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Low Ionic Strength (low + ionic_strength)
Selected AbstractsSpatial Imaging of Cu2+ -Ion Release by Combining Alternating Current and Underpotential Stripping Mode Scanning Electrochemical MicroscopyELECTROANALYSIS, Issue 2-3 2007Dirk Ruhlig Abstract Anodic underpotential stripping voltammetry was integrated into SECM in order to characterize local corrosion of metallic copper deposits on metal surfaces as a model for copper containing alloys. Primarily, the alternating current mode of SECM was applied in an electrolyte of low ionic strength for localizing possible corrosion sites without any perturbation of the corroding surface, e.g., by the presence of any redox mediator. Sequentially, the release of Cu2+ -ions was confirmed and locally visualized at the previously detected electrochemically active sites by means of spatially resolved anodic underpotential stripping voltammetry performed during SECM scanning. Underpotential stripping voltammetry of Cu2+ -ions was performed at a specifically developed 15,,m gold-coated Pt microelectrode used as SECM tip with a detection limit of 0.15,nM Cu2+ (N=4, RSD=6%) for an accumulation of 45,s at ,0.4,V. SECM images of model samples such as copper coated microelectrodes and lacquered metallic copper workpieces demonstrated the feasibility and applicability of combining AC- and underpotential stripping mode of SECM for local visualization of Cu2+ -ion release from corroding surfaces. [source] Disposable Screen-Printed Edge Band Ultramicroelectrodes for the Determination of Trace Amounts of Nitrite IonELECTROANALYSIS, Issue 10 2006Jen-Lin Chang Abstract The application of linear scan voltammetry for sensitive determination of nitrite by using a disposable screen-printed edge band carbon ultramicroelectrode (designated as SPUME) was reported in this study. The measurement with the SPUME can be performed in solutions of low ionic strength, e.g., natural waters, because the ohmic loses are negligible. The limiting oxidation current of nitrite showed a wide linear range up to 3,mM at the SPUME. A relative standard deviation of 2.46% (n=5) for analyzing 5,,M nitrite indicated a detection limit (S/N=3) of 0.38,,M. Real sample analysis of mineral and ground water samples as well as bratwurst food product showed satisfactory results. Since the SPUME is low cost and easy for mass production, the disposable nature further offers to application in diverse field of electroanalytical chemistry. [source] Effect of water composition on phosphorus concentration in runoff and water-soluble phosphate in two grassland soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2006M. Schärer Summary Many irrigation experiments determine phosphorus (P) losses from soil. Often, these studies cannot be compared, because the irrigation water was not characterized. We used calcium-rich tap water and deionized water to investigate the influence of water composition on P concentrations in induced runoff. We irrigated two grassland sites: one acid and one calcareous. Less P was measured in runoff from tap water irrigation than from deionized water, especially for the acid soil. Batch experiments confirmed the findings of the field experiments. Tap water decreased water-soluble phosphate and increased calcium in the solid phase. This interaction increased with decreasing soil:water ratio. Water of low ionic strength gave results comparable to rainwater. Our findings demonstrate that solution chemistry and the soil:water ratio can strongly influence the availability of P for transport. We recommend that P tests or irrigation experiments should use water resembling that of the system of interest. Irrigation experiments aiming to simulate P losses by surface runoff should be carried out with water having a composition comparable to rainwater. [source] Role of electrostatics in the interaction between plastocyanin and photosystem I of the cyanobacterium Phormidium laminosumFEBS JOURNAL, Issue 23 2002Beatrix G. Schlarb-Ridley The interactions between photosystem I and five charge mutants of plastocyanin from the cyanobacterium Phormidium laminosum were investigated in vitro. The dependence of the overall rate constant of reaction, k2, on ionic strength was investigated using laser flash photolysis. The rate constant of the wild-type reaction increased with ionic strength, indicating repulsion between the reaction partners. Removing a negative charge on plastocyanin (D44A) accelerated the reaction and made it independent of ionic strength; removing a positive charge adjacent to D44 (K53A) had little effect. Neutralizing and