Change In Net Surface Charge Research Articles

Unique myoglobin adaptation to endothermy and flight since the origin of birds.

Myoglobin (Mb) mediates oxygen diffusion and storage in muscle tissue and thus is important for the energy utilization and activity of animals. Birds generally have a high body temperature, and most species also possess the capability of powered flight. Both of these require high levels of aerobic metabolism. Within endothermic mammals, bats also independently evolved flight. Although the functional evolution of myoglobins in deep-diving amniote vertebrates has been well-studied, the functional evolution of myoglobin since the origins of both birds and bats is unclear. Here, with Mb-coding sequences from >200 extant amniote species, we reconstructed ancestral sequences to estimate the functional properties of myoglobin through amniote evolution. A dramatic change in net surface charge on myoglobin occurred during the origin of Aves, which might have been driven by positively selected amino acid substitutions that occurred on the lineage leading to all birds. However, in bats, no change in net surface charge occurred and instead, the Mb genes show evidence of strong purifying selection. The increased net surface charge on bird myoglobins implies an adaptation to flight-related endothermic and higher body temperatures, possibly by reducing harmful protein aggregations. Different from the findings of net surface charge, myoglobins of extant birds show lower stability compared with other amniotes, which probably accelerates the rate of oxygen utilization in muscles. In bats and other mammals, higher stability of Mb may be an alternative pathway for adaptation to endothermy, indicating divergent evolution of myoglobin in birds and bats.

The role of surface charge and pH changes in tropical soils on sorption behaviour of per- and polyfluoroalkyl substances (PFASs)

This study investigated the effect of surface charge on the sorption of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexane sulfonic acid (PFHxS) onto 7 tropical soils as a function of pH. The net surface charge became less negative with decreasing pH (from 7.5 to 3.5) in all soils. The rate of change in net surface charge varied from −0.6 to −2.8 (cmol/kg)/pH unit. The effect on sorption behaviour of PFASs was variable among soils. For two soils, the average sorption increased 54- and 45-fold for PFOS, 33- and 9-fold for PFOA, and 39- and 400-fold for PFHxS, across the pH range 7.5 to 3.5. Sorption in another sandier soil showed negligible change with decreasing pH. Sorption in the other soils did not change significantly until the pH decreased to approximately 5.5. The soils with high contents of sesquioxides (Fe and Al oxides) showed the most marked increase in sorption with decreasing pH. This study demonstrated that in addition to hydrophobic interactions with OC and other processes, electrostatic interactions are also important in the sorption process for these chemicals in soils. In acidic, variably charged tropical soils there is the possibility that any PFOS, PFOA or PFHxS sorbed to the soils may become desorbed if management practices (e.g. liming) raised soil pH.

Dependence of interfacial properties of p-Cu2O/electrolyte and p-Cu2O/Au junctions on the electrodeposition bath pH of p-Cu2O films

Improvements in electrodeposited cuprous oxide (Cu2O) junction devices could contribute to development of a wider range of affordable and environmentally friendly electronic devices. In this regard, ability of controlling interfacial properties of contacts of Cu2O thin films with other suitable materials will be a very important property. A study on interfacial properties of p-Cu2O/Au and p-Cu2O/electrolyte junctions was conducted using capacitance-voltage and current-voltage measurements. It was found that pH of p-Cu2O film deposition bath has a significant effect on junction properties of Cu2O. Particularly, flat band potential at p-Cu2O/electrolyte interface and built-in potential at p-Cu2O/Au interface were shifted positively by the increase of deposition bath pH of p-Cu2O films. Also, it was revealed that the shift was more pronounce at p-Cu2O/Au interface compared to that at p-Cu2O/electrolyte interface. The observed shifts in flat band potential and built in potentials were correlated with the shifts in relative band edge positions at the interfaces and with the change in net surface charge on the interfacial layers. It was observed, for the first time, that built in potential at p-Cu2O/Au junction can be controlled with bath pH of p-Cu2O films so that the junction can make either ohmic or non ohmic. Further, it was found that surface modification of p-Cu2O films with sulphidation reduces barrier height at p-Cu2O/Au junction and make the contact ohmic irrespective of bath pH of p-Cu2O films. We report here, for the first time, that relative band edge position at interfaces of electrodeposited p-Cu2O junctions can be controlled with pH of film deposition bath and surface modification. This will be very useful in application of electrodeposited p-Cu2O thin films in solar cells and other junction devices.

Partial oxidation of step-bound water leads to anomalous pH effects on metal electrode step-edges.

The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. Here, we analyze the change in charge and free energies upon adsorption using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (Hupd) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes.

