Dyes Adsorption onto Fe 3 O 4 ‐Bis(trimethoxysilylpropyl)amine Composite Particles: Effects of pH and Ionic Strength on Electrostatic Interactions

2019 ◽  
Vol 4 (2) ◽  
pp. 617-622 ◽  
Author(s):  
Yaoqiang Hu ◽  
Kexin Li ◽  
Yuting Li ◽  
Haining Liu ◽  
Min Guo ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Electrostatic Interactions ◽  
Composite Particles ◽  
Effects Of Ph ◽  
Dyes Adsorption

scholarly journals The effects of pH and various salts upon the activity of a series of superoxide dismutases

1988 ◽  
Vol 251 (1) ◽  
pp. 41-46 ◽  
Author(s):  
P O'Neill ◽  
S Davies ◽  
E M Fielden ◽  
L Calabrese ◽  
C Capo ◽  
...  
Keyword(s):  
Amino Acid ◽  
Ionic Strength ◽  
Active Site ◽  
Electrostatic Interactions ◽  
Ph Dependence ◽  
Basic Amino Acid ◽  
Amino Acid Sequences ◽  
Superoxide Dismutases ◽  
Mammalian Proteins ◽  
Effects Of Ph

The CuZn superoxide dismutases (SODs) from ox, sheep, pig and yeast were investigated by pulse radiolysis in order to evaluate the role of electrostatic interactions between O2.- and SOD proteins in the mechanism of action of the SOD enzymes. The protein net charge in this series varies, as evaluated by the protein pI values spanning over a large range of pH: 8.0 (sheep), 6.5 (pig), 5.2 (ox) and 4.6 (yeast). The amino acid sequences are largely conserved, with the three mammalian proteins being highly homologous and the yeast protein having some distinct variations in the region surrounding the active site. At pH 8.0 the activities of the SODs from various sources are similar, though the minor differences observed suggest that in the highly homologous mammalian series the most acidic protein is the most enzymically efficient one. The pH-dependences of the various activities in the pH range 7-12 are similar, and the related curves are best fitted by two pK values, which are approx. 9.2 and 11.0 for the mammalian enzymes and 9.1 and 11.4 for the yeast enzyme. The activities of the proteins at I 0.1 are decreased by approx. 20% when compared with the activity at I 0.02 at pH 8.5, whereas at pH above 10 the pH-dependence of the activity approaches that determined at I 0.02 and at pH 11.9 the activity is essentially independent of ionic strength. The dependence upon ionic strength also depends on the salt used, with perchlorate being more effective than phosphate or borate or Mops and still effective at pH above 10.5, where the effect of other salts becomes negligible. The dual and concerted dependence of the activities of different SODs on pH and salt concentration is explained with the encounter of O2.- with the active-site copper being governed by the protonation of two positively charged groups in the vicinity of the active site. The gradient between these localized charges and the rest of the protein may explain the different activities of the mammalian proteins at lower pH. On the basis of the sequence variation of the SODs examined it is not possible to definitely identify these groups. Likely candidates are conserved basic amino acid side chains in the vicinity (less than or equal to 1.2 nm) of the active site, i.e. Lys-134 and Arg-141, but co-ordination of OH- in the first copper co-ordination sphere may be an additional factor accounting for the higher pK.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of pH and Anion Species on Cr(VI) Removal by Magnetite

2011 ◽  
Vol 233-235 ◽  
pp. 1055-1058 ◽  
Author(s):  
Hai Tao Ren ◽  
Shao Yi Jia ◽  
Yong Liu ◽  
Song Hai Wu ◽  
Yong Xu Xing ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Hexavalent Chromium ◽  
Electrostatic Interactions ◽  
Batch Experiments ◽  
Critical Factors ◽  
Initial Concentration ◽  
Effects Of Ph ◽  
Anion Species

Magnetite was prepared to remove poisonous hexavalent chromium [Cr(VI)] from aqueous solution. Batch experiments were conducted to measure the effects on removal of Cr(VI) of different parameters such as ionic strength, pH, and initial concentration. Results demonstrated that the removal of Cr(VI) on magnetite was decreased with the increase of pH in the range of 3.4-5.0, but independent of ionic strength. The removal percentage of Cr(VI) also decreased with the increase of Cr(VI) concentration in the range of 50-200 mg/L. At pH 3.5 and 5.0, the presence of SO42−retarded the removal of Cr(VI) via electrostatic interactions and/or competition for surfaces sites on magnetite. The pH of the medium and presence of anion species were critical factors in the removal of Cr(VI) from aqueous solution.