inverting the charge on R93 slowed the reaction down and increased the repulsion. Specific effects of MgCl2 were observed for mutants K53A, R93Q and R93E. Thermodynamic analysis of the transition state revealed positive activation entropies, suggesting partial desolvation of the interface in the transition state. In comparison with plants, plastocyanin and photosystem I of Phormidium laminosum react slowly at low ionic strength, whereas the two systems have similar rates in the range of physiological salt concentrations. We conclude that in P. laminosum, in contrast with plants in vitro, hydrophobic interactions are more important than electrostatics for the reactions of plastocyanin, both with photosystem I (this paper) and with cytochrome f[Schlarb-Ridley, B.G., Bendall, D.S. & Howe, C.J. (2002) Biochemistry41, 3279,3285]. We discuss the implications of this conclusion for the divergent evolution of cyanobacterial and plant plastocyanins. [source] Photoinduced intracomplex electron transfer between cytochrome c oxidase and TUPS-modified cytochrome cFEBS JOURNAL, Issue 18 2000Alexander Kotlyar A novel method for initiating intramolecular electron transfer in cytochrome c oxidase is reported. The method is based upon photoreduction of cytochrome c labeled with thiouredopyrene-3,6,8-trisulfonate in complex with cytochrome oxidase. The thiouredopyrene-3,6,8-trisulfonate-labeled cytochrome c was prepared by incubating the thiol reactive form of the dye with yeast iso-1-cytochrome c, containing a single cysteine residue. Laser pulse excitation of a stoichiometrical complex between thiouredopyrene-3,6,8-trisulfonate-cytochrome c and bovine heart cytochrome oxidase at low ionic strength resulted in the reduction of cytochrome c by the excited form of thiouredopyrene-3,6,8-trisulfonate and subsequent intramolecular electron transfer from the reduced cytochrome c to cytochrome oxidase. The maximum efficiency by a single laser pulse resulted in the reduction of ,,17% of cytochrome a, and was achieved only at a 1 : 1 ratio of cytochrome c to cytochrome oxidase. At higher cytochrome c to cytochrome oxidase ratios the heme a reduction was strongly suppressed. [source] Role of Reduced Ionic Strength and Low pH in Gelation of Chicken Breast Muscle ProteinJOURNAL OF FOOD SCIENCE, Issue 1 2005S. Ke And ABSTRACT: Elastic gels with a high moisture content of 88% were prepared at an acidic pH and low ionic strength. The relationship among pH, ionic strength, water-holding capacity, and fold score of gels was investigated. A decrease of pH from 4.1 to 3.7 or below increased gel elasticity and significantly decreased water loss under pressure (P < 0.05). In the presence of sodium chloride, gels made at pH 3.5 to 3.7 had decreased elasticity and increased water loss under pressure. Prior freezing increased the water loss of gels under pressure. Gels made with phosphoric acid and hydrochloric acid lost less water under pressure than those made with citric acid. The percentage loss of water from cylindrical gels was inversely related to the height of the cylinders, suggesting that surface effects were involved. These results suggest that net positive charges on the protein molecules at low pH produced electrostatic repulsion, which was a major driving force for water uptake in the low-salt gels. [source] Protein adsorption kinetics in charged agarose gels: Effect of agarose content and modelingAICHE JOURNAL, Issue 2 2009Emily B. Schirmer Abstract The adsorption kinetics of myoglobin in charged gels of varying agarose content have been measured macroscopically, through batch uptake experiments, and microscopically, using light microscopy with gels supported in microfluidics chips. The apparent effective pore diffusivities, determined by fitting either set of rate data to the shrinking core model, were greater than the free solution diffusivity and concentration-dependent. Moreover, the microscopically derived concentration profiles were qualitatively different from the predicted ones. Therefore, a new model taking into account an assumed favorable partitioning of the protein in the pore liquid is proposed to describe the adsorption kinetics. The new model yields effective pore diffusivities that are in approximate agreement with the values determined chromatographically under nonbinding conditions and with hindered diffusion theory. In addition, it predicts concentration profiles in the gel that are consistent with those observed microscopically. The overall increase in mass transfer is attributed to the favorable partitioning of the protein in the pores at low ionic strength, which results in a greater diffusional driving force. