversible which results in an integrating sensor device which, in theory, can improve the ability to detect small amounts of the explosive if the exposure time is sufficient in length.

A fluorescence-based chemical sensor for fluorene was created by molecularly imprinting a sol-gel comprising the bridged silsesquioxane, bis(trimethoxysilylethyl)benzene. The template was covalently bound to the sol-gel matrix using a fluorene analogue functionalized silane. After chemical removal of template via cleavage of a carbamate linkage, an amine group was left that provided an attachment site for the environmentally sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazole (NBD). Fluorene binding was detected by a change in NBD fluorescence intensity induced by a difference in the local polarity around the probe when the recognition site is filled. Such an approach eliminated response to nonspecific binding to the matrix. Sensing films deposited on glass slides were shown to have response times of60 s and detection limits below 10 parts-per-trillion. Binding experiments demonstrated that the materials had good selectivity for fluorene over close structural analogues including naphthalene, fluoranthene, and anthracene. However, the sensing design is limited by a lack of reversibility following fluorene binding.

Sol–gel materials that swell six times their dried volume when placed in organic solvents were prepared using the bridged silsesquioxane bis(trimethoxysilyethyl)benzene through base catalysis by tetrabutyl ammonium fluoride. Prior to drying the gels, water and catalyst were rinsed from the solvated matrix and residual silanol groups were derivatized with a chlorosilane (R–Si(CH 3 ) 2 Cl). The swelling behavior was completely reversible when the materials are dried at elevated temperature. Swelling is highly dependent on the processing conditions, including the choice of solvent and catalyst. There is no preferential adsorption of solute molecules to swelled sol–gels despite the diversity of chlorosilanes used to derivatize the materials.

Six fully conserved arginine residues (R129, R131, R235, R291, R319, and R340) closely grouped in the nucleotide binding site of rabbit muscle creatine kinase (rmCK) were mutated; four to alanine and all six to lysine. Kinetic analyses in the direction of phosphocreatine formation showed that all four alanine mutants led to substantial losses of activity with three (R129A, R131A, and R235A ) having no detectable activity. All six lysine mutants retained variable degrees of reduced enzymatic activity. Static quenching of intrinsic tryptophan fluorescence was used to measure the binding constants for MgADP and MgATP. Nucleotide binding was at most only modestly affected by mutation of the arginine residues. Thus, the cluster of arginines seem to be primarily responsible for transition state stabilization which is further supported by the observation that none of the inactive mutants demonstrated the ability to form a transition analogue complex of MgADP·nitrate·creatine as determined by fluorescence quenching assays. As a whole, the results suggest that the most important role these residues play is to properly align the substrates for stabilization of the phosphoryl transfer reaction.

To explore the possibility that asparagine 285 plays a key role in transition state stabilization in phosphagen kinase catalysis, the N285Q, N285D, and N285A site-directed mutants of recombinant rabbit muscle creatine kinase (rmCK) were prepared and characterized. Kinetic analysis of phosphocreatine formation showed that the catalytic efficiency of each N285 mutant was reduced by approximately four orders of magnitude, with the major cause of activity loss being a reduction in k(cat) in comparison to the recombinant native CK. The data for N285Q still fit a random-order, rapid-equilibrium mechanism, with either MgATP or creatine binding first with affinities very nearly equal to those for native CK. However, the affinity for the binding of the second substrate is reduced approximately 10-fold, suggesting that addition of a single methylene group at position 285 disrupts the symphony of substrate binding. The data for the N285A mutant only fit an ordered binding mechanism, with MgATP binding first. Isosteric replacement to form the N285D mutant has almost no effect on the K(M) values for either creatine or MgATP, thus the decrease in activity is due almost entirely to a 5000-fold reduction in k(cat). Using the quenching of the intrinsic CK tryptophan fluorescence by added MgADP (Borders et al. 2002), it was found that, unlike native CK, none of the mutants have the ability to form a quaternary TSAC. We use these data to propose that asparagine 285 indeed plays a key role in transition state stabilization in the reaction catalyzed by creatine kinase and other phosphagen kinases.

