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Analytica Chimica Acta (v.534, #1)
Discriminating binding and positioning of amphiphiles to lipid bilayers by1H NMR by F. Evanics; R.S. Prosser (pp. 21-29).
The binding and positioning in lipid bilayers of three well-known drugs—imipramine, nicotine, and caffeine—have been studied using1H NMR. The membrane model system consisted of “fast-tumbling� lipid bicelles, in which a bilayered lipid domain, composed of the unsaturated lipid, 1,2-dimyristelaidoyl- sn-glycero-3-phosphocholine (DMLPC) was surrounded by a rim of deuterated detergent-like lipids, consisting of 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC-d22). Binding and immersion depth information was obtained by three experiments. (1)1H chemical shift perturbations, upon transfer of the amphiphiles from water to a bicelle mixture, were used to estimate regions of the amphiphiles that interact with the membrane. (2) Water contact to resolvable protons was measured through a Nuclear Overhauser Effect (NOE) between water and resolvable drug and lipid resonances. In the case of both lipids and membrane bound drugs, positive NOEs with large cross-relaxation rates were measured for most resonances originating from the membrane hydrophilic region, while negative NOEs were observed predominantly to resonances in the hydrophobic region of the membrane. (3)1H NMR measurements of oxygen-induced (paramagnetic) spin-lattice relaxation rates, which are known to increase with membrane immersion depth, were used to corroborate conclusions based on chemical shift perturbations and water-ligand NOEs.
Keywords: Bicelles; NMR; Nuclear Overhauser Effects; Membrane-water interactions; Membrane binding; Paramagnetic effects; Oxygen
Molecularly imprinted polymers—potential and challenges in analytical chemistry by J.O. Mahony; K. Nolan; M.R. Smyth; B. Mizaikoff (pp. 31-39).
Among the variety of biomimetic recognition schemes utilizing supramolecular approaches molecularly imprinted polymers (MIPs) have proven their potential as synthetic receptors in numerous applications ranging from liquid chromatography to assays and sensor technology. Their inherent advantages compared to biochemical/biological recognition systems include robustness, storage endurance and lower costs. However, until recently only few contributions throughout the relevant literature describe quantitative analytical applications of MIPs for practically relevant analyte molecules and real-world samples. Increased motivation to thoroughly evaluate the true potential of MIP technology is clearly attributed to the demands of modern analytical chemistry, which include enhanced sensitivity, selectivity and applicability of molecular recognition building blocks at decreasing costs. In particular, the areas of environmental monitoring, food and beverage analysis and industrial process surveillance require analytical tools capable of discriminating chemicals with high molecular specificity considering increasing numbers of complex environmental contaminants, pollution of raw products and rigorous quality control requested by legislation and consumer protection. Furthermore, efficient product improvement and development of new products requires precise qualitative and quantitative analytical methods. Finally, environmental, food and process safety control issues favor the application of on-line in situ analytical methods with high molecular selectivity. While biorecognition schemes frequently suffer from degrading bioactivity and long-term stability when applied in real-world sample environments, MIPs serving as synthetic antibodies have successfully been applied as stationary phase separation matrix (e.g. HPLC and SPE), recognition component in bioassays (e.g. ELISA) or biomimetic recognition layer in chemical sensor systems. Examples such as MIP-based selective analysis of flavones/flavonoids in wine, the determination of mycotoxins in beverages and analysis of organic contaminants in environment samples will elucidate the perspectives of this technology and will be contrasted with the challenges of rational MIP design providing control on binding site density, receptor capacity and selectivity.
Keywords: Polymers; Flavones; Molecularly imprinted polymer
Alteration of the selectivity of hybridization of immobilized oligonucleotide probes by co-immobilization with charged oligomers of ethylene glycol by Paul A.E. Piunno; James H. Watterson; Christopher C. Kotoris; Ulrich J. Krull (pp. 53-61).