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Turbid flow through a tropical reservoir (Lake Dalrymple, Queensland, Australia): Responses to a summer storm eventLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 4 2000John W. Faithful Abstract The first flood event following a prolonged dry period is described for an impoundment, Lake Dalrymple, in tropical north-eastern Australia. The event, in January 1996, generated substantial flow in the two main inflow sources: the Burdekin River from the north and the Suttor River from the south. Flow through the Burdekin River peaked early and then subsided to a lower level, but flow through the Suttor River persisted at a moderate level for over 15 days after the initial inflow. An extensive water quality survey was conducted on 16 January 1996 (seven days after the initial dam overflow) to determine the nature of the inflows originating from the two major subcatchments feeding the reservoir as they entered and passed through the impoundment. The inflow comprising waters of high turbidity and low conductivity occupied the mid-column region along the two major inflow channels through the impoundment to the dam wall. The suspended particulate material in the form of silt and clay sized particles remained in suspension as the flow passed through the reservoir, due in part to the low ionic strength of the inflow and the relative densities of the inflowing and receiving waters. For both river sources, more than 50% of the total nitrogen and almost all of the total phosphorus were bound to the suspended particulate matter. Much of this was exported in the flow over the spillway. The highly turbid nature of the inflow resulted in strong attenuation of down-welling photosynthetically active radiation (up to maximum attenuation values of 12.24 m,1 in the reservoir where the euphotic depth was only 0.38 m). The irradiance reflectance and the scattering coefficient were considerably higher than any reported for other Australian inland waters. Concentrations of viable chlorophyll a in the surface waters were very low (maximum value 3.4 ,g L,1) because of the highly turbid conditions and extensive dilution by the inflow. The results of this study provide an example of the significant impact a large inflow of turbid, low conductance water can have on a large reservoir in the arid tropics following a prolonged dry period. During inflow events such as the one described in this paper, the reservoir becomes riverine in nature, and large amounts of suspended particulate matter and associated nutrients are transported through the reservoir. [source] Hybridization of short complementary PNAs to G-quadruplex forming oligonucleotides: An electrospray mass spectrometry studyBIOPOLYMERS, Issue 4 2009Jussara Amato Abstract We investigated the interaction of the short peptide nucleic acid (PNA) strand [acccca]-PNA with oligodeoxynucleotides containing one, two, or four tracts of TGGGGT units. Electrospray ionization mass spectrometry allowed exploring the wide variety of complex stoichiometries that were found to coexist in solution. In water, the PNA strand forms short heteroduplexes with the complementary DNA sequences, but higher-order structures are also found, with PNA2n·DNAn triplex units, culminating in precipitation at very low ionic strength. In the presence of ammonium acetate, there is a competition between PNA·DNA heteroduplex formation and DNA G-quadruplex formation. Heteroduplex formation is favored when the PNA + DNA mixture in ammonium acetate is heated and cooled at room temperature, but not if the PNA is added at room temperature to the preformed G-quadruplex. We also found that the short [acccca]-PNA strand binds to G-quadruplexes. © 2008 Wiley Periodicals, Inc. Biopolymers 91: 244,255, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Precipitation diagram and optimization of crystallization conditions at low ionic strength for deglycosylated dye-decolorizing peroxidase from a basidiomyceteACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 8 2005Shinya Saijo The growth of suitably sized protein crystals is essential for protein structure determination by X-ray crystallography. In general, crystals are grown using a trial-and-error method. However, these methods have been modified with the advent of microlitre dispensing-robot technology and of protocols that rapidly screen for crystal nucleation conditions. The use of one such automatic dispenser for mixing protein drops (1.3,2.0,µl in volume) of known concentration and pH with precipitating solutions (ejecting 2.0,µl droplets) containing salt is described