Thermochemical Treatment (Thermolysis) of Petrochemical Wastewater: COD Removal Mechanism and Floc Formation

Thermo-chemical precipitation (thermolysis) has been used as a pretreatment method for COD and color reduction from various industrial effluents. This paper reports on the COD reduction from purified terephthalic acid (PTA) wastewater from a petrochemical plant using thermolysis. CuSO4, FeCl3, and FeSO4 were used as chemicals/coagulants for COD reduction. The effect of treatment time, temperature, pH, and chemical dosage on the removal of COD has been studied. FeCl3 was found to be the most effective chemical agent which removed 77.2% COD (from initial COD of 3320 to 765.9 mg/L) at optimum treatment conditions (pH 7, dosage 3 kg/m3 (0.018M), temperature 50 °C, and treatment time 20 min). Temperature played an important role in COD removal. Zeta potential studies depict the change in net surface charge of the particles in all the systems. In the case of CuSO4·5H2O, floc size distribution (number density) shows that bigger flocs were formed at higher temperatures. With iron salts, a decrease in floc size wa...

AlGaN/GaN high electron mobility transistor structures for pressure and pH sensing

Nitride High Electron Mobility Transistor(HEMT) structures are excellent candidates for polar liquid detectors, pressure sensors and piezoelectric-related applications. The changes in conductance of the channel of AlGaN/GaN high electron mobility transistor structures during application of both tensile and compressive strain are reported. For fixed Al mole fraction, the changes in conductance were roughly linear over the range up to 2.7 × 108 N.cm–2 , with coefficients for planar devices of –6.0 +/–2.5 × 10–10 S.N–1 m–2 for tensile strain and +9.5+/–3.5 × 10–10 S.N–1m–2 for compressive strain . The large changes in conductance demonstrate that simple AlGaN/GaN heterostructures are promising for pressure and strain sensor applications. A gateless HEMT structure was also used for sensing different liquids present in the gate region. The forward current showed significant decreases upon exposure of the gate area to solvents (water, acetone) or acids (HCl). Milli ampere changes in the source-drain current are observed relative to the value measured in air ambient .The pH sensitivity is due to changes in net surface charge that affects the relative depletion in the channel of the transistor. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

AlGaN/GaN HEMT based liquid sensors

An AlGaN/GaN high electron mobility transistor structure was used for sensing different liquids present in the gate region. The forward current showed significant decreases upon exposure of the gate area to solvents (water, acetone) or acids (HCl). The pH sensitivity is due to changes in net surface charge that affects the relative depletion in the channel of the transistor. The results indicate that nitride-based heterostructures may have application in integrated chemical, gas and fluid monitoring sensors.

Proteins associated with untransformed estrogen receptor in vitro. Perturbation of hydrophobic interactions induces alterations in quaternary structure and exposure of the DNA-binding site.

Estrogen receptors from calf uteri have been analyzed by high-performance size-exclusion chromatography, chromatofocusing, and DNA affinity chromatography using conditions designed to evaluate the relative contribution of hydrophobic interactions between the steroid-binding subunit and other receptor-associated proteins. The single large (untransformed) species of soluble estrogen-receptor consistently (n = 9) found in calf uteri displayed a rapid change in Stokes radius from 8.0 to 3.5 nm upon exposure to elevated ionic strengths (0.4 M KCl). However, equilibration of the estrogen-receptor complex into urea (up to 6 M) did not dissociate the untransformed receptor into the 3.5-nm receptor form (subunit) observed in hypertonic (0.4 M KCl) buffers. Exposure to 6 M urea did result in conversion of the untransformed receptor (8.0 nm) to a 6.0-6.5-nm receptor form not previously observed in either hypotonic or hypertonic buffers. In the presence of both 6 M urea and 0.4 M KCl, the untransformed estrogen-receptor complex was converted to a smaller receptor form intermediate in apparent size (4.5-5.0 nm) to that observed in 6 M urea or 0.4 M KCl alone. The formation of this 4.5-5.0-nm receptor form was partially estrogen dependent as determined by parallel analyses of unliganded receptor in urea/KCl buffer. The urea-induced change in apparent size (8 nm to 6.0-6.5 nm) at low ionic strength was accompanied by little or no detectable change in net surface charge as determined by chromatofocusing but a complete exposure of the DNA-binding site as evidenced by nearly quantitative interaction with DNA-agarose.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of negative charge in spontaneous aggregation of transformed and untransformed cell lines.