A significant challenge exists in the creation of an environment for immobilized probe oligonucleotides that offer good structural regularity and reproducibility, where nearest neighbour interactions provide for control of selectivity, yet where the degree of hybridization does not alter nearest neighbour interactions. This new work explores whether a “matrix isolation� method will produce the desired environment for the probe molecules. The DNA oligonucleotide probes are polyelectrolytes with charged backbones and significant flexibility. It is possible to isolate the probe molecules by surrounding each, on average, with a sheath of immobilized oligomer that is not based on complementary nucleic acid, yet that is a polyelectrolyte in order to control the surface density and charge within the mixed film. Preliminary work investigates a mixture of dT20 as the probe oligonucleotide, and a 20-mer oligomer primarily containing ethylene glycol phosphate, as a matrix isolation material in a 1:20 mole ratio, respectively. Melt temperature ( Tm) measurements indicate that the thermodynamic stability of the probe molecules can be adjusted using the oligomer matrix to achieve lower Tm values by up to 5°C, with full retention of selectivity for discrimination of single base pair mismatches even under conditions where the probes at a surface are saturated with complementary target.
Keywords: DNA; Fluorescence; Oligonucleotides; Hybridization; Selectivity
Nanoparticle-based optical biosensors for the direct detection of organophosphate chemical warfare agents and pesticides by A.L. Simonian; T.A. Good; S.-S. Wang; J.R. Wild (pp. 69-77).
Neurotoxic organophosphates (OP) have found widespread use in the environment for insect control. In addition, there is the increasing threat of use of OP based chemical warfare agents in both ground based warfare and terrorist attacks. Together, these trends necessitate the development of simple and specific methods for discriminative detection of ultra low quantities of OP neurotoxins. In our previous investigations a new biosensor for the direct detection of organophosphorus neurotoxins was pioneered. In this system, the enzymatic hydrolysis of OP neurotoxins by organophosphate hydrolase (OPH) generated two protons in each hydrolytic turnover through reactions in which P–X bonds are cleaved. The sensitivity of this biosensor was limited due to the potentiometric method of detection. Recently, it was reported that a change in fluorescence properties of a fluorophore in the vicinity of gold nanoparticles might be used for detection of nanomolar concentrations of DNA oligonucleotides. The detection strategy was based on the fact that an enhancement or quenching of fluorescence intensity is a function of the distances between the gold nanoparticle and fluorophore. While these reports have demonstrated the use of nanoparticle-based sensors for the detection of target DNA, we observed that the specificity of enzyme–substrate interactions could be exploited in similar systems. To test the feasibility of this approach, OPH-gold nanoparticle conjugates were prepared, then incubated with a fluorescent enzyme inhibitor or decoy. The fluorescence intensity of the decoy was sensitive to the proximity of the gold nanoparticle, and thus could be used to indicate that the decoy was bound to the OPH. Then different paraoxon concentrations were introduced to the OPH–nanoparticle–conjugate–decoy mixtures, and normalized ratio of fluorescence intensities were measured. The greatest sensitivity to paraoxon was obtained when decoys and OPH–gold nanoparticle conjugates were present at near equimolar levels. The change in fluorescence intensity was correlated with concentration of paraoxon presented in the solution.
Keywords: Organophosphate hydrolase; Enzyme; Biosensor; Paraoxon; Direct detection; Gold nanoparticle; Fluorophore
Effect of solution viscosity on dynamic surface tension detection by Bethany A. Staggemeier; Terry O. Collier; Bryan J. Prazen; Robert E. Synovec (pp. 79-87).