Effects of pH and ionic strength on the cation exchange capacity of soils with variable charge

Soil Research ◽  
1981 ◽  
Vol 19 (1) ◽  
pp. 93 ◽  
Author(s):  
GP Gillman
Keyword(s):  
Ionic Strength ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Exchange Capacity ◽  
Surface Soils ◽  
Ph Values ◽  
Variable Charge ◽  
Effects Of Ph ◽  
Variable Charge Soils

The cation exchange capacity of six surface soils from north Queensland and Hawaii has been measured over a range of pH values (4-6) and ionic strength values (0.003-0.05). The results show that for variable charge soils, modest changes in electrolyte ionic strength are as important in their effect on caton exchange capacity as are changes in pH values.

Evaluation of effects of pH and ionic strength on colloidal stability of IgG solutions by PEG-induced liquid-liquid phase separation

2016 ◽  
Vol 145 (18) ◽  
pp. 185101 ◽  
Author(s):  
Ronald W. Thompson ◽  
Ramil F. Latypov ◽  
Ying Wang ◽  
Aleksey Lomakin ◽  
Julie A. Meyer ◽  
...  
Keyword(s):  
Phase Separation ◽  
Ionic Strength ◽  
Liquid Phase ◽  
Colloidal Stability ◽  
Liquid Phase Separation ◽  
Effects Of Ph ◽  
Liquid Liquid Phase Separation

Effects of pH, aluminium, and soft water on larvae of the amphibians Bufo bufo and Triturus vulgaris

2006 ◽  
Vol 84 (11) ◽  
pp. 1668-1677 ◽  
Author(s):  
Jon K. Skei ◽  
Dag Dolmen
Keyword(s):  
Ionic Strength ◽  
High Mortality ◽  
Bufo Bufo ◽  
Soft Water ◽  
Internal Environment ◽  
Triturus Vulgaris ◽  
Effects Of Ph ◽  
Low Ionic Strength

Larval Bufo bufo (L., 1758) and Triturus vulgaris (L., 1758) were exposed to soft water (0.5 mg·L–1 Ca2+) experimentally acidified to pH 3.9 to 5.9 and total aluminium concentrations of <10, 150, and 300 µg·L–1. Below pH 4.5 both species experienced increased mortality. The LC50 (168 h) for <10 and 150 µg·L–1 Al was pH 4.3 and 4.1 for B. bufo and 4.2 and 4.1 for T. vulgaris. However, Al3+ increased the survival of both species, which may be due to the contribution of Al3+ to the ionic strength. No B. bufo larvae died at pH >4.5, whereas T. vulgaris at higher Al concentrations suffered relatively high mortality at pH 5.1–5.9, where Al occurs mainly as Al(OH)2+ and Al(OH)2+. Unlike external gills (T. vulgaris), internal gills (B. bufo) have their own internal environment and are probably better protected against the presence of these toxic Al species in the water. These Al species thus seem to be toxic to T. vulgaris larvae but not to B. bufo. Chloride was seen to be important for survival in water of low ionic strength, since the survival of T. vulgaris larvae, particularly at low Al concentration, increased at pH levels down to pH 4.3 when the water was acidified with HCl.

scholarly journals Adsorption of Lysozyme Into a Charged Confining Pore

2021 ◽  
Author(s):  
Sidney Carvalho ◽  
Ralf Metzler ◽  
Andrey Cherstvy ◽  
Daniel Caetano
Keyword(s):  
Electrostatic Interactions ◽  
Active Sites ◽  
Coarse Grained ◽  
Pore Surface ◽  
Solution Ph ◽  
Coarse Grained Model ◽  
Egg White Lysozyme ◽  
Constant Ph ◽  
Pka Shift ◽  
Effects Of Ph

Several applications arise from the confinement of proteins on surfaces since their stability and biological activity are enhanced. It is also known that the way a protein adsorbs on the surface is important for its biological function since its active sites should not be obstructed. In this study, the adsorption properties of hen egg-white Lysozyme, HEWL, into a negatively charged silica pore is examined employing a coarse-grained model and constant-pH Monte Carlo simulations. The role of electrostatic interactions is taken into account when including the Debye-Hueckel potentials into the Ca structure-based model. We evaluate the effects of pH, salt concentration, and pore radius on the protein preferential orientation and spatial distribution of its residues regarding the pore surface. By mapping the residues that stay closer to the pore surface, we find the increase of pH leads to orientational changes of the adsorbed protein when the solution pH gets closer to the HEWL isoelectric point. At these conditions, the pKa shift of these important residues caused by the adsorption into the charged confining surface results in a HEWL charge distribution that stabilizes the adsorption in the observed protein orientation. We compare our observations to the results of pKa shift for HEWL available in the literature and to some experimental data.

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