Isoelectric temperature

Surface potential (()s as a function of temperature and kink site density when impurities are allowed to redistribute to their equilibrium distribution. The parameters chosen were impurity concentration C = 10 ppm, B = 0.3 eV, AG = 0.47 - 7.7 kT (= W4. ), AGp = 1.4 - 9.4 kT and have set equal to AGyC W. ). Note that the isoelectric temperature does not vary with the density of available surface sites. 

The swelling of gels is markedly affected by the presence of electrolytes, this effect being a minimum at the isoelectric point of the material. In general, sulphates, tartrates, etc. inhibit swelling, while iodides and thiocyanates promote the swelling. Thus gelatine disperses completely in iodide solution even at low temperatures. 

Sodium Poly(4-styrene sulfonate). The sol—gel processing of TMOS in the presence of sodium poly-4-styrene sulfonate (NaPSS) has been used to synthesize inorganic—organic amorphous complexes (61). These sodium siUcate materials were then isotherm ally crystallized. The processing pH, with respect to the isoelectric point of amorphous siUca, was shown to influence the morphology of the initial gel stmctures. Using x-ray diffraction, the crystallization temperatures were monitored and were found to depend on these initial microstmctures. This was explained in terms of the electrostatic interaction between the evolving siUcate stmctures and the NaPSS prior to heat treatment at elevated temperatures. 

Water-soluble polymers and polyelectrolytes (e.g., polyethylene glycol, polyethylene imine polyacrylic acid) have been used success-hilly in protein precipitations, and there has been some success in affinity precipitations wherein appropriate ligands attached to polymers can couple with the target proteins to enhance their aggregation. Protein precipitation can also be achieved using pH adjustment, since proteins generally exhibit their lowest solubility at their isoelectric point. Temperature variations at constant salt concentration allow for frac tional precipitation of proteins. 

Thermally stable AI2O3 was synthesized as in ref. 5, by hydrolysis of A1 isopropoxide (99.99+% Aldrich Chemicals) dissolved in 2-methylpentane-2,4-diol. The resulting solid was filtered, washed in 2-propanol, and dried in air at 373 K. Then, it was calcined in flowing dry air, while the temperature was raised at 1 K/min to 733 K, when 2.4% HjO was introduced to the flowing air. Afterwards, the temperature ramp was continued to 973 K. The sample was kept at 973 K for 2 h in 7% water. The isoelectric point of the resulting y-Al Oj was pH 8. The BET surface areas were 205 to 235 mVg, and the average pore size radius was around 8.3 nm... 

One solution-based approach that works for gold catalysts, in that it produces highly active catalysts, is the deposition-precipitation (DP) method [8]. The DP method entails adjusting the pH, temperature, and gold concentration of an HAUCI4 solution to form a gold hydroxide species which is then deposited onto the support material [8]. This catalyst precursor is washed, dried, and annealed to form small (<5nm) catalyst particles [9]. The DP method has a number of limitations for example, DP cannot produce Au particles with diameters less than 5 nm on support materials with low-isoelectric points (lEPs) like SiOz and WO3 [5,10,11]. 

The number of binding sites can be determined in this model by a plot of d Ink /dlnm at constant temperature, pH, and ion valency. To do that, it may be assumed that dlny /dlnm is approximately zero. The actual value is -0.04 for 0.1 to 0.5 M sodium chloride and less at lower concentrations. To a first approximation, the stoichiometry of water molecules released by binding protein could be determined from the slope of the plot of dink /dlnm vs. m. However, especially at low salt concentration and near the isoelectric point, the slope of such plots is nonlinear. The nonlinearity may be due to hydrophobic interaction between stationary phase and protein or a large change of ionic hydration on binding.34... 

FIGURE 12 Application of capillary isoelectric focusing (clEF) for the determination of apparent p/ values of rMAb samples. Capillary Bio-Rad Bio-CAP XL capillary (50 pm x 24 cm) ampholyte 80% clEF Bio-Lyte Ampholyte 3-10 (2% solution with 0.5% TEMED, 0.2% HPMC) anolyte 20 mM phosphoric acid catholyte 40 mM sodium hydroxide focusing l5kV (625V/cm) for 5 min mobilization 20 kV (833V/cm) for 25 min with zwitterions (cathodic mobilizer from Bio-Rad) capillary temperature 25°C. (Reprinted from reference 40, with permission.)... 

As described in the previous section, this strain produced significant amounts of three extracellular P-mannanases and a cell-associated P-mannosidase. The three P-mannanases differed in several enzymatic properties including optimum pH for enzyme action, optimum temperature, pH stability, thermal stability, isoelectric point and molecular weight. To elucidate the genetic basis for production of multiple forms,... 

In the first step, 2.2 g of the ethanol-precipitated solid were dissolved in 55 mL of 0.05M sodium phosphate buffer at pH 7.3, the undissolved residue was removed by centrifugation, and the supernatant was added to a 50-mm i.d., 180-mm long DEAE-cellulose column held at room temperature and eluted with 3.33 mL/min of the same buffer. Since the isoelectric point of the desired xylanase was above the buffer pH, it passed through the column without being retarded, and contaminating protein was removed. 

The quantity [k T] is approximately 4 10-14 erg at ordinary room temperature (25°C), and [k T/e] = 25 mV. The magnitude of nel can be estimated from monolayer studies at varying pH. At the isoelectric pH, the magnitude of nel will be zero (Birdi, 1989). These IT versus A isotherms data at varying pH subphase have been used to estimate nel in different monolayers. 

Figure 1. Analytical isoelectric focusing of cellulases from Trichodtrma ree-sei. Detection of CBH I and EG I activities using MeUmbLac, in the absence (A) and presence (B) of 10 mM cellobiose. Lane 1, EG I lane 2, EG I (iso-components) lane 3, CBH I (pi 3.9 component) lane 4, EG I-CBH I mixture). Gels were flooded with the fluorogenic substrate (pH 5.0) and after 5-10 min (room temperature) photographed (Polaroid 57, green filter) on a long wavelength UV-transilluminator (8).

Coagulation, the result of approach, contact and coalescence of the particles of the suspensoid, is evidently hindered by any factor which may retard one of these three actions. The approach of one particle to another is brought about by the thermal or Brownian movement of the particles within the medium and factors such as low temperature, high viscosity of the medium or large particle size will evidently diminish the rate of approach. When the particles are in close proximity to one another, actual contact will be prevented if the particles possess electric charges similar in sign, due to the action of electrostatic repulsion. The particles will possess no net charge, i.e. their surface will be covered with the same number of cations and anions and will not repel one another at the isoelectric point when the capillary attraction can operate effectively (Hardy, Proc. Roy. Soo. LXVI. 110,1900). 

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