Biopolymer solutions

The ionic strength dependence of intrinsic viscosity is function of molecular structure and protein folding, ft is well known that the conformational and rheological properties of charged biopolymer solutions are dependent not only upon electrostatic interactions between macromolecules but also upon interactions between biopolymer chains and mobile ions. Due electrostatic interactions the specific viscosity of extremely dilute solutions seems to increase infinitely with decreasing ionic concentration. Variations of the intrinsic viscosity of a charged polyampholite with ionic strength have problems of characterization. 

Teeuu, D. and Hesselink, F.T. "Power-Law Flow and Hydrodynamic Behavior of Biopolymer Solutions In Porous Media," SPE paper 8982, 1980 SPE Fifth International Symposium on Oilfield and Geothermal Chemistry, Stanford, May 28 30. 

It did not give rise to phase separation or precipitation. Similar behavior was observed when other types of polysaccharides were examined [53,54]. By now all the commercially important polysaccharides have been applied to the fabrication of hybrid silica nanocomposites in accordance with Scheme 3.2. What is more, various proteins have been entrapped in silica by the same means. In all instances the THEOS demonstrated good biocompatibility with biopolymers, even though its amount in formulations was sometimes up to 60 wt%. Biopolymer solutions after the precursor admixing remained homogeneous to the point of transition into a gel state. 

The one-stage process with THEOS proceeds differently (Figure 3.7B). The difference is in the absence of sol nanoparticles in the initial solution. There are entangled macromolecular chains (stage 1, Figure 3.7B). The silica precursor is introduced in a biopolymer solution as a monomer. The experimental results available to date (see Section 3.4.2) demonstrate that instead of sol formation there... 

Vol. 4 The Physical Chemistry of Biopolymer Solutions Application of Physical Techniques to the Study of Proteins and Nuclei Acids R. F. Steiner L. Garone... 

Following on from equation (3.5), we note that it is the value of the second virial coefficient A2 that determines the osmotic pressure of the biopolymer solution ... 

Here, the quantities jn ° and ji are, respectively, the chemical potentials of pure solvent and of the solvent at a certain biopolymer concentration V is the molar volume of the solvent and n is the biopolymer number density, defined as n C/M, where C is the biopolymer concentration (% wt/wt) and M is the number-averaged molar weight of the biopolymer. The second virial coefficient has (weight-scale) units of cm mol g. Hence, the more positive the second virial coefficient, the larger is the osmotic pressure in the bulk of the biopolymer solution. This has consequences for the fluctuations in the biopolymer concentration in solution, which affects the solubility of the biopolymer in the solvent, and also the stability of colloidal systems, as will be discussed later on in this chapter. 

A knowledge of the magnitude of these quantities and their quantitative contributions to /uE can give insight into the detailed character of the intermolecular interactions in a biopolymer solution, including the means by which their properties may be manipulated. The sign of the second virial coefficient provides a simple indicator of the type of interactions... 

In identifying the species in this biopolymer solution, we are following the convention of allocating odd numbers to low-molecular-weight components (solvent, salts) and even numbers to the polymeric components. So, for this system of biopolymeri + biopolymer2 + solvent, there is no component labelled number 3. 

Figure 3.3 Illustration of the calculation of the phase diagram of a mixed biopolymer solution from the experimentally determined osmotic second virial coefficients. The phase diagram of the ternary system glycinin + pectinate + water (pH = 8.0, 0.3 mol/dm3 NaCl, 0.01 mol/dm3 mercaptoethanol, 25 °C) —, experimental binodal curve —, calculated spinodal curve O, experimental critical point A, calculated critical point O—O, binodal tielines AD, rectilinear diameter,, the threshold of phase separation (defined as the point on the binodal curve corresponding to minimal total concentration of biopolymer components). Reproduced from Semenova et al. (1990) with permission.

In general terms, the interactions between the colloidal particles with surfaces covered by adsorbed biopolymer layers can be described qualitatively and quantitatively using the appropriate expression for the potential of mean force W(r). Extending the formalism of equation (3.2), at least four separate contributions to W(r) can contribute to the total free energy of interaction between a pair of colloidal particles in the aqueous dispersion medium (a biopolymer solution) (Snowden et al, 1991 Dickinson, 1992 Israelachvili, 1992 Vincent, 1999 de Kruif, 1999 Praus-nitz, 2003) ... 

Owing to the diverse chemical nature of functional groups in proteins and polysaccharides, they are prone to a variety of types of molecular interactions, both in bulk aqueous media and at air-water or oil-water interfaces. To a first approximation one may consider an adsorbed layer of biopolymers at the interface as simply a special type of highly concentrated biopolymer solution. Thus, the same variety of interactions that are typically found for biopolymers in a bulk aqueous media also occur in biopolymer adsorbed layers at the interfaces in food colloids. Moreover, these same molecular interactions are also involved in the close encounters between pairs of colloidal particles covered by adsorbed biopolymer layers. In the rest of this chapter we shall briefly remind ourselves of the main basic types of intermolecular interactions readers requiring more detailed background information are directed to other sources (Cantor and Schimmel, 1980 Lehninger, 1982 Israelachvili, 1992 Dickinson, 1998 Finkelstein and Ptitsyn, 2002 McClements, 2005, 2006 Min et al., 2008). 

