Bubble rise velocities and drag coefficients in non-Newtonian polysaccharide solutions.

Microbially produced polysaccharides have properties which are extremely useful in different applications. Polysaccharide producing fermentations start with liquid broths having Newtonian rheology and end as highly viscous non-Newtonian solutions. Since aerobic microorganisms are used to produce these polysaccharides, it is of great importance to know the mass transfer rate of oxygen from a rising air bubble to the liquid phase, where the microorganisms need the oxygen to grow. One of the most important parameters determining the oxygen transfer rate is the terminal rise velocity of air bubble. The dynamics of the rise of air bubbles in the aqueous solutions of different, mostly microbially produced polysaccharides was studied in this work. Solutions with a wide variety of polysaccharide concentrations and rheological properties were studied. The bubble sizes varied between 0.01 mm3 and 10 cm3. The terminal rise velocities as a function of air bubble volume were studied for 21 different polysaccharide solutions with different rheological properties. It was found that the terminal velocities reached a plateau at higher bubble volumes, and the value of the plateau was nearly constant, between 23 and 27 cm/s, for all solutions studied. The data were analyzed to produce the functional relationship between the drag coefficient and Reynolds number (drag curves). It was found out that all the experimental data obtained from 21 polysaccharide solutions (431 experimental points), can be represented by a new single drag curve. At low values of Reynolds numbers, below 1.0, this curve could be described by the modofoed Hadamard-Rybczynski model, while at Re > 60 the drag coefficient was a constant, equal to 0.95. The latter finding is similar to that observed for bubble rise in Newtonian liquids which was explained on the basis of the "solid bubble" approach.     

Virial coefficients of protein solutions

An osmometer capable of measuring protein osmotic pressures up to 100 cms. of mercury pressure has been described. The principle of the osmometer is to set a given pressure and to permit the protein concentration to equilibrate with the pressure. The higher virial osmotic coefficients of egg albumin in various electrolytes and in 1 m urea as well as a function of NaCl concentration are reported. The virial coefficients of bovine serum albumin and of bovine methemoglobin in 1 m NaCl are also given. It appears that the primary cause for the departure of the osmotic pressure from ideality is due to the covolumes of the proteins.     

Generalized concentration dependence of globular protein self-diffusion coefficients in aqueous solutions.

The self-diffusion coefficients of globular proteins (myoglobin, bovine serum albumin, barstar, lysozyme) in aqueous solutions at different temperatures and pH values are obtained by pulsed-gradient spin-echo NMR, and their concentration dependence is analyzed. The generalized concentration dependence of globular protein self-diffusion coefficients is empirically established, and compared to the concentration dependence of diffusion coefficients of flexible polymers and rigid Brownian particles.     

Activity coefficients of salts in highly concentrated protein solutions. II. Potassium salts in isoionic bovine serum albumin solutions

Mean activity coefficients of different potassium salts KX (X = F-, Cl-, Br-, I-, NO3-, SCN-) have been measured in concentrated isoionic bovine serum albumin (BSA) solutions, by use of the EMF method with ion-exchange membrane electrodes. These solutions may be regarded as simple model systems for the cytoplasm of living cells as far as the influence of the macromolecular component on the activity coefficients of the salts is concerned. Two series of measurements have been carried out: (a) varying the amount of salt from 0.01 to 0.5 molal and maintaining the BSA concentration constant at 20 wt% and (b) varying the protein concentration up to 25 wt% and keeping the salt concentration constant at 0.1 molal. For all salts studied, the mean activity coefficients in the protein-salt solutions increase as the salt concentration rises, when the protein concentration is maintained constant. In the series of measurements (b) the activity coefficients of all salts change linearly with the protein concentration. Marked qualitative differences, however, were observed depending on the anion species, which could be interpreted in terms of specific ion binding of X- to the protein molecule. By taking into account BSA-bound 'non-solvent' water, the results were analyzed in terms of numbers of anions bound per BSA molecule. Comparison with the results of Scatchard, obtained at low protein concentrations, showed only a very small electrostatic effect of the BSA-(X-)v polyions on the activity coefficient of the salts at higher protein and salt concentrations.     

Biological ion exchanger resins. VII. Counter-ion activity coefficients in solutions of biological polyelectrolytes.

The single ion activity coefficients of K+ and Cl- counter-ions were determined in concentrated polyelectrolyte solutions. The polyelectrolytes investigated included DNA and several proteins. Results indicate that ion gradients of up to 40:1 do not lower the counter-ion activity coefficient below 0.5. Thus, published values of the intracellular activity coefficient of K+ are not incompatible with cellular models utilizing cytoplasmic ion exchange.     