A dynamic surface tension detector (DSTD) was used to examine the molecular diffusion and surface adsorption characteristics of surface-active analytes as a function of solution viscosity. Dynamic surface tension is determined by measuring the differential pressure across the air/liquid interface of repeatedly growing and detaching drops. Continuous surface tension measurement throughout the entire drop growth is achieved for each eluting drop (at a rate of 30drops/min for 2μl drops), providing insight into the kinetic behavior of molecular diffusion and orientation processes at the air/liquid interface. Three-dimensional data are obtained through a calibration procedure previously developed, but extended herein for viscous solutions, with surface tension first converted to surface pressure, which is plotted as a function of elution time axis versus drop time axis. Thus, an analyte that lowers the surface tension results in an increase in surface pressure. The calibration procedure derived for the pressure-based DSTD was successfully extended and implemented in this report to experimentally determine standard surface pressures in solutions of varied viscosity. Analysis of analytes in viscous solution was performed at low analyte concentration, where the observed analyte surface activity indicates that the surface concentration is at or near equilibrium when in a water mobile phase (viscosity of 1.0Cp). Two surface-active analytes, sodium dodecyl sulfate (SDS) and polyethylene glycol (MW 1470g/mol, PEG 1470), were analyzed in solutions ranging from 0 to 60% (v/v) glycerol in water, corresponding to a viscosity range of 1.0–15.0Cp. Finally, the diffusion-limited surface activity of SDS and PEG 1470 were observed in viscous solution, whereby an increase in viscosity resulted in a decreased surface pressure early in drop growth. The dynamic surface pressure results reported for SDS and PEG 1470 are found to correlate with solution viscosity and analyte diffusion coefficient via the Stokes–Einstein equation.
Keywords: Surface activity; Surface tension; Surface pressure; Surfactant; Polymer; Viscosity; Diffusion coefficient
Pressurized liquid extraction using water/isopropanol coupled with solid-phase extraction cleanup for industrial and anthropogenic waste-indicator compounds in sediment by Mark R. Burkhardt; Rhiannon C. ReVello; Steven G. Smith; Steven D. Zaugg (pp. 89-100).
A broad range of organic compounds is recognized as environmentally relevant for their potential adverse effects on human and ecosystem health. This method was developed to better determine the distribution of 61 compounds that are typically associated with industrial and household waste as well as some that are toxic and known (or suspected) for endocrine-disrupting potential extracted from environmental sediment samples. Pressurized liquid extraction (PLE) coupled with solid-phase extraction (SPE) was used to reduce sample preparation time, reduce solvent consumption to one-fifth of that required using dichloromethane-based Soxhlet extraction, and to minimize background interferences for full scan GC/MS analysis. Recoveries from spiked Ottawa sand, commercially available topsoil, and environmental stream sediment, fortified at 4–720μg per compound, averaged 76±13%. Initial method detection limits for single-component compounds ranged from 12.5 to 520μg/kg, based on 25g samples. Results from 103 environmental sediment samples show that 36 out of 61 compounds (59%) were detected in at least one sample with concentrations ranging from 20 to 100,000μg/kg. The most frequently detected compound, beta-sitosterol, a plant sterol, was detected in 87 of the 103 (84.5%) environmental samples with a concentration range 360–100,000μg/kg. Results for a standard reference material using dichloromethane Soxhlet-based extraction are also compared.
Keywords: Pressurized liquid extraction; Solid-phase extraction; Sediment
Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes by Jorge Macanás; Maria Muñoz (pp. 101-108).
Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn2+, Cd2+, Cu2+, Ni2+, Sn2+ and In3+ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn2+ and Cd2+ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.
Keywords: Activated composite membranes; Facilitated transport; Di-(2-ethylhexyl)dithiophosphoric acid; Metal ions; Mass transfer
Development of a class selective immunoassay for the type II pyrethroid insecticides by Sally K. Mak; Guomin Shan; Hu-Jang Lee; Takaho Watanabe; Donald W. Stoutamire; Shirley J. Gee; Bruce D. Hammock (pp. 109-120).