Recombinant rabbit muscle creatine kinase (CK) was titrated with MgADP in 50 mM Bicine and 5 mM Mg(OAc)2, pH 8.3, at 30.0 degrees C by following a decrease in the protein's intrinsic fluorescence. In the presence of 50 mM NaOAc, but in the absence of added creatine or nitrate, MgADP has an apparent K(d) of 135 +/- 7 microM, and the total change in fluorescence on saturation (Delta%F) is 15.3 +/- 0.3%. Acetate was used as the anion in this experiment because it does not promote the formation of a CK.MgADP.anion.creatine transition-state analogue complex (TSAC) [Millner-White and Watts (1971) Biochem. J. 122, 727-740]. In the presence of 80 mM creatine, but no nitrate, the apparent K(d) for MgADP remains essentially unchanged at 132 +/- 10 microM, while Delta%F decreases slightly to 13.2 +/- 0.3%. In the presence of 10 mM nitrate, but no creatine, the apparent K(d) is once again essentially unchanged at 143 +/- 23 microM, but the Delta%F is markedly reduced to 4.2 +/- 0.2%. The presence of both 10 mM nitrate and 80 mM creatine during titration reduces the apparent K(d) for MgADP 10-fold to 13.7 +/- 0.7 microM, and Delta%F increases to 20.6 +/- 0.3%, strongly suggesting that the simultaneous presence of saturating levels of creatine and nitrate increases the affinity of CK for MgADP and promotes the formation of the enzyme*MgADP*nitrate*creatine TSAC. When the fluorescence of CK was titrated with MgADP in the presence of 80 mM creatine and fixed saturating concentrations of various anions, apparent K(d) values for MgADP of 132 +/- 10 microM, 25.2 +/- 1.3 microM, 18.8 +/- 0.9 microM, 13.7 +/- 0.7 microM, and 6.4 +/- 0.7 microM were observed as the anion was changed from acetate to formate to chloride to nitrate to nitrite, respectively. This is the same trend reported by Millner-White and Watts for the effectiveness of various monovalent anions in forming the CK.MgADP.anion.creatine TSAC. On titration of CK with MgADP in the presence of 80 mM creatine and various fixed concentrations of NaNO3, the apparent K(d) for MgADP decreases with increasing fixed concentrations of nitrate. A plot of the apparent K(d) for MgADP vs [NO3-] suggests a K(d) for nitrate from the TSAC of 0.39 +/- 0.07 mM. Similarly, titration with MgADP in the presence of 10 mM NaNO3 and various fixed concentrations of creatine gives a value of 0.9 +/- 0.4 mM for the dissociation of creatine from the TSAC. The data were used to calculate K(TDAC), the dissociation constant of the quaternary TSAC into its individual components, of 3 x 10(-10) M3. To our knowledge this is the first reported dissociation constant for a ternary or quaternary TSAC.

Multilayer protein films in which avidin or streptavidin is used as a cross-linking agent are widely used in bioanalytical laboratories for diagnostics, isolation, and localization. However, compar...

Planar integrated optical waveguides doped with fluorescent hexavalent UO22+ ions were fabricated by a sol−gel dip-coating process. Excitation of a mode in these waveguides produced fluorescence emission that decayed in a highly uniform manner as a function of propagation distance. A comparison of methods for determining waveguide attenuation coefficients by digital photography of the mode demonstrated that imaging the UO22+ fluorescence emission is significantly more precise than imaging the Rayleigh and Mie scattered light. The utility of these waveguides for performing attenuated total reflectance measurements on substrate-supported molecular films was also assessed. Both the fluorescence and scattering methods were used to determine the attenuation coefficient of an adsorbed heme protein monolayer. The fluorescence imaging method was clearly superior; its use enables attenuation measurements of very weakly absorbing, waveguide-supported films to be performed with significantly improved precision.

Molecular orientation in hydrated cytochrome c (cyt c) films formed by adsorption to substrates of differing surface chemistry was investigated. The orientation distribution of the heme groups in the protein films was determined using a combination of two techniques: absorption linear dichroism, measured in a planar integrated optical waveguide-attenuated total reflection geometry, and emission anisotropy, measured in a total internal reflection fluorescence geometry. The mean heme tilt angle and angular distribution about the mean were recovered using a Gaussian model for the orientation distribution. These data are the first orientation distribution measurements reported for protein film assemblies. The results show that a macroscopically ordered film of adsorbed cyt c molecules is produced when a single, high-affinity type of noncovalent binding occurs between the surface of the protein and the substrate surface. For example, electrostatic adsorption of the positively charged protein to the negatively...

