The Rate of the Dehydration of Carbonic Acid and the Effect of Ionic Strength near Neutral pH

1967 ◽  
Vol 20 (1) ◽  
pp. 73-78 ◽  
Author(s):  
E. Magid
Keyword(s):  
Ionic Strength ◽  
Carbonic Acid ◽  
Neutral Ph

Which value for the first dissociation constant of carbonic acid should be used in biological work?

1991 ◽  
Vol 260 (5) ◽  
pp. C1113-C1116 ◽  
Author(s):  
R. W. Putnam ◽  
A. Roos
Keyword(s):  
Ionic Strength ◽  
Activity Coefficient ◽  
Dissociation Constant ◽  
Carbonic Acid ◽  
Mass Action ◽  
Bicarbonate Concentration ◽  
Apparent Dissociation Constant ◽  
Logarithmic Form ◽  
Ion Activity ◽  
Hasselbalch Equation

The apparent first dissociation constant of carbonic acid has been defined in different ways in the literature. Harned and co-workers (8-10) have defined it in terms of molalities of the participating species, including H ions: Ks = mHmHCO3/mCO2. In contrast, Hastings and Sendroy have defined an apparent constant in which acidity is expressed as H ion activity: K'1 = aHmHCO3/mCO2. These constants differ by a factor gamma H, the activity coefficient of H ions at the prevailing ionic strength. Therefore, pK'1 is greater than pKs by an amount equal to -log gamma H, which, at mu = 0.16 M, is approximately 0.1. It is important that the correct value for the apparent dissociation constant or its logarithmic form be entered in the mass action expression or in the Henderson-Hasselbalch equation in order to prevent significant errors in the computation by means of these equations of quantities that cannot be directly measured. Specifically, for the derivation of bicarbonate concentration from PCO2 and pH (-log aH), pK'1 is to be used and not an uncorrected pKs.

On the dissociation of the sheep haemoglobin molecule at neutral pH II. Sedimentation equilibrium measurements

1971 ◽  
Vol 176 (1045) ◽  
pp. 461-480 ◽  
Keyword(s):  
Ionic Strength ◽  
Osmotic Pressure ◽  
High Speed ◽  
Dissociation Constants ◽  
Average Molecular Weight ◽  
Sedimentation Equilibrium ◽  
Neutral Ph ◽  
Haemoglobin Type ◽  
Solvent Control ◽  
Preferential Uptake

The Yphantis method of high-speed sedimentation equilibrium has been used to investigate the dissociation of sheep haemoglobin (type B) at low protein concentration (0.01 to 0.1 g/dl) in both NaCl (buffered and unbuffered) and phosphate buffer solutions at approximately neutral pH, over a range of ionic strength, temperatures of 5 and 25°C being employed. The importance of reliable ‘blank’ solvent control experiments was clearly demonstrated experimentally and weight average molecular weight data were shown to be more reliable than number averages. Apart from work at 25°C and high ionic strengths, the results are compatible with a reversible tetramer-dimer ( α 2 β 2 ⇌ 2 αβ ) dissociation. The dissociation constants obtained showed considerable agreement with those determined by osmotic pressure (reported in the previous paper) for the lower ionic strengths ( I < 1.0), but at 2 mol/l NaCl and 5°C, the sedimentation equilibrium value was 40 % higher. This probably arises through the preferential uptake of water from the high ionic strength solvent, though some dimer-monomer ( αβ ⇌ α + β ) dissociation cannot be completely excluded. On the other hand, in 2 mol/l NaCl at 25°C, the presence of monomeric units was strongly indicated, in conformity with osmotic pressure and other indications. At low NaCl concentrations, the dissociation was not significantly affected by a temperature increase from 5 to 25°C, but in phosphate solutions of comparable ionic strength, significantly less dissociation occurred and an enthalpy increase on dissociation of 55 to 63 kJ/mol was observed.