No correlation between net negative surface charge as determined by electrophoretic light-scattering techniques and the rates of spontaneous aggregation of 3T3MIT and SVPy 3T3MIT cells has been found. Neuraminidase treatment of both 3T3MIT cells and SVPy 3T3MIT cells causes a significant decrease in electrophoretic mobility but only the 3T3MIT cells show an increase in spontaneous aggregation. An increase in spontaneous aggregation of 3T3MIT cells is seen after growth in 200 mM urea for 18 h but no change in net surface charge occurs. The distribution of anionic sites on the membranes of cells was determined using the ultrastructural marker polycationized ferritin. The distribution of polycationized ferritin-binding sites was essentially identical for both cell lines under all conditions when they were labelled at 4 degrees C. When the cells were labelled with polycationized ferritin at 37 degrees C it was found that cells which have a high net rate of spontaneous aggregation also show rearrangement of anionic sites on their surface membrane. Clustering and rearrangement of anionic sites at 37 degrees C correlate with high rates of spontaneous aggregation.

Abnormal leukocyte electrophoretic mobility in myotonic dystrophy

Electrophoretic mobility of polymorphonuclear leukocytes (PMNs) was studied in 10 patients with myotonic dystrophy. The mobility of patients' PMNs differed significantly from that of controls. Following incubation with bacterial chemotactic factor the PMNs from patients showed significantly less change in net surface charge compared to that in controls. Our data support a leukocyte membrane defect in myotonic dystrophy.

Changes in net surface charge of hydrous alumina with phosphate adsorption

ADSORPTION of phosphate on hydrous metal oxides is of considerable importance in soil fertility and eutrophication studies. Phosphate is known to be adsorbed on the hydrous oxides displacing aquo (M–OH2) and hydroxo (M–OH) ligands; its adsorption makes the oxide surface less positive1–3. I report here on a quantitative study in which phosphate was adsorbed on to hydrous oxides, displacing the ligands, and the simultaneous change in the net surface charge was measured.

On the surface coat and flagellar adhesion in trypanosomes.

ABSTRACT Pathogenic trypanosomes in their bloodstream phase have a smooth and compact coat 12–15 nm thick enveloping the entire surface membrane of the body and flagellum. In the sleeping-sickness trypanosome Trypanosoma rhodesiense this coat is absent from the stages of development in the midgut of the tsetse-fly vector and from their counterparts obtained by cultivation of the trypanosome in vitro. In the salivary glands of the vector, however, the coat is reacquired as the trypanosomes transform from epimastigote forms into the metacyclic stage which is infective to the mammalian host. This loss and acquisition of the surface coat can be correlated with the cyclical changes in net surface charge on the trypanosome which have been observed by other workers. The trypanosome populations of successive relapses in- the blood are known to differ in their surface antigens (agglutinogens) and the loss of antigenic identity detected when any of these populations are put into culture indicates that these variable antigens are located in the surface coat. It is suggested that the coat in bloodstream trypanosomes constitutes a replaceable surface which, after being replaced, enables the trypanosome to escape the effects of host antibodies. The coat is therefore an adaptation to life in the bloodstream. Reacquisition of the surface coat by the metacyclic trypanosome after development in the vector may reflect reversion to a ‘basic’ antigenic type at this stage, preparatory to invading the blood of the mammalian host. The surface coat may be removed by the wide-spectrum proteolytic enzyme pronase, and this fact together with evidence from pH/mobility relationships and chemical analysis of the variable antigens suggest that the coat is basically proteinaceous. The coat may facilitate pinocytosis by binding proteins at sites within the pocket surrounding the base of the flagellum. In the non-pathogenic trypanosome T. lewisi a more diffuse filamentous coat is present in bloodstream forms and absent from culture forms. This trypanosome is said to carry a negative charge in both bloodstream and culture phases, so it seems likely that the nature of the coat in T. lewisi is different from that found in the pathogenic trypanosomes. In all these trypanosomes the flagellar membrane adheres to the surface membrane of the body throughout the life-cycle. Along the zone of adhesion lies a regular row of junctional complexes of the macula adherens type which, it is argued, serve in attachment. These attachments persist regardless of changes in the intervening cell surfaces.

Reaction of detergents with Amoeba proteus.

Amoeba proteus moves by the formation of pseudopodia in the direction of travel, and the formation of new pseudopodia may be induced by small local concentrations of some proteins and cationic detergents which are believed to react with anionic groups on the cell surface and lower the surface charge1,2. The importance of changes in net surface charge in providing a mechanism for cell surface transformations has also been emphasized by other workers3. Staining reactions with alcian blue and with toluidine blue show that the surface coat of amoebae is probably composed of negatively charged polysaccharides or mucopolysaccharides4. The haemolytic properties of detergents are well known and, for a series of 12-carbon detergents, are consistent with a reaction involving penetration of a lipid film5. If the mechanism which we have proposed to account for pseudopodium induction by these compounds is correct2, then the lysis of A. proteus by detergents should depend on their reactivity with negatively charged groups on the surface polysaccharide rather than on their ability to penetrate a lipid film.