Molecular orientation in films of yeast cytochrome c immobilized via disulfide bonding between cysteine 102 and the thiol tail groups of self-assembled monolayers (SAMs) coated on planar glass substrates was investigated. The orientation distribution of the heme groups in the protein film was determined using a combination of absorption linear dichroism, measured in a planar integrated optical waveguide-attenuated total reflection geometry, and emission anisotropy, measured in a total internal reflection fluorescence geometry. The mean heme tilt angle and angular distribution about the mean were recovered using a Gaussian model for the orientation distribution. These data are the first orientation distribution measurements reported for a protein film immobilized using a site-directed bonding strategy. The results show that the molecular architecture examined in this study does not produce a highly oriented protein film. A significant fraction of the immobilized cytochrome c is nonspecifically adsorbed to ...

A method to determine the orientation distribution of fluorescent molecules in a thin, substrate-supported film is described. Attenuated total reflection spectrometry on the surface of a planar waveguide is used to measure absorption LD, from which the mean dipole tilt angle in the film is obtained. Steady-state fluorescence anisotropy is measured in a total internal reflection geometry on a film supported on fused silica but prepared under otherwise identical conditions. The angular distribution about the mean can be recovered from the anisotropy measurement by modeling the distribution as a probability density that is specified by two adjustable parameters. The method was tested on Langmuir−Blodgett (LB) films of arachidic acid doped with the fluorescent amphiphiles DiI and BODIPY. In the DiI-doped films, the mean tilt angle was 75° from the surface normal. Assuming a Gaussian distribution, the standard deviation was 12°, indicating a high degree of macroscopic order. In the BODIPY-doped films the distr...

A total internal reflection fluorescence microscope with time-resolved spectroscopy and CCD imaging capabilities is described. The capability of the microscope to selectively detect, via temporal resolution, the presence of a long-lived luminescence label in biological cells in vitro was evaluated. Tb chelates having radiative lifetimes of ca. 1.5 ms were employed as long-lived, extrinsic labels. Microspectroscopy and imaging were performed on mouse 3T3 cells stained with Tb chelates, stained with DiI (an extrinsic membrane label of ns lifetime), and in the absence of an extrinsic label. The results demonstrate the efficiency of using time-resolved detection to discriminate against intrinsic and extrinsic sources of short-lived emission in cultured cells, which enables long-lived, extrinsic luminescence to be selectively detected. Potential applications of this technology are discussed.

The immobilization of proteins by entrapment in optically clear, porous glasses prepared by sol-gel techniques appears to be a promising approach to optical biosensor development. However, little is known about the physical environment of the immobilized protein or the mechanism(s) of entrapment. In this study, absorbance and fluorescence spectroscopies have been used to characterize the properties of two model proteins, bovine serum albumin (BSA) and horse heart myoglobin (Mb), entrapped in wet sol-gel glass bulks. The fluorescence behavior of dissolved and entrapped BSA in the presence of acid, a chemical denaturant, and a collisional quencher was examined. The results show that a large fraction of the BSA added to the sol is entrapped within the gelled glass in a native conformation. However, the reversible conformational transitions that BSA undergoes in solution are sterically restricted in the gel. In contrast, the native properties of Mb are largely lost upon entrapment, as judged by the changes in the visible absorbance spectra of dissolved and entrapped Mb in acidic solutions. Fluorescence studies of dissolved and entrapped apomyoglobin support this conclusion.

ABS Materials has developed a new type of swellable organophilic material that extracts a wide array of dissolved hydrocarbons from oil field waters. With funding from the U.S. Department of Energy (SBIR Program) orchestrated through the National Energy Technology Laboratory, ABS Materials has been engineering systems to use swellable glass to treat flow back waters to remove dissolved organics. Two pilot scale systems were built: a non-regenerating skid-mounted system which handles inputs of up to 4 gal/min and a 60 gal/min trailer mounted system which included a mechanism for swellable glass regeneration.

The application of charge-coupled device (CCD) technology to high-resolution luminescence microscopy is a recent development. The very high sensitivity, linear response, and field uniformity that are characteristic of a slow-scan, scientific CCD camera yield data of sufficient quality to make quantitative image analysis possible. However, the low temporal resolution of current CCD cameras is a major disadvantage. A CCD with a read noise level of less than 10 electrons typically has a readout rate in the 40–200 kHz range, which precludes the acquisition of a time-resolved image integrated over multiple excitation pulses without the use of an external gating device. Imaging in the time domain can potentially increase both the information content and the sensitivity of luminescence microscopy. For example: (1) fluorescent probe distributions can be resolved temporally as well as spatially, yielding improved image contrast; and (2) temporally gated detection of long-lived luminescence discriminates against scattered light and autofluorescence, which can yield improved sensitivity.