A general and broad class selective enzyme-linked immunosorbent assay was developed for the type II pyrethroid insecticides, such as cypermethrin, deltamethrin, cyhalothrin, cyfluthrin, fenvalerate, esfenvalerate and fluvalinate. Polyclonal antibodies were generated by immunizing with a type II pyrethroid immunogen (( RS)-α-cyano-3-phenoxybenzyl ( RS)- cis,trans-2,2-dimethyl-3-carboxyl-cyclopropanecarboxylate) conjugated with thyroglobulin. Antisera were screened against nine different coating antigens. The antibody–antigen combination with the most selectivity for type II pyrethroids such as cypermethrin was further optimized and tested for tolerance to co-solvent, pH and ionic strength changes. The IC50s of the optimized immunoassay were 78μgl−1 for cypermethrin, 205μgl−1 for cyfluthrin, 120μgl−1 for cyhalothrin, 13μgl−1 for deltamethrin, 6μgl−1 for esfenvalerate, 8μgl−1 for fenvalerate and 123μgl−1 for fluvalinate. No cross-reactivity was measured for the type I pyrethroids such as permethrin, bifenthrin, phenothrin, resmethrin and bioresmethrin. This assay can be used in monitoring studies to distinguish between type I and II pyrethroids.
Keywords: Pyrethroid; Insecticide; Pesticide class; Type II; Immunoassay; ELISA
Speciation of the immediately mobilisable As(III), As(V), MMA and DMA in river sediments by high performance liquid chromatography–hydride generation–atomic fluorescence spectrometry following ultrasonic extraction by A. Huerga; I. Lavilla; C. Bendicho (pp. 121-128).
In this work, a fast method is developed for the speciation of As(III), As(V), MMA and DMA in the immediately mobilisable fraction of river sediments (i.e. water-soluble and phosphate-exchangeable) by high performance liquid chromatography–hydride generation–atomic fluorescence detection (HPLC–HG–AFD) after extraction using focused ultrasound. The influence of relevant parameters influencing an ion-pairing chromatographic separation following isocratic elution (i.e. amount of MeOH in the mobile phase, ion pair reagent concentration, pH, flow rate) was studied. Focused ultrasound transmitted from an ultrasonic probe provided the same extractable contents as conventional extraction with no changes in the species distribution. The effect of the drying step over extraction of As species was investigated. The following drying procedures were compared: freeze-, oven-, microwave- and air-drying. No influence of the drying operation on the water-extractable fraction was observed. However, freeze- and air-drying yielded significantly higher phosphate-extractable amounts of As(III) and As(V) as compared to oven and microwaves. Detection limits for the As species were in the range 1.3–4.1ng/g for the water-soluble fraction and 1.6–4.8ng/g for the phosphate buffer exchangeable fraction. The method was applied to the speciation of immediately mobilisable As(III), As(V), DMA and MMA in 11 sediment samples collected along the beds of the Louro River (southern Galicia, Spain).
Keywords: Easily mobilisable arsenic; Speciation; Ultrasound assisted extraction; River sediment; High performance liquid chromatography; Hydride generation; Atomic fluorescence detection; Drying methods
Electronic tongue for quality assessment of ethanol, vodka and eau-de-vie by A. Legin; A. Rudnitskaya; B. Seleznev; Yu. Vlasov (pp. 129-135).
Rapid quality assessment of alcoholic beverages, including brand identification and detection of products of unacceptable quality or counterfeits is an important practical task. In the present work the multisensor electronic tongue system (ET), based on array of potentiometric chemical sensors was applied to recognition and classification of spirits such as vodka and ethanol used for vodka production and also for eau-de-vie in cognac production. The ET system was capable of detecting presence of contaminant substances in vodka in concentrations exceeding allowed levels as well as of distinguishing vodka complying and not complying with state quality standards. Ten brands of vodka produced at the same distillery using water and ethanol of different purity and various taste additives were discriminated using the instrument. The ET could distinguish synthetic and alimentary grain ethanol as well as alimentary ethanol of different grades (i.e. different degree of purification). A feasibility study was run on several eau-de-vie samples, which included fresh and aged eau-de-vie as well as samples produced using different distillation technology and samples kept in contact with different kinds of oak. The electronic tongue showed a promise as an analytical instrument for rapid quality assessment of spirits.