Preparation of Human Plasminogen Suitable as Substrate for Quantitative Determination of Plasminogen Activators

1966 ◽  
Vol 15 (03/04) ◽  
pp. 511-518
Author(s):  
W Berg ◽  
K Korsan-Bengtsen ◽  
J Ygge
Keyword(s):  
Ionic Strength ◽  
Quantitative Determination ◽  
Spontaneous Activity ◽  
Human Plasma ◽  
Gel Filtration ◽  
Plasminogen Activators ◽  
Simple Method ◽  
Neutral Ph ◽  
Human Plasminogen

SummaryA simple method for preparation of plasminogen with low spontaneous activity and soluble at a neutral pH and at physiological ionic strength is described. Euglobulin made from fresh, oxalated, BaSO4-adsorbed, human plasma was first purified by means of gel filtration on Sephadex G-200. After gel filtration, further purification and concentration was done on DEAE-sephadex A-50. The activity was 100-130 casein units per mg tyrosine.

Stability of NADPH: effect of various factors on the kinetics of degradation.

1986 ◽  
Vol 32 (2) ◽  
pp. 314-319 ◽  
Author(s):  
J T Wu ◽  
L H Wu ◽  
J A Knight
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Degradation Rate ◽  
Neutral Ph ◽  
Degradation Reactions ◽  
Hydronium Ion ◽  
Effects Of Ph ◽  
Reaction Orders ◽  
Kinetics Of Degradation ◽  
Kinetics Of

Abstract Seeking to minimize degradation of NADPH during storage, reagent preparation, and assays, we investigated the effects of pH, temperature, and ionic strength as well as the effects of phosphate and acetate. NADH was also included for comparison. Our results indicate that the rate of degradation of NADPH is proportional most importantly to temperature and concentrations of hydronium ion, but also to concentrations of phosphate and acetate. The degradation rate decreased with increasing ionic strength at neutral pH, but increased slightly at lower pH. NADPH generally is less stable than NADH under the same conditions. The reaction orders with respect to hydronium ion and anions were near 1 for NADH degradation reactions, about 0.5 for NADPH. Rate constants for NADH and NADPH differed more at higher pH and lower phosphate and acetate concentrations.

scholarly journals Characterization of binding of human β2-glycoprotein I to cardiolipin

1995 ◽  
Vol 310 (1) ◽  
pp. 315-321 ◽  
Author(s):  
Z Kertesz ◽  
B B Yu ◽  
A Steinkasserer ◽  
H Haupt ◽  
A Benham ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Factor H ◽  
Cation Binding ◽  
Target Antigen ◽  
Sequence Motif ◽  
Complement Factor ◽  
Neutral Ph ◽  
Linear Sequence ◽  
Glycoprotein I ◽  
Beta 2

beta 2-Glycoprotein I-cardiolipin complexes are reported to be a target antigen for the binding of a subset of anti-phospholipid antibodies. The characteristics of binding of beta 2-glycoprotein I to cardiolipin are reported in this paper. Binding at neutral pH is specific, saturable, dependent on ionic strength and independent of bivalent cation. Binding at low pH is qualitatively different from that at neutral pH, and is not dependent on ionic strength. Denaturation of beta 2-glycoprotein I by heat inactivation and reduction/alkylation indicates that beta 2-glycoprotein I-cardiolipin interaction does not require the native three-dimensional structure of beta 2-glycoprotein I, implying that a linear sequence motif may be responsible. Modification of amino acid residues by KCNO treatment completely destroys binding capacity, indicating crucial involvement of lysine residues in binding of beta 2-glycoprotein I to cardiolipin. Complement factor H, which has some similar highly charged linear sequence motifs to beta 2-glycoprotein I and is composed of the same type of protein module, was found to bind to cardiolipin and inhibit the binding of beta 2-glycoprotein I to cardiolipin. Three different lysine-rich segments of the fifth domain of beta 2-glycoprotein I may be involved in binding to cardiolipin.

scholarly journals Solution and surface effects on plasma fibronectin structure.

1983 ◽  
Vol 97 (6) ◽  
pp. 1686-1692 ◽  
Author(s):  
N M Tooney ◽  
M W Mosesson ◽  
D L Amrani ◽  
J F Hainfeld ◽  
J S Wall
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ionic Strength ◽  
Scanning Transmission Electron Microscopy ◽  
Plasma Fibronectin ◽  
Scanning Transmission Electron ◽  
Neutral Ph ◽  
Transmission Electron ◽  
Freeze Dried ◽  
Scanning Transmission

