Protein colloidal electrolyte

Figure 3.1a shows a membrane that is permeable to water and K+ and Cl - ions but impermeable to colloidal electrolytes (polyelectrolytes such as charged proteins). Let a denote the interior of the cell and (3 the extracellular region. In the absence of the poly electrolyte, water, K + and Cl" partition themselves into the two sides such that the chemical potentials of each species are the same inside as well as outside, as thermodynamics would demand. Moreover, the requirement of electroneutrality in both ot and (3 demands that the concentrations of each species K + and CP be the same on either side of the partition. 

Some Properties of Interfacial Films of Colloidal Electrolyte-Protein Complexes... 

Proteins in the body liquids may be considered as a colloidal electrolyte solute in a water solvent. Contact with water is the natural state of a protein. In more or less dry form, a protein powder loses some of its electrolytic character it loses the charged double layer on the surface and behaves electrically very differently from protein with water. Such materials may well be mixed conductors—electronic in the dry state and ionic with water content. Keratin is a more or less dry protein found in the natural state of no longer living biological materials such as hair, nails, and the stratum corneum. The water content of such materials is dependent on the relative humidity of the ambient air. The question of ionic or electronic conductivity in proteins is important, and an electronic conduction mechanism must be considered in many cases. 

We prefer the concept association colloids above other terms — for example colloidal electrolyte — because we want to leave open the possibility that non-electrolytes or undissociated electrolytes form particles with colloidal properties by association. Tlie association of small molecules or ions into micelles seems to us the more characteristic, not the electrolyte character which naturally plays a great part in soap solutions. Indeed particles which owe their character as colloids to their large molecules (for example proteins) also come under the concept of colloidal electrolyte. 

As mentioned in 2.7 unlabeled or not fully labeled colloids are unstable, especially sensitive to electrolytes, therefore an efficient labeling strategy is needed The protein of interest is dissolved in 200 FI of water at 1 mg/ml. Serial dilutions (1 5 to 1 10) of the protein in distilled water are prepared with lOOFl of volume each. 500 FI of the pH-adjusted gold sol is added to each tube, and after 10 minutes 100 FI of 10% NaCl (electrolyte) in distilled water are added. Tubes with stabilized, means sufficiently covered colloids will maintain a red color, unstable gold sol will turn to violet and blue and finally flocculate. The second tube containing more protein than the one whose color changes to blue is sufficiently covered. With the optimal pH and amount for adsorption determined, the protein-colloid solution is prepared in the desired amount. Excess protein is removed by centrifugation, the pelleted colloid particles are re-suspended in a small volume to prepare more concentrated solutions. Often the use of protein concentrators (Centriprep spin columns) is preferred to remove protein and concentrate the colloids. 

Since proteins are colloidal electrolytes, they also played a pivotal role at this Meeting. F.G. Donnan discussed measurements of the electrovalency and osmotic pressure of protein solutions. G.S. Adair of Cambridge applied the theories of J. Willard Gibbs [6] to protein systems. 

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

The fluid portion of the blood, the plasma, accounts for 55 to 60% of total blood volume and is about 90% water. The remaining 10% contains proteins (8%) and other substances (2%) including hormones, enzymes, nutrient molecules, gases, electrolytes, and excretory products. All of these substances are dissolved in the plasma (e.g., oxygen) or are colloidal materials (dispersed solute materials that do not precipitate out, e.g., proteins). The three major plasma proteins include ... 

To eliminate the threat of shock, replenishment of the circulation is essential. With moderate loss of blood, administration of a plasma volume expander may be sufficient Blood plasma consists basically of water, electrolytes, and plasma proteins. However, a plasma substitute need not contain plasma proteins. These can be suitably replaced with macromolecules ( colloids ) that like plasma proteins, (1) do not readily leave the circulation and are poorly filtrable in the renal glomerulus and (2) bind water along with its solutes due to their colloid osmotic properties. In this manner, they will maintain circulatory filling pressure for many hours. On the other hand, volume substitution is only transiently needed and therefore complete elimination of these colloids from the body is clearly desirable. 

PLASMA. The portion of the blood remaining after removal of the white and red cells and the platelets it differs from serum in that it contains fibrinogen, which induces clotting by conversion into fibrin by activity of the enzyme thrombin. Plasma is made up of more than 40 proteins and also contains acids, lipids, and metal ions. It is an amber, opalescent solution in which the proteins are in colloidal suspension and the solutes (electrolytes and nonelectrolytes) are either emulsified or in true solution. The proteins can be separated from each other and from the other solutes by nltrafiltration, nltracentrifugation, electrophoresis, and immuno-chemical techniques. See also Blood. 

Electrolyte-mediated coagulation forms the basis for creating all gold conjugates with other molecules. If macromolecules such as proteins are present in the colloidal suspension as the electrolyte concentration is raised to surpass the negative repulsion effects, then adsorption will occur with the protein molecules instead of with other... 

J.M. Perri, Jr. and F. Hazel, Effect of electrolytes on the foaming capacity of alpha soybean protein dispersions, J. Phys. Colloid Chem. 51 (1947) 661-666. 

The present article was stimulated by the recent experimental data on protein-covered latex colloidal systems immersed in various electrolyte solutions NaCl, NaNC>3, NaSCN and Ca(NOg)2, which showed strong specific anionic effects on the restabilization curves.1 In the opinion of Lopez-Leon et al.,1 the above polarization model for double layer/hydration forces could explain only some of their experiments, but not all of them. However, they assumed that at pH = 10 the adsorption of anions was negligible hence specific anion effects could not be predicted by their association with the positive sites of the surface. Furthermore, at pH = 4 they assumed the... 

It is clear that a perfect agreement with experiment cannot be provided by a theory which ignores the additional interactions between ions, and ions and surfaces, not included in the mean field potential (such as image forces,14 excluded volume effects,15 and ion-dispersion16 or ion-hydration forces17). However, it will be shown that the experimental results reported by Lopez-Leon et al.1 can be more than qualitatively reproduced for uniunivalent electrolytes by the present polarization model for hydration/double layer forces, if one accounts for the association equilibria with the surface sites for all the ions present in the electrolyte (H+, OH , anions, and cations).11 Some additional reasons for the quantitative disagreements, involving the structural modifications of the adsorbed protein layer and the nonuniformity of the colloidal particles, will be also noted. 

As can be inferred, electrophoretic mobility depends on solution ionic strength since double layer thickness decreases with increasing electrolyte concentration. It also depends on the surface charge of the particles. If this charge varies in colloidal particles of similar dimensions then electrophoresis provides a basis for their separation. An example of this is in proteins, where the surface charge varies with pH in a different way according to the protein identity. 

Electrolytic conductance, a property of the so called conductors of the second class, is encountered mainly in the case of salts in dissolved, melted and solid state. Among these compounds are sulphates, halides, nitrates, silicates, also many oxides, hydroxides, sulphides and so on. The same group includes also the potential electrolytes, i. e. the substances from which ions are formed only in mutual reaction with a solvent (solutions of acids in basic solvents, solution of bases in acid solvents, further amines and different chlorine derivatives of organic compounds in liquid sulphur dioxide, nitro-compounds in liquid amines etc.). Finally also numerous colloidal solutions (such as proteins and soaps) conduct the current like electrolytes. 

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