In addition to the considerations mentioned above, it is rather important to keep in mind that a common aspect in determining the overall thermodynamic behaviour of a biopolymer solution/dispersion is the necessity of taking into account all of the component interactions. This includes the interactions of the biopolymer(s) with the water molecules, including both hydration (attraction) and dehydration (release), as well as the interactions amongst the water molecules themselves. 

The membrane osmometer is a device for measuring the osmotic pressure, n, of a biopolymer solution separated from the pure solvent by a semi-permeable membrane (Tanford, 1961 Edmond and Ogston, 1968 Tombs and Peacocke, 1974 Edsman and Sundelof, 1987 Amur et al.,... 

A2 from equation (5.16) or the cross second virial coefficient from equation (5.17). In turn, this knowledge of the second virial coefficients and their temperature dependence allows calculation of the values of the chemical potentials of all components of the biopolymer solution or colloidal system, as well as enthalpic and entropic contributions to those chemical potentials. On the basis of this information, a full description and prediction of the thermodynamic behaviour can be realised (see chapter 3 and the first paragraph of this chapter for the details). 

Using the Gibbs-Duhem law (m djU + m2djU2 = 0) (Prigogine and Defay, 1954), the equilibrium osmotic pressure in the biopolymer solution can... 

The enthalpy change associated with formation of a thermodynamically ideal solution is equal to zero. Therefore any heat change measured in a mixing calorimetry experiment is a direct indicator of the interactions in the system (Prigogine and Defay, 1954). For a simple biopolymer solution, calorimetric measurements can be conveniently made using titra-tion/flow calorimeter equipment. For example, from isothermal titration calorimetry of solutions of bovine P-casein, Portnaya et al. (2006) have determined the association behaviour, the critical micelle concentration (CMC), and the enthalpy of (de)micellization. 

With a ternary system of type biopolymer/ + biopolymey + solvent, in order to characterize all the different pair interactions, the following heat effects, Q, should be measured in flow mode (Semenova et al., 1991) (i) biopolymer, solution diluted by pure buffer, Q (ii) biopolymey solution diluted by pure buffer, Qp and (iii) mixed (biopolymer, + biopolymey) solution diluted by pure buffer, Qijh. The specific enthalpy of interaction between biopolymer, and biopolymey can then be obtained from... 

Biopolymers are, of course, poly electrolytes. This means that electrostatic repulsion between them, as well as the contribution of counterions to the total free energy of the system, are to be included amongst the key factors affecting the character of the biopolymer interactions, and hence the stability of mixed biopolymer solutions with respect to phase separation (Antipova and Semenova, 1997 Grinberg and Tolstoguzov, 1997 Polyakov et al., 1997 Semenova, 1996 Wassennan et al., 1997). For... 

Firoozmand, H., Murray, B.S., Dickinson, E. (2009). Interfacial structuring in a phase-separating mixed biopolymer solution containing colloidal particles. Langmuir, 25, 1300-1305. 

The observed frequency dependent behavior of biopolymer solutions often resembles that of polar liquids and their solutions in nonpolar solvents, the most conspicuous differences being the very large effects of small concentrations of solute and the much lower frequencies. The classic theory of Debye (6) for polar liquids and solutions assumes N independent permanent dipoles of moment p reorienting in an applied field E(t) =... 

The present evidence is thus that kinetic effects may account for half or more of permittivity decreases of ionic solutions and this may be an important factor in determing the amplitude of the Y dispersion in conducting biopolymer solutions and lead to revisions in estimated nature and amount of bound water. The effect may also have some bearing on dielectric properties of cell interiors and membranes if these have appreciable conductances. It would seem premature to attempt definitive answers to such questions until the relative importance of static and kinetic effects in presumably simpler ionic solutions has been better established experimentally in comparison with theory which treats them self-consistently. 

The essential requisite for the present scenario is the unique property of the charged torus, that is, its instability to thicken beyond a certain size. Therefore, its applicability is not limited to the case, in which the torus thickness is limited by the electrostatic mechanism. For example, we expect that surfactant molecules, which are sometimes used as condensing agents, may affect such structural property through the packing inside folded structures. Note also that the presence of the finite-sized bundles is rather ubiquitous in other semiflexible polyelectrolyte systems and biopolymer solutions. Seeking for its consequences would be a yet uncultivated problem. 

Figure 3.1 illustrates the phase behaviour of mixed biopolymer solutions (Tolstoguzov... 

Figure 3.1. Main trends in the behaviour of mixed biopolymer solutions. Schematic representation of the four possible results obtained by mixing solutions of biopolymers a protein and a polysaccharide a protein and another protein a polysaccharide and another polysaccharide.

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