As assessed by electron microscopy, the reported shape of the plasma fibronectin molecule ranges from that of a compact particle to an elongated, rod-like structure. In this study, we evaluated the effects of solution and surface conditions on fibronectin shape. Freeze-dried, unstained human plasma fibronectin molecules deposited at pH 7.0-7.4 onto carbon films and examined by scanning transmission electron microscopy appeared relatively compact and pleiomorphic, with approximate average dimensions of 24 nm X 16 nm. Negatively stained molecules also had a similar shape but revealed greater detail in that we observed irregular, yarn-like structures. Glutaraldehyde-induced intramolecular cross-linking did not alter the appearance of plasma fibronectin. Molecules deposited at pH 2.8, pH 9.3, or after succinylation were less compact than those deposited at neutral pH. In contrast, fibronectin molecules sprayed onto mica surfaces at pH 7, rotary shadowed, and examined by transmission electron microscopy were elongated and nodular with a contour length of 120-130 nm. Sedimentation velocity experiments and electron microscopic observations indicate that fibronectin unfolds when it is succinylated, when the ionic strength is raised at pH 7, or when the pH is adjusted to 9.3 or 2.8. Greater unfolding is observed at pH 2.8 at low ionic strength (less than 0.01) compared with material at that pH in 0.15 M NaCl solution. We conclude that (a) the shape assumed by the fibronectin molecule can be strongly affected by solution conditions and by deposition onto certain surfaces; and that (b) the images of fibronectin seen by scanning transmission electron microscopy at neutral pH on carbon film are representative of molecules in physiologic solution.

scholarly journals The binding of key fishy off-flavor compounds to silver carp proteins: a thermodynamic analysis

RSC Advances ◽  
2020 ◽  
Vol 10 (19) ◽  
pp. 11292-11299
Author(s):  
Saiqi Gu ◽  
Wangli Dai ◽  
Yunqing Chong ◽  
Fei Lyu ◽  
Xuxia Zhou ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Thermodynamic Analysis ◽  
Silver Carp ◽  
High Ionic Strength ◽  
Flavor Compounds ◽  
Neutral Ph

Myosin was shown to be the primary binding receptor of the four KFOCs and showed the strongest binding under neutral pH and high ionic strength. Its affinity for 1-octen-3-ol was the highest.

Heteroaggregation of micro-polystyrene in the presence of amorphous iron hydroxide (ferrihydrite)

2020 ◽  
Author(s):  
Johanna Schmidtmann ◽  
Georg Papastavrou ◽  
Nicolas Helfricht ◽  
Stefan Peiffer
Keyword(s):  
Ionic Strength ◽  
Zeta Potential ◽  
Iron Hydroxide ◽  
Hydrodynamic Diameter ◽  
Plastic Pollution ◽  
Sem Images ◽  
Ph Values ◽  
Neutral Ph ◽  
Monovalent Ions ◽  
Repulsive Forces

&lt;p&gt;Plastic pollution in the marine and terrestrial environments is ubiquitous and a widespread problem. While the occurrence of plastics and microplastics, as well as their effects on marine and freshwater organisms, have already been investigated in numerous studies, so far only little attention has been paid to the fate, transport, and transformation processes of microplastics in the environment. In this work, the aggregation behavior of polystyrene (PS) microplastics in the presence of ferrihydrite, a natural inorganic colloid, was studied using zeta potential and hydrodynamic diameter measurements, as well as scanning electron microscope (SEM) techniques, considering the influence of pH and ionic strength. An increase of pH led to a more negative surface charge of PS. Furthermore, increasing concentrations of NaCl and CaCl&lt;sub&gt;2&lt;/sub&gt; showed that mono- and divalent cations influence the zeta potential in a different way. Divalent ions compress the electric double layer more efficiently compared to monovalent ions, which resulted in a decrease of repulsive forces. Studies on the heteroaggregation between PS and ferrihydrite showed that the highest aggregation took place at neutral pH values. Aggregate sizes in samples with neutral pH increased significantly compared to more acidic and alkaline pH values. Furthermore, the results indicated that at neutral pH values, ferrihydrite completely covers the PS surface. SEM images and hydrodynamic diameter measurements revealed that the heteroaggregation between PS and ferrihydrite increased with ionic strength. Our results demonstrate that the fate of microplastic particles in aquatic systems can be strongly influenced by natural colloidal water constituents, such as iron hydroxides.&lt;/p&gt;

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