Keywords: Electronic tongue; Multisensor systems; Recognition; Spirits; Vodka; Eau-de-vie
Development of a Cr(III)-specific potentiometric sensor using Aurin tricarboxylic acid modified silica by Rakesh Kumar Sharma; Ashu Goel (pp. 137-142).
A new chelating resin, Aurin tricarboxylic acid modified silica, was synthesized. The resin behaves as a selective chelating ion exchanger for Cr(III) at a pH 3.8–5.5. A polyvinyl chloride-based membrane electrode of the modified silica has been fabricated and explored as sensor for Cr(III) ions. The membrane works well over the concentration range 7.0×10−6 to 1×10−1M of Cr(III) with a Nernstian slope of 19.0mV per decade of concentration. The response time of the sensor is 10s and it can be used for a period of 5 months. The performance of the sensor is best in the pH range 3.5–6.5 and it also works well in partially non-aqueous medium. The selectivity coefficient values depicts that the membrane exhibits good selectivity over a number of interfering ions. Moreover, the membrane sensor has been applied to analyse the concentration of chromium in certified steel sample and food materials with greater than 97% accuracy.
Keywords: Chromium(III); Aurin tricarboxylic acid modified silica; Membrane sensor
Determination of the rate of production and dissolution of biosilica in marine waters by thermal ionisation mass spectrometry by Rudolph Corvaisier; Paul Tréguer; Charlotte Beucher; Marc Elskens (pp. 149-155).
A new method is described for a precise and simultaneous determination of the rate of production and dissolution of biosilica in marine waters, using isotopic dilution technique. No HF or F2 is required for chemical preparations as the change in isotopic composition is measured on silica producing SiO2− ions. The seawater sample flask is spiked with30Si(OH)4 (<10% of increase in situ concentration) and incubated in in situ conditions. At the end of incubation, changes of the30Si:28Si ratios in particulate and liquid phases are measured by using a thermal ionisation mass spectrometer Finnigan THQ. The relative analytical precision of the isotopic ratio measurements is <0.5%. The limit of detection of the change in isotopic ratio during incubation is 0.02atom%. The overall repeatability determined on eight subsamples (average production: 0.23μMday−1; average dissolution: 0.07μMday−1) is ±0.02 and ±0.01μMday−1 for production and dissolution, respectively. Using mass and isotopic balances of the particulate and dissolved phases in the incubation flask, the best estimates for production and dissolution rates are calculated iteratively. This method was applied to 112 samples of marine waters (production, range: 0.00–2.38μMday−1; dissolution, range: 0.00–1.18μMday−1).
Keywords: Thermal ionisation mass spectrometry; Silica; Silicon isotopes; Marine chemistry
Assessing the non-specific hydroxyl radical scavenging properties of melanoidins in a Fenton-type reaction system by Francisco J. Morales (pp. 171-176).
Soluble high molecular weight fraction (>10kDa, named melanoidins) was isolated from Maillard reaction model systems, coffee, beer and sweet wine by ultrafiltration. Deoxyribose method was adjusted for measuring the hydroxyl radical scavenging properties of melanoidins. The presence of competitive melanoidins with deoxyribose forOH decrease the rate of deoxyribose degradation. Possible interferences to the deoxyribose method have been evaluated. Most of isolated melanoidins exhibited a variable and measurable non-site-specific hydroxyl scavenging activity in a Fenton-type reaction system. The iron reducing properties of melanoidins at the reaction conditions were evaluated with ferrozine. It has established a kinetic approach to assess the second rate constants of hydroxyl radical scavenging reactions of melanoidins. This approach may be a valuable tool for addressing the structure–activity relationships of melanoidins in a future. There is no correlation between browning (absorbance at 420nm) and efficiency for scavenging hydroxyl radicals in solution.
Keywords: Maillard reaction; Melanoidins; Hydroxyl radical; Antioxidant activity