here. The results of the experiments are relevant to a crystallization approach based on a two-step procedure: screening for the crystal nucleation step employing robotics followed by optimization of the crystallization conditions using incomplete factorial experimental design. Large crystals have successfully been obtained using quantities as small as 3.52,mg protein. [source] Influence of dT20 and [d(AT)10]2 on Cisplatin Hydrolysis Studied by Two-Dimensional [1H,15N] HMQC NMR SpectroscopyCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2005Jo Vinje Dr. Abstract The influence of the presence of DNA on the kinetics of cisplatin (cis -[PtCl2(NH3)2]) aquation (replacement of Cl, by H2O) and anation (replacement of H2O by Cl,) involved in the hydrolysis of cisplatin have been determined by two-dimensional [1H,15N] HMQC NMR spectroscopy. Single-stranded dT20 and double-stranded [d(AT)10]2 oligonucleotides were used as DNA models, avoiding guanines which are known to react rapidly with aquated cisplatin forms. Reactions starting from cis -[PtCl2(15NH3)2], or from a stoichiometric mixture of cis -[Pt(15NH3)2(H2O)2]2+ and Cl, (all 0.5,mM PtII; in ionic strength, adjusted to 0.095,M or 0.011,M with NaClO4, pH between 3.0 and 4.0) were followed in an NMR tube in both the absence and presence of 0.7,mM dT20 or [d(AT)10]2. In the presence of dT20, we observed a slight and ionic-strength-independent decrease (15,20,%) of the first aquation rate constant, and a more significant decrease of the second anation rate constant. The latter was more important at low ionic strength, and can be explained by efficient condensation of cis -[Pt(15NH3)2(H2O)2]2+ on the surface of single-stranded DNA, in a region depleted of chloride anions. At low ionic strength, we observed an additional set of [1H,15N] HMQC spectral signals indicative of an asymmetric species of PtN2O2 coordination, and we assigned them to phosphate-bound monoadducts of cis -[Pt(15NH3)2(H2O)2]2+. Double-stranded [d(AT)10]2 slowed down the first aquation step also by approximately 15,%; however, we could not determine the influence on the second hydrolysis step because of a significant background reaction with cis -[Pt(NH3)2(H2O)2]2+. [source] Charge Transport in Redox Polyelectrolyte Multilayer Films: The Dramatic Effects of Outmost Layer and Solution Ionic StrengthCHEMPHYSCHEM, Issue 13 2010Dr. Mario Tagliazucchi Abstract The redox switching kinetics, that is, charge transfer and transport in layer-by-layer-deposited electroactive polyelectrolyte multilayers is systematically studied with variable-scan-rate cyclic voltammetry. The experiments are performed with films finished in the redox polycation (an osmium pyridine,bipyridine derivatized polyallylamine, PAH-Os) and the polyanion (polyvinyl sulfonate, PVS), in solutions of different electrolyte concentrations. A modified diffusion model is developed to account for the experimentally observed dependence of the average peak potential with the scan rate. This model is able to describe both the redox peak potential and the current, providing information on the electron-transfer rate constants and the diffusion coefficient for the electron-hopping mechanism. While the former does not vary with the ionic strength or the nature of the outmost layer, polyanion-capped films present an electron-hopping diffusion coefficient at low ionic strength that is three orders of magnitude smaller than that for PAH-Os-capped films. The effect is offset at high ionic strength. We discuss the possible causes of the effect and the important consequences for electrochemical devices built by layer-by-layer self-assembly, such as amperometric biosensors or electrochromic devices. [source] Role of pH and Ionic Strength on Water Relationships in Washed Minced Chicken-breast Muscle GelsJOURNAL OF FOOD SCIENCE, Issue 3 2003H.G. Kristinsson ABSTRACT The relationship between pH, ionic strength, and water balance of chicken-breast muscle gels was investigated. An increase in gel pH (pH 6.4 to 7.4) without added NaCl led to dramatic increases in water-holding capacity and water uptake (P < 0.05). Gels at 150 mM NaCl exhibited less ability to adsorb water than salt-free gels (P < 0.05 at pH 6.8 to 7.4) and had lower water-holding capacities (P < 0.05) and fold scores at and below pH 7. Varying salt concentration of the gel-bathing solutions had dramatic effect on the water uptake of the gels. The results show that strong water-absorbing gels can be produced at low ionic strengths and suggest that the negative charge of the muscle proteins is the driving force for water uptake and retention. [source] | |||||||||||||