pH Unit Range Research Articles

A low-cost lab-on-a-chip device for marine pH quantification by colorimetry

This paper presents a novel lab-on-a-chip for seawater pH measurement that features in-situ, autonomous, long-term and low-cost measurements. It comprises a poly(dimethylsiloxane) microfluidic system and an integrated low-cost optical-electronic system that uses light emitting diodes as light source and photodiodes as the detectors. The pH measurement is based on the colorimetric method, by optical absorption, using the meta-Cresol Purple (mCP) as indicator dye. Only 9.6 μL of this mCP is needed to perform the pH measurement. Under the developed optimized conditions presented here, e.g., microfluidic channels geometry, indicator dye and seawater volumes, the device has a resolution of 0.002 pH units for the 7.500–8.200 seawater pH units range, with a significantly reduction of the optical path length to 5 mm and a total detection time of about 8 min. The lab-on-a-chip features high sensitivity, linearity and reproducibility. This approach will allow, in the future, the lab-on-a-chip to be moored in a submerged base, located in the depth of the ocean due to its inherent pressure independent operability, in opposition to conventional electrochemical methodologies.

Intramembrane Proton Binding Site Linked to Activation of Bacterial Pentameric Ion Channel

Prokaryotic orthologs of eukaryotic Cys-loop receptor channels recently emerged as structural and mechanistic surrogates to investigate this superfamily of intercellular signaling proteins. Here, we examine proton activation of the prokaryotic ortholog GLIC using patch clamp electrophysiology, mutagenesis, and molecular dynamics (MD) simulations. Whole-cell current recordings from human embryonic kidney (HEK) 293 cells expressing GLIC show half-maximal activation at pH 6, close to the pK(a) of histidine, implicating the three native His residues in proton sensing linked to activation. The mutation H235F abolishes proton activation, H277Y is without effect, and all nine mutations of His-127 prevent expression on the cell surface. In the GLIC crystal structure, His-235 on transmembrane (TM) α-helix 2, hydrogen bonds to the main chain carbonyl oxygen of Ile-259 on TM α-helix 3. MD simulations show that when His-235 is protonated, the hydrogen bond persists, and the channel remains in the open conformation, whereas when His-235 is deprotonated, the hydrogen bond dissociates, and the channel closes. Mutations of the proximal Tyr-263, which also links TM α-helices 2 and 3 via a hydrogen bond, alter proton sensitivity over a 1.5 pH unit range. MD simulations show that mutations of Tyr-263 alter the hydrogen bonding capacity of His-235. The overall findings show that His-235 in the TM region of GLIC is a novel proton binding site linked to channel activation.

The reliability of mire water pH measurements—A standard sampling protocol and implications to ecological theory

Abstract The frequency distributions of mire water pH are often bimodal in data sets covering the poor-rich gradient in vegetation. Area-representative data sets of pH could indicate ecologically meaningful differences between regions, independent of differences in mire classification. Comparisons of pH results are, however, hindered by differences in water sampling methods. We conducted a field survey to assess variation of water pH related to the poor-rich gradient, the water-table-depth gradient, time of day, aeration of samples, and different methods of obtaining water samples. Considerable diurnal and fine-scale vertical and horizontal variation of pH was found in samples obtained by depressing from bryophyte capitula or directly from open water surfaces. A diurnal pattern of lower pH at night and higher at day was found, typically with a 0.5–1.0 pH unit range. Open surface-water samples showed a wide range of fine-scale horizontal variation (pH 4.6–8.0) in Scorpidium-flarks, while pipe-well samples ...

Comparison of chromatography and desiccant silica gels for the adsorption of metal ions—I. adsorption and kinetics

In this study desiccant silica gel (DSG) was compared with chromatography silica gel (CSG) for its ability to remove metal ions including Pb 2+, Cu 2+, Ni 2+, Zn 2+, Cd 2+ and UO 2 2+ from solution. The equilibration time was shorter for UO 2 2+ (less than 1 h) than for the heavy metal ions (2–3 h) and adsorption by DSG took longer to reach equilibrium compared with CSG, probably due to the smaller mean diameter of its pores. The adsorption process showed first order kinetics for all the metals studied. The mass transfer coefficients and overall rate constants were determined for each of the metals. The adsorption rates of the metal ions, in order of decreasing magnitude, were UO 2 2+>Pb 2+>Cu 2+>Zn 2+>Ni 2+>Cd 2+ for both DSG and CSG. Metal uptake was found to increase rapidly within a two pH unit range characteristic for each metal. The adsorption of the metal ions obeyed the Langmuir isotherm and followed the preferential order UO 2 2+>Pb 2+>Cu 2+>Ni 2+>Zn 2+>Cd 2+. Similarity of the isotherms for the individual metals was observed for both DSG and CSG, indicating a comparable removal capacity of DSG and its possible use as an alternative to CSG in adsorption applications. Adsorption from lead(II)–uranium(VI) solutions showed that the uptake of each metal was considerably reduced with an increasing concentration of the other, the adsorption of lead(II) being more strongly influenced by uranium(VI) than vice versa due to the higher affinity of silica gel for the latter.

Energetics of Electron Transfer at the Nanocrystalline Titanium Dioxide Semiconductor/Aqueous Solution Interface: pH Invariance of the Metal-Based Formal Potential of a Representative Surface-Attached Dye Couple

Mediator-based spectroelectrochemical assessment of the metal-centered formal potential (EfRu) of a representative inorganic dye, Ru(4,4‘-(CH2PO3)-2,2‘-bipyridine)310-, bound to a nanocrystalline titanium dioxide film shows that the potential is insensitive to changes in solution pH, despite significant shifts in the conduction band edge energy (ECB) of the underlying semiconductor electrode in response to the same environmental perturbations. The observations are important in the context of recent work showing that back-electron reactivity for the same semiconductor/dye combination is pH independent over a 19 pH unit range, despite apparent changes in back-reaction driving force of greater than 1.2 eV over the same interval (Yan, S.; Hupp, J. T. J. Phys. Chem. 1996, 100, 6867). In particular, the spectroelectrochemical findings serve to rule out a suggested alternative interpretation of the unusual kinetic effects whereby the crucial energy difference quantity, ECB − EfRu, remains fixed because of compen...

Differentiation of tobacco mosaic virus strains by differences in pH of maximum optical density

Oster's turbidimetric technique for determining the pH of maximum aggregation of viruses was used in an attempt to differentiate four wild and nine mutant strains of tobacco mosaic virus. This involved the addition of dilute HCl to salt-free solutions of viruses until the maximum turbidity, as measured by a colorimeter, was reached. The pH values for the 13 strains used in the tests were within 1 pH unit range; those for Type and nine of its mutants were within a 0.22 pH unit range. Results were reproducible within 0.06 pH unit in tests of the same virus sample, at several concentrations, and for different preparations of the same strain. A mixture of viruses behaved like a single strain, giving the same type of turbidity curve with just as sharp a break; however, the pH of maximum turbidity of the mixture was just halfway between those for the separate strains. Thus, such a test does not distinguish a single strain from a mixture. Comparison of differences among strains in rates of movement in Turkish tobacco showed that the pH of maximum turbidity probably is not related to the time required for the virus to move from the inoculated mid-leaf to the top of the plant.