Activity coefficients of KCl in highly concentrated protein solutions

As a contribution to the understanding of the thermodynamic state of single salts in living systems, the activity coefficients of KCl were determined in concentrated bovine serum albumin (BSA) solutions. The concentration range studied was 0.01 to 0.5 M KCl and zero to 18% wt BSA, thus amply covering physiological conditions. The activity coefficients of the salt were measured using the EMF method with ion exchange membrane electrodes. Keeping the salt concentration constant, the activity coefficients of the salt decrease linearly with protein concentration, the effect being more pronounced for low salt content. The maximal deviations of the activity coefficients with respect to those in pure salt solution amount to ca. 40% for 0.01 M KCl and 18% wt BSA. The results were interpreted on the assumption of the superposition of three effects i.e. water bound to BSA molecules as non-solvent water, specific Cl^– ion binding and the electrostatic interactions of the polyions with the salt ions. In view of the results it can be concluded that only a small portion of simple intracellular ions are bound, based on the assumption that the cytoplasm of living cells may be regarded as a concentrated protein-salt solution.     

Retention of trypsin and chymotrypsin proteolytic activity in sodium dodecyl sulfate solutions.

The catalytic activity of trypsin and chymotrypsin is sufficiently resistant to denaturation by solutions containing 1% SDS to result in serious alterations in SDS-polyacrylamide-gel electrophoretic profiles. This resistance to denaturation is apparently enhanced by the presence of macromolecular substrate. Heating at 100°C in 1% SDS for 5 min completely abolishes proteolytic activity.     

Activity coefficients of salts in highly concentrated protein solutions: I. Alkali chlorides in isoionic bovine serum albumin solutions

In order to understand the thermodynamic state of simple salts in living cells, the mean activity coefficients of LiCl, NaCl, KC1, RbCl, CsCl were determined in concentrated isoionic bovine serum albumin (BSA) solutions by use of the EMF method with ion exchange membrane electrodes. The protein concentration range extended up to 22 wt %, whereas the salt concentration was kept constant at 0.1 mole per kilogram water. These solutions may be regarded as crude but appropriate model systems for the cytoplasm of cells as far as type and magnitude of the macromolecular component influence on the chemical potential of the salts is concerned. The mean stoichiometric activity coefficients of the alkali chlorides in the isoionic BSA solutions decreased linearly with the protein molality; this decrease, however, did not exceed ca. 10% compared with the pure 0.1 molal salt solutions. Only very small differences in the behaviour of the different alkali chlorides were observed. The results may be interpreted by the superposition of the effects of specific Cl^? ion binding to BSA and BSA bound “non-solvent” water with probably electrostatic long range interactions of the BSA(Cl^?)_v polyions with the salt ions in solution. The resulting mean activity coefficients, corrected for ion binding and non-solvent water, showed a very slight linear dependence on the protein concentration. The departure from the value in the pure 0.1 molal salt solutions did not exceed ± 2%.     

Activity coefficients of counterions in solutions of diethylaminoethyl dextran hydrochloride

Activity coefficients of counterions in solutions of diethylaminoethyl dextran hydrochloride have been determined. It has been observed that they increase with decreasing concentration of the polyelectrolyte. The experimental values have been compared with those calculated using Oosawa's theory of activity coefficients. The calculated values are higher than those observed, which suggests that the rodlike model on which Oosawa's theory is based is inadequate for the present case. Activity coefficients of counterions of some solutions containing NaCl and KC1, respectively, have also been determined. It has been found that the additivity rule for activity of counterions applies for these solutions.     

Haemolysis of various mammalian erythrocytes in sodium chloride, glucose and phosphate-buffer solutions.

Mouse, rat, rabbit, hamster, cow, pig, sheep, guinea-pig, dog and human erythrocytes were studied. A 0.9% or stronger solution of sodium chloride completely prevented haemolysis; sheep and pig erythrocytes appeared the more fragile, while human and dog erythrocytes were not haemolized in concentrations of 0.4% or more. Haemolysis of human, rabbit, cow, hamster, guineapig, pig and sheep erythrocytes was not observed in solutions of 0.4% or more of glucose. Except for sheep, human and dog erythrocytes, haemolysis was depressed in rate but not completely prevented by phosphate-buffer solution of pH 7.0.     

Self-association of sodium cholate in isotonic saline solutions

The self-association of dialyzed solutions of sodium cholate in isotonic saline solutions has been studied by vapor pressure osmometry and sedimentation equilibrium. These studies were carried out at 25, 31 and 37 degrees C. In all experiments the self-association could be described as a two-equilibrium constant, indefinite self-association in which odd species beyond monomer were absent. The plots of M1/Mna or M1/Mwa vs. c were quite smooth with no sharp breaks; this suggested that there were no critical phenomena. The temperature dependence of the self-association was quite small. Our results are in accord with other studies on sodium cholate which indicate that the self-association involves several species, and that it is not a monomer-n-mer self-association.